Multi-stage solvent circulation absorption enhancement: System optimization for energy-saving CO2 capture

One of the major barriers in industrial applications of solvent-based CO2 capture is the significant energy consumption required for absorbent regeneration. In this study, a novel multi-stage circulation (MSC) CO2 absorption process was proposed, which implemented independent regulation of each stage, resulting in enhanced CO2 capture performance and reduction of CO2 regeneration duty. The MSC absorber was designed with four stages from bottom to top, each serving distinct functions, including CO2 enrichment, CO2 main absorption, CO2 capture efficiency enhancement and aerosol capture. Simulation of the MSC process achieved a rich ethanolamine (MEA) solvent CO2 loading of 0.512-0.570 mol CO2/mol amine, which was 8.1 %-9.9 % higher than typical process. The effects of test duration, amine solution flow rates, reaction temperatures and inlet CO2 concentrations on CO2 absorption performance were studied using the MSC experimental platform. The CO2 regeneration duty reduced by over 13.2 % of the MSC process compared to a typical process using 25 wt% MEA solution and by over 22.9 % using piperazine (PZ)/N-methyldiethanolamine (MDEA) solution. Furthermore, the utilization of NH3/K2CO3 solution achieved an energy consumption reduction of over 41.7 %, resulting in a CO2 regeneration duty as low as 2.02 GJ/t CO2 (1.84 GJ/t CO2, subtracting the heat loss). Meanwhile, potential strategies for optimizing parameters of MSC process were proposed to address the complex and volatile conditions.