MODELING, SIMULATION, OPTIMIZATION AND CONTROL OF MULTISTAGE FLASHING(MSF) DESALINATION PLANTS .1. MODELING AND SIMULATION

Multistage flashing (MSF) processes can be represented by both steady- state and dynamic models. The former is a useful tool for the design, understanding and optimization of existing as well as new plants. Dyna mic models are required for solving problems in the transient phase. T his, in turn, includes problems such as control strategies, stability assessment, process interactions, trouble shooting, start-up, load cha nges and shutdown scheduling. This part of the paper offers an assessm ent of modelling and simulation studies for the MSF plants. Normally a n MSF process is a nonlinear recycle process with a closed loop inform ation flow. Solution methods recognising these features must be used. One is the simultaneous approach (equation oriented) and the other is stage by stage (sequential) approach. Advantages and disadvantages of both the solution procedures are discussed, in view of minimizing the computational effort. In general, computer based process simulation ca n be done either by using a specific (specially developed) program or by applying a general purpose simulation package. For several reasons, a specific program is preferred for the MSF process simulation. An av ailable general simulator, however, can be used to get initial simulat ion results. In this paper, use of both types of programs is evaluated for the steady-state and dynamic simulations of the MSF plants. Appli cations of steady state modelling for parametric studies, such as desi gn prediction of long-term operation and optimization, as well as of d ynamic modelling for off-line and on-line simulation, like training si mulator, investigation of dynamic behaviour, and implementation of adv anced control strategies are discussed in the paper.