Investigation of heavy metal partitioning influenced by flue gas moisture and chlorine content durin

Available online at www.sciencedirect.comJOURNAL OFENVIRONMENTALScienceDirectSCIENCES上ISSN 101-07472-JES ;www.jesc.sc.cnVLLInvestigation of heavy metal partitioning influenced by flue gas moisture andchlorine content during waste incinerationQinghai Li, Aihong Meng, Jinyan Jia, Yanguo Zhang*Department of Thermal Enginering, Key Laboratory for Thermal Science and Power Engineering of the Ministry of Education of China,Tsinghua Universit, Beijing 100084, China. E-mail: ligh@ tsinghua .edu.cnReceived 17 July 2009; revised 1 January 2010; accepted 18 January 2010Abstracthe impact of moisture on the partitioning of the heavy metals including Pb, Zn, Cu and Cd in municipal solid waste (MSW)was studied in a laboratory tubular fumace. A thermodynamic investigation using CHEMKIN software was performed to comparethe experimental results. Simulated waste, representative of typical MSW with and without chlorine compounds, was bumed at thebackground temperature of 700 and 950°C, respectively. In the absence of chlorine, the moisture content has no evident efeet on thevolatility of Pb, Zn and Cu at either 700 or 950°C, however, as fue gas moisture increasing the Cd distribution in the bottom ashincreased at 700°C and reduced at 950°C, respectively. In the presence of chlorine, the fue gas moisture reduced the volatility of Pb,Zn and Cu due to the transformation of the more voltile metal chlorides into less volatile metal oxides, and the reduction became. For Cd, the chlorine promotes its volatility through the formation of more voltile CdCl2. As aresult, the increased moisture content increases the Pb, Zn, Cu and Cd concentrations in the bottom ash, which limits the utilization ofthe bottom ash as a construction material. Therefore, in order to accumulate heavy metals into the fly ash, MSW should be dried beforeincineration.Key words: heavy metals; partitioning; moisture; chlorine; municipal solid waste incinerationDOI: 10.1016/S1001-0742(09)60174-1Introductionfurmaces of MSW incinerators are usually simulated intubular fumaces (Wochele and Stucki, 1999; Tan et al,Incineration plays an important role in municipal solid2007) which are also extensively used in heavy metalswaste (MSW) management. In China, MSW heating valuepartitioning studies due to their simplicity and repeatabilityis generally low and the moisture content is high (Chen(Chiang et al, 1997; Wang et al, 2001; Zhao et al,et al, 2008). The high moisture in the MSW and fue gas2004). Therefore, the tubular furmace was an experimentalstrongly infuences the combustion (Saito et al, 2001) andapproach to investigate the effects of fue gas moisturepollutant emissions (Li et al., 2008, 2009). The dryingand MSW chlorine content on the heavy metal partitioningbehaviors, of MSW have been experimentally investigatedduring waste incineration.(Zhang, 2007a) for reducing the moisture content in theAn equilibrium analysis is another effective approachMSW and flue gas to maintain stable combustion.for explaining qualitatively the general behavior of mostMoreover, Jiang et al. (2007) reported that bottom ashmetals (Abanades et al, 2002; Tan et al, 2007). The chem-contained more than 80% of Cu, 74%- 94% of Zn, 27%-istry and volatility of heavy metals such as Cd, Cu, Pb and53% of Cd, and 46% 79% of Pb, and fy ash contained Zn in the grate MSW-fired incinerator were extensively6.93%- -29.18% of Cl and 4.48% -24.84% of SiO2. Sinceinvestigated using equilbrium calculations. Morf et al.the heavy metal emissions during MSW incineration were(2000) found no evident impact of moisture on the heavystrictly regulated, a great amount of attention has beenmetal partitioning in an actual incinerator. However, Zhaopaid on the partitioning of the heavy metals during MSWet al. (2004) showed that increasing moisture reduced theincineration (Vernet, 1991; Zhang et al, 2008a). Thevolatilization of Pb and Zn which agreed with calculatedfactors affecting element behaviors in MSW incineratorsresults of Verhulst et al. (1996). The calculated result alsowere investigated by Belevi and Moench (2000). Theshowed中国煤化工Ch rasomateeffect of sulfur and chlorine compounds on Cd partition-into Pb上intheflyashbying has also been studied (Zhang et al, 2008b, 2007b;using tl;YHCNMH Glaglations (Durlak etChen et al, 2008). The complex ransfer processes in theal., 1991. awuawn, IIUIIC uay augment the moistureinfluence, as a result, the partitioning of higher volatile* Corresponding author. E mail: zhangyg@tsinghua.cdu.cnNo.5Lovestigation of beavy metal partitioning infuenced by fue gas moisure and chlorine content during waste incineration61metals was infuenced by the moisture and chlorine con- obtained by the mass weight absorbed in the silica gel andtent.the calibration gas volume.Due to the limnited knowledge on the partitioning of Pb,1.2 MaterialsZn, Cu and Cd at typical conditions for MSW combustion,the impact of moisture on the partitioning of Pb, Zn, CuThe simulated MSW used in this study was preparedand Cd in the presence or absence of chlorine under sim- based on the typical components of MSW from Chineseulated MSW incineration conditions was experimentallycities, using typical materials with the known compositionsidentified in the present study. Thermodynamic calcula-(Table 1). In the simulated wastes, flour, paper, sawdust,tions were also performed to understand the speciation.cotton cloth, polystyrene and inert materials (5% SiO2 and5% Al2O3) were used to simulate the physical components1 Experimentof typical actual wastes, including food residue, paper,wood, textiles, plastic and incombustible materials (such1.1 Experimental apparatusas, glass, ceramic, metal and sand). The contents of sim-ulated MSW are listed in Table 2. The moisture content,The apparatus used in this study including anone of the major factors infuencing the partitioning, waselectrically-heated tube furmace and a sampling train 0calculated to be 5% for the simulated MSW according toimpingers was described in the previous works (Zhangthe individual component moisture contents. The originalet al, 2007b, 2008b). The fue gas stream first flowedmoisture in the simulated MSW was then augmented bythrough the 0.3-um quartz fber filter (99.99% collectionwater bath to get desired moisture in fue gas. Becauseeficiency), then through the impinger train consisting ofthe background heavy metal concentrations in artificialseven impingers in series immersed in an ice water bath tocomponents were negligible, Cd, Pb, Zn and Cu werecapture Pb, Zn, Cu, Cd and their compounds. The primaryadded to the simulated MSW in the form of acetates to giveair and the secondary air were arranged in the fumace todesired Cd, Pb, Zn and Cu concentrations of 400, 1500,provide eficient sample combustion. The moisture in the1200 and 1200 mg/kg MSW samples, respectively.primary air for changing the water vapor content in the fuegas was introduced by a constant temperature water bath 1.3 Experimental proceduresystem. The moisture content in the primary air dependedThe effects of moisture content in fue gas on Pb,on the water bath temperature at a fixed primary air rateZn, Cu and Cd partitioning were first determined for theand the water level in the conical flask. The moisturesimulated MSW without chlorine addition. Then threecontent calibration system consisted of a gas supply vessel,levels of chlorine (0%, 1%, and 5%) were added to studycontrol valve, drier, water bath, heat tracing and silica geltheir impact on heavy metal volatility. The combustionbottle, as shown in Fig. 1. Assuming that the primary air isexperiments were carried out at 700C for low temperaturean ideal gas, the moisure content, d, defined as the volume incineration and 950°C for high temperature incinerationratio of water vapor to dry air in the primary air can bewithin 6 min combustion. The water vapor content inprimary air was regulated to be 0% with no water bath,Control valveHeat tracing12.9% in 60°C water bath and 39.4% in 96°C water bath,respectively. Suficient combustion air to ensure completesample combustion was supplied by a compressor with atotal fow rate of 13 L/min (10 L/min from the primaryair supply and 3 L/min from the secondary air supply)at ambient temperature and atmospheric pressure. AfterSilica gel Thermostat water bathhumidification systemdesired furmace temperature was reached, the combustionexperiment was started by gradually pushing the quartzboat (Illed with the simulated MSW sample) forward intoEmpy/Silica gel.the central part of the combustion chamber within 30 sec.The sample movement from the left side opening of theFlg.1 Moisture clibration systcm.quartz tube to the centre simulated drying/pyrolysis thatoccur at beginning of MSW incineration (Cheng et al.,Table 1 Simulated MSW (municipal solid waste) components (g)FlourPaperPolystyreneSawdustCotton clohSiO2Al2O3Total weightMoisture0.8.50.20.10.0.05Thble2 Chemical composition of s中国煤化工_Ultimate analysis (w.%) (dry basis)Moisture (毗%):MYHCNMH(C Ctals (mgkg)CHNCuZn43.275.8238.681.670.535.03JDND5.97IDND: not detected.QinghaiLi etal.Vol. 222007). At the end of the combustion, the air supply waslevels to those reported in literature (Chiang et al, 1997)turned off and the quartz boat was pulled out of the quartz and meet basic experimental requirements.tube to be cooled for measurement. The residue in theThe experimental apparatus and analysis were used toquartz boat was then transferred to a beaker as bottom ashstudy the efect of moisture on the heavy metal distribution.sample for beavy metal concentration analysis.Chlorine was then added (1% PVC and 5% PVC) to studythe synergistic effect of chlorine and moisture together on1.4 Analysis of heavy metal contentthe heavy metal partitioning.At the end of each batch combustion experiment, theresidues in the quartz boat were cllcted as bottom 2 Thermodynamic equilibrium simulationsash while combustion gas samples were taken from theimpingers. The total particulate matter (fy ash) was de-Thermodynamic equilibrium calculations were per-termined from the mass collected on the filter and theformed to predict the efect of moisture content on thematerial that condensed on the connecting tube, fllowing heavy metal partitioning and speciation. The thermody-standard recovery procedures USEPA Method 5. The largenamic equilibrium simulations principally delineate thevolume of liquid and its dilute particulate matter in thestable phases that form at specific operating conditions.impingers was digested according to USEPA MethodsDuring combustion, the MSW is a multi-component and3005a and 3010a. For the carbon in the sampling filter,multiphase system. At equilibrium state the system freethe filter sample was digested by HNO3-HCIO3 accordingenergy is minimized. By combining energy minimizationto H/T64.3-2001. The bottom ash was digested followingwith the mass conservation constaints a series of algebraicUSEPA Method 3050 because of is lage amount of equations for the equilibriun sysem composition wasparticulate matter. Since the surface of the quartz boat developed (Cheng et al, 2007). The solid wastes usedcould possibly be covered by heavy metals due to thein the model simulations were assumed to consist ofsintering at high temperatures, the quartz boat was flledmajor elements C, H, N, O, and S listed in Tables 2with HNO3-HCI (volume ratiomn, 3:1) solution to digestfor and 3. The equilibrium calculations were performed at1 hour on an electric heating plate after each experiment.1 atm pressure and 750, 950 and 1150°C, respectively,The digestion solutions from the quartz boat and thetypically representing the lowest, normal (Durlak et al,residue in the quartz boat were analyzed together as the 1997) and exreme high incineration temperatures. For allfinal bottom ash sample. The digested solutions of bottm calculations the excess air ratio was 1.5 which is typicalash, fy ash and fue gas (absorbed in solution) were then for MSW burning.separately determined using inductively coupled plasma-A total of ten elements (C, H, O, N, s, Cl, Pb, Zn, Cuatomic emission spectrometry (CP-AES, IRIS Advantage, and Cd) were considered in the equilibrium calculations.Thermo Elemental, USA). Using mi to denote absoluteThe gas phase compounds (H2, HO2, O, OH, CO, CO2, N2,heavy metal mass of bottom ash, m2 to denote absoluteNO, NO2, sO, SO2, SO3, H2S, CIO, CIOH and HCI) ofC,heavy metal mass captured by quartz tube and filer exclud- H, 0, N, S and Cl and Pb, Zn, Cu and Cd species in the gasing the filter iself heavy metal content, and m3 to denote and condensed phases listed in Table 3 were all included.absolute beavy metal mass in the fue gas absortbed in theThe final equilibrium state was obtained by determnining allimpingers, heavy metals in the bottom ash, fly ash and fuepossible species that could be derived from the input.gas can be expressed by the normalized distribution factorφ3 Results and discussion91.2or3 =m1 (m2 or m3)3.1 Relationship between the MSW moisture and fuem1+m2+m3gas moisture contentSince very few heavy metals were detected in the fuegas, m2 and mz were combined together. Therefore, theThe equilibrium calculation input consisted ofC, H, 0,distribution factor in the bottom ash, φ1，ilustrates the N, s, CI, Pb, Cd, Zzn, Cu and gaseous 02, with the moisturecomplete heavy metal partitioning. The maximum error in the fue gas regarded as extra reactants in the form offor the bottomn ash distribution did not exceed+ 1% for liquid H2O. For equilibrium calculation convenience therecovery rates larger than 70% and did not exceed士4% for moisture content in the fue gas was transferred to therecovery rates between 50% and 70%, which are similar moisture content io the MSW sample. For example, 0%,Table3 Pb, Zn, Cu and Cd species in the gas and condensed phasesPbZnCuGas phaseCd, CdO, CdCl2, CdsPb, Pb2. PbH, PbO,Zn, ZnC2, ZnSCuCl, CuzC3, Cu,Pbs, PbCI, PbCl2CnO Cu2, CuSSolid phaseCdCl2, CdO, Cd(OH),Pb, PbO, PbzO4,中国煤化II0,Cu2O,CI.C2,Cds, CdSO4, CdCO3PbO2, PbS, PbCl, PbO-PbCO3,, Cu2OSO4, Cus,PbO.PbSO4, PbSO4-2PbO,YHCN MH GCnoSCcorPbSO,3PbO, PbSO4.4PbOLiquid phaseCd, CdCl2 .Pb, PbO, Pbs, PbCl2Zn, ZnCl2Cu, Cu2S, CuClNo.5763120011509C for the 950°C furnace b;kground temperature,1100-which means that the real experimental furmace tempera-ture varies with time. Thus, the background temperatures6 1000are only characteristic of the temperature ranges in realfurmaces. Furthermore, the combustion of the batch fuel900sample in the quartz burner tube was completed within 100Fumace temperature 700C800sec and then the furnace temperature quickly leveled off.700The weight of the residue in the boat varied finely after6 min combustion, which was also pointed by Zhao et alL.600(2004), thereby, the combustion time was set to 6 min.510020Figure 3 shows the impact of the moisture content in theTime (sec)fue gas on the heavy metal (Pb, Zn, Cu and Cd) partition-Fig2 Temperature variations in the combustion zone at diferenting characteristics at the two background temperatures ofbackground temperatures.700 and 950°C without chlorine addition. Cd is much morevolatile than Pb, Zn and Cu without extra chlorine. As the30% and 60% moisture contents in the MSW samples rep-moisture content in the primary air was increased from 0%resent 9%-12%, 13% -20%, 25% -35% moisture contents,to 39.4%, the vlilitieis of these four heavy metals exhibitrespectively, in the flue gas for excess air ratios of1.2-1.8. diferent trends. For Pb, Zn and Cu paritining withoutchlorine addition as shown in Fig. 3a-c, 81.0%- -86.6%3.2 Impact of moisture at different temperaturesof Zn is concentrated in the bottom ash as the moistureFigure 2 shows the temperature variation in the com-increases from 0%- -39.4%, whereas the moisture in thebustion zone at 700 and 950°C representing the furmaceAue gas has very litle efee on Pb and Cu volaility withbackground temperatures with MSW sample combustion.changes of no more than 2% for these heavy metals in theThe curves in Fig. 2 show that maximum fue gas tem-bottom ash. Since Zn recovery rate is rather low, the resultsperature in the combustion zone during both the volatiletaking into account the errors suggest that the moisturerelease and the fixed carbon combustion stages reached have no obvious impact on Pb, Zn and Cu partitioning950°C for the 700°C furmnace background temperature, andwithout chlorine.The equilibrium compositions of Pb and Cd species as口700C withoutCl 88 950Cc witbouta1003_00厂R 80E 80个600ti 4040 t20 t39.4Moisture content (%)Moisture content (90)100 nod80 f60上0上20个中国煤化工12.9MYHCNMHG-.Mosture content (%)Fg3 Efet of Aue 8as moisture on hevy metal pritinig at dferete tepentures间) Pb; (6)Zn;(&)Cu; (d)ca.764QinghaiLi cal.Vol. 22.4-8-- + PbO(B)+ PbO(3)+ Cd() ，十PbO PbSO,()- + CdO(3)量0-十PboO)是0.40.10.20.052025FRg4 Efcot of moitre on beary meul seciaion at 950°C回)P; 6)Cd. g gas pbae; s oid pek; iquid pae.a function of moisture content at 950C without chlorine3.3 Impact of moisture at diferent chlorine contentscomputed by using CHEMKIN sofware are shown in Fig.4. The equilibrium composition represents the most stableThe efet of moisture on Pb, Zn, Cu and Ca pritioningchemical composition within a system for a specific set ofin he bottom ash is shown in Fig. 5. The pesence ofconditions. Thus the calculated equilibriumn compositionchlorine enhances the heavy metal volatility which reducesrepresents the preferred chemical speciation for a specificthe heavy metals in the bottom ash as the moisture contentstate, which in turn, suggests the chemical reactions that increases. The Pb fraction (Fig. 5a) in the bottom ashmay occur within the system. The equilibrium calculationincreased by 16.2%,乙n (Fig. 5b) increased by 12.7% andresults shown in Fig. 4a indicated that solid PbO.PbSO4Cu (F) increased by 4.7% as the moisture contentswas transformed int gascous PbO which was slightlyvaried from 0% to 39.4% with 1% low chlorine, At 5%diferent from the experimental findings. This iference chlorine, Pb fraction in the bottom ash increasedby 12.7%,may be atributed to not including Al and Si in theZn increased by 32.7% and Cu increased by 25.7%. Theseequilibrium calculation. Zhang and Yao (2006) made aeffects off moistursture on heavy metal partitioning coincidesimilar equilibrium calculation and found that lead silicate with the fact pointed by Zhao et al. (2004) that increasedcould inhibit the gaseous PbO formation, Equilibrium moisture reduces the volatilization of all chemical formscalculations including Al and Si at the same temperatureofPb and Zn and copper oxide. Figure 5d shows the efetshow thsolid PbSiO3 and PbSO4.PbO are dominant of moisture on the partitioning of Cd with strong volatil-species and the moisture content has no effect on Pb ity. Without chlorine, the increased moisture significantlyspeciation, which agrees with the experimental result in reduces Cd distribution in the bottom ash as the volatilityFig. 3a. The thermnodynamic calculations for Zn and Cuof Cd increases with increased moisture. However, in theshowed that: (1) Zn is mainly present as ZnO whichpresence of chlorine, the moisture content has no obviousis the most dominant species at 950°C and not afectedeffect on Cd partitioning, mostly due to the high volatilityby the moisture content; (2) CuO is dominant species at of Cd metal and chloride that infuence the partioning950C and is not afected by moisture content. Thee efectsstronger than moisture content.of moisture on Zn and Cu partitioning suggested by theThe thermodynamic calculation results also show thatcalculations agree with the experimental results in Fig.3b,the mechanisms for the efect of moisture on the heavymetal partitioning are very diferent with and withoutFigure 3d sbows that the dribution of Ca in thechlorine. In the presence of chlorine the efects of moisturebottom ash increased from 30.2% to 62.2% at 7009C andon the heavy metal partitioning shown in Figs. 6, 7 areeaffrom 16.7% to 5.3% at 950°C as the moisturequite diferent. Theincreased moisture in the fue gascontent increased from 0% to 39.4%. This indicates thatfavors the transformation of more volatile and low boilingthe efet of moisture on Cd volatility difers at dfferentpoint heavy metal choride into less volatile and highertemperatures. The equilibrium calculation showstboiling point heavy metal oxide (such as PbO, ZnO,CuO,primarilypresent as oxide and sulfate at low temperatureCu2O or CdO). The experimental results givenin Fig. 5(700°C). Increasing of moisure content can enhance theshow similar infuence of the moisture on heavy metaltransformation of Cd from sulfate t0 oxide. The strongvolatility at high and low chlorine contents. The mosurehermal sability of Cd oxide increases the distribution ofcontent strongly afts the Pb partitioning at the highCd in the bottom ash aat high temperature. However, thechlorine concentration but has a weak efect at low chlorineequilibrium calculation for Cd at high temperature (950*C) concer3on Zn partitioningis stroshown in Fig. 4b indicates that moisture favors transfer ofchloril中国煤化工raion than at iowsolidCdO into gaseous Cd which reduces the Cd in bottomdoesHCNMHGchlorine conditionash. Overall, thexperimental and equilibrium calculation品paritining. Theresults at 950°C for Cd agree well.experimental result for the Cd partitioning shown in Fig.5d prially agrees with the equilibrium calculation shown.No.5Investigation of heary metal partitioning infuenced by fue gas moisture and chlorine cootent during waste incineration765in Fig. 6d. Both the experimental and calculation resultsat low chlorine concentration is due to the transformationindicated that chlorine promotes Cd volatility throughof CdCl2(g) into CdO(s) promoted by increased moisture.more volatile CdCl2 formation. The decreased volatilityAt high chlorine concentrations the gaseous CdCl2 and口WithoutCl e7 1.0%Cl 5.0%Cl10106b86040室20经20.0013.0039.40Moisture content (%)Moisture contcnt (%)100d|0to3.00Flg5 Efect of flue gas moisture on heavy metal partitioning at difereat al concentations and 950°C. (a) Pb; (b) Zn; (C) Cu; (d) Cd.1.1.00.0.6 t一= - ZnCI2(g)- + PbCI(g)-←PbO()一. - ZnO(9)0.4153025303515 303:Moisture content in fluc gas (%)Moiture content in flue gas (%)- CuC()tcCu(s)0.8CuO(s)Cu2O(s)-十Cd(g)十CdCl2(g)-←CaO(S)中国煤化工1530JMHCN MHGe,Moisture content in flue gas (%)F1g6 Effect of moisture on beavy metal speciatio at 1% chlorine and 950。C. (a) Pb; (6) Zn; (Q) Cu; (d) Cd.766QinghaiLi etal.Vol. 221.0 r.0b|一一CuCI(g)、.8-- CuzCl;(g).6+.6--一ZnCl2(g)0.4-号0.4-.2-30 35Moisture content in flue gas (%)Flg7 Effect of moisture on heavy metal speciationon at 5% chlorine content and 950°C (间) Zn; (b)Cu.PbCLx(g) at 0% moisturePbO(s) at 60% mosue-● - CdCL(g) at 0% moisture●CdO(s) at 30% moisturePbCIr(g) at 30% moisturePbO(g) at 0% moistureCdO(s) at 60% moistureCdCl[(g) at 30% moisturePbCIL(g) at 60% moisturePbO(g) at 30% moistureCd(g) at 0% moisturePbO(s) at 0% moisturePbO(g) at 60% moistureCdCl(g) at 60% moistureCd(g) at 30% moisturePbO(s) at 30% moisture-▼- CdO(s) at 0% moistureCd(g) at 60% moisture.0[.8.850.6-04-0.2-o.0L二6008010001200Temperature(C)Temperature (C)CuC(g) at 0% moistureCuO(s) at 0% moisture1- ZnC[(g) at 0% moisture-▼ - ZnO(s) at 0% moistureCuCl(g) at 30% moistureCuO(s) at 30% moistureZnCL(8) at 30% moisture●Zn0(s) at 30% moistureCuC(g) at 60% moistureCuO(s) at 60% moistureZnCL(g) at 60% moisture- 4- ZnO(s) at 60% moisture"三↓三↓二手三::8-.66.4-.景04-)2 to.oL0.0800Fig 8 Effects of temperature and moisture on hbeavy metal speciation at 1% chlorine content and 1.5 excess air ratio.Cd are the dominant species so Cd is almost completelyincinerator system, only equilibrium calculations werevolatilized into the fy ash and fue gas. As a result, theused to investigate the effects of temperature and excessmoisture has no apparent effect on the Cd partitioning atair on heavy metal speciation.high chlorine concentration.Equil中国煤化工-ples consting of3.4 Impact of temperature and excess air1% PV:nd 60% moisturecontentYHC N M H Gere performed toSince the excess air ratio and real combustion tem-identify une eeCls of temperaure ana moisture on heavyperature cannot be effectively adjusted in the laboratorymetal partitioning. The equilibrium calculations shown inNo. 5Investigation of heavy metal pritioning infuenced by fuc gas moisture and chlorine content during waste incineration67Fig.8 indicate that the moisture content promotes the utilization as construction materials. Therefore, the MSWtransformation of Zn and Cu chlorides into their oxides.should be dried before its incineration to partition morePb and Cd paritioning is only slightly influenced by heavy metals into the fly ash.the moisture content for temperatures of 700 _900°C. AtAcknowledgmentstemperatures of 900 -12009C the effects of temperature andmoisture on Pb and Cd partitioning become stronger. IfThis work was parially supported by the National Nat-temperature drops greatly due to the moisture addition, ural Science Foundation of China (No. 50776007) and thethe temperature efect becomes dominant and, as a result, Bijing Municipal Science and Technology Comissionthe moisture increasing leads to an increase in the gaseous under the Municipal Solid Waste Development ProgramPb chloride. A similar result was observed by Durlak et (No. H020620330120). Ph.D student Sun Jin is warmlyal. (1997) for equilibrium calculations ,with the moisture thanked for much assistance with the equilibrium calcu-content increasing from 8% to 37% and the temperature lations. The authors also thank anonymous reviewers fordecreasing from 1050 to 850°C. In other cases, if the their constructive comments.moisture increase leads to only a small temperature drop,the moisture, as dominant efect on heavy metal, may then Referencesreduce Pb chloride formation. This similar Pb, Zn, Cu, Cdpartitioning in dyestuff incineration was thermodynamical- Abanades s,Flamant G, Gagnepain B, Gauthier D, 2002. Fately simulated by Tan et al. (2007); however, the temperatureof heavy metals during municipal solid waste incineration.effects on heavy metal partitioning given by them only par-Waste Management and Research, 20: 5568.tially agree with the result in this aricle, especially forthe Belevi H, Moench H, 2000 Factors determining the elementtransitional temperature where the gaseous phase rapidlybehavior in municipal solid waste incinerators. 1. Fieldstudies. Environmental Science and Technology, 34: 2501-rises and the solid phase sharply drops, which is lowerthan that predicted by Tan et al. (2007). The errors mayChen Y, Zhang Y G, LiQ H, Zhuo Y Q, Chen C H, 2008. Efectsbe due to different model simplfcation, model input andof chlorides on Cd partitioning and speciation in a simulatedelement interactions, which suggest that thermodynamicMSW incinerator. Ervironmental Science, 29: 1446 -1451.equilibrium clculains require experimental veification ChengHF,Zhang YC, Meng AH,LiQH.200 Municipl soiddue to the complexity of the incineration process.waste fueled power generation in China: A case study ofThe equilibrium calculations show that excess air ratiowaste-to-energy in Changchun city. Environmental Sciencehas almost no impact on heavy metal partitioning, whichand Technology, 41: 7509 -7515.agrees with the results given by Abadades et al. (2002) Chiang K Y, Wang Ks, LinFL, Chu W T, 1997. Chloride efetewhen excess air ratio is more than 1.2. In commercialon the speciation and portioning of heavy metal during theincinerators, a higher excess air ratio can result in moremunicipal solid waste incineration process. The Science ofthe Total Environment, 203: 129 -140.fine particles carried out of furmnace, so that a higher excessDurlak s K, Biswas P, Shi J C, 1997. Equilibrium analysisair ratio can increase heavy metal distribution in fy ash.of the efect of temperature, moisture and sodium contenton heavy metal emissions from municipal solid waste4 Conclusionsincinerators. Journal of Hazardous Materials, 56(1-2): 1-The impact of moisture content in the fue gas on the Jiang J G, Xu x, WangJ, Yang s J, Zhang Y, 2007. Investigationvolatility of heavy metals was experimentally and thermo-of basic properties of fly ash from urban waste incineratorsdynamically investigated for typical MSW materials.in China, Joumal of Environmental Sciences, 19(4): 458 -Without chlorine, the moisture content has no evidentLiQ H, Zhang Y G, ChenC H, Dang W D, Meng A H, 2008.effect on the volatility of Pb, Zn or Cu at aither 700Experimental study of moisture impact on municipal solidor 950°C experimental background furmace temperatures,waste icineration. 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