Feedforward control of a binary high purity distillation column

Feedforward and PID-SISO feedback control are compared on a pilot plant scale distillation column which is operated in the LV-configuration. For the rejection of disturbances in the feed concentration, a simple empirical feedforward control algorithm is presented. Final steady-state values of the manipulated variables are computed from quadratic equations in x(F), which are easily fitted to simulation or plant data. Experimental results for PID-and feedforward control are compared. The need for dynamic filtering of manipulated variables is demonstrated. While direct setting of the manipulated variables may disturbe the system unnecessarily, second order filtering achieves very fast disturbance rejection. The impact of errors in the disturbance measurement on the control performance is investigated. The feedforward algorithm is intentionally kept simple, to allow easy implementation on a standard decentralized control system.