  Waste heat recovery in the energy intensive industry is one of the most
important measures for the mitigation of climate change. The utilization of
just a fraction of the theoretically available waste heat potential would lead
to a significant reduction of the primary energy consumption and hence a
reduction of greenhouse gas emissions. 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, investigations focus on the pressure drop and powder hold-up in a
packed bed thermal energy storage that is operated with a gas-powder two phase
exhaust gas as heat transfer fluid with the ultimate goal 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. Further, the
radial distribution of the powder hold-up in the packed bed is observed to be
even which indicates that there is no risk of random flow channel formation
that could affect the thermal performance (storage capacity, thermal power
rate) of the system. The results reinforce the great potential of packed bed
thermal energy storage systems for waste heat recovery in the energy intensive
industry.
