A Study Of Marine Seawater Desalination & Energy Reserve Technology

As an individul unit, the ship sails on the ocean for different tasks. Great quantity fresh water is needed for equipments and members, such as fresh water for boiler, desel motor, high pressure compressure, especially for ships propeled by steam turbine power plant, Most great displacement ships are equipted with seawater desalination plants for fresh water supply. The normal desalination technology used on ships is distallation or reverse osmosis. In this thesis, different kinds of marine desalination plants were analisized, such as 5T/d and 50T/d single-effect distillation plants,45T/d multi-stage flash distillation,2.5T/d and 5T/d reverse osmosis plants, the 5T/d mechinacal vapor compression desalination plant, and the distillation plant using heat pump as source of heat energy. The improvement methods to reserve energy for different kinds of marine desalination plants were gotten.For ships propeled by steam turbine power plants, the high quality fresh water consumption makes the distillation plant be used porpularly. In this thesis, based on analisizing the marine 50T/d distillation plant, an improving method by adding a steam-ejector to form marine vapor compressure desalination plant was presented. By thermo-dynamic calculation, a steam-ejector for vapor compressure desalination was designed. It was found that with an ejector to improve the single-effect distillation to form vapor compression distillation, the motive steam consumption was sharply discreased from 50T/d to 23T/d. For the distillation plant, a steam-ejector was designed and numerical sinmulinked. For different motive steam pressures and evaporate temperatures, the work characteristics of steam-ejector were gotten. It is usable for steam-ejector designing.With the development of reverse osmosis technology, more and more reverse osmosis plants were used on ships for fresh water supply. With the marine 5T/d RO plant, different work pressures, feed water concentritions and temperatures, and the PH of seawater were tested. With the ROSA5.0 software developed by DOM's company, the basic datas of the plant were calculated. Comparing with the test datas, it was found that the calculation datas were accordingly to the test datas. The conclusions are usable for reverse osmosis plant operation.To reduce the power consumption of reverse osmosis deslination plant, by analysizing the different kinds of energy recovery equipments, a new structure pressure exchanger was designed for marine 150T/d reverse osmosis plant. And the calculation method was given. The main characteristic of this pressure exchanger is that the fluid ducts of the rotor unit are in curve. With the fluid flow through ducts, rotor can turn itself. Calculation and analisis shows that with this pressure exchange unit, the power consumption of this plant reduced more than 60%.