THERMO-ECONOMIC ANALYSIS OF AN INTEGRATED SUPERCRITICAL CO_2 BRAYTON CYCLE AND MULTIPLE EFFECT DESALINATION SYSTEMS

摘要

A thermo-economic analysis is carried for the current integrated supercritical carbon dioxide (sCO_2) Brayton cycle with both multi-effect desalination coupled with mechanical vapor compression (MED-MVC) and conventional MED system. The conventional MED system uses hot water as the heat source by recuperating the waste heat from the sCO_2 cycle. The MED-MVC system uses a vapor compressor to eliminate the need to condense the water vapor in the last effect of the MED system. The advantage of the MED-MVC is the ability to recuperate part of the waste heat of the sCO_2 cycle through preheating the seawater feed directed to the first effect. Forward feed configuration is selected since high feed temperature can be accommodated for the MED-MVC. On the other hand, in the case of conventional MED, high feed temperature is limited to the last effect temperature. To satisfy the demand of approximately 2,500 families, the water production capacity is 1,250 m~3/day, and 20 MW of electrical power is needed. The electrical power generated from the sCO_2 cycle is also used to drive the MVC unit and operate the feed, brine and distillate pumps in the MED system. Results reveal that both MED and MVC systems are capable to achieve the selected production capacity. The specific power consumption, universal performance ratio, and total water price for MED systems are 1.22 kWh/m~3, 56.51 and 0.69 $/m~3, respectively; whereas the MED-MVC systems are 10.22 kWh/m~3, 27.35 and 0.84 $/m~3, respectively. The cost of electricity is 0.029 $/kWh.