bhatt a pot 2002

Potential of fly ash utilisation in India

Ujjwal Bhattacharjee, Tara Chandra Kandpal *Centre for Energy Studies, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110 016, India

Received 12 June 2000

Abstract

A simple framework for the estimation of fly ash utilisation potential in India is presented. It also enablesestimation of associated resource savings. Results of some typical calculations are presented and describedbriefly.

1. Introduction

Coal-based thermal power installations in India contribute about 65% of the total installedcapacity for electricity generation. In terms of energy supply the contribution is even higher, asthese plants meet base load requirements. In order to meet the growing energy demand of thecountry, coal-based thermal power generation is expected to play a dominant role in the futureas well, since coal reserves in India are expected to last for more than 100 years [1].

Indian coals have a very high ash content. The ash content of coal used by thermal powerplants in India varies between 25 and 45%. However, coal with an ash content of around 40%is predominantly used in India for thermal power generation. As a consequence, a huge amountof fly ash is generated in thermal power plants, causing several disposal-related problems. In spiteof initiatives taken by the government, several non-governmental organisations and research anddevelopment organisations for fly ash utilisation, the level of fly ash utilisation in the countrywas estimated to be less than 10% prior to 1996-97 [2]. Globally, less than 25% of the total annualfly ash produced in the world is utilised [3]. However, in Germany, Belgium and Netherlands morethan 95% of the total fly ash produced during 1996 was reportedly used [4]. In the United King-dom, fly ash utilisation was around 50% during 1998 [5]. On the other hand, in the USA andChina, huge quantities of fly ash are produced (comparable to that in India) and its reportedutilisation levels were about 32% and 40%, respectively, during 1995 [6].

152 U. Bhattacharjee, T.C. Kandpal/Energy 27 (2002) 151-166

The problems associated with the low level of fly ash utilisation include inconsistency in thequality of the fly ash produced (even from the same power plant) as the quality of coal receivedby power stations may vary considerably, the costs involved in transportation of fly ash from thepower plants to the consumption points, and consumer preference for products made from freshmaterials over those produced from recycled wastes. In India, the problem is further compoundedby the use of wet fly ash collection systems by a large number of power plants, which results indegradation of the pozzolanic characteristics of the ash, an essential ingredient for several ash-based products. Unavailability of appropriate cost-effective technologies for fly ash utilisation hasalso led to low levels of its utilisation in India.

In a regulation issued by the Ministry of Environment and Forests (MOEF) in 1999, it wasstipulated that all new coal thermal power plants should be able to use 100% of the fly ash theyproduce within the first nine years of operation. For existing power plants, MOEF has set a timeperiod of 15 years for 100% fly ash utilisation from the date of issue of the regulation [7]. Thispaper presents an analysis of the potential possibilities for fly ash utilisation in the country inview of the above-mentioned regulation.

For adoption of safe and economically viable alternative(s) of fly ash utilisation, it is crucialthat all potential fly ash utilisation options are properly assessed and evaluated to enable formu-lation and implementation of a proper plan of action. In the present work, an attempt has beenmade to estimate the potential of fly ash utilisation in some selected routes (as detailed data onall possible routes of fly ash utilisation are not available). The resource savings associated withthese fly ash utilisation routes have also been estimated.

2. Annual fly ash generation in India

The annual amount of fly ash generated will depend on (1) gross electricity generation in thecountry, (2) the fraction of gross electricity generation based on coal, (3) the overall thermalefficiency of energy conversion in the power plants, (4) the calorific value of the coal (in MJ/tonneof coal) and (5) the ash content of the coal used. The following linear regression of the finalelectricity consumption, C(t), on the Gross Domestic Product, GDP(t), is obtained for India:

C(0=-86,572+134 GDP(t), i?2=0.99, (1)

where C(t) is in gigawatt hours (GWh) and the GDP values at factor cost are in constant (1980-81) billions of rupees,1 and t=1 for the year 1980-81. R2 represents the coefficient of determi-nation. Data on electricity consumption and GDP have been used for the period 1980-81 to 1994-95 [8-10].

The gross electricity generation, G(t), has been estimated from electricity consumption, C(t),by assuming that a certain fraction, fu of G(t) is used as auxiliary consumption for operation ofthe plant and that a fraction, f2, of the electricity available at the station bus bar is lost in trans-mission and distribution along with unaccounted losses. Thus,

U. Bhattacharjee, T.C. Kandpal/Energy 27 (2002) 151-166 153

The annual coal requirement (in million tonnes), Acoal(t), for electricity generation is estimated as:

(3)

where f3 represents the fraction of G(t) that is based on coal and h is the overall efficiency ofenergy conversion in coal thermal power plants in India. It is assumed that ith grade coal (withuseful heat content, UHVi, in MJ/tonne) meets a fraction ai of the total coal used for elec-tricity generation.

If it is assumed that fly ash is a certain fraction,f4, of the total ash produced, the annual amountof fly ash generation (in million tonnes), Afa(t), can be estimated as:

al(t), (4)

where bi represents the ash content of the ith grade coal. The coal grade and its amount usedwould usually depend upon the distance of the power plant from the coal pithead and also uponthe prevailing environmental regulations. F and G grade coals are normally used in pithead powerplants, whereas several power plants located at large distances from the mines use better qualitycoals [11].

3. Fly ash utilisation potential

Major areas of fly ash utilisation are (1) making of bricks/blocks, cellular concrete productsand lightweight aggregates, (2) manufacture of cement and asbestos, (3) road construction and(4) embankment, backfill, land development, etc. [3,5,12,13]. The present analysis considers flyash utilisation in cement production, brick manufacture and construction of road embankments,since these routes can accommodate a major portion of the ash produced.

3.1. Fly ash utilisation in cement production

Cement production can absorb large amounts of fly ash. In Israel, out of the 6060 thousandtonnes of total fly ash produced during the period 1982-95, 3910 thousand tonnes of fly ash wereused for cement production, which is around 65% of the total fly ash generated [13]. Fly ash canbe used in the production of Portland Pozzolana Cement (PPC) in three different ways: (1) as araw material along with limestone in the cement kiln, (2) grinding of fly ash and cement in themill and (3) blending of Ordinary Portland Cement (OPC) with fine fly ash.

In the present work, the annual cement production, Acement(t), is projected on the basis of thefollowing linear regression of annual cement production on GDP contribution of the constructionsector, GDPCS(t), at factor cost using the relevant data for the period 1980-81 to 1995-96[9,10,14,15]. Therefore,


Aement(0=-26.40+0.000798GDPCS(0, i?2=0.978, (5)

where Acement(t) is in million tonnes and the GDPCS(t) values are given in constant (1980-81)billions of rupees; and t=1 for 1980-81. R2 is the coefficient of determination.

PPC production in India during the early to mid 1980s was more than 50% of the total cementproduction [14]. Its production level decreased gradually due to non-conformity in the quality ofPPC, mainly contributed by a lack of availability of fly ash in dry form. The level of PPC pro-duction during the 1990s remained less than 20% of the total cement production [16]. It isexpected that PPC production will gain momentum in due course of time with imposition of theregulation for fly ash utilisation [7].

It is assumed that initially (at t=0) a fraction f5 of the total cement production in the countrymakes use of fly ash. This fraction is assumed to increase asymptotically to f6 in a period of Tyears. The amount of fly ash used in cement production in any specific (tth) year can, therefore,be estimated as:

wheref7 represents the fraction of fly ash in PPC (per unit mass). A derivation of Eq. (6) is givenin Appendix A.

3.2. Fly ash utilisation in brick manufacture

A huge amount of fired clay bricks are manufactured in the country. The bricks are usedprimarily for the construction of houses and other civil works. The number of clay bricks producedduring the eighth five-year plan (1992-1997) was estimated at around 231 billion units [17].Production of clay bricks in such large quantities has adverse implications for topsoil and hencethe agricultural productivity of the land. In the present work, the annual number of bricks manufac-tured in the country has been estimated through an assessment of the annual incremental normativeshelter/housing requirements. It has been assumed that: (1) the total number of houses constructedin a year can be estimated as the ratio of the annual growth in population to the average householdsize Y; (2) an average house requires nV m3 of bricks in its construction; (3) the volume of atraditional unit of brick is Vbrick m3; (4) the ratio of permanent houses to total housing requirementsis r1; (5) a fraction f8 of the total brick requirements is used for the housing sector (as bricks arealso required for other civil construction activities); and (6) a fraction f9 of the total bricks pro-duced is rejected in the process of brick manufacture. The total annual number of bricks manufac-tured, Nbricks(t), can therefore be estimated as:

where P(t) represents the total population in the country in the tth year and gi is the populationgrowth rate for the ith block of years (in the present work, a constant population growth rate hasbeen assumed for a block of five years). The relevant data for the period 1989-90 to 1995-96


for population and its growth rate in India have been used [15]. The value off8 has been assumedto be the average of the estimates given in two independent studies for brick requirements in thecountry [18].

It is assumed that the fraction of bricks using fly ash (of the total brick production in thecountry) increases linearly fromf10 (at t=0) tof11 in a period of T years. Since there are severaltypes of fly ash brick manufactured (Clay Fly Ash bricks, Fly Ash Sand Lime bricks, Fly AshSand Lime Gypsum bricks, etc.), it is assumed thatj different types of fly ash brick are manufac-tured and that the jth type of brick (with fly ash fraction sj) contributes a fraction ej of the totalfly ash bricks manufactured. Therefore, fly ash utilisation (in million tones), Afa-brick(t), that couldbe achieved in brick manufacture can be estimated as:

where dcb represents the density (kg/m3) of the clay brick and t=0 for the year 1999-2000.

3.3. Fly ash utilisation in the construction of road embankments

National and state highways are often constructed on raised embankments and soil is normallyused for this purpose. Fly ash can also be used for the construction of road embankments. Around18.5% of the total fly ash produced in Israel during 1982-95 was used for construction of embank-ments [13]. In the present work, the projection of incremental lengths of national and state high-ways is obtained using their compounded annual average growth rate during the period 1980-81to 1995-96 [19]. The amount of fly ash (in million tones) that may be utilised for constructionof road embankments can be estimated as:

j\ 1soilF1, (9)

where R(t) represents the incremental road length in the tth year. Once again, it is assumed thatthe fraction of road embankments constructed using fly ash increases linearly fromf12 (at t=0) tof13 in a period of T years. F1 is the soil replacement factor by fly ash (the soil substitution by flyash) and dsoil (in kg/m3) is the density of soil. The road embankments are assumed to be oftrapezoidal shape with top width, height and slope being W (m), H (m) and S, respectively.

The total fly ash utilisation (as a fraction of the fly ash produced), Ufa(t), through all of theabove-mentioned routes can be calculated as:

T A f _ a-PPC(t)+Afa-brick(t)+Afa-emb(tU d t )

4. Estimation of resource savings associated with fly ash utilisation

Fly ash utilisation will lead to savings in natural resources, mainly the land (and soil), water,coal and limestone. Large-scale utilisation of fly ash in the manufacture of bricks and the construc-


tion of road embankments will release considerable amounts of land. Water will be saved due toreduced fly ash disposal from power plants. PPC production will lead to reduced coal consumptionas well as savings in limestone due to reduced clinker requirements.

4.1. Land saved

Fly ash utilisation would lead to reduced land/soil requirement for (1) ash ponds, (2) clay brickproduction and (3) the construction of road embankments.

The land saved (in hectares) due to brick manufacture, Lbrick(t), reduced ash pond size, Lash

pond(t), and construction of road embankments, Lemb(t), can be expressed as:

t=UE~L

Lashpond , 1 E Ufa(t)Afa(t) (12)dfaHdyke (=1

and

respectively, where Z (in m) is the depth of quarry (the depth of quarry for construction of roadembankments may, however, be quite different from that for clay brick manufacture). dfa is thedensity of fly ash (in kg/m3). Hdyke (in m) represents the height of the ash dyke and UEL is theuseful economic life of the plant. In Eq. (12), it is assumed that even for increased fly ash utilis-ation levels the maximum height of the ash dyke shall remain the same.

4.2. Water saved due to reduced ash disposal

Ash is mixed with water to form slurry. The slurry is then pumped and disposed to the ashpond through pipelines. Water saved annually due to increased fly ash utilisation (reduced storagerequirements) can be estimated as:

, (14)d f a

where SPCwater is the specific water requirement per unit volume of fly ash disposed.

4.3. Coal saved due to PPC production

The thermal and electrical energy required for production of PPC is less than that required forproduction of OPC [20]. Generally coal is used as the source of thermal energy in cement plants.If the specific thermal energy consumption (in kg/tonne of cement) in the production of OPC and


PPC are SPCth1 and SPCth2, respectively, and corresponding values of specific electrical energyconsumption (in kWh/tonne of cement) are SPCel1 and SPCel2, respectively, the amount of coal(in million tonnes) saved (in million tonnes), CPPC(t), due to fly ash utilisation in the productionof PPC can be estimated as:

/ 2 ) ( r ? l^j j J,(SPCel1 - SPC e / 2 ) ( r ? l^j j J, (15)where UHV is the useful heat value content (in MJ/tonne) of coal used in cement plants.

4.4. Limestone saved due to PPC production

Limestone is required in the process of clinker production. The clinker requirements for theproduction of OPC and PPC are not equal and also vary with the process adopted for clinkerproduction, i.e. dry, semi dry and wet processes. The clinker consumption for production of PPCis less than that consumed in the production of OPC in all processes of cement production [20].The amount of limestone saved (in thousand tones), LSPPC, due to the production of PPC can beestimated as:

(16)

where SPCOPC and SPCPPC are the specific clinker consumption per unit of cement produced forOPC and PPC, respectively.

5. Key assumptions and input parameters

Results of some typical exemplifying calculations are presented in this paper. While the broadframework developed in the paper has been followed for these calculations, the following simpli-fying assumptions have also been made. Table 1 presents the values of input parameters used inthe present work.

1. The thermal (coal), hydro and nuclear mix for power generation has remained almost unchangedduring the last 10 years [8]. In the present analysis, the contribution of coal-based electricityin the gross electricity generation is assumed to remain the same for the study period.

2. Of the total coal used for thermal power generation, around 36% was consumed in pitheadpower plants in 1997. The corresponding figures were 43% and 21%, respectively, for plantslocated within and beyond 1000 km of the coal mine [21]. It is assumed that this distributionwill remain the same during the study period.

3. Around 10% of the total coal supply to power plants is G grade coal, which has an ash contentof about 46% [11]. It is assumed that 50% of this G grade coal can be beneficiated prior toits use in power plants.

4. Cement production and consumption in a year are assumed to be the same.5. A certain volume of fly ash substitutes an equivalent volume of soil.


Table 1Input parameters used

Symbol Unit Value Reference/Remarks

c b

dsoil

hhf 4

f5f6f7f8hf10f11

HHdyke

SPCel1

SPCel2

TUELUHVUHVi

kg/m3

kg/m3

kg/m3

Fraction

FractionFractionFractionFractionFractionFractionFractionFractionFractionFractionFractionFractionFractionFactor%

mmTypes of brickm3

RatioFraction

Slope

kg/tonne of cement

kWh/tonne of cement

FractionFractionYearsYearsMJ/tonneMJ/tonne

17707501100(a) 0.5(b) 0.50.0760.220.690.80.180.500.200.700.050.010.100.050.200.71997/98 to 2001/02: 2.14%

2002/03 to 2006/7: 2.1%2007/08 to 2011/12: 2.05%115230.9 (two rooms consideredan average size house)0.75(a) 0.25 (fly ash clay brick)(b) 0.60 (fly ash sand limebrick)1 in 210:1233222118750.850.9610, 15, 203014,133C=22,028D=19,102E=15,800F= 12,03 8G=7733

[25]

(a) Fly ash clay brick(b) Fly ash sand lime brick[8][8][8]

[16][13,14]Maximum 30% [13]Average value used [18]

18.5% use in Israel [13]Maximum 75% [26][13], for base figure ofpopulation growth rate (2.14%)

In equal quantilitiesfor [27]

[18](a) Maximum 35% [26](b) Maximum 85% [26]

[28][20][20][20][20][20][20]

[11][11]

(continued on next page)


Table 1 (continued)

Symbol

Vbrick

wYZai

bi

bi

n

Unit

cm3

mPersons per housemFraction

%

%Efficiency

Value

22.9 cmxll.2 cmx7.0 cm75.4531.5Pit head: 0.36<1000km: 0.43>1000 km: 0.21G=46.09%F=38.62%E=32.10%D=26.38%C=21.30%32±2 (32% ash content used)0.30

Reference/Remarks

[27]

[29]

[21]

[11]

[28][8]

6. While calculating the annual brick requirements, the bricks required for repair and maintenanceof existing buildings and also for dilapidated structures have not been considered.

7. The analysis assumes that, from certain existing levels of fly ash utilisation in the productionof cement, bricks and construction of road embankments, along with corresponding desiredsaturation levels of its utilisation in respective applications will be achieved in a certain timeduration. These initial levels of fly ash utilisation in different applications are based on theavailable data in the literature [16], whereas the target levels of fly ash utilisation are basedon the extent of success reported in other countries [13,14]. Three different time frames havebeen considered for achieving the expected levels of fly ash utilisation.

6. Results and discussion

Table 2 presents the projected values of gross electricity generation, the amount of coal requiredfor electricity generation and the annual amount of fly ash produced. While the gross electricitygeneration is primarily based on the regression of final electricity consumption on the gross dom-estic product in India and also takes into account the auxiliary consumption for operation of powerstations and the losses in transmission and distribution, the estimation of amount of coal requiredand fly ash produced has been arrived at by considering the future coal mix for electricity gener-ation (in respect of their useful heat value and ash content). Table 2 also presents a comparisonof the results obtained for gross electricity generation in the present analysis with that of the long-term energy demand forecasts of the 16th Electricity Power Survey of India for three differentyears [22]. The annual coal requirement projected in the present analysis is 436 million tonnesin 2006-07, as against an estimate of 447 million by the Council of Power Utilities [11].

A regulation of the MOEF also stipulates that for all coal-based thermal plants located beyond1000 km from the coal mine, it would be mandatory for these plants to use beneficiated coal


Table 2Table 2Projected values of gross electricity generation, coal requirement and fly ash generation

Year Gross electricitygeneration (TWh)

491522555589624662702744787833881932985

Coal requirement(million tonnes)

288306325345366388411436461488516546577

Fly ash generation(million tonnes)

7782879297

103110116123130138145154

16th EPSprojections ofelectricityrequirement (TWh)[22]

1999-20002000-012001-022002-032003-042004-052005-062006-072007-082008-092009-102010-112011-12

555

719

975

from 1 June 2001 [23]. This may lead to a qualitative (and quantitative) redistribution in the mixof different grades of coal utilised for electricity generation in the future and, consequently, leadto a change in the amount of fly ash produced. From Fig. 1 it can be observed that the growthrate in fly ash generation is less than that for coal requirement. This is particularly due to theeffect of coal beneficialtion considered in the present work.

I I

Annual Coal Requirementfin million tonnes)

" " " Total Fly Ash Generation{in million tonnes)

2003-04 2005-06Year

Fig. 1. Projected values of coal requirement and fly ash generation.


Table 3 presents the projected values of cement production, brick manufacture and annualincremental road lengths in India. The projected brick requirements for the housing sector in thecountry is 55.4 billion units and 64 billion units in 2001-02 and 2010-11, respectively, as againstthe values of 61 billion units and 73 billion units estimated by Development Alternatives [18].The estimates for cement production (in million tones) obtained in the present work are 95 and122 for the years 2001 and 2006, in comparison with the projections of 112.9 and 163.6 milliontonnes by Das and Kandpal [24].

Table 4 presents the projected values of the amounts of fly ash utilised in brick manufacture,cement production and construction of road embankments for three different time horizons of 10,15 and 20 years. It may be observed that around 50% of the total amount of fly ash utilised isabsorbed in the production of PPC. Therefore, fly ash utilisation in cement manufacture shouldbe encouraged.

Fig. 2 presents the projected fly ash utilisation in the selected routes considered in the presentwork during the period 1999-2000 to 2009-10. These results are based on the assumptions that,by the terminal year of stipulated time period (10/15/20 years), (1) 50% of cement productionwill be PPC using fly ash, (2) 10% of the bricks produced will use fly ash and (3) 20% of theincremental road length will use fly ash for construction of road embankments. It may be notedthat 100% fly ash utilisation as envisaged by MOEF does not appear to be practically feasible.

Table 5 presents the projected resource savings (coal, water, land and limestone) due to fly ashutilisation through the selected routes under three different time frames considered in the presentwork. Land saved due to reduced fly ash disposal in ash ponds has been calculated for an economiclife of 30 years for coal-based power plants. It is estimated that around 10,000, 9596 and 9164hectares of land would be saved due to reduced fly ash storage requirements in the time framesof 10, 15 and 20 years, respectively.

Table 3

Projected values of cement production, brick manufacture and incremental road length

Year Acement(t) (million tonnes) Nbrick(t) (billion units) R(t) (km)

1999-2000 85 76 35402000-01 90 77 36092001-02 95 79 36802002-03 100 79 37512003-04 105 81 38242004-05 111 82 38992005-06 116 84 39752006-07 122 86 40522007-08 129 86 41312008-09 135 88 42112009-10 142 89 42932010-11 149 91 4377


Table 4Projected values of fly ash utilisation in PPC production, construction of road embankments and brick manufacture

Year

1999-2000

2001-02

2003-04

2005-06

2007-08

2009-10

Fly ash utilisation routes

Cement productionConstruction of roadembankmentsBrick manufactureTotalCement productionConstruction of roadembankmentsBrick manufactureTotalCement productionConstruction of roadembankmentsBrick manufactureTotalCement productionConstruction of roadembankmentsBrick manufactureTotalCement productionConstruction of roadembankmentsBrick manufactureTotalCement productionConstruction of roadembankmentsBrick manufactureTotal

Fly ash utilised

= 1 0 years

3.061.23

1.025.316.052.04

2.9911.539.402.92

5.0317.3511.303.86

7.2922.4512.774.87

9.5127.1514.185.95

12.0832.21

(million tonnes)

= 1 5 years

3.061.23

1.025.315.511.78

2.359.648.142.39

3.7214.2410.413.03

5.2418.6912.283.72

6.7322.7313.944.46

8.4626.85

T=20 years

3.061.23

1.025.314.981.66

2.038.667.212.12

3.0612.399.452.62

4.2216.2811.513.15

5.3420.0013.403.72

6.6423.77

7. Conclusion

A simple framework for estimation of fly ash utilisation potential in India has been developed.Fly ash utilisation in cement production, construction of road embankments and manufacture ofbricks has been considered. The results obtained for the projected levels of fly ash utilisationclearly show that in spite of assuming quite optimistic levels of fly ash use in the three appli-cations, the overall fly ash utilisation is less than 25% of the total fly ash produced. Therefore,either a much more aggressive fly ash utilisation strategy has to be developed and executed orthe extent of the fly ash utilisation target (or the year of achieving a specified target) should bereviewed by MOEF.

Table 5Projected resource savings (coal, land, water and limestone)

O

§

Resources saved

Land (hectares) Water (million m3) Coal (thousand tonnes)Limestone (thousandtonnes)

1999-20002001-022003-042005-062007-082009-10

7M0years

200447706991

12781603

T=15years

2003685427359291148

T=20years

200382461607754921

T=10years

711542331299362429

T=15years

71129190249303358

T=20years

71116165217267317

7M0years

72715432233268430343368

T=15years

727130819342474291813,1

T=20years

72711821713224427353184

7M0years

300863799234

11,09612,54213,923

T=15years

300854047994

10,22812,06513,687

T=20years

3008488970819279

11,30913,165


I 15.00

2003-04 2005-06

Year

Fig. 2. Projected levels of fly ash utilisation in India.

Appendix A. Derivation of the expression for fly ash utilisation potential in PPCproduction

It is assumed that initially (at t=0) a fraction f5 of the total cement production in the countrymakes use of fly ash. This fraction is assumed to increase asymptotically to f6 in a period of Tyears. Therefore, the time variation of fly ash utilisation in PPC production may be expressed as:

fs=--f6

1+a expbt

Since, at t=0,

f5 = f61+a expb(0) ,

then

Similarly, at t=T,f5 approachesf6 (say, f5=0.998f6). Therefore,

fc0.998/6=

l+\fj-l I expbT

and

.(A1)

(A2)

(A3)

(A4)

The extent of fly ash utilisation in PPC production is given by a fraction, f7. The values of a and


b can be substituted in Eq. (A1) to obtain the following expression [Eq. (6)] for the fly ashutilisation potential in PPC production:

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bhatt a pot 2002

Documents

gross domestic product

tile manufacturers federation

central statistical organisation

gross electricity generation

central electricity authority

incremental road length

fly ash utilisation

fly ash generation