Cyclic Creep and Mechanical Performances of the Packed-Bed Thermal Energy Storage Tank with Molten Salt Epcm Particles

Abstract

In the concentrating solar power (CSP), the high-temperature creep and alternating stress could lead to molten salt leakage in the packed-bed thermal energy storage (TES) tank with encapsulated phase change materials (EPCMs). In the study, considering the cyclic thermal and truly mechanical loads in charging and discharging, a coupled thermal-mechanical integration model is established. Based on this model, the cyclic creep and mechanical characteristics of the packed-bed TES tank with EPCMs are studied. The results are concluded as follows: The temperatures of tank wall and packed-bed exhibit periodical variation in multi-cycles, and the wall temperature change rate is obviously lower than the packed-bed region. Meanwhile, in the daily cycle, the wall temperature distribution curve could be divided into 6 parts: sharply rise and slowly increase stages in charging, gently rise stage after charging, decline slowly and sharply decrease stages in discharging, and slowly decrease stages after discharging. Especially, the wall dynamic temperature has a significant influence on its creep performance. For example, the creep phenomenon would firstly occur on wallboards 1-4 in charging, then happens on wallboards 5-6 when experiences another 6.5h after charging. Besides, the wallboards daily creep time is obvious different, the damage time of top wallboard 1 and bottom wallboard 6 are 14h and 3h, respectively. And within the 25ys design life, the creep time 105,000h of wallboard 1 which occupies 49.7% of the total operation time is almost 4.7 times of wallboard 6. Moreover, the stress which exhibits periodical tendency in cycles is influenced greatly by the wall temperature difference, and the wallboards 1-5 is always in the elastic state with lower stress level (30-80MPa). However, due to the higher temperature gradient, the peak stress which is higher than the yield strength always occurs on the fillet weld location in wallboard 6.

Keywords: Solar power tower, Molten salt, Thermal Energy Storage, Packed-bed, Creep, Mechanical