Thermodynamic analysis of a poly-generation system for electrical power, cooling and desalinated water

Nowadays, designing new poly-generation systems is needed to meet the increasing community’s demands of electrical energy, space cooling and fresh water. This should take more attention especially with the increasing conventional fossil fuel energy costs, freshwater shortage and CO2 emission. This work presents the thermodynamic analysis of a sustainable poly-generation thermal system that can produce electricity, space cooling and desalinated water. The proposed system combines a Concentrated Solar Power (CSP), Steam Rankine Cycle (SRC), Multi Effect Distillation (MED) system and Absorption Refrigeration System (ARS). The system design target is to provide communities in remote areas with all needs of water, electricity and cooling using low-grade heat from green solar energy. In the solar field, solar irradiation is collected by Parabolic Trough Collectors (PTC) to heat the working fluid (Therminol-VP1 heat transfer oil). Thermal oil transfers the absorbed heat to the SRC that generates the required electrical power and provides both MED and ARS with a proper heating steam required depending on the demand loads. The developed model is used to design a pilot test unit of 10 kW electrical power, 1.7 m³/day of desalinated water and 3.6 TR cooling load capacity. Flow, heat, and exergy destruction rates for each component of the system are obtained. Performance parameters of the subsystems forming the plant are also evaluated. Results revealed that the PTC represent the most critical part in the system from the exergetic point of view as it experiences 84.65% of the total system exergy destruction the required PTC area is 83.12 m². For the ARS unit, exergy loss is about 2.2 kW, 36.22% and 28.87% of this value occur in absorber and generator respectively. MED unit simulation results demonstrated that the gain ratio and specific heat transfer area are 2.29 and 144 m²/kg/s respectively. The exergy destruction in the MED unit is 1.8244 kW (66.43% in evaporators and 33.57%in condenser). The ARS coefficient of performance and second law efficiency were 0.7755 and 59.24% respectively.