Preparation and Characterization of Refuse Derived Fuel for Pyrolysis and Gasification by Bindless H

Jun.2004Journal of China University of Mining &. TechnologyVol. 14 No. 1Preparation and Characterization ofRefuse Derived Fuel for Pyrol ysisandGasification by Bindless High PressureBriquetting Technol ogyZHANG Xian-sheng(张宪生)'，XIE Qiang(解强)1.2,LI Wei(厉伟)'， SHEN Ji-min(沈吉敏)'(1. School of Chemical Engineering and Technology, CUMT，Xuzhou ,Jiangsu 221008，China;2. School of Chemical and Environmental Engineering, CUMT ,Beijing 100083 China)Abstract: A new type of refuse derived fuel (RDF) for pyrolysis and gasification was prepared from municipal solidwaste (MSW ) in the presence of a small quantity of coal by bindless high pressure technology at room temperature.The physicochemical property of RDF was tested. Orthogonal experiment method was used to optimize the processparameters using dropping strength (mechanical strength) and thermal stability of the RDF as indices for quality ofRDF. The result shows that the mixture of MSW and coal with a total moisture ranging from 5% to 17% can beeasily compressed into RDF briquettes at a pressure above 70 MPa. When the briquetting pressure is higher than100 kN and moisture content is about 10%，the qualified RDF can be obtained. The orthogonal experiment showsthat the moisture can greatly affect the mechanical strength of RDF，while all the technique parameters have noobvious influence on thermal stability of RDF. The optimal parameters are a shaping pressure of 106 MPa, amoisture content of 10%，and a coal content of 20%.Key words: municipal solid waste; refuse derived fuel; preparation ; orthogonal experimentCLC number: X 705Document code: AArticle ID: 1006-1266(2004)01-0006-07Refuse derived fuel (RDF ) from municipalincineration process ”.In the light of dioxinsolid waste ( MSW ) is of manyfavorableformation mechanism an innovative technology wasperformances such as uniform size distribution,proposed and developed by the Research Center fohomogeneous composition，, high caloric value, andMSW and Biomass to Energy Technology， Chinaeasy in being handled in both transportation andUniversity of Mining and Technology. Thisstockpile.Therefore,various techniques oltechnology can be described as“preparation of RDFpreparating RDF have been developed and applied in-controlled pyrolysis of RDF at low temperaturerecent years- 1-21.Generally，RDF is utilized mainlywith the aim to dechlorination- gasification of charmeans of incineration for energy-recovery.derived from RDF pyrolysis to produce cleanHowever，some issues related to the MSW /RDF .gas”[4]. The results of TG FTIR study of RDFincineration have appeared, e. g. low combustionpyrolysis showed that during heat treatment under aefficiency，dioxin pollution， corrosion of boiler中国煤化工1evolved and aromaticcomponents caused by acidic flue gases ( mainly:THCN M H Gifferent temperatures,HCI )，which results in a high costs of theindecating that the tormation of polychlorinatedReceived date: 2003-11 -09Foundation item: Foundation of Education Department of Jjangsu Government for Commercialization of High Technology Developed inUniversities.Biograph5方数据Xian sheng(1972 ), male, from Jining, Shandong Province. Graduate student, engaged in the research on treatmentand utilization of solid wastes.ZHANG Xian-sheng et al.Preparation and Characterization of Refuse Derived Fuel ..dibenzo- p- dioxinsand/orpolychlorinatedother is pre-compacting the presorted and crusheddibenzofurans ( PCDD/Fs) can be partly or evenMSW under a medium pressure followed bycompletely prevented when gases from differentbriquetting it in the presence of high activetemperature ranges are separately utilized, becauseadditives. Both processes were thought to be aonly when Cl source and dioxinprecursorscomplex technique with a high cost and a high(aromatic compounds ) appear simultaneously canenergy consumptionl8l. Furthermore, the additionPCDD/Fs be synthesized4I. Preparation of qualifiedof inorganic additives also means the decrease ofRDF for pyrolysis and gasification， as one of theheating value[9].most important constituting techniques in theinnovative technology mentioned above, had been1Samples and materialsstudied5.60. Results of previousinvestigation1.1 Samplesdemonstrated that the addition of a certain amountMSW sample used was collected in Xuzhouof coal played an essential role[-6].Shangshan incineration plant. It was hand sorted toAccording to the classification of Americanpapers，plastic/rubber， wood， cellulose， metal,Society for Testing and Materials(ASTM)[7, RDFglass, and ceramics. All components were air driedfor pyrolysis and gasification prepared by theand shredded into particles with a size less than 3authors belongs to the densified refuse derived fuelmm before briquetting. Composition of the MSW(d- RDF，or RDF-5). Generally， there are twosample is showed in Table 1 and its characterizationmethods to prepare d-RDF it[8]: one is pre-is given in Table 2. Coal used was from Xuzhoucompacting the presorted and crushed MSW under aQishan Coal Mine. The specification of coal is alsohigh pressure followed by briquetting it in theshowed in Table 2.presence of low active additives to form RDF-5; theTable1 Composition of municipal solid waste sample, wB/ % (as received )PaperPlastics/ rubberWoodFiberMetalGlasporcelain and ceramicsOthers”0.1720. 580.764.571. 073. 3569. 50slag, soil, gravel, material less than 10 mm in size (fine slag，soil, sawdust, and fruit tegument )Table 2 Characterization of the municipal solid waste sample and Qishan coaltwB/%MadAdVarFCat .CafHaOautNatrSr.dClaQmet.nd/(kJ. kg-1)MSW10.23 52. 8073.50 26. 5052.29 6. 4537. 950. 180.341.147 476.2Coal2.319.43 38. 12 61. 8878. 664.9514. 531.230.5729 910.5t By difference1.2 Apparatus2 ExperimentalEquipment used includes a crusher ( SPC-240)，a hydraulic pressure machine (NYL2000). .Combustible fractions of MSW, coal, and slagStandard instruments for testing pyrolysis andweremixed proportionally. The feedstock forgasification properties were utilized. The mold for .briquettes with prescribed moisture content waspreparating cylindrical RDF with a diameter of 30obtained by adding a certain amount of water intomm and height of 30 mm was also used(Fig. 1). .the shredded mixture in an air-tight plastic bag ,中国煤化工h peridically strring to:TYHCNMHGhofthemoisture.Then.the feedstock was pre-compacted under 35 MPabefore it was flled in the mold. After the pistonsand the mold were well aligned， pressure wasapplied uniformly at a rate of approximately 2. 4士Fig. 1 Mold for briquetting RDF0.2 MPa/s. When pressure reached the prescribed8Journal of China University of Mining &. TechnologyVol. 14 No. 1value，it was either held for a certain time orweights of char (derived from RDF carbonization)released immediately depending on whether thewere measured before and after screening, and theholding pressure was needed. Briquettes ( densifiedweight percentage of char with the size bigger thanoval- shaped RDF ) would be punched out right after6 mm (TS+6) and weight percentage of char withthe pressure was released.size smaller than 1mm (TS. -1) were calculated asThe measurement and analysis of properties ofprimary and auxiliary indices to thermal stability.RDF briquettes were conducted in 2 min, 24 h，10For the dropping test, slight adjustment was maded, respectively, after RDF briquettes were preparedin the analysis procedure: the RDF briquettes wereand exposed in the air.dropped from 2 m twice onto a concrete floorSo far there have been no established standardsinstead of a steel plate as recommended in standard.for the analysis and test of RDF in China.The weights of the RDF briquettes with size moreHowever, standards for coal analysis are oftenthan十25 mm before and after dropping wereadapted in studies of solid energy- containingmeasured and the weight percentage was calculatedsubstances, such as carbonaceous shale, coal refuse,as an index to dropping resistance.as well as MSW and RDF. Thus in this study3 Factors Influencing the Quality of RDFcomposition and properties of RDF were analyzedandtested according) the coal analysis3.1 PressuresstandardsI0].RDF briquettes were prepared from feedstockThermal stability and dropping strength ("coldwith a moisture less than 5% and the coal less thanstability”，or“ mechanical strength”) of RDF20% at different briquetting pressures withoutbriquettes were tested according to China Coalholding time after prescribed briquetting pressureAnalysis Standards MT/T924- 2003，MT/T925-had reached. The appearance description， dry2003，respectively. For the thermal stability test,density and mechanical strength of briquettes werethe RDF was carbonized followed by screening. Thegathered in Table 3.Table 3 Specifications of RDF briquettes prepared at various briquetting pressuresBriquetting pressureDry densityb Dropping Resistance /Description of appearance"p/MPap/(g.cm-a)3Poor, tending to loose and deform7Fair, dim surface. tending to fall apart when touched with finger1. 4541.4106Good, glossy surface, not tending to crash when touched with finger1.4753.5Exellent, smooth surface ，not crashing when touched with finger .59.8180Good, expanding，cracks in surface, not crashing when touched with finger1.4957.1a. The briquettes' integrity was graded as“poor",“fair”, “good" and“excellent ”according to their appearance ，rigidity ，surface smoothness,and shape. b, c. The results were measured in 2 min after ejection of the briquettes from the mold.As showed in Table 3，a high briquettingcertain shape with low intensity and fragile. Withpressure within a certain range is favorable forthe proceeding of briquetting，the pressure increasesquality of RDF. The minimum briquetting pressuregradually and gets high enough to make it possibleis about 70 MPa, at which the density of the RDFfor particles to be deformed, and the deformed andis more than 1. 45 g●/cm*. Dry density andenlarged interface among particles results in andropping strength of RDF decreases with the中国煤化工，there isa limit to theincrease of briquetting pressure when the pressure is .:YHc N M H G the briqueting pressurehigher than 140 MPa. The reason can be elucidatedis higher than 140 Mra，the increase of pressureeasily. At the beginning of briquetting process, themay bring on destroying the uniform particles ofvolume of the feedstock reduces fast as briquettingcoal and/or slag. Meanwhile, the internal elasticitypressure ingr数准vithout deformation of particles.in some components in feedstock begins to play anAs a result， RDF briquettes can be formed in aimportant role. If the briquetting pressure is tooZHANG Xian-sheng et al.Preparation and Characterization of Refuse Derived Fuel ... .9high (e. g.180 MPa in Table 3)，a rebound ofwas measured in 2 min after ejection of briquettesparticles in briquettes and crack of RDF as well asfrom the mold ,and the results are showed in Fig. 3.the descent of the strength will occur after thepressure releases. Fig. 2 shows the appearances ofdifferent RDF briquettes prepared at variouspressures.3.2 Holding time细) 70 MPa向) 106 MPa0 s and 10 s holding time were applied whenprescribed briquetting pressure had reached with theaim to investigate the effect of holding time oncharacteristics oRDF briquettes.In theexperiments the briquetting pressure was fixed at106 MPa，while the moisture of feedstock withte) 140 MPa(d) 180 MPa20% of coal and 20% of incombustible componentsFig. 2 RDF briquettes prepared at various pressuresfrom MSW was 5%，10%，and 17%. The density1.60L.60合L.55. L.551.S51.50置1.45望1.49器1.451.401.40-1.351.35 L13370 80 90 10010 120130 1407080901001101201301407080900100 120130 140p/MPapMPa(u) wonistre)-5%(b) wfmoisture) 10%(C) wfmotsture)-17%Fig.3 Effects of briquetting pressure and holding time on density of RDF briquettes(measured in 2 min after preparation)As showed in Fig. 3，10 s holding time isstored and transported before it is used. Thus thefavorable for improving the density of briquettes.stability of dimensions and density of RDFThe lower the pressureis, the more significant thebriquettes in room temperature during a certaineffect of holding time. Besides, the effect of holdingperiod is of great significance for their practicaltime on briquette density is relevant to the moistureutilization.content of the feedstock. So the holding time hasLongitude dilatability with storage time wasonly a slight influence on density when moisture istested ( Fig.4 )，indicating that the maximum10%.dilatability occurred at 2 min after ejection of3.3 Storage timebriquettes from the mold. And the higher theIt is well known that RDF will be temporallymoisture content in feedstock is, the greater the1.55W,(Water)二1.50 t一17%曼1.40.5中国煤化工10 100 1000 0000 1000012000 16000r/minMYHCNMHG(a) Longtudinal exparsion(b) Dry densityFig.4 Variation of longitudinal dimension and dry density of RDF briquettes with storage time(Feedstock: moisture 5%，coal 20%，briquetting pressure 106 MPa, no holding time)dilatability will be. The dilation of briquettes madeby feedstock containing 5% moisture lasted for 10Journal of China University of Mining &. TechnologyVol. 14 No.1days，and the dry density kept decreasing. Thiswas performed in 10 days ( RDF briquettes weremight be caused by the fact that the paper in RDFstored in open air during that time) after ejection ofabsorbs moisture from air and the expands.briquettes from mold and the results were gathered4 Optimization of Parametersin Table 5.Table 4 Orthogonal table Lg(34 ) for experimentsBased on results of investigation of singleof process parameters optimizationfactor，the key influencing process parameters onfactorsspecification of RDF including briquetting pressure，level(A)(B)(C)(D)moisture,slag content, and coal content irp/MPaw(slag)/% w(M)/% w(coal)/%feedstock were recognized. Orthogonal Table L71(51C10621020(34) ( Table 4) was employed in experiments to142302:optimize these process parameters. CharacterizationTable 5 Results of the orthogonal experimentswSlag)/%w(M)/% .w(coal)/%Dropping resistance/ %Thermal stability * /%78.55.473. 833.13(14.826.72(2571. 8621.956.5210.31760. 765.879. 3221. 867. 647.2935.255. 71776. 5668.96756. 74nz63. 04765. 99760. 29771. 303n360.7236. 92750. 2251. 440R7. 330.39. 633 .18. 74719. 863n’5. 06716. 3676.1339. 7m2’12. 6676. 8672.810. 233rs’14. 1338. 63312.93311. 9339. 066.9.56.82. 233* weight percentage of char with size bigger than 13 mm after thermal stability test4.1 Direct analysisIn the light of principles of statisticsi11]， theEffects of process parameters on droppinginfluencing order of process parameters on droppingresistance and thermal stability are showed inresistance is moisture, coal content, slag content ，Fig. 5.and briquetting pressure. However ，the influencingorder on thermal stability is moisture， briquetting60人pressure, slag content, and coal content.占号404.2 Variance analysisAAABBBCCGDDDOn the basis of data in Table 6，it can beFactorsconcluded that briquetting pressure in the range of.厂一中国煤化工ffet on both droppingYHCN MH Glity of RDF briquettesAA2A.B.B2B,CIC2C,DD2D3Thus" briquetting pressure can be neglected in(b)variance analysis.V ariance analysis was conducted to determineFig. 5 Effects of process parameters on droppingthe influencing degree of process parametersce and thermal stability( moisture，slag content， and coal content ) onZHANG Xian-sheng et al.Preparation and Characterization of Refuse Derived Fuel .. .1characterization of RDF briquettes. The results ofvariance analysis were showed in Table 6 and 7.Table 6 Variance anal ysis of process parameters on dropping resistance of RDF briquettesDeviationF reedom .Mean square deviationMoisture content (B)2527.45.1 263. 7330. 03Slag content (C)528.15264. 07Coal content (D)634.73317. 377.54Error (Qr -QQ2 -Qu)84.1842.09Total Q3 774. 50Table 7 Variance analysis of process parameters on thermal stability of RDF briquettesSourceFreedomBriquetting pressure (A)142. 1271. 06.17.41153. 1876. 59.18.7790. 7045. 3511.11Error (0-20QQ-Q2)8.164.08.394.16Provided that a=5%，the value of F。(2,2)content in feedstock is less than 10%14]. In the endwill be 19C12]. Fp in Table 6 is greater than 19,optimum process parameters were determined asindicating that the moisture has significant effect on10% of moisture, 10% slag content, and 20% coaldropping strength of RDF，while both Fc and Fcontent in feedstock， as well as 106 MPa ofare smaller than 19， i.e.，changes of slag contentbriquetting pressure.and coal content will have only a lttle influence on4.3 Supplementary experimentdropping strength. In Table 7, FA,Frand Fc are allAs the optimum process parameters determinedsmaller than 19，which demonstrate that no processby orthogonal experiments do not appear in Tableparameter has great effect on thermal stability of5，supplementary experiment was carried out tRDF briquettes.verify the results. The characteristics of RDFBecause the drying operation cost in RDFbriquettes prepared by optimized process parameterspreparation depends on the moisture content oare showed in Table 8 and char reactivity of RDFfeedstock-13]，the conclusion is of significance thatcan be found in Fig. 6.qualified RDF can be prepared when the moistureTable 8 Characteristics of RDFws/%Dry density/DroppingStatic mechanical Ash melting point/Qner.ad/MadAVarS.d(g. cm- 8) resistance /%strength /N(kJ.kg-1)2.58 39.04 66. 420.561.181.46 _784261 16011 960. 1800r80-5Concl usions6020 tPyrolysis- gasification process is a promising900 800 900 100011001200technology for the treatment and utilization ofTemperaurerCmunicipal solid waste. The results of investigationFig.6 Char reactivity of RDF briquettesshow that qualified RDF briquettes for pyrolysis andIt can be seen from Table 9 that droppinggasification can be prepared by bindless highstrength of RDF is higher than 78%， static中国煤化工>om temperature.mechanical strength is 426 N per briquette and ash:MYHCNMHGetersdeterminedbymelting point is 1 160C，which meets the demandorthogonal experiments are as 10% of moisture,>f gasification[14].As showed in Fig. 6， the .10% of slag content, and 20% to coal content inreactivity of carbonized RDF is also high enough tofeedstock，as well as 106 MPa of briquettingbe used in万痧敗辗on[14].pressure.Journal of China University of Mining &. TechnologyVol. 14 No. 1References[1] Chang Y H, Chen W C, Chang N B. Comparative evaluation of RDF and MSW incineration [J]. Journal of HazardousMaterials, 1998，58(1-3): 33-35.[2] Saxena SC, Rao N S. Fluidized -bed incineration of refuse- derived fuel pellets [J]. 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