Abstract
Low-temperature heat utilization can be applied to waste heat from industrial processes or renewable energy sources such as geothermal and ocean energy. The most common low-temperature waste-heat recovery technology is the organic Rankine cycle (ORC). However, the phase change of ORC working fluid for the heat extraction process causes a pinch-point problem, and the heat recovery cannot be efficiently used. To improve heat extraction and power generation, this study explored the cycle characteristics of the trilateral flash cycle (TFC) in a low-temperature heat source. A pinch-point-based methodology was developed for studying the optimal design point and operating conditions and for optimizing working fluid evaporation temperature and mass flow rate. According to the simulation results, the TFC system can recover more waste heat than ORC under the same operating conditions. The net power output of the TFC was approximately 30% higher than ORC but at a cost of higher pump power consumption. Additionally, the TFC was superior to ORC with an extremely low-temperature heat source (<80 °C), and the ideal efficiency was approximately 3% at the highest work output condition. The TFC system is economically beneficial for waste-heat recovery for low-temperature heat sources.
Highlights
In the past, low-temperature heat recovery was not widely used due to low energy prices and technical barriers
Power and thermal efficiency of the trilateral flash cycle (TFC) increased with the evaporation temperature
Results and thermal efficiency of the TFC increased with the evaporation temperature
Summary
Low-temperature heat recovery was not widely used due to low energy prices and technical barriers. Among all the waste-heat utilization technologies, the organic Rankine cycle (ORC) is a mature technology that features high reliability and low cost. It is arguably the most efficient energy conversion solution for low-temperature waste-heat power generation at present [2,3], and it is widely used to recover industrial waste heat [4,5,6,7], geothermal energy [8,9], biomass heat, and solar thermal energy [10,11,12]. The pinch point limits the energy capture efficiency and increases waste heat [14]
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