Thermodynamic analysis of a waste heat utilization based efficient liquefaction and low-temperature adsorption carbon capture hybrid system

Abstract

Cryogenic CO2 capture can obtain high-pressure and pure CO2, but existing methods are inefficient as they usually discharge the waste heat of refrigeration. Therefore, a new hybrid system is proposed to recycle the waste cooling, heat, and uncondensable CO2 of liquefaction CO2 capture into low-temperature adsorption CO2 capture. This enhances the overall energy efficiency and the CO2 recovery rate over existing cryogenic CO2 capture without external input. Moreover, it enables practical sub-zero temperature CO2 adsorption while lowering the desorption temperature to 70 °C. This system is analyzed by coupling the liquefaction CO2 capture and low-temperature adsorption CO2 capture thermodynamic models, whose heat and cooling needs are compared to that available by a vapor compression cycle. Results show that for 10% mol. CO2 flue gas, the proposed system is optimal at −53 °C and 5 MPa to yield a 2nd law efficiency of 9%, a CO2 recovery rate of 80%, and specific energy consumption of under 1.65 MJ/(kg of CO2). As the cooling demand is typically twice the heat needed for sorbent regeneration, a vapor compression cycle designed to meet the former can naturally meet the latter. Ultimately, the new hybrid system represents a new carbon capture technology with better potential to achieve carbon neutrality via waste heat utilization.