Vacuum pressure swing adsorption system for N₂/CO₂ separation in consideration of unstable feed concentration

In this study, an efficient PID control system has been designed for a vacuum pressure swing adsorption (VPSA) process which used silica gel to capture CO₂ from dry flue gas. Changes of CO₂ composition in feed gas are set as disturbances and vary from 12.0 to 15.0% to make simulation work more closely to reality. Meanwhile, adsorption step time duration was set to change consistently according to the feedback of CO₂ purity in product. PID control strategy built in software gPROMS is employed in this paper. The competence of the control system is firstly analyzed by a transient impulse of CO₂ content in feed gas (15.0% dropped to 12.0%). Then random pulse is added to test the ability of the control system to reject the unknown disturbances and track the set point. Detailed changes in bed under open and closed-loop are listed and made comparisons. Results demonstrate that the model shows an enhanced performance in the presence of random disturbances under closed-loop control compared with the open-loop operation. And this proves that closed-loop feedback PID control can be used to improve the CO₂ capture of VPSA process operations.