Seawater desalination by multi-stage flash distillation (MSF) is still the predominant method, particularly in larger dual-purpose plants. However, the increased energy cost has increased the compatability of reverse osmosis very much during recent years. A comparative economic study of RO and MSF in the Middle East with capacities of up to 50 MIGD is discussed with particular reference to the parameters of influence.
Different membranes have been taken into consideration, but the most extensive calculations have been made for the new Permasep B-10 6840 T Permeator from Du Pont with improved temperature and pressure characteristics as well as membrane flux decline. An important economic factor is the membrane replacement rate. A strategy for the control of membrane performance and the replacement of membranes in order to minimize the operation cost is proposed. This computer control will also indicate, whether or not the pre-treatment has to be improved.
Competitive distillation systems other than MSF, such as multi-effect distillation methods, are included in the cost calculations for plants up to 10 MIGD capacity. Such systems, which have been developed recently, offer lower operation costs than MSF. The favourable economy offered by reverse osmosis suggests other RO applications apart from new desalination plants, viz. the retrofitting of old distillation plants. -The hybrid RO-MSF desalination plant has several benefits, e.s. decreased post-treatment costs-and improved water quality by-blending distillate and RO permeate as well as greater flexibility and more efficient operation in dual-purpose plants.