Thermo-mechanical analysis of packed beds for large-scale storage of high temperature heat

Thermal storage systems are central elements of various types of power plants operated using renewable and conventional energy sources. Where gaseous heat transfer media are used, a regenerator-type heat storage with a packed bed inventory is a particularly cost-effective solution. However, suitable design tools to analyse the thermo-mechanical aspects of large-scale storage of high temperature heat are currently still missing. As a basis for such a tool, this contribution presents a novel approach for the prediction of the thermo-mechanical behaviour of such storage under thermo-cyclic operation. The relevant relations are formulated on the basis of the discrete element method (DEM). Here, the forces interacting between spherical particles are calculated by spring, dashpot and friction models and the resulting translations and rotations are determined solving Newton's equations of motion. Coupling these equations with a simplified thermal model that considers the heat resistance within the particles allows for investigation of the thermo-mechanical behaviours of a packed bed. For adequate implementation of this new approach and for reduced computational effort, a time-step control has been implemented and validated. Initial simulation results include the temporal and spatial displacements as well as the forces acting on the individual bodies for a thermo-cyclic operation.