Energetic, exergetic, economic and environmental (4E) analysis and multi-factor evaluation method of low GWP fluids in trans-critical organic Rankine cycles

Abstract

Environmentally-friendly working fluid selection and multi-objective evaluation have been paid a great attention in organic Rankine cycle (ORC). Based on a modified analytic hierarchy process, a multi-factor evaluation method for trans-critical ORC (TORC) is developed first. The multi-factor indicator consists of eight indicators including energetic, exergetic, economic and environmental criteria (4E). The net power output, system efficiency, total exergy loss, exergy efficiency, cost per unit of time, electricity production cost, dynamic payback period, and emissions of CO2 equivalent (ECE) during life-time are considered. R134a, R32, R1270, R290 and R1234yf are selected as potential working fluids. The results show that the performance of R134a is the best followed by R32, R290, R1270 and R1234yf when only thermo-economic performances are considered. R290 shows the maximum comprehensive emission reduction of 8019 tons CO2, eq during life-time followed by R1270 being 7529 tons CO2, eq. The primary source of ECE from R134a, R32, R1270 and R290 is fluid leakage, accounting for over 68–83%. In multi-factor evaluation, R290 and R1270 exhibit higher feasibility level than R134a when the environmental impact is paid great attention. The multi-factor evaluation method is effective and valid to conduct comprehensive feasibility evaluation for decision-making.