Multi-factor evaluation method for the assessment of trans-critical organic Rankine cycle with low GWP fluids

Abstract

In this work, a multi-factor evaluation indicator method for the feasibility assessment of trans-critical organic Rankine cycles with low GWP fluids R134a, propane and R1234yf is developed. Analytic Hierarchy Process (AHP) method is used for the selection and weight allocation of multi-indicator. Moreover, the trans-critical ORC with R134a is analyzed and compared with the ones with propane and R1234yf in given heat source temperature of 150°C. The analysis takes into account inevitable irreversibility, investment cost, emissions of CO2 equivalent based on life-cycle in the heat exchangers, turbine and pump, and for working fluids. The results show that R134a has the optimal thermo-economic performances but the worst environmental impact. The net power output, thermal efficiency, exergy efficiency of system reaches 90.16kW, 12.71%, 52.34%, respectively, and the cycle irreversibility of 108.09kW, EPC of 0.0698$/kWh, PPD of 6.27 years and ECE of 22.46 tons CO2,eq are attainable for propane. Operation phase produces the maximal emissions of CO2 equivalent (ECE) for R134a, while construction phase produces the maximal ECE for propane and R1234yf. According to the multi-factor evaluation indicator, R1234yf is feasible only when environmental impact is paid high attention to, and propane is more feasible than R1234yf to be as a substitute of R134a thanks to its better thermo-economic performances close to those of R134a, and the minimal environmental impact.