Packed bed thermal energy storage for waste heat recovery in the iron and steel industry: A cold model study on powder hold-up and pressure drop

Abstract

Waste heat recovery in the energy intensive industry is one of the most important measures for the mitigation of climate change. The present study examines the integration of a packed bed thermal energy storage for waste heat recovery in the iron and steel industry. Along with the highly fluctuating availability of excess heat the main difficulty of waste heat recovery in industrial processes is the high amount of powder that is transported by the hot exhaust gases. Therefore, the experimental investigations in this study focus on the powder hold-up and pressure drop in a packed bed thermal energy storage that is operated with a gas-powder two phase exhaust gas as heat transfer fluid. The ultimate goal is, to assess its suitability and robustness under such challenging operational conditions. The results indicate, that 98% of the powder that is introduced into the system with the heat transfer fluid during charging accumulates in the packed bed. Remarkably, most of the powder hold-up in the packed bed is concentrated near the surface at which the heat transfer fluid enters the packed bed. When reversing the flow direction of the heat transfer fluid to discharge the storage with a clean single phase gas, this gas is not contaminated with the powder that has been accumulated in previous charging periods. The entirety of these findings reinforces the suitability of packed bed thermal energy storage systems for waste heat recovery in the energy intensive industry.