Experiment And Molecular Modelling Of The Reaction Process And Mechanism Of Key Organic Components In Biomass During Chemical Looping Combustion

The efficient conversion and clean utilization of biomass resources are of great importance in the fields of energy resources,ecological environment,and sustainable development.As a renewable energy source of large reserves,wide distribution,and carbon neutral combustion,biomass can effectively alleviate the world energy crisis,reduce greenhouse gas emissions,and is expected to achieve partial replacement of traditional fossil energy.Chemical looping combustion can significantly reduce energy consumption and efficiently achieve carbon separation and capture.Applying biomass to chemical looping technology will help mitigate the greenhouse effect and achieve efficient use of biomass.In this work,the depolymerisation process and microscopic mechanisms of chemical looping combustion of key organic components in biomass are systematically investigated using thermal analysis,in situ infrared,reaction kinetic analysis,and molecular dynamics simulations,taking cellulose,xylan,and lignin as the key organic components in biomass.The main conclusions are as follows:1.The combustion characteristics of key components from biomass during chemical looping depolymerization were dynamically analyzed using in situ infrared and thermogravimetric analyzers.The experimental results showed that the CO2 peaks of the key biomass components were significantly enhanced during the chemical looping combustion process,indicating that the Fe2O3 oxygens released increased from the increase in temperature,which promoted the combustion of biomass.The results of TGA study showed that the addition of Fe2O3 could reduce the onset temperature of biomass cracking,and the lattice oxygen released from Fe2O3 could promote the depolymerization of biomass.The chemical looping depolymerization processes of biomass key components were all divided into three stages:volatile analysis out and combustion stage,semicoke conversion combustion stage and coke combustion stage.And the kinetics of chemical looping combustion reactions to key components of biomass were studied by model-free and modeling methods.The results showed that activation energy of the three polyme during the chemical looping depolymerizationr was mainly due to the different degrees of reduction of the main biomass components to the oxygen carriers.The chemical looping combustion process of key biomass components was visualized using the ReaxFF MD method.It was found that the biomass components generally during chemical looping depolymerization followed the free radical chain reaction theory.After the addition of Fe2O3,the reactive radicals generated by biomass cracking reacted with the lattice oxygen released from the oxygen carrier to generate CO2 precursor molecules,and then further radical reactions occured to generate CO2.The complex reaction network of CO2 generation and release during biomass chemical looping combustion under the action of iron-based oxygen carriers was finally obtained.2.The effect of blending ratio to the mixed combustion performance of key biomass components and their synergistic effect was investigated using a thermogravimetric analyzer.The results showed that the TG-DTG curves for the combustion of cellulose with xylan and cellulose with lignin could be obtained by linear summation of the TG-DTG curves for the depolymerization of cellulose,xylan and lignin alone,respectively.The interaction between xylan and cellulose was enhanced with the increase of xylan blending ratio.The mixed fraction of cellulose and lignin produced a facilitation effect between the two in the main combustion phase(190～607℃),and the facilitation effects increased from the increase in the blending ratio.The interaction between the two weakened in high temperature environments(607～647℃).The activation energies of cellulose/xylan and cellulose/lignin at different blending ratios were calculated by model-free method.Xylan blending ratio of 60%was the most suitable mixing ratio,E value was the smallest.Co-combustion of cellulose with lignin increased the activation energy during combustion.Fourteen solid-solid reaction kinetic models were used to investigate the different mechanistic functions of the different stages of the mixed components.