A Novel Combined Low Temperature Cycle for Electricity and Fresh Water Production

Abstract

This work is an extension and modification of the novel thermal cycle reported in the study “TechnoEconomic Evaluation of a Novel Thermal Cycle for Electricity Generation and Fresh Water Production From Solar Ponds.â€‌ For low temperature power generation, such as the case of solar ponds or a field of solar flat plate collectors (60–90 آ°C), it is a common practice to use an organic Rankine cycle. The novel cycle uses water vapor as a working medium under pressure values lower than atmospheric. This is achieved by a turbovapor generating unit, a conventional lowpressure steam turbine, and a condenser working in an open cycle. Such a plant has a low thermal efficiency which approaches 12%, because of the small temperature range between evaporator and condenser (80–30 آ°C). The ratio of fresh water to electric power is also fixed for a certain temperature range (e.g., 14 tons/MW h for temperatures of 80 آ°C evaporator and 30 آ°C condenser). To increase the thermal utilization of the available heat flux and to achieve a variable fresh water production, a conventional multistage flash evaporation plant (MSF plant) is incorporated between the evaporator and condenser. The thermodynamic analysis of the plant shows that the thermal utilization of the available energy may reach 90%, while the amount of fresh water could be raised from 14 tons/MW h to 300 tons/MW h, for the same temperature range. This system has the advantage of being selfsufficient, yielding a net electric power after having supplied its own needs of pumping power.