Low-grade thermal energy utilization through using organic Rankine cycle system and R1233zd(E) at different heat source temperatures

Abstract

The organic Rankine cycle (ORC) is a promising thermal-electric conversion technology for low-grade thermal energy utilization, however, its performance is significantly varied by the heat source condition. In this study, a compact ORC system using R1233zd(E) was built in Harbin, China for low-grade thermal energy utilization, and the thermal performances of the system at different heat source temperatures (HST, 80, 100, and 120 °C) and heat-source mass flow rates (mhs, 0.011 ∼ 0.346 kg/s) were investigated and presented. The results showed that the heat source conditions (HST and mhs) primarily influenced the ideal bubble point temerature difference (BPTD), outlet pressure, and super-heating degree (SHD) of the evaporator. With the increases in HSTs and mhs, the net output power, thermal efficiency, electricity generation and electricity generation efficiency varied in the ranges of 0.04 ∼ 0.77 kW and 0.9 % ∼ 7.1 %, 0.02 ∼ 0.51 kW and 0.5 % ∼ 4.7 %, respectively. The biggest thermal efficiency (7.1 %) and electricity generation efficiency (4.7 %) of the ORC were obtained at the HST of 120 °C, mhs of 0.09 kg/s. The results also showed that the disadvantages of low-temperature thermal energy could be compensated by improving the mhs, providing more possibilities for the efficient utilization of ORC systems driven by low-grade thermal energies.