Development of a computer-package for MED plant dynamics

(T)his paper describes a computer package (SIMED) that we have developed to simulate the dynamics of different Multi-Effect Evaporators systems. SIMED is intended to serve as an educational tool to study in particular the MED coupling to nuclear reactors such as GT-MHR, PBMR (high temperature reactors), PWRs, or to fossile energy sources such as the gas turbine combined cycle or the simple oil or gas burners. It is designed to improve the understanding of the MED process, develop a control strategy for plant dynamics and optimise process operating conditions. SIMED supports mainly two flow configurations-depending on the seawater feed system architecture: (1) typical MED, in which sea water is preheated in the final condenser then fed to all effect in parallel. (2) MED with sea water preheat in the final condenser (and other MED effects) then fed to first effect. For each configuration the heat source could be either hot water, provided by an intermediate loop, interface between the nuclear reactor and the desalination process, or the steam, provided by a flash tank, a device used to produce steam trough the depressurisation of hot water based on an intermediate loop. SIMED runs under the Windows 9x/2000/XP operating system. It offers a user-friendly graphical user interface consisting of two modules; the Simulation Wizard and the Post Processor. Simulation Wizard's role is to guide the user through the steps required to create data files for simulation. These steps include the choice of system architecture, components characteristics, scenarios, and calculation options. Processor is built around tools for the display of simulation resystem flow sheets, variation of important parameters etc. The physical models of SIMED derive from basic mass, energy and momentum conservation equations and supplementary correlation for heat transfer and physical properties. Conservation laws are applied separately to fluid phases (brine pool, vapour space) in system components such as MED effects, condensers, coolers, pumps and ducts. A mathematical model of the whole process is generated automatically depending on user choices concerning system architecture. The models, and the results of their application, in particular to a PWR+MED system, show very promising results.