Numerical study on thermal stress and cold startup induced thermal fatigue of a water/steam cavity receiver in concentrated solar power (CSP) plants

Abstract

The high temperature receivers in CSP plants should startup frequently, so the thermal stress and the fatigue failure are critical important for its safety and stability. In our present study, a computation model is proposed for a water/steam cavity receiver in CSP plant. The model couples the light propagation, the light-heat conversion, the thermo-elasticity and the thermal fatigue analysis together. Monte Carlo ray tracing method (MCRT), finite volume method (FVM) and boiling heat transfer are coupled to get the thermal boundary of the boiling panel. Finite element method (FEM) is adopted to obtain the temperature and stress–strain distribution of the boiling panel. Elastic stress analysis and equivalent stress fatigue assessment method is used to investigate the fatigue failure of the boiling panel. Two different structures of the boiling panel are researched, following results are obtained: The heat flux on the boiling panel is highly non-uniform and it results in the similar non-uniform distributions of temperature and stress-strain as well as the displacement of the boiling panel. The non-uniform stress-strain leads to the warping of the boiling panel and the largest displacement is in the direction normal to the heat absorbing surface toward the cavity internal, the largest displacement range is 17 cm. Fins of the boiling panel at the elbow region (case-1 in the present study) can lead to hot spots of which the temperature is extremely higher than that of boiling tubes, cutting off the fins at the elbow region (case-2 in the present study) can eliminate the hot spots and has no impact on temperature distribution of the boiling panel’s main part. The temperature difference on the cross section of the boiling tube is very high (about 130 °C while the heat flux is about 350 kW/m2) both in radial and circumferential direction, and this high temperature difference results in the high thermal stress on the boiling panel and the maximum thermal stress occurs at the welding region. The welding quality has a significant impact on the fatigue failure of the boiling panel. For a receiver design life of 20 years, membrane wall with cutting off the fins at the elbow region (case-2 in the present study) is a good design and the welding quality level 3 should be ensured at least and only one cold startup for a day is permitted.