Comparative Study on Parallel Feed and Mixed Feed LT-MED Desalination Systems

Based on the mass and energy conservation equations, the mathematical models of a parallel feed and a mixed feed LT-MED desalination system were established, in which included evaporator, condenser, preheater, brine cooler etc. The steam temperature loss was considered which was caused by the boiling point elevation (BPE) of sea water and the flow resistance when steam flowing through tube bundle, demister and pipeline between adjacent effects. And the physical parameters of sea water were considered as the function of temperature and concentration. A computer program was designed to solve the models. Taking actual project into account, comparative study on parallel feed and mixed feed LT-MED desalination systems was done under different factors impacting on the system performance, which included the number of evaporators, the heating steam temperature of the first effect and the rated water production. The results show that when the other factors are unchanged, the more the number of evaporators, the better the performance of mixed feed system compared to the parallel feed system. The impact of the heating steam temperature of the first effect on the performance difference of the two systems is very little. The less the rated water production, the better the performance of mixed feed system compared to the parallel feed system.