Case study: Repowering of ORC system by means of experimental test bench with supercritical carbon dioxide, proposal, and field experience improvements

Abstract

Although organic Rankine cycles (ORCs) have cornered the small-scale energy harvesting market, the generation capacities produced by sCO2 cycles far exceed those of ORCs, reaching higher powers and efficiencies. This paper analyzes the results of the field tests performed in 2022 at the Grupo Dragón, Nayarit, Mexico, facilities, in which the objective was to validate the operation of the ORC IDEA-10 system with a capacity of up to 10 kWe. The thermodynamic states reached during the test time lapses in which there was full operational stability and with direct loads are analyzed. The results obtained together with proposals for improvement led to compare the performance of ORCs with sCO2 systems for low temperature geothermal sources. The efficiencies of simple sCO2 cycles (5.32%) turned out to be lower than that of ORC at the same temperatures (9.7%), however, the efficiency of the sCO2 cycle improved notably in a regenerative configuration, given the properties of CO2 near its critical point, reaching efficiencies above 25% even at low temperatures compared to conventional ORCs with efficiencies below 10%. Finally, the basis for the implementation of sCO2 in low enthalpy geothermal applications was established, designing an experimental circuit with results obtained in the literature.