Effects of preheater arrangement on performance of MED desalination system

Preheating seawater before it flows into the evaporators in multi-effect distillation (MED) system could improve the system performance. The number and position of the preheaters play an important role in the thermal performance. A comparison of systems with different numbers and positions of preheaters was performed. On the premise of the constant distillate production, taking the 10-effect evaporation desalination system as an example, the effects of preheater arrangement on the gained output ratio (GOR) of the system and the total heat transfer area of the evaporators (A(total)) were analyzed. By adopting the equal temperature difference design method, a mathematical model was developed for the system performance analysis under different preheater arrangements. The results indicated that the GOR and A(total) are changed obeying some rules when the position of the preheater changes in one evaporator group or in different evaporator groups. In addition, with the increase in the number of preheaters, the mean GOR rises, the mean A(total) grows and the promotion space of system performance improves. The research provides a certain guiding direction for the optimization of desalination devices.