Using expansion units to improve CO2 absorption for natural gas purification - A study on the hydrodynamics and mass transfer

Abstract

Abstract The usage of capillary tubes for CO2 absorption suffers from small residence time, which leads to reduced performance for large throughput. This work presents a method of connecting expansion units to capillary tubes to serve as a residence time delayer. The effect of the expansion unit on gas–liquid hydrodynamics, pressure drop and mass transfer coefficient (kLa) are investigated under various operating pressures up to 4.0 MPa, for both physical and chemical absorption. A novel periodic jetting flow is found in the expansion unit, which can intensify the CO2 absorption. Experimental results show that the strategy can significantly decrease the pressure drop while maintaining the absorption performance to a large extent. The overall kLa for physical and chemical absorption are correlated to pressure drop, respectively. Besides, CO2 loading in rich absorbents increases dramatically compared to literature studies with only micromixers or capillary tubes, which is beneficial to regenerate solvent. The study verifies the concept that pre-treatment with water can largely reduce the usage of amines, and can also provide a guide for process design in natural gas purification such as biogas recovery.