Syngas Production Via Chemical Looping Gasification Of Biomass And Reforming Of Tar With Cu/Ni/Olivine

With the increasing shortage of fossil energy and environmental pollution,biomass as a clean renewable energy has attracted great attention in the world.Biomass chemical looping gasification(CLG)technology is one of the novel technology of biomass energy.Biomass CLG technology can not only make full use of renewable energy and reduce the use of fossil energy,but also improve the utilization efficiency of biomass and reduce pollution emissions.The oxygen carrier(OC)plays an important role during the biomass CLG process acts as oxygen carrier and tar destruction catalysis.In this thesis,the CLG of cotton stalk from Xinjiang province were carried out with Cu/Ni/Olivine under different gasification condition.The steam reforming of tar with toluene as a model compound has been carried out using Cu/Ni/Olivine as catalyst.Firstly,bimetallic Cu/Ni/Olivine OCs were prepared with impregnation method for CLG.The OCs characterized using BET,SEM,XRD and TPR to investigate the physicochemical property of OCs before and after CLG.The cyclic redox behaviors and oxygen carrying capacity(Ro)of OCs were evaluated by thermo-gravimetric analysis(TGA).Result shows that the anti-sintering ability of the oxygen carrier gradually improved with the increasing Cu/Ni ratio.The Olivine behaves as suitable OC support with oxygen carrying capacity(R_o=1.07).The redox reactivity of all of the OCs kept well during multiple redox cycles.The Ro of OCs progressively increased with the Cu/Ni ratio.The CLG has been carried out with Cu/Ni/Olivine as oxygen carrier,using Xinjiang cotton stalk as biomass material,in fixed reactor.The effect of Cu/Ni ratio,gasification temperature,steam to biomass ratio(S/B),oxygen carrier to biomass ratio(OC/B)on CLG of cotton stalk has been studied in a fixed bed.By comparing the product gas concentration,carbon conversion,H₂+CO yield and gas yield over the invested OCs,the Cu9/Ni6/Olivine was found to demonstrate the best comprehensive CLG performance due to the synergistic effect of Cu and Ni.The maximum gas yield,H₂+CO yield and carbon conversion with Cu9/Ni6/Olivine can be obtained at the S/B of0.8 and OC/B of 2.Compare to theoretical value,65%of lattice oxygen has been supplied by Cu9/Ni6/Olivine during actual CLG process.Besides,the Cu9/Ni6/Olivine OC displayed better reactivity due to basic crystalline phase being preserved well during multiple CLG cycles.The steam reforming reaction of toluene(biomass model tar compound)with the Cu/Ni/Olivine was studied.The effects of Cu/Ni composite ratio,reaction temperature,steam to carbon ratio(S/C),liquid hourly space velocity(LHSV)on the activity of the catalyst were investigated.The stability,regeneration and repeatability performance of the Cu3/Ni12/Olivine catalyst were investigated under the optimal conditions.The results show that Olivine using as catalyst shows a certain catalytic activity.The increase of Ni/Cu ratio was favorable for the improvement of the catalytic performance of the catalyst,and exhibits a certain synergy.The appropriate addition of steam has a better effect of removing carbon deposition,which was beneficial for the activity.When the steam is stopped from addition,the coke deposition attached to the catalyst surface will quickly result in deactivation of catalyst.The appropriate S/C is helpful to eliminate carbon deposition.The increase of the reaction temperature can significantly improve the catalytic performance of the catalyst.The Ni12/Cu3/Olivine catalyst exhibited better catalytic stability and reusability in toluene steam reforming reaction.In addition,the characterization method such as XRD,SEM,TG,Raman were applied to analysis the composition,structure,carbon deposition content and carbon deposition type of the spent catalyst.The results show that the active components Cu and Ni of the spent catalyst exist as the form of metallic Cu and Ni,which can promote the steam reforming reaction of toluene well.The coupling of Ni and Cu elements exhibited a good anti-coking performance and catalytic activity of tar catalytic conversion.The proper steam and high temperature are conducive to the carbon removal reaction.The catalytic activity is not only affected by the amount of carbon deposited on its surface,but also by the type of carbon deposition.The main reason of catalyst deactivation is ascribed to massive formation of graphite-type carbon.