Abstract
The supercritical carbon dioxide (S-CO2) power cycle is a promising development for waste heat recovery (WHR) due to its high efficiency despite its simplicity and compactness compared with a steam bottoming cycle. A simple recuperated S-CO2 power cycle cannot fully utilize the waste heat due to the trade-off between the heat recovery and thermal efficiency of the cycle. A split cycle in which the working fluid is preheated by the recuperator and the heat source separately can be used to maximize the power output from a given waste heat source. In this study, the operating conditions of split S-CO2 power cycles for waste heat recovery from a gas turbine and an engine were studied to accommodate the temperature variation of the heat sink and the waste heat source. The results show that it is vital to increase the low pressure of the cycle along with a corresponding increase in the cooling temperature to maintain the low-compression work near the critical point. The net power decreases by 6 to 9% for every 5 °C rise in the cooling temperature from 20 to 50 °C due to the decrease in heat recovery and thermal efficiency of the cycle. The effect of the heat-source temperature on the optimal low-pressure side was negligible, and the optimal high pressure of the cycle increased with an increase in the heat-source temperature. As the heat-source temperature increased in steps of 50 °C from 300 to 400 °C, the system efficiency increased by approximately 2% (absolute efficiency), and the net power significantly increased by 30 to 40%.
Highlights
Research Division of Environmental and Energy Systems, Korea Institute of Machinery and Materials, Department of Energy Technology, Korea Institute of Energy Technology (KENTECH), 200 Hyuksin-ro, This article is based on a paper presented at the 33rd International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems held from 29 June to 3 July 2020
A supercritical carbon dioxide (S-CO2 ) power cycle has been studied for diverse applications including nuclear, concentrated solar, fossil fuel, and waste heat recovery [1], and the supercritical CO2 (S-CO2) power cycle has been optimized for each application [2]
The S-CO2 power cycle for waste heat recovery can lead to high cycle efficiencies and a substantial reduction in size compared to alternative power cycles
Summary
A supercritical carbon dioxide (S-CO2 ) power cycle has been studied for diverse applications including nuclear, concentrated solar, fossil fuel, and waste heat recovery [1], and the S-CO2 power cycle has been optimized for each application [2]. S-CO2 recompression Brayton cycle for a high-temperature heat source are significantly different from those of the split S-CO2 power cycle for a gas turbine WHR in this study. With variation of the waste heat source, the high-pressure side of the cycle is carefully optimized for the maximum net work, as it is typical that the optimal high pressure of the cycle in the split S-CO2 power decreases with a decrease in the heat source temperature This is very different from the reheated and simple recuperated S-CO2 power cycles for engine waste heat recovery [21], in which a higher maximum pressure of up to bar can always increase the net work of the cycles
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