Hybridization of Innovative Seawater Thermal Desalination Technologies up to ZLD with sCO2 Concentrated Solar Power Plants

The work proposes an insight into an innovative combination of thermal seawater desalination technologies (forward osmosis and membrane distillation) fed by sensible waste heat recovered from the cooler of a supercritical CO2 cycle of a concentrating solar plant. The sensible heat at low temperature, from 50 to 75 °C, is exploited in the forward osmosis plant adopting a thermo-responsive draw agent, where 60% of available freshwater is separated from the seawater with a thermal consumption of 89 kWhth/m3. At temperatures up to 90 – 100 °C, the rejected heat is used in the vacuum membrane distillation plant with an innovative layout, bringing the brine close to crystallization and entailing a thermal consumption of 187 kWhth/m3. Finally, a crystallizer operated with the sensible low temperature heat from the cycle precipitates the salts, recovering part of them. The work presents a novel integration in series of various thermal desalination technologies to approach zero liquid discharge and includes the system hybridization with a next generation renewable concentrating solar plant, demonstrating the technological attractiveness in both technologies. With simulations of annual performances of the solar-power section, assuming a 100 MWel CSP plant in Sevilla, the annual freshwater production is evaluated at 3.39 Mm3/year, with 32 kton/year of salts separated and 4040 equivalent operating hours. The proposed configuration leads to overall specific thermal consumption of 156 kWhth/m3, a level lower than conventional desalination solutions at constant output products, with water recovery ratio of 95%, thus reducing the issues related to brine management of commercial plants.