Abstract
In S-CO2 recompression Brayton cycle, use of intercooling is a way to improve the cycle efficiency. However, it may decrease the efficiency due to increase of heat rejection. In this work, two S-CO2 recompression Brayton cycles are investigated using the thermodynamic model. The first cycle has intercoolings in a main compression and a recompression process (MCRCIC) and the second cycle has an intercooling in only the recompression process (RCIC). The thermal efficiencies of both cycles are compared with that of S-CO2 recompression Brayton cycle with intercooling in the main compression process (MCIC). Effects of a split fraction (SF) and a ratio of pressure ratio of the recompression (RPRRC) on the thermal efficiencies of MCRCIC and RCIC are also studied. The study results show that the intercooling of recompressor in MCRCIC and RCIC can reduce the compression power. However, it also rejects heat from the cycle and this leads to increasing added heat in the heater. The thermal efficiency of MCRCIC and RCIC are, then, lower than that of the MCIC. For the effects of RPRRC and SF to the thermal efficiency of the cycles, in general, when RPRRC increases, the thermal efficiency decreases due to increasing rejected heat. The increase in SF causes increasing thermal efficiency of the cycles and the thermal efficiency, then, decrease when SF is beyond the optimal value.
Highlights
The supercritical carbon dioxide (S-CO2) Brayton cycle is a promising technology for the power conversion cycle due to high thermal efficiency, simple cycle layout, and compactness of turbomachinery [1] The CO2 critical point is at 7.3773 MPa and 304.1282 K [2]
In the comparison of thermal efficiency, setting the same value of split fraction (SF) in the comparison may cause the argument that main compression and a recompression process (MCRCIC) may have higher thermal efficiency than that in the simulation result and its thermal efficiency may be higher than that of main compression process (MCIC), if MCRCIC is operated at the optimal SF and optimal ratio of pressure ratio of the recompression (RPRRC)
The effect of intercoolings applied in the main compression and the recompression processes in the supercritical carbon dioxide recompression Brayton cycle was studied
Summary
The supercritical carbon dioxide (S-CO2) Brayton cycle is a promising technology for the power conversion cycle due to high thermal efficiency, simple cycle layout, and compactness of turbomachinery [1] The CO2 critical point is at 7.3773 MPa and 304.1282 K [2]. Ahn et al [1] summarized that for Brayton cycle, S-CO2 provided a better efficiency than air They pointed out that S-CO2 Brayton cycle technology could be used with nuclear, waste heat and renewable heat sources. Cheang et al [5] analyzed different SCO2 power cycle layouts and compared them to a steam Rankine cycle. In their analysis, it was found that the recompression cycle was the most efficient. The result showed that the efficiency of S-CO2 recompression Brayton cycle was always above 40% and the recompression Brayton cycle was more efficient than the simple Brayton cycle
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