Performance analysis of feedback-controlled preheating process for molten salt storage tanks

Preheating is a crucial preparatory process in the operation of molten salt storage tanks, aimed at mitigating thermal shock and preventing potential structural damage before the first-time salt charging process. Adequate preheating ensures the proper functioning of a tank. This study introduces a feedback-controlled preheating process, where the inlet temperature of the preheating nozzle is adjusted based on the average temperature of the monitoring points along the lower tank wall. The preheating process is simulated by computational fluid dynamics (CFD) method to analyze the flow and thermal characteristics. Results after preheating show that significant temperature differences occur near the bottom and sidewall regions directly affected by the inlet hot air jet, as well as in the roof region influenced by the consequent elevated circular flow. Temperature differences in the weld region are generally pronounced in the vertical direction than in the circumferential direction, with a maximum temperature gradient of 19.67 K/m. Additionally, thermal shock at the molten salt direct impact locations on the tank bottom and the contact points at the large fillet weld during the first-time salt charging process is analyzed. Temperature differences at the bottom impact points are relatively low. However, a notable temperature difference of 32.35 K is observed at the weld contact point, indicating the necessity for monitoring weld temperatures.