Chapter 4 - Multiple Effect Evaporation

Abstract

This chapter evaluates the performance of the multiple effect evaporation desalination processes. Performance analysis of various configurations shows that the best performance is obtained for the parallel/cross flow multiple effect evaporation (MEE). However, the parallel flow system has similar performance characteristics; moreover, its design, construction, and operation is simpler. Operation of both systems is favored at higher temperatures because of the drastic reduction in the specific heat transfer area. However, operation at lower temperatures gives higher thermal performance ratio and lower specific flow rate of the cooling water. Final selection of the most efficient and least expensive system and operating conditions necessitate full system optimization. The developed models should prove to be highly valuable in selecting and determining the characteristics of the optimum system. Comparison of the multistage flash desalination (MSF), forward feed, parallel, and parallel/cross flow MEE systems show several advantages of the forward feed MEE over the other systems. It is certain that the engineering design of the forward feed MEE is more energy efficient since it has the lowest specific power consumption, specific heat transfer area, and specific cooling water flow rate. Advantages of the forward feed MEE over the MSF system are found in the lower number of effects and specific power consumption. The forward feed and parallel flow MEE systems have similar or higher thermal performance ratio than the MSF system, however, the number of effects is only 12 for the MEE systems, while it is equal to 24 stages in the MSF system. Also, the MSF system has higher specific power consumption, which is required for pumping the brine circulation stream.