Numerical Simulation Of Char Burnout Process Under Oxy-fuel Combustion Conditions

Oxyfuel technology is currently effective techniques for CO2 capture and emission reduction. The paper studied the carbon burnout process under oxyfuel combustion condition, and developed a carbon burnout model suitable for oxyfuel combustion, and discussed the impact of pressure, which laid the foundation for the study of elevated pressure oxyfuel combustion technology. Contents include the following three parts:Firstly, based on the carbon burnout kinetics CBK model, the model was modified in aspects of the gas physical parameters, diffusion coefficient and react ion mechanism, and then compared with experimental results to validate the model accuracy and applicability.Secondly, basing on the modified model, the paper simulated the burnout process of Datong coal under O2/N2 and O2/CO2 atmosphere and compared with the pulverized coal burnout experiments on the flat-flame flow reactor system, and then analyzed the influence of reaction atmosphere, oxygen concentration, particle size, coal rank and coal gasification reaction on the burnout process under oxyfuel conditions. The results showed that increasing oxygen concentration, using low rank coal or reducing particle size could improve coal char burnout characteristics; compared to conventional air combustion, gasification reaction had significant contribution to char burnout under oxyfuel conditions, and the contribution of the gasification reaction increased with the decrease of the oxygen concentration, or with the increase of gas phase temperature.Finally, the paper simulated Datong coal burnout process under pressurized oxyfuel combustion conditon, and then detailly analyzed the impact of environmental pressure on char conversion characteristics, particle temperature, particle size, particle burning rate and gasification reaction contribution. It was found that under the circumstances of a certain reaction gas volume ratio, increasing the environmental pressure contributed to coal burnout, and could accelerate the consumption of coal particles, which led to the decrease of particle size. And under different background atmosphere, coal particle temperature and particle burning rate showed different trends: Compared with atmospheric oxyfuel combustion, the contribution of gasification reaction under pressurized oxyfuel combustion was obviously larger and increased with the improving environmental pressure.