Concentrated Solar Tower Power Plant using Slag as Inventory Material for a Thermal Energy Storage (TES)

Abstract

Concentrating solar tower power systems using air as a heat transfer fluid (HTF) have a promising potential for a high solar-to-electric efficiency due to the high conversion temperature. For a successful market introduction, efficient, cost-effective and up-scalable solutions for the thermal energy storage (TES), a central plant component, are a prerequisite. Regenerator-type storages based on solid heat storage media are well suited to the needs. Here, slag pebbles from steel industry as an inventory material offers cost reduction potentials. However, further investigations are needed to clarify open questions concerning the implementation in large installations in combination with slag pebbles as inventory. The European project RESLAG is dedicated to this. Thermo-mechanical challenges arise during thermal cycling of the TES due to thermal expansion of the slag pebbles. This effect causes two major consequences for the pebble bed. Firstly, the contact forces between pebbles increase, resulting in a higher risk of damaging single pebbles. Secondly, the exerted pressure on the surrounding container walls rises, which needs to be considered when dimensioning the container and the inner insulation. For the thermo-mechanical calculations of the packed bed discrete element method (DEM) is used. A simplified DEM model will be presented, which allows calculating very quickly conservative estimates of the forces and stresses in the bed and the container wall. Results will be presented for large scale designs of slag based TES in concentrating solar tower power systems with air as HTF.