Thermo-economic analysis and comparison of a CO2 transcritical power cycle and an organic Rankine cycle

• Thermo-economic evaluation of low temperature geothermal power cycle.
• A thermo-economic model is built by interconnecting different sub-models.
• The regenerator could increase the thermal performance of the power cycles.
• The subcritical ORC performance is better in terms of thermodynamic property.
• The regenerator increases CO2 transcritical power cycle's economic performance.

CO2 transcritical power cycle (CDTPC) and organic Rankine cycle (ORC) can effectively recover low grade heat due to their excellent thermodynamic performance. This paper conducts thermo-economic analysis and comparison of a CDTPC and an ORC using R123, R245fa, R600a and R601 as the working fluids driven by the low temperature geothermal source with the temperature ranging from 90 °C to 120 °C. The two power cycles are evaluated in terms of five indicators: net power output, thermal efficiency, exergy efficiency, cost per net power output (CPP) and the ratio of the heat exchangers’ cost to the overall system's cost (ROC). Results indicate that the regenerator can increase the thermodynamic performance of the two power cycles. The ORC working with R600a presents the highest net power output while the highest thermal and exergy efficiencies are obtained by the regenerative ORC working with R601. The maximum net power output of the regenerative CDTPC is slightly higher than that of the basic CDTPC. The CDTPC has a better economic performance than ORC in terms of CPP and under a certain turbine inlet pressure the CPP of the regenerative CDTPC is even lower than that of the basic CDTPC.