ELECTRICITYStudy on CO2 Emission Reduction fromChinese coal-Fired power plantsBetween 1993 and 2010By Wang Shichang, Wu YuxianSchool of Energy, Power and Mechanical Engineering, North China Electric Power University2. Architecture Editorial Department, China Electric Power Press LtdAbstract: Based on the Chinese thermal coal and power generation data, such as ultimate analysis, proximateanalysis, low heat value(LHV) on as received basis, power generation volume, thermal coal consumptionvolume and net coal consumption rate, several mathematical models for calculating CO, reduction by Chinesecoal-fired power plants are established. Calculations of the CO, emission factor(CEF), the CO, emissionvolume and reduction volume are made according to these models. The calculation results reveal that between1993 and 2010, the CO, emission volume reached 31.069 Gt, reduced by 0.439 Gt, averaging 28.83 Mt eachKeywords: coal-fired power generation; CO, emission reduction; CO, emission factorIntroductioncarried out strictly by coal-fired power units in Chinaand the electro static precipitator(ESP) became thCoal is the major primary energy and the major dust removing equipment. From 2003 to 2011, strictersource for electricity production in China. The total standards in dust emission were carried out by coal-firedraw coal consumption for power generation was about power units, and at the same time, flue gas desulfurization1.6 Gt in 2011, accounting for about 51% of the total (FGD)was carried out compulsorily, bag filters(BF)andraw coal production of the year. Therefore CO, emissions FGD equipment became the standard equipment for envi-mainly come from coal-fired power production. From ronmental protection in coal-fired power plants in China1949 to 1993, the mainstream coal-fired utility boilers in From 2012 to 2016, NO, will be compulsively scrubbedChina ranged between 6-100 MW. From 1993 to 2003, from the flue gas of coal-fired utility boilers, and selectedthe mainstream coal-fired utility boilers in China were de- catalyzed reduction(SCR)equipment will become theveloped from 100-Mw high-pressure units and 200-Mw standard installation in coal-fired power plants in Chinasuper-high-pressure units to 300-MW subcritical units. These environmental protection installations willSince 2003, the mainstream coal-fired utility boilers have increase the auxiliary power consumption and the netbeen developed from 300-MW subcritical units to 600-Mw coal consumption rate, which makes CO, emissionssupercritical units and 1 000-MW ultra-supercritical units. increase indirectlyThe increase of single unit capacity and steam pressureand temperature decreased the net coal consumption rate,Based on the data of generation volume, net coalwhich has decreased the CO, emissions by coal-fired consumption rate and raw coal consumption volume frompower productionthe year b中國煤化工 and combinedwith the calCNMH emission factorFrom 1993 to 2002, standards in dust emission were (CEF) for CHineseI coaLs, tne quantitative calcula312012.4 ELECTRICITYSEEtion on CO, emission and reduction volume is carried out sion of CO contents in fly gas, Formula(4)is achievedin this paper.for calculating the Co contents on as received basis infly ash. Therefore, the carbon contents in coal convertedData sources and calculating methodto CO,, i.e. the burning-out carbon contents can becalculated by Formula (5). Formula(6) is for calculatingData sourcesCEF T67. Assuming that the average CO concentrationThe data of carbon content on as received basis(C_) in flue gas is 200 mg/Nm, the regression formula forand low heating value on as received basis(o )are calculating LHV on as received basis is as shown infrom the research results of 158 groups of coal by primary Formula(7), where P, is the annual electricity generaticanalysis and ultimate analysis 4. The data of generation 0 I TWh, b is the net coal consumption rate, g/kWh, M,volume, net coal consumption rate and raw coal consump- is the annual raw coal consumption, 10 kt. The annualtion volume are from the year Book of China Electric CO, emissions can be calculated by Formula( 8), the coPower-3(see Table 1). The data of unburned carbon emission intension can be calculated by Formula(9),contents in fly ash and bottom ash are from one subcriti- and the reduction of co, emissions each year can be calcal 300-Mw boiler firing sub-bituminous coal and two culated by Formula(10), where mco, and mco,represent600-MW supercritical boilers firing bituminous coal and the co, emission intension of the previous year and thelignite. The data of Co concentration in flue gas is from very year respectivelydomestic research results 5C=7.267+2.1760mx+00092am(%)(1)Table 1 Main parameters of coaH-fired power generation28147+28147exp(1036840)(%P,(Twh) M,(Gt)b, e/kwh)Year GenerationR盤 w coalNet coalGross coal16817+16818eXp(666631)(%)(3)Coa2002015+000171Q+1.17836×10ga(%)(4+Char +cco,(%)(5)19970.4940.471(kgCO, /MJ)300Q0.48220000.528Qx=0.29308Pb/M1(M/kg)(7)1204057635715790.7650.875M(4=2930.8×b×CEF×10° Gt/year)(8)370200628601.379367mco,=Mco,/(0.1P)(Mt/TWh)27211.2881.1843012AMco, =(mco, I -mco, o (0.1P)(Mt/year)(10)201034171.590312Discussion and analysisNote: M, of 1997, 2004-2006 is estimated value.Calculation resultsMathematical modelsThe data in Table 2 and Table 3 are calculated withThrough regression of the 158 groups of coal data, Table 1 and formulas 1-10. Table 2 shows the carbonthe relationship between Car and LHV is achieved as contents in fly ash(C., bottom ash(C,, the con-shown in Formula(1). Through regression of unburned verted carbon contents of Co in flue gas(Co )and thecarbon contents in fly ash and bottom ash, formulas burnout carbe中國煤化工e3 displays the(2)and (3)are achieved for calculating the unburned calculatedcarbon contents on as received basis. Through regres- tion volumeYHCNMHGSSIon and reducELECTRICITY 2012. 4EECIRICIYTable 2 Calculation results of burnout carbonoperation of bag filters, FGD and SCR equipment increased the net coal consumption rate. The trend of bYear Cshown in Fig. 2 reflects the combination of the increasef unit capacity, the1993 62.46 0.628 0.416 0.066 61.35 perature and the operation of bag filers and FGD and199462260.6260418006661.15 SCR equipment1995612306150.42899660.570.60904340.06462.0806240.4206097199863.65064104040.0662.54199965400.6590.3870.0654940.650.39200686383200163580.640062010.6240.4200.06660.9061.56061904250065604500560.7806110432006559.6820060.437200759590.59804440.0640.584045898770471Fig 2 Net coal consumption rate ofcoal-fired generationDiscussion and analysis of the resultsEffects of carbon contentsOver the same period, the gross coal consumptionFig. I shows the data of Table 2. From Fig. I it can be rate,bo, reduced year by year and the difference betweenseen that aftercalculato,fa, ar 0.6%, C a 20.4% and b and b, became continuously smaller, which means thatO a 0.065%, totaling 1.06.5%. When calculating co, the auxiliary electricity consumption rate decreases yearemIssions,Cfa. ar,Cba.nd C must be deductedon year. By the end of 201l, SCr equipment had not beenO. arinstalled in all the coal-fired utility boilers in China. Between 2012 and 2016, SCR equipment will be installedand operated in almost all the coal- fired utility boilers64compulsorily. Therefore, the difference between b and bcannot be reduced infinitely.58卜Variation of average LHV and CEFFig. 3 and Fig. 4 demonstrate the data of Table 3. FromA▲Fig. 4 it can be seen that the average Lhv (e met a)rangesfrom 23. 15 MJ/kg to 22 42 MJ/kg over the period between1993 and 1996, from 22 42 MJ/kg to 24.28 MJ/kg over00L押押小小少少少小the period between 1996 and 1999, and from 24.28 MJ/kgto 20.98 MJ/kg over the period between 1999 and 2010.Fig. 1 Carbon contents of Chinese thermal coalsConsidering the fluctuation of coal prices, coal-fired powerplants had to purchase the cheap blend coal with lowerLHV to reduce their operation costsEffects of gross coal consumption rate and netcoal consumption rateFrom Fig. 3, it can also be seen that CEF increasesFrom Fig. 2 it can be seen that between 1993 and from 97. 18 kgCO to 97.26 kgCO/GJ in the period be-2010, the net coal consumption rate, b, decreased year tween 1993 and 1996, decreases from 97.26 kgCO2GJ toby year, which leads to the decrease of CO, emission 97.09 kgCOYH中國煤化工1996and1999,intension(moo, see Fig 4)and indirect cO, emission and increases7.49 kgCO,/GJreduction(see Fig. 4). However, the installation and over the periCNMHG1O. Compared332012. 4 ELECTRICITYEEwith the calculated LHV, g xr, it can be concluded thatburning coal with lower LHV will increase CO, emis-sIonsTable 3 Calculation results of CEF and64cO. emission reductionCEF(, /G)24CEFYear23(Jkg) gco,/ G)(Gtyear)(MtTW199323.1597.1823071,20122.679723996224297261051.1914.565Fig 3 CEF and LHV on as received basis199723.0097.19L.101.18423.6l97.14171199924.281.161.156-15.13697.101261.13622.336200123581.116-23.796200322971.102200522.5097.252.681.07441940各△M(M)200697311.0354601221o1→200821.509739-85.5792009214997400.99043.723乎∮少炒心少少少201020983.32971ig. 4 CO2 emission, reduction volume andemission intensionTrend of Co, emission and reductionFrom Fig 4, it is obvious that the CO, emission intension mco. reduced and CO, emission volume Mco.increased between 1993 and 2010. Although Mo de- that Ca (%)increases linearly with the increase of LHVcreased in 2007 and 2008, it began to increase since (0 ). From Fig. 6 it can be seen that when get aris2009, which means the strong demand for electricity by lower, CEF is higher, which is correspondent with thethe development of domestic economy. Between 1993 trend in Fig 3and 2008, the reduction volume AMo improved continously with the maximum of 85.59 Mt/year in 2008. BFrom 1993 to 2001, the average increase of coal-firedween 2008 and 2010, AMoo kept around 62.0 Mt/year power generation per year was 9.46% with the raw coalThe reduction of CO, emissions is benefitted mainly consumption increase of 7. 40%. From 2001 to 2010, thefrom the replacement of small capacity coal-fired power annual average increase of coal-fired power generationunits with large capacity coal-fired power units with su- was 18.76% with the raw coal consumption increase ofpercritical/ultra-supercritical steam pressure and steam 18.36%. It is obvious that the increase of raw coal fortemperaturepower production is lower than that of power generationTo solve this problem, blend coal with lower LHVRelationship between CEF and LHV(Onetadopted by coal-fired power plants. Therefore, theThe relationship between CEF, Ca and LHv(2et ar) average LF中國煤化工 een reduced andof the 158 types of Chinese thermal coals is studied CEf has beas shown in Fig. 5 and Fig. 6. From Fig. 5 it can be seen Fig. 5 andCNMHGshown in Fig 334- ELECTRICITY 2012. 4LECTRICITYcreases linearly with LHV (on as received basis). However LhV of blend coal is lower while CeF of blend coalis higher2)Between 1993 and 2010, the average LHV on asreceived basis reduced from 23. 15 MJ/kg to 20.98 MJ/kg3)Between 1993 and 2010, the CO, emissions byChinese coal-fired power generation accumulated to31.069Gt4) Between 1993 and 2010, the reduction of coemissions by Chinese coal-fired power generation reached0.439 Gt with the annual average reduction of 28.83 Mt.5)Between 1993 and 2010, the co emission intensionwas lowered from 1.210 Mt/TWh to 0.971 Mt/TWhFig 5 Relationship between Car and Qnet.6) Between 1993 and 2010, CEF varied between97. 18 kgCO,/GJ and 97.49 kgCO,GJReferences[1] Zhou X Q, Cheng Z Z. Yearbook of China Electric0.14Power 1993 [M]. Ist Edition. Beijing: China ElectricPower Press. 19930.12[2] Zhou X Q, Cheng ZZ. Yearbook of China ElectricPower 2001 [M]. Ist Edition. Beijing: China ElectricPower Press. 2001008[3 Editorial Committee of Yearbook of China ElectricPower. 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