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Energy and Exergy Analyses of a New Combined Cycle for Producing Electricity and Desalinated Water Using Geothermal Energy
Published: 31 October 2013 by MDPI in The 3rd World Sustainability Forum session Energy Efficiency and Renewable Energy Sources
Abstract: A combined cycle for generating electrical power and desalinated water is proposed and analyzed thermodynamically. The cycle, which utilizes geothermal energy, is a combination of the power-producing ammonia-water Kalina cycle, an absorption heat transformer with lithium bromide as working fluid and desalination facilities for removing salt from sea water. A parametric study is carried out to determine the effect of such parameters as the pressure at the turbine inlet, the ammonia water concentration in the transformer and the temperature of the hot water at the evaporator exit, on the first and second law efficiencies as well as on the distilled water flow rate. The results indicate that within specified ranges of these parameters, the energy and exergy efficiencies vary between 16 - 18.3% and 62.64 -69.48%, respectively. Comparing the Kalina and the proposed cycle, it is observed that the first and second law efficiencies are enhanced by around 12% and 24%, respectively, as the absorption heat transformer cycle is added to the Kalina cycle. The proposed cycle could produce 2.94 MW of electrical power and 0.34 kg/s desalinated water by means of extracting 89.3 kg/s of geothermal water at 124 oC from the earth.
Keywords: Geothermal energy; Kalina cycle; lithium bromide-water absorption heat transformer; Ammonia water mixture; second law efficiency