Process mode results for the AA1 example simulation

We wish to see the overall impact on the cycle efficiency for the cases that we define in Process mode results for the AA1 example simulation. Based on the results of the case studies, we can identify an optimum turbine outlet pressure that maximizes the cycle efficiency. Then, we can use this pressure to determine the optimum flowrate through the bypass compressor.

We first begin by varying the turbine outlet pressure from 6 MPa to 15 MPa at a constant Heater outlet temperature. The efficiency of the system reaches a local maximum before steadily dropping again. The following figure displays the relationship between the cycle efficiency and the turbine outlet pressure.

Based on this relationship, the optimum value for the turbine outlet pressure is approximately 9 MPa. The critical pressure of CO2 is known to be 7.38 MPa. Our optimum pressure is slightly beyond the critical pressure; if we operate at the optimum pressure, we reduce the work needed to subsequently compress CO2.

We then fix the turbine outlet pressure at the optimum value and vary the bypass compressor flowrate to determine the optimum flowrate. If the flowrate through the bypass compressor is too high, the main compressor product cannot substantially cool the turbine product at the low temperature recuperator. Similarly, if the flowrate through the bypass compressor is too low, the turbine product loses too much heat at the low temperature recuperator, which the turbine then gains. The following figure displays the relationship between the cycle efficiency and the bypass compressor flowrate.

We find that the optimum bypass compressor flowrate is approximately 30 kg/s.