Thermodynamic and economic sensitivity analyses of a geothermal-based trigeneration system; performance enhancement through determining the best zeotropic working fluid

Abstract

In this paper, a novel geothermal-based trigeneration system producing electricity, cooling, and freshwater is devised. The whole setup comprises a flash-binary geothermal cycle, an ejector refrigeration cycle, a dual-pressure organic Rankine cycle, and a reverse osmosis unit. In the dual-pressure organic Rankine cycle, the utilization of the zeotropic mixture is examined for performance improvement. The overall system is analyzed from energy, exergy, and economic viewpoints. Likewise, the system is inspected by the thermodynamic and economic sensitivity analyses based on the best working fluid. By specifying the Butene/Isopentane zeotropic mixture as the best working fluid, it is revealed that from 10932kW of the input exergy to the system, 5561.74kW is destructed within different components. In this way, the recovered exergy rate by net output electricity is equal to 3633.33kW, by cooling load is 1663.44kW, and by freshwater is 104kW. Also, the optimum net output power and total energy and exergy efficiencies were obtained to be 3.65 MW, 25.06%, and 35.06%, correspondingly. In this situation, the sum unit cost of products and payback period of the system were 14.50 $.GJ−1 and 3.66 years, respectively.