Dynamic creep and stress 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 stress concentration greatly affect the safety performance of the packed-bed thermal energy storage (TES) tank with encapsulated phase change materials (EPCMs). Therefore clearly analyzing the dynamic creep and stress distribution is an effective way to optimize the mechanical performance of EPCM-TES tank. In the study, a commercial scale EPCM-TES tank applied in 50MWe tower plant is designed. Then an integration model coupling FVM and FEM applied in EPCM-TES structure is established, where the real mechanical loads and cyclic temperature distribution are considered in stress analysis model. Based on the coupled model, the dynamic creep and stress performances of the EPCM-TES tank in charging and discharging are studied. The results are concluded as follows. (1) In charging, when the tank wall is gradually heated, the creep damage is produced on wallboards installed above 4.4 m height. Because of the tank wall continue to be heated by the high-temperature EPCMs fillers after charging, the creep phenomenon further occurs on the rest of wallboards installed below 4.4 m height. In discharging, when the tank wall is cooled by cold salt, the creep damage of the whole wallboard can be avoided. (2) The creep damage time of tank wallboards varies greatly along the height direction. In 25ys design life, the maximum creep time happens on top wallboard which is 105,000 h and occupies almost 47.9 % of the total operation time. (3) Most wallboards installed above 2.2 m height are always in elastic state with lower stress level in charging and discharging, whereas the plastic damage induced by stress concentration always occurs at the fillet weld location of bottom wallboard in charging. The study provides insights on the optimization design of the molten salt EPCM-TES tank in CSP for lower stress level and creep damage time.