Multi-objective metaheuristic optimization of combined flash-binary geothermal and humidification dehumidification desalination systems

This paper proposes two configurations of combined flash-binary geothermal systems for simultaneous power production and water purification. The binary cycles which are combined together in "Series" and "Parallel" configurations are Organic Rankin Cycle (ORC) and Humidification Dehumidification (HDH) desalination system. Some zeotropic mixtures are also utilized as the working fluids of the ORC unit. Based on the thermodynamic analysis, a single-objective Particle Swarm Optimization (PSO), and then a multi-objective Particle Swarm Optimization (MOPSO) are performed on the systems whose two objectives are total output work, (W)over dot(tot), and produced freshwater, (m)over dot(pw). The single-objective optimization results show that the utilization of the zeotropic mixtures in both of the configurations gives higher output work. However, although the use of zeotropic mixtures does not affect the Parallel system's water purification, it leads to lower freshwater production in the Series system. The maximum amounts of (W)over dot(tot), and (m)over dot(pw) in the single-objective optimization are 5.72 (MW) and 3.93 (kg/s), which are obtained from the Series and the Parallel configurations respectively. The multi-objective optimization, however, gives more reliable outcomes. According to the results of the MOPSO algorithm, the maximum amount of the 1st optimization objective, (W)over dot(tot), for both systems, is 5.87 (MW) and also the maximum value of the 2nd objective, (W)over dot(pw), for both configurations is 11.42 (kg/s). On the other hand, the multi-objective optimization demonstrates that the Series configuration has a better performance than the Parallel system.