Model based control for reverse osmosis desalination processes

Computer simulations were performed using the Dynamic Matrix Control (DMC) algorithm for the control of a reverse osmosis (RO) desalination pilot plant. The plant dynamics were modeled by the use of empirical transfer functions developed at the Kuwait Institute for Scientific Research. The two output variables considered were: production flow rate and product water electrical conductivity as a measure of purity. With the selection of proper tuning constants the DMC approach allows for substantial improvement over proportional-integral (PI) control based on the integral square error (ISE) performance criterion. A setpoint change in production flow rate was considered in the simulations since this type of change is the one most likely to occur in an RO plant. For the same magnitude setpoint change in flowrate, the ISE results for the flowrate were comparable between the two controllers; however, the ISE results for conductivity were substantially better using DMC control. The ISE for conductivity using the PI controller is 1688.92 while for the DMC controller, with the proper tuning parameters the ISE may be much less than 1.0. These results indicate that much more flexibility in the operation of an RO plant is available with DMC control.