Multistage Circulation Absorption Improvement: Simulation and Energy-Saving Evaluation of an Innovative Amine-Based CO2 Capture Process

High energy consumption poses a critical challenge in the context of postcombustion CO2 capture (PCCC) processes. In this study, an innovative approach with a multistage circulation (MSC) process was proposed, which divided the absorber into three vertically arranged stages, each performing different functions, including CO2 efficient capture, CO2 absorption enhancement, and CO2 enrichment. The analysis using the rate-based model in Aspen Plus was conducted. Compared to the conventional process, the MSC process resulted in an increase in the CO2-cycling capacity and a reduction in regeneration duty. Several key parameters, including piperazine (PZ)/N-methyldiethanolamine (MDEA) ratio, CO2 capture rate, intercooling temperature, CO2 lean loading, and stripping pressure, underwent optimization. Additionally, modifications, such as rich solvent split and lean vapor recompression, led to a further decrease in regeneration duty. Through combining parameter optimization and process modification within the MSC framework, a low regeneration duty of 2.16 GJ/t CO2 was achieved, a reduction of 28% compared to the conventional process. Correspondingly, the total equivalent work was reduced to 0.211 MW h/t of CO2, representing a reduction of 11%. Finally, improvements for further reducing the regeneration duty based on the MSC process were proposed. This study has shown a novel method for designing PCCC system, offering important implications for achieving energy-efficient carbon capture.