Analysis of direct capture of CO 2 from ambient air via steam-assisted temperature–vacuum swing adsorption

Abstract

In this work, direct air capture (DAC) via adsorption is studied through the design and analysis of two temperature–vacuum swing adsorption (TVSA) cycles. In the first part, a novel way of describing the adsorption of CO 2 in presence of water vapor is proposed for co-adsorption kinetic and thermodynamic data gathered from the literature. Secondly, two TVSA cycle designs are proposed: one with a desorption step via external heating, and one with a steam purge. A schematic method for the determination of the cycle step times is proposed and a parametric study on the operating conditions is performed via cycle simulations using a detailed, first principles model. Finally, the two cycles are compared in terms of CO 2 production and energy consumption. The parametric study on the desorption time shows that there is a desorption time yielding the highest CO 2 production at low energy consumptions. Low evacuation pressures are necessary to reach high CO 2 production, but higher evacuation pressures show to be always favorable in terms of specific electrical energy requirements. A steam purge requires an additional thermal energy cost, but it not only allows decreasing the specific electrical energy consumptions, it also enhances CO 2 desorption kinetics and allows reaching higher CO 2 productions at milder evacuation pressures. The results of this work present the possibility to directly relate the availability of power and heat to the design of the cycle.