trends in the use of coal ash

Trends in the use of coal ash

Lesley L Sloss

CCC/22

October 1999

Copyright © IEA Coal Research 1999

ISBN 92-9029-332-2

Abstract

This report investigates the physical and chemical characteristics of coal ash resulting from changing practices in plant operationin response to the demands of environmental regulations. The influence of fuel characteristics is summarised, including theeffects of cofiring coal with other materials such as biomass and wastes. Effects due to changes in boiler operation are covered aswell as the optimised use of reagents and additives in particulate, SO2 and NOx emissions control systems to maintain the qualityof fly ash. More coal ash can be used if its characteristics meet the standards in the construction industry and it is competitivewith conventional materials. Data on the production and use of coal ash in different countries and the discernible trends in theapproach to ash use are also summarised.

Extract from De Architectura by Marcus Vitruvius Pollio, one of Caesar's engineers (Samarin, 1997)There is a kind of powder from natural causes producing astonishing results. It is found in the neighbourhood of Baiaeand in the country belonging to the towns around Mount Vesuvius. This substance, when mixed with lime and rubble, notonly lends strength to buildings of other kinds but, even when piers of it are constructed in the seas, they set hard underwater.

Acronyms and abbreviations

AASHTO American Association for State Highway and Transportation OfficialsACAA American Coal Ash AssociationADAA Ash Development Association of AustraliaAFBC atmospheric fluidised bed combustionASTM American Society for Testing and MaterialsAWDS ash water dense suspensionBFBC bubbling fluidised bed combustionCAAA Clean Air Act Amendments, USACAER Center for Applied Energy Research, USACAFA chemically activated fly ashCAPD coal ash properties databaseCARRC Coal Ash Resources Research ConsortiumCCB coal combustion by-productCCP coal combustion productCCUJ Centre for Coal Utilisation, JapanCEGRIT Central Electricity grit samplerCEN Comité Europeèn de Normalisation (European Committee for Standardisation)CFA cement bound fly ashCFBC circulating fluidised bed combustionDAP dry additive processECOBA European Association for Use of the By-Products of Coal-Fired Power Stations eV, GermanyECU European Currency UnitEPRI Electric Power Research Institute, USAESP electrostatic precipitator(s)ETSU Energy Technology Support Unit, UKEU European UnionEWC European Waste CatalogueFABM fly ash bound mixturesFBC fluidised bed combustionFETC Federal Energy Technology Center, USAFGD flue gas desulphurisationFOCUS furnace on-line combustion systemGDR former German Democratic RepublicGFA granular fly ashHHV higher heating valueIGCC integrated gasification combined cycleIME Israel Ministry of the EnvironmentIMP Institute of Materials Processing, USAISO International Standards OrganisationIVO Imatran Voima Oy, FinlandKSF potassium silicate fertiliserLAC lignite-based activated carbonLFA lime fly ashLOI loss on ignitionMCI Mineral Control Instrumentation Ltd, USAMTU Michigan Technological University, USAMWe megawatt electricMWt megawatt thermalNTPC National Thermal Power Corporation, IndiaPFBC pressurised fluidised bed combustionRCRA Resource Conservation and Recovery Act, USASCEG South Carolina Electric and Gas, USASCR selective catalytic reductionSDA spray dryer absorbentSECV State Electricity Commission for Victoria, AustraliaSNCR selective non-catalytic reductionSTI Separation Technologies Inc, USATAM thermally active marbleth% percentage by thermal (energy) inputUSDA United States Department of AgricultureUS DOE United States Department of EnergyVCN Vulstof Combinatie Nederland, Netherlands

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3Trends in the use of coal ash

Contents

1 Introduction 5

2 Coal ash characteristics 62.1 Ash types 6

2.1.1 Pulverised coal ash 62.1.2 FBC ash 62.1.3 Gasification residues 7

2.2 Chemical and physical characteristics 72.2.1 Chemical composition 72.2.2 Chemical characteristics 92.2.3 Physical characteristics 9

2.3 Comments 12

3 Market specifications and standards 133.1 Classification 133.2 Specifications 143.3 Market forces 15

3.3.1 Requirement for raw materials 163.3.2 Legislation and guidelines 163.3.3 Perception and definition 173.3.4 Marketing 183.3.5 Agencies 19

3.4 Comments 19

4 Improving fly ash quality 214.1 Fuel type 21

4.1.1 Coal switching and blending 214.1.2 Cofiring 23

4.2 Operating conditions of the plant 244.2.1 Start up and other non-standard conditions 254.2.2 Low NOx burners 254.2.3 SCR and SNCR 274.2.4 Limestone addition for sulphur control 274.2.5 Sorbent addition for trace element control 284.2.6 ESP and baghouses 28

4.3 Handling, storage and transport 294.4 Processing and beneficiation 30

4.4.1 Size classification 304.4.2 Agglomeration 314.4.3 Grinding/micronisation 314.4.4 Blending/mixing processes 314.4.5 Flotation 324.4.6 Conditioning/dewatering 324.4.7 Electrostatic separation 324.4.8 Ammonia removal 324.4.9 Magnetic separation 334.4.10 Chemical treatment 334.4.11 Combined systems 33

4.5 Quality control, quality assurance and certification 334.6 Comments 35

5 Coal ash production and utilisation 365.1 Country studies 375.2 Comments 46

6 Applications and disposal 476.1 Applications 47

6.1.1 Engineered fill and fillers 476.1.2 Cement, concrete and mortar 496.1.3 Secondary products 506.1.4 Filler 516.1.5 Pollution control 516.1.6 Agriculture and fisheries 526.1.7 Materials recovery 53

6.2 Disposal 536.3 Comments 53

7 Conclusions 55

8 References 57

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1 Introduction


It is becoming increasingly common for fly ash from coal-fired power plants to be thought of as a commodity ratherthan a waste. Fly ash has been a composite in concrete formore than 60 years and its use in this sector is becomingrelatively common. In addition to being an inexpensive rawmaterial, fly ash enhances many of the necessary propertiesof cement and concrete. More novel, specialised and valuableapplications for fly ash are being developed all over theworld.

Although the use of fly ash is increasing in many developedand developing countries, the production rate of fly ash isalso increasing with the rising trend in coal use. Ashproduction from a typical 800 MWe coal-fired power plantburning internationally traded coal may be around 700 t/day.However, the combustion of coal with high ash contents, suchas Indian coals with up to 40% ash, can produce much higherquantities of fly ash, up to 4000 t/day. Unless the usage of flyash continues to increase, problems with fly ash storage anddisposal will continue and, in some areas, become worse. It isbecoming more important that the potential for the utilisationof ash be fully recognised.

In addition to the increase in the amount of pulverised coalash, there is an increase in the amount of ash being producedfrom other power generating systems such as fluidised bedcombustion (FBC) boilers. Ashes with new properties andcharacteristics are also being produced from plants whichcofire coal with other fuels such as biomass and wastematerials. Further, pollution control systems such as low-NOx burners and catalytic and non-catalytic flue gastreatment systems are causing distinct changes to theproperties of ash produced. It is important that the propertiesof ash from new and modified systems be studied andunderstood to ensure that suitable applications are found forthis ash.

Appropriate management and marketing in addition tolegislative forces has led to 100% ash utilisation in countriessuch as the Netherlands. Other countries are striving toachieve a similar level of success but are hindered by barriersin areas such as ash management, marketing, legislation andstandards and, even now, misconceptions over the suitabilityof ash in many applications.

This report deals with ash from the combustion of coal andrelated fuels in pulverised coal combustion systems and alsoin advanced systems such as FBC boilers and gasifiers. Thisreport assumes a level of background knowledge such as thatwhich would have been gained by reading previous reportsby IEA Coal Research on these topics (Sloss and others,1996; Sloss, 1996). This report does not include residuesfrom flue gas desulphurisation systems which were dealt within a separate report by IEA Coal Research (Clarke, 1993).

2 Coal ash characteristics

One of the major barriers to the use of fly ash is its highlyvariable chemical and physical nature (Rostam-Abadi andothers, 1996). The characteristics of the ash are determinedby the mineralogical composition of the fuel and the designand operating conditions of the combustion or conversionprocess. The basic chemical and physical properties of flyash have been studied extensively and are reviewed inprevious reports by IEA Coal Research (Sloss and others,1996; Sloss 1996). Rather than repeat the information onthese properties in detail, Section 2.1 reviews the propertiesof residues produced from different combustion systems. Thiswill introduce the basic characteristics of ashes which arerequired for the different specifications and standardsdiscussed in Chapter 3. This will also lay a foundation ofunderstanding for the discussion of how changes in operatingconditions can affect the ash, which is the subject ofChapter 4. Section 2.2 gives a brief summary of the majorproperties which affect the use of residues in the applicationsto be discussed in Chapter 6.

2.1 Ash types

One of the major distinctions made between ash types is thecombustion system in which they were created. The majorityof ash produced is fly ash from pulverised coal combustion.For example, as shown in Figure 1, 71% of the coalcombustion by-products produced in the European Union in1997 was fly ash from pulverised coal-fired plants. Around11% was bottom ash from pulverised coal-fired units, 4%boiler slag from pulverised coal-fired units and only 2% wasfrom fluidised bed combustion (FBC) units. Residueproduction from integrated gasification combined cycle(IGCC) systems was not significant enough in Europe toappear in the figure. The following sections brieflysummarise the types of ash produced by the majorcombustion systems.

2.1.1 Pulverised coal ash

Between 10 and 25% of the ash produced in a pulverisedcoal-fired power plant is bottom ash or clinker. Bottom ashis coarse material (from below 1 mm in diameter to largeclumps) and is produced from the sintering of mineral matter(Okamoto, 1998). Dry bottom boilers are designed tomaintain the ash in the hopper in a powdery non-sticky state.Many such systems have clinker grinders to reduce the sizeof coarse material. Coal with low fusion temperatures canproduce running slag. This can clog up the hopper and causemaintenance problems. Wet bottom boilers are more suitablefor such coals as the slag flows into a collection tank in aliquid form (Carpenter, 1998).

The use of bottom ash is commonly determined by physicalcharacteristics such as grain size distribution, soundness,staining potential and colour. The coarse, fused and glassytexture makes it ideal as an aggregate. However, if the ironpyrite content is above 3% staining can be caused in someapplications. The iron pyrite content can be kept below thislevel by keeping iron pyrites and other mill rejects separatefrom the bottom ash. Bottom ash may be screened to keepthe grain size distribution suitable for specific applications(Ramme and Kohl, 1997).

Up to around 5% of the fly ash produced in a plant may appearin the economiser ash collection system. The average particlediameter of economiser and air pre-heater ash is around 30 µm(Okamoto, 1998). It is common for the economiser ash to beincluded with the electrostatic precipitator (ESP) or baghousefly ash and is rarely, if ever, marketed as a separate ash type.The term fly ash is normally assumed to apply to ash which iscaught either in an ESP or baghouse and this is where around70–85% of the ash produced in a coal-fired power plant iscollected. Fly ash from pulverised coal-fired boilers consists offine particles, mostly 1–50 µm in diameter. The amount of ashproduced is related to the amount of mineral matter in the coal,the coal heating value and the plant heat rate. In general, thehigher the mineral matter content of the coal, the more residuesproduced. For example, a typical 500 MWe plant firingbituminous coal with 9.5% ash would produce more than120 t/y ash (bottom ash and fly ash), whereas Montana PowderRiver Basin coal with only 3.7% ash would give rise to around43 kt/y total ash (Pavlish and others, 1994).

Pulverised coal-fired power stations usually operate attemperatures of up to around 1500°C and with high qualityfuels. This leads to fly ash which has quite distinct chemicaland physical characteristics from that produced in FBC units orgasifiers.

2.1.2 FBC ash

FBC units generally operate at lower temperatures (up to

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SDA-product 1%FBC-residues 2%

FGD-gypsum 11%

Boiler slag 4%

Bottom ash 11%

Fly ash 71% Combustion residues 88.0%

FGD-residues 12.0%

Total production 63 million tonnes

Figure 1 Production of clean coal by-products inthe European Union in 1997 (Dietz, 1999)

around 850°C, depending on the type of system) thanpulverised coal-fired units. Most systems produce two typesof residue – bed ash and fly ash. According to Robl (1999)bottom ash from FBC systems is coarse and difficult tohandle in comparison with the finer fly ash collected in thecyclone or baghouse. FBC units are commonly used to burnlower grade coal and/or coal with a high sulphur content.Due to their mode of operation they typically produce alarger amount of residue than pulverised coal combustionsystems, excluding flue gas desulphurisation (FGD) residues.This is due to the amount of limestone used to attain the highCa:S molar ratio required in FBC units. For example, for90% SO2 removal an FBC unit requires a Ca:S ratio between2:1 and 5:1 whilst wet lime/limestone scrubbers and spraydry scrubbers at pulverised coal fired plants require ratiosaround 1:1 and 1½:1. This can result in a high amount ofresidue from larger FBC units. For example, the 165 MWePoint Aconi plant, Nova Scotia, Canada, will consume about400 kt of coal and 150 kt of limestone per year, generatingabout 188 kt of residues. This volume is about 2.5 times thatproduced by a 165 MWe conventional pulverised coal firedplant burning the same coal with no SO2 control (Scott andCarpenter, 1996).

The relatively low temperatures in the different FBC systemsmean that ash melting is not common and the ashcomponents are therefore mainly crystalline. The key fuelproperties which can influence the residue characteristicsfrom FBC boilers are sulphur content, ash content and ashcomposition as well as the size and friability of the fuelminerals. The chemistry of the sorbent is also important asthis ends up in the residue too (Cobb and others, 1997).

Circulating FBC units (CFBC) differ from other FBC units inthat ashes collected in the cyclone are recycled into thefurnace for re-combustion. The cycling of the fuel allowsmore efficient sulphur capture than in other systems.Residues are collected from the bottom of the boiler (bedash) and from downstream ESP or baghouses (fly ash). Thereare over 100 CFBC systems in operation ranging in size frombelow 50 MWt up to the 250 MWe unit in Gardanne, France.Like other FBC systems, CFBC boilers produce largeamounts of residues. Conn and others (1997b) estimate that,depending on fuel and sorbent type, a 300 MWe CFBC boilermay generate between 100 kt and 1000 kt of residue per year.Disposal costs for this amount of residue can be in excess ofseveral million dollars. In pressurised FBC (PFBC) systemscombustion takes place under high pressure (1–2 MPadepending on the load). Unlike the CFBC systems, ashcollected in the cyclone is not normally recycled andtherefore residue is collected from three sites: the bottom ofthe boiler, the cyclone and the ESP or baghouse (Sloss,1996).

2.1.3 Gasification residues

Gasifiers operate at temperatures of up to 2000°C with highlyreducing atmospheres converting coal to a combustible gas,fine particulates and ash or slag. Gasifiers can be of severaltypes:


Coal ash characteristics

● Lurgi fixed bed gasifiers producing dry ash andgranulated vitreous solids;

● entrained flow gasifiers producing vitreous slag; and● fluidised bed gasifiers producing dry or agglomerated

ash, depending on the operating temperatures and fusiontemperature of the ash.

In slagging gasifiers the mineral matter in the coal is meltedand extracted as molten slag which is then solidified andcollected. The majority of the residues from IGCC systemsare produced as slag or agglomerated ash from the bed,although some is collected as fly ash (<50%). Fluidised bedgasifiers operate at temperatures which do not cause ashfusion and the residues produced are either ash or partiallybound agglomerated ash. Fluxes such as limestone are usedin some IGCC systems to moderate ash fusion temperatureand control slag viscosity. The additives change the chemistryand mineralogy of the residues produced (Sloss, 1996).

2.2 Chemical and physicalcharacteristics

It is important to review the characteristics affected by thechemistry of the ash in order to relate the different ash typesto possible applications. Influential characteristics includeboth the chemical composition of the ash as well as thephysical size and shape of the fly ash particles.

2.2.1 Chemical composition

As mentioned before, the composition of the ash dependslargely on the composition of the coal. Over 80% of fly ashfrom pulverised coal combustion consists of silica (SiO2),alumina (Al2O3) and iron oxide (Fe2O3). Oxides of calcium,magnesium, titanium, sulphur, potassium, sodium andphosphorus may also be present. The presence of traceelements in fly ash depends on the volatility of each traceelement and the surface area available. There appears to bean inverse relationship between some trace elementconcentration on a particle and the particle size. This is dueto the proportionally greater surface area on smaller particles(Sloss and others, 1996).

Coal contains some radioactive elements which also appearin the ash at slightly enhanced concentrations, especially insome Greek lignites (Wiegers, 1999). The US EPA definescoal ash as a diffuse naturally occurring radioactive material,its most benign classification. The radionuclides in coal andash do not need to be reported under any legislation (EPRI,1998b). However, it is recognised that some residues maycause exposure to some radiation. In 1996 the EUimplemented the Basic Safety Standards (BSS) councildirective which lays down the standards for health protectionof the general public and workers against the dangers ofionising radiation. As a result a concerted action group hasbeen set up in which institutes, consultants and concernedindustries are represented. This group is working to evaluatethe radioactive threat, if any, from all construction materialsincluding naturally occurring radioactive materials. Since flyash from some coals can contain radioactive trace elements,

Table 1 Bulk chemical analyses of low and highlime fly ashes, wt% (Scheetz and others,1998b)

Oxide <10% CaO >20% CaO Ordinary Portlandcement*

SiO2 52.5 ± 9.6 36.9 ± 4.7 21.8Al2O3 22.8 ± 5.4 17.6 ± 2.7 5.4Fe2O3 7.5 ± 4.3 6.2 ± 1.1 0CaO 4.9 ± 2.9 25.2 ± 2.8 64.0MgO 1.3 ± 0.7 5.1 ± 1.0 2.0Na2O 1.0 ± 1.0 1.7 ± 1.2K2O 1.3 ± 0.8 0.6 ± 0.6SO3 0.6 ± 0.5 2.9 ± 1.8 2.1

Moisture 0.11 ± 0.14 0.06 ± 0.06LOI 2.6 ± 2.4 0.33 ± 0.35 0.6

* data from Suzuki (1998)

fly ash is included in the ongoing research. The study isincomplete and, as yet, it is unclear whether the radioactivityof fly ash would have to be determined before its approval asa construction material in the future. Preliminary riskmodelling has suggested that some fly ashes with relativelyhigh radionuclide contents could exceed threshold levels forconstruction uses. However, a report performed on behalf ofthe Dutch authorities concluded that fly ash use should not beof concern in this respect (Wiegers, 1999).

FBC residues differ from pulverised fly ash primarily due tothe use of sorbent for SO2 control. The use of limestone leadsto higher amounts of calcium in the residue. FBC ashes cancontain from 15–35% CaO in the form of a complex mixtureof fuel-derived components such as anhydrite, free lime and asmaller amount of other calcium compounds such as calciumferrites, silicates, aluminates and aluminosilicates (Anthonyand others, 1999). If dolomite is used instead of lime, thenthe concentration of magnesium is higher in the residue. Theuse of dolomite also leads to larger quantities of residue forthe same Ca:S ratio. The presence of lime and calciumsulphate in FBC residues makes them alkaline. Alkalinity canmake disposal a problem but can enhance the use of residuein uses such as agriculture (see Chapter 6). Trace elementsreleased during FBC combustion are most likely to be presentin the form of crystalline compounds in the surface layers offly ash particles (Steenari and others, 1997).

Lecuyer and others (1994) note that the ash sulphate contentof CFBC residues directly results from the initial fuel sulphurcontent because of the high efficiency of desulphurisation inthe system. The lime content of some CFBC residues may belower than expected in smaller units and pilot plants if theresidence time is not long enough to allow completesulphation. The bed off-take from CFBC systems containsless carbonate, carbon and unburned carbon than the finesdue to the longer residence time in the boiler. Theconcentrations of trace elements in CFBC residues essentiallyreflect the initial fuel composition. Unlike residues frompulverised coal combustion with lime addition, there is noinverse relationship between trace element concentration andparticle size.

The lower requirement for sorbent in PFBC systems changesthe characteristics of the residues compared to other FBCsystems. In PFBC systems the limestone sulphation proceedswithout calcination resulting in residues with a low free limecontent and with most of the residual limestone remaining ascalcium carbonate (Scott and Carpenter, 1996). In PFBCsystems the major phase is commonly calcite whereas inCFBC anhydrite is more dominant (Sloss, 1996).

Between 70 and 90% of gasifier slags are comprised of SiO2,Al2O3 and CaO. The CaO content is dependent on the addedfluxes. In IGCC systems fluxes such as limestone are addedto moderate ash fusion temperature and control ash viscosity.IGCC slags are intermediate in composition betweenpulverised fly ash and blast furnace slag (Sloss, 1996)

The mineralogy of ashes from pulverised coal combustionreflect the bulk chemistry of the coal used and thecombustion temperature. Fly ash from pulverised coal

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combustion is predominantly amorphous glass or carbon butcan also contain 11–48% crystalline matter, largely mullite,quartz, haematite, magnetite, anhydrite, tricalcium aluminate,melitite, periclase and lime (Sloss and others, 1996). Higherrank coals with typically low CaO content consist of a muchsimpler group of crystalline phases and a larger proportion ofalumina substituted silica-rich glassy phase. Lower rank coalsinclude as many as 15 or 20 crystalline phases including aglassy phase which is more alumina-rich and silica-poor.Table 1 shows the common minerals present in low and highlime fly ashes from pulverised coal combustion of a range ofeastern and western US coals (Scheetz and others, 1998).Also included in this table is the bulk chemical analysis ofordinary Portland cement for comparison (Suzuki, 1998).

The mineralogy of FBC residues depends not only on themineralogy of the coal but also the mineralogy of thelimestone or dolomite and any other bed materials. Table 2shows the mineralogy of FBC residues from different fuels(Scheetz and others, 1998). FBC wastes are typically high infree lime (CaO), anhydrous calcium sulphate (CaSO4) orsulphite (CaSO3) and are pozzolanic. Concentrations of SiO2,Al2O3 and Fe2O3 comprise 5–50% of the ash. If dolomite isused rather than lime then the concentration of MgO will behigher (Cobb and others, 1997). Because of the lowertemperatures in FBC systems, mineral phases such asmuscovite, quartz and hematite may be present in muchhigher concentrations in the residues (Lecuyer and others,1994).

Table 2 Mineralogy of various FBC residues(Scheetz and others, 1998b)

High Btu anthracite Waste anthracite Bituminous

Quartz (SiO2) Quartz Quartz*Anhydrite (CaSO4) AnhydriteCalcite (CaCO3)Portlandite [Ca(OH)2] PortlanditeEttringite [Ca6(SO4)3:32H2O)Calcium sulphide (CaS)

* depends upon exposure of ashes to water

CFBC residues generally contain high contents of lime andcalcium sulphate. Residues from the Provence 250 MWeCFBC unit in France contains anhydrite CaSO4, CaO, CaS,quartz and traces of hematite (Lecuyer and others, 1997).Quartz and anhydrite tend to be the main crystalline speciesin CFBC. Residues from the Tidd PFBC plant in the USA(no longer in operation) contained dolomite, anhydrite,periclase and calcite. IGCC slags tend to contain smalldispersed crystalline grains of Fe-aluminosilicate minerals setin a glassy matrix. Secondary minerals such as portlanditeand gypsum can result from reactions of residues with waterand CO2 (Sloss, 1996).

2.2.2 Chemical characteristics

The major chemical properties of fly ash which affect its usein applications such as cement and concrete includepozzolanicity and reactivity.

A pozzolan is a siliceous or siliceous and aluminous materialthat in itself possesses little or no cementitious value but will,in divided form, combine with lime in the presence of waterto form cementitious compounds. Most fine fly ashes(<5 µm) react with CaO in water to act as a pozzolan. Fly ashwith low calcium content is pozzolanic whereas fly ash withhigh calcium content is hydraulic, that is, it becomes solidwhen mixed with water. Fly ash reacts with lime to formwater-insoluble calcium silicate and calcium aluminate,which are highly cementitious. The presence of Ca-aluminosilicates in fly ash is thus one of the sources of self-binding properties. The most important parameters withrespect to the pozzolanicity of fly ash appear to be the ratioof CaO/(SiO2 + Al2O3), the fineness and particle surface areaand the presence of crystalline minerals. Many attempts havebeen made to relate the basic chemical content of ash,determined by standard tests, to pozzolanic activity and thesuitability of any individual ash to its use in concrete andcement. However, experts such as Manz (1998) suggest thatno prediction system is perfect and that each ash should betested in practice in the chosen application. Tests should beperformance based, that is they should apply directly to thefinal product rather than to the raw material as thecharacteristics of the raw material will not necessarilyguarantee an acceptable final product.

Studies by Kataoka and Ogata (1998) in Japan have shownthat fly ash which has been stored for long periods may havelost some of its pozzolanic and strength forming propertiesbut can still be of use in road construction and similarengineering works.

Calcium oxide exhibits cementitious behaviour and thereforepromotes the use of FBC ash in construction uses. Accordingto Schmaltz (1997) the advantageous chemical characteristicsof most FBC residues over fly ash from pulverised coal-firedunits include:● they may be expansive, especially bed off-take;● they may be cementitious;● they can produce significant strength in cementitious

reactions; and● they are alkaline.



Excessive CaO in some FBC residues, especially CFBCresidues, can lead to hydraulic problems with swelling andcracking requiring pre-hydration of the residues prior to use(Scott and Carpenter, 1996). CFBC residues generate a lot ofheat on addition of water leading to problems with swellingand cracking, depending on the amount of CaO present.Relatively little is known about PFBC ash characteristics otherthan that they have extremely low free lime contents (1% orless) and extremely low elemental carbon (Anthony andothers, 1997). The lower free lime content makes PFBCresidues self hardening but less prone to secondary reactionsand cracking making them more marketable than other FBCresidues (Scott and Carpenter, 1996). Some IGCC residueshave cementitious properties but this varies greatly with themineralogy and the sodium content of the feed coal. Lowsodium, glassy slags have poor cementitious properties andmelted ashes lose their cementitious properties when quenchedunless activated by NaOH-rich solutions (Sloss, 1996).

It is fairly well established that the most important parameterswith respect to reactivity are calcium content and particle sizedistribution. Variations in other chemical constituents of the flyash appear to have no effect on its reactivity (Manz, 1998).High calcium fly ashes have increased reactivity over lowcalcium ashes. However, high calcium ashes have lowerresistance to chemical attack with regard to sulphates andalkali-silica reactions. High calcium ashes also have reducedefficiency in controlling expansion due to the alkali-silicareaction. The crystalline free lime leads to poor soundness infinal products but this effect can be controlled with grinding orthe addition of appropriate mineral admixtures (Qiang, 1997).As mentioned above it is not possible to make assumptions onash performance based on its chemistry. Appropriate tests arestill required to predict the performance of any particular flyash in concrete (Manz, 1998).

CFBC residues are especially reactive and normally requirestabilising by conditioning with water whereas PFBC residuescontain less free lime and are therefore less reactive (Sloss,1996). Anthony and others (1999) have studied the reactivityof ashes from both CFBC (183 MWe Point Aconi plant inCanada) and BFBC (bubbling FBC; 160 MWe TennesseeValley Authority Plant, USA) units. It was found that, withrespect to the bed ash, the exothermic reactivity was directlyproportional to the CaO content of the ash. However, this wasnot true for the fly ash. The fly ash released 4–5 times asmuch heat as the bed ash and the reaction was also an orderof magnitude faster. The reactivity of the ashes alsodecreased noticeably with time (within a 48 hour period) andwas affected by the particle size of the ashes. It wassuggested that the conditioning of the bed ash would be farmore difficult than the conditioning of the fly ash from theseunits. Anthony and others (1999) also emphasised that themethod used to determine the CaO content of the ash isimportant as errors of 40% or more and not uncommon if thecorrect procedure is not used. The interested reader isreferred to the original article for more detailed information.

2.2.3 Physical characteristics

The morphology of fly ash particles varies with the

combustion conditions. Bottom ash from pulverised coalcombustion units with dry bottom boilers is a mixture ofglassy material, partly fused residues and agglomerated ash.Bottom or slag from wet bottom boilers is generally black,shiny and vitreous (Sloss and others, 1996). Fly ash frompulverised coal combustion contains mostly sphericalparticles with a small amount of cenospheres and irregular-shaped particles (Bouzoubaâ and others, 1997). Hollowcenospheres have specific characteristics which make themsuitable for high-profit applications (see Section 6.1.3).

Ash from FBC systems has more irregular shaped particlesand less spheres than pulverised coal fly ash (Shintani andothers, 1998). Ash from CFBC systems are generally irregularshaped with variable granulometry and correspond to particlesof unburned muscovite, mica, quartz and haematite. Most ofthe particles produced in the 259 MWe CFBC unit inProvence, France, are roughly shaped but microspheres couldalso be detected (Lecuyer and others, 1997). Large unburnedparticles may also be found containing organic componentsand sometimes Ca and S are also present. Very rarely, glassysmooth microspheres of Al and Si can be found. Althoughwetted CFBC residues can produce crystals of Al, S and Cawith traces of Si, no ettringite is found (Lecuyer and others,1994). PFBC residues consist mainly of a mixture ofamorphous glass and crystalline phases and some unburnedmaterial and, as in other FBC residues, the particles areirregular in shape. The morphology of IGCC residues variesfrom system to system with the gasification process and themethod used for slag cooling. Fluidised bed gasifiers producefree or agglomerated ash whereas in agglomerating systemsthe ash is bound together with low melting point Fe-aluminosilicates (Sloss, 1996).

One of the important parameters to the end users of fly ash isthe particle size distribution. Particle size distribution iscrucial to many applications such as cement and concrete andis included within standards and specifications for thesematerials in most countries (see Chapter 3). The specificsurface area of fly ash may be considered more importantthan the particle size distribution as this relates more toreactivity and interactions with other particles. However,particle size distribution is easier to measure than specificsurface area. The physical properties of fly ash relate to thesize distribution – to the average particle size; the residue ona 45 µm sieve; and the gross surface area per unit weight ofparticle (Ban, 1997). Increased fineness generally impliesincreased reactivity, handleability and higher compressivestrengths in the final product. Coarser fly ash particles arecaught in the first section of an ESP or baghouse and thefiner particles pass further through. However, all ashes fromsuch systems are collected together so no particle sizeseparation is achieved as a result. Several beneficiationsystems have been designed to improve the particle sizedistribution of fly ash to suit the client. Such systems arediscussed in more detail in Section 4.4.

Qiang (1997) has reviewed the characteristics of many flyashes and has shown that the larger size fractions (>150 µm)tend to have the highest loss on ignition (LOI). LOI is theterm used to specify the amount of unburnt carbon or unburntcoal constituents in the fly ash. No distinct pattern could be

10 IEA Coal Research


found for the distribution of other minerals, such as CaO,between size fractions. Size classification such as sieving issometimes used as a method for reducing the LOI of fly ash(see Section 4.4) (Sloss and others, 1996).

The cycling process of CFBC boilers and the finer feedstockresults in smaller fines and, since smaller particles are morecohesive, the fines are more prone to caking (Scott andCarpenter, 1996). In PFBC systems, where residues arecollected in one or more cyclones, the fines collected in theprimary cyclone are coarser than that in the second cyclone(Shintani and others, 1998). This reflects the distribution offly ash in pulverised coal fired units where the finer ashpenetrates further through the particle collection systems. Themajority of FBC residues are below 0.2 mm in diameter.IGCC slags from different systems generally have similarparticle size distributions to each other with the majority inthe 0.5–4 mm range (Sloss, 1996).

Bulk density is a measure of the density of a granularsubstance. The relative density of fly ash depends on theshape and chemical composition of the fly ash particles.Higher calcium fly ashes from generally lower rank coalstend to have higher (up to 25%) bulk densities than lowcalcium fly ashes, up to 2630 kg/m3 (Qiang, 1997). FBCresidues also tend to be more dense than pulverised coal flyash (Shintani and others, 1998). Higher density is anadvantage for FBC residues which are to be disposed of asthis means that more material can be placed at a disposal sitebefore it is filled. Also, the higher density the compactedresidue, the lower its permeability. The bulk density of IGCCresidues is lower than that for sand and gravel but within thetypical range for various coal combustion residues(1000–1600 kg/m3) (Sloss, 1996).

Factors such as boiler design, operating conditions orcomposition of the coal can lead to inefficient combustion.This, in turn, will lead to unburnt carbon in the ash. Forsome coal ashes there is a disagreement in the LOI and theactual unburnt carbon due to other components in the ashwhich may be volatile or decompose on heating. Switching tolow NOx burners can cause major increases in unburnedcarbon. This is discussed in more detail in Section 4.2.2.

According to Okamoto (1998) the unburnt carbon content ofthe ash tends to be higher the lower the ash content of the coal.Coal with a high combustibility will have a low proportion ofunburned carbon whereas a coal with a high proportion offixed carbon (with the fuel ratio increasing) will lead to anincreased level of unburned carbon. When coals with muchdifferent fuel ratios are blended, the coal with the higher fuelratio will have a greater effect on the unburned carbon content.In addition to the coal characteristics, boiler operation alsoaffects the unburned carbon. Even when coal of the samebrand is used it is often found that combustion in a largecapacity boiler leads to an unburned carbon level of only3–4% or less whereas its combustion in a small capacity boilerresults in a much higher unburned carbon level of 15–20% ormore (Okamoto, 1998).

LOI is one of the most important parameters considered forfly ash use in construction applications. Unburnt carbon can

adversely affect air entraining admixtures and can also causediscolouration of the final product. Although it is generallyaccepted that carbon in ash is detrimental to fly ash use inconcrete, Belz and Pellequer (1998) have run many tests inItaly which suggest that there is little or no effect of the LOIon the strength and properties of the final concrete. Theytherefore argue that the limits of 7% LOI or below set bymany countries are unnaturally low and are preventing theuse of otherwise acceptable fly ash. McCarthy and Dhir(1999) also suggest that up to 8% LOI has little effect oncompressive strength, although a 25% reduction in frostresistance was noted at the higher LOI concentrations.Coppola and others (1998) studied the performance ofdifferent fly ashes in cement and found that a fly ash with anLOI of 11.3%, way above the required limit, consistentlyperformed better than a fly ash with an LOI of 4.19%. Thiswas assumed to be due to the specific composition of the firstfly ash which made it act as a better pozzolan despite thehigher amount of LOI material. The question of whetherspecifications for parameters such as LOI should be animportant part of cement and concrete specifications is alsodiscussed in Section 3.2.

Although more dated information has suggested that CFBCresidues can have unburnt carbon contents up to 20%, therecycling of the fuel in such systems generally maintains alow unburnt carbon content. The unburnt carbon content ofPFBC residues is normally much lower than in CFBCresidues. The bed off-take contains <1% unburnt carbonwhereas the ash from the primary cyclones tends to be morevariable in LOI. The unburnt carbon content of IGCCresidues can be relatively high, depending on the conditionsof the system. In some cases the residues can be re-burned togenerate steam and reduce the carbon content beforeutilisation or disposal (Sloss, 1996).

The capture of mercury in fly ash is of particular interest.Mercury is very volatile and its emissions are of concern. Ithas been suggested that the unburnt carbon in fly ash couldbe effective in capturing mercury and thus reducingemissions from the stack. However, according to Hassett andEylands (1997) the capture efficiency of mercury does notcorrelate with LOI values. It appears that there are differentforms of carbon present in ash and some of these forms maybe less effective than others at capturing mercury.

Measuring the carbon content of fly ash prior to marketing isessential to determine whether the ash complies with thestandards and specifications for different applications.Although carbon in ash can be monitored manually once theash has been collected, on-line monitoring of carbon in ashis becoming increasingly popular. On-line monitoring allowsnot only the possibility of grading the ash as it is producedand storing it in differently graded silos, it also provides theopportunity for plant managers to adjust combustionconditions to increase combustion efficiency. Boileradjustments can be made which will not only increase thequality of the fly ash but also increase overall plantcombustion efficiency.

Most of the common carbon in ash monitors available arebased on isokinetic systems which remove a representative



sample of fly ash from the flow path using a timed samplingsystem. The sample is then analysed either with an in situanalyser or sent for analysis in a laboratory elsewhere. Suchsystems include those produced by M&W Askerteknik(Denmark), Clyde-Sturtevant (UK), Mineral ControlInstrumentation (MCI) Ltd (Australia), Rupprecht andPatashick (USA), and CAMRAC (USA). Most of thesesystems are based on the CEGRIT (Central Electricity GritSampler) originally developed by the UK Central ElectricityGenerating Board. These extractive systems have thedisadvantage that the samples collected may not be trulyrepresentative of the whole fly ash flow and they are prone toblockages and other operating problems. Non-extractiveapproaches, where the carbon in monitored in the duct itself,are preferable. The FOCUS (Furnace On-line CombustionSystem) unburned carbon module produced by AppliedSynergistics (USA) is an example of a commercial systemwhich is non-extractive and analyses the sample while it is inthe stack (ETSU, 1997).

The Energy Technology Support Unit in the UK has reviewedother on-line carbon in ash monitors being developed. Theseinclude the back-scattered light method being developed byImperial College, London, UK. This system has been foundto be very coal specific, requiring calibration to each coalused. Another system is the infrared emission spectrometrymethod being developed by Advanced Fuel Research andABB (USA). Iowa State University (USA) are developing aphotoacoustic method which correlates the carbon content tothe radiation absorption of particulate matter and thetransferral of heat (ETSU, 1997).

Portable carbon in ash monitors are also available. Palcic(1998) describes three such units which can be taken to silosand storage plants for immediate measurement of carbon infly ash samples. These systems also have to be calibrated forthe specific coals used. Prices range from $16,000 to$50,000.

A novel new process has been developed by Schneider andothers (1998) at the Vienna University of Technology,Austria. The system uses light reflectance to measure thecarbon in ash samples which are removed in an on-linemanner. The system differs from others in that it recognisesthat iron oxide particles also reflect light and can giveartefactual measurements. Iron oxide particles cannot becrushed easily whereas carbon particles can. By subtractingthe difference in reflectance before and after the sample iscrushed, a more accurate measurement of the carbon in theash is achieved. The system is already being usedsuccessfully at the Dürnrhor Power Plant in Austria wheresamples are taken once per hour from different points in thestorage area and feed lines.

All of the systems discussed in this section are still at thedevelopment stage and few are being used on full-scaleplants. The major problem appears to be the lack ofunderstanding of the physical and chemical properties ofcarbon in ash and the ash itself and the oversimplifiedassumptions which must be made in order to design a simplemeasurement system.

2.3 Comments

Fly ash is complex and variable in nature, varying withfactors such as coal characteristics, combustion conditionsand sorbent use. The lower temperatures of FBC systemsresult in fines which are different in mineralogy from the flyash from pulverised coal combustion. The use of sorbents inFBC systems also results in residues which contain moreproducts of lime.

The variations seen in fly ash from any combustion systemare not sufficiently predictable for fly ash from any individualcoal-fired unit to be considered consistent. Properties such asLOI and the particle size distribution and the grossmineralogical characteristics of each ash must be measured toensure its suitability for any individual application. Perhapsthe most important conclusion of a review of ashcharacteristics should be that gross generalisations cannotand should not be made.



Table 3 Fly ash standards of some countries (Shao and others, 1997)

Nations China USA England Germany

Name of standard GB 1596 91 ASTM C618 94 BS3982 84 DIN1045

Grade of fly ash I II III N F C I II

Fineness: 0.045 mm, % � 12 20 45 34 34 34 12.5–30 30–60 –*

Specific surface (cm2/g) > – – – – – – – 1250–4250 2000†

LOI, % � 5.0 8.0 15.0 10.0 6.0 6.0 7.0 12.0 5.0

SO3, % � 3 3 3 4 5 5 2.5 2.5 4.0

Ratio of water required, % � 95 105 115 115 105 105 95 – –

Ratio of water content, % � 1 1 – 3.0 3.0 3.0 0.5 1.5 –

28 d comp. strength, % > 75 62 – 75 75 75 – – –

* now limited to �50% on 40 µm sieve, as regulated by the Building Authorities† not required any more

3 Market specifications and standards


Chapters 2 of this report demonstrated how variable fly ashescan be with respect to both physical and chemicalcharacteristics. This variability has been one of the majorbarriers to the acceptance of fly ash into many market places.In order to promote the idea that fly ash can be a predictablecommodity, specifications and standards have been adoptedin many countries. Further, marketing and managementprojects have been set up to promote and advertise the use offly ash actively in a more widespread manner.

3.1 Classification

The many classification systems for fly ash were reviewed inthe previous report by IEA Coal Research (Sloss and others,1996), the most common of which can be summarised asfollows:● grading systems: based on either fineness and/or loss on

ignition or physical state (such as conditioned, stockpiledand ponded);

● the triangular system: seven classes based on sialic,calcic and ferric contents; and

● the ASTM system.

The ASTM (American Society for Testing and Materials)system is the most common and is the basis for most of thesystems used in other countries (Manz, 1998). The fly ash isdivided into three distinct classes within ASTM C618 asshown in Table 3, although only Classes F and C arecommonly used. Table 3 also includes details of grading orclassification systems used in other countries. Not included inTable 3 are the more common assumptions made to separateClass F and C ash which are:

Class C 50% [SiO2 + Al2O3 + Fe2O3] 6% LOIcementitious and pozzolanic properties;generally from lignite and subbituminous coals

Class F 70% [SiO2 + Al2O3 + Fe2O3] 12% LOIpozzolanic but not cementitious; generally from bituminous and anthracite coals

This system is confusing as it implies that only fly ash frombituminous and anthracite coals are suitable for cementproduction. In fact, many lignite and subbituminous fly ashescan meet the requirements for Class F and would therefore besuitable for use. The reason for the generalisation is that thesystem was developed in the USA where one third of the coalburned in power stations in the USA is Powder River Basincoal which has a low ash content and produces Class C flyash. Other US coals, including Texas lignite, tend to produceClass F fly ash (Lister, 1997).

It is well established that the most important parameters offly ash with respect to cement and concrete applications arethe calcium content and particle size distribution. Manz(1999) suggests that such a system, based on the CaO contentalone, should be adopted everywhere. The AmericanAssociation for State Highway and Transportation Officials(AASHTO) has recognised this and set its own standardAASHTO M295 which divides the ash according to its CaOcontent (Manz, 1999):● Type F CaO <8%● Type CI CaO 8–20%● Type CH CaO >20%.

A similar system is being adopted in Canada where three

Table 5 Physical requirements for fly ash under EN 450 and ASTM C618 (vom Berg and Puch, 1993)

Parameter EN 450* ASTM C618 Class F

Amount retained when wet seived on 45 µm sieve, max % 40 34Activity index at 7 days, min % of control – 75Activity index at 28 days, min % of control 75 75Activity index at 90 days, min % of control 85 –Activity index with lime at 7 days, min kPa – 5500Water requirement, max % of control – 105Autoclave expansion or contraction, max % – 0.8Le Chateler expansion, max mm 10† –

Uniformity requirements:Percentage retained on 45 µm sieve, max % points from average 10 5Specific gravity, max % variation from average – 5Specific gravity, max kg/m3 variation from average 150 –

* all requirements specified as characteristic values† only for fly ash with free CaO <2.5% and >1%

Table 4 Chemical requirements for fly ash underEN 450 and ASTM C618 (vom Berg andPuch, 1993)

Parameter EN 450 ASTM C618

SiO2 + Al2O3 + Fe2O3, min % – 70.0Loss on ignition, max % 5.0* 6.0†Chloride, max % 0.10 –Free calcium oxide (CaO), max % 2.5‡ –Moisture content, max % – 3.0Available alkalies as Na2O, max %§ – 1.5

* fly ash with LOI up to 7% by mass may also be accepted on anational basis

† up to 12% may be approved by the user if either acceptableperformance records or laboratory test results are madeavailable

‡ more than 1% and less than 2.5% is acceptable if complyingwith soundness requirements

§ optional requirement

different grades of fly ash are specified according to theirCaO and LOI content (Manz, 1998):● Class F CaO <8%, LOI <8%● Class CI CaO 8–20%, LOI <6% ● Class CH CaO >20%, LOI <6%

This standard still includes the requirements for limited LOI. Ithas been questioned whether the LOI of fly ash is as importantas it is often assumed to be. This idea was introduced inSection 2.2. Several studies have shown that high LOI ashescan be used in many cement and concrete applications as longas other, more important, chemical and physical requirementsare met. The negative effects of the limits on LOI on ashmarketing are also discussed in Section 3.2.

Vliegasunie, the fly ash association in the Netherlands, has itsown fly ash grading system which helps the purchaser choosea suitable ash for the required application (Oosterndorp,1997; Moret, 1999):● V0 fly ash with a product certificate based on EN450

requirements● V1 carbon content <5%; >70% passing 45 micron sieve;● V2 carbon content <7%; Al:Si >0.40;● V3 no specification.

Other individual countries, including China and Russia, havetheir own standards and specifications (Pavlenko and others,1998).

The classification systems discussed here aim to simplify thechoice made by the purchaser when selecting ash for a specificapplication. However, these different classes do not necessarilydivide the ashes into those which are appropriate and thosewhich are not appropriate for any individual use. Rather, thepurchaser must still test individual ashes to ensure that all oftheir characteristics and properties meet the specificationsrequired for any individual project. Manz (1999) emphasisesthe need for better understanding of the relationship betweenfly ash characteristics and its behaviour in differentapplications. At the moment the understanding of fly ashchemistry is insufficient to allow a simple classification systemto be established which could be used for predicting the


Market specifications and standards

suitability of an ash for any application. Hence the need forspecifications for fly ash behaviour in different applications.The following sections review the problems and the separatespecifications with which fly ashes must comply.

3.2 Specifications

Specifications are set in individual countries for fly ash use ina number of applications. The aim of these specifications isto set minimum requirements for the performance of fly ashin laboratory conditions. Table 3 showed some classes of flyash in different countries as set within specifications for flyash use in concrete. Distinct specifications have also been setin individual states in the USA and other countries for fly ash(or other ‘waste’ material) use in structural fill, soilstabilisation, subbase, base course and similar applications.Most of these are based on or similar to the ASTM C618standard set in the USA or the EN450 standard set in Europe.These two standards are compared in Tables 4 and 5. A newEuropean concrete specification standard, EN 206 is to beintroduced in 1999 (McCarthy and Dhir, 1999).

The large number and variability of these specificationsshould serve to demonstrate the amount of disagreement as towhich characteristics of fly ash make it suitable for anyapplication. The suitability of fly ash for any purpose isprimarily determined by its passing the specific tests set outin any standard or specification. Typical tests for fly ashapplicability to construction uses are listed in Table 6(Brendel and other, 1997). It has been emphasised manytimes that many of the methods for testing fly ashperformance are not appropriate. It has been shown that,whilst some ashes may fail some of the standard tests, theycan still produce totally acceptable final products. Forexample, in Section 2.2.2 several studies were cited that therequirements for the LOI in ash to be below 7% is excludingmany ashes from use which would produce totally acceptablecement and concrete products.

In many specifications, only the use of fly ash frompulverised coal combustion is considered. As mentioned inChapter 3, many specifications automatically exclude fly ashderived from the co-combustion of alternative fuels from usein cement and concrete without any potential for proving thatthe ash may indeed be suitable. In the Netherlands,Vliegasunie is actively working to find new ways of sellingash from the cofiring of biomass materials such as wastewood, sewage sludge, paper sludge and phosphor furnacegas. The Civil Engineering Centre for Research andRegulations in Gouda has a research committee working toproduce supplementary regulations for the use of fly ash fromcofiring in concrete. Within this project the subject of the ‘Kvalue’ will be discussed. The K value is the degree to whichfly ash contributes to the binding of concrete in the place ofcement (Vliegasunie bv, 1997).

A similar problem is seen with the automatic exclusion ofresidues from advanced coal use technologies such as FBCand IGCC from use in applications such as cement in someplaces. A survey of the use of CFBC residues in differentstates in Northern America gives a detailed account of wherethey are authorised and where they are simply allowed.Examples include states such as Ohio and Texas whereCFBC residues may be used in almost everything fromcement and concrete products to structural fills, grouting,plastics/paints/metals, concrete blocks and ceramics. In other



states, such as Nevada and New Hampshire, no suchauthorisations exist, although this does not necessarily meanthat CFBC residues could not be used in these areas. Ratherit may imply that CFBC residues are not common in theseareas and therefore such applications are not common(Klein, 1999a).

In addition to CFBC residues being automatically excludedfrom many specifications, Blondin and Anthony (1994) pointout that none of the common tests for additives in cement aresuitable for determining the potential for using CFBCresidues in concretes. Therefore CFBC residues are failingspecifications and tests when in fact they may well producequality final products. Blondin and Anthony suggest that newcriteria be set based on the adequate performance of the finalproduct which is, after all the aim of all construction projects.

In Japan the problem with over-rigid standards has beenrecognised. The Japanese Fly Ash Society is working withthe electric power companies and the Ministry ofInternational Trade and Industry to amend the Japanesestandards for fly ash use in concrete. The amendment aims topromote the use of ash by expanding the applicable area ofthe current standards. Even fly ashes discarded due to theover-specification of the current standards can be usedefficiently if dealt with appropriately. New standards arerequired which apply to the different qualities of ashesavailable (Kanatsu and others, 1998).

3.3 Market forces

The successful marketing of fly ash appears to be verydependent on location. It also depends on such factors asopportunity for sales as well as many legal and institutionalbarriers. As shown in Chapter 5, some countries arecontinually achieving 100% or more fly ash utilisationwhereas other countries have utilisation rates below 10%.Although to some extent part of the problem in somecountries is the delay in the recognition of the potential forfly ash use, there are also problems with market forces andother economic and legal limitations. Brendel and others(1997) have reviewed the barriers to clean coal by-productuse and have categorised them into four groups:

Table 6 Typical tests for clean coal by-product utilisation (Brendel and others, 1997)

Chemical Physical EngineeringSolids analysis (major solids in ash) Gradation CompactionLeachate analysis (EP toxicity) Fineness (% passing no 325 sieve) Shear strengthpH Specific gravity CompressibilityLoss on ignition Moisture content PermeabilityFlash point Particle shape and texture Pozzolanic activityOil and grease solids Age hardening% volatile solids Bulk densityCorrosiveness California bearing ratio

Stabilised Variations in ash produced Variations with exposure, storage/pondCompressive strength Within a unit Dry storage/stockpileDurability Between unitsPermeabilityAge hardening

● institutional barriers, where there are problems withexisting standards and specifications for fly ash whichare not always in favour of fly ash, problems with a lackof knowledge of fly ash by the end users and the fact thatnatural materials may be more readily available and costeffective;

● regulatory barriers, which include the definition of coalby-products as waste in some areas and the lack ofguidelines for beneficial use;

● legal barriers include the lack of a commercial code forash transactions and the question as to whether utilitiesshould be liable for any environmental damages whichmay occur through ash use; and

● miscellaneous barriers such as the lack of a consistentpricing policy and the predatory pricing of competitivematerials.

The following sections outline briefly some of the practicalfactors which can affect the movement of fly ash into theconstruction materials market place.

3.3.1 Requirement of raw materials

When raw materials are limited or expensive, the use of flyash becomes more economically tempting to the constructionindustry. It has been suggested that the high fly ash utilisationrate in the Netherlands (>100%) is due to the fact that fly ashdisposal is prohibited. Also, the properties of fly ash areactually superior to the naturally available aggregates such assand and gravel. That is, fly ash has become an advantageousraw material rather than just an optional one. Similarly, flyash use in large cities can be above the national average asfly ash is readily available in large amounts in the local area.For example, Shanghai (see also Section 5.1) has a 100%utilisation rate for fly ash compared with less than 50% forthe whole of China and this is due simply to the shortages ofbuilding materials. Belgium currently has an ash utilisationrate exceeding the rate of ash production in the country. Thisis due to the importation of fly ash from Germany and theNetherlands to meet construction requirements(vom Berg, 1998).

In the USA, in terms of total domestic output of producedmineral commodities, clean coal by-products rank behind onlysand and gravel and crushed stone and rank ahead of Portlandcement and iron ore (Stewart and Kalyoncu, 1999). There isobviously plenty of fly ash to be used and yet fly ash useremains relatively low at 32%. This is probably because noneof the raw materials are in short supply. The building industrycan pick and choose which materials it wants and is likely toopt for the more well known, established materials than newermaterials such as fly ashes. In the USA Renninger (1998)predicts that clean coal by-products will have to be 15–20%cheaper to penetrate strong existing markets.

One of the continuing problems affecting the movement offly ash as an alternative to natural materials in theconstruction industry is its seasonal availability. Theproduction of fly ash varies throughout the year, reflectingthe fluctuating requirement for electricity. The greatestproduction period is commonly the winter. However, the



greatest demand for fly ash arises in the summer monthswhen outside construction tends to be at its highest rate.Further, the requirement for ash is greatest at the onset of aproject and then tails off as the project nears completion. Themost common way to solve this mismatch of supply withdemand is some form of storage. Many storage options areavailable, a few of which are outlined in Sections 4.3 and 4.5in Chapter 4.

Despite the clearly demonstrated advantages of using fly ashin applications such as concrete (see Chapter 4), there arestill a few reservations perceived by some end users. Theseinclude concerns over decreased abrasion resistance, lowstrength gain, air entrainment problems and other physicalfactors which may or may not apply to any particular ash inany individual application. However, perhaps the moreimportant concerns are the lack of information on ashperformance, any such information is hard to find and oftensketchy or specific to a particular use, and questions over theconsistent supply of a guaranteed product (Baweja andNelson, 1998). Hence the need for the quality assurance andquality control considerations to be discussed in Section 4.5.

3.3.2 Legislation and guidelines

To a great extent, the existing legislation, specifications andguidelines are not working to promote the use of fly ash. Asdiscussed above, many of the existing specifications forcement and concrete require that the ash come frompulverised combustion of bituminous coal or anthracite.Residues from FBC and IGCC systems will also be excludedautomatically from many applications. Until the currentstandards and specifications are amended, ash produced fromcofiring waste fuels or from more advanced combustionsystems, cannot be sold in the existing marketplace in someareas. In addition to excluding particular ash types, somelegislated standards also limit the quantity of ash which canbe used. For example, Section 5.1 cites the situation in Israelwhere currently the use of ash in cement is limited to 10%whereas in many other countries 65% or more fly ash can beused in some situations. Either such standards should beupdated or else new performance-oriented fly ash standardsshould replace these prescriptive ones.

Brendel (1997) agrees that the regulations and legislation areless than ideal in the USA and elsewhere. In many states inthe USA, clean coal byproducts are regulated as solid wasteswhich means that their use requires specific case-by-caseapproval and long-term environmental monitoring. There isno coherent policy among federal and state agenciesregarding the beneficial use of these materials which has leadto overly conservative requirements. Other legal barriersinclude the liability of the ash supplier for damages whichmay occur through ash use.

Tuttle (1997) cites the following from the US DOE report toCongress on the use of coal combustion byproducts:

...the lack of specific guidelines for use of coalbyproducts has lead to overly conservative regulatorypractices, often involving case-by-case approval...

Tuttle warns that, although legislative action could be used toenhance ash use, it can also be unpredictable and would notguarantee success.

In addition to legislation and guidelines on ash use, directiveson fly ash disposal can affect the amount of ash used. Insome locations ash disposal is too cheap or too easy anoption. The price of landfill can greatly affect the decision ofa power plant manager on whether to dispose of ash or putgreater effort into finding some market for it. Increasingdisposal costs is one method to promote the increased use ofash in some countries. The UK Finance Act of 1996classified coal ash as ‘inactive’ and subject to a tax of £2/t(around $3/t; Kyte and Lewis, 1997). This is a lower rate oftax than other ‘waste’ materials (the standard landfill cost hadbeen £13/t in 1992). It has been argued that this cost is toolow and does not act as an incentive to use ash. It issignificantly lower than landfill costs in other countries suchas Denmark ($45/t in 1992), France ($5/t in 1997; expectedto increase soon), Germany ($51/t in 1992), Japan ($4/t in1996) Norway ($64/t in 1992), Sweden ($45/t in 1992) andthe Netherlands ($38/t in 1992, now illegal) (Sinozaki andothers, 1997; Morris and others, 1998; Blondin, 1998).

In addition to making ash disposal more expensive, thepromotion of ash use through guidelines and even taxincentives is becoming more common. Countries such asJapan have recycling and reclamation laws or guidelineswhich promote the effective use of ‘waste’ materials such asfly ash (Ban, 1997).

In an attempt to enhance the use of fly ash rather than itsdisposal, the Government of India has taken the followingpromotive actions (Krishnamurthy, 1999):● exemption of excise duty on production of building

materials using 25% or more fly ash as a raw material;● exemption of the customs duty on the import of

machinery and tools required for the production of flyash based building material products such as bricks,lightweight aggregates, and lightweight cellular concrete;

● exemption of excise duty (in excess of 5%) on fly ashhandling systems subject to the condition that the systemis intended for pollution control purposes;

● the Ministry of the Environment and Forest brought out anotification in 1996 stipulating that all brickmanufacturing units within a 50 km radius of anythermal power plant must use fly ash in optimalproportion for making bricks;

● in pursuance of the Supreme Court Notification, claybricks operating in Delhi have been asked to shift orchange their units to ash based brick units.

In addition to the above measures by Central Government,certain state governments within India offer sales tax benefitsfor ash based products.

Similar policies have already been implemented in China(Shao and others, 1997). The Chinese government isconsidering adjusting tax systems to favour the use of wastesover the extraction of raw materials. It is also aiding thedevelopment of large waste utilisation plants and new methodsfor ash and slag utilisation (Ma, 1997). Chinese environmental



law also now also requires that plants are fitted with both wetand dry ash collection systems to promote ash use (Pu, 1997).Other examples of changes in legislation to promote ash useinclude the zero tax on some ash applications and reduction ofroad tolls for the transportation of fly ash within some regionsof China (Lianglong, 1997).

vom Berg (1998) suggests that, although the state caninterfere by imposing charges or taking incentive measures(such as tax relief options), it always falls upon the powerplant operator to provide for the prerequisites for fly ashutilisation and to develop industrial markets.

3.3.3 Perception and definition

The term ‘waste’ is often applied to fly ash causing, to someextent, prejudice against its use. In the EU (European Union)Directive on the European Waste Catalogue (EWC) waste isdefined as ‘any substance or object in the categories set outin a given Annex which the holder discards or intends or isrequired to discard’. A catalogue is drawn up to cover alltypes of waste, irrespective of whether the substance isutilised or disposed of. Power station by-products have beenlisted under waste index number 10 – ‘Inorganic waste fromthermal processes’ and also under subcategories 10 01 –‘Wastes from power stations and other combustion plants’.This overlap between waste and product is currently thesubject of much debate within the EU (Thamm, 1997).

Thamm (1997) reviewed the different marketing strategiesbeing used in Germany to promote coal ash as a valuablecommodity rather than a waste. In this review he included thefollowing table as an indication of the change in attitude ofthe construction industry to hard coal fly ash in Germany:

1970 First building inspectorate permit as a concreteadditive

1974 Marks of conformity granted by the Institute fürBautechnik, Berlin (DIBt)

1984 Acknowledgement of the advantageouswater:cement ratio achieved with fly ash

1994 First European building materials standard (EN 450)for fly ash

1995 Acknowledgement of the decreased cement contentin concrete: applications extended to pre-tensionedpre-stressed concrete

1996 Inclusion in German Building Standards List AAcknowledgement for applicability to liquidimpermeable concretesAcknowledgment for sulphate resistant concrete

The table shows that there can be a long lag time between theintroduction of a potential commodity into the market and itsfinal acceptance into standard use. For developing countriessuch as India and Israel, such a slow acceptance processwould be a major problem in environmental terms.

Table 7 Market potential for clean coal by-products in the USA (from Renninger, 1998)

Market Market size Potential saving by using clean coal by-products

Portland cement 80 Mt/y $560 M in sales plus $200 M in avoided disposal costspozzolan cement 777 kt/y FBC product $5.5 Mflowable fill NS $835 M in sales plus $565 M in avoided disposal costsstructural fill and roadbed material NS $340 M in sales plus $270 M in avoided disposal costsacid mine drainage remediation 100 Mt/y $750 Magricultural soil amendment 2.8 Mt/y $200 M

NS not specified

3.3.4 Marketing

Cornelisson (1997) produced the diagram shown in Figure 2.The chart summarises how in the past fly ash has beenregarded as waste but how, over time and with positivemarketing, quality control and upgrading has led to ashshifting from a waste to a valuable resource.

In the right situation, there is a significant amount of profit tobe made from the use of fly ash. This has been recognised bysome companies which have been set up specifically tomarket fly ash. Examples of these can be found by a simplesearch on the internet and include Boral MineralTechnologies (USA), ISG Resources Inc (USA), WallaceIndustries (USA), Ash Resources Pty (Republic of SouthAfrica), Pozzolanic Industries (NSW, Australia), and TanveerEnterprises (New Delhi, India). In countries such as theNetherlands and Belgium, joint companies have been set upby the power plant operators and the cement industry and/orpower stations to ease the movement between ash productionsites and ash markets.

According to Fisher and others (1997), ash marketerstypically buy concrete quality ash from ash generators ataround $2/t and deliver it to concrete manufacturers at a costof $20/t. Once transport and handling costs are removed, thenet profit is around $6/t. This is not an insignificant amountconsidering that fly ash is still thought of as waste in manyareas. This is even more significant when one considers thatdisposal costs can range from $6–27/t (Fisher and others,1997). Costs as high as US$100/t have been quoted for ashdisposal at some power plants in Japan (Carpenter, 1998).



Renninger (1998) has considered the total market potential forfly ash in the USA. Table 7 lists the most likely markets forclean coal by-products in the future and the potential profitsand savings which could be made if these markets weretargeted correctly. According to Renninger, every avoided costdollar from the use of a by-product versus straight land fillingis better than a dollar in gross revenue since there is anassociated overhead cost with revenue generation.

In countries such as the USA, with deregulation and theincrease in the number of power plants being run privatelyand for profit, there will be a tendency for plants to operateon the lowest costs possible and this will include acceptingthe lowest bids for ash disposal or utilisation. According toBennett (1997) this will negatively impact the quantities ofcoal by-products marketed in the long term. He warns thatutilities will continue to see their disposal expenses climbunless they stimulate market growth through incentives. Headvises that there should be an effort to expand applicationsand technologies that ultimately will drive disposal volumesand expenses towards zero while increasing both the demandand price for clean coal by-products.

On a more individual scale, each power plant should considerits own individual situation and how steps could be taken toturn fly ash into a commodity. As Callaway (1997)emphasises, coal-fired power plant operators should now starttreating their fly ash ‘disposal’ as a business opportunity. Thisincludes all areas of marketing from product evaluation,through storage, transport and delivery to new productdevelopment and customer support. Trehan andothers (1997a,b) have estimated the applications which wouldbe required to use up the ash produced from a 2000 MWethermal power station in India. Bearing in mind that Indiancoal is very high in ash (see Section 5.1) and assuming that10 kt of ash were produced every day, this could be used tosupply:● 50 brick plants producing 5 million bricks per day; or● 20 lightweight aggregate/block plants producing 13 kt

per day; or● 25 cement plants producing 75 kt per day.

Although coal-fired power plants in other more developedcountries with lower ash content in the coal would produceless than 10% of this amount of ash in a day, it stillrepresents a significant potential with respect to theconstruction industry.

Brendel and others (1997) emphasise the importance of anindividual marketing strategy which includes an initial

timeby-product

resource

valuableresource

waste

value

niches

utilisation

introductionutilisation

storage

upgrading

QC(upgrading)

QC0

Figure 2 Trends in by-products marketing(Cornelisson, 1997)

market research programme to ascertain potential markets inthe local area and to ensure that the fly ash is produced in themost appropriate manner to suit these markets. Brendel andothers describe the important factors in any such program,including assessing the availability of fly ash (seasonality),evaluation of the local markets, avoided disposal cost analysisand an economic evaluation. The latter may look somethinglike this:● sales revenue (including transportation) $30/t● avoided disposal cost $10/t● direct marketing cost $2/t● bulk-haulage cost $0.3/t-mile● total marketing benefit $30 + 10 – 2.00 = $38.00● economic market radius $38.00/0.3 = 127 miles (around

200 km)

This hypothetical example would suggest that the sale of flyash for the cement market should be limited to a 127 mile(200 km) radius around the plant to remain economicallyfeasible.

Some power plants are beyond this stage and are taking theprocess one step further to the point where the power plantitself is marketing the ash as a finished product for sale. Forexample, the construction of a total fly ash utilisation systemis being built at Abakan power plant in Russia as shown inFigure 3. Between 20 and 30% of the processed ash and slagis sold to builders and 70 to 80% is used for producing



various types of concretes and bricks. By using the waste ashfrom the plant and taking advantage of the energy and steamproduced at the plant, the cost of manufacturing productssuch as bricks and ready-mix concrete is up to 75% lowerthan elsewhere (Pavlenko and others, 1998).

3.3.5 Agencies

Countries such as the Australia, the Netherlands, the UK andthe USA have their own fly ash associations to promotebetter understanding of fly ash use in their country. Theseassociations also interact on an international level. ECOBA,the European Association for use of by-products of coal-firedpower stations, was formed in 1990 and has members from11 member states of the European Union (Belgium, Finland,France, Germany, Greece, Italy, Netherlands, Portugal,Republic of Ireland, Spain, and the UK) and one from theCzech Republic. Since 1993, ECOBA and the American CoalAsh Association (ACAA) have been connected by a‘memorandum of understanding’ to allow an increase in theexchange of information. Further, in 1997 the CCUJ, theJapanese Centre for Coal Utilisation, has joined ECOBA asan affiliate member. ECOBA provides information on newapplications for fly ash. The aims of ECOBA are (Dietz,1998):● creation of a favourable technical, legislative and

regulatory climate for the use of clean-coal by-productsin Europe;

● promotion of the recognition and acceptance of cleancoal by-products as secondary raw materials;

● representation of the ECOBA-members in the technicalcommittees of CEN; and

● exchange of experience and knowledge between ECOBAmembers.

The ACAA is similar with a ‘mission to advance themanagement and use of CCBs (clean coal by-products, nowtermed CCP – coal combustion products) in ways that aretechnically sound, commercially competitive andenvironmentally safe’. The ACAA conducts an annual surveyof clean coal byproducts and use and issues an annual reportof the data (Brendel and others, 1997).

3.4 Comments

Ashes can be classified according to certain chemicalcharacteristics using a number of different systems. However,none of these systems directly relate to the suitability of theash to any particular use. Specifications and tests are used tocharacterise the reactivity and behaviour of the ash in afurther attempt to predict its suitability for use. Althoughthese specifications and tests can determine that an ash insuitable for construction use, they tend to be overly specificand exclude the use of ashes which would otherwise beacceptable. Ashes from advanced coal use technologies andfrom the cofiring of coal with other materials areautomatically excluded from many applications whereas infact they may perform well. An ideal system would beperformance testing where any ash can be used as long as itproduces a satisfactory product. However, ash would not be

Figure 3 Schematic diagram of total utilisation ofash and slag from a thermal power plant(Pavlenko and others, 1998)

considered a valuable commodity without some form ofguarantee of its likely performance. Quality ashes can beproduced consistently from some power plants and, as longas the necessary handling and storage facilities are available,can be graded and classified and sold on as a guaranteedproduct.

Despite being a potentially valuable commodity there are stillmany barriers to the use of fly ash in many countries. Whereraw materials are cheap and widely available then ash is notas valuable as it might be in an area where raw materials aremore scarce. If land filling is a cheap and easy option thenthe processing and storage of ash for sales is not economic.Tax incentives and changes in disposal requirements canmake it harder for ash to be wasted, but this approach onlyworks if there is a suitable market for the ash beingproduced.

The work of agencies such as the ACAA and ECOBA topromote the free exchange of information can helpconsiderably to promote the use of fly ash.



4 Improving fly ash quality


Chapter 2 briefly summarised the characteristics of ash whichare important for their use and also the different types of ashproduced in different combustion systems. This chapterconcentrates more on how changes in fuel, plant operationand pollution control systems can affect the characteristics ofthe ash and its marketability. Where possible, an indication isgiven of how any detrimental effects of such changes can beameliorated or compensated for. Improving ash quality willensure that more ash meets the standards and specificationsdiscussed in Chapter 3.

In 1997 the American Coal Ash Association (ACAA) startedto develop a database management system which will coverfuel source, burning conditions, collection and storagemethods and analytical results. The database will allow theuser to assess interactions between sample generation and ashproperties. Figure 4 shows the conceptual data model for thedatabase. The database includes data on over 800 coal fly ashsamples from the Coal Ash Properties Database (CAPD)produced by the Coal Ash Resources Research Consortium(CARRC). O’Leary and others (1997) review the database indetail highlighting the many advantages of having suchinformation in an easily accessible form. A similar databaserelating ash quality to coal type and combustion conditions isalso being developed by Vliegasunie in the Netherlands (vomBerg, 1998). The information on such databases can beaccessed by members to give suggestions for uses fordifferent fly ash samples. New markets may becomeapparent. It may be possible to predict changes in fly ashquality by comparing the effects of changes in fuel oroperating conditions in similar plants elsewhere.

4.1 Fuel type

As mentioned in Chapter 2, the composition and properties offly ash depend to some extent on the type and origin of thefuel used. The following sub-sections review how changes inthe fuel used and the cofiring of coal with other fuels canalter the characteristics of the fly ash.

4.1.1 Coal switching and blending

A separate report by IEA Coal Research deals with the effectof switching to cheaper coals on ash formation (Carpenter,1998). Most of the concerns raised in that report relate to theeffect of poorer quality of the coal on the power plant and ashhandling facilities. Poorer coals commonly contain higherquantities of ash which, in turn, lead to higher amounts ofcoal residues which have to be used or disposed of. However,a high ash content in coal can promote fly ash marketabilityby ‘diluting’ the residual carbon content of the ash. Carpenter(1998) cites case studies where the addition of Powder RiverBasin coals to bituminous coal feeds in some power plantsdecreased the carbon content of the fly ash. This was foundto be the case at the St Clair power plant, MI, USA, where,

after changing to Powder River Basin coals, the fly ashbecame marketable (Evans and others, 1991). Equipmentproblems relating to coal fineness in such situations canactually increase the carbon in ash content, making the ashunsaleable. When coals with different fuel ratios are blended,the coal with the higher fuel ratio usually has a greater effecton the unburnt carbon content of the ash (Okamoto, 1998).Carpenter (1998) warns that inaccurate blending of coals canresult in poor combustion that will affect the fly ash qualityand its sale.

Affolter and others (1997) studied the effect of different coaltypes on bottom ash and fly ash at a 500 MWe power plant inKentucky, USA. Changes in the chemistry of the coal werefound to be reflected in the chemistry of the ashes. Changeswere noted in shape, fineness, particle-size distribution anddensity of the fly ash produced. Such changes could lead tochanges in the adsorption of selected elements on the ash.The relationship between the feed coal and the ash chemistrywas not easy to interpret. Further study by the same researchgroup (Brownfield and others, 1997) concluded that high-sulphur feed coals lead to ash with higher As, Ca, Cd, Fe, Mnand Zn than low sulphur coals because of the higher contentsof calcite, pyrite, sphalerite and magnetite. The low sulphurcoal ash is higher in Li, Al and Si due to higher contents ofkaolinite, illite and mica.

Fly ash from the combustion of brown coal is more variable,comprising silt-sized, spherical particles of cementitious ash,char (coarse unburnt woody waste) and sand. The proportionsof these constituents depend upon the presence of woodymaterial and sand inter-burden in the coal (Williams, 1996).Brown coal is commonly combusted in either FBC systemsor other systems using lime. The resulting ashes are thereforealkaline with pozzolanic and hydraulic properties.

vom Berg and Puch (1993) reviewed the effect of fuel typeon the trace element content of the ash in FBC systems. Ingeneral, bituminous coal ashes contain higher amounts oftrace elements than brown coal ashes. FBC ashes frombituminous coal-fired plants are characterised by a relativelyhigh chromium content (<0.1 mg/l in leachate analysis) whilebrown coal ashes contain high concentrations of chloride(980 mg/l in leachate analysis). Brown coal ash is alsoreported to have very low heavy metal contents but highcontents of boron (Meyrahn and others, 1997). In wood andother vegetable matter used for combustion the ash formingspecies are generally present in organic molecules and ionsdissolved in the cell fluid. Peat, almost an intermediatebetween wood and coal contains both mineral grains andorganically associated ions (Steenari and others, (1999).However, the variation between the chemistry of coals andcoal types is so great that no generalisations can be madewhich would apply to the trace element or mineral content.

Klein (1999b) has compared the different components of coaland waste coal combusted in CFBC units in the USA. Waste


Improving fly ash quality

unit IDcyclone burner typecyclone burner manufacturercyclone NOX ctrl methodcyclone NOX ctrl manufacturercyclone SO2 ctrl methodcyclone SO2 ctrl manufacturer

CYCLONE

unit IDunit namecombustion typeunit size MWplant nameplant addressowner operator nameowner operator address

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unit IDPC burner configurationPC burner manufacturerPC NOX ctrl methodPC NOX ctrl manufacturerPC SO2 ctrl methodPC SO2 ctrl manufacturer

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unit IDfurnace typesteam generator typefurnace manufacturersteam generator manufacturer

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unit IDdesign fuel namedesign mine namedesign mine locationdesign seamdesign fuel rank

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unit IDfuel feed systemash removal system

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ANALYSIS

Figure 4 Conceptual data model for a coal ash properties database (O’Leary and others, 1997)

coal has a lower HHV (high heating value) and carboncontent and a much higher ash content which will ultimatelylead to a greater amount of ash produced in the residues. Onaverage anthracite culm, anthracite silt and bituminous gobhave at least four times as much ash on a weight percentbasis as anthracite coal, subbituminous coal, bituminous coaland lignite. The waste coals also tended to have slightlyhigher contents of silicates but lower iron oxide contents.Table 8 shows the effect of different fuel types on the amountand type of ash produced in a 300 MWe CFBC boiler.

Conn and others (1997a and b) has considered the effect offuel type on the marketability of fines collected from CFBCboilers. Table 9 shows the potential uses for the residues froma 300 MWe CFBC boiler firing fuels such as anthracite culm,high sulphur bituminous coal and petroleum coke. It is clearfrom the table that different fuels lead to residues which aresuited to very different applications.



No data were available on the effect of fuel type on PFBCand IGCC residues.

4.1.2 Cofiring

As with blending of coals, cofiring of coal with othermaterials can affect the chemistry and physical characteristicsof the ash. Although this may or may not affect the suitabilityof the ash for construction uses, the current relevantEuropean standard, EN 450 Fly ash for concrete, states thatthe fly ash has to come from furnaces fired with pulverisedbituminous coal or anthracite. Until this standard is amended,ash produced from cofiring, such as that discussed in thesections below, cannot be sold in the existing marketplace inEurope. Similarly, the American Society for Testing andMaterials (ASTM) specifications used in the cement industryalso specify the use of fly ash from coal combustion only.

Table 8 Comparison of quantity of residue generated by a 300 MWe CFBC boiler firing different coals(Klein, 1999b)

Fuel Eastern US Midwest US Western US US Great Petroleumanthracite high sulphur (Utah) Plains cokeculm bituminous bituminous lignite

Ash, as-rec'd, wt.% 30 15 8 10 0.5

Sulphur as-rec'd, wt.% 0.5 3.0 1.0 0.7 5.0

HHV, as-rec'd, Btu/lb 7000 12,500 13,500 8000 15,000(MJ/kg) (16.28) (29.07) (31.40) (18.61) (34.89)

Ca/S ratio 3 2.0 2.5 1.5 1.8

Ash rate, 103 t/y 612 328 138 212 330

Comment fuel ash mostly sorbent fuel ash alkaline ash sorbentand sorbent and sorbent

Table 9 General utilisation potential of CFBC residues by fuel type (Conn and others, 1977a)

General ash Petroleum Anthracite Low S High S Medium Srequirements coke culm bituminous gob bituminous bituminous

ConstructionC or F fly ash FAS>50/70 L M M L M

SO3 <5Structural fill High FAS and/or M H H M H

free CaORoadbase High FAS and/or H H H M H

free limeAgriculture Equivalent H L L H L

CaCO3 >60%

Waste treatmentSolidification Free CaO >20% H L L H LStabilisation SO3 highN-Viro Free CaO >20% H L L H L

Utilisation potential: L = low. M = moderate. H = high

Problems with these standards were discussed in more detailin Chapter 3.

The consideration of the effects of cofiring other materialssuch as straw, wood, refuse-derived fuel, sewage sludge andtyre-derived fuels with coal are discussed in more detail in aseparate report by IEA Coal Research (Davidson, 1999). Inthat review the effects of the different fuels on themarketability of the ash were discussed and are summarisedhere with additional material added where relevant.

BiomassThe Federal Energy Technology Centre (FETC) of the USDOE is working with the Electric Power Research Institute(EPRI, USA) on the cofiring of coal with a number ofbiomass wastes such as switch grass, wheat straw, rice straw,almond hulls, almond shells, olive pits, paper and wood. Inaddition to evaluating the effect of the change in the ashcomposition on the applicability of the fly ash to constructionuses, the project is working towards developing an actionplan to accelerate the acceptance of mixed ashes (Feeley,1998). No results have been published as yet.

Ash produced from co-combustion of coal with straw is ofpoor marketability due largely to the high concentration ofpotassium and chlorine in straw. Studies from Scandinavia,where cofiring of coal with straw is most common, indicatethat when straw is added at greater than 10th% the ashbecomes unacceptable for cement production and at greaterthan 20th% the ash is unsuitable even as an additive incement (Davidson, 1999). However, a study by Wieck-Hansen and Hansen (1998) suggested that the type of coalused was important. If low sulphur coal is used, then ashfrom co-combustion with 10th% straw may still be ofadequate quality for cement production.

An earlier study by Wieck-Hansen (1996) on the use of50th% straw and coal in CFBC systems found that thepotassium concentrations were so high that cement andconcrete applications were impossible. However, since themajority of the potassium present was either water soluble(35%) or acid soluble (90%), washing may produce a fly ashwhich could be used.

WoodAccording to the review by Davidson (1999), most cofiringwith wood does not have a detrimental effect on the fly ashproduced and the ash is still suitable for cement and concreteapplications. The one major effect noted was a change in theamount of fly ash produced. At the 635 MWe Gelderlandpower plant in the Netherlands, when waste wood substitutedfor 45 kt of coal there was a reduction of 4 kt/y ash since theash content of wood is ten times less than that of coal.

Steenari and others (1999) compared the combustion of coal,peat and wood in a 12 MWt CFBC boiler in Sweden. Thecombustion of wood produced ash with high calciumcontents and also elevated concentrations of K, Mg, Mn, Znand Cd. Cofiring of coal, peat and wood chips in the sameplant in Sweden showed an increase in calcium due to thehigh calcium content naturally occurring in wood. Wood alsohas a relatively high content of potassium and magnesium.



The clay minerals in peat give rise to an increase in thealuminium content of the ash and resulted in ash with solublesilica. In all ashes the leaching of major and trace elementswas ‘very low’ (Steenari and others, 1997).

In an IEA CR review of cofiring coal with waste, Ekmannand others (1996) cite information suggesting that, althoughash from wood combustion alone is suitable for fertiliser forreforestation, ash from cofired wood and coal is no longersuitable due to less favourable qualities.

Refuse-derived fuelCofiring of waste materials such as municipal solid wastewith coal can increase the concentration of heavy metals inthe fly ash, especially mercury. However, leaching tests haveindicated that, with the exception of aluminium, leaching ofthese species is within recommended limits (Davidson,1999). A study by Sundermann and others (1995) of cofiringmunicipal waste with coal in an FBC unit found that the ashcould easily be dumped or reprocessed as building material.However, the bag filter ash had to be discarded (less than2.5% of the total ash produced).

Sewage sludgeCofiring coal with sewage sludge, which has only one third ofthe heating value of coal, increases the amount of ashproduced by around five times. Even at 5 th% cofiring theamount of ash doubles. Despite this, no detrimental effect onthe quality of the ash was noted, even when consideringindividual trace element concentrations. Phosphorus, zinc andcadmium may be enriched on some particles, but not to anydetrimental level when less than 10% sewage sludge is used.When firing greater amounts of sewage sludge, some metalsmay become loaded in the smaller size ash fractions makingthe ash unsuitable for cement manufacture in countries such asGermany where relevant standards apply (Davidson, 1999).

Tyre-derived fuelAccording to Tesla (1994) cofiring of coal with scrap tyrechips in a chain grate stoker produced ash which is similar tothat produced from coal alone. The bottom ash from suchcombustion has been used as a road traction agent and the flyash was used in cement making.

4.2 Operating conditions of theplant

Section 2.1 summarised the different ash types produced bydifferent combustion systems (pulverised coal units, FBCsystems and gasifiers). This section will concentrate on theeffect of pollution control systems on fly ash. Since the mostcommon FGD systems (wet lime/limestone gypsumscrubbers) are fitted downstream of fly ash capture systems,the installation of most FGD does not have an effect on flyash quality and is not discussed here.

Low NOx burners and other primary measures for NOxcontrol have been found to have largely detrimental effects onfly ash characteristics. For example, according to Fisher andothers (1997), the control technologies implemented tocomply with the US regulations promulgated for the 1970’s

Clean Air Act along with the 1990 Clean Air ActAmendments (CAAA) have had a significant impact on theusage of fly ash in the concrete industry. In fact, it has beenestimated that, in the USA, 700 kt/y of quality ash iscontaminated due to the NOx reduction rules alone and thatthis could increase to 7 Mt by the year 2000. This would beequivalent to a loss of revenue of more than $150 M/y.However, this figure assumes that no steps are being taken toreduce the increased carbon in ash, which is not the case asdiscussed in the following section.

4.2.1 Start up and other non-standardconditions

The quality of fly ash can be influenced by the mills, fans,burners, burner controls, boiler controls and boilerconfiguration. For example, the flame temperature and rate ofcooling affect the formation of the glassy mineral surface offly ash particles which is the source of their pozzolanicreactivity. Coal mill settings directly affect the fly ashfineness. The mill fineness, mill loading, excess air, burnerdesign and balance of burning conditions in the furnace allaffect the LOI (Lister, 1997). Clearly if anything occurs toupset the smooth running of any of these systems, there couldbe a negative effect on the quality of the ash.

Start-up and shut-down periods generally give rise to lessefficient combustion conditions and therefore also affect suchparameters as the LOI. Data cited in the previous IEA CoalResearch report on this subject (Sloss and others, 1996)suggested that ash produced during start-up and shut-downperiods gave rise to problems with expansion of concrete andreduced resistance to sulphate attack. Oil burning duringstart-up and for flame stabilisation at low loads leaves an oilresidue in the ash (Lister, 1997). Unburned oil residue in flyash is known to cause problems with the use of ash as apozzolan. Unburned oil also aggravates problems of erraticair entrainment in fly ash concrete and may even affect thecolour of the resulting concrete (Sloss and others, 1996).

Large-scale coal-fired power plants are run to achievemaximum efficiency over extended periods and, excludingstart-up and shut-down periods, should not undergo a lot ofminor adjustments during combustion. In practice, plantsdealing with large changes in demand, such as those in theUSA, can go through large changes in output on a daily basis(Robl, 1999). Industrial boilers are easier to control on a finerlevel. Barnes (1998) describes the study of combined NOxand carbon in ash control in small scale boilers. Boilers canbe run with a minimum back-end oxygen level of 5%. Thiseliminates carbon monoxide spiking and reduces the carboncontent of the ash. It was found that the LOI of the ash couldbe reduced further by running the boiler at a higher back-endoxygen concentration. In addition it was noted that reductionof the boiler load increases the LOI of the ash ‘significantly’.

Although detrimental effects of non standard boiler operationon fly ash are well known, no data have been found relatingto how such fly ash is handled. In some cases it may beblended with other ash, in other cases it may be disposed ofseparately.



4.2.2 Low NOx burners

In another report by IEA Coal Research on plant upgrading,Scott (1997) summarised the main effects of low NOxburners on fly ash as follows:● size: low NOx combustion appears to produce coarser

ash than uncontrolled combustion;● shape: the particles are more angular and irregular than

the predominantly spherical particles produced fromuncontrolled combustion; and

● carbon content of the ash: tends to increase whencombustion conditions are modified to reduce the rate ofNOx emissions.

With respect to size and shape, the size distribution of fly ashparticles can change after retrofitting of low NOx burners. Ingeneral the proportion of fly ash to bottom ash increases andthe fly ash is more porous and friable (Scott, 1997). However,these effects are considered less important with respect to themarketability of the ash than the increase in unburnt carbon.Low NOx burners are designed to generate a cooler flamewhich increases the unburned carbon content of fly ash, thusreducing its marketability. According to Lister (1997) ‘lowNOx conversion doubles LOI’. Levels of LOI in ash haverisen from below 4% to over 15% due to the introduction oflow NOx burners. High LOI can lead to problems with airentrainment in concrete (see Chapter 6). The standardsreviewed in Chapter 3 for cement and concrete productionspecify that the LOI of fly ash must be below 5% in somecountries. Low NOx burners can therefore reduce previouslymarketable fly ash to an unmarketable quality (Fisher andothers, 1997).

Hower and others (1997b) carried out a study on the effect ofconversion of tangential and wall-fired units to low NOxburners at a mid-western US plant firing high sulphur Illinoisbasin coal. It was found that the carbon content of the ashincreased following the conversion. In units 1 and 2 of theplant studied this increase was not enough to make the flyash unsaleable. However, the fly ash from unit 3 may havetoo high a carbon content to be used as a pozzolan inPortland cement following the conversion. The particle sizedistribution of the fly ash before and after conversion foreach of the units is shown in Figure 5. Samples werecollected from different bins in the ESP of each unit. Forunits 1 and 2 only the bins on the ‘hot-side’ of the ESP wereaccessible for sampling. The arrangement of the ESP bins inunit 3, both ‘hot-side’ and ‘cool-side’ are also shown inFigure 5. For units 1 and 2 the pre-conversion fly ash is finerthan the post-conversion ash. The same is also true for unit 3where it was also demonstrated that the ash in the second rowESP bins was finer than that in the first row. The increase incoarseness has been attributed, to some extent, to a relativeincrease in quartz following conversion. The lowertemperature of the low NOx burner causes a decrease in themelting of quartz. The distribution of carbon in ash relative tothe particle size distribution varied from unit to unit. Thepetrography of the fly ash samples was also studied beforeand after conversion and was found to change. Figure 6summarises the data from one of the ESP bins in unit 1 of theplant. There was a noticeable shift of some of the minerals to

the smaller size fractions following conversion. Hower andothers (1997b) conclude by warning that all fly ashes shouldbe retested following such conversions to determine whetherthe ash is still suitable for any intended purpose.

The carbon content of the fly ash can be kept under control tosome extent by finer grinding of the coal and increasedattention to coal and air distribution in the boiler. Hower andothers (1997a) compared the fly ash from the 200 MWetangentially-fired John Sevier Fossil Plant in Rogersville, TN,USA before and after the conversion of the plant to low NOxburners. It was found that, by proper maintenance of thepulverisers to maintain improve the percentage of fines in thefeed coal and concomitant improvements in the air:fuel ratio,the carbon in ash content of the fly ash actually decreasedafter the installation of the low NOx burners. The fly ashafter conversion was coarser and it was found that, despitethe lower overall carbon in the post-conversion ashes, therewas increased carbon in the fine-size range which may stillhave an impact on the utilisation of the fly ash. The postconversion ashes had partially-melted coal particles presentwith recognisable vitrinite and liptinite macerals representing



Configuration of ESP bins for unit 3

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Figure 5 Particle size analysis for –500 meshfraction combined with wet-screeningresults

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25

30

100 x 200 200 x 235 235 x 500 -500

b)

Carbon formsUnit 1/Bin 15 post-NOX Inertinite

Anisotropic Coke

Isotropic Coke

Figure 6 Carbon forms in each size fraction forpre-combustion and post-conversionsized fly ashes



the non-combusted cores of much larger particles. The quartzcontent of the post-conversion ashes was also higher as aresult of the lower combustion temperatures of the low NOxburners. Hower and others (1997a) concluded that thereactivity of the inorganic fraction of the ash may beinfluenced by the reduced combustion temperaturesemployed in low NOx combustion.

In order to increase the marketability of fly ash as a concreteadditive following the introduction of low-NOx burnersthroughout the Netherlands, a sieving plant was built in 1995to reduce the loss on ignition whilst increasing thehomogeneity of the product. The plant can store up to 41 ktof ash (vom Berg, 1998). American Electric Power have usedan electrostatic separation process to improve fly ash from aplant fitted with low NOx burners (Huang and others, 1997).Fisher and others (1997) have developed a process known asASH PROTM Liberation Process to ameliorate the negativeaffects of both low NOx burners and flue gas treatments suchas selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). All of these beneficiationprocesses are discussed in more detail in Section 4.4 below.

The American Coal Ash Association (ACAA, 1997) haspublished an analysis of the effect of the US EPA NOxemissions reduction programme on coal ash using a life cycleassessment approach. The analysis evaluated the situationbefore and after the implementation of Phase II of the NOxreduction programme were:● Pre-phase II – fly ash is used as a material to replace

cement in concrete production; and● Phase II – fly ash is less useful as a cement material due

to the effects of low NOx burners but is still acceptablefor structural fill.

Considering emissions as well as solid wastes, the studyindicated that in Pre-phase II, CO2 emissions from cementproduction were reduced due to the replacement of cementwith fly ash. However, Phase II yielded lower NOxemissions due to the presence of the low NOx burners. Theconclusions of the study were that, from a life cycleperspective, the environmental flows were generally loweroverall from Pre-phase II, with the exception of NOx. Ineither case, fly ash will be used beneficially, thereby savinglandfill space.

4.2.3 SCR and SNCR

Both high dust SCR (selective catalytic reduction) and SNCR(selective non-catalytic reduction) for NOx control use ureaor ammonia injection processes to convert NOx to harmlessby-products. However, this process leaves the ashcontaminated with residual ammonia. The ammonia contentof fly ash before SCR and SNCR installation is commonlyaround 10 ppm and can increase to around 20–50 ppm afterinstallation. As the efficiency of the catalyst decreases overtime and this may be dealt with by increasing the amount ofammonia injected (Scott, 1997). Residual ammonia in fly ashfrom some low NOx treatments have been measured at over700 ppm. Ammonia can cause health and odour problems(Fisher and others, 1997).

The most common ammonia compound present in the fly ashafter such treatment is ammonium bisulphate (NH4HSO4)although other compounds may be present, such asammonium sulphate [(NH4)2SO4], ammonium carbonate[(NH4)2CO3], ammonium bicarbonate (NH4HCO3), andammonium chloride (NH4Cl). The compounds have differentdecompositional temperatures and therefore their presencewill depend on flue gas and fly ash properties. A Germanstudy on fly ash affected by an SCR installation found thatthe ammonia was present in the form of ammoniumbisulphate at a concentration of 200 ppm but that thisconcentration did not affect the workers and the odour wasbarely detectable. In another study the 300 ppm ammonia inthe fly ash was found to have no effect on the concreteproperties tested (Fisher and others, 1997). A further study byvan der Kooij (1997) at the Maas power station in theNetherlands showed that, as a result of the installation of anSCR system, ammonia was present on the fly ash in the formof ammonium sulphate. Again the only problem reported wasthe emissions of ammonia in poorly ventilated areas. Ashsamples with up to 200 ppm ammonia were used to createconcrete floors in enclosed areas. Although the ammoniaconcentrations were around 27 ppm as the concrete waspoured (detectable by smell), the concentration was reducedto 5 ppm or less within 8–10 hours. Ash samples with100 ppm ammonia or less did not produce a smell. Thepreparation of concrete with fly ash containing 300 ppm ormore ammonia in enclosed spaces could result in exposureconcentrations exceeding the 25 ppm maximum allowable inthe Netherlands.

According to the US EPA (1997) ammonia slip, and thereforeammonia in fly ash, can be controlled by systemmodifications. The report also points out that a large portionof eastern and midwestern US bituminous coal fly ash isacidic and therefore the spontaneous release of ammoniafrom these fly ashes may not be of concern. A review ofplants in the USA with SCR fitted indicated that most werestill selling fly ash and that fly ash contamination was notreally an issue. However, despite the fact that ammoniacontamination may not be a technical problem in fly ash use,it is still an aesthetic barrier. The ASH PROTM LiberationProcess has been designed to remove residual ammoniumcompounds from fly ash. The process uses temperatures of300°F (150°C) or higher for residence times of one minute ormore to liberate the ammonia from the fly ash. The ammoniais then recycled (Fisher and others, 1997).

4.2.4 Limestone addition for sulphurcontrol

Lime and similar sorbents are added to some boilers for SO2

control. The effect of the lime on the characteristics andreactivity of the ash has been covered in Chapter 2 and inprevious reports by IEA Coal Research (Sloss and others,1996; Sloss, 1996). However, lime addition can also affectthe ash in other ways. Kakaras and Vourliotos (1995) studiedthe fly ash collected in the baghouse on a semi-industrialscale 1.2 MWt CFBC plant at Niederaussem, Germany whichwas burning Greek lignite. When the plant was runningnormally the carbon in ash content was around 2.1%.

Table 10 Effect of activated carbon and lime on fly ash (Pflughoeft-Hasset and others, 1997)

Analyses Baseline LAC Lime ASTM C618 Specificationsinjection added Class F Class C

Silicon dioxide, % 21.90 21.30 15.80Aluminium oxide, % 12.90 12.50 8.68Iron oxide, % 9.23 8.56 6.34Total, % 43.30 42.40 30.80 70 min 50 minSulphur trioxide, % 10.00 10.60 14.30 5 max 5 maxCalcium oxide, % 21.50 21.50 35.90Moisture content, % 0.08 0.12 0.08 3 max 3 maxLoss on ignition, % 0.04 1.14 0.66 6 max 6 maxAvailable alkali, % 5.65 5.80 4.67 1.5 max 1.5 maxFineness, retained on No. 325 sieve, % 2.77 3.37 13.39 34 max 34 maxCement activity index @ 7 days, % 102 110 96 75 min 75 minCement activity index @ 28 days, % 94 93 90 75 min 75 minWater requirement, % 95 96 98 105 max 105 maxAutoclave expansion, % 0.19 0.18 0.31 0.8 max 0.8 maxSpecific gravity, % 2.82 2.72 2.70Maximum dry density, pcf 108.0 105.8 102.0Optimum moisture content, % 20.5 20.5 26.0

the LAC and lime treated samples. The table also includesdetails of the current ASTM specifications for classificationof fly ash, as discussed in Chapter 3. The CaO and SO3

content of the ash increased as expected and the fineness wasalso noted to decrease. The use of LAC increased the LOI asexpected but this increase was not enough to be detrimentalto the marketing of the ash.

4.2.6 ESP and baghouses

ESP are divided into two main types by temperature – hotside ESP (350–380°C) and cold side (120–180°C) ESP. Atthe lower temperature in coal-side ESP the fly ash has amaximum electrical resistance. Coal with a low sulphurcontent (<0.1%) and a low NaO2 content (<0.1%) mayproduce ash which is captured with poor efficiency in suchsystems (Okamoto, 1998).

The fly ash caught in hot-side ESP is reported to be coarserthan that found in cool-side ESP. The concentration of themore volatile trace elements, such as Zn, As, Cd and Pb,increased from the hot side ESP to the cool side ESP. This isdue to the cooling effect and the greater surface area to sizeratio of the finer particles. Breit and others (1996) alsoreported a difference in the trace element concentration ofash caught on the hot and cold side of ESP units but alsonoted variability in the measurements of up to 160% forelements such as Se. The concentration of potentialhazardous elements was found to be consistently higher inthe coal side rather than the hot-side ash. The difference wasreported to be due to the differences in the abundances ofglass, spinels and residual carbon between the fly ashes ineach area. The differences in composition could also be duein some part to condensation. The smaller, cooler particles inthe cold-side fly ash would favour condensation of elementsfrom the exhaust gas.

According to Meij and others (1985) the collection efficiencyof ESP depends upon the electrical resistance of the ash



However, during the addition of lime at a high Ca:S ratio of3.12 there was an increase in the unburned carbon content toas much as 13.1%. When the Ca:S ratio was lowered to 2.67the value for unburned carbon was 8.3%. If the Ca:S ratiowas decreased further to 2.01 the unburned carbon content inthe ash dropped to an average of only 2.1% after 2 hours ofnormal operation.

Thermally active marbles (TAMs) can be used as sorbents inplace of limestone and related products. The injection ofTAMs into all major classes of boilers is reported to providea much more efficient control of SOx than limestone. It hasalso been found that TAMs improve the combustionefficiency of boilers and thus lower the unburned carboncontent of the ash. Baer and Luftglass (1997) report on theuse of TAMs in CFBC boilers where the unburned carbon inthe bed ash and the fly ash were reduced by over 30%. Theysuggest that TAMs could be used in pulverised coal-firedsystems to reduce the unburned carbon content of the ash.Initial studies of the process, known commercially asNOVACON, at a small scale pulverised plant showed that theprocess also lead to coarser ash which could aid recovery inESP and baghouses.

4.2.5 Sorbent addition for traceelement control

In the future, flue gas treatment for trace element control,especially mercury, may become necessary on some coal-fired power plants. If this is the case then sorbents such asactivated carbon may be used. These sorbents may be usedeither in combustion or post-combustion arrangements.Pflughoeft-Hassett and others (1997) have tested the potentialeffects of such sorbents on the fly ash produced. Pre-combustion treatment with lime and, separately, post-combustion treatment with lignite-based activated carbon(LAC) was tested on a pilot-scale combustion unit burningBeulah lignite. Table 10 shows the chemical and physicalcharacteristics of the baseline ash (no sorbent treatment) and

29


which, in turn, depends upon its chemical and mineralogicalcomposition. The collection efficiency will be positivelyinfluenced by S>>Na>Fe,K and negatively influenced by Ca,Mg> Si, Al. The concentrations of these elements becomemore important when the sulphur content of the coal is low(<0.6%) and if the NaO2 +K2O concentration of the ash isbelow 1.5% and the MgO+SiO2+Al2O3+CaO is greater than85%.

Baghouses are more common than ESP in FBC systems.ESP are less efficient at capturing FBC ash than pulverisedcoal ash because of the higher electrical resistivity and thesmaller particle size of the FBC ash. ESP and baghousesmay be prone to problems with the fineness of ash fromCFBC systems and the cohesiveness caused by the use ofsorbents for SO2 control. These problems, plus the increasedabrasiveness of the ash, can lead to increased maintenancerequirements on these baghouses (Scott and Carpenter,1996).

Although SO3 is often used to condition ESP and enhance flyash capture in pulverised coal-fired units and FBC systemsthere has been nothing published to suggest any notabledetrimental effects on the fly ash. Lister (1997) notes thatsodium compounds used to decrease fly ash resistivity in ESPsystems can also raise the alkali content of the fly ash andthus lower its marketability. Ammonia is an alternativeconditioning agent for ESP, and is used with low sulphurcoals which produce fly ash that does not respond to SO3

conditioning. Such ammonia conditioning is often requiredunder CAAA permitting in the USA. However, this injectionof ammonia can lead to contamination of the fly ash withhigh levels of ammonia compounds, up to 2500 ppm in somecases. These compounds would be released in an alkalineenvironment such as a concrete slurry. Although the ammoniahas not been reported to cause any negative effects on thetechnical quality of the ash, the ammonia release causespotential health and odour problems (Fisher and others,1997). Effects of ammonia contamination on fly ash are moreprominent when ammonia is used in SCR and SNCRsystems. These effects were therefore discussed in moredetail in Section 4.2.3 above.

According to Lister (1997) baghouse collection equipmentprovides a more uniform collection pattern than precipitators.Some differences in layering may develop in the hoppersbetween cycles due to the falling of coarser material to thehopper whilst the finer material sticks to the bags. When thebags are cleaned a layer of fine material is deposited on topof the coarser ash in the hopper. Hower and others (1997)studied the fly ash caught in a 200 MWe plant fitted withmechanical collectors and hot and cold side ESP. The resultsindicated that the coarser ash was caught in the mechanicalseparators. In ESP systems the distribution of fly ash throughthe precipitator and other particle collection systems is noteven. Around 70–90% of the fly ash entering the ESP settlesin the first row of bins. Then 70–90% of the remainder settlesin the second row and so on. It is common for the ash in thefirst row to be coarser that succeeding rows. The LOI may behigher in either the first or last rows depending on theparticle size gradation of carbon compared to the particle sizegradation of the ash (Lister, 1997).

4.3 Handling, storage and transport

Ash can be absorptive and reactive and therefore the way it ishandled can either improve or lower its marketability. Inmodern power plants the fly ash is transferred to a storage siloand supplied to the consumer in a dry form. Storage facilitiescan be silos made of conventional steel or concrete or flatbuildings where removal is achieved by mobile equipment.Converted oil tanks and concrete free standing domes can alsobe used. In Germany the increase in the utilisation rate of hardcoal fly ash to almost 100% is reported to be due, at least inpart, to measures taken to expand the existing silo space forinterim storage (Puch and vom Berg, 1997). Similarapproaches to storage of ash are being taken in theNetherlands and Denmark and are being proposed in China(see Chapter 5). Lister (1997) emphasises the importance ofstorage of fly ash to provide a reliable flow of fly ash tomarkets despite high demand and low production times. Herecommends a storage volume equivalent to 10% of the annualplant production to ensure that saleable fly ash does not haveto be disposed of during high production periods. Figure 7shows a simulation of storage requirements versus sales toachieve 100% fly ash sales at a typical coal-fired power plant.

Dürnrohr Power Station in Austria is a good example of howstorage of ash works to enhance sales. The power station hasa long-term supply agreement with the cement industry forfly ash delivery. The plant produces 1–5 t/h coarse ash (slag)and 15–20 t/h fly ash (ENV, 1998). The fly ash producedfrom the plant is immediately transferred to one of six10 x 30 m silos. To compensate for the difference betweenproduction of fly ash during the winter and the demand bythe cement industry during warmer months a high-capacitysilo was erected to hold 36,000 m3 of fly ash. Any ‘excess’fly ash from the plant is transferred to the stockyard the baseof which is sealed with a special foil to ensure that noleakage occurs. The rainwater falling onto the stockpile iscollected and used in the desulphurisation unit. Thesurrounding groundwater is tested frequently to ensure thatthe stockyard is properly sealed. This fly ash can bereclaimed at a later stage (ENV, 1998).

If silo or other dry storage facilities are not available then theash may have to be stored in a wet form. High calcium

Figure 7 Simulation of storage requirements for100% fly ash sales (Lister, 1997)

Trends in the use of coal ash

transportation. The AWDS process produces a slurry of fly ashand water which is pumped to a disposal site or used assubsidence control in backfill for mines. The AWDS processwas tried on CFBC residues and also CFBC residues whichhad been subjected to the CERCHAR process. TheCERCHAR process involves the two-stage hydration of highlime coal combustion residues under pressure with superheatedsteam. The process achieves the 100% conversion of lime toportlandite. The study concluded that the AWDS method wasideal for the disposal of CFBC in mines but that thecombination of the CERCHAR process and the AWDS methodwas less than ideal as the slow strength development of thematerials could be problematic in the field.

The transport of ash to the final point of sale or use is one ofthe highest costs in fly ash management. Some miningcompanies now use the same trucks that were used to supplycoal to the power plant to return the ashes to the mine for useas mine backfill or disposal (see Chapter 6). This reducestransport costs significantly. The economics of fly ashtransport within a fly ash marketing and managementprogramme was discussed in more detail in Chapter 3.

4.4 Processing and beneficiation

There are an increasing number of practical and commercialsystems available for improving the quality of fly ash.Schulze and Appenzeller (1998) have reviewed the differentsystems which are commercially available and havesummarised these in Figure 8. Each of the processes includedin the figure and any other relevant processes will bereviewed briefly in the following sections starting with thesimple physical processes and moving on to more complexsystems.

4.4.1 Size classification

The most common methods of classification are screening



(Class C) fly ashes are self-cementitious if exposed to waterand therefore wet storage should be avoided, if possible.Even when stored dry, it has been reported that pulverisedcoal ash shows a decrease in maximum dry density and anincrease in porosity with storage time. In countries such asIndia it is common for all fly ash to be stored wet in ponds.Ranganath and others (1998) have studied this ponded ashand found that it contains both reactive, small particles andnon-reactive or poorly reactive large particles and, as a result,loses its pozzolanicity. This makes the ash particularlydifficult to handle and sell. The use of ponded ash as apozzolan would only be possible if the non-reactive largesized particles could be separated out. Ranganath and others(1998) conclude that the practice of wet disposal isdetrimental to the use of ash and should be avoided.

Wet ash handling systems, such as those used in India, can beupgraded. For example, a wet bottom system at the 300 MWePtolemais Power Plant in Greece has been replaced with anew dry, ash recycling system. The novel system has thepotential to return high carbon ash to the boiler for re-combustion. The bottom ash and fly ash produced in theupgraded system are now suitable for sale to the constructionindustry (Heliostat Ltd, 1997).

In Australia in the past it was standard practice for fly ashfrom both coal and brown coal to be mixed with water anddisposed of by pumping to an ash impoundment (Williams,1996). However, since 1996 most fly ash from black coal iscompacted to a medium density at an optimum moisturecontent of 30% and placed in special storage with thepotential for future utilisation. The cost of this type of storageis at least $4/t (excluding the cost of site preparation). For the5.8 Mt of fly ash in excess of what is used in Australia, thismeans a cost of $33 million/year. This is considerably moreexpensive than the $21 million/year spent on land filling the7 Mt of excess fly ash produced in 1992 (Samarin, 1997).

Burwell and others (1995) describes the Polish AWDS (ashwater dense suspension) method for ash management and

Activity index

Particle size

Unburned content

Free lime content

SO3, CI, Na2O etc.

Bulk density, H2O, pH

Trace elements No effect

Class

ificat

ion

Agglo

mer

atio

n

Burni

ng

Mixi

ng p

roce

ss

Homog

enisa

tion

Condi

tioni

ng

Sint

erin

g pr

oces

s

Ash Parameter

Practical method

Possible method

Influence unknown

Legend

Process

Figure 8 Methods for fly ash processing



and sieving into different size classes. To some extent theparticle size is related to the carbon content with the finerfractions having lower LOI. In practice, the separation limitof the separation process can be adjusted such that the finematerial falls below the maximum limit for the unburnedcarbon content. The processing and blending plant atMaasvlakte in the Netherlands includes sieving as part of theblending process (see further details in Section 4.4.4). TheShin-Ta power plant in Taiwan is fitted with a three-dimensional vibrating sieving machine which divides the ashinto four distinct size fractions for separate sale (Sloss andothers, 1996).

Air classification is a well established system similar tosieving but achieves separation primarily as a result ofdifferent aerodynamic properties of different size fractions.Examples include the fly ash processing unit at Castle Peak Bin Hong Kong which is based on an air classification systemof 150 t/h capacity. The processed fly ash is high grade with87.5% of the ash passing through a 45 µm sieve (Schulze andAppenzeller, 1998). KEMA in the Netherlands aredeveloping an air classification system with a capacity of2 t/h (Sloss and others, 1996). A variable classificationcyclone device has been developed in Japan for theclassification of fly ash. The system improves the specificsurface area of the ash and reduces the LOI by 20–30%(Morizaki, 1998). Hassan and Cabrera (1998) describe theeffect of air classification on fly ashes from Drax PowerStation in the UK. The conclusions were that the process wasmost effective for improving the fineness and lime reactivityof coarse fly ash. Concrete made from the processed ash wassuperior to that made with ordinary Portland cement.Cornelissen and van den Berg (1998) also emphasise thebeneficial effect of classification on the properties of fly ashwhich make it ideal for use in cement and concrete.

4.4.2 Agglomeration

Agglomeration is a method of concentrating the ash intodiscrete pellets for easier storage and/or transport.Agglomeration processes are based on the addition of water,binding agents or moist bulk materials (sludge) usually ingranulators, mixers, roll presses and similar machinery(Schulze and Appenzeller, 1998). Fly ash that has beenagglomerated can be ground or micronised to release the flyash for use in the construction industry. Ground agglomeratedfly ashes have been reported to have lower compressivestrengths than the original untreated ash (Sloss, 1996).

4.4.3 Grinding/micronisation

Fly ash is a mixture of particles of many different sizes. Insome applications, such as high strength and high durabilityconcretes, finer fly ash (<10 µm) would be preferable. Airclassification could separate out the particles below this sizebut this would generally amount to less than 10% of the flyash used. Grinding or micronisation could reduce all theparticles to below the maximum size specified. Cornelissen(1997) describes the enhanced performance of micronised flyash in concrete. Bouzoubaâ and others (1997) also describes

the grinding together of fly ash, cement clinker and gypsum.The crushing of cenospheres and larger particles in fly ashresults in higher specific gravity and fineness and thereforehigher pozzolanic reactivity. The final cement and concretehave higher strengths with no negative effects on workability.However, in practice grinding of ash is difficult because of itsflowing nature and is consequently expensive (Robl, 1999).

4.4.4 Blending/mixing processes

The concentration of LOI in fly ash can be evened out byblending of different ashes. Low LOI ash which easily meetsthe specifications required can be blended with otherwiseunsaleable high LOI ash to produce an acceptable blend.Simple mixing can be achieved by simultaneouslydischarging two pneumatic conveying lines in the same pointon the storage silo while controlling the flow rate of each.Gravimetric blending with accurately weighed volumes ofeach ash in a dry powder blender produces more uniformblending results (Lister, 1997).

Perhaps the best example of a large-scale blending process isthe SMZ or Maasvlakte Fly Ash Processing plant establishedin 1995 by Vliegasunie which stores and blends fly ash forsale in the Netherlands and abroad. The principal objective ofthe plant is to produce a constant quality of ash for thecustomers. The intake silo consists of 9 bins: 3 receivingbins, 4 blending bins, 1 ship loading bin and 1 bin for storageof the high carbon fly ash from the sieving operation. Thetotal capacity of the plant is 40 kt. The plant processesaround 184 kt of ash per year with a maximum processingcapacity of 250 kt/y, blending high quality ash with lowerquality ash to produce a product which is of an acceptablequality for sale to the cement and concrete industry. Themixing capacity of the plant is around 150 t/h (Oostendorp,1997). Most of the fly ash processed at the plant is from theadjacent Maasvlakte power plant, although some ash arrivesby truck and barge. The final processed and graded product istransported to customers also by truck and barge. Thecharacteristics of the intake fly ash are provided by the ashsupplier and checked at random at the plant. The finalcharacteristics of the processed ash are kept on a fly ashinformation system which is used to record the quality of theash in each storage bin and to match these with therequirements of the customer. The final product isaccompanied by a product certificate which guarantees thecustomers a quality of ash which will produce excellentconcrete (Moret and van den Berg, 1997). An excellentreview of the Maasvlakte plant is given by Moret (1995) andthe interested reader is referred to this publication for furtherinformation. A similar system is in operation at the CastlePeak B plant in Hong Kong which processes ash from a totalof 4120 MWe generating capacity burning oil and more than20 different types of coal. The China Cement Company haslocated a cement plant a couple of hundred yards away fromthe plant to minimise transport costs (Schulze andAppenzeller, 1998).

The Mehrum power plant in Germany is equipped with twohomogenising silos for fly ash. As one silo fills up, thesecond is homogenising. The four different sections of the

Station. The fly ash from two other plants, McMeekin andUrquhart, is also beneficiated at the new plant which hasbeen in operation since mid-1998 and the ash is marketed bySoutheastern Fly Ash Co. The plant is designed to producearound 160 kt of beneficiated fly ash per year (EPRI, 1998a).

4.4.7 Electrostatic separation

Triboelectrostatic separation is based upon the principle thatcarbon is positively charged and ash is negatively charged.By passing ash through a specially designed electric field thecarbon content of the ash can be reduced to a saleable level.Because charge and charge transfer are also dependent onparticle size, triboelectrostatic separation may be performedin conjunction with size classification (Stencel, 1998).

Separation Technologies Inc (STI) have installed anelectrostatic separation system for fly ash beneficiation at theBrayton Point Power Plant in New England, USA. The1100 MWe plant produces around 220 kt of fly ash per year.Due to the installation of low NOx burners, the carboncontent of the ash had become unacceptable (6–25%). Theprocess produces fly ash with a carbon content below 5%plus some residual fly ash with high carbon content(15–20%). This residual fly ash is either used as flowable fillor landfilled (Bittner and others, 1997).

Keun and others (1997) describe a bench-scale triboelectricsystem being developed in Korea which can reduce the LOIfrom 7% to 3% with 80% recovery of the ash.

4.4.8 Ammonia removal

As discussed in Section 4.2, some ESP conditioning systemsand flue gas controls for NOx emissions can lead to anincrease in the amount of ammonia in the ash to the pointwhere the ammonia is detrimental to fly ash sales. Fisher andBlackstock (1997) report on the production of the ASH



homogenising silos are fluidised alternately and aeration ofthe fly ash is achieved. Following homogenisation, the fly ashis tested and commonly sold for filler in concrete (Schulzeand Appenzeller, 1998).

4.4.5 Flotation

The simplest form of flotation separation is the skimming ofcenospheres from the surface of fly ash ponds. More complexflotation systems use frothing and other agents to separatematerials in a liquid state. Froth flotation has been consideredas a means of separating carbon from fly ash. Rubenstein andHall (1998) describe a multi-component columnar flotationcell for the processing of fly ash produced at theNovocherkassk power plant in Rostov, Russia. Pilot studiesindicate that the processed ash is suitable for use in theconstruction industry and for sorbents for water cleaning.However, the major disadvantage of flotation technologies isthat the final products are in water and require furtherprocessing or drying. Although flotation processes for fly ashtreatment have been designed and proposed in recent years(Sloss and others, 1996), none of these appear to havereached commercial scale.

4.4.6 Conditioning/dewatering

The term conditioning refers to the moistening of the fly ashfor subsequent transport as well as to the quenching of thefree lime content for storage (Schulze and Appenzeller,1998). This is most commonly applied to residues which arehigh in lime, that is FBC residues. Conditioning processestypically involve two stages of water addition to control theheat of reaction and the final condition of the ash material.Since PFBC residues are generally lower in free lime thanother FBC residues, their water requirement is lower. IGCCresidues do not generally require conditioning. However,residues from fluidised bed gasifiers are similar toatmospheric FBC (AFBC) residues and can be treated in asimilar manner (Sloss, 1996).

The opposite arrangement occurs when fly ashes frompulverised coal combustion have been ponded or stored inlagoons and the material is required in a dry form. Screening,thickening and vacuum drying processes have been developedfor several sites in Australia and France (Sloss and others,1996) but seem to be designed on a case-by-case basis.

4.4.6 Carbon burn-out

Carbon burn-out is a method used to combust the remainingcarbon from the fly ash after it has left the boiler. Excess airis required and most systems are based on fluidised bedtechnologies. Since the fly ash itself is inert, no other bedmaterials are required. Figure 9 shows a photograph ofProgress Materials’ Carbon Burn-Out facility beingcommissioned in South Carolina, USA. The plant willcombust the residual carbon in 165 kt/y of pulverised fly ash(Hay, 1998). South Carolina Electric and Gas (SCEG) haveinstalled a full-scale carbon burn-out plant at the Wateree

Figure 9 Progress Materials’ Carbon Burn-OutFacility at South Carolina Electric andGas’ Wateree Power Plant (photographcourtesy of Peter Hay, Progress Materials Inc)



PROTM Liberation Process which is reported to improve thequality of ashes with both high LOI and ammoniacontamination. The process is reported to reduce theconcentration of ammonia from as high as 2500 ppm to lessthan 100 ppm. The ammonia released can be recycled. Theprocess is based upon heating of the ash to temperaturesabove 300°F (150°C) for at least one minute. Unpublisheddata suggests that there may be problems with this system(Robl, 1999).

4.4.9 Magnetic separation

Magnetic separation of fly ash produces ferromagneticmaterial. In the system described by Honaker and others(1998) the amount of magnetic material in the sample wasincreased from 11.5% in the feed fly ash to 98.9% in the finalproduct with a mass yield of 13.2%. Work in the CzechRepublic aims at recovering Ti and Al from fly ash from theVresova power plant using the Bayer and caking methods.Around 65% of the Al and 62% of the Ti can be recovered(Fecko and Cablik, 1998). Other systems have been proposedfor the recovery of metals such as silver, gold and platinum(Badulsecu and Andras, 1997) but none has reachedcommercial scale. Removing the magnetic fraction from flyash, using an electromagnet, can produce ash which may givea higher flowability to mortars (Sloss and others, 1996).Removal of the magnetic fraction of fly ash is most commonin combined systems (see Section 4.4.11 below).

The mineral components of residues from FBC systems arediluted with sorbents and therefore metal extraction is lessfavourable than for fly ash and unlikely to be economic. Therecovery of metals from IGCC residues would also beunlikely to be economic unless a particular element werepresent in significantly elevated concentrations. Gasificationslags can contain up to 25% Al2O3 in a readily extractableform and iron, as magnetite, may also be recoverable ifpresent in iron-rich nodules in the slag (Sloss, 1996).

4.4.10 Chemical treatment

Fly ash with a low pozzolanic activity can be made morereactive by the addition of small amounts of Na2SO4 orCaCl2. However, Na2SO4 can lead to sulphate attack inconcrete if present in sufficient quantities and CaCl2 cancause problems with corrosion. The use of these agentsshould therefore be controlled very carefully. Calciumcarbonate can be used in cement and fly ash grouts toimprove setting times (Sear, 1999). The negative effect ofhigh LOI (>5%) on air entrainment in concrete can bereduced by selecting a suitable air entrainment agent whichdoes not react with the unburnt carbon.

Ash for use in land reclamation and agricultural uses is mostsuitable when it is low in leachable salts, acidity and boronconcentrations. These factors can be reduced by storing theash in a lagoon or allowing the ash to be ‘weathered’ overtime.

The hydration of FBC residues, especially CFBC residues, to

decrease their reactivity and increase their handleability wasdiscussed in Section 4.3. By controlling the hydration rateand performing a second lime hydration step at a highertemperature, the resulting residues can be dry and still besuitable for cement and concrete applications (Sloss andothers, 1996).

4.4.11 Combined systems

There are several examples of pilot or commercial scalesystems which combine two or more of the beneficiationprocesses discussed above. For example, the systemdeveloped at the Southern Illinois University in conjunctionwith CQ Inc (USA) combines dry and wet magneticseparation, dry fluidised bed gravity separation (for removalof unburned carbon) and cyclone technology for both wetclassification and gravity concentration. The system thereforeproduces four valuable by-products – fly ash derivedmagnetite, a pozzolanic portion, cenospheres and unburnedcarbon. Predictions have been made for a 25 t/h processingplant using ash from a 500 MWe power station burning coalwith 10% ash. Taking into account the marketing potential ofall four products, it is estimated that the plant could run at aprofit of $2 M after tax (Honaker and others, 1998).

The Institute of Materials Processing at MichiganTechnological University (IMP/MTU), USA, has patented awet beneficiation process which removes residual carbon,magnetic particles and cenospheres from ash from plantsfitted with low NOx burners. The process produces ash whichis of a clean and fine enough quality to use as a filler inplastics (Huang and others, 1997). Ciccu and others (1997)report on a similar system being developed and used in Italy.

Badulsecu and Andras (1997) describe a theoreticalcombined system for the gravimetric separation of fly ashfollowed by a magnetic separation stage. The process isaimed at the recovery of useful metals such as silver, goldand platinum from the cleaned ash. Although mathematicalmodels are discussed as to how such recovery could be made,no indication is given of how economical or practicallyfeasible such a process would be.

4.5 Quality control, qualityassurance and certification

If fly ash is to continue to be accepted in the market place as avaluable commodity then it must be made available inadequate quantities and at the quality required to ensure itssuitability. It is becoming increasingly common for fly ash tobe collected as efficiently as possible and handled in such away as to maximise and maintain its best characteristics.Sections 4.3 and 4.4 considered how the handling, storage andprocessing of fly ash can be optimised to produce a qualityproduct. This section concentrates on how the quality of ashcan be assured within the normal operation of a power plant.

According to Lister (1997), quality control and assurance iseasiest to achieve when sales are a small fraction of the totalfly ash production. As mentioned in Section 4.2.6, the

Blending and mass storage allow for providing a consistentsupply of materials despite the fluctuation in the productionrate.

Ban (1997) describes the ash quality control system inoperation at Hekinan Thermal Power Plant in Japan, asshown in Figure 11. The system incorporates a vacuum toconvey the ash from the primary collection areas throughsampling and analysis systems to final storage in gradedsilos. The system measures unburned carbon with an on-lineanalyser using laser beam diffraction. Chemical componentssuch as SiO2, SO3, Al2O3, Fe2O3, CaO, MgO, Na2O and K2Oare measured by X-ray fluorescence. The information fromthese and other analysers are compared with the referencevalue of the quality standard of the ash to select theappropriate silos for storage.

In some situations, the standard of the fly ash is simplyassumed to be acceptable for purpose by the buyer. Forexample, in Denmark, fly ash can be sold with no guaranteeat all. According to Elsam ‘the sale and use of the fly ash isbuilt on a relationship of trust between the customers and thepower plant as the fly ash is neither analysed before it isdelivered to the receiving silos nor even before it is used’.However, this situation is quite unique and no doubt built onmany years of successful business. Many power plants do nothave this advantage. Quality control and quality assurance aretherefore advantageous as the final ash can be considered tobe a guaranteed product. In Europe, fly ash which passes thespecifications outline in EN450 (Tables 4 and 5 in Chapter 3)will be marked with a CEN (Comité Europeèn deNormalisation; European Committee for Standardisation)guarantee symbol. The committee decision on this CENmarking system is still under discussion and should bedecided by 2003. A similar system in Australia allows ash to



particle size distribution between individual hoppers ofparticle collection systems such as ESP is not even. Listersuggest that samples should be collected from individualhoppers in ESP or baghouses and, if possible, related to plantoperating parameters such as unit load and the mills on line.Samples from each hopper can be characterised for propertiessuch as LOI and fineness and then selective collection canprovide the properties required by the buyer. Storage of thecollected fly ash can be sorted into different grades of qualitywith the poorest quality fractions requiring some sort ofbeneficiation process or disposal. If high or total fly ash salesare required then a higher level of quality control is required.Lister (1997) recommends the approach shown in Figure 10.

Fly ash processequipment

Massstorage

Offsite low LOIfly ash

Salessilo

Blending

Selectivecollection

Low LOI

Rawmaterialsilo

Power plant

Alternateproducts

Figure 10 Typical facilities requirement for 100% flyash sales (Lister, 1997)

Unb

urne

d c

arb

onan

alys

er

Par

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siz

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alys

er

Ele

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tary

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oile

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o.3

unit

Sm

okes

tackEP

2 SEP3 S

EP4 S

Selected siloindicator

Ashsampler

Samplecollector

Reductiondevice

Intermediateash tank

Data onash siloselected

Classifier

Ash storage silo

Sampleconveyor

Dual divider

Data onboiler operating

perametersEvaluator for

quality acceptance

EP1 S

ECo

DeNOx

A

H

BA DC

Figure 11 Schematic diagram of ash quality control system (Ban, 1997)



be certified with a ‘Standards Mark’ which meets the criteriaof an ISO (Internation Standards Organisation) Type 5standard scheme. Similar quality assurance schemes work incountries such as the Netherlands and Germany. This makesthe ash far more marketable to end users but is not alwaysnecessary.

4.6 Comments

Changes in coal type and addition of alternative fuels to theboiler can significantly alter the chemical and physicalcharacteristics of ash. The installation of new pollutioncontrol systems for SOx and NOx can also affect the fly ash,often with detrimental results. Plants previously producinghighly saleable ash may start producing ash which hasbecome unmarketable. In some cases alterations in plant andpollution control system operation can remediate theseeffects. In other cases fly ash beneficiation processes areused. Many systems are commercially available to alter suchparameters in the ash as particle size distribution, LOIcontent, ammonia content and metal content. Blending ofashes can also produce larger quantities of saleable ash fromseparate ashes which may have been unmarketable alone. Ithas been argued that many of these processes are altering, atcost, characteristics of fly ash which are not important totheir performance in many applications. This argument wasdiscussed in more detail in Chapter 3.

It is interesting to note that there is one treatment of fly ashwhich has increased ash sales dramatically in countries suchas Germany, the Netherlands and Denmark and is beingadopted in other countries such as China. This treatment isnot a beneficiation process but is, in fact, simply ensuringadequate dry storage facilities. The effect of adequate storageand other management practises on fly ash sales arediscussed in more detail in the next chapter.

Table 11 Fly ash production and use in different countries

Country Year Amount produced, Amount used, Comments*kt %

Australia 1997 9,000 ~50% (Nelson, 1999) includes 35% used in mine backfill, oftenassumed to be disposal; sales amounted to 13%suggesting an increase of 2% in sales since 1992

Austria 1998 250 >80% (Klemm, 1999)Belgium 1997 640 105% (vom Berg, 1998) data suggest an increase of up to 32%

in use since 1992. Fly ashes are imported from Germanyand the Netherlands

Canada 1996 4,190 12-30% (Venta, 1999)China 1995 100,000 42 (Pu, 1997) data suggest an increase of up to 5% in use

since 1992Denmark 1998 920 80% (Poulsen, 1999)Finland 1997 500 ND (Sevelius, 1997) around 40% of ash was used in 1993 but

no new data have been published since thenGermany 1996 – hard coal 7,420† 100% (Puch and vom Berg, 1997)

1997 – brown coal 9,360 91% (VGB, 1998)India 1997 50,000 7.4% Ash utilisation has steadily increased from 2.3% in 1993

to 7.4% in 1997 (Rangaswamy and Kumar Dy, 1998)Israel 1995 74 88% (Foner and Robl, 1997) Italy 1997 700 100% (Belz, 1998) data suggest an increase of up to 12% in

use since 1994Japan 1996 7,320 67 (Owada and others, 1998) data suggest an increase of up

to 5% in use since 1993Netherlands 1998 1023 >100% (Vliegasunie bv, 1999) previously stored fly ash is being

reclaimed; land filling of fly ash is now illegalPoland 1997 20,000 65% (GUS, 1998)Sweden 1996 <225 20-25% (Hinderson, 1999) data suggest an increase in use of

5–10% since 1992UK 1998 <10,000 50% (McCarthy and Dhir, 1999) utilisation rate seems steadyUSA 1997 54,710 32% (Stewart and Kalyoncu, 1999) utilisation rate seems

steady

ND no data available yet* increases are calculated against the data published in the previous report by IEA Coal Research on fly ash (Sloss and others, 1996)† includes ash from all large hard coal combustion sources, including FBC

5 Coal ash production and utilisation


The management of increasingly large quantities of ash isbecoming a concern in many countries.

For every tonne of coal combusted or converted, between 40and 400 kg of ash is produced (Kyte and Lewis, 1997). Thereis no up to date information available relating to total globalproduction and use of fly ash from coal combustion.However, data are available for individual countries. Table 11summarises the information included in this chapter andshows that production and utilisation rates vary greatly fromcountry to country.

ECOBA, the Technical Association of Large Power PlantOperators in Europe, has published statistics relating to theproduction and use of fly ash for the whole of Europe. Onaverage, around 30% of the by-products from coalcombustion in the European Union (EU) are from thecombustion of bituminous coal and 35% are from lignitecombustion. Figure 1 in Chapter 2 showed the proportion of

different by-products produced from all hard coal and lignitethermal power plants in the 15 states of the European Unionin 1997. As shown in the figure the total amount of ash andgypsum produced from coal use within the EU was 63 Mt.Although no data on total by-product utilisation are availablefor 1997, data for 1996 indicate that around 46% of the totalby-products were used, around 25% were land-filled, 23%were disposed of and 6% were placed in temporarystockpiles. The individual rates of utilisation of fly ash varyfrom country to country within Europe from 100% in somecountries such as the Netherlands, down to 10% in others(Dietz, 1998 and 1999; see Table 11 and individual sectionsbelow).

The utilisation rate for bottom ash in Europe was 41% andthe applications for 1996 are shown in Figure 12. Up to100% of the boiler slag produced in the EU is used, althoughno data were provided on the applications (Dietz, 1998).Figure 13 shows the different applications in which fly ash is

used in the EU in 1997. Of the total of 16.2 Mt fly ash whichis used, around 40% of the total produced, more than half isused in cement and concrete manufacture (Dietz, 1999).

5.1 Country studies

The following sections present the available data on theamount of ash produced in individual countries and howmuch of this ash is used or disposed of. Where possible, anindication is given of any management or marketingapproaches which have proven successful in the promotion ofash use. Chapter 6 discusses the different applications for flyash which are common in the countries discussed.

Australia

Data from the Ash Development Association of Australia


Coal ash production and utilisation

(ADAA) indicate that the amount of ash produced from hardcoal has been increasing steadily, as shown in Table 12. Thetable also includes data on the ash usage in 1997. Althoughonly 11.3% of the hard coal fly ash was used in cement, asmuch as 35% was used within power stations and mines forinternal works such as roads, embankments and mine fill.Around 50% of the fly ash was placed into storage. Ash saleshave also been increasing during this period, as shown in thefinal column in the table. External sales (outside the powerplant) amounted to 9% of the total in 1991 and this increasedto 13% by 1997. The increase in values after 1994 reflect thecommencement of the substantial market of lagoon ash andfurnace bottom ash for structural fills. The percentage of flyash used in cementitious applications has increased from5.1% in 1975, through 9.7% in 1991 to 11% in 1997(Nelson, 1999).

Over 600 kt/y fly ash is produced from brown coalcombustion in the Latrobe Valley power stations. Thecomposition of the ashes vary greatly. Most of the ash iscollected in wet settling ponds prior to ‘disposal’, mainly asbackfill in mines. Soluble components of the wet ashingsystem (Na, Ca and Mg salts) are disposed of by pipeline intothe sea. Around 1% of the brown coal fly ash is used as anagricultural fertiliser/neutralising agent due to the high limeand magnesia content.

The SECV (State Electricity Commission for Victoria) hasencountered funding problems for work on fly ash in cementand the production of extractable saleable products from theash such as magnesium chloride, sodium sulphate andunburnt carbon. Low ash coals lead to high LOI (>50% insome cases), even with efficient combustion. Some of thiscarbon can be collected for use as low grade adsorbents orfor briquetting for smokeless fuel. However, there have beenno funds to test this at pilot scale (Allardice, 1999).

Figure 12 Utilisation of bottom ash in the EuropeanUnion in 1996 (Dietz, 1998)

Figure 13 Utilisation of fly ash in construction andcivil engineering in the European Unionin 1997 (Dietz, 1998)

Table 12 Ash produced at Australian powerstations in 1997, kt (Nelson, 1999)

Year Bottom ash Fly ash Total ash Sales

1991 699 6764 7463 9%1992 724 7000 7724 9%1993 747 7180 7927 10%1994 773 7378 8151 11%1995 789 7580 8369 15%1996 822 7976 8798 10%1997 844 8180 9024 13%

Estimated ash usage and storage in 1997

Application Total %

Cementitious use 1020 11Internal use (power stations and mines) 3175 35Bulk fill 270 3Other uses 80 <1Placed into storage 4479 50

Total 9024 100

Austria

According to Klemm (1999) there is no official registrationof fly ash use in Austria and therefore there are no officialdata available. However, current total fly ash production hasbeen estimated at around 250 kt/y. The production of fly ashfrom hard coal combustion in Austria in 1994 was estimatedat around 150 kt/y suggesting an increase in fly ashproduction between 1994 and 1999. The utilisation rate forfly ash was reported to be around 80% in 1994. No update onthis value has been published, although it is known that‘most’ of the fly ash produced from hard coal combustion isbelow the 5% limit for unburned carbon and is sold to theconcrete and cement industry (Schulze and Appenzeller,1998). The concrete industry pays up to 200 ATS/t (around$11/t) for good quality fly ash whereas the cement industrypays only 40 ATS/t (around $2/t). Fly ash from ligniteproduction is either improved in quality to produce a productcalled ‘Flual’ or used for soil stabilisation together withdifferent lime brands (Klemm, 1999).

Belgium

Of the 0.72 Mt of fly ash produced in Belgium in 1996, 95%were used. Up to 61% of the ash used was for cementproduction, 28% as a concrete additive and the remainder forconcrete blocks and asphalt fillers (vom Berg, 1998). In 1997the amount of fly ash produced decreased slightly to 0.64 Mtbut the utilisation rate increased to almost 106% due to theuse of stored fly ash from previous years (Electrabel, 1997).The demand for fly ash in Belgium actually exceedsproduction and therefore fly ash is imported from Germanyand the Netherlands (vom Berg, 1998).

Although there are no fly ash processing plants in Belgium,the ash undergoes quality surveillance before being deliveredto the customer by rail or silo-track. Large capacity silos (upto 40,000 m3) are installed at some power plants to reducethe difference between production in winter and use insummer (vom Berg, 1998). There is a company set up jointlyby the power plant operators and the cement industry inBelgium to market clean coal by-products actively(Electrabel, 1997).



Brazil

Coal-fired power plants are mainly found in the very southernstates of Brazil. Production and use of fly ash in Brazil in1997 was as follows (kt):

Bottom ash Fly ashProduction Use Production Use

Rio Grande do Sul 390 135 1075 186Santa Catarina 338 105 552 178Brazil total 728 240 1627 364

Bottom ash is most commonly used for bulk fill and fly ashfor cementitious applications (Rodhe and others, 1999).

Canada

The most recent data available for Canada suggests thatalmost 6.29 Mt of ash was produced in 1996 and that 4.19 Mtof this was fly ash. Estimates for fly ash utilisation rangefrom 12% to 30%, although it is known more accurately that14.5% of the fly ash generated in 1995 was used in cementand concrete production. Further data suggest that there hasbeen an 17.6% increase in the amount of fly ash used inconcrete between 1988 and 1995 (Venta, 1999).

China

China has one of the largest coal mine resources in the worldand is very dependent upon coal for power production. As aconsequence China also produces a significant amount of flyash – almost 100 Mt in 1995. Data on fly ash production anduse in China are listed in Table 13. Fly ash production isexpected to reach over 150 Mt/y by the year 2000 (Pu, 1997).

The utilisation rate of fly ash in China as a whole isincreasing at a steady rate, but varies from region to regionand from plant to plant. A 100% utilisation rate for fly ash isnow achieved by more than 60 power plants. The utilisationrate in the economically developed coastal area is higher thanfor areas inland and is also higher in larger cities(Lianglong, 1997). For example, in cities such as Shanghai,where there is a shortage of construction materials and other

Table 13 Pulverised fly ash production and use in China, kt/y (Pu, 1997)

1988 1989 1990 1991 1992 1993 1994 1995

Total production 55494 62154 67790 74830 79820 86000 91140 99360

Total utilisation: 14206 16000 19750 23210 25470 29930 37000 41450of which:

Building materials - - 6610 7236 8921 10427 10800 12440Building construction - - 1240 2017 2294 3386 2970 4150Road construction - - 2330 3214 5566 7434 10470 12920Backfill - - 5050 7484 4851 4623 8040 8450Agricultural and other - - 4520 3259 3838 4060 4720 3490

Utilisation rate, % 25.6 25.7 29.1 31.0 31.9 34.8 40.5 41.7

resources, fly ash is a valuable commodity and the utilisationrate is approaching 100%. In 1990 the total amount of flyash produced in the Shanghai area was 2545 kt. Of this total,46.1% was used, largely in road construction (77% of thetotal). By 1996 the total fly ash production had increased to4390 t of which 99.3% was used, 44% in road construction,15% in concrete and mortar, 11% each in backfill andsuburban uses, 10% in wall materials and 9% in cement(Pu, 1997).

Most of the fly ash is produced from the power plants in awet form, although it can be collected dry if the userspecifies that this is necessary. The Chinese EnvironmentalProtection Law now requires that all new plants are fittedwith simultaneous wet and dry collection systems to saveenergy and natural resources (Pu, 1997).

Fly ash which is not used is disposed of in landfill. In recentyears, 1666 ha of land were required annually for thedisposal of fly ash and by 1995 the total area occupied hadreached 25,333 ha. Further, in 1995 around 900 kt of fly ashwas discharged into water systems directly, amounting to0.9% of the fly ash production. This dumping was banned atthe end of 1995. Since 1985, China has had policies andrules relating to the use of ash including requirements forsuitable storage and disposal, and standards for fly ash use inconstruction (Shao and others, 1997). Tax incentives havealso been introduced to enhance fly ash use such as zerotaxes on some applications and the reduction of road tolls forthe transport of fly ash (Lianglong, 1997).

Czech Republic and Slovakia

Around 1.2–1.7 Mt of fly ash is produced in Slovakia eachyear. This is in addition to the 350 Mt produced and ‘stored’in the former republic of Czechoslovakia (Floreková andMichalíková, 1997).

Denmark

In 1996 the production of fly ash in Denmark was estimatedat around 1.6 Mt/y with the utilisation rate at about 65%(Schulze and Appenzeller, 1998). By 1998, total productionhad decreased to around 920 kt of which 740 kt (80%) wereused. The decreased rate of ash production between 1996and 1998 was due to the lower rate of coal use which islikely to continue as a result of the new measures for CO2

control in Denmark (Poulsen, 1999). Due to the closure ofold and relatively inefficient combustion units, around 90%of the fly ash produced in Denmark is now of EN450 quality(see Chapter 3) which means it is of high enough quality tobe sold directly for cement and concrete production. Almosthalf of this material is low-alkali fly ash. The domesticmarket is now close to being full. In the near future, theelectricity market will be liberated. This may cause problemswith fly ash marketing as it will be almost impossible topredict the times and amounts of production of fly ash andmajor variations in production may be seen. Companies likeElsam are therefore investing in storage facilities with largecapacities to maintain supplies to existing and potential



customers. Denmark now has six ship loading silos for thetransport of fly ash over extended distances (Poulsen, 1998).

Finland

The annual production of fly ash in Finland amounts to500 kt (unspecified year). Around 100 kt of this arises fromthe Helsinki Energy Works (Sevelius, 1997) and just over260 kt is produced by power stations owned by IVO (ImatranVoima Oy, 1997). Data from Mroueh (1999) for 1996 putcoal fly ash production at 380 kt/y with 50% being used for‘earthworks’ (backfilling), 5–10% in asphalt filler and 5–10%from cement and concrete production. Of the 95 kt of bottomash produced, 80% was used in backfilling applications.Around 130 kt of fly ash is produced from peat combustionand 78 kt of this is used in backfilling. A further 300 kt of flyash is produced from cofiring of coal with wood.

The amount of fly ash used in cement applications hasdecreased as cement producers are now using moreblast-furnace slag. The National Development Programme2000 for Community Waste Management requires that theutilisation of waste is doubled by the year 2000 (no base yearquoted) and that the amount dumped is reduced to half. Thisrequirement will include ashes from coal-fired power plants(Sevelius, 1997).

Germany

Germany burns both hard coal and brown coal and in 1996coal-fired power stations firing hard coal produced around4 Mt of fly ash compared to 8 Mt of fly ash from the browncoal fired plants (vom Berg, 1996).

Table 14 shows the production and utilisation of residuesfrom hard coal-fired plants in Germany between 1985 and1996 (Puch and vom Berg, 1997). The production rates ofmost of the by-products have been increasing since 1985. Forexample, hard coal fly ash production has increased by morethan 1.3 Mt. The increase in the amount of fly ash was due tothe conversion from melting chamber furnaces to dryfurnaces. Since this conversion is largely completed, thestabilisation of the production of fly ash is expected. Duringthis period the utilisation rate for all by-products hasincreased by 19.1% to 99.1%. (Puch and vom Berg, 1997).

Most (60%) of the boiler slag is used in earth and road worksand in waste disposal site construction. The remainder is usedin bricks (14%), concrete and cement products (12%),abrasive (6%), mortar (5%) and other construction uses (3%).Bottom ash is also used largely for earth construction androad construction (60%) and the remainder is used inlightweight aggregate in bricks and mortar for walls. Around98% of the fly ash from hard coal combustion is used in theconstruction industry and in underground mining. Themajority of the fly ash (67%) is used as a concrete additive inready mixed concrete, concrete products and prefabricatedconcrete elements, 17% is used as mortar for mining andpneumatic packing, 12% for earth and road construction and4% for mortar, bricks, floor paving and plaster. The increase

in the utilisation rate of hard coal fly ash is reported to bedue, at least in part, to measures taken to expand the existingsilo space for interim storage. The introduction of wet fluegas desulphurisation has resulted in a decrease in theproduction of what is termed DAP ash – dry additive processash. DAP is still produced, largely from smaller industrialfurnaces and 100% is used in the same sorts of processes asFGD ash. The utilisation of FBC ash has increased to 99.3%.



The FBC ash is used as mortar in mining and forunderground packing and it is also being investigated forused in road construction.

Plants firing lignite rather than hard coal also produce bottomash, fly ash, DAP ash and FBC ash and the production ratesof these are shown in Table 15. The decrease of over 6 Mtbetween 1990 and 1997 was due to the reduction in the use of

Table 14 Production and utilisation of combustion residues from hard coal-fired power plants in Germanybetween 1985 and 1996, Mt/y (Puch and vom Berg, 1997)

1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996

Total coal use 46.3 ND 51.0 49.0 42.6 46.2 53.1 50.8 52.9 53.7 52.8 54.1

ProductionBoiler slag 3.84 ND 3.56 3.17 2.78 2.64 2.93 2.86 2.66 2.56 2.62 2.36Bottom ash 0.33 ND 0.36 0.36 0.39 0.41 0.46 0.43 0.45 0.44 0.51 0.55Fly ash 2.78 ND 2.90 2.95 3.11 3.50 3.72 3.73 3.87 3.87 3.80 4.12DAP ash ND ND ND ND 0.03 0.03 0.04 0.04 0.01 0.01 0.01 0.01Fluidised bed ash ND ND ND ND 0.26 0.27 0.31 0.31 0.33 0.40 0.39 0.39

Total 6.95 ND 6.82 6.48 6.57 6.85 7.46 7.37 7.32 7.28 7.33 7.42

Utilisation rate, %Boiler slag 96.0 ND 98.2 98.3 97.8 98.5 99.7 99.7 98.6 99.8 100 100Bottom ash 96.0 ND 69.4 65.6 70.9 72.1 89.0 96.5 95.1 94.1 96.1 97.4Fly ash 80.0 ND 82.8 84.7 87.6 87.5 94.2 94.8 97.3 97.7 97.9 99.1DAP ash ND ND ND ND 100 100 100 100 100 100 100 100Fluidised bed ash ND ND ND ND 64.3 68.3 70.9 81.8 91.6 90.1 91.5 99.3

ND no data availableDAP dry additive process ash

Table 15 Production and utilisation of combustion residues from lignite-fired power plants in Germanybetween 1990 and 1997*, Mt/y (Puch and vom Berg, 1997; VGB, 1998)

1990 1991 1992 1993 1994 1995 1996 1997

Total lignite use 210 195 167 166 174 169 165 161

ProductionBottom ash 3.06 2.76 2.44 1.96 2.13 1.98 2.01 1.80Fly ash 12.90 11.68 9.94 8.39 8.54 7.36 8.01 7.26DAP ash 0.24 0.21 0.20 0.09 0.07 0.05 0.05 0.05Fluidised bed ash 0.04 0.06 0.07 0.06 0.18 0.20 0.26 0.25

Total 16.23 14.71 12.64 10.50 10.93 9.59 10.33 9.36

Utilisation rate, %Bottom ash

Construction/mining ND 9.4 8.1 6.9 6.9 2.6 3.5 2.3Filling of open pit mines ND 89.5 90.5 92.1 92.5 96.1 96.5 97.7

Fly ashConstruction/mining ND 1.4 3.8 9.9 9.9 6.3 5.6 8.6Filling of open pit mines ND 98.5 96.0 89.8 89.9 93.7 94.4 91.4

DAP ashConstruction/mining ND 1.9 1.0 29.2 28.0 58.7 61.2 57.4Filling of open pit mines ND 98.1 99.0 70.8 72.0 41.3 38.8 42.6

Fluidised bed ashConstruction/mining ND 35.7 49.3 55.7 50.5 42.0 36.5 NDFilling of open pit mines ND 64.3 50.7 44.3 49.5 53.0 59.0 ND

* there were no reliable data from the former German Democratic Republic for any time prior to 1991, therefore the data starts in 1991ND no data availableDAP dry additive process ash

Table 16 Amounts of fly ash produced, used and disposed of in Israel, kt (Foner and Robl, 1997)

1993 1994 1995 Total 1982-95

Total production 647 657 742 6121

Utilisation/disposalCement production 424 66% 444 68% 636 86% 3950 65%Embankments 152 23% 162 25% 20 3% 1131 18%Disposal at sea 71 11% 51 7% 86 11% 1040 17%

lignite in power plants in the former German DemocraticRepublic (GDR). The increase in FBC ash was due to the startup of several new FBC plants. The vast majority (94.5%) oflignite ash in used in the recultivation of open-pit mining eitheron its own or together with FGD gypsum and/or FGD wastewater. This is an ideal arrangement as the brown coal-firedpower plants are generally located close to open cast mines(vom Berg, 1996). DAP and FBC ash are also used as limefertilisers in agriculture and forestry, as asphalt fillers, as fillingin underground mines, as lime substitutes in the production ofsand-lime bricks and in sewage sludge conditioning.

The quality assurance and marketing of fly ash in Germany isoperated by subsidiaries of the power plant companies and byindependent enterprises. There are no commercial fly ashbeneficiation processes in operation. However, operationalmeasures in the power plant ensure that the fly ash complieswith the specifications of the consumer industries(vom Berg, 1998).

India

Indian coal has a high ash content (25–45%) and a lowcalorific value (3500–4000 kcal/kg or 14.7–16.7 GJ/kg).India relies on coal for around 70% of the total powerproduced and as a result produced around 50 Mt/y of fly ashin 1997. About 7.4% of this has been utilised in various areassuch as cement manufacture, building materials,embankments and development of low lying areas(Rangaswamy and Kumar Dy, 1998). In view of thecontinuous rise in demand, the total installed capacity willincrease to 170 GWe by 2012. As 70% of this power will becoal based, the ash production is likely to be around174 Mt/y. This would require about 40,000 hectares ofvaluable land for constructing more ash storage ponds. Indiais therefore working towards more productive uses of ash inapplications such as structural fill and road construction(Trehan and others, 1997a,b). The Indian Ministry of Powerhas suggested a number of moves to enhance fly ash use suchas the banning of clay based brick and other kilns within50 km radius of all coal based power stations and also theabolition of excise duty on fly ash based products(Rangaswamy and Kumar Dy, 1998). Such measures werediscussed in more detail in Chapter 3.

Italy

Around 700 kt/y of fly ash is produced in Italy and 100% ofthis material is used (Belz, 1998). In 1995 10% of the ash



produced was processed in some way to enhance itsmarketability (Schulze and Appenzeller, 1998).

Israel

Since 1982, all new major generating capacity in Israel hasbeen based on coal. Table 16 shows the increase in theamount of fly ash produced and used in Israel since 1993.The amount of fly ash which can be used in cement is limitedby the Israel Standard to 10% which is very low since up to65% replacement by fly ash is acceptable in some cements.Dumping of the fly ash at sea was found to cause damage towildlife in the area and has been banned by the IsraelMinistry of the Environment (IME). The IME has also beenreluctant to approve the use of landfills for fly ash. Further,limited land around the power stations does not allow thebuilding of fly ash embankments. This means that Israel has amajor fly ash problem. By the year 2001 Israel will produceover 1 Mt of ash annually of which less than half can be usedby the cement industry under the current regulations. TheCenter for Applied Energy Research (CAER) at theUniversity of Kentucky, USA, has been studying the fly ashproblem in Israel. Initial studies have shown that the fly ashis generally of good quality Type F (pozzolanic,see Chapter 3). The marketability of the ash could beimproved by relatively simple separation processes such asair or hydraulic classification. The fly ash could then be usedas a pozzolan in cement, as a fine aggregate and other useswhich could lead to total marketability of the fly ash in Israel(Foner and Robl, 1997).

Japan

The use of coal is increasing in Japan and the production offly ash is estimated to increase to over 13 Mt by the year2005 from around 7.3 Mt in 1996. Around 70% of the fly ashproduced in 1996 was used and the remainder ‘disposed of’in land reclamation. Table 17 shows the coal ash productionand use from both electricity generation and industrybetween 1993 and 1996 and predictions for up to 2010. Bothproduction and use of ash increased during this period.Table 18 shows the areas in which the ash was used. As withmost other countries, the majority of fly ash is used in thecement and concrete industry. According to a review bySchulze and Appenzeller (1998), around 25% of the fly ashproduced in Japan in 1995 was processed to enhance itsmarketability. The expected increase in ash production inJapan could lead to ash being wasted if it is not marketed inthe correct manner. The CCUJ, Centre for Coal Utilisation

Japan, is working on establishing a coal ash distributioncentre at one of three proposed sites on the coast. Ash couldbe shipped in by suppliers to the distribution centre whichshould be built in an area of high demand and then



distributed to users by land (Owada and others, 1999).Natural sources of high quality silica are near depletion inJapan which will help increase the demand for alternativematerials such as fly ash in the future (Okamoto, 1998).

Table 17 Coal ash production and use in Japan between 1993 and 1996 and predictions for the future, t/y(Owada and others, 1998)

1993 1994 1995 1996 2000 2005 2010

Coal combustedElectricity generation 33,104 38,508 40,413 41,182Industry 11,781 11,942 13,124 13,320

Total 44,885 50,450 53,537 54,502

Coal ash productionElectricity generation 69.3% 72.4% 72.3% 73.4% 77.8% 83.2% 83.7%Industry 30.7% 27.6% 27.7% 26.6% 22.2% 16.8% 16.3%

Total 6,504 6,630 7,237 7,323 10,058 13,919 14,935

Ash from electricity generationAmount used 56.3% 57.5% 60.5% 63.8%Amount disposed of 43.7% 42.5% 39.5% 36.2%

Ash from industryAmount used 74.2% 83.2% 84.5% 87.7%Amount disposed of 25.8% 16.8% 15.5% 12.3%

Total ash used 61.8% 64.6% 67.1% 70.2% 74.7% 81.8% 83.0%

Total ash disposed of 38.2% 35.4% 32.9% 29.8% 25.3% 18.2% 17%

Table 18 Coal ash use in Japan in 1996 (Owada and others, 1998)

Application Amount used % of total

Cement Total 3295 65.14Raw material for Portland cement 2938 58.09Cement admixture and fly ash cement 261 5.16Ready-mixed concrete admixture 96 1.90

Public works Total 547 10.81Backfilling material in coal mines 254 5.02Soil amendment 148 2.93Public works 89 1.76Public works for electric power plants 9 0.12Subgrade stabilisation 49 0.97Asphalt filler 1 0.02

Construction works Total 384 7.59Construction material board 270 5.34Artificial lightweight aggregate 39 0.77Concrete product 75 1.48

Agriculture, forestry and fisheries Total 95 1.88Fertiliser 46 0.91Soil improvement material 31 0.61Thawing material 18 0.36

Other industries Total 737 14.57Sewage treatment 5 0.10Iron manufacture 37 0.73Other 695 13.74

Grand total 5058 100

The Netherlands

Coal is used for around 30% of the heat and powergenerating capacity in the Netherlands. This capacity is splitbetween four generating companies and a few smaller privateunits (Oostendorp, 1997). The production rates for thedifferent ash types between 1996 and 1998 in kt were(Vliegasunie bv, 1997; 1999):

1996 1997 1998

Pulverised coal fly ash 837 907 1023Pulverised coal bottom ash 130 169 147Coal-gasification fly ash 2.5 7 12Coal gasification slag 11 28 28

In 1996, 94 kt of bottom ash was sold amounting to 72% ofproduction. The remainder was placed in temporary storageas a reserve for large-scale projects. Of the 95,500 t sold,35.5% was used in road construction, 41.5% in concreteblock manufacturing and 23% in other applications(Vliegasunie bv, 1997). By 1998 30% of the bottom ash wasbeing used in road construction and 50% in concrete blockmanufacturing (Vliegasunie bv, 1999).

Since the beginning of the 1990s, fly ash utilisation in theNetherlands has exceeded 100%. Fly ash is now re-claimedfrom storage at power utilities and also imported fromGermany. This situation has arisen, to some extent, due to theDutch legislation which prohibits fly ash disposal(vom Berg, 1998).

At the moment the fly ash utilisation in the Netherlands is asfollows (vom Berg, 1998; Vliegasunie bv, 1999):

1996 1997 1998

Cement industry (in Portland cement 60% 71% 69%clinker or as fly ash cement)

Production of artificial aggregate 20% 15% 14%(Trade mark: Lytag)

Asphalt filler, concrete additive and 20% 14% 17%other applications

In order to increase the marketability of fly ash as a concreteadditive following the introduction of low-NOx burners



throughout the Netherlands, a sieving plant was built in 1995to reduce the loss on ignition whilst increasing thehomogeneity of the product. The plant can store up to 41 ktof ash (vom Berg, 1998). This sieving plant processes andupgrades fly ash for the concrete and cement industry. In1996 it processed 120,600 t of ash, equivalent to 14.4% ofthe pulverised coal fly ash production in that year(Vliegasunie bv, 1997). It has been estimated that around40% of the fly ash produced in the Netherlands in 1995 wasprocessed in some way to improve the quality (Schulze andAppenzeller, 1998). It is likely that the proportion of fly ashwhich is processed has increased since then.

The processing of fly ash is carried out by Vliegasunie, ajoint subsidiary of the power plant operating companies. Themarketing is carried out by VCN (Vulstof CombinatieNederland), a cooperative company set up by Vliegasunie(Wiegers, 1999). The cooperation between the utilities,Vliegasunie and fly ash based industries is shown inFigure 14 (Oosterndorp, 1997). The Aardelite and Lytagprocesses are discussed in more detail in Section 6.1. In 1998the turnover of Vliegasunie amounted to NLG 40,998,000(equivalent to over $24 million) (Wiegers, 1999).

Around 13,710 t of gasification slag were used in roadconstruction in 1996, this included slag stockpiled from1995. In addition 1220 t of gasification fly ash were suppliedas a base material for the production of artificial gravel(Vliegasunie bv, 1997).

Poland

According to data from the Polish Central Statistical Office(GUS, 1998), the production of fly ash was as high as26.6 Mt/y in 1990 but has been steady at around 20 Mt since1995. The utilisation rate has increased from 42.5% in 1990to 65% in 1997. The remainder of the ash is stockpiled withpotential for reclamation.

Russian Federation

In Russia over 75 Mt of ash products are produced annuallywith less than 15% of this ash being used (Rubenstein andHall, 1998).

Figure 14 Organisation of fly ash utilisation in the Netherlands (Oostendorp, 1997)

Sweden

Few data are available on the production and use of coal ashin Sweden. The estimate for the total ash produced from coalcombustion in 1996 was 180–225 kt/y. Ash fromco-combustion of coal and biomass was around 20 kt/y andfrom co-combustion of peat and biomass was around 24 kt/yin 1992. A more recent estimate by Hinderson (1999) as aresult of a survey of all plants puts the total ash productionlower at around 117 kt/y with another 50–70 kt/y arisingfrom co-combustion plants. It has been estimated that amaximum of around 40–50 kt of coal ash are used per year,around 20–25% of the total, although this varies substantiallydepending on demand from the construction industry. Themost important applications are as fill in construction androad base and for covering and stabilisation of waste. Fly ashis also used in a form of cement known as Cefyll. Ash fromCFBC and PFBC units have been used in the stabilisation ofwaste. Residues from peat combustion are largely land filledalthough tests are being carried out on the application of peatash for use on forests and peat moors (Hinderson, 1999).

UK

In 1995 a total of 6.4 Mt of fly ash and 1.6 Mt of bottom ash



was produced in the UK. Over 40% of the material producedin England and Wales was utilised (Kyte and Lewis, 1997). In1997/98 around 7.1 Mt of fly ash were produced in the UKof which 3.6 Mt (over 50%) was utilised (Kyte, 1999). Over10 Mt of furnace bottom ash was also produced (Sear, 1999).Coal use in the UK is decreasing and therefore the amount ofash being produced will also be decreasing (Kyte, 1999).Figure 15 shows the major applications for fly ash use in theUK. The UK has extensive experience in using fly ash inconcrete with well-documented cases dating back to the1950s (McCarthy and Dhir, 1999). According to Kyte andLewis (1997) the sales of ash are handled on a project byproject basis and are heavily dependent on central and localgovernment programmes for projects such as major roadconstruction or improvement schemes.

Around 8% of fly ash in the UK is classified to removecoarser ash material for compliance with BS3892 Part 1 –Pulverised fly ash for concrete (Sear, 1999).

USA

Total ‘clean coal by-product’ (CCB) or CCP (coalcombustion product) as it is now called, production in 1996was around 90 Mt and increased to more than 95 Mt in 1997.This value includes pulverised coal fly ash as well as ash

Aerated concrete blocks 10.2%

Disposal 43.6% Non aerated blocks 0.9%

Lightweight aggregate 2.3%

Bricks and ceramics 0.2%

Grouting 5.1%

General fill 2.3%

Structural fill 3.2%

Infill 1.1%

Landfill, land reclaimation and restoration 9.8%

Concrete addition 8.0%

Blended cement 2.8%Stockpiled 6.9%Cement raw material 3.2%Other uses 0.5%

Utilisation of fly ash from power stations - 1997

Figure 15 Typical fly ash utilisation in the UK

from FBC and FGD units This increased matched theincrease of 2.8% in the amount of coal burnt by utilities. Theuse of CCPs increased from 12.3% in 1996 to more than 33%in 1997. The data for 1997 are shown in Table 19. It has beenpredicted that US coal production will increase by 1% peryear to 1268 Mt in the year 2015 and that most of thisincrease will be for domestic consumption. This will lead to aconcurrent increase in CCP production (Stewart andKalyoncu, 1999).

Bottom ash is largely used in on-site operations at the powerplants leaving no excess for external sales. Around 2.6 Mt ofboiler slag was produced in 1996, nearly all of which wassold for blasting grit and roofing granules. In the same year14.5 Mt of bottom ash was produced. Figure 16 shows themajor uses of bottom ash and fly ash in the USA. In 1996,53.52 Mt of fly ash was produced in the USA from coal-firedpower plants. Of this, around 7.25 Mt were marketed as aconcrete admixture and another 7.25 Mt were used in otherapplications leaving just over 39 Mt requiring disposal(Balsamo, 1998).

Currently around 77% of bottom ash and 75% of fly ash inthe USA is disposed of in disposal ponds and landfills.Around one third of this material is placed in ponds. At themoment the use of ponds is inexpensive and can providedecades of storage. The remaining two thirds of the ‘waste’fly ash and bottom ash are disposed of in landfills. In 1998land filling could cost as little as $1.25/t, although $5–10/t ismore typical. However, in urban areas, private landfillscharge up to $30/t and long hauling distances can double thiscost (Balsamo, 1998).

Klein (1999b) has reviewed the production and utilisation ofFBC ash in the USA and the results are shown in Table 20.



Although the total amount of FBC ash has been increasing,the rate of utilisation has also been increasing to a pointwhere 75% of the ashes produced are used in a beneficialmanner. The majority of the ash (61%) is used in miningapplications, for example backfilling of abandoned mines.

Table 19 Clean coal by-product production and use in the USA, 1997, Mt (metric) (Stewart and Kalyoncu,1999)

Fly ash Bottom ash Boiler slag

Total (dry and ponded)Production 54.71 15.35 2.49Disposed 35.55 9.88 0.39Removed from disposal 1.20 0.44 0.27Stored on-site 3.17 1.43 0.07

Total usedCement/concrete/grout 8.55 0.55 0.01Flowable fill 0.35 0.01 0.00Structural fill 2.61 1.26 0.08Road base/subbase 1.29 1.17 0.00Mineral filler 0.26 0.12 0.10Snow and ice control 0.00 0.66 0.05Blasting grit/roofing granules 0.00 0.15 2.08Mining applications 1.28 0.15 0.00Waste stabilisation/solidification 2.83 0.19 0.00Agriculture 0.03 0.01 0.00Miscellaneous/other 0.33 0.38 0.03

Total use 17.54 4.63 2.34

Individual use 32.1% 30.2% 94.1%

Figure 16 Major uses of fly ash and bottom ash inthe USA (Balsamo, 1998)

Table 20 Production and use of FBC wastes in the USA between 1990 and 1995, kt (Klein, 1999b)

1990 1991 1992 1993 1994 1995

Total generated 1669 3561 3561 4524 5551 6044

Total disposed of 37% 32% 32% 29% 27% 25%

Usage, %Mining applications 59 61 61 56 55 61Waste stabilisation/solids 0 2 2 4 6 6Structural fill 0 2 2 5 5 5Other 0 0 0 1 3 1Agriculture 4 3 3 2 2 1Flowable fill 0 0 0 0 0 1Cement 0 <1 <1 0 0 0Total used beneficially* 63 68 68 68 70 75

* any disagreement between totals generated and the totals used/disposed of is assumed to be in stockpiles

The Federal Energy Technology Center (FETC) at the USDepartment of Energy (US DOE) have invested in a longterm project for developing and promoting the use of allCCPs. The aim of this project is to reach 50% utilisation ofCCPs by 2010. They also aim to have complete sampling andcharacterisation of these materials so that the public andregulatory agencies accept disposal or utilisation of CCPs asroutine business practices (FETC, 1998). As a result of thisproject, the US DOE hopes to eliminate the term ‘waste’from common vernacular and relace it with ‘coal combustionby-product’ (Renninger, 1998).

5.2 Comments

The use of coal is increasing in most countries and, as adirect consequence, the amount of ash produced isincreasing. The ash utilisation rate in Europe is an average of41% with some countries using less ash than others. Forexample, countries such as Germany, Italy and theNetherlands are now using all of the ash produced inbeneficial applications and in countries such as Austria,Belgium, Denmark, Japan, Poland, and the UK the utilisationrate is 50% or above. In other countries the utilisation rate islower, such as China (42%), Sweden (20–25%) and the USA(30%). The differences in utilisation rates reflect the differentsituations in each country. Factors such as disposal costs,transport distances, availability of raw materials and nationalguidelines and regulations all affect the ease with which flyash and fly ash products can be moved into the market place.



Table 21 Uses of coal combustion by-products (Reninger, 1998)

Application Bottom ash Fly ash Boiler slag FBC solids

Aggregate, block X XAggregate, lightweight XAgricultural lime XBlasting grit XCement manufacture XConcrete, ready-mix XDrybed material XFill, flowable XFill, structural X X XFilter media XFuel, alternate XIce control XLadle topping XPipe bedding XPotting soil filter XRoad base XRoad surfacing XRunning tracks XSoil amendment X X

6 Applications and disposal


The previous chapters have given an introduction to fly ashcharacteristics and the different approaches to fly ash use indifferent countries. This chapter concentrates on the potentialuses for fly ash which are common today. A short review ofdisposal options is also included for those situations whenutilisation is not possible.

6.1 Applications

The uses for ash in the various countries above aredetermined by the different physical and chemicalcharacteristics of the ash. Table 21 shows a simplifiedsummary of the potential applications for the different ashtypes (Reninger, 1998). Rather than discuss theseapplications in detail, this section is intended to update theprevious reports on the different areas in which fly ash can beused and the benefits of doing so (Sloss and others, 1996;Sloss, 1996).

6.1.1 Engineered fill and fillers

Fill is an application where alternative material is used as aninert, bulking agent in place of standard materials such assoil. Fly ash without pozzolanic activity can be used toreplace earthen fills. There are a number of physicalrequirements for fills which are covered by relevant standardsin some countries. For example, an American Society forTesting and Materials standard (ASTM E 1861) was issued in1997 in the USA for guidance on the use of fly ash, bottomash and FGD materials in fills.

The geotechnical characteristics of fly ash are similar to those

of fine grained non-cohesive soils which makes it suitable forload bearing on roads, low-storey buildings with minimalsettlement. However, because of its non-cohesive nature, flyash fills need to be paved or covered with a top layer of soilto prevent dusting, erosion, frost heave and to encourage thegrowth of vegetation. There are many examples of fly ashfills. For example, in the USA 408 kt of clean coal by-products were used as embankment fill for an expressway inPittsburgh, PA, saving US $1 M (Balsamo, 1998).

Although the moisture content of fly ash for such fills isimportant for compactability, pond ash is still suitable for thispurpose (Sear, 1999). Slurried fly ash with a some additionalcement can be used as a flowable backfill which hardensstronger than compacted soil or aggregate. Such flowablebackfill can be used to fill voids under floors, around pipes,in abandoned tunnels and other confined areas (Balsamo,1998). Flowable fill may also be used to fill abandoned steamheating service tunnels, backfilling utility trenches, fillingabandoned underground storage tanks and under poor qualitysoils (Ramme and Kohl, 1997). The strength of flowable fillsand backfills can be adjusted so that the mixture’s strength ismore like soil than concrete. The softer dense mixes providestrength and coverage but can be dug out at a later date ifnecessary (Naquin, 1998).

Krug and others (1998) describe the use of fly ash fromlignite combustion in Germany for backfilling in open castlignite mines. This helps facilitate the restoration of the landfor agriculture and forestry uses.

Technological and economic experience with using FBCresidues is limited and so structural fill is an easy option andwill remain the most widely practised option for the

management of FBC residues for many years to come. Anadvantage of FBC material is that it can mitigate acid minesoil conditions and thus help reclaim strip mined land(Balsamo, 1998). Chugh and others (1997) describe the useof FBC for subsidence control in abandoned mines. Speciallydesigned hydraulic systems can pump FBC ash (bottom ashand fly ash) with FGD waste at rates of 105 t/h or more. Thestrength of the material is suited for this purpose but the wearon the pumping system can be of concern. According toSutterer and others (1997) the use of FBC materials forbackfilling has been shown to be adequate for roof support inthe short term, long-term performance remains less defined.Swelling and dissolution could reduce long term performancein wet applications. CFBC ash from bituminous coals issuggested as an ideal candidate for flowable fill and backfill(Conn and others, 1997b). CFBC ashes have low unit weightand moderate cementitious properties which make them idealfor engineered fill. PFBC residues have good compactioncharacteristics and self-hardening properties which give themsignificant benefits over other fill materials such as fly ash. Ifthe PFBC ash is high in lime (>1.9%) may have expansionproblems and require pre-hydration prior to use. IGCCresidues are similar to pulverised fly ash in their applicabilityto structural fill and some IGCC residues may have self-hardening properties which would be beneficial in manyapplications (Sloss, 1996).

Ash haul-backThe placement of ash in as backfill in a mine is commonlyconsidered to be a disposal option in the USA whereas it isconsidered an application in other countries. State regulationsfor mine backfill usually include a disposal plan, ashcharacterisation, water monitoring, a reclamation plan and ameans of addressing the hydrogeological consequences of thefill. The placement of ash in a mine may be limited to theamount of coal removed and to locations above the water table.Ash haul-back is the term used to describe the transport of ashback to the mine, usually for ‘disposal’ or backfill, using thesame vehicles which are used to deliver the coal to the powerstation or boiler. This is a service which may be offered by themining company to coal users. Slurried ash may also bedisposed of in mines down to 15% solids. The mine water mustbe treated before discharge (Balsamo, 1998).

Ash haul-back has many advantages including (Gray andGray, 1998):● ‘disposal’ occurs in an already disturbed area and avoids

the requirements for new disposal sites;● the ash can help neutralise acid mine soils and mine

overburden which are common at coal mines; and● low permeability ash reduces mine water flow through

the backfill and reduces leaching of acidic species andmetals.

Sevim and Renninger (1998) describe a computer modelwhich can help determine the feasibility and economics ofthe transportation of by-products from power plants back tomines and the subsequent placement of the byproductsunderground using a hydraulic injection system.

Roads and highways Bottom ash and fly ash can be used separately or combined


Applications and disposal

to make base courses for roads and highways. Cementstabilised fly ash has been used for sub-base courses of roadsin many locations, for example the highway of the port ofPori in Finland (ECOBA, 1998b). According to Saylak andothers (1997) the use of bottom ash as an aggregate for bothroadway surfaces and base courses has been limited due to itsabsorbency and friability. The absorbency tends to increasethe demand for asphalt binder whilst the friability affects theability of the structure to withstand the crushing effects oftraffic loads. Saylak and others have shown that coating theash with liquid sulphur fills the voids on the surface of theash particles and increases their crush resistance.

According to ECOBA (1998b) there are three fly ash boundmixtures (FABM) which can be prepared for road base, sub-base and capping in road construction:● cement bound fly ash (CFA);● granular material bound with fly ash and lime (GFA);

and● lime bound fly ash (LFA).

These materials have been used to create roads in countriessuch as the UK. For example, a CFA road base was made inNottinghamshire using 7% cement and 93% fly ash (ECOBA,1998b).

In 1993, 5 kt of fly ash lime additive mixture was used forroad subbase in France for the Meru to Paris highway(Wiegers, 1999). The US DOE and Consol Inc in Pittsburgh,PA, USA are constructing a plant which will convert acombination of scrubber sludge, fly ash and lime into afinished aggregate that can meet highway constructionspecifications. Initially a test plant will be built which runs ataround 230 kg/h. If this test plant is successful, a full scaleplant will be built with a capacity of 50 t/h (US DOE, 1998).

Ash from Sasol pulverised coal-fired power plants in SouthAfrica is being used in road construction applications. Thebulk density (1570 kg/m3) is lower than that of crushed stoneaggregate (2200 kg/m3) and it is more uniform in grading andtherefore is much more user-friendly in labour-intensiveconstruction (Bergh and Hendricks, 1997). Fly ash can alsobe used in the asphalt mixture for the pavement. The use offly ash is said to have more than doubled the bearing strengthof the road compared to conventional natural aggregates(ECOBA, 1998b).

Ghafoori and others (1998) report on the use of Class F flyash and FBC ash for the production of pavements. The flyash/FBC mixture had little or no expansion and thepavements remained crack-free for at least three years. Theself-hardening properties of PFBC residues make them idealfor strength development following compaction in roadapplications, although pre-hydration may be necessary toavoid expansion (Sloss, 1996).

IGCC residues have the strength and resistance requirementsto be used as unstabilised road bases but may be too fine.Coarser aggregates can be added to reduce the fineness. Thefused mineral ash produced as a byproduct at Sasol’s coalgasification process in Sasolburg will be used in theconstruction of roads in Gauteng, South Africa, from the

beginning of 1999. The blend, known as ‘Premamix’ isreported to be less expensive than other construction materialsand is also faster and easier to use. The cost of ten trialsections of road by the Gauteng Department of Transport, thePremamix roads cost around $12/m3 as compared with around$28/m3 for crushed stone and R180/m3 for waterboundmacadams. The production rates were also reported to be fivetimes faster with Premamix (Bresler, 1998). The lack ofcoarseness in IGCC residues makes them less suitable forsurface pavement applications (Sloss, 1996).

6.1.2 Cement, concrete and mortar

As shown in Chapter 5, a large proportion of the fly ash usedin many countries is used in cement and concrete productssuch as ready mixed concrete, concrete blocks, pre-castconcrete and grout. For many of these applications the fly ashmust meet some standardised physical and chemicalspecifications. These specifications vary from country tocountry and were discussed in Chapter 3.

The first major use of fly ash was in dams where the primaryreason was the heat reduction during pouring (Robl, 1999).The other benefits obtained when using fly ash in concreteare well established and include (Ramme and Kohl, 1998):● increased strength;● reduced permeability;● reduced shrinkage;● increased abrasion resistance;● reduced bleeding;● lower water demand;● lower concrete cost;● improved workability;● improved pumpability; and● improved durability.

Examples of the successful use of fly ash in cement andconcrete in Europe include (ECOBA, 1998a):● the Castor and Pollux towers in Frankfurt, Germany,

which are built on a concrete base containing 120 kg/m3

ash. The fly ash was used as it produced a low hydrationheat during formation of the foundation;

● the underground railway, Vienna, Austria, which requiredconcrete which was impermeable to water as well assulphate resistant;

● the Paulaurent dam, France. The use of fly ash concretein the dam limits the heat production during hardeningand decreases the risk of cracking due to thermal stress.A special binder was used which comprised 60% blastfurnace slag and 40% fly ash from a thermal powerstation in France. The total ash used amounted to 10 kt;

● the East Bridge project in Copenhagen, Denmark, whichhas 47 kg/m3 of fly ash in the Portland cement in thepylons. The fly ash ensured a lower water to cementratio; and

● the dam of Permantokoski hydro power plant andValajaskoski hydro power plant in the North of Finlandcontaining cement with between 20 and 30% fly ash.The fly ash was used to give a low hydration cement.

These are just a few examples of the major construction



projects in Europe where fly ash was specifically chosenbecause it provided properties which were superior tostandard materials. These projects have been based largely onfly ash from pulverised coal combustion of standardisedquality.

Typically fly ash is used to substitute around 15% of thecement in a concrete mix (Balsamo, 1998). In Japan a newproduct with a high fly ash content has been produced called‘Ashcrete’. Up to 65% ash by weight can be used makingthe concrete 30% cheaper than normal and also 30% lighterin weight. By using a super-fluidising mixing method theAshcrete is mixed by a series of vibrations, avoiding anyliquid state. The lowered requirement for water gives betterstrength and less cracking on drying (Hazama Corp, 1998).

Autoclaved cellular concrete blocks are lightweight blocksproduced from cement containing fly ash. They have soundinsulation and low thermal conductivity and can be sawn andnailed like wood. Although such blocks are widely usedthroughout Europe they were only approved for building usein the USA in 1997. Studies are now going ahead to evaluateblocks made with up to 70% fly ash. In addition to buildingconstruction, autoclaved cellular concrete blocks can be usedin mining for constructing emergency fire walls andstoppings (Balsamo, 1998). Baykal and Mehmetolu (1997)describe a novel method using crushed ice and rubber tointroduce air voids into compacted rubber/fly ash blockswhich can be used as crash barriers.

CAFA, chemically activated fly ash, is a cementitiousmaterial made from fly ash and activating chemicals. Whenmixed with fine and coarse aggregates, CAFA producesconcrete with high compressive strength (16,000 psi), a lowprocessing temperature (130–200°F) and an increasedresistance to repeated freeze and thaw cycles (Rostami andSilverstrim, 1997).

Zhang and others (1997) describes the use of up to 60 wt%fly ash in glass fibre reinforced cementitious composites. Theash prevented the glass fibres from chemical attack from thematrix but resulted in brittleness under accelerated aging.Further research was recommended.

High calcium fly ash from the combustion of lignite orsubbituminous coal can lead to poor soundness in cement.However, this effect can be reduced by grinding the ash orusing mineral admixtures and controlling the mix of theconcrete. The use of high calcium ash in the correct mannerin concrete can greatly reduce the cement content (>50%)and therefore lead to economic benefits (Qiang, 1997).

CFBC ash does not normally conform to either US orEuropean standards as a component or additive in concrete asthe SO3 content is too high and the SiO2 and Al2O3 contentsare too low. Also the available free lime content can causestructural damage in concrete, despite the cementitiousproperties of FBC ash (Conn and others, 1997b). AlthoughCFBC residues cannot be used in cement as an admixture itmay be used in concrete blocks. CFBC bottom ash can beused as an aggregate in concrete blocks. CFBC fly ash whichhas the same properties as Class C and Class F fly ashes (see

Chapter 3) can be used as a partial replacement for Portlandcement in some blocks with moderate strength for residentialuse rather than heavy construction applications (Conn andothers, 1997b).

PFBC residues can have self-hardening properties but havenot been found useful as pozzolans. Instead, PFBC residuescan be used as filler for cementing materials as long as theLOI is within acceptable levels. The use of dolomite in somePFBC systems causes excessive MgO leading to swelling incement products. IGCC residues can be used at up to 20%replacement in cements with excellent strength development(Sloss, 1996).

Sutterer and others (1997) describe the use of AFBC residueswith aggregate and conventional ash to provide a pozzolanfor the production of no-cement concrete. It was found thatpre-hydration of the AFBC ash with around 10% water wasnecessary to control expansion and to reduce the heat ofmixing to tolerable levels. Without pre-hydration, specimensexhibited unacceptable swelling. A new hydration process hasbeen developed which converts the free lime content ofCFBC ash to Portlandite. A 30 kt/y hydration demonstrationunit began operation at the Gardanne plant in France. Theplant began as a hydration unit for pulverised coal fly ash toproduce a hydrated ash registered under the nameGARDANEX II. A new 3 t/batch demonstration plant is nowrunning for hydration of ash from the 250 MWe CFBC unitno 4 of the SOPROLIF plant at Gardanne (Blondin andAnthony, 1994). Shintani and others (1998) point out that,although PFBC residues do not meet the Japaneserequirements for use in cement and concrete, they can beused as admixtures at lower concentrations and still providesome pozzolanic activity.

Almost all types of coal ash can be used in mining mortars.Bottom ash is used mainly in granular mortars whereas flyash produces powdery and granular mortars. FBC ash is alsouseful as a mortar due to its hydraulic properties. FBC ash’sself-setting properties make it ideal for filling cavities(ECOBA, 1998b). Scheetz and others (1998a and b) describeseveral successful examples of FBC ash and water as grout inhalting the severe acid mine drainage from a pyrite-richsurface coal mine in sites in Pennsylvania, USA.

Fly ash can be used neat to prepare grouts or can be mixedwith Portland cement. Fly ash grouts have been used inprojects such as strengthening embankments, railways tracks,bridge abutments and for void filling in abandoned sewersand mine shafts (ECOBA, 1998b).

Despite the fact that fly ashes are used extensively in theconstruction industry, only one case has been found wherethe material produced caused major problems. An apartmentbuilding in Richmond, VA, USA, which had been built withconcrete containing fly ash and scrubber solids, collapsed in1998. The fly ash had been sourced from an independentpower/cogeneration facility. No specific factor has beenblamed for the problem (Power, 1999).

In addition to the improved physical characteristics ofcements and concrete containing fly ash, other secondary



environmental benefits have been noted. For example, inorder to produce one tonne of ordinary Portland cement, 110kg of fuel oil are required and one tonne of carbon dioxide isreleased into the atmosphere. By the year 2000, cementmaking technologies will be responsible for 10% of the totalglobal CO2 production from human activities. By replacingsome of the Portland cement with fly ash, some of this CO2

production may be avoided (Samarin, 1997). A similar studyin Canada by Venta (1999) suggested that if fly ash wereused to replace up to 60% of the cement in all concreteproduced in Canada after the year 2000 a reduction of almost3.6 Mt of CO2 emissions would be possible, contributingsubstantially to Canada’s efforts to reduce greenhouse gasemissions under the Kyoto protocol.

6.1.3 Secondary products

Bottom ash and some IGCC residues can be used directly asa substitute for natural aggregates. Aggregates can also bemade from fly ash with or without the addition of other wastematerials by pelletising and sintering in an oven. Such pelletscan be made to the required size and can be used to preparelight-weight concrete with a high compressive strength(ECOBA, 1998b). Perhaps the most successful examples oflightweight aggregates from fly ash are the Lytag andAardelite processes in the the Netherlands. The Lytag processuses 150 kt of fly ash per year. The process began in 1985and process around 8 t fly ash per hour into pellets inspecified sizes between 2 and 12 mm in diameter. TheAardelite process began in 1993 and uses 280 kt/y fly ash.The installation processes around 50 t of dry material perhour including 4 t/h of lime (Oosterndorp, 1997). Actualproduction rates are usually slightly lower than full capacity.In 1997 a total of 128 kt of Aardelite and Lytag wasproduced. In 1998 the Aardelite plant was sold and is nowused for a different process involving ash. Aardelite plants arealso operating in Florida, USA (1988), India (1994) andSpain (1997), all at a capacity of 200 kt/y (Wiegers, 1999).

Ramme and Kohl (1997) describe the Wisconsin ElectricPower Company’s plant for producing lightweightaggregates made from coal combustion fly ash andmunicipal and paper mill wastewater sludges. The product,Minergy LWATM, can be used in a wide range of concreteproducts, paving or any application that requires the use ofstone, sand or gravel.

CFBC residues can be mixed with water and briquetted toproduce synthetic aggregates. PFBC residue mixtures (bedofftake and fines) are well suited for use as syntheticaggregates in fills and road building, although the frostresistance may be low. IGCC slags can be used to createlightweight and ultra-lightweight aggregates for specialistuses. The sale price of such aggregates can be $220/t ormore, whilst the production costs are less than $33/t makingthis a profitable approach. It may also be possible to useCFBC and IGCC residues in the Aardelite and Lytagaggregate processes mentioned above (Sloss, 1996).Although IGCC residues are not suitable for use aspozzolans in cement or concrete, they can be used asaggregates. However, the coarseness and sharpness of some

of the grains within IGCC residues may make themunsuitable for this purpose (Tanosaki and others, 1998).

In Germany, sand-lime bricks are made from boiler slag, flyash, lime and water and autoclaved at high pressure andtemperature. These bricks are used in house construction(ECOBA, 1998a). Roy (1997) compares five different brickmaking processes in India using from 50 to 80% fly ash inbrick manufacture.

Research groups such as Materials Technology Inc and LosAlamos National Laboratory, USA, have developed severalchemical methods to promote the pozzolanic activity andcementitious properties of fly ash using alkali activationmethods. Fly ash can be activated with sodium hydroxide andamorphous silica, calcium oxide and aluminium hydroxide toform chemically bonded ceramics. Subsequent treatmentwith supercritical carbon dioxide leads to high strengthcement (Chordia, 1997). Jones and others (1997) describe anew process to produce supercritical ash ceramics from evenClass F fly ashes using supercritical CO2.

Eisele and others (1997) describe the use of pulverised coalfly ash and FBC ash as binder for iron-ore pellets with highcrushing strength. If the ashes used had low CaO contentsthen CaO had to be added to achieve the required bindingstrength. The FBC ash had more suitable CaO content thanthe pulverised coal ash, although slaking was required toensure that the pellets did not crack upon firing.

6.1.4 Filler

In addition to acting as a bulking and filling agent inapplications such as backfills and road construction, fly ashcan also be used as a filler in more specialised fillerapplications such as the manufacture of plastics, paints,varnishes and refractory applications. Fly ash as a filler inaluminium results in a composite of lower density and lowerthermal expansion which could be a major advantage inseveral applications (Rohatgi and others, 1998). Cenospheresfrom fly ash are particularly valued in filler applications.Cenospheres are hollow fly ash particles with relativedensities less than 1.0 which can be harvested by skimmingfrom the surface of disposal lagoons or ponds. Thelubricating effect of the spherical particles gives excellentflow properties to the product. Although there are sometimesproblems with colour and size range, cenosphere productsoften out-perform other competitive products and they arehighly sought after in applications such as fillers and paints.They have four times the filling capacity of most other fillersand give improved thermal and electrical properties. Perhapsthe most interesting applications for fly ash cenospheres arein the space shuttle, in ski poles and as a coating for racingyachts (ECOBA, 1998b).

According to Kruger (1996) around 1 t of South African coalgives rise to only 1 kg of cenospheres. In South Africa,cenosphere products such as Ashref, Hollocast, Kerapour,Kerapump, Keretuff, Allulite and Keralite are wellestablished in the market place. In Germany, cenospheres cancost as much as 1000 DM/t (around $520/t) and are required



in quantities up to 50 kt/y making an ideal marketplace forfly ash products (Schulze and Appenzeller, 1998). Yuying andothers (1997) describes the production of a ‘fillingmasterbatch’ from cenospheres, carrier resin and othercoupling agents. The material has proven to be an ideal fillerin polyolefin plastics. The masterbatch is now being used innumerous factories in the Fujian province of China where ithas proven to be of excellent quality and low cost.

Fitzgerald (1998) describes a proposed process for theconversion of fly ash, bottom ash and FGD ash into materialsuitable for ettringite synthesis. Ettringite can be used asbinder or filler in many applications. The proposed processwould combine the ashes with CaCO3, grind them and thentreat them in a kiln to produce a clinker type material. Flyash with a carbon content over 5% would also be acceptablefor this process whereas it would normally be excluded fromother cement making processes. The process is estimated tocost 22 ECU/t to process the ash but the final product couldsell for up to 45 ECU/t.

6.1.5 Pollution control

Type F (pozzolanic; see Chapter 3) fly ash has been used forwaste stabilisation projects, for example the solidification ofsteel industry waste containing hazardous levels of metalssuch as lead, cadmium, zinc and hexavalent chromium. Oncestabilised, these wastes comply with leaching standards andcan be disposed of far more easily (Rodriquez-Piñero andothers, 1998). Krug and others (1998) describe the use of flyash from lignite combustion in Germany for binding wastefrom refuse incineration, allowing it to be land filled safely.The proportions of 35% by weight of lignite ash with 50% byweight of refuse incineration plant ash produces a stable solidmaterial with ‘good’ compressive strength development.

The stabilisation of polyethylene terephthalate plastic wastefrom municipal solid waste with fly ash has been shown toproduce a potentially useful composite material. The fly ashserved as a filler but also served as a heat conductor,decomposition inhibitor and lubricating agent. The product isbeing proposed as a new lightweight building material. Fullscale tests have been performed by IBR in the Netherlands onthe use of a sludge stabilisation product comprising up to80% fly ash for sewage sludge stabilisation (Wiegers, 1999).

Kahl and others (1997) describe the use of brown coal fly ashfor the fixing and disposal of FGD wastewater. The projectis working on conversion of the ash/water mix from a wasteproduct into a material which may be used as a barrier inwaste dump construction. POZ-O-TEC is a fairly wellestablished building material manufactured from lime, water,fly ash and FGD sludge. It is used in many highways in theUSA and Japan. The autoclaved lightweight and aeratedconcrete blocks are used throughout Europe and China(Sinozaki and others, 1997).

CFBC and PFBC residues have been shown, at bench-scale,to be suitable for the stabilisation of metal-laden hazardouswastes. However, it has so far proven difficult to place thesematerials into the marketplace because of the continued

perception of CFBC and PFBC ashes as hazardous wastesthemselves (Cobb and others, 1997). CFBC ash can be used topasteurise and stabilise municipal waste sludge. The N-ViroEnergy System is based on such a process with the endproduct being applicable in agriculture, topsoil establishment,turf, parks, pastures, land reclamation and landfill cover (Connand others, 1997b). The CaO content of FBC ashes provide thecharacteristics to dry and pasteurise pathogens, reduce odoursand provide granular consistency in municipal wastewatertreatment plant sludges (Schmaltz, 1997).

The chemical characteristics of some fly ashes make themsuitable as sorbents for pollution control in flue gases.Jozewicz and others (1997) describes the use of fly ashesfrom Upper Silesian coals in Poland to produce a materialcalled ADVACATE. The reaction of the fly ashes withcalcium hydroxide produces reactive sorbents which can beused in FGD systems. The best sorbents were produced whenthe fly ash is slurried with the calcium hydroxide. The mostimportant component in the fly ash appeared to be the silicaand the sorbent activity increased with increasing content ofground fly ash. Similar studies have been carried out in Spainby Fernandez and others (1997) who combined fly ash withhydrated lime in a Parr Pressure reactor to produce sorbentsfor desulphurisation projects.

Zeolites are sorbents used for cleaning contaminants such asammonium and heavy metals from water. The chemical,mineralogical and textural features of fly ash make it suitableas a starting material for the synthesis of zeolites (Querol andothers, 1998). Zeolites can be produced from fly ashes by anumber of methods. KEMA in the Netherlands has recentlydeveloped a process which produces pure zeolites from flyash without the residual fly ash contamination which occurswith other systems. Up to 85 g of pure zeolite can beproduced per kg of fly ash using the KEMA method(Hollman and Steenbruggen, 1997). High LOI fly ash canalso be processed for absorbing organic and organo-metalliccompounds from dyes and residue dye effluents (Graham andothers, 1997).

FBC ash can be used to help mitigate acid mine soils andacid mine drainage problems. This idea was introduced inSection 6.1.1 on fill. The US Department of Agriculture(USDA) Agricultural Research Service has published aguidance document on the use of FBC ash as a soilamendment. Use of FBC or any other ash for this purposerequires the submission of chemical analyses to the miningagency (Balsamo, 1998). The application of fly ashescontaining lime on acid soils has beneficial effects onvegetation (see Section 6.1.6 to follow).

6.1.6 Agriculture and fisheries

In addition to acting as fills in place of earth in someprojects, the minerals and trace elements present in coal ashhas been known for years to have a beneficial effect on somesoils and vegetation. Bottom ash has been used to amendheavy clay agricultural soils in areas such as southeastWisconsin, USA. Corn and soya grew well on the amendedsoils indicating that the bottom ash was of use as a substitute



for lime to reduce soil acidity and may positively increasesoil yields. Blends of bottom ash and fly ash have also beenshown to provide vital micronutrients to topsoils (Rammeand Kohl, 1997). According to ECOBA (1998b) both boilerslag and bottom ash are widely used as substrate additives forgardening. Bottom ash possesses a high capacity for waterretention and boiler slag can act as a drainage medium. Thepermanent pore volume supplied supports plant growth andallows air filtration to roots. Fly ash improves the structure ofsoils by increasing the water retaining ability and the aerationof the soil. It can also act as a growth improver by facilitatingthe uptake of vital nutrients by crops without causing anyaccumulation of heavy metals (Kyte and Lewis, 1997).

Fly ash has been used as fertiliser in countries such as Japansince the 1950s or before. By 1990 production and sales offly ash fertiliser known as KSF (potassium silicate fertiliser)had reached 50 kt/y (Arai, 1998). In the USA, 27 Mt ofagricultural limestone was used in 1981 for the amendmentof soil acidity. This is obviously an important potentialmarket for ashes which contain lime.

The variation in both the characteristics of different ashes andthe characteristics of different soils mean that the correct ashhas to be matched with the correct soils and test carried outto ensure that the match is suitable. Ritchey and others(1997) describe different methods for determining thesuitability of ashes to different soils. They emphasise,however, that such tests should be backed up with more long-term studies of how the ashes affect soils over extendedperiods of time and any subsequent effects on vegetation orlivestock. For example, applications of unweatheredsubbituminous fly ash as a soil amendment can increase theconcentration of water soluble boron in the soil to levelswhich are toxic to barley and smooth brome. Also, due to thefly ash related increase in plant available molybdenum thereis an increased risk of molybdenosis disease in cattle feedingon vegetation from fly ash amended soils. Fly ash applicationis most suited to soils deficient in selenium and boron(Hammermeister and others, 1998). However, fly ash canlead to the accumulation of selenium in plants growing onlandfills. Woodbury and others (1999) have found that addinggypsum, another byproduct from power plants fitted withFGD systems, reduces the selenium uptake to acceptablelevels. In Finland, coal fly ash cannot be used as fertiliserbecause of the high levels of cadmium.

FBC residues are rich in CaO (lime and anhydrite) and aretherefore alkali and suitable for use as lime fertilisers inagricultural applications. In Germany Rückstandskalk is thebrand name of FBC residues which is sold as fertiliser. FBCresidues have also been used in Germany for theneutralisation of acidic forest soils (ECOBA, 1998b).

The US Department of Agriculture has published a manualfor applying AFBC residues to agricultural lands whichincludes the following recommendations (USDA, 1988):● AFBC residues with lime equivalences of less than 30%

are not recommended for application;● AFBC residues should not be applied at more than

2.8 short tons per acre (2.84 t/ha) because of the risk ofexcessive levels of soil pH and changes in soil physical

properties due to the cementitious nature of AFBCresidues; and

● proper precautions must be taken in line with US healthand safety requirements for the handling of causticAFBC residues.

There are many projects around the world where fly ash beingused for sea mounts and artificial sea walls and reefs. Forexample, Suzuki and Takahashi (1997) describe the use of flyash concrete blocks as sea mounts to increase marineproductivity. Ashcrete, the high fly ash concrete described inSection 6.1.1 above, is being used to create large scale seamounts called ‘super ridges’ in deep waters around Japan forthe development of new fishing grounds. Suzuki (1998) hasestimated that a 1 GWe coal-fired plant would produce over10 Mt of ash in 30 years, enough to produce 18 km of superridges 30 m high, 120 m wide at the base and 300 m long atthe base. In addition to provide new breeding ground for fishstocks, such super ridges could help reduce coastal erosion.

American Electric Power Co, Columbus, OH, USA,manufacture six-sided honeycomb shaped blocks from fly ashfor erosion control on waterways and seafronts. The blocksare made up of 27% unit weight and 40% unit volume of coalfly ash. The plant can use up to 5 kt fly ash/y, only a fractionof the 285 kt produced there annually although it could beupgraded to produce 35 kt/y. The blocks, known as Seabees,are easy to use and cost-competitive (Swanekamp, 1999).

Ramme and Kohl (1997) describe research into the use of flyash block reefs in fresh water. Although the researchindicated that such reefs may be beneficial to the fishing inthe area, as was the case in similar projects in the Gulf ofMexico and the Atlantic Ocean, the project was cancelled dueto the lack of a permit from the Wisconsin Department ofNatural Resources.

6.1.7 Materials recovery

Some fly ash treatment and separation processes, discussed inChapter 4, can help recover individual metals and mineralsfrom fly ash. The recovery of metals such as aluminium andiron and iron oxide have been investigated by a number ofresearch groups. Fly ash can also be used to produce carbon forcarbon black, industrial graphite or activated carbon. Althoughsuch materials recovery is possible, it is not yet established ona commercial scale (Sloss and others, 1996). According to Robl(1999) the use of fly ash carbon is very problematic and it isproving difficult to recover very pure fractions.

Hazelwood Power in Australia is performing pre-feasibilitystudies with HRL Technology on a 34 kt/y magnesium plantusing Morwell coal fly ash which contains about 20% MgOas feedstock (Allardice, 1999).

6.2 Disposal

There is some confusion over the term ‘disposal’ when it isapplied to fly ash. In some situations the mode of disposal isconsidered beneficial, for example the backfilling of mines.



This mode of disposal can therefore be interpreted as anapplication for fly ash or as a storage option for reserves forfuture applications. This can lead to conflicting data whenconsidering the total amounts of fly ash used and disposed ofin different countries. In this report, disposal of fly ash doesnot include backfill, but rather disposal concerns the use ofspecially created disposal sites.

In countries such as the UK the operator of the power plant isrequired to obtain a licence which applies to the handling,transport and storage and disposal of the fly ash, often with arequirement for the control of dust blow while in transit(Kyte and Lewis, 1997). If the disposal site is close to thepower station then a conveyor belt system may be used. Forexample, ash from the 4000 MWe Drax Power Station in theUK is mixed with 10–20% water and conveyed to a local sitewhere it is being used to construct an artificial hill on landpreviously occupied by ammunition bunkers. Once therequired height is reached a surface layer of soil is addedprior to the return of the land to agricultural use (Kyte andLewis, 1997). For longer distances the ash may be convertedto a slurry and transported in hydraulic pipelines to disposallagoons. Successive lagoons can be created, one above theother, by allowing the first to drain and solidify. This lagoonash can be extracted for subsequent use (Kyte and Lewis,1997). Ghosh and others (1998) describe the combination offly ash ponds with less than 50% soil to create land whichcan support vegetables and food crops with negligibleleaching problems.

In 1992 the US EPA exempted fly ash from conventionalpulverised fossil fuel combustion from the hazardous wasteregulations but did not exempt FBC wastes from theregulation due to a lack of information. However, work sincethen has indicated that AFBC waste are as clean or betterthan those from conventional boilers with respect to leaching(Conn and Sellakumar, 1997). Klein (1999a) reviews thedisposal of CFBC ashes in the USA. Much of the material isdisposed of in landfill or surface impoundments with orwithout co-disposal of other wastes such as brine sludge,dredged soils, lime sludge. Klein (1999a) also includesdetails of the liner types used. These include re-compactedclay/shale, bedrock and synthetic plastic. CFBC wastes canbe problematic in their disposal due to the large quantities ofunslaked lime which can react exothermically causingswelling. Any landfill constructed with CFBC must be wellplanned and well monitored as landfill failures can beextremely expensive to remediate. PFBC residues have lessof a swelling problem but, if dolomite was used as thesorbent, MgO in the ash can lead to cracking in the landfillsite. IGCC residues are relatively inert an cause no problemsin landfill situations (Sloss, 1996).

The cost of disposal and its influence on the use or disposalof fly ash was discussed in more detail in Chapter 3.

6.3 Comments

The benefits of fly ash use in structural fill and concrete arewell established. New and more specialised uses for fly ashare continually being developed. By converting fly ash into

more specialised products such as cenospheres, zeolites andceramics, the marketing potential is increased as is therevenue from what would previously have been consideredwaste material. However, barriers to the use of different ashesin structural applications still remain. These are largely due tothe significant variations in fly ash characteristics and theunpredictability of its potential in any individual application.As discussed in Chapters 2 and 4, variations in ashcharacteristics can occur with changes in fuel type, boilerconditions and other power plant parameters but these can, tosome extent, be either controlled or remediated to ensure thatfly ash remains a valuable commodity.



7 Conclusions


Fly ash can be a valuable commodity. However, ashes fromdifferent combustion systems have very differentcharacteristics and properties which make them more or lesssuitable for different applications. For example, bottom ash iscoarser than fly ash. Residues from FBC systems, such asCFBC and PFBC, tend to be more reactive and areconsidered more difficult to find uses for than fly ash frompulverised coal combustion. Gasification residues are mainlyglassy slags with properties which are quite distinct fromother coal ashes.

Classification systems are used in many countries but at themoment they are less than ideal. The lack of understanding offly ash characteristics means that problems relating ashchemistry to performance will remain for some time yet.Specifications have been set to test the suitability of ash inindividual construction uses. However, these specificationsare currently too strict and limit ash use on insufficientgrounds. In many situations the overly stringentspecifications are excluding the use of ash which wouldproduce a totally acceptable product.

In order to enhance ash sales, ash can be quality assured andsold as a valuable commodity. Despite approaches such asthis, many barriers remain. Table 22 shows a selection of

perceived barriers to ash use along with suggestedapproaches to overcome these obstacles. All the suggestedapproaches have been discussed in the body of this reportand, on many occasions, have been shown to be successful.Perhaps the most successful step to enhance ash marketabilityat any plant is the storage of large quantities of ash in dryform. Dry storage facilities avoid the wastage of ash inlagoons and ponds whilst equalising the supply of ashthroughout the year, despite seasonal variation in ashproduction. Specialised storage of ashes segregated by sizeand/or other parameters allows the sale of ash for morespecialised, and thus more profitable, applications. Theinstallation of large storage facilities has been one of themain factors which has led to total ash sales in countries suchas Denmark, Germany and the Netherlands.

Although markets exist and, in many situations fly ash issuperior to other raw materials, the infrastructure fordelivering quality ash to the end user has to be in place toguarantee sales. Factors such as disposal costs, transportdistances, availability of raw materials, national guidelinesand regulations can all limit the ease with which a powerplant manager can find a buyer for his ash.

If ash is being introduced into a new marketplace then the

Table 22 Perceived barriers to ash use and how they may be overcome

Barriers to ash use Suggested approaches Details

No demand for ash use in the local area/ extended distance from plant to consumer Construct new cement and brick plant near the power plant Sections 3.3 and 5.1

Sell ash to central handling and distribution agent Section 3.3Mismatch between ash production and demand Create suitable storage facilities Sections 3.3, 4.3 and 4.5Natural raw materials are cheaper Create tax incentives for ash use Sections 3.3 and 5.1

Set guidelines for minimum re-use of ash Section 3.3Disposal is the easy option Increase landfill taxes Section 3.3

Create tax incentives for ash use Sections 3.3, and 5.1Disposal is necessary Use ash in back-fill and mine-fill applications where some

benefits can still be attained Section 6.1Ash is collected in a wet system Change collection system to a dry system Section 4.3Ash has been ponded for some time Drying and re-classification may be possible Section 4.4

Consider agricultural uses or back-filling Section 6.1.1 and 6.1.6Ash characteristics do not meet specifications Beneficiation of ash Section 4.4Ash characteristics do not meet specifications, despite the final product being adequate Change standards and specifications to be more

performance based Sections 3.1, 3.2 and 3.3.2Fly ash is too variable Stabilise conditions - fuel type, combustion conditions, etc Sections 4.1 and 4.2Installation of control technologies has changed the ash characteristics Re-optimisation of combustion conditions Section 4.2

Beneficiation of ash Section 4.4Sale of fly ash is not economical Beneficiation of ash to higher quality product Sections 4.4

Development of more specialised applications Section 6.1Consumer will not accept ash fromCFBC or IGCC Perform specific tests to prove adequacy of the ash in practice Sections 3.1, 3.2 and 3.3.2

Change standards and specifications to be less limiting Sections 3.1, 3.2 and 3.3.2Consumer will not accept ash from cofiring Perform specific tests to prove adequacy of the ash in practice Sections 3.1, 3.2 and 3.3.2

Change standards and specifications to be less limiting Sections 3.1, 3.2 and 3.3.2Consumer is wary of use of ash Marketing and promotion to overcome false assumptions Section 3.3

buyer will be wary of the suitability of the ashes for purpose.In some places there can be problems with variation in ashcharacteristics.

Changes in the mineralogy and chemistry of ash occurs in allcoal conversion systems when changes are made incombustion conditions and fuel type. The installation ofpollution control systems can also alter the ash. Low NOxburners can increase the carbon in ash significantly (morethan double). Sometimes adjustment of the boiler canremediate this effect. Otherwise some form of ashbeneficiation may be required. Ammonia injection to enhanceESP performance or in SCR and SNCR systems can lead tohigh quantities of ammonia in the ash. Although this does notaffect the performance of the ash in concrete applications, thesmell can be detrimental and can exceed environmentalhealth regulations. Again processing of the ash may benecessary.

Ash produced from coal combustion systems which is notsuitable for use in construction applications can be processedto enhance its marketability. Various beneficiation methodsare commercially available such as blending, sieving,grinding, carbon burn-out, electrostatic separation, magneticsremoval and chemical treatments. However, new ash, ashfrom a plant which has undergone some change in operatingconditions and even ash which has been processed usingsome form of beneficiation system, still has to be tested to besuitable for application. Gross assumptions cannot be maderelating ash characteristics to final performance in anyapplication.

As the rate of coal consumption increases around the world,so does the rate of ash production. Countries such asBelgium, Germany, Italy and the Netherlands use all of thecoal ash they produce and some even import ash fromsurrounding countries. The rate of ash utilisation in countriessuch as Austria, Denmark, Japan, Poland and the UK is above50% and increasing at a steady rate. However in somecountries the ash utilisation remains low due to remaininginstitutional, legislative and perceived barriers. The averagerate of utilisation of ash in Europe is 41%. Production of ashin countries such as India is becoming a problem as themarkets and applications which exist in more developedcountries have not yet been established.

The major use of fly ash produced around the world is in themanufacture of cement and concrete. Many other uses arepossible including engineered fill, grouts, road constructionand more specialised applications such as the manufacture oflightweight aggregates, cenospheres and zeolites. Bottom ashis commonly used in concrete blocks and road construction.The particular characteristics of residues from FBC systems,such as CFBC and PFBC, make them more difficult to findapplications for. This difficulty is as much with theperception of FBC materials as being ‘difficult’ as it is withthe residues actually being problematic to work with. FBCresidues are, in fact, often ideal for specific uses such asengineered fill and waste stabilisation. Gasification residuesare mainly glassy slags which can be used for roadconstruction or can be processed to create specialised andhighly profitable products such as aggregates.


Conclusions

As ash production continues to increase it will become moreand more important that steps are taken to ensure fly ash use.Countries such as the Netherlands, which have an excellentapproach to ash use, can serve as models for other countriesto follow, although each country will have its own uniqueproblems to deal with. Internationally active agencies such asthe ACAA, and ECOBA are ideally positioned to ensure thatinformation on ash use is available to all ash producingnations so that lessons can be learned and passed on.

7 References


ACAA, American Coal Ash Association (1997) Analysis ofcoal ash uses before and after the EPA’s nitrogen oxidesemission reduction program goes into effect, using the lifecycle assessment approach. Alexandria, VA, USA, AmericanCoal Ash Association, 43 pp (Sep 1997)Affolter R H, Brownfield M E, Breit G N (1997) Temporalvariations in the chemistry of feed coal fly ash and bottomash from a coal-fired power plant. In: Proceedings of the1997 International ash utilisation symposium: pushing theenvelope. 20-22 Oct 1997, Lexington, KY, USA, Universityof Kentucky Center for Applied Energy Research/FUEL/USDOE/FETC, pp 757-764 (Oct 1997)Allardice D (1999) Mulgrave, Victoria, Australia, HRLTechnology Pty Ltd, Personal communication (Aug 1999)Anthony E J, Iribarne A P, Iribarne J V (1997) Thecharacterisation of solid residues from PFBC boilers.Canadian Journal of Chemical Engineering; 75; 1115-1121(1997)Anthony E J, Jia L, Caris M, Preto F, Burwell S (1999)An examination of the exothermic nature of fluidised bedcombustion residues. Waste Management; 19; 293-305(1999)Arai J (1998) Tokyo, Japan, EPDC Coal Tech Co Ltd,Personal Communication (1998)Badelescu C, Andras I (1997) Mathematical model setup ofthe dependence between the hydrodynamic parameters ofhydrogravimetric concentration of ash processing in case ofthermoelectric plant ash recycling. In: Mine planning andequipment selection. Strakoš V, Kebo V, Farana R, Smutn(eds), Rotterdam, The Netherlands, A A Balkema,pp 831-833 (1997)Baer S H, Luftglass B K (1997) Reducing unburned carbonin ash with thermally active marble sorbents. In:Proceedings: 12th International symposium on coalcombustion by-product (CCB) management and use. 26-30Jan 1997, Orlando, FL, USA. Alexandria, VA, USA,American Coal Ash Association, pp 81.1-81.8 (Jan 1997)Balsamo N (1998) Beneficial use of coal combustionproducts. World Coal; 7 (3); 50-55 (Mar 1998)Ban K (1997) Development of fly ash quality control system.In: Proceedings of the international conference on powerengineering 97 ICPE-97, Volume 2, 13-17 Jul 1997, Tokyo,Japan. Tokyo, Japan, Japan Society of Mechanical Engineers,pp 161-166 (1997)Barnes D I (1998) Utilisation of ash from industrial boilers.Paper presented at: European Coal and Steel Communityworkshop on solid waste from coal utilisation. 27-28 Oct1998, Vienna, Austria, 2 pp (Oct 1998)Baweja D, Nelson P (1998) Supplementary cementingmaterials: their acceptance in Australian specifications. In:Fly ash, silica fume, slag and natural pozzolans in concrete:Proceedings of the 6th CANMET/ACI InternationalConference, Volume 1. Bangkok, Thailand 1998. Malhotra VM (ed), Canada, ACI International Ltd, 475-487 (1998)Baykal G, Mehmetolu (1997) Void introduced compactedrubber-fly ash as crash cushions. In: Proceedings: 12th

International symposium on coal combustion by-product

(CCB) management and use. 26-30 Jan 1997, Orlando, FL,USA. Alexandria, VA, USA, American Coal Ash Association,pp 52.1-52.7 (Jan 1997)Belz G (1998), PISA, Italy, ENEL, Personal Communication(Oct 1998)Belz G, Pellequer A (1998) Influence of coal fly ash qualityon concrete durability. Paper presented at: European Coaland Steel Community workshop on solid waste from coalutilisation. 27-28 Oct 1998, Vienna, Austria, 3 pp (Oct 1998)Bennett B H (1997) The changing face of the utility industryand its impact on coal combustion by-product management.In: Proceedings: 12th International symposium on coalcombustion by-product (CCB) management and use. 26-30Jan 1997, Orlando, FL, USA. Alexandria, VA, USA,American Coal Ash Association, pp 93.1-93.5 (Jan 1997)Bergh A O, Hendricks P J (1997) The use of Sasol ash inlabour-based road construction. In: Proceedings of the 1997International ash utilisation symposium: pushing theenvelope. 20-22 Oct 1997, Lexington, KY, USA, Universityof Kentucky Center for Applied Energy Research/FUEL/USDOE/FETC, pp 773-779 (Oct 1997)Bittner J, Gasiorowski S, Tondu E, Vasiliauskas A (1997)STI fly ash separation system: operating history at NewEngland Power’s Brayton Point power plant. In: Proceedings:12th International symposium on coal combustion by-product(CCB) management and use. 26-30 Jan 1997, Orlando, FL,USA. Alexandria, VA, USA, American Coal Ash Association,pp 64-64.5 (Jan 1997)Blackstock T (1997) Coal combustion by-products:opportunities for utilisation. In: Proceedings of the Americanpower conference: Volume 59-2. McBride A E (ed) 1-3 Apr1997, Chicago, IL, USA, Chicago, IL, USA, Illinois Instituteof Technology, pp 1151-1154 (1997)Blondin J (1998) Mazingarbe, France, CERCHAR, PersonalCommunication (Oct 1998)Blondin J, Anthony E J (1994) A selective hydrationtreatment to enhance the utilisation of CFBC ash in concrete.Paper presented at: 49th annual Purdue University IndustrialWaste Conference, 9-11 May 1994, West Lafayette, Indiana,USA, 5 pp (May 1994)Bouzoubaâ N, Zhang M H, Bildeau A, Malhotra V M(1997) The effect of grinding on the physical properties of flyashes and a Portland cement clinker. Cement and ConcreteResearch; 27 (12); 1861-1874 (Dec 1997)Brandstetr J, Havlica J (1996) Phase composition of solidresidues of fluidised bed coal combustion, quality tests andapplication possibilities. Chemistry Papers: 50 (4); 188-194(1996)Breit G, Eble C, Finkelman R (1996) Systematicinvestigation of the compositional variations in solid coalcombustion waste products. In: 13th annual internationalPittsburgh Coal Conference proceedings, Vol 2. 3-7 Sep1996, Pittsburgh, PA, USA. Pittsburgh, PA, USA, Universityof Pittsburgh, pp 1356-1361 (1996)Brendel G F (1997) Removing institutional, legal andregulatory barriers to coal combustion by-product utilisation.In: Proceedings of the 1997 International ash utilisation

symposium: pushing the envelope. 20-22 Oct 1997,Lexington, KY, USA, University of Kentucky Center forApplied Energy Research/FUEL/US DOE/FETC, pp 602-605(Oct 1997)Brendel G F, DiGioia A M, Tyson S S (1997) Developingan effective CCB marketing program. In: Proceedings: 12th

International symposium on coal combustion by-product(CCB) management and use. 26-30 Jan 1997, Orlando, FL,USA. Alexandria, VA, USA, American Coal Ash Association,pp 94.1-94.23 (Jan 1997)Bresler A (1998) Modderfontein, North Rand, Republic ofSouth Africa, Independent Consultant, PersonalCommunication (Oct 1998)Brownfield M E, Cathcart J D, Affolter R H (1997)Characterisation of feed coals and waste products from acoal-burning power plant in Kentucky. In: Proceedings of the1997 International ash utilisation symposium: pushing theenvelope. 20-22 Oct 1997, Lexington, KY, USA, Universityof Kentucky Center for Applied Energy Research/FUEL/USDOE/FETC, pp 780-792 (Oct 1997)Burwell S M, Anthony E J, Berry E E (1995) AdvancedFBC ash treatment technologies. Paper presented at: 13th

international conference on fluidised bed combustion. May1995, Orlando, FL, USA, 7 pp (1995)Callaway D W (1997) CCB management: a businessperspective for utility managers. In: Proceedings: 12th

International symposium on coal combustion by-product(CCB) management and use. 26-30 Jan 1997, Orlando, FL,USA. Alexandria, VA, USA, American Coal Ash Association,pp 92.1-92.10 (Jan 1997)Carpenter A M (1998) Switching to cheaper coals for powergeneration. IEA CCC/01, London, UK, IEA Coal Research,87 pp (Apr 1998)Chordia L (1997) Production processes and economics. In:Proceedings of the 1997 International ash utilisationsymposium: pushing the envelope. 20-22 Oct 1997,Lexington, KY, USA, University of Kentucky Center forApplied Energy Research/FUEL/US DOE/FETC, pp 575-585(Oct 1997)Chugh Y P, Dutta D, Powell E, Renninger S (1997)Development and demonstration of blind undergroundplacement technologies for coal combustion by-products forsubsidence control in abandoned mines. In: Proceedings ofthe international symposium on clean coal technology.18-20 Nov 1997, Xiamen, China, Beijing, China, China CoalIndustry Publishing House, pp 762-772 (1997)Ciccu R, Ghiani M, Peretti R, Serci A, Zucca A (1997)Electrostatic separation of unburnt coal for fly ashbeneficiation. In: Proceedings of the 20th Internationalmineral processing congress. Volume 5: Waste treatment,recycling and soil remediation. 21-26 Sep 1997, Aachen,Germany. Clausthal-Zellerfeld, Germany, GMDBGesellschaft fuer Bergbau, Metallurgie, Rohstoffe- undUmwelttechnik, pp 135-146 (1997)Clarke L B (1993) Management of FGD residues. IEACR/62. London, UK, IEA Coal Research, 82pp (Oct 1993)Cobb J T, Clifford B V, Neufeld R D, Pritts J W, BeeghlyJ H, Bender C F (1997) Laboratory evaluation andcommercial demonstration of hazardous waste treatmentusing clean coal technology by-products. In: Proceedings ofthe 1997 International ash utilisation symposium: pushingthe envelope. 20-22 Oct 1997, Lexington, KY, USA,


References

University of Kentucky Center for Applied EnergyResearch/FUEL/US DOE/FETC, pp 286-296 (Oct 1997)Conn R, Wu S, Sellakumar K (1997a) Environmentalassessment and utilisation of CFBC ash. Paper presented at:International Pittsburgh Coal Conference 1997, Sep 1997,People’s Republic of China, 19 pp (Sep 1997)Conn R, Wu S, Sellakumar K (1997b) Characterisation andmanagement of CFB ash. In: Proceedings of the internationalsymposium on clean coal technology. 18-20 Nov 1997,Xiamen, China, Beijing, China, China Coal IndustryPublishing House, pp 752-760 (1997)Coppola L, Troli R, Zaffaroni P, Belz G, Collepardi M(1998) Influence of unburned carbon in the performance ofconcrete mixtures. In: Fly ash, silica fume, slag and naturalpozzolans in concrete: Proceedings of the 6th CANMET/ACIInternational Conference, Volume 1. Bangkok, Thailand1998. Malhotra V M (ed), Canada, ACI International Ltd,257-265 (1998)Cornelissen H A W (1997) Micronized fly ash: a valuableresource for concrete. In: Proceedings: 12th Internationalsymposium on coal combustion by-product (CCB)management and use. 26-30 Jan 1997, Orlando, FL, USA.Alexandria, VA, USA, American Coal Ash Association,pp 46.1-46.11 (Jan 1997)Cornelissen H A W, van den Berg J W (1998) Fly ashcustomisation for defined performance concretes. In: Flyash, silica fume, slag and natural pozzolans in concrete:Proceedings of the 6th CANMET/ACI InternationalConference, Volume 1. Bangkok, Thailand 1998.Malhotra V M (ed), Canada, ACI International Ltd, 239-256(1998)Davidson R M (1999) Experience of cofiring waste withcoal. IEACR CCC/15. London, UK, IEA Coal Research, 6 pp(Feb 1999)Dietz S (1998) Utilisation of CCPs in Europe. Paperpresented at: ECOBA/ACAA Joint Workshop. Jun 1998,Toronto, Canada. Essen, Germany, ECOBA, 17 pp (Jun 1998)Dietz S (1999) Press Release. Essen, Germany, ECOBA,2 pp (May 1999)ECOBA, European association for the use ofby-products of coal-fired power stations eV (1998a)Information Bulletin 1: Hard coal fly ash in concrete. Essen,Germany, ECOBA, 8 pp (1998)ECOBA, European association for the use ofby-products of coal-fired power stations eV (1998b)Information Bulletin 2: Selected applications ofconstruction materials from power plants. Essen, Germany,ECOBA, 12 pp (1998)Eisele C, Kawatra S K, Banerjee D D (1997) Utilisation offly-ash an inorganic pellet binder. In: Proceedings of the 20thInternational mineral processing congress. Volume 5: Wastetreatment, recycling and soil remediation. 21-26 Sep 1997,Aachen, Germany. Clausthal-Zellerfeld, Germany, GMDBGesellschaft fuer Bergbau, Metallurgie, Rohstoffe- undUmwelttechnik, pp 121-134 (1997)Ekmann J M, Smouse S M, Winslow J C, Ramezan M,Harding N S (1996) Cofiring of coal and waste. IEA CR/90,London, UK, IEA Coal Research, 68 pp (Aug, 1996)Electrabel (1997) Environmental report 1997. Belgium,Electrabel, vp (1997)EPRI, Electric Power Research Institute (1998a) Newtechnology helps fly ash recycling business and benefits the

environment. Energy News. Palo Alto, CA, USA, EPRI,Electric Power Research Institute, 3 pp (June 1998)EPRI, Electric Power Research Institute (1998b) Coal ash:its origin, disposal, use and potential health issues.Environmental Focus. Palo Alto, CA, USA, EPRI, ElectricPower Research Institute, 12 pp (1998)ETSU (1997) On-line measurement of pulverised fuel andcarbon-in-ash. ETSU-TSR-003. Harwell, Oxfordshire, UK,Energy Technology Support Unit, 8 pp (Mar 1997)Evans J J, Dugliss W G, Larochelle M, Paavola J O,Sausser R, Van Horn G R, Young A (1991) Experience withblending, handling and combustion of low cost western coals.In: Proceedings of the American Power Conference, Chicago,IL, USA, 29 Apr - 1 May 1991. Chicago, IL, USA, IllinoisInstitute of Technology, vol 53-II, pp 883-887 (1991)EVN, Energie Versorgung Niederösterreich (1998)Dürnrhor Power Station: a milestone in environmentalprotection, Vienna, Austria, EVN Energie-VersorgungNiederösterreich Aktiengesellschaft, 27 pp (1998)Fecko P, Cablik V (1998) Possibility of obtaining Ti and Alfrom light ash of Vresova power plant with help of Bayer andsintering method. In: 4th conference on environment andmineral processing. Part II. Fecko P, Bulawa M, Holik M(eds). TU Ostrava, Czech Republic, VSB - TechnicalUniversity, pp 667-676 (Jun 1998)Feeley T (1998) Pittsburgh, PA, USA, Federal EnergyTechnology Centre/US DOE, Personal Communication (1998)Fernandez J, Renedo J, Garea A, Viguri J, Irabien J A(1997) Preparation and characterisation of fly ash/hydratedlime sorbents for SO2 removal. Powder Technology; 94 (2);133-139 (Dec 1997)Fisher B C, Blackstock T (1997) Fly ash beneficiation byammonia removal. In: EC-Vol 5, 1997 Joint PowerGeneration Conference, Volume 1.2-5 Nov 1997, Denver CO,USA, New York, NY, USA, ASME, pp 169-173 (1997)Fisher B C, Blackstock T, Hauke D (1997) Fly ashbeneficiation using an ammonia stripping process. In:Proceedings: 12th International symposium on coalcombustion by-product (CCB) management and use.26-30 Jan 1997, Orlando, FL, USA. Alexandria, VA, USA,American Coal Ash Association, pp 65.1-65.8 (Jan 1997)Fitzgerald F D (1998) Upgrading of coal ashes anddesulphurisation residues to provide high value products.Report no COAL R150. Harwell, Oxfordshire, UK, EnergyTechnology Support Unit (ETSU), 45 pp (1998)Floreková L, Michalíková F (1997) Possibility of complexsolving problems of energetical wastes - fly ashes. In: Mineplanning and equipment selection. Strakoš V, Kebo V, FaranaR, Smutn (eds), Rotterdam, The Netherlands, A A Balkema,pp 855-858 (1997)Foner H A, Robl T L (1997) Coal use and fly ash disposalin Israel. Energeia; 8 (5), 1-3 (1997)Ghafoori N, Wang L, Kassel S (1998) Field pavementsusing conventional and clean coal technology by-products.In: Environmental issues and waste management in energyand mineral production. Paamehmetolu A G and Özgenolu A(eds), Rotterdam, Netherlands, Balkema, pp 501-508 (1998)Ghosh R, Sinha T K, Saxena N C (1998) Environmentalissues of disposal of wastes from thermal power plants. In:Proceedings of the 7th national symposium on environment.Danbad, India, Indian School of Mines, pp 219-223(Feb 1998)


References

Graham U, Robl T L, Groppo J, McCormick C J (1997)Utilisation of carbons from beneficiated high LOI fly ash:adsorption characteristics. In: Proceedings of the 1997International ash utilisation symposium: pushing theenvelope. 20-22 Oct 1997, Lexington, KY, USA, Universityof Kentucky Center for Applied Energy Research/FUEL/USDOE/FETC, pp 29-36 (Oct 1997)Gray R E, Gray T A (1998) Coal combustion ash haulback.In: Proceedings of the 25th Anniversary and 15th NationalMeeting of the American Society for Surface Mining andReclamation. Mining - gateway to the future. 17-21 May1998, St Louis, Missouri, ISA, Princeton, WV, USA,American Society for Surface Mining and Reclamation,pp 645-650 (1998)GUS, Gwny Urzd Statystyczny, Central Statistical Office,Poland (1998) Ochrona rodowiska 1998 (Environment1998). Warsaw, Poland, GUS, Gwny Urzd Statystyczny,Central Statistical Office, vp (1998)Hammermeister A M, Naeth M A, Chanasyk D S (1998)Implications of fly ash application to soil for plant growthand feed quality. Environmental Technology; 19 (2), 143-152(Feb 1998)Hassan K E, Cabrera J G (1998) The use of classified flyash to produce high performance concrete. In: Fly ash, silicafume, slag and natural pozzolans in concrete: Proceedings ofthe 6th CANMET/ACI International Conference, Volume 1.Bangkok, Thailand 1998. Malhotra V M (ed), Canada, ACIInternational Ltd, 21-36 (1998)Hassett D J, Eylands K E (1997) Mercury capture on coalcombustion fly ash. In: Proceedings of the 1997 Internationalash utilisation symposium: pushing the envelope. 20-22 Oct1997, Lexington, KY, USA, University of Kentucky Centerfor Applied Energy Research/FUEL/US DOE/FETC,pp 264-272 (Oct 1997)Hay P (1998) USA, Progress Materials Inc, PersonalCommunication (Aug 1998)Hazama Corp (1998) New, strong fly ash concrete: Ashcrete.Tokyo, Japan, Hazama Corporation, 8 pp (1998)Heliostat Ltd (1997) Installation of dry bottom ash system inunit IV of Ptolemaida Power Station. In: 1997 Solid FuelsContractors Meeting, 8-10 Oct, 1997, Athens, Greece.Marousi, Greece, Hleiostat Ltd/European Commission DGXVII, pp 42-50 (Oct 1997)Hinderson A (1999) Älvkarleby, Sweden, VattenfallUtveckling AB, Personal Communication (May 1999)Hollman G G, Steenbruggen G (1997) Synthesis of purezeolites from powder coal fly ash. In: Proceedings of the1997 International ash utilisation symposium: pushing theenvelope. 20-22 Oct 1997, Lexington, KY, USA, Universityof Kentucky Center for Applied Energy Research/FUEL/USDOE/FETC, pp 7-20 (Oct 1997)Honaker R Q, Mondal K, Arnold B, Shirey G (1998)Generating products from coal combustion fly ash usingphysical separations. In: Environmental issues and wastemanagement in energy and mineral production.Paamehmetolu A G and Özgenolu A (eds), Rotterdam,Netherlands, Balkema, pp 565-572 (1998)Hower J C, Robl T L, Rathbone R F, Schram W H,Thomas G A (1997a) Characterisation of pre- and post- NOxconversion fly ash from the Tennessee Valley Authority’sJohn Sevier Fossil Plant. In: Proceedings: 12th Internationalsymposium on coal combustion by-product (CCB)

management and use. 26-30 Jan 1997, Orlando, FL, USA.Alexandria, VA, USA, American Coal Ash Association,pp 39.1-35.13 (Jan 1997)Hower J C, Rathbone R F, Robl T L, Thomas G A,Haerberlin B O, Trimble A S (1997b) Case study of theconversion of tangential- and wall-fired units to low-NOx

combustion: impact on fly ash quality. Waste Management;17 (4); 219-229 (1997)Huang X, Hwang J Y, Gillis J M (1997) Processed low NOx

fly ash as a filler in plastics. In: Proceedings: 12th

International symposium on coal combustion by-product(CCB) management and use. 26-30 Jan 1997, Orlando, FL,USA. Alexandria, VA, USA, American Coal Ash Association,pp 22.1-22.24 (Jan 1997)IVO, Imatra Voima Oy (1997) Environmental Report 1997.Finland, IVO, Environmental Protection Division, vp (1997)Jagiella D (1997) Reuse of coal combustion by-products: anew profit center. In: Proceedings of the American powerconference: Volume 59-2. McBride A E (ed) 1-3 Apr 1997,Chicago, IL, USA, Chicago, IL, USA, Illinois Institute ofTechnology, pp 812-817 (1997)Jones R, Baglin F, Schreifels W A (1997) Supramics -introduction to supercritical ash ceramics. In: Proceedings ofthe 1997 International ash utilisation symposium: pushingthe envelope. 20-22 Oct 1997, Lexington, KY, USA,University of Kentucky Center for Applied EnergyResearch/FUEL/US DOE/FETC, pp 21-28 (Oct 1997)Jozewicz W, Chang J C S (1988) Characterisation ofadvanced sorbents for dry SO2 control. Reactivity of Solids;6; 243-262 (1988)Jozewicz W, Hall B W, Marchant G H, Sedman C B(1997) Demonstration of ADVACATE flue gasdesulphurisation in Poland. In: Proceedings of the 4th

International conference on technologies and combustion fora clean environment. 7-10 Jul 1997, Lisbon, Portugal,Instituto Superior Técnico, paper no 27.28 (Jul 1997)Kahl D, Piper K, Zabel P (1997) Concepts for theutilisation of Lausitz brown coal fly ash. VEAGKraftwekstechnik -English Issue; 77 (2), 137-143 (Feb 1997)Kanatsu T, Ito K, Takahashi M (1998) Fly ash JIS kaiseino torikumi to hinshitsu no genjo. (Amendment of JISspecifications for fly ashes and their current properties.)Denryoku Doboku; 274; 50-55 (Mar 1998) In JapaneseKataoka T, Ogata N (1998) Chozoshita sekitanbai nokogaku tokusei to dorozai eno tekiyo. (Engineeringcharacteristics and applicability as road constructionmaterials of stored coal ashes.) Denryoku Doboku; 274;44-49 (Mar 1998) In JapaneseKeun L J, Chan K S, Won S N, Hyun K D, Geun O J(1997) Triboelectrostatic separation of unburned carbon fromfly ash for ash recycling. Journal of the Korean Institute ofResources Cycling; 6 (3); 15-21 (Sep 1997) In KoreanKlein C (1999a) Synthèse du retour d’expèrienceinternational de gestion des cendres de chaudières à litfluidisé. Première partie: Amérique du Nord. Report no EPIEGT 9900045. Paris, France, Electricité de France, CentreNational D’Equipement Thermique, 80 pp (March 1999) InFrenchKlein C (1999b) Annexes due rapport EPIE GT 9900045.Synthèse du retour d’expèrience international de gestion descendres de chaudières à lit fluidisé. Première partie:Amérique du Nord. Report no EPIE GT 9900052. Paris,


References

France, Electricité de France, Centre National D’EquipementThermique, 48 pp (March 1999) In FrenchKlemm F (1999) Austria, EVN, Personal Communication(Mar 1999)Krishnamurthy R (1999) New Delhi, India, NationalThermal Power Corporation Ltd, Corporate Centre, AshUtilisation Division, Personal Communication (Aug 1999)Krug M, Neuroth M, Miskiewicz K, Gies H (1998) Use ofpower station by-products in hydraulically hardeningimmobilisation systems. VGB PowerTech; 78 (3); 91-99(1998)Kruger R A (1996) The use of cenospheres in refactories.Energeia: 7 (4), 1-3 (1996)Kyte W S (1999) Coventry, UK, PowerGen, EnvironmentUnit, Personal communication (Aug 1999)Kyte W S, Lewis M D (1997) The management, utilisationand disposal of residues from coal-fired power plants. In:Indo-European seminar on clean coal technology and powerplant upgrading: technical papers. 14-16 Jan, 1997, NewDelhi, India, New Delhi, India, National Thermal PowerCorporation, pp 81-90 (1997)Lecuyer I, Biocchi S, Ausset P, Lefevre R (1994) Chemicaland physical characterisation of desulphurisation ashes: thecase of CFBC residues. In: Flowers’94: Proceedings of theFlorence World Energy Research Symposium: energy for the21st century: conversion, utilisation and environmentalquality, 6-8 July 1994, Florence, Italy, Padova, Italy, SGEditorial, pp 773-780 (1994)Lecuyer I, Leduc M, Lefevre R, Ausset P (1997)Circulating fluidised bed combustion ash characterisation -the case of the Provence 250 MW unit. Report noEDF—97-NB-00091. Chatou, France, Electricite de France,vp (May 1997)Lianglong W (1997) A study of the comprehensiveutilisation of fly ash and its sustainable development inChina. In: Proceedings of the joint conference of the CSCEand CSAE. Volume 5: Sustainable development, environment,geotechnical engineering, transportation. 27-30 May 1997,Sherbrooke, PQ, Canada. Montreal, PQ, Canada, CanadianSociety for Civil Engineering, pp 37-43 (1997)Lister R A (1997) Facilities requirements for 100% fly ashsales. In: EC-Vol 5, 1997 Joint Power GenerationConference, Volume 1.2-5 Nov 1997, Denver CO, USA, NewYork, NY, USA, ASME, pp 153-158 (1997)Ma R (1997) Producing building materials with industrialwaste. China Coal: English Supplement; 3; 42-43 (1997)Manz O E (1998) Coal fly ash: a retrospective and futurelook. Energeia; 9 (2); 1-5 (1998)McCarthy M J, Dhir R K (1999) Towards maximising theuse of fly ash as a binder. Fuel: 78 (2); 121-132 (Jan 1999)Meij R, van der Kooij J, van der Sloot H A,Koppius-odink J M, Clement L J (1985) Emissions andcontrol of particulates of coal-fired power plants. In:Proceedings of the second US-Dutch Internationalsymposium on aerosols. Lee S D, Schneider T, Grant L D,Verkerk P J (eds), Williamsburg, VA, USA. Chelsea, MI,USA, Lewis Publishers, pp 427-440 (1985)Meyrahn H, Paeffgen H P, Reich-Walber M, Greif H G(1997) Utilisation of Rhenish brown coal fly ash. VGBKraftewerkstechnik - English Issue; 77 (1), 60-64 (Jan 1997)Michaylov M (1996) Application of fly ash from powerplants for prevention and suppression of sponcom. In:

Proceedings of the 1st International symposium on mineenvironmental engineering. 29-31 Jul 1996, Kütahya-Türkiye,Turkey. England, UK, Brunell University, pp 214-221 (1996)Moret J B M (1999) de Bilt, The Netherlands, Vliegasunie,Personal Communication (Jul 1999)Moret J B M (1995) Maasvlakte fly ash plant. World CementBulk Materials Handling Review 1995; pp 16-20 (1995) Moret J B M, van den Berg (1997) Maasvlakte fly ashprocessing plant. In: Proceedings: 12th Internationalsymposium on coal combustion by-product (CCB)management and use. 26-30 Jan 1997, Orlando, FL, USA.Alexandria, VA, USA, American Coal Ash Association,pp 66.1-66.12 (Jan 1997)Morizaki H (1998) Verification test and study for coal ashquality improvement. Interim report. Giken Jiho; 90; 87-94(Mar 1998) In JapaneseMorris J R, Phillips P S, Read A D (1998) The UK landfilltax: an analysis of its contribution to sustainable wastemanagement. Resources, Conservation and Recycling; 24 (2);259-270 (1998)Mroueh U (1999) Finland, VTT, Chemical Technology Dept,Personal Communication (Aug, 1999)Naquin D (1998) Rising from the ashes: coal ash inrecycling and construction. Waste Age; 29 (2); 61-69 (Feb1998)Nelson P (1999) Sydney, NSW, Australia, Ash DevelopmentAssociation of Australia, Personal Communication (May1999)Okamoto A (1998) Evaluation method for thermal coalquality (Japan). Coal and Safety; 12; 18-39 (Mar 1998) O’Leary E M, Peck W D, Pflughoeft-Hassett D F (1997)Development of a database management system for coalcombustion by-products (CCBs). In: 12th internationalsymposium on management and use of coal combustion by-products. 26-30 Jan 1997, Orlando, FL, USA, Grand Forks,ND, USA, Energy and Environmental Research Centre, 25 pp(Jan 1997)Oostendorp F E (1997) Processing the right buildingmaterials with fly ash content. In: Indo-European seminar onclean coal technology and power plant upgrading: technicalpapers. 14-16 Jan, 1997, New Delhi, India, New Delhi,India, National Thermal Power Corporation, pp 153-158(1997)Owada T, Ebara N, Ozasa K (1998) Present status ofeffective use of coal ash and study on coal ash distributionsystem in Japan. Paper to be presented at: 13th InternationalACAA symposium on management and use of coalcombustion products. Tokyo, Japan, CCUJ, 15 pp (1998)Palcic T (1998) Pittsburgh, PA, USA, Penn Worldwide Inc,Personal Communication (Sep 1998)Pavlish J H, Anderson A A, Craig N C, Mehta A (1994)Using the CQIMTM to evaluate switching to western low-sulphur coals. In: Engineering Foundation conference oncoal-blending and switching of low-sulphur western coals,Snowbird, UT, USA, 26 Sep - 1 Oct 1993. Bryers R W,Harding N S (eds) New York, NY, USA, American Society ofMechanical Engineers, pp 421-440 (1994)Pavlenko S, Shishkanov A, Bazhenov Y (1998)Technological complex for utilisation of high-calcium ashand slag for Abakan Thermal Power Plant. In: Fly ash, silicafume, slag and natural pozzolans in concrete: Proceedings ofthe 6th CANMET/ACI International Conference, Volume 1.


References

Bangkok, Thailand 1998. Malhotra V M (ed), Canada, ACIInternational Ltd, 79-90 (1998)Pflughoeft-Hassett D F, Dockter B A, Eylands K E,Hassett D J, Pavlish J H (1997) Impact of mercury emissioncontrol technologies on conventional coal combustion by-product management. In: Proceedings: 12th Internationalsymposium on coal combustion by-product (CCB)management and use. 26-30 Jan 1997, Orlando, FL, USA.Alexandria, VA, USA, American Coal Ash Association,pp 42.1-42.13 (Jan 1997)Poulsen N B (1998) Fredericia, Denmark, Elsam, PersonalCommunication (Aug 1998)Poulsen N B (1999) Fredericia, Denmark, Elsam, PersonalCommunication (Aug 1999)Pu W (1997) The utilisation situation and future prospect offly ash utilisation in Shanghai City and whole China. In:Proceedings of the international symposium on clean coaltechnology. 18-20 Nov, 1997, Xiamen, China, Beijing, China,China Coal Industry Publishing House, pp 614-624 (1997)Power (1999) Fly ash implicated in building fiasco; new usessought. Power; 143 (2); 4-5 (Mar/Apr 1999)Puch K H, vom Berg W (1997) Byproducts from coal-firedpower plants. VGB Kraftwerkstechnik; 77 (7); 550-556 (1997)Qiang X (1997) Characteristics of high calcium fly ash andits application to concrete. In: Proceedings: 12th

International symposium on coal combustion by-product(CCB) management and use. 26-30 Jan 1997, Orlando, FL,USA. Alexandria, VA, USA, American Coal Ash Association,pp 83.1-83.7 (Jan 1997)Querol X, Umaña J C, Alastuey A, López-Soler A, PlanaF, Tartera J (1998) A potential application of fly ash: zeolitesynthesis. In: Proceedings of the 8th Australian Coal ScienceConference, 7-8 Dec 1998, New South Wales, Australia.NSW, Australia, Australian Institute of Energy, pp 363-368(1998)Ramme B W, Kohl T A (1998) Wisconsin Electric’s coalcombustion products utilisation program. In: Proceedings of theAmerican Power Conference, Volume 60-11, Chicago, Illinois,USA, Illinois Institute of Technology, pp 887-894 (1998)Ranganath R V, Bhattacharjee B, Krishnamoorthy S(1998) Influence of size fraction of ponded ash on itspozzolanic activity. Cement and Concrete Research; 28 (5);749-761 (1998)Rangaswamy A, Kumar Dy M (1998) Fly ash utilisation -Indian scenario. Paper presented at: InternationalConference on Fly ash Disposal and Utilisation. 20-22 Jan1998, India, vp (1998)Renninger S (1998) An overview of the United StatesDepartment of Energy’s coal combustion by-productutilisation program. In: Proceedings of the 25th Anniversaryand 15th National Meeting of the American Society forSurface Mining and Reclamation. Mining - gateway to thefuture. 17-21 May 1998, St Louis, Missouri, ISA, Princeton,WV, USA, American Society for Surface Mining andReclamation, pp 637-644 (1998)Ritchey K D, Clark R B, Baligar V C (1997) Methods forpredicting agronomic response to coal combustion byproductapplication on acid soils. In: Proceedings: 12th Internationalsymposium on coal combustion by-product (CCB)management and use. 26-30 Jan 1997, Orlando, FL, USA.Alexandria, VA, USA, American Coal Ash Association,pp 2.1-2.11 (Jan 1997)

Robl T (1999) Lexington, Kentucky, USA, University ofKentucky, Personal Communication (Sep 1999)Rodríguez-Piñero M, Fernàndez Pereira C, Ruiz deElvira Francoy C, Vale Parapar J F (1998) Stabilisation ofa chromium-containing solid waste: immobilisation ofhexavalent chromium. Journal of the Air and WasteManagement Association; 48; 1093-1099 (1998)Rohatgi P K, Iksan H, Guo R Q, Qui X (1998) Thermalexpansion of aluminum-fly ash composites. In: Proceedingsof the American Power Conference, Volume 60-11, Chicago,Illinois, USA, Illinois Institute of Technology, pp 878-882(1998)Rohde G M, Zwonok O, Silva N I W (1999) Brazil,CIENTEC, Personal Communication (1999)Rostam-Abadi M, DeBarr J A, Rapp D A, Hughes R E,Chou M, Banerjee D (1996) Marketable products from flyash and FGD residues. In: Asia-Pacific conference onsustainable energy and environmental technology. 19-21 Jun1996, Singapore, China. Singapore, China, World ScientificPublishing Co, pp 475-486 (1996)Rostami H, Silverstrim T (1997) Chemically activated flyash concrete. In: Proceedings: 12th International symposiumon coal combustion by-product (CCB) management and use.26-30 Jan 1997, Orlando, FL, USA. Alexandria, VA, USA,American Coal Ash Association, pp 53.1-53.10 (Jan 1997)Roy S S (1997) Draft strategy for utilisation of coal ash inIndia. In: Proceedings: 12th International symposium on coalcombustion by-product (CCB) management and use. 26-30Jan 1997, Orlando, FL, USA. Alexandria, VA, USA,American Coal Ash Association, pp 35.1-35.18 (Jan 1997)Rubenstein J B, Hall S T (1998) Improved utilisation of flyash through beneficiation. In: Proceedings of the XIIIInternational coal preparation congress. Volume II. 4-10 Oct1998, Brisbane, Australia, Indooroopilly, Qld, Australia,Australian, Coal Preparation Society, pp 562-569 (1998) Ruppel T C (1998) Unburned carbon on fly ash: a burningissue for coal-fired utilities. Energeia; 9 (1); 5-6 (1998)Samarin A (1997) Total fly ash management: from conceptto commercial reality. Australian Coal Review; 4, 34- 37(Nov 1997)Saylak D, Estakhri C K, Chimakurthy H (1997) The useof sulphur-modified bottom ash as an aggregate in asphalticconcrete mixtures. In: Proceedings: 12th Internationalsymposium on coal combustion by-product (CCB)management and use. 26-30 Jan 1997, Orlando, FL, USA.Alexandria, VA, USA, American Coal Ash Association,pp 86.1-86.24 (Jan 1997)Scheetz B E, Menghenini M J, Hornberger R J, Owen TD, Schueck J, Giovannitti E (1998a) Beneficial use of coalash in mine reclamation and mine drainage pollutionabatement in Pennsylvania. In: Tailings and Mine Waste 98:Proceedings of the 5th international conference on tailingsand mine waste, 26-28 Jan 1998, Colorado, USA. Rotterdam,The Netherlands, AA Balkema, pp 795-805 (1998)Scheetz B E, Silsbee M, Schueck J (1998b) Acid minedrainage abatement resulting from pressure -grouting ofburied bituminous mine spoils. In: Tailings and Mine Waste98: Proceedings of the 5th international conference ontailings and mine waste, 26-28 Jan 1998, Colorado, USA.Rotterdam, The Netherlands, AA Balkema, pp 859- 870(1998)Schmaltz T C (1997) A brief review of fluidised bed boiler


References

combustion parts of EPA’s fossil fuel combustion Bevillstudies under RCRA. In: Proceedings of the 13th annualfluidised bed conference,17-19 Nov 1997, Lake Charles,Louisiana, USA. Burke, VA, USA, Council of IndustrialBoiler Owners, pp 309-318 (1998)Schneider A, Chabicovsky R, Aumüller A (1998) On-linemeasuring of carbon in fly ash. Paper presented at: EuropeanCoal and Steel Community (ECSC) workshop on solid wastefrom coal utilisation, 27-28 Oct 1998, Vienna, Austria, 5 pp(Oct 1998)Schulze J K, Appenzeller G (1998) Economically profitableconcepts of fly ash processing and homogenisation. VGBPower Tech; 78 (4); 92-97 (1998)Scott D H (1997) Improving existing power stations tocomply with emerging emissions standards. IEACR/92.London, UK, IEA Coal Research, 76 pp (Mar 1997)Scott D H, Carpenter A M (1996) Advanced power systemsand coal quality. IEACR/87. London, UK, IEA CoalResearch, 99 pp (Mar 1996)Sear L K A (1999) Wolverhampton, UK, UK Quality AshAssociation, Personal Communication (Jul 1999)Sevelius D (1997) Product design based on waste. In:Proceedings of the 1997 International ash utilisationsymposium: pushing the envelope. 20-22 Oct 1997,Lexington, KY, USA, University of Kentucky Center forApplied Energy Research/FUEL/US DOE/FETC, pp 37-42(Oct 1997)Sevim H and Renninger S (1998) Integrated engineeringand cost model for management of coal combustion by-products. In: Environmental issues and waste management inenergy and mineral production. Paamehmetolu A G andÖzgenolu A (eds), Rotterdam, Netherlands, Balkema,pp 501-508 (1998)Shao J, Li H, Zhu S, Wang Z (1997) Fly ash utilisation inChina. In: Proceedings of the 20th International mineralprocessing congress. Volume 5: Waste treatment, recyclingand soil remediation. 21-26 Sep 1997, Aachen, Germany.Clausthal-Zellerfeld, Germany, GMDB Gesellschaft fuerBergbau, Metallurgie, Rohstoffe- und Umwelttechnik,pp 109-119 (1997)Shintani N, Saitou T, Sasaki H, Kita T (1997)Mineralogical and chemical properties of mortarincorporating coal ash produced by fluidised bedcombustion. In: Fly ash, silica fume, slag and naturalpozzolans in concrete: Proceedings of the 6th CANMET/ACIInternational Conference, Volume 1. Bangkok, Thailand1998. Malhotra V M (ed), Canada, ACI International Ltd,431-441 (1998)Shintani N, Saito S, Kita T (1998) Kaatsu ryudoshosekitanbai (PFBC hai) no yuko riyo ni kansaru kenkyu(Effective utilisation of coal ashes exhausted from PFBC).Denryoku Doboku; 274; 15-20 (Mar 1998) In JapaneseSinozaki S, Ozasa K, Ichikawa T (1997) Present status ofeffective use of coal ash in Japan and the role of Centre forCoal Utilisation, Japan (CCUJ). In: Proceedings: 12th

International symposium on coal combustion by-product(CCB) management and use. 26-30 Jan 1997, Orlando, FL,USA. Alexandria, VA, USA, American Coal Ash Association,pp 34.1-34.14 (Jan 1997)Sloss L L (1996) Residues from advanced coal-usetechnologies. IEAPER/30. London, UK, IEA Coal Research,40 pp (Nov 1996)

Sloss L L, Smith I M, Adams D M B (1996) Pulverisedcoal ash - requirements for utilisation. IEACR/88. London,UK, IEA Coal Research, 88 pp (Jun 1996)Steenari B M, Schelander S, Lindqvist O (1997) Chemicaland leaching characteristics of ash from combustion of coal,peat and wood in a 12 MWth CFB - a comparative study. In:Proceedings of the 1997 International ash utilisationsymposium: pushing the envelope. 20-22 Oct 1997, Lexington,KY, USA, University of Kentucky Center for Applied EnergyResearch/FUEL/US DOE/FETC, pp 666-673 (Oct 1997)Stencel J M (1998) Extracting greater value fromcombustion ash using a new, dry processing method. In:Proceedings of the 36th Annual Kentucky Coal UtilisationConference, 12-14 May 1998, Lexington, Kentucky, USA.Kentucky, USA, CAER, Center for Applied Energy Research,47-48 (1998)Stewart B, Kalyoncu R (1999) Trends in coal combustionproducts production and use. Paper to be presented at: ACAA13th International Symposium on the management and use ofcoal combustion products, 11-14 Jan 1999, Orlando, FL,USA, 12 pp (1999)Sundermann B, Rubach T, Rensch H P (1995) Feasibilitystudy on the co-combustion of coal/biomass/sewage sludgeand municipal solid waste for plants with 5 and 20 MWthermal power using fluidised bed technology. In: APASClean Coal Technology Programme 1992-1994. Volume II:Combined combustion of biomass/sewage sludge and coals.Final reports. Stuttgart, Germany, University of Stuttgart,Institute for Process Engineering and Power PlantTechnology, 30 pp, paper B21 (Sep 1995)Sutterer K G, Hopkins T C, Graham U, Sweigard R J(1997) Geomechanical considerations for coal combustionbyproducts in engineering applications. In: MiningEngineering: Transactions of the Society for mining,metallurgy and exploration Inc. Volume 302. Littleton, CO,USA, Society for Mining, Metallurgy and Exploration Inc,pp 65-68 (Oct 1997)Suzuki T (1998) Tokyo, Japan, Hazama Corporation,Personal Communication (1998)Suzuki T, Takahashi M M (1997) Enhancement of coastalupwelling by man-made sea-mounts constructed by fly ashconcrete blocks for the increase of marine productivity. In:Oceanolgy International 97 Pacific Rim, Extending the reachof ocean technologies. Conference proceedings Volume 1.Surrey, UK, Spearhead Exhibitions Ltd, pp 89-109 (1997)Swanekamp R (1999) Recycled coal ash tames shorelineerosion. Power; 143 (2); 21 (Mar/Apr 1999)Tanosaki T, Matsumoto M, Izumi K, Nambu M, Inoue K(1998) Utilisation of IGC slag to cement-concrete material.In: International conference on ash behaviour control inenergy conversion systems - proceedings. Yokohama, Japan,18-19 Mar 1998. Tokyo, Japan, Tokyo University ofAgriculture and Technology, p 231-241 (Mar 1998)Tesla M R (1994) Scrap tires process turns waste into fuel.Power Engineering; 98 (5); 43-44 (May 1994)Thamm H W (1997) Marketing of power plant by-productsin Germany. In: Proceedings: 12th International symposiumon coal combustion by-product (CCB) management and use.26-30 Jan 1997, Orlando, FL, USA. Alexandria, VA, USA,American Coal Ash Association, pp 33.1-33.14 (Jan 1997)Trehan A, Krishnamurthy R, Kumar A (1997a) NTPC’sexperience in ash utilisation. In: Indo-European seminar on


References

clean coal technology and power plant upgrading: technicalpapers. 14-16 Jan, 1997, New Delhi, India, New Delhi, India,National Thermal Power Corporation, pp 159-168 (1997)Trehan A, Krishnamurthy R, Kumar A (1997b) Utilisationof coal ash in India. In: Proceedings of the 1997International ash utilisation symposium: pushing theenvelope. 20-22 Oct 1997, Lexington, KY, USA, Universityof Kentucky Center for Applied Energy Research/FUEL/USDOE/FETC, pp 615-622 (Oct 1997)Tuttle T E (1997) Removing barriers: the Illinois ash useamendment. In: Proceedings of the 1997 International ashutilisation symposium: pushing the envelope. 20-22 Oct 1997,Lexington, KY, USA, University of Kentucky Center forApplied Energy Research/FUEL/US DOE/FETC, pp 586-594(Oct 1997)USDA, US Department of Agriculture (1988) Manual forapplying fluidised bed combustion residue to agriculturallands. Report no ARS-74, Springfield, VA, USA, NationalTechnical Information Service, 15 pp (1988)US DOE, US Department of Energy (1998) Pollution toproducts - DOE, Consol to turn coal wastes into roadconstruction material. DOE Fossil Energy Techline. Pittsburgh,PA, USA, Federal Energy Technology Centre, 2 pp (1998)US EPA, US Environmental Protection Agency (1997)Final Report: performance of selective catalytic reduction oncoal-fired steam generating units. Report no 6204-J.Washington, DC, USA, US EPA, Office of Air and Radiation,59 pp (Jun 1997)van der Kooij J (1997) Arnhem, The Netherlands, NV Sep,Personal Communication (1997)Venta G K (1999) Potential for reduction of CO2 emissionsin Canada through greater use of fly ash in concrete. Paperpresented at: CANMET/ACI International Symposium onConcrete Technology for Sustainable Development,Vancouver, BC, Canada, 19-20 Apr 1999, 12 pp (Apr 1999)VGB, Technische Vereinigung derGrosskraftwerksbetreiber ev (1998) Auswertung derVGB-Umfrage über Aufkommen und Verwertung vonNebenprodukten aus Kohlekraftwerken 1991 bis 1997.Bereich “Umweltschutz, Nebenprodukte und Chemie”. Essen,Germany, VGB Technische Vereinigung derGrosskraftwerksbetreiber ev, 25 pp (Jul 1998)Vliegasunie bv (1997) Jaarverslag ‘96 GKE NVGemeenschappelijk KolenbureauElektriciteitsproduktiebedrijven/Vliegasunie bv (AnnualReport 1996). De Bilt, the Netherlands, GKE Vliegasunie,65 pp (1997) In Dutch and EnglishVliegasunie bv (1999) Jaarverslag ‘98 GKE NVGemeenschappelijk KolenbureauElektriciteitsproduktiebedrijven/Vliegasunie bv (AnnualReport 1996). De Bilt, the Netherlands, GKE Vliegasunie,vp (1999) In Dutch and Englishvom Berg W (1997) Commercial use of coal combustion by-products in Europe. Reprint of paper presented at: IndoEuropean seminar on clean coal technology and power plantupgrading. India, NTPC, National Thermal PowerCorporation Ltd, 7 pp (1997)vom Berg (1998) Utilisation of fly ash in Europe. In:Proceedings of the International conference on fly ashdisposal and utilisation. 20-22 Jan 1998, New Delhi, India.New Delhi, India, Central Board of Irrigation and Power,Vol 1, pp 8-13 (Jan 1998)

vom Berg W, Puch K H (1993) Utilisation of residues fromfluidised bed combustion plants. VGB Kraftwerkstechnik;73 (4); 330-334 (1993)Wieck-Hansen K (1996) Summary of Midtkraft report.Provided by Peter Overgaard, Midtkraft, Denmark (1998)Wieck-Hansen K, Hansen P B (1998) Characterisation offly ash from co-combustion of biomass in a pulverised coalfired power boiler. Poster presented at the 10th Europeanconference on Biomass for Energy and Industry, Würtzburg,Germany, 8-11 Jun 1998Wiegers R (1999) Haelen, The Netherlands, IBR ConsultBV, Personal Communication (Aug 1999)Williams D J (1996) Management of solid wastes. In:Environmental management in the Australian minerals andenergy industries: principles and practices. Mulligan D R(ed) Sydney, NSW, Australia, University of New South WalesPress, pp 157-188 (1996)Woodbury P B, Arthur M A, Rubin G, Weinstein L H,McCune D C (1999) Gypsum application reduces seleniumuptake by vegetation on a coal ash landfill. Water, Air andSoil Pollution; 110 (3-4); 421-432 (1999)Yuying Z, Jian L, Longmei L (1997) Study and applicationof a new filling-master batch modified with the power fly ashglass-microballoon. In: Proceedings of the internationalsymposium on clean coal technology. 18-20 Nov 1997,Xiamen, China, Beijing, China, China Coal IndustryPublishing House, pp 688-695 (1997)Zhang Y, Sun W, Pan G, Shang L (1997) The effect of highcontent of fly ash on the properties of glass fibre reinforcedcementitious composites. Cement and Concrete Research;27 (12); 1885-1891 (Dec 1997)


References

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