High-Temperature Thermal Energy Storage for Innovative Hybrid CSP/PV Plants : A Comprehensive Design Optimization

Sammanfattning: By means of a literature review, critical parameters in the context of thermal energy storage systems, particularly packed bed thermal energy storage systems are identified. The goals of this thesis project are to come up with an optimized design for a PBSTES and to evaluate the thermal performance of alternative storage materials derived from byproducts of industrial processes and natural rocks in order to reduce the environmental impact of the designed system. Several CFD simulations have been performed in order to test these materials and optimize the system designusing COMSOL Multiphysics. In order to optimize the design of the packed bed TES system, given the boundary conditions provided, the dimension and arrangements of the two packed bed layers and the dimension of the pellets contained in each layer has been varied, and different system configurations with different pressure drops and thermal performance have been obtained. Through sensitivity analyses, an optimized design consisting of larger pellets (12.41 mm) in a slightly thinner inner layer (0.219 m) and smaller pellets (4.85 mm) in a larger outer layer (0.256m) is obtained. This optimized design is then tested using the alternative materials that have been identified as potential alternative filler materials which are copper slag, steel slag, aluminum dross, ceramic waste, and basalt. Granite is also tested as it has been identified as a common choice of filler material in literature and it is therefore used as a benchmark for the other materials to be compared against. The performance of these materials is then evaluated based on the identified KPIs: thermal efficiency of the systems, energy capacity of the materials, and thermocline thickness. Based on the outcomes of the KPI, copper slag, steel slag, aluminum dross, and ceramic wastes displayed better performance than granite. Among natural rocks, basalt showed better thermal performance and improved efficiency compared to granite making it a viable alternative in applications requiring the use of natural rocks as filler materials.This project showed that recycled materials and byproducts of energy intensive industries, particularly copper slag, represent a promising alternative as storage material in sensible packed bed thermal energy storage systems by reducing the environmental impact of these systems while guaranteeing appropriate performance.