Optical-thermal-mechanical characteristics of an ultra-high-temperature graphite receiver designed for concentrating solar power

Abstract

Increasing the fluid outlet temperature of the solar receiver is a promising approach to improve the power cycle efficiency of concentrating solar power. However, the receiver can be potentially damaged by thermal stresses introduced by the high and nonuniform temperature. To capture solar energy safely at ultra-high temperature, we designed a plant-scale receiver using liquid tin as the heat transfer fluid. In the receiver, a secondary concentrator was designed to improve the concentration, and a cylinder-cone graphite cavity was designed to enhance the solar absorption. Meanwhile, the entire receiver was enclosed in an argon environment to protect it from oxidation. After the design, an optical-thermal-mechanical sequential simulation was conducted to evaluate the receiver performance. Based on the simulation, the cylinder length was optimized at the extreme condition with the incident radiative power of 600 kW and the inlet fluid temperature of 1573 K, obtaining an optimized receiver with the cylinder length of 900 mm. Then, performance evaluation indicated that the optimized receiver can operate safely and achieve a receiver efficiency of 60.4%-89.2% with an inlet temperature of 573–1573 K when the incident power is within 300–600 kW. However, if the incident power becomes much higher, the graphite cavity will fracture, especially at relatively low temperature of around 873 K. Moreover, the effects of mass flow rate and cooling conditions were studied, indicating that increasing the mass flow rate at higher temperature has a greater effect on improving the receiver efficiency. Meanwhile, it was found that ambient air cooling is sufficient for the glass cover. However, an additional forced convective cooling device is necessary for the secondary concentrator. These results indicated that the designed receiver is promising for capturing solar energy at high temperature up to 1573 K.