Chemical-looping gasification of biomass in a 10k Wth interconnected fluidized bed reactor using Fe2

第42卷第8期燃料化学学报Vol. 42 No. 82014年8月.Journal of Fuel Chemistry and TechnologyAug.2014文章编号: 0253-2409( 2014 )080922-10Chemical-looping gasification of biomass in a 10 kWinterconnected fluidized bed reactor using Fe203/ Al2O3 oxygen carrierHUSEYIN Sozen, WEI Guo-qiang, LI Hai-bin, HE Fang, HUANG Zhen( CAS Key Laboratory of Renewable Energy, Guangzhou Institute ofEnergy Conersion , Chinese Academy of Sciences ( CAS), Guangzhou 510640, China)Abstract: The aim of this research is to design and operate a 10 kW hot chemical-looping gasification (CLG) unit using Fe2O3/Al2O3 as an oxygen carrier and saw dust as a fuel. The effect of the operation temperature on gas composition in the air reactor andthe fuel reactor, and the carbon conversion of biomass to CO2 and CO in the fuel reactor have been experimentally studied. A total60 h run has been obtained with the same batch of oxygen carrier of iron oxide supported with alumina. The results show that COand H2 concentrations are increased with increasing temperature in the fuel reactor. It is also found that with increasing fuel reactortemperature, both the amount of residual char in the fuel reactor and CO2 concentration of the exit gas from the air reactor ardegreased. Carbon conversion rate and gasification efficiency are increased by increasing temperature and H2 production at 870 Creaches the highest rate. Scanning electron microscopy ( SEM), X-ray diffraction ( XRD) and BET-surface area tests have beenused to characterize fresh and reacted oxygen carrier particles. The results display that the oxygen carrier activity is not declined andthe specific surface area of the oxygen carrier particles is not decreased significantly.Keywords: chemicalooping gasification; hot model; biomass; Fe2O;/ Al2O, ; dual circulating fluidized bedCLC number: YQ016Document code: ACarbon dioxide emitted from fossil fuel powerbasic principles as CLC with the main difference thatplants accounts for roughly 20% of the greenhousethe final products in CLR or CLG are synthesis gaseffect and climate change. There are some novel( H2 and CO ) instead of full combustion finaltechnologies being developed to reduce and captureproducts like CO, and H,O, and heat'the CO2 emissions from conventional power plants.Different metal oxides as oxygen carrier, such asChemical-looping combustion ( CLC) is one of the .Ni, Cu, Fe, Mn, Co and some mixed metal oxidestechniques used to combine fuel combustion and CO2have been proposed for CLC recently. Generally, Nicapture at the same time without any need of airand its corresponding oxide show relatively higherseparation unit.Chemical-loopingcombustionoxidation and reduction rates than other metals but it(CLC) is a new combustion technique where anis an expensive and hazardous candidate.Copperoxygen carrier is used to transfer oxygen from the airoxide indicates high reactivity in the redox reactionreactor to the fuel reactor， omitting direct contactwith air and fuel in CLC tests. But CuO hasbetween air and fuel. Thus， CO2 and H,O areagglomeration and softening problem because of itsinherently separated from the other noncondensiblelow melting point. A further problem with CuO atcomponents of the flues gas， such as N, and unusedhigh temperatures ( 870 C) is that CuO canO,[2,3]. Then， the CO， can be recovered bydecompose to Cu2O that can lower oxygen capacitycondensing the vapor of water without energy penaltyfor oxidizing fuel. Oxides of Mn and Co have showedand the dewatered CO2 can be captured anda rather poor reactivityh6sequestrated or/ andcan be used for otherIron oxide is cheaper than CuO and NiO andapplications. The properties of the oxygen carrierenvironmentally friendly. All iron compounds haveare important for the experiments of the process ofhigher level of melting points and can stand cyclicCLC，and an oxygen carrier should have highreactions in the fuel and air reactor of CLC7I .reactivity，high oxygen transport capacity， highAccording to the thermodynamic analysis for ironresistance to attrition, and cheap and environmentallyoxygen carriers, the complete fuel conversion to CO2friendly. Chemical-looping reforming ( CLR ) orand中国煤化工hen Fe,O, is prtillychemical-looping gasification ( CLG) uses the samereduide is still an attractiveYHCNMHGReceived date: 2014-04-11; Received in revised form: 2014-05 -30.Foundhtion item: Supported by the National Natural Science Foundation of China (51076154); National Key Technology Research & DevelopmentProgram of 12 th Five-year of China ( 2011BAD15B05).Corresponding author: E-mail: lihb@ ms. giec. ac. cn.本文的英文电子版由EIsevier 出版社在ScienceDireet.上出版( htp:// www. sciencedirect. com/ science, jourmal/ 18725813).第8期HUSEYIN Sozen et al: Chemical-looping gasification of biomass in a 10 kW......923oxygen carrier for the industrial application of CLC oral-14] has experimented for the catalytic performancesCLG as its easy availability and low price even theof natural Ca-based catalysts ( dolomite andcapacity of Fe2O3 for transferring oxygen is onlylimestone) and synthetic Ca-based catalysts， which0.5 mol of O2 delivered per 3 mol of Fe,Oz. For thehave been used for improving biomass rice strawmentioned advantages, Fe2Oz on Al2O3 support hassteam gasification in a circulating spout-fluid bedbeen selected as oxygen carrier for the present work.reactor. Li et al5J has presented on the biomassGaseous fuels such as methane, hydrogen, anddirect chemical looping ( BDCL ) process， ansyngas from coal gasification and solid fuels like coal ,alternative process, which has the potential to thermopet coke, char and biomass can be use as fuel in CLCchemically convert biomass to hydrogen and/oror CLG[9]. Most of the researches on oxygen carrierelectricity with high efficiency. Process simulationhave been performed in a laboratory fluidized bedhas been investigated by ASPEN Plus, and then datareactor and thermo gravimetric analyzers ( TGA )，were obtained from the multistage model. Hybridand few of them studied on dual or interconnectedpoplar as biomass fuel and oxygen carrier of 66. 2%fluidized bed reactor with solid fuels. The oxygenFe2O3 and 33. 8% SiC by weight were used duringcarrier reactivity should cover number of cycles, andthe study. Gnanapragasam et al6] has reported on thehe reactivity of the oxygen carrier should stand toperformance of four different coals and biomass withthermal stresses and accumulative chemical reactionsiron oxide-based direct chemical looping combustionduring the cyclic operations.system, the impact of fuel blend ( mix. of coal andLimited number of studies can be seen on usingbiomass)on hydrogen production was compared.oxygen carriers for CLC with biomass solid fuel in a .When biomass was blended with 20% coal by mass，continuous CLC or CLG reactor in the literature. For10% additional hydrogen was produced. Gu et althe quoted two-stage dual fluidized bed gasificationhas studied on chemical looping combustion o1( T-DFBG) devises, Xua et all0] has studied the usebiomass and coal conducted in a 1 kWn continuousof a two-stage fluidized bed ( TFB) to replace thereactor with Australian iron ore as a oxygen carrier.single-stage bubbling fluidized bed gasifier involvedThe effect of temperature on gas composition of bothin the normally encountered dual fluidized bedhe fuel reactor and the air reactor， conversiongasification ( N-DFBG) systems, gasifying dry coffeeefficiency of carbonaceous gases， carbon capturegrounds in two 5. 0 kg/h. Shen et al0] hasefficiency and oxide oxygen fraction were investigate.experimented on the CLC of biomass in a 10 kWthVirginie et al18] has provided that the Fe/ olivinereactor with iron oxide as an oxygen carrier. A totalcatalyst effectiveness regarding tar primary reduction30 h of test was achieved with the same batch of ironduring biomass gasification in dual fluidized beds. Itoxide oxygen carrier. The results showed that the COwas found that Fe/ olivine materials had a doubleproduction from biomass gasification with CO, waseffect on tar destruction. On the one hand, they weremore temperature dependent than the CO oxidationacted as a catalyst for tar and hydrocarbon reforming.with iron oxide in the fuel reactor, and an increase inFurthermore, they could act as an oxygen carrier thatthe fuel reactor temperature produced a highertransfers oxygen from the combustor to the gasifier ,increase for the CO production from biomassand part of the oxygen is used to burn volatilegasification than for the oxidation of CO by ironcompounds. The catalyst was fairly stable because theoxide. Zhang et al' 121 has studied on simulation ofresult was confirmedduring 48 hcontinuousmethanolsynthesis via H2 -rich biomass-derivedoperation. Song et al19] has investigated hydrogensyngasfromstraw biomass gasification inproduction from biomass gasification in a laboratoryinterconnected fluidized beds. In the case of CaCO3scale apparatus of interconnected fluidized beds. Thecatalysis，the effects of operating parameters ,effects of gasifier temperature and steam/ biomassincluding gasification temperature and pressure ,ratio on the composition of hydrogen-rich gas, carbonsteam/ biomass ratio, and liquefaction temperature andgasification of biomass. carbon combustion o1pressu on the methanol yield were analyzed. Acharyabion中国煤化工f biomass, tar contentet al131 has investigated on H2 production processand|Y片CNMHGsed.Mendiaraetal20employing fluidized-bed technology from agriculturalhas studied biomass combustion in a continuous CLCbiomass sawdust with in situ CO2 capture and sorbentunit using pine wood as fuel and iron ore as anregeneration. The system efficiency of the chemical-oxygen carrier. High carbon captures ( >95% ) werelooping gasification process at an ideal scenario wasachieved in the interval 880 ~915 C using both steamfound to be 87. 49% with biomass as fuel. Xie etand CO2 as gasifying agents. Tar compounds were924燃料化学学报第42卷.detected at the fuel reactor outlet. After 78 hdiffraction ( XRD) and BET-surface area tests havecontinuous operation, no change was detected in thebeen used to characterize fresh and reacted or usedphysical and chemical properties of the oxygen carrieroxygen carrier particles.particles. Gu et al[21]has prepared biomass-to-synthetic natural gas ( SNG) using calcium looping1 Thermodynamics analysisgasification ( CLG) with CaO sorbent ( CLG-SNG)In the continuous tests，the reactions between theviathermochemicalmethods.Interconnectedreduced iron basedoxygen carriers withthefluidized beds were adopted for repeated carbonation/combustion air in the air reactor are as follows:4Fe,O4+O2- >6Fe2O3calcination cycles of CaO sorbents in the gasificationunit. A process simulation was conducted based or4FeO+O,- >2Fe,O,the chemical equilibrium method using the AspenWhen the biomass is feeded into the bedPlus. Then, the effects of some key variables on thematerials of the fuel reactor， an intensive contactthermodynamic performances ,such as the gasbetween hot oxygen carrier particles and biomass willcomposition，yield of SNG ( YSNG)，cold gashappen, following by the intense exchange of heat.efficiency ( η cold) ，the overall energy efficiencyThe biomass is immediately heated up to the bed(η), energy efficiency (ψ) of the process, and thetemperature in the fuel reactor. Then, devolatilizationunit power consumption ( WSNG) were investigated.and gasification of biomass has taken place in theBiomass is called as any organic matter, which islower zone of the bubbling fluidized bed. The mainavailable on a renewable basis ，including agriculturalreactions probably are pyrolysis and gasification ofcrops，plants and agricultural wastes and residues,biomass and boudouard in the fuel reactor:wood and wood wastes and residues，animal wastes ，C,H2O→char + tar + syngasmunicipal wastes, and aquatic plants. This renewable(CO, H2, CO,, CH4，C,H2m )resource can be converted into electricity, chemicals ,Boudouard: C+CO2-→2CO(4)hydrogen, heat and liquid fuels. Biomass conversionThe main reduction reactions of oxygen carrieris less carbon and pollutant intensive when comparedparticle with pyrolytic and syngas products of biomassto fossil based fuels. Furthermore, these renewableare presented below in the fuel reactor1.23 :matters are abundantly available and widelyCO + 3Fe2O3→CO2+ 2Fe3O,distributed in the any part of the World. As source ofCO + Fe2O3→CO2+ 2FeOrenewable clean energy，biomass can achieve the goalCO + Fe,O4→CO2+ 3FeO(7)of CO2 zero-emissions and reduce the climate changeCO+FeO-→CO2+Feand greenhouse effect in the industrial and powerH2+ 3Fe2O3→H2O + 2Fe;O4(9)utilization. Nowadays， biomass development andH2+ Fe,O,→H,O + 2FeO. (10)employment in energy production has gained greatH2+ Fe,O.→H2O+ 3FeO(11)attention from all over the world 2 " . Sawdust of pineH2+ FeO- + H,O+ Fe. (12)has been selected as biomass fuel in this work for theCH4+ 3Fe,O,→2H2+ CO + 2Fe,O,( 13)above mentioned reasons.CH,+ 4Fe2O3→2H,O + CO2 +8FeO(14)CLG rather than CLC in this experiment isCH.+ 4Fe,O,→2H2O + CO2+ 12FeO(15)employed as electricity prices in China is nearly fixedCH4+ 4FeO→2H2O + CO2+4Fe(16)and there are lots of imports on transport fuels andC+3Fe2O3→CO+2Fe,O. (17)natural gas. When pure and high quality H2 and COC + 2 Fe,O,-→CO2+ 4FeO(18)are mixed as syngas, it is able to produce FT gasolineTherefore，these reactions occur sequentially ancand diesel, and synthetic methane .simultaneouslyduringbiomasspyrolysis andThe performance of chemical-looping gasificationgasification in the presence of oxygen carriers.(CLG) of biomass as fuel has been experimentallyfinal products of biomass gasification are determinedinvestigated in the 10 kWb reactor with Fe, O3/AI2O,by the interaction of a couple of above mentioned(70% :30% by weight) as an oxygen carrier in the中国煤化工present work. A total 60 h cyclic test has beenof iron oxygen carrierachieved with the same batch of oxygen carrier. Theby gTHC N M H Gcelerate the process ofeffect of the fuel reactor temperature on produced gasbiomass gasification. In addition， the tar would be :composition of the fuel reactor and the air reactor ，decomposed to small molecular weight gases in theand the conversion of biomass carbon to gases in thepresence of iron oxide as follows'2fuel reactor has been experimentally reported.Tar→H, +CO+hydrocarbon AH > 0 (19)Scanning electron microscopy ( SEM )，X-rayIn comparison to traditional biomass gasification ,第8期HUSEYIN Sozen et al: Chemical-looping gasification of biomass in a 10 kW......925the chemical reactions in the process of CLG are more1 100 C for 6 h. Thus, dried oxygen carriers withcomplicated due to the presence of oxygen carrier.color changed in grayish are obtained. After drying, aBiomass gasification and oxygen carrier reductionmanual system is used to grind and collect particleswith biomass syngas occur simultaneously in CLG.with an appropriate sizes. Thus， shaking sieves areThe other reactions involvedin the biomassused after hand selection. The process is repeatedgasification have relation with water produced duringuntil the desired particle size is achieved.the oxygen carrier reduction by syngas components.2.2 Setup of interconnected fluidized bedSimilar reactions also occur when steam is used asreactor and procedurefluidizing gas. These reactions are shown as follows :The reactor is constructed with a 904 L stainlessWater gas: C + H,O(g)→H2+ CO( 20)steel. The details of the reactor system are shown inWater-gas shift: CO + H,O(g)→H2+ CO,Figure 1.(21 )Steam reforming: CH4+ H2O(g)- →3H2+ CO日+8.3[7元-4(22)RugThe flue gas exhausting from in the fuel reactoris gas mixture of H2，CO2，CO and CH. Theparticles of reduced oxygen carrier in the bubblingfluidized bed return back to the air reactor via a lower11loop seal.2 Experimental?-个品o应7)-122.1 Materials24Sawdust of pine selected from Guangdong]T23T1~T26 thermno semsors (C)province ( China) is used as fuel in the tests. The13PI~P8 presure sensors (kPa)sample size is ranged 250 ~ 425 mm. It has been driedQ1~Q5 air flow meters (m2/h)14biomass flow direction●for 8 h at 105 C before experiment. The ultimateoxidized oxygen carriersanalysis of the pine ( w%，dry basis) is 46. 44%reduced oxygen carrierocarbon, 6. 21% hydrogen, 0. 05% nitrogen, 0. 01%Figure 1 View of the reactor system of thesulfur and 47. 29% oxygen ( by difference). Its lowerhot model of laboratory unit in G.I. E. C.heating value was 18. 707 HHV ( kJ/kg, db). The1: air reactor gas flow; 2: air reactor riser;proximate analysis of the pine ( w%，dry basis) was3: cyclone for air reactor; 4: depleted gas;8.39% moisture, 84. 31% volatile， 6. 88% fixed5: synthesis gas; 6: cyclone for fuel reactor;7: upper loop seal; 8: fuel reactor; 9: biomass stirrer;carbon and 0. 42% ash. The oxygen carrier used in10: balance gas; 11: biomass tank; 12: biomass feeder;this work is Fe, O3/ Al2O, particles which are prepared13: fuel reactor gas flow; 14: down loop sealby mechanical-mixing method.2.1.1 Particle making and pelletizationTheexperimentsfochemical-loopingThe pelletization procedure involves two maingasification ( CLG) of iron oxide and support withsteps. The first step involved is the powderalumina as an oxygen carrier with biomass as fuel arepreparation which processes the raw powders into aconducted in a 10 kW continuous reactor ofcomposite powder, and the second step is the actualinterconnected fluidized beds as prototype which is .pelletization of the powder. The powder preparation isconsist of a fast fluidized bed as an air reactor， theperformed by dry mixing 70% Fe2O3 powder andfirst cyclone for depleted gas of the air reactor， a30% Al2O3 as the support. The large pelletizer has abubbling bed as fuel reactor, the second cyclones forhopper which stores the powder and feeds into asynthesis gas of the fuel reactor and two loop seals.rotary die set. The rotary die has a matching punchThe one seal for entrance of the fuel reactor after theset which presses the powder into a pellet. The sticksfirst中国煤化工P seal and the other forof oxygen carrier are produced by sharing action ofexitair reactor is namedtwo screws which are interaction and mutual rotatingdow.MYHcNMHGizedbedhasacrclarwith each other in the machine. After mixing iscolumn of 50 mm in inner diameter and 2 100 mm incomplete，the powder will have preparated into aheight with a perforated plate as an air distributor orwide range of sizes ranging from the desired particlethe bottom of the reactor system. The bubbling bedsize under 1 mm to up to 1 cm in diameter in reddishhas a similar shape with 150 mm in inner diameter andcolor. Then, they are calcinated in a small oven at926燃料化学学报第42卷.500 mm in height with a perforated plate as an airThe reactant and synthesis gas product components aredistributor again. The two reactors are joined togethercollected to gas bags for offline gas chromatographby a rectangular loop seal with a cross section of40 xanalysis. All experiments are performed at85 mm2 and a height of 280 mm.atmospheric pressure and room temperature except theStrong solids mixing， recirculation of oxygenreactor system. Experimental conditions for 20 ~60 hcarriers and long residence time of biomass particleslong-term test with biomass ( pine sawdust ) as fuelare very important for a high rate of carbonare given in Table 1.conversion efficiency in CLC or CLG. For this reason2.3 Oxygen carrier characterizationsa bubbling fluidized bed is adopted for the fuelThe crystalline phases of the fresh and reactedreactor. The fuel reactor has two parts， of which theoxides are analyzed by XRD ( X' Pert PRO MPD )major part is named as the reaction chamber and thewith Cu Ka radiation, operating voltage of 40 kV andminor one is the inner seal. The reaction chamber iscurrent of 40 mA with a step size of 0.001 6 and theused for biomass gasification and oxygen carrierdiffraction angle (20) scanned from 10° to 90°. Thereduction with syngas from biomass gasification. Themorphology of the Fe, O3/Al2O,-type oxides isinner seals having a height 320 ( mm ) allowstudied by scanning electron microscopy ( SEM) on amovement of oxygen carriers from the reactionHitachi S4800 instruments. The magnification ofchamber in the fuel reactor to the down loop seal then15000 (15 K) times is selected to analyze the surfaceto air reactor. At the same time, it prevents the by-micrographs of oxygen carrier. The BET surface areapassing of the flue gas from the air reactor to downanalyses sre experimentally investigated by N2loop seal and then to the fuel reactor. The down loopphysisorption using a Micromeritics ASAP 2010seal and the inner seals have roles in preventing gasinstruments.Thesamples of Fe2O3/ Al2O-typeleakage between the reactors. The oxygen carrieroxides are degassed under vacuum at 493 K for 6 hparticles carried in the synthesis gas in the fuel reactorbefore tests.are separated by the second cyclone for the fuel2.4 Data evaluationreactor.The lower heating value (LHV, kJ/m') of theThe heat required for the biomass gasificationgas products is calculated by equation:and oxygen carrier reduction with biomass syngas isLHV = 126 Vco+ 108 Vn2+ 359 Vcu,+ 635 VC.Hmachieved by means of the circulation of oxygen carrier(23 )particles between the air reactor and the fuel reactor.where V'co， VH，VcH, and VC,Hm are the volume :The biomass and reduction of oxygen carrier in thefractions of CO, H2，CH, and C,Hm in the productfuel reactor is an endothermic process， while thegas from fuel reactor, respectively.oxidization of oxygen carrier with air in the air reactorGas yield ( G, ) is the volume of gas productsis exothermic one. As a result, there is a temperatureunder standard state generated from unit mass ofdifference between the fuel reactor and the air reactor.biomass，which is calculated as :The oxygen carrier particles are heated up in the airG,= vg/mp(24)reactor by exothermic reactions and then release givenwhere vg is the volume of the gas products irheat in the fuel reactor by circulation of oxygen carrierstandard state and m, is the mass of the biomass.particles.Carbon conversion efficiency ( ηc )is anAt the beginning of a test, the heating of the twoimportant parameter to evaluate the performance ofreactor beds are electrically heated separately thatbiomass gasification. It is defined as the proportion ofsupplies heat for start-up and compensated heat lossthe carbon converted into gaseous products to the totalduring a continuous operation. When the temperaturecarbon in the biomass fed into the fuel reactor. Theof the two beds is electrically heated to 750 C, the air .carbon conversion efficiency, ηc, is calculated by thereactor is fluidized with air and the fuel reactor isfollowing equation.fluidized with N2 individually. Thermocouples annc=12x(vco+Vco. +VcH, + 2vcHm )xG,/22.4xpressure transducer are located at different points of(298中国煤化工(25)the reactor system as shown in Figure 1. Operating|YHCNMHGhe gas yield which isconditions can be rearranged at any time by thedefinea as the volume OI gas products under standardsoftware on the computer and control panel. Thestate generated from unit mass of biomass, w is theoutlets from the air reactor and fuel reactor arecarbon content of biomass and V'co2， Vco，VcHg， aninduced with suction pump to an ice-water coolerVCcH are the volume fractions of CO2, CO, CH4 andwhere the steam (if any) is condensed and removed.C2Hm in the flue gas, respectively.第8期HUSEYIN Sozen et al: Chemical-looping gasification of biomass in a 10 kW......927Table 1 Operational conditions of the interconnected fluidized bed reactorNo.Operating parameter and design valuesValuethermal power / kW10biomass fuel as saw dust power /(kW●h~')0biomass fuel as saw dust stock particle size d/ mm250 ~ 425stored biomass m/kg4. 8biomass fuel flow/ feeding rate (on dry basis) qm/(kg .h1)1.1oxygen carrier ( bed materials )70% Fe2O3/30% Al2O3total bed inventory m/kg6.8bed material particle size d/ mm0.25 ~0.425oxygen carrier/ biomass mass ratio1:1.17operating temperature t/C750 ~ 90011air inlet temperature t/C2002outlet gas temperature t/C17813outlet cold fuel gas temperature tC2164air flow mass controller for the air reactor q/(m’●h~')12N2 flow mass controller for the fuel reactor q/(m' . h-' )6N2 flow mass controller for the upper loop seal q/(m' . hr')N2 flow mass controller for the down loop seal q/(m’. h-' )38N2 flow mass controller for the balance q/(m' . h-')19gas residence time in the fuel reactor ( gasifier) t/s20biomass residence time in the fuel reactor ( gasifier) t/s721operating pressure p/kPa1.2522fluidization velocity of the fuel reactor/(m●s")1.1 ~1.523fluidization velocity of the air reactor /(m●s-' )1.3~1.624bed diameter of the fuel reactor d/ mm15025ed (max. ) height of the fuel reactor d/ mm50026freeboard diameter of the air reactor d/ mm5027height of the air reactor d/ mm2 10028fluidization pipe diameter for T1-26 and P1-8 d/ mm .29fluidization pipe diameter for Q1 d/ mmfluidization pipe diameter for Q2-5 d/ mmGasification efficiency (η) is defined as the ratioair flow of the air reactor bed is kept on 12 m’/h.of the calorific value of the gas products from unitThe N2 stream flow of the fuel reactor bed is kept onmass biomass gasification to the total calorific value6m'/h. The experiment for chemical-loopingof the unit mass of biomass. It is calculated as:gasification ( CLG) of biomass is investigated at aη= LHV●G,/Q(26 )fuel reactor temperature varied from 750 to 900 C andwhere G, ( m'/kg) is the gas yield， LHVa continuous period of 60 h is completed. The effect(kJ/m3) and Q。( kJ/kg) are the calorific value of theof the fuel reactor temperature on the performance ofgas products and the biomass at room temperature ,chemical-looping gasification ( CLG) of biomass isrespectively.investigated with the oxygen carrier.CO selectivity Sco (%) = ( moles of CO3. 1Effect of temperature on both fuelproduced)/( total moles of CO and CO2 produced) xreactor and air reactor100%(27)"he operation temperature is very important andH，selectivity sμ, (%) = ( moles of Hcritical for chemical-looping gasification ( CLG) ofproduced)/( total moles of biomass usedx0. 67 ) Xbiomass in the dual fluidized beds. The temperatures(28 )of the frgl roogtnr soriad, frrn 750 to 900 C in the中国煤化工”testsof temperature on the3Results and discussion:TYHC N M H Gactor is shown in FigureLong term experiment of 20 ~ 60 h is established2.with the same batch of iron oxide particles withoutThe concentration of CH。in the flue gas of the :adding any fresh oxygen carrier particles into the hotfuel reactor is kept at below 10% in the fuel reactorsystem reactors and the feeding rate of biomass is kepttemperature ranging from 750 to 900 C. However,as constant at 1. 1 kg/h during the experiments. TheCO concentration of the flue gas of the fuel reactor928燃料化学学报第42卷.significantly increases with an increase of the fuelresidual char carried with porous structure of thereactor temperature until 810 C and then it isoxygen carrier from the fuel reactor burnt with hot airmaintainedaround 55%.Correspondingly，CO2in the air reactor bed. The concentration of CO2 in theconcentration of the flue gas of the fuel reactor isflue gas of the air reactor decreases with an increasedecreased until 810 C，then shows almost stabilizedof the fuel reactor temperature, as illustrated in Figureline around 25% ~ 30% between 810 ~ 900 C, and3. The chemical looping gasification with biomass infinally H, concentration reaches the highest at 870 Cthe fuel reactor is highly endorsed by an increase ofas shown in Figure 2. As results of endothermicreaction temperature. The amount of residual char inreactionsn the fuelreactor; CO and H2the fuel reactor decreases with an increase of the fuelconcentrationsare increasedwith increasingreactor temperature. By increasing of the fuel reactortemperature.temperature, both the amount of residual char in theuel reactor and CO2 concentration of the exit gas70from the air reactor are decreased.The influence of the temperature on the gas--H2selectivity is also investigated, as shown in Figure 4.一+CH,4030 t-0- CO,60+ CO50+H号401030740 760 780 800 820 840 860 880 900 920Temperature 1/CFigure 2 Influence of temperature on thegas concentrations on the fuel reactorAs shown in Figure 3, the flue gas compositionTemperature t/Cof the air reactor affected by the fuel reactorFigure 4 Influence of temperature on the gas selectivitytemperature is also tested. The oxygen concentrationin the flue gas of the air reactor is maintained aroundIt shows that carbonconversion rate and20.0%，which is the amount of unreacted O2 fromgasification efficiencyincrease with increasingfeeded air with oxygen carrier in the air reactor. Andtemperature and H2 production at 870 C reaches theN2 also shows stable line around 75% .highest rate.The influence of the temperature on the carbon80 Fconversion rate and gasification efficiency alsoincrease with increasing fuel reactor temperature as40 F-←codisplayed in Figure 5.员10090一一C conversiong 80F- gas efficiency元70Fso中国煤化工Figure 3 Influence of temperature on the .gas concentrations in the air reactorMYHCNMHGThere are some CO2 in the flue gas from the airreactor. There can be two reasons for this presence.Figure 5 Influence of temperature on the carbonOne is the by-passing of CO2 gas from the fuel reactorconversion rate and gasification efficiencybed to the air reactor bed and the second reason is第8期HUSEYIN Sozen et al: Chemical-looping gasification of biomass in a 10 kW......929The gasification efficiency has showed similarby biomass syngas in the fuel reactor and then Fe, O,graphs to H2 as efficiency is decreased with decreasingis fully oxidized to Fe,O， in the air reactor. TheH2 productions.produced oxygen carriers can be used in a chemical3.2 0xygen carrier characterizationlooping gasification of biomass havinggoodThe air flow of the air reactor bed, N2 stream ofreproducibility and stability.the fuel reactor bed, and biomass feed are stoppedafter ending of the all experiment procedures. Thefreshoxygen carrier particles are collected, sampled andin__ Jiesi Jlsli _xcie ....sealed for characterization analysis after cooling of theafter 20 htwo reactor beds at room temperature.3.2.1 X-ray diffraction ( XRD )The fresh and used Fe2O3/ Al2O3-type oxides areafter 40 hexamined by XRD to identify the crystalline phasesformed. XRD patterns of the fresh ，reduced oxidesafter 60 hfor 20, 40, 60 h cycles are depicted in Figure 6.As can be seen from the Figure 6， theii iimin ......appearance of the oxygen carrier with the synthesis304(809020/(°) .JCPDS ( Joint Committee on Powder DiffractionFigure 6 XRD spectra for fresh and used oxygen carrier in aStandards) card have the best matching standarddual circulating fluidized bed unit from the air reactorFe2O3/ Al2O, characteristic diffraction peaks. And●: Fe2O3;■: Al2O; V: Fe,O, .after 20 ~ 60 h cycle peaks and fresh oxygen carrier toobtain a good match oxygen carrier indicating that3.2.2 SEM micrographsoxygen carrier after 60 h cycle does not change itsThe micrographs of the fresh and used Fe,O3/crystal form and no chemical change occur in the fuelAl2O3 are characterized by SEM. Before ( freshreactor. It also shows that the Fe2O3 phase of theones) and after 20, 40, 60 h the reacted oxygenoxygen carrier is completely reduced to Fe, O, phasecarriers pictures are exhibited in Figure 7.(a)GIEC80-84 2.0 kV 5.1 mmx15.0k SE(M)2013-3-18 16: 08 3.00 uGIEC80-592.0 kV 4.3 mmx15.0 k SE(M )2013- 10-12 10: 42 3.00 um中国煤化工YHCNMHGGIEC80-54 2.0 kV 4.4 mmx15.0 k SE(M)2013-10-12 10: 323.00 u GIEC80-90 2.0 kV 4.2 mmx15.0k SE(M)2013-10-1211: 283.00 uFigure 7 SEM analysis before and after the reaction of oxygen carrier(a): fresh; (b): after 20h; (c): after40h; (d): after 60 h30燃料化学学报第42卷The fresh Fe2O3/Al2O3 oxygen carrier is aboutexperimental results. Compared to BET analysis3 ~9 μm in irregular cubes and a gap exists betweenresults show no significant decrease in the specificthe porous particles. Al2O3 particles as inert supportsurface area .to Fe,O3 are distributed in the pores of the particle3.2.3 Specific surface area analysissurface of Fe2O3 as can be seen from the electronHigh internal surface area of the oxygen carriermicrograph in Figure 7( a). After 20 h the reactioncan help to promote the diffusion and capturizing Ocycle Fe2O3 oxygen carrier particle size becomesmolecular oxygen from air in the air reactor andsmaller and more orderly arrangement to attach to thedelivering the lattice oxygen in the oxygen carrier inaluminum oxide surface. The pores become morethe fuel reactor for fuel reductionand/orstructured and the surface area of oxygen carrierdecarbonization. Therefore, high specific surface areaincreases as shown in Figure 7(b). After 40 h cycle,of produced oxygen carrier is very advantageous forOxidative iron particle size is further reduced and thethe chemical looping gasification of biomass. Thesintering phenomenon is not observed. For the oxygenBET method is used for the analysis of the changes incarrier particles and the biomass, due to multiple airthe specific surface area of prepared oxygen carriersreact with the lattice oxygen and molecular oxygen inafter reduction reaction and as a fresh ( no used) inand out of channel gap, the oxygen carrier particlesthis experiment. The results are shown in Table 2. Aspromote the emergence of a porous shape than furthercan be seen from the table， after 20 ~ 60 h ofincrease the surface area， which helps to promotechemical looping gasification for biomass， oxygenchemical looping gasification of biomass with oxygencarrier surface area and the average pore size arcarrier as indicated in Figure 7 ( c ). After 60 hincreased. At the first cycle for 20 h they arecirculating oxygen carrier, part of the particle size isincreased more rapidly and then more slowly ，whichincreased, but still maintained a crystalline iron oxideis consistent with the experimental results of SEMparticles as seen in Figure 7( d). The oxygen carrieranalysis.activitydoes notdeclinebased onpreviousTable 2 BET surface area analyses for fresh and used oxygen carriersIron-based oxygen carriers BET-surface area A/(m2.g') Total pore volume v/( mL.g' )Average pore size d/ nmFresh O. C.1. 7270.00388.73After 20 h2.0220.006412.02After 40 h2. 7030.017025.22After 60 h2. 7670.02130. 37From the BET analysis it is found that the surfaceXRD and BET. The CO and H, concentrations arearea, total pore volume and average pore size of theincreased relative to the increase of the temperature ofiron-based oxygen carrier are increased after thethe fuel reactor, and CO2 concentration decreases withreaction in fuel reactor. There is no decreased reactivethe increase of the temperature of both the fuel and airoxygen carrier and10significantsinteringreactor. The H2 concentration reaches the highestphenomenon. Therefore， the synthesis gas fromlevel at 870 C. Biomass gasification efficiency andbiomass with the iron-based oxygen carriers has goodcarbon conversion increases accordingly with thereaction stability after 60 h cycle reaction. Thus, theyincrease of the temperature of the fuel reactor. Acan be used as oxygen carrier in biomass chemical900 C gasification efficiency is 78% and carbonlooping gasification.conversion efficiency is near to 90%. The feedingrate of biomass in the fuel reactor should match the4 Conclusionsamount of oxygen carrier circulation. After 60 h theIn the present study， a novel interconnectediron-based oxygen carrier does not show polymorphfluidized bed device for chemical looping gasificationchan中国煤化工ce area. There is noof biomass with man made low cost oxygen carriers issigniphenomenon. Theredeveloped. The effect of the reactor temperature onis nMHCNMH Giheperformance of thethe flue gas composition, gasification efficiency andreduction reaction, indicating that it has good stabilitycarbonconversionrateare experimentallyand resistance to sintering， and is suitable as ainvestigated. The characterizations of the fresh andchemical looping gasification of biomass with theused iron-based oxygen carrier are studied by SEM ,iron-based oxygen carrier.第8期HUSEYIN Sozen et al : Chemical-looping gasification of biomass in a 10 kW......931References[1] RODHE H. A comparison of the contribution of various gases to the greenhouse efect[J]. Science, 1990, 248 (4960): 1217-1219.[2] MATTISSON T, GARCIA-LABIANO F, KRONBERGER B, LYNGFELT A, ADANEZ J, HOFBAUER H. Chemical-looping combustionusing syngas as fuel[J]. Int J Greenh Gas Con, 2007, 1(2): 158-169.[3] MATTISSON T, LYNGFELT A, CHO P. 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