research article influence of sorbent characteristics on...

Hindawi Publishing CorporationJournal of CombustionVolume 2013 Article ID 438384 12 pageshttpdxdoiorg1011552013438384

Research ArticleInfluence of Sorbent Characteristics on Fouling andDeposition in Circulating Fluid Bed Boilers Firing High SulfurIndian Lignite

Selvakumaran Palaniswamy1 M Rajavel1 A Leela Vinodhan1

B Ravi Kumar1 A Lawrence1 and A K Bakthavatsalam2

1 Bharat Heavy Electricals Limited Tiruchirappalli Tamil Nadu 620 014 India2National Institute of Technology Tiruchirappalli Tamil Nadu 620015 India

Correspondence should be addressed to Selvakumaran Palaniswamy pskumaran9454gmailcom

Received 9 August 2013 Revised 28 September 2013 Accepted 1 October 2013

Academic Editor Michael Fairweather

Copyright copy 2013 Selvakumaran Palaniswamy et al This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

125MWe circulating fluidized bed combustion (CFBC) boiler experienced severe fouling in backpass of the boiler leading toobstruction of gas flow passage while using high sulfur lignite with sorbent calcium carbonate to capture sulfur dioxide Opticalmicroscopy of the hard deposits showed mainly anhydrite (CaSO

4) and absence of intermediate phases such as calcium oxide or

presence of sulfate rims on decarbonated limestone It is hypothesized that loose unreacted calcium oxides that settle on tubes aresubjected to recarbonation and further extended sulfation resulting in hard deposits Foul probe tests were conducted in selectedlocations of backpass for five different compositions of lignite with varied high sulfur and ash contents supplied from the minesalong with necessary rates of sorbent limestone to control SO

2 and the deposits build-up rate was determined The deposit build-

up was found increasing with increase in ash content of lignite sorbent addition and percentage of fines in limestone Remedialmeasures and field modifications to dislodge deposits on heat transfer surfaces to handle the deposits in ash conveying system andto control sorbent fines from the milling circuit are explained

1 Backdrop

India with growing energy consumption is looking at utiliz-ing all its potential energy resources in the most economicand environmentally sustainable manner Coal will continueto be the major energy source in India due to its availabilityPer capita consumption of electricity and GDP growth hasdirect relation and energy intensity in developing countrieslike India is comparatively more than the developed worldand the gap between supply and demand is ever increasingThe demand for all forms of energy is expected to increasesubstantially in the foreseeable future and is expected to getdoubled by 2030 Although coal would continue to be amajor energy source in India due to its availability ligniteis fast emerging as an alternate source of fuel for electricitygeneration In India the total lignite potential is 4177 milliontonnes Indian lignites have a typical analytical range of ash

content of 15 to 35 sulfur content of 10 to 70 andmoisture content of 10 to 45The varieties found in Gujaratand Rajasthan region have moderate to high sulfur (1 to7) content It has become an economic necessity to usethese lignites for power generation in view of spurt in energydemand with SO

2emission controlled Circulating fluid

bed combustion (CFBC) technology is employed consideringthe impurities moisture ash and sulfur content and widevariations in lignite Hence the share of lignite-based pit headthermal projects in Gujarat and Rajasthan is increasing Thesize of CFB boilers in India using lignite has reached alreadyover 250MWe and set to increase above 500MWe and thatunderlines the importance

Slagging fouling and ash deposition are major problemsexperienced in PF boilers In contrast agglomeration of bedparticles in fluidized bed combustion system is consideredas a primary operational issue Interaction and coalescence

2 Journal of Combustion

of bed particles and ash (sintering) are considered to be theprincipal sources of agglomeration in CFB boilers employingbedmaterial and fuel ash as binary system Chokingblockingin fuel path is another peculiar operational problem expe-rienced worldwide in CFB boilers firing pet-coke low rankcoals and biofuels [1]

Lignite mineralogy greatly influences combustion behav-ior Agglomeration and cloggingblocking are experienceddue to sintering of lignite ash with limestone (sorbent) atlower temperature regime in which CFB boilers operate(640ndash960∘C) At this low temperature range the extensiveknowledge built with respect to slagging fouling and cor-rosion phenomenon occurring at higher temperatures inpulverized fuel combustion may not be applicable In CFBboilers ash sintering contributes to deposit formation incyclone return leg and postcyclone flue gas channel (back-pass) [1] In operating units rapid sintering lead to heavyagglomerate formation which finally inhibited circulation indense phase areas (such as seal pot) and in the backpassUnderstanding the sintering behavior of fuel is required forresolving such problems

Over the past decades designers and operators of flu-idized beds have been concentrating on developing the CFBCtechnology by establishing the optimumoperating conditionsand troubleshooting associated with refractory and so forthDue attention has not been paid to understand the limestonecharacteristics that are important for efficient capture of SO

2

Present work describes influence of limestone and its grain sizein blockingclogging of cyclone and hard deposits in second passof CFB boiler during combustion of high sulfur lignite with highash content (20 to 30) in CFB units in Giral Rajasthan stateof India

2 Operational Issues

High sulfur content lignite available atGiral BarmerDistrictand Rajasthan state is used as fuel These lignites had posedseveral operational issues during initial stage of commission-ing and stabilization High sulfur in the lignite needs highlimestone feed rates to control emissionsHigh limestone feedrates caused huge quantities of backpass deposits which ledto obstruction of gas flow passage Despite providing steamsoot blowers for clearing the deposits obstruction of gas flowincreased with increase in limestone feed rate

21 Cyclone Standpipe Blockage During commissioning ashholdup occurred in cyclone standpipe at low loads of about20 to 40MW Ash analysis of the hold-up material is carriedout

22 Backpass Fouling Sulfur dioxide emitted during com-bustion is absorbed in situ by adding limestone of size lessthan 10mm The CFB boiler experienced fouling in super-heaterreheater (SHRH) coilswhile adding required quantityof limestone (Figure 1) Heavy and rapid deposit buildup hasbeen experienced on the flue gas side of the heat transfertubes Deposit buildup was most severe at low temperaturesuperheater (LTSH)-SH 1B tube bank Also growth of ashdeposit in final stage reheater tube bank was observed during

the initial period of operation These deposits increasedgas-side pressure drop and in turn increased loading ofinduced draught (ID) fans with high current causing boilertrips

Consequently CFB boiler was required to be operatedwith less quantity of limestone which resulted in more sulfurdioxide emissions The fouling took place mostly in LTSHcoils of backpass which is placed between reheater and econ-omizer Due to fouling in the backpass fly ash particlescollected in hoppers of economizer and in other zones gotsintered during intermittent storage Nonoperation of sootblowers (SB) and water ingress while starting soot blowingcaused cakes formation Dislodgement of such cakes leadsto difficulty in ash evacuation Deashing system pump waschocked often due to sintered particles (lumps) formed dueto water ingress

3 Experiments Laboratory and Field

31 Lignite Six samples (sample 1 to sample 6) of highsulfur lignite collected from GiralRajasthanIndia (coveringa range of high sulfur content) are considered for the presentstudy of backpass fouling propensity of the high sulfur fuelsin CFB boiler All the fuel samples are prepared in accordancewith ASTM-D 2013 The as-received solid fuels are crushedto pass a number 4 sieve (475mm) and then air drieduntil the loss in weight is not more than 01 per hourAir dried samples are again crushed to pass a number 72mesh (212 microns) Samples of sizes less than 72 mesh areused for analyses of proximate ultimate and calorific valuesAdequate quantity of ash of each fuel is generated usingproximate analyses at 750∘C for further analyses of chem-ical composition ash fusion temperature The proximateultimate and gross calorific values of the samples werecarried out using TGA 701 proximate Analyzer (LECO)Elemental analyzer Vario EL III and PARR Isoperibol BombCalorimeter respectivelyThe chemical composition of asheswas carried out by ICP- AES Perkin Elmer

32 Limestone The sorbents are characterized based onthe CaCO

3content particle size distribution of the parent

sorbent and a relative sulfation reactivity parameter [3]Calcium utilization in general increases as the sorbentsparticle size decreases As the particle size distribution of thefeed sorbent changes in a CFB due to attrition it is taken forgranted that the feed size distribution of limestone (input) isnot as important as the resultant sorbent size distribution inthe boilerOn the contrary mathematical model results showthat sulfur capture efficiency is related to particle attri-tionfragmentation of sorbent inventory in addition to inputparticle size distribution to the performance of circulatingfluidized bed CFB combustors [4]The physical and chemicalproperties of a sorbent are important when evaluating foruse in CFB application Sorbents although chemically similarmay have different sulfation performance Extensive litera-ture studies on process of desulfurization in CFBC show thatsorbent conversion degree is dependent not only on residencetime in combustor but also on its porosity pore structureand pore size distribution [5]The detailed analyses of Indian

Journal of Combustion 3

Reheater-II

Superheater-III

Superheater-IB

Additional LRSB-2nos above SH-III coil

at front side

Additional LRSB-4nos between RH-2

banks

Additional LRSB-2 nosat existing manhole

door location betweenRH-2 and SH-1B at rear

side

Existing manhole doorshifted in between LRSB

to accommodateadditional LRSB

Top of superheater 1B left-before

Top of superheater 1B left-after

660 ∘Cndash720 ∘C



(a)


at front side

Reheater-II

Superheater-III

Superheater-IB


banks



side


additional LRSB

Top of reheater first bank middle-before

Top of reheater first bank middle-after to accommodate




(b)

Figure 1 Deposits in superheaterreheater coils before and after introduction of high pressure soot blowers and location of additional sootblowers in backpass

limestones-chemical composition calcium and magnesiumcarbonate contents that are used in CFB were performedusing Inductively Coupled Plasma-Atomic Emission Spec-troscopy (ICP-AES) Perkin Elmer Optima 2000 DU andusing Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS) Perkin Elmer Sulfation of limestones of different sizefractions showed that sorbent requirement (g of sorbg of sulfur)is less for finer size fractions [6]

33 Deposit Sampling Using Probes and Field Experiment

331 Deposit Probes Field experiment using deposit probesis taken up as the wide range of characterization of the select-ed limestones with respect to their potential difference asdesulfurisation agents in CFBC boilers yielded no definitiveevidence of the fouling and deposition faced in the operatingunits


Compressed air outlet

Metal temperature measurement thermocouple

Compressed air inlet

(a)

(b)

(c)

Figure 2 (a) Schematic sketch of probe to collect fouling samples (b) steel probe with rings [2] and (c) foul probe with deposits

A deposit probe is a good tool for finding out the mech-anisms of deposit formation Air cooled deposit probes oftype Figure 2 was used for sampling of deposits which areequipped with detachable rings [2] The temperature of theprobe can be controlled by varying flow rate of pressurized airFor each test a new probering is used and the weight of theprobering is checked before and after exposure Taking intoaccount exposure time a rate of deposit buildup (g(m2 h))can be calculated Deposited probesrings are stored foranalysis

Deposits were collected from three different locations inthe backpass after SH-1B in between RH-2 bundles and afterRH-2 (Figure 3) Chemical composition analysis of the probedeposits is carried out The sieve analysis of deposits showssignificant share of particles smaller than 50120583m size It wasclear that addition of limestone significantly increased theformation of hard deposits compared to firing only lignitethat is without any limestone

332 Particle Size Distribution of Injected Lime The sieveanalysis of collected deposits showed that these deposits werebuilt up mainly by fine lime particles injected into furnaceFigure 4 shows distribution of the particle size for twosamples done by wet sieving The share of particles smallerthan 50 120583m size indicated that fine fractions were higher thanenvisaged during design (0 to 5 less than 50 120583m) Earlierresearchers have shown that the particle size distribution ofsorbent could significantly affect deposit formation rate [2]

4 Results and Discussions

Analyses of proximate ultimate and gross calorific value andchemical composition of ashes for the seven lignite samplesare listed in Table 1 Analysis of chemical composition of thehold-up material in the cyclone standpipe is furnished inTable 2 Detailed limestone analyses-chemical compositioncalcium and magnesium carbonate contents for the Indianlimestones that are used in CFB are furnished in Table 3Fouling probe test conditionmeasurement details are fur-nished and the chemical composition analysis of the probedeposits is furnished in Table 4 Mineralogy of the probedeposits as determined by XRD is furnished in Table 5

41 Correlation with Conventional Ash Deposition IndicesVarious conventional indices based upon ash chemistry havebeen calculated as indicators of slagging and fouling propen-sity [7] Values for the following indices for the high sulfurlignite samples 1 to 7 are given in Table 1

Silica ratio = SiO2(SiO2+ Fe2O3+CaO +MgO)lowast100

Baseacid ratio = (Fe2O3+ CaO + MgO + Na

2O +

K2O) (SiO

2+ Al2O3+ TiO

2)

Iron index = Fe2O3lowastBA

Ironcalcium ratio = Fe2O3CaO

Iron + calcium in ash = Fe2O3+ CaO


Table 1 Proximate ultimate chemical composition of ash ash fusion temperatures and ash deposition indices of high sulfur lignite

Sample ID Sample 1Lignite Giral

Sample 2Lignite Giral




Sample 6Standpipe blockage

GiralProximate analysis (wt on air dried basis)

Moisture 118 100 296 291 150 96Volatile matter 375 295 278 284 337 378Ash 186 345 156 139 187 268Fixed carbon 321 260 270 286 326 258Gross calorific value Calg 4865 3445 3645 4059 4720 4030

Ultimate (wt on air dried basis)Carbon 516 385 353 395 491 410Hydrogen 38 25 26 26 33 40Nitrogen 06 06 09 08 07 06Sulfur 694 55 41 47 670 40

Chemical composition of ash (wt )SiO2 259 392 410 362 251 341Al2O3 126 275 220 177 142 148Fe2O3 288 165 214 257 264 119TiO2 13 21 23 24 15 16CaO 83 42 37 51 66 33MgO 33 21 22 22 31 13Na2O 72 14 17 28 83 41K2O 03 06 04 04 03 02SO3 110 62 57 72 137 287

Ash fusion temperatures ∘C (oxidizing atmosphere)Temperatures 1 2 3 4 5 6Deformation T1 gt1152 1267 1275 1311 gt1152 1244Softening T2 gt1214 1290 1300 1321 gt1214 1260Hemisphere T3 gt1230 1307 1333 1364 gt1230 gt1300Fusion T4 gt1250 1377 1360 1385 gt1250 gt1300

Ash deposition indicesSi ratio 3906 6322 6002 5231 4101 674Baseacid 120 036 045 064 178 041Iron index 3456 593 963 1645 470 49FeCa 347 393 578 504 40 36Fe + Ca 371 207 251 308 330 152

Table 2 Cyclone outlet standpipe blockagemdashchemical composition of fuellowast ash and clinkers

Material Na2O MgO Al2O3 SiO2 SO3 P2O5 K2O CaO Fe2O3 TiO2

Fuel ashmdashTable 1 sample 6 41 13 148 341 287 mdash 02 33 119 16Black clinker 26 18 38 64 371 01 01 308 169 04Brown clinker 24 16 45 72 297 03 04 315 218 06Grey clinker 21 11 36 64 350 03 01 319 189 06lowastTable 1 sample 6

The interpretation of such ash deposition indices requirescaution as these have been developed for a particular rangeor type of coal and influence of boiler designoperatingconditions is not accounted Ash chemistry indices do notcount the mineralogical mode of occurrence of the elements

of concern and mineral associations both of which areequally important as the ash chemistry in determination ofslagging and fouling With the above limitations it can beseen from Table 1 that the values for most of the commonash deposition indices suggest that the lignite samples would


Table 3 Elemental analysismdashcalcium and magnesium carbonate contents of limestones

Limestone sample ID (1) SLPP (2) Ariyalur (3) NLC Barsingsar (4) Kutch (5) Giral RajasthanAl2O3 426 172 074 278 198BaO 002 001 000 000 001CaO 386 484 521 450 473Fe2O3T 1232 227 028 163 079K2O 003 020 004 031 020MgO 089 035 037 124 071MnO 034 004 001 003 002Na2O 002 009 002 021 010P2O5 013 016 007 008 008SiO2 638 475 205 696 681SrO 002 001 003 007 003TiO2 043 008 003 023 010LOI (900∘C) 344 394 414 394 386CaCO3 g100 g of stone 7052 8867 957 8204 8730MgCO3 g100 g of stone 19 074 08 267 154

Table 4 Deposit sampling using probes

(a) Foul probe test conditionsmdashposition windward

Test serialnumber Gas temp ∘C Probe temp

∘CExposurehours

Limestonetonneshr SO

2ppm

Rate ofbuildupgm2 hr

Lignite fired duringtest Giral samplenumbers (Table 1)

1 685 500 05 0 gt5000 62 Sample number 22 635 500 05 0 gt5000 34 Sample number 33 720 600 05 0 gt5000 73 Sample number 24 680 500 2 5 1800 39 Sample number 35 690 500 05 8 1800 27 Sample number 46 700 500 2 12 1200 61 Sample number 2

(b) Chemical composition of foul probe deposit samples

Serial number Na2O MgO Al2O3 SiO2 SO3 K2O CaO TiO2 MnO Fe2O31 33 35 122 205 18 03 112 23 01 2862 32 23 162 299 80 04 46 15 02 3373 45 38 159 252 150 04 93 21 02 2374 07 11 51 77 368 00 384 07 00 955 08 09 41 65 396 00 390 05 00 866 07 09 48 73 378 01 399 06 00 79

have a high propensity to form ash deposits [8 9] Thevalues in bold and italics indicate high propensity for ashdeposition Agglomeration can start well below the ash fusiontemperatures in fluidized beds for lignite and influence ofNa2O(AFTdecreases) andAl

2O3(AFT increases) onTurkish

lignite was studied by earlier researchers [10]

42 Sulfation of Free Lime in Backpass of Boiler The inves-tigations of the deposit hardening phenomenon in the CFBboilers have been widely discussed as the occurrence of threetypes of deposit consolidation mechanisms [11 12] Two outof the three consolidation mechanisms result in increase involume of free CaO rich zones in deposits Fine sorbent

Table 5 Ash mineralogymdashXRD

Lignite Giral sample 2 Table 1Mineral matter presentQuartz (SiO2) 12Anorthite 30Diopside 25Maghemite 39Hematite 105Anhydrite 784Hexahydrite 05Total 1000


Reheater-II

Reheater-II

Superheater-III

Superheater-III

Superheater-IB

∘C

660ndash720 ∘C

610ndash640 ∘C

530ndash590

SH-1BLow temperature SH

FBHE FBHE

ESP

Airheater

Backpass

Combustor

Cyclones2 nos

ECO-IV

ECO-III

ECO-II

ECO-I

Figure 3 General arrangement of CFBC boiler and backpass

20 32 4575

125

212

355500

7101000

0

10

20

30

40

50

60

70

80

90

100

10 100 1000

Pass

ing

()

Rajasthan-Giral lime

Test 1Test 2

(120583m)

Figure 4 Shares of particles smaller than 50 120583m in limestone sam-ples

particles settled either on the tube surface or in the cavernson the ldquoroughrdquo surface of the old deposits (Figure 5) areexposed to SO

2-containing flue gasesThese sorbent particles

are fine (ie not captured in the cyclone) and the majority

of particles are already calcined before entering the secondpass of the boiler During their residence on tube surfaces inthe convective section these particles undergo a continuoussulfation through an exothermic reaction (1) The sulfationprocess is described by the following overall reaction [2]

CaO + SO2+1

2O2997888rarr CaSO

4+ 481 kgmol (1)

Further if the temperature of flue gas in vicinity of the sorbentparticle is sufficiently high then the local temperature of thedeposits is likely to exceed the sintering temperature due toexothermic reaction and hence as a result the agglomerationcould occur

It had been shown by earlier researchers that the agglom-eration can occur between 750 and 950∘C via the secondmechanism the extended sulfation process [12] The temper-ature for optimumsulfur capture is about 850∘C [13]The issueto be understood is whether there exists an optimum temper-ature range for extended sulfation (long term) [14] Sulfationappears to be the dominant agglomeration mechanism insystems that use high sulfur fuel with calcium-based sorbentsfor low ash fuels like pet-coke [15] The deposits are shownto be composed predominantly of CaSO

4and in some cases

almost pure CaSO4[16 17] Low temperature (down to

750∘C) agglomeration mechanism may be via carbonationand then sulfation [18]

Herein the fuel used is lignite having ash content rangingfrom 15 to 35 and the gas temperature range where thedeposits occurred is from 600∘119862 to 720∘119862


CaO

MacroporesMicropores

Sulfated lime

Unreacted lime

CaCO3 CaSO4

Flue gas temp based lt750 ∘C recarbonation

Extended sulphation gt750 ∘C causing hard deposits

CaO + CO2 + 12 O2hArrCaCO3

minusCO2+ SO2 + 12 O2

4CaCO3 + SO2rArrCaSO + CO2

Figure 5 Consolidation mechanismsmdashsulfation of free lime

In CFBC sulfation is followed by carbonation of CaO andthese reactions can be represented as follows [11]

CaCO3997888rarr CaO + CO

2(calcination) (2)

CaO + CO2997888rarr CaCO

3(recarbonation) (3)

CaCO3+ SO2+1

2O2997888rarr CaSO

4+ CO2

(extended sulfation)(4)

Carbonation mechanism dominates between temperaturerange of 650 and 790∘C at typical CO

2partial pressures

(15 kPa) in a CFB boiler which is much faster than sulfationand is then followed by sulfation of the deposit

A third possible mechanism thought to cause agglomer-ation is hydration followed by carbonation [12] This type offouling is not common in FBCs because they are normallyoperated at temperatures well above at which Ca(OH)

2is sta-

ble under atmospheric conditions (le450∘C) The hydrationreaction may be represented by the following equation

CaO +H2Olarrrarr Ca(OH)2 (5)

This must be followed by carbonation at temperatures below450∘C via the following reaction

Ca(OH)2+ CO2larrrarr CaCO

3+H2O (6)

Traditional fouling mechanism due to presence of elementsthat are associatedwith ash softening ormelting in particularK Na and V is not applicable for the fuels studied due to lowlevels of Na K and V present [19]

43 Detailed Analysis of Ash Forming Matter in the Giral Lig-nite Giral lignite has high ash content 15 to 35 (Table 1)which makes it unique with respect to quantum of ash andthe rate at which it was deposited at the backpass The prin-cipal ash forming elements that play significant role in thefireside problems of the boiler as indicated by mineralogyof the lignite (determined by XRD) are aluminum silicate(kaolinite minerals) and iron compounds (pyrite FeS

2)

With no limestone addition the flue gas was estimatedto contain around 6900 ppm SO

2(with 61 sulfur in fuel

and 3 O2in flue gases) With 12 th limestone addition the

corresponding emissions measured were 1400 ppm SO2 The

tests were conducted at site to study reactions of lime particlesin flue gas to understand the formation of deposits containingvarious calcium compounds The boiler load was varied byincreasing the lignite feed and corresponding increase in thelimestone to control the SO

119909level The very fine limestone

particles were calcined and less than 50-micron level escapedout of the cyclone to backpass and settled over the superheaterand reheater coils As seen in Table 4 chemical compositionanalysis indicates that adding limestone changes the wholechemistry of the deposits mainly from silicon-aluminum-iron-based deposits (samples 1 to 3) to calcium-based deposit(samples 4 to 6) The calcium compounds present are mainlyCaO CaCO

3 and CaSO

4as seen in XRD (Table 5)

The root cause of the fouling problem is carbonationand then sulfation reactions of the limestone particles Looselimestone particles deposit sinter on surfaces and form harddeposits particularly in flue gas temperature range around500ndash700∘C As explained earlier it can be safely concludedat Rajasthan-Giral that recarbonation reaction is dominantin range of 650ndash750∘119862 and the extended sulfation reaction(dominant in range of 750ndash850∘119862) leads to hardened deposits

Ash formed due to combustion of high sulfur lignitedoes not form (sticky or sintering) deposits without lime-stone addition These hard deposits were formed due tofine calcined limestone particles (lt50120583m) that leave thecyclone These particles settle on the superheater surfacesand react with CO

2between 650 and 750∘C leading to

recarbonation and then with SO2between 750 and 850∘C

furthering extended sulfation forming sintered and harddeposits (Figure 6) The hypothesis is that in CFBC carbon-ation takes place as a dominant reaction forming calciumcarbonate (at temperature range of 650 to 790∘C) and thenextended sulfation takes place between 750∘C and 850∘CTheenvironment of flue gas and exothermic reactions contributesto the conversion of the deposits already formed as calciumcarbonate into calcium sulfateThe particles settle as deposits


101214161820222426283032343638404244

250300350400450500550600650700750800850900950

Back

pass

hei

ght (

m)

Flue gas temperature profile

Reca

rbon

atio

n

Reca

rbon

atio

n w

ith

exte

nded

sulp

hatio

nRe

carb

onat

ion

with

Sulp

hatio

nSH3

RH2

Economiser

SH1B

Flue gas temperature (∘C)

Figure 6 Recarbonation and extended sulfation range and location

on the tube surface continue their reaction journey and formas calcium sulfate

44 Optical Microscopy Optical microscopy of the depositsamples shows a layered structure (Figure 7) defined mainlyby mineralogical variation principally in anhydrite (CaSO

4)

and iron oxides Giral ashes are unusual in the occurrenceof complete sulfation of the decarbonated limestone withno evidence of either the occurrence of intermediate phasessuch as calcium oxide or the presence of sulfate reactionrims (Figure 5) on decarbonated limestone [16 17] Reasonfor this unusual behavior is the high sulfur content of theGiral lignite which might have resulted in complete sulfationof the limestone Additional factor is the greater proportionof fine particles in the milled Giral limestone which wouldreact completely [6] This observation is supported by theoccurrence of fine anhydrite particles in the Giral backpasssample and a subsequent increase in grain size in the back endof the boiler suggesting that winnowing of the fine particleshas occurred in the hotter sections of the backpass

5 Field TrialsModifications andImprovement Carried out

51 Standpipe Blockage The chemical compositions ofthe lignite (Table 1) cyclone ash (Table 2) and limestone(Table 3) were analyzed During commissioning cyclonestandpipe choking due to clinkers (Figure 8) with low com-bustor temperature of less than 750∘C was noticed Theanalysis reveals that the composition does not vary muchand contains mostly calcium oxide (CaO) The phenomenonof recarbonation of calcined limestone (CaO + CO

2rarr

CaCO3) unreacted with sulphur dioxide was suspected as a

root cause for loose bonding of material at cyclone standpipeleading to blockage of cyclone [20] This is reflected in thecyclone ash analysis by the presence of free lime (Table 2)The following steps were taken (a) limestone feed sizewas checked with more sampling (b) excessive limestonefeed rate was reduced (c) the operation procedure wasrevised to maintain higher combustor temperature beforestarting limestone addition and (d) automatic pincing air

(a)

(b)

Figure 7 (a) Photomicrograph of superheater deposit Reflectedlight images showing curvilinear layering (b) Photomicrograph ofanhydrite CaSO

4iron oxide Fe

2O3layermdashin transmitted polarised

light-white anhydrite and dark brown iron oxide grains

(a)

(b)

Figure 8 Cyclone outlet standpipe clinkers


025

57510

12515

17520

500 540 580 620 660 700 740 780 820 860 900 940

Equilibrium of free calcium oxide in CFB environment

CaO is more stable

Typical CFB operating regime

Vol o

f CO

2(

)

Vol of CO2

CaCo3 is more stable

Operating temperature (∘C)

in this zone

Use of limestone tobe carefully regulated

Figure 9 Recarbonation-prone regime for limestone addition

arrangements at junction of the cyclone and standpipe todisturb the agglomeration were incorporated

After incorporation of changes in operation procedureand with pincing air arrangements the issue was resolvedThe timing of pincing was reduced by maintaining temper-ature above regime of recarbonation at the cyclone stand-pipe Figure 9 shows specific recommendations for avoidingrecarbonation-prone regime for limestone addition [20]Thecurve denotes the limit of equilibrium of calcium com-pounds As shown in the equilibrium diagram (Figure 8)CaCO

3is stable on the left side of the line whereas CaO is

stable on the right side In the field CaOwas found abundantbecause of excess limestone added to the furnace When thetemperature was reduced to recarbonation range sticky car-bonate causing agglomeration blocked (Figure 8) the cyclonestandpipe

52 High Pressure Soot Blowing High pressure soot blowingwas introduced in the final superheater (FSH) and reheater(RH) and in low temperature superheater (LTSH) Afterincrease in soot blowing pressure from 10 to 20 kgcm2gdeposits were completely eliminated Deposits could beremoved easily nearer to the soot blower location anddeposits located away from lance accumulated proportionalto distance from soot blower Because continuous sootblowing was needed to keep the boiler surfaces clean addi-tional soot blowers were introduced at selected locations asshown in Figure 1 and deposits were eliminated completely(Figure 1)

53 Limestone Size Distribution Lignite without limestoneaddition caused little or no hard deposit buildup in the back-pass of CFB boilerThe severity of the fouling (hard deposits)was clearly dependent on the amount of limestone additionDeposits contained very small fines of less than 50120583m sizefractions It was found that 30ndash40 of the feed limestone wassmaller than 50 120583m (Figure 4) Both dry and wet sieving testsindicated fine fractions were higher than envisaged duringdesign (0 to 5 less than 50120583m) Excess quantity of fineslt50120583m generated in the milling process was removed byproviding a separate elimination line (Figure 10) In additionthe deashing arrangement was improved by introduction of

Bagfilter-1

Bagfilter-2

Bagfilter-3

RAL

Screw feeder-2

Screw feeder-3

Suction fan

Proposedline

Truck

Slide gatevalve

Nb 150 line

Side gatevalve

Exhaust

BIN-1

Figure 10 Lime mill arrangement for segregation of lime powderparticles less than 50 microns

Existing hopper

Extended hopper

Isolation gate

Fluidising pad

Discharge chute

Plant air for fluidisation

Screen

Figure 11Modified arrangement of economizer hopper for removalof bigger particles

fluidizing pad at the discharge end and increase in diameterof discharge chute A screen is provided inside hopper closeto the outlet chute to separate ash particles below 6mm intothe ash evacuation system (Figure 11)

6 Conclusions

Sorbent limestone is used widely in CFB boilers effectively tocontrol sulfur dioxide emissions Hard deposits were formedin backpass of CFB boiler while using high sulfur Indianlignite and limestone sorbent to control SO

2 In addition

large quantum of loose deposits caused severe blocking of thesecond pass Unreacted calcium oxides that settled on heattransfer tubes at temperature between 650∘C and 750∘C weresubjected to recarbonation and further extended sulfationwhich resulted in the hard deposits Elimination of fines


less than 50 120583m in feed limestone could effectively reducethe hard deposits formation in backpass of CFB boiler Thisconfirms the finding of the previous studies carried out atother institutions firing high sulfur but low ash fuels Rate ofbuildup of deposit and chemistry of deposits in backpass ofCFB boiler were studied using special foul probes The rateof buildup of deposit was proportional to the increase in ashcontent of lignite and sorbent feed rate Solution to control thefouling in 125MWe CFB boiler is to minimize the amount offree lime particles (CaO) in the system formed due to excessaddition of fines in feed limestone (less than 50 120583m)The finefractions of limestone feed lt50120583m coming out of millingcircuit were removed by providing an elimination line

Other CFB boiler operational issues faced namelycyclone standpipe blockage cleaning the heat transfer sur-faces deposited with huge quantum of loose ash and ashevacuation to separate the large size depositsparticles wereeffectively resolved through introduction of pincing airat the junction of cyclone and standpipe high pressure(20 kgcm2g) soot blowing in selected locations and incor-poration of fluidizing pads and screens in ash hoppersrespectively

Frequent soot blowing and provision of soot blowers atadditional locations were effective in clearing the huge quan-tum of loose deposits

Abbreviations

AFT Ash fusion temperatureASTM American Society for Testing MaterialsAl2O3 Aluminum oxide

CaCO3 Calcium carbonate

CaO Calcium oxideCaSO

4 Calcium sulfate

CFBC Circulating fluidized bed combustionGDP Gross domestic productLTSH Low temperature superheaterLRSB Long retract soot blowerMWe Mega Watt electricalRH ReheaterSH SuperheaterSiO2 Silicon dioxide

SO2 Sulfur dioxide

TGA Thermogravimetric analysisXRD X-ray diffraction

Acknowledgment

The authors thank the Management of BHEL for the oppor-tunity to present their views through this paper on thisimportant topic The views expressed in this paper are thoseof the authors and not necessarily those of BHEL

References

[1] A Lawrence V Ilayaperumal K P Dhandapani S V Srini-vasan M Muthukrishnan and S Sundarrajan ldquoA novel tech-nique for characterizing sintering propensity of low rank fuelsfor CFBC boilersrdquo Fuel vol 109 pp 211ndash216 2013

[2] R Kobyłecki S Gołąb L Krzemien J Tchorz and ZBisCzęstochowa ldquoFouling in the back pass of a large scaleCFBCrdquo inProceedings of the 9th International Conference onCir-culating Fluidized Beds 2008

[3] S V Pisupati and A W Scaroni ldquoSorbent characterizataion forFBC applicationrdquo in Proceedings of the 10th Annual FluidizedBed Conference 1994

[4] M Fabio S Piero S Fabrizio and U Massimo Sulfur uptakeby Limestone based sorbent particles in CFBC the influence ofattrition fragmentation on sorbent inventory and particle sizedistribution-CFB 10 2011

[5] M Olas and R Kobyłecki BisZmdashSimultaneous calcination andsulfation of limestone based sorbents in CFBC-effect ofmechanical activation-CFB 9 2009

[6] S J Hari and V P Sarma A Study on Indian Limestones For Sul-fur Capture-The EMS Energy Institute and John andWillie LeoneDepartment of Energy Mineral Engineering The PennsylvaniaState University 2012

[7] Common slagging and fouling indices httpwwwcoaltechcomauLinkedDocumentsSlaggingampFoulingpdf

[8] Rod Hatt Coal Combustion IncCorrelating the slagging ofa utility boiler with coal characteristics-http651636271PDF20FilesCorre Slag efc3pdf

[9] R C Attig and A F Duzy ldquoCoal ash deposition studies andapplication to boiler designrdquo Proceedings of American PowerConference vol 31 pp 290ndash300 1969

[10] H Atakul B Hilmioglu and E Ekinci ldquoThe relationshipbetween the tendency of lignites to agglomerate and their fusioncharacteristics in a fluidized bed combustorrdquo Fuel ProcessingTechnology vol 86 no 12-13 pp 1369ndash1383 2005

[11] E J Anthony A P Iribarne J V Iribarne R Talbot L Jia andD L Granatstein ldquoFouling in a 160MWe FBC boiler firing coaland petroleum cokerdquo Fuel vol 80 no 7 pp 1009ndash1014 2001

[12] E J Anthony R E Talbot L Jia and D L GranatsteinldquoAgglomeration and fouling in three industrial petroleum coke-fired CFBC boilers due to carbonation and sulfationrdquo Energyand Fuels vol 14 no 5 pp 1021ndash1027 2000

[13] P F B Hansen K Dam-Johansen L H Bank and K Oster-gaard ldquoSulphur retention on limestone under fluidized bedcombustion conditions An experimental studyrdquo in Proceedingsof the 11th International Conference on Fluidized Bed Combus-tion pp 73ndash82 April 1991

[14] E J Anthony and D L Granatstein ldquoSulfation phenomena influidized bed combustion systemsrdquoProgress in Energy andCom-bustion Science vol 27 no 2 pp 215ndash236 2001

[15] E J Anthony A P Iribarne and J V Iribarne ldquoA new mecha-nism for FBC agglomeration and fouling in 100 percent firingof petroleum cokerdquo Journal of Energy Resources TechnologyTransactions of the ASME vol 119 no 1 pp 55ndash61 1997

[16] E J Anthony A P Iribarne and J V Iribarne ldquoFouling ina utility-scale CFBC boiler firing 100 petroleum cokerdquo FuelProcessing Technology vol 88 no 6 pp 535ndash547 2007

[17] E J Anthony L Jia andK Laursen ldquoStrength development dueto long term sulfation and carbonationsulfation phenomenardquoCanadian Journal of Chemical Engineering vol 79 no 3 pp356ndash366 2001

[18] E J Anthony and L Jia ldquoAgglomeration and strength develop-ment of deposits in CFBC boilers firing high-sulfur fuelsrdquo Fuelvol 79 no 15 pp 1933ndash1942 2000

[19] E J Anthony F Preto L Jia and J V Iribarne ldquoAgglomerationand fouling in petroleum coke-fired FBC boilersrdquo Journal of


Energy Resources Technology Transactions of the ASME vol 120no 4 pp 285ndash292 1998

[20] M Lakshminarasimhan B Ravikumar A Lawrence and MMuthukrishnan High Sulfur Lignite Fired Large CFB BoilersDesign amp Operating experience International Confon Cir-culating Fluidized Beds and Fluidization Technology-CFB 102011

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Active and Passive Electronic Components

Control Scienceand Engineering

Journal of



RotatingMachinery


Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

Acoustics and VibrationAdvances in



Electrical and Computer Engineering

Journal of

Advances inOptoElectronics


Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of


Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



of bed particles and ash (sintering) are considered to be theprincipal sources of agglomeration in CFB boilers employingbedmaterial and fuel ash as binary system Chokingblockingin fuel path is another peculiar operational problem expe-rienced worldwide in CFB boilers firing pet-coke low rankcoals and biofuels [1]

Lignite mineralogy greatly influences combustion behav-ior Agglomeration and cloggingblocking are experienceddue to sintering of lignite ash with limestone (sorbent) atlower temperature regime in which CFB boilers operate(640ndash960∘C) At this low temperature range the extensiveknowledge built with respect to slagging fouling and cor-rosion phenomenon occurring at higher temperatures inpulverized fuel combustion may not be applicable In CFBboilers ash sintering contributes to deposit formation incyclone return leg and postcyclone flue gas channel (back-pass) [1] In operating units rapid sintering lead to heavyagglomerate formation which finally inhibited circulation indense phase areas (such as seal pot) and in the backpassUnderstanding the sintering behavior of fuel is required forresolving such problems

Over the past decades designers and operators of flu-idized beds have been concentrating on developing the CFBCtechnology by establishing the optimumoperating conditionsand troubleshooting associated with refractory and so forthDue attention has not been paid to understand the limestonecharacteristics that are important for efficient capture of SO

2

Present work describes influence of limestone and its grain sizein blockingclogging of cyclone and hard deposits in second passof CFB boiler during combustion of high sulfur lignite with highash content (20 to 30) in CFB units in Giral Rajasthan stateof India

2 Operational Issues

High sulfur content lignite available atGiral BarmerDistrictand Rajasthan state is used as fuel These lignites had posedseveral operational issues during initial stage of commission-ing and stabilization High sulfur in the lignite needs highlimestone feed rates to control emissionsHigh limestone feedrates caused huge quantities of backpass deposits which ledto obstruction of gas flow passage Despite providing steamsoot blowers for clearing the deposits obstruction of gas flowincreased with increase in limestone feed rate

21 Cyclone Standpipe Blockage During commissioning ashholdup occurred in cyclone standpipe at low loads of about20 to 40MW Ash analysis of the hold-up material is carriedout

22 Backpass Fouling Sulfur dioxide emitted during com-bustion is absorbed in situ by adding limestone of size lessthan 10mm The CFB boiler experienced fouling in super-heaterreheater (SHRH) coilswhile adding required quantityof limestone (Figure 1) Heavy and rapid deposit buildup hasbeen experienced on the flue gas side of the heat transfertubes Deposit buildup was most severe at low temperaturesuperheater (LTSH)-SH 1B tube bank Also growth of ashdeposit in final stage reheater tube bank was observed during

the initial period of operation These deposits increasedgas-side pressure drop and in turn increased loading ofinduced draught (ID) fans with high current causing boilertrips

Consequently CFB boiler was required to be operatedwith less quantity of limestone which resulted in more sulfurdioxide emissions The fouling took place mostly in LTSHcoils of backpass which is placed between reheater and econ-omizer Due to fouling in the backpass fly ash particlescollected in hoppers of economizer and in other zones gotsintered during intermittent storage Nonoperation of sootblowers (SB) and water ingress while starting soot blowingcaused cakes formation Dislodgement of such cakes leadsto difficulty in ash evacuation Deashing system pump waschocked often due to sintered particles (lumps) formed dueto water ingress

3 Experiments Laboratory and Field

31 Lignite Six samples (sample 1 to sample 6) of highsulfur lignite collected from GiralRajasthanIndia (coveringa range of high sulfur content) are considered for the presentstudy of backpass fouling propensity of the high sulfur fuelsin CFB boiler All the fuel samples are prepared in accordancewith ASTM-D 2013 The as-received solid fuels are crushedto pass a number 4 sieve (475mm) and then air drieduntil the loss in weight is not more than 01 per hourAir dried samples are again crushed to pass a number 72mesh (212 microns) Samples of sizes less than 72 mesh areused for analyses of proximate ultimate and calorific valuesAdequate quantity of ash of each fuel is generated usingproximate analyses at 750∘C for further analyses of chem-ical composition ash fusion temperature The proximateultimate and gross calorific values of the samples werecarried out using TGA 701 proximate Analyzer (LECO)Elemental analyzer Vario EL III and PARR Isoperibol BombCalorimeter respectivelyThe chemical composition of asheswas carried out by ICP- AES Perkin Elmer

32 Limestone The sorbents are characterized based onthe CaCO

3content particle size distribution of the parent

sorbent and a relative sulfation reactivity parameter [3]Calcium utilization in general increases as the sorbentsparticle size decreases As the particle size distribution of thefeed sorbent changes in a CFB due to attrition it is taken forgranted that the feed size distribution of limestone (input) isnot as important as the resultant sorbent size distribution inthe boilerOn the contrary mathematical model results showthat sulfur capture efficiency is related to particle attri-tionfragmentation of sorbent inventory in addition to inputparticle size distribution to the performance of circulatingfluidized bed CFB combustors [4]The physical and chemicalproperties of a sorbent are important when evaluating foruse in CFB application Sorbents although chemically similarmay have different sulfation performance Extensive litera-ture studies on process of desulfurization in CFBC show thatsorbent conversion degree is dependent not only on residencetime in combustor but also on its porosity pore structureand pore size distribution [5]The detailed analyses of Indian


Reheater-II

Superheater-III

Superheater-IB


at front side


banks



side








(a)


at front side

Reheater-II

Superheater-III

Superheater-IB


banks



side


additional LRSB






(b)









(a)

(b)

(c)










2O +

K2O) (SiO

2+ Al2O3+ TiO

2)





























∘CExposurehours


2ppm













Reheater-II

Reheater-II

Superheater-III

Superheater-III

Superheater-IB

∘C

660ndash720 ∘C

610ndash640 ∘C

530ndash590


FBHE FBHE

ESP

Airheater

Backpass

Combustor

Cyclones2 nos

ECO-IV

ECO-III

ECO-II

ECO-I


20 32 4575

125

212

355500

7101000

0

10

20

30

40

50

60

70

80

90

100

10 100 1000

Pass

ing

()


Test 1Test 2

(120583m)






CaO + SO2+1

2O2997888rarr CaSO

4+ 481 kgmol (1)



4and in some cases





CaO


Sulfated lime

Unreacted lime

CaCO3 CaSO4









2(calcination) (2)



CaCO3+ SO2+1

2O2997888rarr CaSO

4+ CO2



2partial pressures



2is sta-





3+H2O (6)



2)








3 and CaSO








101214161820222426283032343638404244

250300350400450500550600650700750800850900950

Back

pass

hei

ght (

m)


Reca

rbon

atio

n

Reca

rbon

atio

n w

ith

exte

nded

sulp

hatio

nRe

carb

onat

ion

with

Sulp

hatio

nSH3

RH2

Economiser

SH1B





4)




2rarr



(a)

(b)


4iron oxide Fe



(a)

(b)



025

57510

12515

17520

500 540 580 620 660 700 740 780 820 860 900 940


CaO is more stable


Vol o

f CO

2(

)

Vol of CO2



in this zone









Bagfilter-1

Bagfilter-2

Bagfilter-3

RAL

Screw feeder-2

Screw feeder-3

Suction fan

Proposedline

Truck

Slide gatevalve

Nb 150 line

Side gatevalve

Exhaust

BIN-1


Existing hopper

Extended hopper

Isolation gate

Fluidising pad

Discharge chute


Screen



6 Conclusions


2 In addition






Abbreviations




4 Calcium sulfate


SO2 Sulfur dioxide


Acknowledgment


References

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










Reheater-II

Superheater-III

Superheater-IB


at front side


banks



side








(a)


at front side

Reheater-II

Superheater-III

Superheater-IB


banks



side


additional LRSB






(b)









(a)

(b)

(c)










2O +

K2O) (SiO

2+ Al2O3+ TiO

2)





























∘CExposurehours


2ppm













Reheater-II

Reheater-II

Superheater-III

Superheater-III

Superheater-IB

∘C

660ndash720 ∘C

610ndash640 ∘C

530ndash590


FBHE FBHE

ESP

Airheater

Backpass

Combustor

Cyclones2 nos

ECO-IV

ECO-III

ECO-II

ECO-I


20 32 4575

125

212

355500

7101000

0

10

20

30

40

50

60

70

80

90

100

10 100 1000

Pass

ing

()


Test 1Test 2

(120583m)






CaO + SO2+1

2O2997888rarr CaSO

4+ 481 kgmol (1)



4and in some cases





CaO


Sulfated lime

Unreacted lime

CaCO3 CaSO4









2(calcination) (2)



CaCO3+ SO2+1

2O2997888rarr CaSO

4+ CO2



2partial pressures



2is sta-





3+H2O (6)



2)








3 and CaSO








101214161820222426283032343638404244

250300350400450500550600650700750800850900950

Back

pass

hei

ght (

m)


Reca

rbon

atio

n

Reca

rbon

atio

n w

ith

exte

nded

sulp

hatio

nRe

carb

onat

ion

with

Sulp

hatio

nSH3

RH2

Economiser

SH1B





4)




2rarr



(a)

(b)


4iron oxide Fe



(a)

(b)



025

57510

12515

17520

500 540 580 620 660 700 740 780 820 860 900 940


CaO is more stable


Vol o

f CO

2(

)

Vol of CO2



in this zone









Bagfilter-1

Bagfilter-2

Bagfilter-3

RAL

Screw feeder-2

Screw feeder-3

Suction fan

Proposedline

Truck

Slide gatevalve

Nb 150 line

Side gatevalve

Exhaust

BIN-1


Existing hopper

Extended hopper

Isolation gate

Fluidising pad

Discharge chute


Screen



6 Conclusions


2 In addition






Abbreviations




4 Calcium sulfate


SO2 Sulfur dioxide


Acknowledgment


References

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation













(a)

(b)

(c)










2O +

K2O) (SiO

2+ Al2O3+ TiO

2)





























∘CExposurehours


2ppm













Reheater-II

Reheater-II

Superheater-III

Superheater-III

Superheater-IB

∘C

660ndash720 ∘C

610ndash640 ∘C

530ndash590


FBHE FBHE

ESP

Airheater

Backpass

Combustor

Cyclones2 nos

ECO-IV

ECO-III

ECO-II

ECO-I


20 32 4575

125

212

355500

7101000

0

10

20

30

40

50

60

70

80

90

100

10 100 1000

Pass

ing

()


Test 1Test 2

(120583m)






CaO + SO2+1

2O2997888rarr CaSO

4+ 481 kgmol (1)



4and in some cases





CaO


Sulfated lime

Unreacted lime

CaCO3 CaSO4









2(calcination) (2)



CaCO3+ SO2+1

2O2997888rarr CaSO

4+ CO2



2partial pressures



2is sta-





3+H2O (6)



2)








3 and CaSO








101214161820222426283032343638404244

250300350400450500550600650700750800850900950

Back

pass

hei

ght (

m)


Reca

rbon

atio

n

Reca

rbon

atio

n w

ith

exte

nded

sulp

hatio

nRe

carb

onat

ion

with

Sulp

hatio

nSH3

RH2

Economiser

SH1B





4)




2rarr



(a)

(b)


4iron oxide Fe



(a)

(b)



025

57510

12515

17520

500 540 580 620 660 700 740 780 820 860 900 940


CaO is more stable


Vol o

f CO

2(

)

Vol of CO2



in this zone









Bagfilter-1

Bagfilter-2

Bagfilter-3

RAL

Screw feeder-2

Screw feeder-3

Suction fan

Proposedline

Truck

Slide gatevalve

Nb 150 line

Side gatevalve

Exhaust

BIN-1


Existing hopper

Extended hopper

Isolation gate

Fluidising pad

Discharge chute


Screen



6 Conclusions


2 In addition






Abbreviations




4 Calcium sulfate


SO2 Sulfur dioxide


Acknowledgment


References

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation


































∘CExposurehours


2ppm













Reheater-II

Reheater-II

Superheater-III

Superheater-III

Superheater-IB

∘C

660ndash720 ∘C

610ndash640 ∘C

530ndash590


FBHE FBHE

ESP

Airheater

Backpass

Combustor

Cyclones2 nos

ECO-IV

ECO-III

ECO-II

ECO-I


20 32 4575

125

212

355500

7101000

0

10

20

30

40

50

60

70

80

90

100

10 100 1000

Pass

ing

()


Test 1Test 2

(120583m)






CaO + SO2+1

2O2997888rarr CaSO

4+ 481 kgmol (1)



4and in some cases





CaO


Sulfated lime

Unreacted lime

CaCO3 CaSO4









2(calcination) (2)



CaCO3+ SO2+1

2O2997888rarr CaSO

4+ CO2



2partial pressures



2is sta-





3+H2O (6)



2)








3 and CaSO








101214161820222426283032343638404244

250300350400450500550600650700750800850900950

Back

pass

hei

ght (

m)


Reca

rbon

atio

n

Reca

rbon

atio

n w

ith

exte

nded

sulp

hatio

nRe

carb

onat

ion

with

Sulp

hatio

nSH3

RH2

Economiser

SH1B





4)




2rarr



(a)

(b)


4iron oxide Fe



(a)

(b)



025

57510

12515

17520

500 540 580 620 660 700 740 780 820 860 900 940


CaO is more stable


Vol o

f CO

2(

)

Vol of CO2



in this zone









Bagfilter-1

Bagfilter-2

Bagfilter-3

RAL

Screw feeder-2

Screw feeder-3

Suction fan

Proposedline

Truck

Slide gatevalve

Nb 150 line

Side gatevalve

Exhaust

BIN-1


Existing hopper

Extended hopper

Isolation gate

Fluidising pad

Discharge chute


Screen



6 Conclusions


2 In addition






Abbreviations




4 Calcium sulfate


SO2 Sulfur dioxide


Acknowledgment


References

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










Reheater-II

Reheater-II

Superheater-III

Superheater-III

Superheater-IB

∘C

660ndash720 ∘C

610ndash640 ∘C

530ndash590


FBHE FBHE

ESP

Airheater

Backpass

Combustor

Cyclones2 nos

ECO-IV

ECO-III

ECO-II

ECO-I


20 32 4575

125

212

355500

7101000

0

10

20

30

40

50

60

70

80

90

100

10 100 1000

Pass

ing

()


Test 1Test 2

(120583m)






CaO + SO2+1

2O2997888rarr CaSO

4+ 481 kgmol (1)



4and in some cases





CaO


Sulfated lime

Unreacted lime

CaCO3 CaSO4









2(calcination) (2)



CaCO3+ SO2+1

2O2997888rarr CaSO

4+ CO2



2partial pressures



2is sta-





3+H2O (6)



2)








3 and CaSO








101214161820222426283032343638404244

250300350400450500550600650700750800850900950

Back

pass

hei

ght (

m)


Reca

rbon

atio

n

Reca

rbon

atio

n w

ith

exte

nded

sulp

hatio

nRe

carb

onat

ion

with

Sulp

hatio

nSH3

RH2

Economiser

SH1B





4)




2rarr



(a)

(b)


4iron oxide Fe



(a)

(b)



025

57510

12515

17520

500 540 580 620 660 700 740 780 820 860 900 940


CaO is more stable


Vol o

f CO

2(

)

Vol of CO2



in this zone









Bagfilter-1

Bagfilter-2

Bagfilter-3

RAL

Screw feeder-2

Screw feeder-3

Suction fan

Proposedline

Truck

Slide gatevalve

Nb 150 line

Side gatevalve

Exhaust

BIN-1


Existing hopper

Extended hopper

Isolation gate

Fluidising pad

Discharge chute


Screen



6 Conclusions


2 In addition






Abbreviations




4 Calcium sulfate


SO2 Sulfur dioxide


Acknowledgment


References

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










CaO


Sulfated lime

Unreacted lime

CaCO3 CaSO4









2(calcination) (2)



CaCO3+ SO2+1

2O2997888rarr CaSO

4+ CO2



2partial pressures



2is sta-





3+H2O (6)



2)








3 and CaSO








101214161820222426283032343638404244

250300350400450500550600650700750800850900950

Back

pass

hei

ght (

m)


Reca

rbon

atio

n

Reca

rbon

atio

n w

ith

exte

nded

sulp

hatio

nRe

carb

onat

ion

with

Sulp

hatio

nSH3

RH2

Economiser

SH1B





4)




2rarr



(a)

(b)


4iron oxide Fe



(a)

(b)



025

57510

12515

17520

500 540 580 620 660 700 740 780 820 860 900 940


CaO is more stable


Vol o

f CO

2(

)

Vol of CO2



in this zone









Bagfilter-1

Bagfilter-2

Bagfilter-3

RAL

Screw feeder-2

Screw feeder-3

Suction fan

Proposedline

Truck

Slide gatevalve

Nb 150 line

Side gatevalve

Exhaust

BIN-1


Existing hopper

Extended hopper

Isolation gate

Fluidising pad

Discharge chute


Screen



6 Conclusions


2 In addition






Abbreviations




4 Calcium sulfate


SO2 Sulfur dioxide


Acknowledgment


References

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










101214161820222426283032343638404244

250300350400450500550600650700750800850900950

Back

pass

hei

ght (

m)


Reca

rbon

atio

n

Reca

rbon

atio

n w

ith

exte

nded

sulp

hatio

nRe

carb

onat

ion

with

Sulp

hatio

nSH3

RH2

Economiser

SH1B





4)




2rarr



(a)

(b)


4iron oxide Fe



(a)

(b)



025

57510

12515

17520

500 540 580 620 660 700 740 780 820 860 900 940


CaO is more stable


Vol o

f CO

2(

)

Vol of CO2



in this zone









Bagfilter-1

Bagfilter-2

Bagfilter-3

RAL

Screw feeder-2

Screw feeder-3

Suction fan

Proposedline

Truck

Slide gatevalve

Nb 150 line

Side gatevalve

Exhaust

BIN-1


Existing hopper

Extended hopper

Isolation gate

Fluidising pad

Discharge chute


Screen



6 Conclusions


2 In addition






Abbreviations




4 Calcium sulfate


SO2 Sulfur dioxide


Acknowledgment


References

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










025

57510

12515

17520

500 540 580 620 660 700 740 780 820 860 900 940


CaO is more stable


Vol o

f CO

2(

)

Vol of CO2



in this zone









Bagfilter-1

Bagfilter-2

Bagfilter-3

RAL

Screw feeder-2

Screw feeder-3

Suction fan

Proposedline

Truck

Slide gatevalve

Nb 150 line

Side gatevalve

Exhaust

BIN-1


Existing hopper

Extended hopper

Isolation gate

Fluidising pad

Discharge chute


Screen



6 Conclusions


2 In addition






Abbreviations




4 Calcium sulfate


SO2 Sulfur dioxide


Acknowledgment


References

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation













Abbreviations




4 Calcium sulfate


SO2 Sulfur dioxide


Acknowledgment


References

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation














RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation







