Thermodynamic analysis of combined electric power generation and water desalination plants

The performance of three systems combining reverse osmosis (RO) to produce drinkable water and a steam power plant is modeled and calculated. The RO subsystem incorporates a power recovery unit: a hydraulic turbine in the first two cases and a pressure exchange unit (PES) in the third case. The coupling between the RO and power plant subsystems is only mechanical in the first case (the power plant provides mechanical power to the pumps of the RO subsystem) while in the two other cases the coupling is both mechanical and thermal (part of the heat rejected by the condenser of the power plant is transferred to the seawater). The effects of feed water flow rate and salinity, energy recovery system (hydraulic turbine or pressure exchanger) and operating pressures on the energy and exergy efficiencies and on the permeate quantity and quality are analyzed. Energy and exergy fluxes for all the components, as well as the quantity of drinkable water produced by each of these systems, are also compared for identical operating conditions.