Cogeneration Using Multi-Effect Distillation and a Solar-Powered Supercritical Carbon Dioxide Brayton Cycle

Supercritical carbon dioxide (sCO₂) Brayton cycles are considered to be a potentially viable option for reducing the cost of electricity generation from solar power tower plants, owing to theoretically high efficiency, low compressor work, and compact turbomachinery. These cycles have relatively high heat rejection temperatures (>70 °C), which are ideal for integration with multi-effect distillation (MED) for distillate generation from seawater, without being a parasitic load to the power plant as compared to cogeneration with steam Rankine cycle. The intermittency of solar radiation reduces the annual capacity factor of concentrating solar power (CSP) plants to about 50–60% even with a molten salt storage tank of 10-h. This reduces the annual distillate generation and increases the cost of the distillate. A novel concept to reduce distillate cost is introduced, whereby the waste heat from the sCO₂ Brayton cycle is stored. A two-tank demineralized water storage tank is selected and is shown to allow for the integration of a smaller MED system operating at an increased capacity factor. The optimal storage tank design reduces the distillate cost by 19% and increase the MED capacity factor from 46.4% to 75%. Different coastal locations with good solar resource are studied for cogeneration with the CSP-sCO₂ Brayton cycle. Techno-economic analysis shows the cost of distillate produced by MED is 16% cheaper than the distillate produced from reverse osmosis system for Yanbu, Saudi Arabia.