Multistage flash desalination combined with thermal vapor compression

A novel system is proposed to increase the performance of the multistage flash desalination process (MSF) by combination with thermal vapor compression (TVC). The proposed system integrates the vapor compression unit within the conventional MSF brine circulation configuration without variations in the process layout. Two schemes are evaluated, which includes vapor entrainment and compression from the heat recovery or rejection sections. These schemes may call for use of one or two jet ejectors depending on the required compression range. Performance evaluation for the proposed schemes is made as a function of the top brine temperature and location of vapor entrainment. Results show that the increase in thermal performance ratio of the proposed system over the conventional MSF varies between 6 and 16%. Additional power savings are realized as a result of 62-74% reduction in the specific flow rate of cooling water to the system. Use of high pressure steam results in 60% size reduction in the diameter of the steam piping system. Use of the steam jet ejector, eliminates the control loops and process units for throttling and desuperheating, which are found in conventional MSF. Vapor entrainment and compression from the stages of the heat recovery section gives higher thermal performance ratio and lower specific heat transfer area than for vapor entrainment from the heat rejection stages. However, the main advantage for vapor entrainment and compression from the heat rejection stages is that the specific flow rate of cooling water is lower by 40%. Gains and features of the proposed vapor compression modes would reduce the unit product cost as a result of reduction in the capital and operating costs of the process. (C) 2000 Elsevier Science S.A. All rights reserved.