Characteristics Investigation On Biomass Chemical Looping Gasification In Multicomponent System Based On Fe₂O₃ And Composite Oxygen Carriers

Chemical looping gasification?CLG?,as a promising technology for carbon capture,mainly converts hydrocarbons into combustible syngas with the oxygen provided by oxygen carriers,and has received attention in the application of biomass energy.When iron-based oxides are used as oxygen carriers,the concentration of H₂ and CO in the syngas can be increased.Therefore,it is significant to further investigate CLG of biomass based on iron-based oxygen carriers.In this paper,the iron-based oxygen carriers were used in the fixed-bed reactor to study the influencing factors such as temperature,oxygen carrier,steam and CaO in CLG of straw.Compared with straw pyrolysis,the oxygen carrier Fe₂O₃ proved advantageous to the secondary gasification reaction to form CO and CO₂ in CLG,and improved the gasification efficiency and carbon conversion rate,reaching 62.57%and 86.85%?900??respectively.It was also found that CO was further oxidized to CO₂ at high Fe₂O₃/C molar ratio,which resulted in a decreased gasification efficiency and low heat value of syngas.Therefore,a conclusion was drawn that the most optimized Fe₂O₃/C molar ratio was 0.2.In addition,the alkali metals in the biomass evaporated as KCl and NaCl into gas phase and retained as alkali metal oxide at high temperature,resulting in coking,slagging and heating surface corrosion.In the mean time,the oxygen carrier was mainly converted to Fe and sintering phenomenon was serious at high temperature.Therefore,the most optimized temperature was set to 800°C in order to ensure the performance of the oxygen carrier and gasification efficiency.Based on the previous research,steam and CaO were added to CLG,and found that the addition of steam facilitated both the reforming reaction and water gas shift reaction to produce more gaseous products,especially H₂.Depending on gas yield and gasification efficiency,the requirement of steam was sufficient for CLG at steam flow n=0.6 r/min.It was also confirmed that CaO had a positive effect in gasification and the addition in the ratio of CaO/C=1 was adequate for syngas production.Moreover,CaO mainly played a role as CO₂ absorbent at low temperature but as catalyst above 700°C.However,the catalysis of CaO received the major attention because of its availability for high syngas yield?1.367m³/kg?and efficiency?gasification efficiency was 88.81%and carbon conversion efficiency was 89.28%?at 800°C.CaO was found to retard the sintering and porosity reduction of Fe₂O₃,the oxygen carrier,by covering Fe₂O₃ and forming calcium ferrites during multiple redox cycles.In order to improve the stability of the oxygen carrier and in view of the action of calcium ferrite Ca₂Fe₂O₅,the composite oxygen carriers Ca₂Fe_2-xMn_xO₅ were prepared via sol-gel method.In TG-FTIR analysis,it was found that Ca₂Fe_2-xMn_xO₅ promoted the secondary cracking reaction in CLG.In the late reaction stage,CO₂ reacted with C to form CO,which caused slightly lag of CO release.Moreover,doping a small amount of Mn helped to reduce the reaction temperature of the secondary gasification and increase the selectivity of syngas,but doping a large amount of Mn did not have a significant effect.In multiple redox cycles of Ca₂Fe₂O₅ and Ca₂Fe_1.9Mn_0.1O₅,it was found that the anti-sintering performance of both is better than that of Fe₂O₃,and Ca₂Fe_1.9Mn_0.1O₅ had advantages in terms of syngas selectivity and gasification efficiency.