Performance assessment of a Geo-OTEC-driven triple-ejector flash power-refrigeration cycle integrated with freezing desalination

Raw natural gas produced in offshore gas platforms carries a substantial amount of low-grade geothermal heat. This study presents a triple-ejector flash power-refrigeration cycle (TEFPRC) integrated with a freeze desalination and compares its performance with a single-ejector configuration (SEFPRC). In both the cycles, geothermal heat of raw natural gas is used as the heat source, while cold deep seawater serves as the condenser-cooling medium. R152a is selected as the working fluid due to its low GWP. By maintaining positive pressure, it also reduces the air infiltration risk into the refrigerator-evaporator maintained at −15 °C. The results show that the TEFPRC outperforms the SEFPRC in terms of 2ndlaw efficiency, achieving 27.2% as opposed to 22.8%. The TEFPRC can generate about 1667 kW of power and 0.74 kg/s of freshwater at maximal 2ndlaw efficiency. The minimum payback period (PBP) of the TEFPRC is approximately 6.35 years, which is shorter than the minimum 8 years PBP of the SEFPRC. When operated to minimize the PBP, TEFPRC generates 1627 kW of power and 1.22 kg/s of desalinated water. Corresponding levelized electricity cost is about $0.0735/kWh, comparable to coal-based power generation. Overall, the proposed system is feasible for combined power generation and water desalination on offshore gas platforms.