Abstract
Geothermal energy is a characteristic of widely distributed, high capacity factor, high reliability, and lower environmental impact potential values. And it will play an important role in achieving the goal of carbon neutral carbon peak. Nonetheless, geothermal energy presents its own particular challenges, i.e., the high investment cost and long payback period. The binary flashing cycle (BFC) system is proved to be a promising power generation technology due to the efficient and full utilization of a low-grade heat source. While the economic performance still needs further evaluation, in the present study, the thermo-economic comparison between organic Rankine cycle (ORC) and the BFC for geothermal energy has been investigated. R245fa has been chosen as the working fluid. Considering the thermodynamic and economic performance simutaneously, several evaluation indicators were selected including thermal efficiency, exergy efficiency, net power output per ton geothermal water, heat exchanger area, and heat recovery efficiency, and the system modeling and comparison were presented. The simulation results reveal that the BFC system obtains 32% more net power output than the ORC system under the working conditions investigated. The heat recovery efficiency of the BFC is 1.96 times as much as that of the ORC, which indicates that the BFC can realize the full utilization of low-grade energy. And more heat exchanger areas are required in the BFC system. What is more, the preliminary discussion of the economic feasibility of BFC system applied in the FengShun geothermal power plant is presented. The payback period of the BFC is just 6.0 years under the generation pressure of 600 kPa. It is indicated that the BFC system has obvious economic benefits, especially in a nonflowing geothermal well.
Highlights
At the 75th sessions of the UN General Assembly in September 2020, China announced her pledge to reach peak emission by 2030 and carbon neutrality by 2060 (Mallapaty, 2020)
To fill up this research gap, thermo-economic comparison between the organic Rankine cycle (ORC) and the binary flashing cycle (BFC) driven by geothermal energy is conducted
To simplify the ORC and BFC system model, the following assumptions are listed as follows (Van et al, 2014)
Summary
At the 75th sessions of the UN General Assembly in September 2020, China announced her pledge to reach peak emission by 2030 and carbon neutrality by 2060 (Mallapaty, 2020). Great efforts were made to boost the ORC performance, the ORC thermal efficiency is generally less than 12%, which limits the commercial application (Basaran and Ozgener, 2013) It is not well optimized from the viewpoint of thermodynamics. Yuan and Michaelides (1993) conducted a comparative study, and indicated that, under the optimum design conditions, the BFC may provide up to 25% more power than the ORC. Michaelides (2016) found the BFC has less total entropy production compared with the ORC system It is deemed as a future cycle to make the geothermal plants economically competitive. At the respective optimal evaporation temperature, the net power outputs per ton geothermal water of the ORC and BFC are 8.77 and 10.09 kWh/t. To fill up this research gap, thermo-economic comparison between the ORC and the BFC driven by geothermal energy is conducted.
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