Enhancement of existing MSF plant productivity through design modification and change of operating conditions

Abstract

This study investigates the possibility of capacity enhancement of two brine recycle-MSF (Multi-Stage Flash) plants. The first has a conventional design whereas in the other the distillate from the heat recovery section is diverted, after cooling, to the town water tank. Thus the distillate from the recovery section is prevented from successive re-flashing in the heat rejection section. Also the distillate corridor from the heat rejection section is removed and condensate from heat rejection stages is collected individually into a common header after flashing and cooling to form a second product stream. Both plants incorporate a nanofiltration unit for the partial removal of bivalent scale forming ions from the makeup stream to enable operation at elevated TBT. Under the same operating conditions, it was found that the modified design exceeds the conventional one only by about 2% increase in distillate capacity. At the maximum recycle rate, 85% of the maximum recycle pump capacity, the increase in top brine temperature from 110°C to 130°C results in product capacity increase of 49.1 and 49.74% for the conventional and modified plants respectively. In many instances it was necessary to install additional pumping capacity to one or more of the process streams.