Experimental and Simulation Study on CO2 Adsorption Dynamics of a Zeolite 13X Column during Blowdown and Pressurization: Implications of Scaleup on CO2 Capture Vacuum Swing Adsorption Cycle

A 13X column vacuum swing adsorption (VSA) has been widely studied as a promising separation process for postcombustion carbon capture, as it has been claimed that it would be more economical than conventional amine capture processes. To advance its commercial application, however, it is crucial to have VSA achieve an excellent bed productivity, well beyond the current level, to enable the process to work for a larger CO2 emission plant in an affordable size. From the perspective of adsorption process design, its bed productivity could be improved by reducing the adsorption cycle time. In other words, the pressure change between adsorption and desorption steps must take place as quickly as possible. In this study, CO2 adsorption dynamics of a 13X column during the pressure-changing steps, i.e., blowdown and pressurization, were investigated by both experiments and numerical simulation. As a result, it transpires that the blowdown time must be extended greatly with increasing column length due to the pressure change being hindered by the pressure drop building up inside the column. In the stark contrast, the pressurization time is rarely affected by the column length, but it can be controlled easily by the rate of pressure change on one column end. This result implies that the bed productivity would be compromised greatly in scaling up a 13X VSA, because of the cycle time having to be extended long enough to accommodate the stretched blowdown time. To address this scale-up issue, we proposed an adsorption column design technology that involved stacking low-height, packed-bed adsorption modules vertically. The new adsorption column design paved the way for enabling a 13X VSA to achieve as high a productivity as its lab-scale unit, no matter what size it is to be scaled up to, without having to adjust the bead size.