Preliminary Characterization of the Desolination Project Demo Plant: Design and Off-Design Operability

This work presents the preliminary performance of the simple recuperative transcritical power cycle of the DESOLINATION project demo plant. The cycle operates with the CO2+SO2 mixture and it is air-cooled, built in a CSP-like environment with high radiation and high ambient temperature. The axial turbine, with a flowrate of 0.2 m3/s at its inlet, imposes the size of the cycle at 1.8 MWel. Innovative recuperators and primary heat exchangers with internal gyroid structures are adopted, modelled with a simplified approach in MATLAB by fitting results of CFD simulations. By modelling the cycle off-design in sliding pressure, cycle efficiencies above 30% can be obtained, even at part load. Fixing a high ambient temperature at design conditions, the cycle cannot operate with ambient temperatures below 30°C if the condenser fans work at fixed speed, whereas ambient temperatures of 10°C are possible modifying the air velocity. By preliminary sizing the system piping, it is determined that the overall cycle inventory depends only on the conditions in the condenser, determined by the ambient temperature. Accordingly, an inventory variation of around 300 kg must be handled to correctly operate in off-design.