Process simulation of multi-stage chemical-looping combustion using Aspen Plus

In recent years, Chemical-looping combustion (CLC) is increasingly being considered as a promising technology to increase the efficiency of carbon capture in coal-fired power plants and for reducing CO2 emissions into the atmosphere. The char gasification step required in the CLC process when using solid fuels such as coal is slow and often incomplete, which limits the rate of fuel conversion. The concept of multi-staged fuel reaction is proposed as an improvement to the original CLC concept to address this issue. System-level simulations of the single-stage, two-stage and four-stage CLC processes are conducted in Aspen Plus using a plug flow reactor model for the gasification step to incorporate the reaction kinetics into the simulation. By varying the reactor size and examining the char conversion and net energy output, the optimum reactor size for each multi-stage configuration is determined. The effect of multi-staging on the exhaust composition is also investigated. The results of the simulations show that multi-staging allows the use of multiple smaller reactors with the same total volume without incurring any penalty on the net energy output.