Application Of Low Temperature Multi-effect Desalination Technology In Large Power Station

To solve the problem of the growing shortage of fresh water, China has begun to construct some seawater desalination projects since the 1980s. Up to now such projects have been built or are to be built mainly in the design of Reverse Osmosis technology, and seldom of distillation technology. Although the latter is internationally regarded as one mature technology, it is seldom used for large scale power plant projects in China and its design experience is difficult for us to acknowledge and grasp. Therefore an application of the design of distillation seawater desalination technology for different project shall be paid much attention on for us. This paper is on a comprehensive study on such system.This paper has mainly studied and analyzed the design and applications of the low temperature multi-effect desalination and multi-flash evaporation technologies technically and economically, with the conclusion that the former is better than the latter in the aspect of operation temperature, heat transfer efficiency, cost of water tonnage, and water making cost, consequently that it should be recommended to be chosen in the design of distillation seawater desalination technology. And then the paper has studied and analyzed the key factors which influence the low temperature multi-effect desalination system of gain operation ratio, seawater quality and seawater's supercooling degree etc. The paper also tells that not only single factor should be considered in the following detail design process, but an optimized combination under common action of different factor be tried to find out.The paper has studied on the basis of the above theory and analyzed technically and economically the construction condition and steam extraction condition of unit 8 of Suralaya project in India, and confirmed the option of gain operation ratio of not less than 8 with turbine four-stage steam extraction.For this option, heat and mass balance has been calculated with the sea water temperature of 30℃or 32.5℃, and load of 50%,75%,100%or 110%, with the conclusion of the best operation condition at the 100%load with the max. gain operation ratio, and min. water making cost.In order to realize technical advancement and min. occupation of land, an optimized design has been realized in the project at the factors of pre-treatment system, thermal vapor compressor position, vacuum extraction system, seawater makeup style, decrease seawater's supercooling degree, as a result that the technical and economic target achieved in the application of this technology can measure up to the advanced level of the same type projects in our country. This research has got much experience in the design and optimization for low temperature multi-effect desalination system which can provide some reference for the design and construction of some subsequent similar projects.