Design and optimization of integrated direct-contact membrane distillation and supercritical CO2 Brayton cycle systems for water cogeneration

Abstract

Membrane distillation is an emerging desalination technology using low-grade heat for sustainable water production. This paper proposes a novel integrated design of direct-contact membrane distillation process and a closed supercritical CO2 Brayton cycle for water cogeneration. The membrane distillation uses the waste heat rejected by the Brayton cycle for seawater desalination without consuming high grade energy, as compared to the cogeneration with reverse osmosis. The design includes a “split flow” coupling of Brayton cycle's cooling water to fully utilize the temperature gradient of the waste heat for membrane distillation. A mathematical model is also developed to evaluate and optimize the thermo-economic performance of the systems. The proposed integrated design is applied to a 50 MWe supercritical CO2 recompression Brayton cycle power plant combined with membrane distillation to demonstrate its efficacy. Results show that the proposed design can achieve a levelized water production cost of 1.39 $/m3 with a water production capacity of 2.06 × 105 m3/year, outperforming the design without the “split flow”.