Study On Gas-solid Flow And Reaction Characteristics Of Coal Chemical Looping Combustion In A Double Circulating Fluidized Be

China’s coal-dominated energy structure is unlikely to be replaced in the short term.Efficient CO₂ capture and clean utilization in the process of coal combustion is an effective way to achieve"carbon peak"and"carbon neutrality".Chemical looping combustion（CLC）is a technology that can capture and utilize CO2 efficiently.In this work,a multiphase particle-in-cell（MP-PIC）method is established to investigate the heat transfer property and internal reaction dynamics of CLC system in the pilot-scale three-dimensional dual-circulating fluidized bed model with ilmanite as oxygen carrier and coal as fuel.By comparing the experimental data with the simulation results,the feasibility of the selected model is verified.The multi-scale gas-solid phase fluid dynamics and interphase heat and mass transfer characteristics in the CLC process are revealed.The main conclusions are as follows:The solid phase heat and mass transfer characteristics involved in the CLC process in the full loop of the double circulating fluidized bed are systematically studied,and the influence of different operating parameters on the solid heat and mass transfer characteristics of the whole CLC system is analyzed.The results show that the EMMS-Matrix drag model combined with reaction kinetics successfully predict heterogeneous flow structures and the CLC process.Pol ydispersity by thermochemical conversion gives rise to the size-induced segregation phenomenon in the apparatus.Feeding ports of coal and char respectively in the FR and AR perform significant influences on the thermochemical quantities of particle species.Generally,The temperature in the AR is higher than the FR.The coal HTCs from 50 W/（m²·K）to 300W/（m²·K）occupy more than 90%,demonstrating the uniform heat transfer performance in the FR.The oxygen carrier HTC rapidly decreases to the value of about150 W/（m²·K）and then increases to the peak value at the height of z/Z=0.3.The solid residence time（SRT）distributions of oxygen carriers show an early peak with a long tail.Enlarging the gas flow rate in the AR and the size of the oxygen carrie r increases the residence time of oxygen carriers in the FR.A larger gas flow rate in two reactors causes smaller residence time because oxygen carriers.The thermophysical and chemical properties of gas-solid two-phase reactor are studied,and the influence of various operating parameters on the thermophysical and chemical properties of the whole CLC system is analyzed.The results show that:The results show complex distributions of gas and solid fluxes in the region close to the riser inlet,due to the vigorous gas-solid interactions and the solid material exchanged.Solid back-mixing close to the wall can be observed.The combustible gas species is the largest close to the feeding port and decreases along with the FR height.Along with the bed height,the gas temperature increases in the AR but decreases in the FR,respectively.As compared with other operating parameters,the gas flow rate obviously affects the temperature distribution and the species content in two reactors.In conclusion,it is reasonable to use the MP-PIC model to explore the thermodynamic and hydrodynamic characteristics of CLC process in a circulating fluidized bed.The numerical simulation results of current work have certain guiding significance for the design,operation and optimization of CLC units in the actual engineering process.