Review of various combinations of a multiple effect desalination plant (MED) and a thermal vapour compression unit

Abstract

For remote areas where the fresh water demand could reach several million gallons per day, the design of desalination plant should be based on the following criteria: (1) Low specific heat consumption to produce the required amount of fresh water, (2) Moderate maximum brine temperature in the range of 65 to 70°C to avoid scaling and corrosion problems, and (3) Easy and trouble-free operation with a minimum number of operators. The design and development of desalination plant utilising the operating principle of moderate temperature vapourization, together with the use of thermal vapour compression unit, has so far produced satisfactory results which should be the basis for the design of future installations to achieve greater improvements, in overall performance. Normally a typical multiple effect desalination plant, with 7 or 8 effects has a performance ratio less than 8. By the installation of thermocompression unit to bridge certain number of effects, the performance ratio will increase to 11:1 or even higher. The production could be increased 20% higher than nominal rated output, if the maximum brine temperature is raised to 70°C (5°C higher than normally designed TBT for such system which is 65°C).