Investigation of an organic Rankine cycle (ORC) incorporating a heat recovery water-loop: Water consumption assessment

Abstract

This paper presents a thermodynamic analysis of an organic Rankine cycle with a water-loop (ORC-WL) as an efficient means of heat regeneration and saving Water Consumption (WC). The ORC-WL was simulated with wet, dry and isentropic refrigerants such as R717, R600a and R1234yf, respectively, in order to compare its technical performance to the conventional ORC (C-ORC) and ORC with internal heat exchanger (ORC-IHE). The thermodynamic analysis developed in the EES software was used to carry out the Energy Efficiency (EnE), Exergy Efficiency (ExE), Net Power Output (NPO), and WC as comparison performance parameters. A specific study has shown that the ORC-IHE, due to its remarkable contribution to the degradation of available energy and with a high WC compared to that of C-ORC, can be disqualified in favour of the ORC-WL which considerably improves these parameters thanks to the water-loop. For the same operating conditions and with reference to R600a, When C-ORC exhibited an EnE of 8.70 %, an ExE of 67.01 %, NPO of 8.57 kW and WC of 0.71 kg.s−1, those of ORC-IHE were 10.08 %; ExE of 64.87 %; NPO of 9.11 kW and WC of 5.30 kg.s.-1, respectively, whereas those of ORC-WL were 9.95 %, 84.85 %, 9.95 kW and 0.82 kg.s−1, respectively. The study on monitoring of evaporating temperature, superheating, and pinch showed that the ORC-WL can operate with evaporating temperature and superheating above 90 °C and 15 °C, respectively. A pinch of no more than 3 °C, on the other hand, is ideal. Finally, wet refrigerants are not suitable for ORC-WL, and dry refrigerants offer better performance than isentropic refrigerants,