Analysis of a new design of a multi-stage flash–mechanical vapor compression desalination process

Abstract

A new design for a multi-stage flash–mechanical vapor compression (MSF–MVC) desalination process was investigated. The analysis of the proposed MSF–MVC system was performed based on the energy, exergy and thermoeconomic methodologies. The considered system was investigated under different operating conditions using a developed Design and Simulation (VDS) software. To examine the performance of the proposed process, a comparison with the conventional MSF desalination process was performed. Thermoeconomic results show that the best operating suction pressure for the compressor is 8 kPa and the best top brine temperature is 110°C. The effect of the stages number of the heat recovery section was studied, and the results show that the low unit product cost was obtained at 20 stages. The effect of the temperature difference across the vent chamber was measured, and the results show that the lower unit product cost was 6°C. Thermoeconomic analysis shows that the last stage (vent chamber) had the highest value of the sum of capital and operation and maintenance costs in addition to the exergy destruction cost. Also, the last stage had a higher relative cost difference and lower exergetic efficiency. This in turn shows that a reduction in the exergy destruction within the vent chamber reduced the unit product cost. The performance ratio of the proposed MSF–MVC system was 2.4 times the performance ratio of the conventional MSF process. The heat transfer area of the MSF–MVC system was 57% higher than that of conventional MSF. The exergetic efficiency of the MSF–MVC system was 67% higher than that of MSF. The thermoeconomic results show that the unit product cost of MSF–MVC, under the specified conditions, was calculated by 2.0 $/m 3; this value is 25% less than that of the conventional MSF process.