Comparison study of trilateral Rankine cycle, organic flash cycle and basic organic Rankine cycle for low grade heat recovery

Organic Rankine Cycle (ORC) has been widely used for the recovery of low-grade heat into power such as solar energy and industrial waste heat. The overall thermal efficiency of ORC is affected by large exergy destruction in the evaporator due to the temperature mismatching between the heat source and working fluid. Trilateral Cycle (TLC) and Organic Flash Cycle (OFC) have been recognized as potential solutions because of their better performance on temperature matching between the heat source and working fluid at the evaporator. In this study, thermodynamic models of above three cycles are established in MATLAB/REFPROP. Results indicate that TLC obtains the largest net power output, thermal efficiency and exergy efficiency of 13.6 kW, 14.8% and 40.8% respectively at the evaporation temperature of 152℃, which is 37% higher than that of BORC (9.9 kW) and 58% higher than that of OFC (8.6 kW). BORC is more suitable under the conditions low evaporation temperature is relatively low due to the achieved maximum net power output, thermal efficiency and exergy efficiency. OFC has the minimum net power output, thermal efficiency and exergy efficiency under all the conditions of evaporation temperature compared to TLC and BORC. As for the UA value, TLC has the largest one ranging from 7.9 kW/℃ to 8.8 kW/℃ under all conditions while OFC gains the minimum UA value at low evaporation temperature and BORC gains the minimum UA value at high evaporation temperature