Thermodynamic efficiency of trilateral flash cycle, organic Rankine cycle and partially evaporated organic Rankine cycle

Highlights: • A new point of view on the efficiency of TFC, ORC and PE-ORC plants is drawn. • A new modelling method of thermodynamic efficiency is introduced and applied. • Different working fluids and "natural" operating conditions are investigated. • Novel results about thermodynamic efficiency of TFC, ORC and PE-ORC are reported. • At certain conditions, the efficiency of PE-ORCs may outperform ORC and TFC. Emerging and promising ways of utilizing any heat sources from geothermal, solar, combustion, and industrial waste heat may be the application of power plants that are operating according to conventional Rankine cycle (RC), organic Rankine cycle (ORC), trilateral flash cycle (TFC) employing different types of expansion (i.e., volumetric expanders or turbine). In this paper, the studies about partially evaporated ORC (PE-ORC) was carried out; furthermore, it reports on novel results related to the comparison of thermodynamic efficiency of TFC, ORC and PE-ORC. These results were obtained by modelling the system operations computed with MATLAB and the thermal properties library taken from CoolProp and REFPROP. The calculation was based on selected different types of working fluid classified by A, C, Z, M, N points (conventionally categorized by dry, wet, and isentropic working fluids) and the upper-lower operating temperature. The obtained results explain a new point of view on the efficiency of TFC, ORC and PE-ORC plants, that in some of the conditions (i.e., one can find certain combinations of working fluid quality, maximal and minimal cycle temperature), the efficiency of PE-ORCs outperforms TFC and ORC. It means that at certain temperature ranges and conditions when starting the expansion step from a partially evaporated state, it may be recommended to improve the performance of the cycle. It seems that obtained results offer new insight to scientists and engineers in designing the thermal power plant working under a subcritical cycle with high-temperature heat sources or a low-temperature heat sinks employing the selection of working fluids and different types of expanders.