Performance evaluation and optimization of the MSF desalination plant

In this chapter, a steady state mathematical model for multistage flash (MSF) desalination plants is developed. The model is based on basic principles of physics and chemistry that describe the physical phenomenon occurring in the process. The input plant parameters that are known to affect the performance of the MSF desalination plant are taken into account in the construction of the model. These parameters include makeup flow, brine recycle flow, seawater flow, seawater temperature, seawater concentration, top brine temperature, steam temperature and the plant load. For each stage, the developed model predicts the temperatures of the brine, distillate and cooling brine, and the flow rates of brine outlet and distillate production. For the purpose of this study, one of the MSF plant is selected for investigation. The developed model is evaluated with the MSF plant vendor simulation results and its actual operating data. Model predictions matched well with the vendor simulation results and the plant operating data. Thus, the developed model is sufficiently accurate and model predictions will be reliable over complete operating plant range. The developed model is thus used to carry out the optimization of the MSF plant performance with an objective to maximize its performance ratio or maximize its distillate production rate. It was found that the main variables that affect the performance of the plant were the top brine temperature and the brine recycle flow rate. This model can be used for determining the optimum controller's set points of a running MSF desalination plant at different loads to maximize the water production or minimize the energy consumption or any other required objective function. This model can be integrated with the plant control software, and the optimum set points for controllers can be evaluated off line whenever plant loads are changed or management requirements change.