Model reduction and robust control of multi-stage flash (MSF) desalinationplants

An orthogonal collocation method is used for the reduction of a large nonli near model of a multi-stage flash (MSF) desalination plant. The real plant located in Saudi Arabia consists of 19 stages in the heat recovery section and three in the heat rejection section. It is shown that three collocation points, i.e., two for the heat recovery section and one for the heat rejec tion section, are sufficient for a good representation of the full-order mo del for both steady-state and dynamic behavior. The reduced model is then u sed for a robust controller design of the plant using a constrained nonline ar model predictive control (NLMPC) strategy. Numerical simulations show th at the controlled system obtained when the reduced model is used for output prediction yields the same performances as with the full-order model but w ith a considerable reduction in the computational time and a much easier tu ning of the controller.