Multi-aspect evaluation and optimization of a tri-generation scheme integrating a geothermal power plant with a salinity-gradient solar pond

The present study deals with the investigation of a tri-generation layout driven by geothermal and solar energy to produce electricity, cooling, and freshwater. The geothermal plant is composed of a steam flash cycle (SFC), a modified Kalina cycle (MKC), and a subsystem based on liquefied natural gas (LNG). In the configuration, the heat from a salinity-gradient solar pond (SGSP) is utilized to generate power in a trilateral cycle (TLC). The waste heat of the SFC, MKC, and TLC is recuperated by three thermoelectric generators (TEGs). The sum of electricity produced by the SFC and TLC is employed to desalinate seawater by a reverse osmosis system. Moreover, the output power of the Kalina-LNG cycle is considered the electricity production of the configuration. The favorable cooling is produced through the evaporator of the MKC. The system evaluation contains thermodynamic and exergy-economic analyses and three-objective optimization of the configuration utilizing two scenarios. The outcomes of the first optimization scenario reveal an exergy efficiency (ηex) of 27.92 %, a total cost rate (C˙tot) of 267.5 $h−1, a payback period of 0.358 years, and a specific cost of tri-generation (ctri) of 21.09 $GJ−1 for the system. However, these values were calculated as 31.6 %, 278.4 $h−1, 0.408 years, and 19.46 $GJ−1, respectively, for the second optimization scenario. These values suggest a proper thermodynamic performance with regard to the type of heat sources and a suitable economic performance since one of the system products is freshwater. ηex and specific cost of products improve compared to the SGSP-based systems thanks to the combination of the SGSP system and the geothermal plant.