Experimental study on MSW gasification and melting technology

Available online at www.sciencedirect.comJOURNAL OFENVIRONMENTAL中ScienceDirectSCIBNCESISSN 1001-0742JE SCN11-2629/XL电Joumal of Envioamnental Sciences 19(2007) 1398- 1403www.jcsc.ac.cnExperimental study on MSW gasification and melting technologyXIAO Gang'2, JIN Bao-sheng', ZHONG Zhao -ping'，CHI Yong2, NI Mingjiang2, CEN Ke-fa,XIAO Rui', HUANG Ya-ji', HUANG He31. Key Labornatory of Clean Coal Power Generation and Combustion Technology of Miristry of Education, School of Energy and Emvironment,Southeast University, Nanjing 210096, China. E-mail: xiaogangtianmen@seu.edu.cn2. State Key Laboratory of Clean Energy UTilization, Zhejiang Universin, Hangzhou 310027, China3. Cllge ofLjfe Science and Pharmaceutical Engineering. Nanjing University of Technogs Nanjing 210009, ChinaRcceived 27 January 2007; revised 7 May 2007; accepted 12 July 2007AbstractIo order to develop municipal solid waste (MSW) gasifcation and melting technology. two preliminary experiments and a principleintegrated experiment were fulflled respectively. The gasification characteristics of MSW were studicd at 500- 750°C when equivalenceratio (ER) was 0.2- -0.5 using a fluidized-bed gasifer. When temperature was 550 -700°C and ER was 0.2 -0.4. low heat value (LHV)of syngas reaches 4000- -12000 kJ/Nm'. The meting characteristics of fy ash were investigated at 100-14609C using a fixed-bedfurnace. It was proved that over 99.9% of dioxins could be decomposed and most heavy-metals could be solidifed when temperaturewas 1 100-1300°C. The principle integrated experiment was carried out in a fuidized-bed gasification and swirl-melting system. MSWwas gasifed eficiently at 550 -650°C, swir-melting furace maintains at 1200-1300°C stably and over 95% of fy ash could be caughtby the swirl-melting fumace. The results provided much practical experience and basic data to develop MSW gasification and meltingtechnology.Key words: municipal solid waste (MSW); Buidized-bed gasification; switl-melting; characteristicsIntroductionsists of a rotaing pyrolysis drum beated indirectly by fluegas and a melting fumace at 1250-14009C (Kawai et al,With expanding population of China, yields of munici-2000). Thermoselect process, it consists of a degasificationpal solid waste (MSW) increases sharply in recent twentychannel heated indirectly by hot medium, an oxygen-years and now reaches over 150 x 106 t/a (National Bureaublown gasification and fixed-bed melting fumace at aboutof Statistics of China, 2005), as displayed in Fig.1. Itis re-2000°C (Calaminus and Stahlberg, 1998); Von Roll RCPported that about 2/3 of cities are surrounded by MSW, andprocess: it consists of an oxygen-blown grate type gasi-many environmental problems have been caused in China,fication charmber and an oxygen-blown combustion andincluding pollution of water sources and soil, emission ofmelting furnace at 1400°C (Malkow, 2004), and direct-green house gas, epidemic disease, etc. (Nie, 2000). It is .meling process: gasification and melting are completed inurgent to find a suitable way to efficiently dispose MSW.a single furmace with rich-oxygen-air blowing (ShohichiGasification and melting technology are considered toand Moribhiro, 2002), etc. However, there is no report aboutbe an eficient means to dispose MSW with less emission.application of MSW gasifcation and melting technology inEspecially, it can sharply reduce emission of dioxins anddeveloping countries.beavy metals, which are strongly concemed by publicMany valuable researches of this area have been re-when MSW is combusted (Hu et al, 2006; Wang et al,ported in China. Liu et al. (1999) compared various2006; Suzuki andTakahashi, 2002; Shohichi and Morihiro,technologies of MSW disposal, and considered thermal2002; Si et al, 2006; Guan and Peart, 2006; Li et al, 2006;technology was potential in China. Ni et al. (2006), Xiao etYan et al, 2006). Several gasification and melting pro-al. (2006a; 2007) studied the gasification characteristics ofcesses bave been proposed and industrialized in developedcomponents in MSW and concluded that organic compo-countries. For example siemens/KWU process, which con-nents could be gasified eficiently at 500-700°C. Chi et al.(2005_ed the characteristicsProject supported by the Open Foundation of State Key LaboratoryofHC中国煤化Ibused/asined, andof Clean Energy Utilization of China (No. ZJUCEU2006004)。theconsid using additives atHi-Tech Researcb and Devclopmacat Program (863) of China (No500-MHCN MHCSy).ng Bang ea.2006AA020101) and the National Basic Research Program (973) of(2006) investigated the characteristics of dioxins and heavyChina (No. 2005CB221202, 2007CB210208). *Coresponding author,E-mail: xiaoganguiaomen@ seu.cdu.cn.metals when fy ash was melted and find it is an efficientNo.11Experimental study on MSW gasication and meling technology1399is heated by hot fue gas from oil combustion chamber.16040The hot fue channel is made of homocentric stainless20-steel tube with 150 mm inside diameter. MSW is fed by ascrew which locates 500 mm above the air distributor. Thetemperatures of dense part and sparse part of the gasifierare detected by K-type thermocouples, which locate 350mm and 2000 mm above the air distributor respectively.1991991 192 991941999 19197 19 99900 2000 062 200 200Air is preheated in the oil combustion chamber and sentinto the gasifer through the air distributor. Sand, whichFie 1 Amount of municipal solid waste (MSW) in China.is 0.7-1.0 mm diameter, is acted as bed materials. Thesampling point of syngas located after the cyclone. Theway to control dioxins and heavy metals.On the basis of these researches. two preliminary experi-meter, a sampling pump, and a gas chromatography. Thements and a principle integrated experiment were designedgas chromatography (GC9890A) is provided by Renhuaand fulfiled systemically in this study. It hbopes to facilitateGas Chromatography Exploitation and Application Centerthe development of MSW gasification and meling technol-of Nanjing, China. H2, N2. CO, CO2 and CH4 are detectedogy in China.by two thermal conductivity detectors (TCD) using argonas carrying gas at 60°C; CzH4, C2H6, C3Hg, C4H1o etc. are1 Methods and materialsdetected by a fame ionization detector (FID) using N2 ascarrying gas at 200°C.1.1 Gasification experimentsMSW was simulated according to the average propor-1.2 Melting experimentstion of organic components (dry basis) in actual MSWFly ash involves in the melting experiments wasof China (Xiao, 2006b), and it was used as materials ofobtained from a MSW combustion plant of ZhejiangProvince, China, and the characteristics are displayed inexperiments, as shown in Table 1.Table 2.Table 1 Charncterstics of stonlative MSW for gasifia tioTable 2 Charecteristics of fly sh (%)Organic components (%)SiO2Al2O3CaOTiO2FerO3KitcbenPlastic Wood andPaper Texile valble (kJ/kg)garbageyard waste17.663.9434.792.6612.042017960CuOZnCI2ZnOP20s2S8.0.5037The experiments of MSW gasification were carried outat a fuidized-bed gasifer, as displayed in Fig.2. Thefuidized-bed gasifier is made of stainless steel tube withThe melting experiments were carried out in a fixed-bed4000 mm in height and 100 mm inside diameter, whichfurnace of 600 mm in height and 100 mm inside diameter,a8 shown in Fig.3. It is equipped with an electric heatingsystem (12 kW) and a B-type thermocouples to control13.. 14上16temperature in range of 400- 1600°C. ln experiments,the furmace was maintained at designed temperature, and12/Syogssamplcs were sent into the furmace quickly; after 60min, melted slag was moved out. Slag was grained anddissolved firstly, and then wait is analyzed by an atomicabsorption spectrophotometer and Finngan Voyager mass造spectrometer (LRMS) with a gas chromatograph (HRGC)10工世.MW.早「而水吕吕Fig 2 Dusration of fidied-bed gasir (1) F.D. fn; (2) flow meter,中国煤化工热(3) oil bumer; (4) combustion chamber, (5) air prtheater, (6) inlet ofngfYHCN MHG"Cuu咖hot fue chanel; (11) fuidized-bed gasifer; (12) outlet of bot fuc; (13)cyclone; (14) sampling point; (15) filter; (16) sampling pump: (17) syngasanalyzer; (18) accumulative flow-nmeter.Pig. 3 Ilustration of fixed bed melting fumact.1400XIAO Giang et al.VoL 19to detect heavy metals and dioxins respectively. The ex-mentioned above. The other is a swirl-melting fumace,periments of dioxins were performed by the State Key which is made of a corundum tube with 1500 mm in heightLaboratory of Clean Energy Utilization, Zhejiang Univer-and 300 mm inside diameter. A B-type themocouplesity, all isotope standards were purchased from Wellingtonlocates 400 mm below the inlet of syDgas. Melting slaglaboratories, Canada or Cambridge Isotope Laboratory,xits from the bottom of the fumace, and drops into aUSA. The toxicity was ransformed into toxicity equiva- quenching pool. The exit of fue gas locates about 1000lence factor-value (TEF)-values according to the USEPAmm above the quenching pool. After a sampling point,method 8280B.flue gas is introduced into a scrubber and discharged fromthe stack. Syngas was analyzed as the methods above, and1.3 Principle integrated experimentsflue gas is detected by SAE-19 type analyzer, which wasOn the basis of the characteristics of MSW of China, provided by MRU Corp. Gemman.raw materials of the principle integrated experiment wereprepared as shown in Table 3.2 Results and discussionThe principle integrated experiments were carried outusing a fuidized-bed gasification and swirl-melting sys-2.1 Analysis of gasification experimentstem, which contains two main parts, as shown in Fig.4. OneFor avoiding over oxidation of metals in MSW, tem-is a gasifer, which is the same to the fuidized-bed gasiferperature of the gasification should be controlled belowTable 3 Character'tlcs of MSW (dry basts) for principle tntegrated700°C (Suzuki and Takahashi, 2002; Shohichi and Mori-experimentshiro, 2002; Si et al, 2006; Guan and Peart, 2006). ToComponents (%)Lowbeat faciltate MSW gasification smoothly, temperature shouldKitchen Plastic Wood and Paper Textile Ash valuebe maintained over 500°C (Ni et al, 2006; Xiao et al,garbageyard waste(J/kg)2006a, 2006b, 2007), or the reactants will jam the gasifier.48.816.086.40.20 14368In this study, the fux of preheated air was adjusted in therange of 6-10 Nm'/h and MSW was fed at rate of2-6 kg/b.MSW was gasified at 500- -750°C when ER was 0.19 -0.5.丛2Pulvorization windThe syagas was collected by a gasbag and analyzed by aCombustiod wisdgas chromatography. The results are displayed in Table 4.Siumplingpoint1←8H, CH4, co, C2H4 and other C.Hm are the main con-F.D.tmtributing components in syngas, which determine low heat1value (LHV) of syngas, which is an important parameterfor gasifcation. Generally, LHV of syngas increases with9increasing temperature or decreasing ER. When tempera-↓]ture is about 500C and ER ranges from 0.2 to 0.4, LHVpoimtof syngas lies in range of 2800- 4200 kJ/Nm3. While when| Hottemperature is 550 700°C and ER ranges from 0.2 tog0.4, LHV of syngas reaches about 4000-12000 kJ/Nm'.F.D.fanIt seems that higher temperature facilitate enhancement of. 8/I/6321LHV. When ER ranges from 0.38 to 0.5, LHV of syngasis obviously lower than that when ER is 0.19- 0.29; when(1) stack; (2)L. D. fan; (3) scrubber; (4) quenching pool; (5) wind box; (6)ER is lower than 0.15, gasification can hardly completedexit of slag; (7) combustion chamber; (8) oil burmer; (9) feeding syslem;in time and the gasifer will be jammed by reactants.(10) fuidized-bed gasifer, (11) swi-melting furnace; (12) oil burner.Theoretic estimation indicates that it is enough to facilitateTable 4 Experinental results of MSW gastflcationFeeding FluxBRof Tempera- Tempera-Main components of syngasLHV ofrate ofof airgasifi- ture ofture ofsyogasMSW(Nm2/M)cation gasifica-peheated CO2 H2 N2 CH4 CO C2H4 C2H6 CzHg C4Ho (J/Nm3)(kg1)tion (°C)air(C)2.30.50 72035268.4 2.63.240.11 0.060.23 44596202830.1326112902.8208859.6 3.8; 3.89 0.12 0.05 0.45 588329666.8 1.8) 2.16 0.16 0.02 0.36 3786281.67.9 0.9 5.0 1.58 0.17 0.05 0.4227430.2948.21.41 9237307653中国煤化工0.3 384928269.344.3THCNM HG 2.10 1195830860.33.2UU.43 U.uy0.9455885072794.261.6 1.8 9.5 ，1.89 0.28 0.090.39 4179LHV: low heat value.No.11Experimental study oa MSW gasifcation and melting technology1401melting furmace running smoothly when LHV of syngasThe experiments of decomposition ratio of dioxins andreaches over 4000 kJ/Nm'. It is suitable when temperaturesolidification ratio of heavy metals were carried out atand ER ranged from 550°C to 700°C and from 0.2 to 0.41100-1460°C in the fixed bed. The contents of dioxins inrespectively in gasifer.original fy ash and melted slag were detected by State KeyLaboratory of Clean Energy Uilization, Zhejiang Univer-2.2 Analysis of melting experimentssity and the results are shown in Table 5. It indicates thatIt is reported that when MSW is combusted, there aremore than 99.9% of dioxins were decomposed when tem-72%ofZn,24%ofCr,46%ofCd,30%ofNi,36%perature was over 1 100°C, and when temperature achievedof Cu, 86% of Pb and over 90% of dioxins in fy ash1460°C, no dioxins can be detected by the instrument(Sakai and Takatsuki, 2000; Takaoka et al, 1997;Li, 2002;(precision: 1 pg/g).Lu, 2004; Hutzinger et al, 1985; Stanmore, 2004). ItHeavy metals are also pollutants in fy ash. The con-means that the emphasis should be focused on fly ash totents of heavy metals were detected by atomic absorptioncontrol the emission of dioxins and heavy metals. Meltingspectrophotometer and the results are displayed in Tableis considered an environment friendly to dispose fly ash 6. Generally, solidifcation ratios decreased when tem-eficiently (Takaoka et al, 1997; Wenger and Farouk,perature ranged from 1100 to 1460°C for volatilization.The solidification ratio of Ni reached over 95% roughlyln this study, three characteristics of fly ash meltingwhen temperature was 1 100- -1300°C. The solidificationwere reported, including melting point, decompositionratio of Cd and Cu fuctuate around 50% when temperatureof dioxins, and solidifcation ratio of heavy metals. Theincreased from 1100 to 1460°C. Solidification ratios ofmeling point is filld by pyramid method and the resultsCr, Pb and Zn droped sharply when temperature increasedare shown in Fig.5. It indicates that fy ash can be melted from 1300 to 1460°C, which indicates that it is not suitablewhen temperature is over 1100°C if residue time is longwhen temperature is over 1300°C.enough. In order to secure fy ash molten completely and23 Analysis of principle integrated experimentsrapidly, temperature of the melting furnace should be over1200°C in industrial plants.On the basis of the results of preliminary studies, aprincipie integrated experiments were designed and ful1200filled using a fuidized-bed gasification and swirl-meltingsystem.The samples of syngas and fue gas were analyzed, andthe results are shown in Table 7.它1100The results demonstrate that ER of gasification is one of■the most important parameters for this system. When ERof gasification decreases from 0.4 to 0.2, temperature of1000gasification will decrease from 650 to 570°C, and LHVof syngas will decrease from 7200 to 3800 kJ/Nm3 approximately. When ER of combustion is 1.2, temperature900DSTof swirl-melting furmace increases with increasing feedingrate rather than LHV of syngas. The fly ash in fue gasFig. 5 Meting point of fly ash. DT: deformed temperature; ST: softranges 1.6- -1.7 gNm', which means over 95% ash havetemperature; FT: fuid temperature.been caught by swirl-melting furmace. The percents of SO2and NOx are stable and lower than the criterion of China.Table 5 Contents o dioxins in original fty ash and slagDue to the residue time is only 2- 3 s in the melting furmace,MaterialsContent of dioxinsDecompositionhe percent of CO reaches 200 -350 ppmy, which can be(ng:TBQAkg)natio (9%)resolved voluntarily in industrial plants.275Actually in industrial plant, loss of emission is lessSlag from 1100C0.04299.9685%. The estimation of thermal balance indicated thaSlag from 1300C0.026MSW of 7000 9000 kJ/kg can be treated by gasificatioaSlag from 1460°C0100.000and melting technology, and sieving MSW is a practicalTEQ: toxicity equivalence quantity.scheme for China currently (Xiao et al, 2006c).Thble 6 Contents of heary metsls ia orlginml ly asb and slhgItemNCCrXuP1ZnOniginal fty ash (ng/kg)135.154.4271.6977.11300.0809.0Slag from 1100^CHeavy metals (mg/kg)133.424.803.4653.7Solidifcation ratio (%)98.74 .45.59中国煤化工380.80Slag from 1300°C128.326.1Sotidfication ratio (%)94.9747.98MHCNM H G343Slag from 1460*C113.627.5143.4461.5365.1337.5Solidifiation ratio (%)84.09S0.5552.7947.2328.0854.801402XIAO Gang et al.VolL. 19Table 7 Results o prinipke tntegr ted experumentuOperating parameter121Fluidized-bed gasificationFeeding rate of MSW (gh)5.7.5Flux of air (Nm?/h)ER of gasification0.40.Tempcratune of gasication (°C)647604Temperature of preheatcd air (°C)308319323LHV of syngas (UJ/Nm3)388454697222Swil-melting fumacePlux of air (Nm/B)1830ER of combustion12.2Temperature of meling fumace (C)123712061293Pollutants in flue gasFly ash in fue gas (gNm3)1.71.6Percent of Co in fue gas (ppmv)346263197Percent of SO2 in fue gas (ppmv)5365Percent of NOx in flue gas (ppmv)76823 ConclusionsScicnce, 27(11): 2288 2292.Jin B s, Wang X T, Zhong ZP et al.2005. 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