Simulation of multistage flash desalination process

The majority of large-scale desalination plants in the Arab Gulf area employ the multistage flash (MSF) processes. F processes are energy intensive and it is, therefore, essential to search for design and operating conditions which lead to reduction of energy dissipation and consequently lower water production cost. This paper reports a simulation study which was carried out to examine to what extent the thermal irreversibility of an MSF process is influenced by variation of the most important design and operating parameters. The impact of variation of top brine temperature, umber of stages and terminal temperature approach on the distiller performance ratio and irreversibility were explored and presented graphically in the term of thermal grids. The simulation study revealed that within the selected range of number of stages (16-40) and top brine temperature (90-120 degreesC), the MSF distiller irreversibility is highly Iced by the number of stages and to a lesser extent by the variation of the top brine temperature. The simulated are compared with one year operating data obtained from an MSF distiller. The distiller is a cross-tube configuration, which consists of 22 stages and operating at a top brine temperature ranging between 90 to 98 degreesC. Using steady state simulation program, an envelop of possible operating conditions is constructed for the distiller to :interrelate performance ratio, production, recycle flow and top brine temperature. Stage-wise simulation of individual transfer coefficients and fouling factors showed that both clean overall heat transfer coefficients (U-c) and fouling as (FF) are stage dependent and conversely the operating overall heat transfer coefficient (U-D) is to a great extent dependent. The dependence of the distiller irreversibility on the process conditions is reported. The distiller exergy,losses varied between 52 and 62 kJ/kg of distillate, Process details, which are responsible for distiller irreversibility are pinpointed and opportunities for better utilization of available energy are discussed.