Multi-objective optimization of two double-flash geothermal power plants integrated with absorption heat transformation and water desalination

Two configurations of double-flash geothermal power plants, one is combined with water desalination and one integrated with absorption heat transformation and water desalination, are proposed and investigated from the viewpoint of exergoeconomics. The main purpose of investigated systems is the simultaneous generation of electrical power and distilled water. A three-objective optimization procedure is performed to determine the optimal design points, considering for all configurations the decision parameters to be the pressures of low and high-pressure flash chambers and the temperatures of the evaporator and generator. The optimization aims to minimize the product unit cost, while maximizing the electric power generated and the production rate of distilled water. The Pareto frontiers for each configuration are drawn as part of the procedure. It is shown that, at constant and equal pressures of the high-pressure flash chamber, the product unit cost for the system combined with the absorption heat transformer is the lower of the two systems considered. In addition, under the optimized conditions, the product unit costs are approximately equal for the two studied configurations. However, the value of generated power for the system with an absorption heat transformer is about 17% greater than for the alternate system. Moreover, the system integrated with an absorption heat transformer has higher thermal and exergy efficiencies, at about 20% and 3%, respectively.