The control of the vacuum swing adsorption process for air separation

Control of pressure and vacuum swing adsorption systems is challenging due to the unsteady state nature of the processes and the high degree of system non-linearity. System purity. flow rates and pressure must be regulated to within small tolerances to ensure compliance with customer requirements. Traditionally, industry has applied multiple, individual PID controllers to pressure swing plants to provide the required control. However, control problems in the field have arisen due to the fact that the plants operate in a batch-like manner and are highly non-linear resulting in PID loop interaction and instability. This paper describes the experimental operation of the oxygen VSA process, with the PID scheme implemented on a pilot scale VSA plant and shows the open and closed-loop response of system purity, flow rate and process pressures to changes in external and internal disturbances. Limitations of the PID scheme are highlighted.