Energy consumption by multi-stage flash and reverse osmosis desalters

Kuwait and most of the Gulf countries, depend mainly on desalted water from the sea for satisfying their fresh water needs. These countries are using the multi-stage flash (MSF) desalting system, as the work horse' for their water production. This system is less efficient in energy consumption as co mpared to the reverse osmosis (RO) system. Moreover, large units based on t he MSF system have to be combined with steam or gas turbines power plants f or better utilization of steam supplied to the MSF units at moderately low temperature and pressure (as compared to steam produced by large steam gene rators). The value and the cost of the thermal energy supplied to the MSF d esalting system depends on the method of supplying this energy. This steam can be supplied directly from a fuel operated boiler or heat recovery steam generator associated with a gas turbine. It can also be supplied from the exhaust of a steam back pressure turbine or bled from condensed extraction steam turbine at a pressure suitable for the desalting process. Any energy comparison should be based on simple criteria, either how much fuel energy is consumed to produce this energy or how much mechanical energy is needed per unit product. The energy consumed in the light of the practice used in most Gulf countries are discussed here. In this study, reference desalting and power plants are used for comparison purposes. This study shows that sh ifting from MSF desalting system to the RO system can save up to 66% of the fuel energy used to desalt seawater. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.