Techno-economic optimization of coupling a cascaded MED system to a CSP-sCO2 power plant

Integrating a multi-effect distillation (MED) process with a concentrated solar power (CSP) plant can enable a sustainable solution to meet our global society's increasing energy and freshwater demands. This integration makes possible the ‘free’ reuse of waste heat from an advanced power block, albeit at slightly reduced thermal efficiency. As such, this study can be considered a pioneering analysis of the potential of integrating a cascaded MED system with a supercritical CO2 (sCO2) cycle, which provides two main innovations: (a) a highly efficient sCO2 cycle is proposed to mitigate the energy efficiency penalty of the more traditional (Rankine Cycle) in CSP-Desalination (CSP-D) coupling, and (b) a cascaded MED system is proposed to recover much more of the rejected waste heat than a single MED configuration. These two innovations were explored in detail by employing an in-house thermo-economic numerical model, which was validated using literature data. It was found that 4-MED systems maximized the distillate production, with 57% waste heat energy recovery compared to 26% energy recovery using a single-MED system. Encouraged by this positive performance boost, an economic feasibility analysis was conducted by considering the installation site (i.e., pipeline distance from the coastline and the direct normal irradiance (DNI) resource) and the potential revenue from a power purchasing agreement (PPA) and a water purchasing agreement (WPA). It was found that the desalination process has a negligible effect on the payback due to the limited water production (i.e., ∼1 million m3/yr) compared to the high electricity generation (i.e., ∼190 GWh/yr). Thus, reducing the power block's investment cost and installing the plant in high PPA markets (i.e., above 20 UScents/kWh) represent the two most significant factors for improving the plant's feasibility. It was also found that a 0.6 kWh/m2day of additional DNI is required to offset each 100 km of pumping energy consumption (fo