Thermodynamic Performance Analysis of Combined Recompression Supercritical Carbon Dioxide (SCO2): Organic Rankine Cycle (ORC) for Waste Heat Recovery

An energy and exergy-based performance evaluation of combined recompression supercritical carbon dioxide Brayton cycle and organic Rankine cycle (SCO2/ORC) is presented. A parametric investigation has been performed by varying input parameters such as compressor outlet pressure , SCO2 turbine temperature , SCO2 mass flow rate , flow split fraction, LTR effectiveness and HTR effectiveness. R1234ze, R1234yf, and R245fa working fluids were considered in the bottoming cycle of SCO2/ORC. Results obtained revealed that the R1234ze-based SCO2/ORC system demonstrated the highest thermal and exergy efficiency of 55.87% and 73.13% respectively, at  = 30MPa and  = 3900C; 51.47% and 80.39% at  = 3kg/s when the split fraction is between 0.357 and 0.4; 52.19% and 71.44% at  = 0.95; and 52.19% and 71.44% at  = 0.95. However, the R245fa-based SCO2/ORC system is observed to have the lowest thermal and exergy efficiency. The maximum exergy destruction is seen to occur in the gas heater with 36.97% (8.45kW) of input exergy destroyed in this component. It is followed by the recompression compressor at 17.17% (3.93kW) and the SCO2 turbine at 16.03% (3.67%), with the ORC pump at 0.157% (0.036kW) having the least exergy destroyed.