Thermal performance analysis of a solar-driven supercritical CO₂ split-flow recompression Brayton cycle

ABSTRACT

Solar is a clean and renewable energy, and is considered as the desired heat source of supercritical CO₂ Brayton cycle. The heliostat field and cavity receiver of DAHAN tower solar thermal power station in China are used for analyzing the geometric relations between the sun, heliostat field and the receiver. The ray-tracing method is applied to establish a model to calculate the heat flux distribution of heating surface in the receiver. According to the absorbed heat, the supercritical CO₂ split-flow recompression Brayton cycle model can be built via the Aspen HYSYS software. The uneven distribution on the heating surfaces represents a higher heat flux at the center of the spot and a lower heat flux away from the spot. The maximum heat flux is 224 kW·m⁻² at 9:00 am, 349 kW·m⁻² at 12:00 noon, and 215 kW·m⁻² at 3:00 pm. Based on this distribution, the thermal efficiency of DAHAN tower solar thermal power station can be obtained by modeling. Compared with the steam Rankine cycle, the thermal efficiency of supercritical CO₂ Brayton split-flow recompression cycle has a 50% increment. Subsequently, the effects of the split-flow ratio, the inlet temperature and pressures of turbo expander and main compressor, and the heat absorption on the thermal performance of system are obtained. Finally, the optimal parameters are obtained as follows: the split-flow ratio is 0.605, and the inlet pressures of turbo expander and main compressor are 24 and 7.9 MPa, respectively. These interesting findings are particularly significant for the application of supercritical CO₂ split-flow recompression Brayton cycle system and the operating parameters’ selection in solar thermal power generation stations.

KEYWORDS:

• Thermal performance
• solar thermal system
• supercritical CO₂
• split-flow recompression
• Brayton cycle

Acknowledgments

We would like to appreciate for the support of National Natural Science Foundation of China (Grant no. 51961135102) and Shaanxi Science and Technology Foundation (Grant no. 2020JQ-774).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [51961135102] and Shaanxi Science and Technology Foundation [2020JQ-774].