Converting a geothermal-driven steam flash cycle into a high-performance polygeneration system by waste heat recovery: 3E analysis and Genetic-Fgoalattain optimization

Abstract

The present study authenticates that the waste heat of a geothermal steam flash cycle is recuperated efficiently via embedding an organic flash cycle and an LiCl–H2O absorption refrigeration system in the high-temperature flow path and placing a hot water production unit in the low-temperature flow path. Consequently, the waste heat of both high and low-temperature flows of the steam flash cycle is recovered. There is still heat loss in the organic flash cycle that has the potential to be recovered. In this respect, an expander and a thermoelectric generator are respectively employed instead of the throttling valve and condenser of the organic flash cycle to convert the waste energy of the organic flash cycle into power. The overall power generated in the organic flash cycle is transmitted to an electrolysis unit to produce hydrogen. The multi-objective optimization of the designed system indicates an exergy efficiency of 30.89%, which is 15.74% points higher than the case for the sole generation of electricity by the steam flash cycle. At the optimal point, the rates of output work, heating, cooling, and hydrogen are equal to 757.1 kW, 8567 kW, 3017 kW, and 1.627 kg h−1, respectively. The comparison between the performance of the system and three similar geothermal-based systems for polygeneration purposes reveals that in addition to the highest exergy efficiency, the proposed system is superior in terms of the unit cost of polygeneration, with a value of 5.98 $ GJ−1.