Analysis of a high-performance polygeneration system for efficient waste heat recovery of an organic flash cycle: Multi-criteria analysis and optimization

The waste heat from a geothermal-driven organic flash cycle has an outstanding potential to be recuperated. The present research is an effort to recover the thermal losses of a geothermal-based organic flash cycle to a feasible extent by employing a configuration that has not been studied in the literature. In this respect, the energy losses in the high-temperature and low-temperature throttling stages of the organic flash cycle are recuperated in a screw expander and an LiCl-H2O absorption chiller, correspondingly. Moreover, the heat loss in the condenser of the organic flash cycle is recovered in a Seebeck power generator, and the electricity produced in the expander and Seebeck generator is transmitted to a proton exchange membrane electrolyzer to generate hydrogen. In addition, a heat exchanger is embedded to produce hot water utilizing the residual energy of the geothermal water before reinjection. The proposed system is analyzed by the engineering equation solver from energy, exergy, and exergoeconomic standpoints. The exergoeconomic analysis is performed by employing the specific exergy costing method, and multi-objective optimization is carried out utilizing MATLAB software. The optimized thermo-economic performance of the system reveals that the heat loss recovery enhances the useful exergy of the system by producing 178 kW of exergy rate for cooling, heating, and hydrogen. Thus, the exergy efficiency of the polygeneration system is obtained as 30.3%, which is 10.5% points higher than the case of electricity generation by the turbine of the flash cycle. Above all, the low unit cost of polygeneration and payback period, respectively equal to 7.3 $GJ- 1 and 1.4 years, make the designed system superior when is compared with similar geothermal-based polygeneration systems.

Automated summary

This research explores a new configuration to recover thermal losses in a geothermal organic flash cycle and generate electricity and hydrogen. The optimized thermo-economic performance of the system shows significant improvement and it has lower cost and payback period compared to similar geothermal polygeneration systems.