Transient model, simulation and control of a single-effect mechanical vapour compression (SEMVC) desalination system

Desalination is a highly complex process, which requires an efficient and accurate control system in the plant to maintain operation at optimum conditions that result in energy savings and in preventing scale formation. A study of a multi-input multi-output (MIMO) control of mechanical vapour compression desalination systems is presented. A transient model was developed to describe the significant dynamics of a vapour compression desalination system. A dynamic model was simulated using the Matlab program to provide physical insight into the system’s dynamic behavior. Two efficient PID controllers for both distillate and evaporation temperature were developed to attain good performance.

Simulation results confirm that the PID controller presents a significant improvement of MVC operation and is adequate to overcome the effect of inlet mass flow rate disturbance and set point tracking of the distillate mass flow rate. It is shown that it is feasible to use two controllers to protect MVC from disturbance and secure the target value of distillate; at the same time, energy conservation is secured via two manipulated variables — vacuum pressure and pressure of superheated vacuum.