Thermal desalination from rejected heat of power cycles working with CO2-based working fluids in CSP application: A focus on the MED technology

This work analyses the integration of concentrated solar power plants based on innovative sCO2 cycles and transcritical CO2-based mixtures cycles with thermal desalination plants adopting the conventional MED technology. In these cogeneration plants, all heat rejected from the cycle is exploited by the desalination system, avoiding any parasitic electric consumption of the fans of the air-cooled heat rejection unit. The MED layout proposed exploits both latent effects, from 3 to 8, and sensible effects, to match at best the temperature level at which the heat is available from the power cycles, delivered to the desalination plant through an intermediate loop of demineralized water. The cogenerative solution is designed in all its components and proposed in this work as a 100 MWel solar tower CSP plant located in Sevilla, resulting in a yearly production of around 400 GWhel/year and between 3.5 and 4.2 Mm3 of freshwater produced, depending on the configuration analysed. Various power cycle layouts are investigated, working with both sCO2 and the innovative CO2 + C6F6 mixture as working fluids. Regarding the solar plant, detailed models for the solar field optical analysis and the receiver thermal analysis are adopted. The seawater desalination plant, when coupled with this category of CSP plants, presents a thermal consumption between 180 and 140 kWh/m3. Finally, the cogenerative plants performances are compared in terms of levelized cost of electricity, with a slight edge for the innovative mixture cycles, and levelized cost of water, in a range between 1 and 2 $/m3.

Automated summary

This work analyzes the integration of concentrated solar power plants with thermal desalination plants using innovative sCO2 cycles and transcritical CO2-based mixtures cycles. The proposed cogeneration plants efficiently utilize heat rejected from the power cycles for desalination, resulting in significant energy savings. Detailed models for the solar field and receiver are adopted, and the seawater desalination plant shows a thermal consumption ranging from 180 to 140 kWh/m3. The cogenerative plants' performances are compared in terms of the levelized cost of electricity and water, with the innovative mixture cycles having a slight advantage.