Process control in water desalination industry: an overview

Process control is an essential part of the desalination industry that requ ires for operation at the optimum operating conditions an increase in the l ifetime of the plant and reduction of the unit product cost. A review is pr esented for the commonly used and newly developed control and instrumentati on in MSF and RO plants. Process control may be as simple as an on/off valv e that is triggered upon offset of the system measured parameters from the desired set-point. More classical and commonly used controllers have combin ed proportional, integral, and derivative (PID) systems. Also, proportional /integral (PI) controls are used in industry. Controls selection aims at fa st response, high stability, and minimum disturbance to the system. Less co mmon controllers include fuzzy logic-based systems. Early testing of such s ystems shows the need for mathematical analysis of various control loops wi thin the plant, development of control rules, and development and testing o n industrial scale. Supervisory systems such as model predictive control ar e also considered to obtain an integrated control systems of the whole plan t. It should be stressed that although the desalination plants are highly c omplex, accurate and detailed mathematical models for steady state and proc ess of various desalination processes are found in the literature. Such mod els are necessary for studying plant performance, various control strategie s, and forms an essential part for any serious analysis and development of novel and new control systems.