| Facing the increasingly serious fossil energy crisis and environmental pressure,it is urgent to find suitable renewable energy as a substitute for fossil energy.Biomass energy,as a renewable energy source with a wide range of raw materials,low cost and low pollution,is more and more favored by researchers from all over the world.At present,the domestic chemical looping gasification technology is mainly used in the direction of coal combustion and gasification.The research on biomass chemical looping gasification technology is not deep enough,so the research of biomass chemical looping gasification technology is of great significance.In this paper,a combination of impregnation and mechanical mixing is used to prepare composite oxygen carriers with different ratios of Fe2O3/CaO.The effect of adding CaO on the gas composition of chemical looping gasification is compared in a fixed bed reactor,which screen out the best ratio of Fe2O3/CaO,and then the oxygen carrier recycling performance test was carried out to determine the regeneration and recycling performance of the CaO/Fe2O3 composite oxygen carrier.And the effect of biomass raw materials,reaction temperature,mass ratio of steam to biomass,and mass ratio of oxygen carrier to biomass on the components of biomass chemical looping gasification products and greenhouse gas emissions were studied.Then,the oxygen carriers before and after the reaction were characterized,and the reaction mechanism of chemical looping gasification was analyzed by comparing with the experimental results.Finally,the effect of different additives(CuO,MgO,NiO,K2CO3,ZnO)on the corn straw chemical looping gasification experiment was investigated.The experimental results show:(1)The addition of CaO can significantly increase the quality of syngas.The content of H2 in the syngas is significantly increased(from 30.8%to 47.3%),and the content of the main components(H2,CO)of the syngas has increased significantly(from 61.8%to 75.4%),accompanied by a reduction in greenhouse gas content from 38.3%to 24.6%).CaO promotes the decomposition of tar in the gasification process into H2 and small molecular aromatic hydrocarbons.However,more CaO will also adhere to the surface of the oxygen carrier,which results in the content of CO and CH4 is reduced.When CaO/Fe2O3=2,the CaO/Fe2O3 composite oxygen carrier is more active in the chemical looping gasification reaction of corn straw,and plays a strong role in carrying lattice oxygen,catalyzing tar cracking,and absorbing CO2.(2)When corn straw are used as biomass raw materials,the content of H2 in syngas can reach 49.11%.High temperature can promote the pyrolysis reaction(endothermic reaction)of the biomass,and the high temperature can also promote the oxygen carrier’s ability to release lattice oxygen and the catalytic ability,thereby increasing the gas yield.The adsorption effect of CO2 by CaO mainly occurs in the low temperature stage.When the temperature is too high,the adsorption weakens.Steam can achieve the effect of adding hydrogen and oxygen to the chemical looping gasification reaction of corn straw.Thereby increasing the H2 yield and syngas yield,at the same time,steam can increase the degree of water vapor shift reaction.The addition of oxygen carrier can provide sufficient lattice oxygen for the gasification reaction,and has the effect of promoting the reaction,but excessive amount of oxygen carrier will reduce the content of H2 and CO in the syngas,and increase in the content of greenhouse gases.When the mass ratio of oxygen carrier to biomass(OC/B)is 1,the H2/CO in the syngas reaches its peak,and the syngas yield is the highest at this time.(3)Through XRD,SEM,and BET characterization methods,it is found that the effective components(CaO and Fe2O3)in the fresh CaO/Fe2O3 composite oxygen carrier are evenly distributed.As the times of reaction increasing,the CaO and Fe2O3 of the CaO/Fe2O3 composite oxygen carrier will become Ca2Fe2O5 crystals,which can still play the role of the fresh oxygen carrier.At the same time,combined with the experimental results to analyze the chemical looping gasification that the fresh oxygen carrier and the regenerated oxygen carrier participate in.The gas composition and content in the reaction products did not change much;the XRD patterns of the composite oxygen carrier with,different additives showed that the reaction of K2CO3,CuO,NiO and the CaO/Fe2O3 composite oxygen carrier produced new compounds,which may affect the role of CaO/Fe2O3 composite oxygen carrier in the chemical looping gasification reaction of corn straw. |
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