Numerical induced thermal stresses on walls of thermocline storage tank
Thermal Energy Storage (TES) systems are central elements of various types of power plants operated using renewable energy sources. Packed bed TES can be considered as a cost–effective solution in concentrated solar power plants (CSP). Such a device is made up of a tank filled with a granular bed through which heat-transfer fluid circulates. However, in such devices, the thermal stresses may accumulate from cycle to another due to differential thermal dilatation between filler and tank walls, leading to plastic deformations in the tank shell and the failure of the tank might happen. This paper aims at studying the evolution of tank wall stresses over thermal cycles, taking into account both thermal and mechanical loads, with a numerical model based on the discrete element method (DEM). A higher thermal expansion coefficient is used for the wall compared to the granular medium, allowing the settlement of particles during the loading phases, then an increase of induced stresses during the unloading phases due to the wall contraction against the settled particles. Simulations were performed to study two different thermal configurations: (i) the tank is heated homogenously along its height or (ii) with a vertical gradient of temperature. Then, the resulting loading stresses applied on the tank are compared as well the response of the tank wall.
Keywords: Renewable energy, Thermal effects, Discrete element method, Concentrated solar power, Power plants, Oceanography, Numerical methods