Experimental study and numerical modelling of high temperature gas/solid packed-bed heat storage systems

Abstract

Two pilot-scale regenerative heat storage systems have been tested by the French Alternative Energies and Atomic Energy Commission (CEA). The first one is a 1.1-MWhth structured packed bed consisting of ceramic plates forming corrugated channels. The second one is a 1.4-MWhth granular packed bed consisting of basaltic rocks enclosed by refractory walls. The two regenerators were tested over a hundred of thermal cycles between 80°C and 800°C with different fluid mass flows. Both systems showed their ability to store heat efficiently and to provide thermal energy at a stable temperature for the most part of the discharge process. The granular packed bed exhibited large transverse thermal heterogeneities due to flow channelling in the corners of the cross section. However, this phenomenon appears not to have degraded significantly the thermal performances, and the average one-dimensional thermal behaviour of the system may be assessed thanks to the surface weighted average of the temperature over the bed cross section. Compared to the granular packed bed, the structured bed showed comparable thermal performances while inhibiting flow heterogeneities and reducing by up to 54% the average pressure drop. Furthermore, at the end of the test campaign, the packed beds were observed and compared from a mechanical point of view. The thermal results were successfully simulated over numerous charge/discharge cycles thanks to a onedimensional numerical model. This is significant since the discrepancies between experimental and numerical results are likely to accumulate from a cycle to the other. The model considers the packed beds as continuous and homogeneous porous media but takes account of the conduction resistances within the solid filler and the walls. The pressure drop of the beds was computed using a correlation developed thanks to a previous CFD study for the structured packed bed, and the Ergun equation for the granular packed bed. Compared to experimental data, these correlations enabled to estimate the order of magnitude and the evolution trend of the pressure drop with an average deviation ranging from-7.2% to +61.9%. For the granular packed bed, these deviations are ascribed to the flow heterogeneities and the shape of the rocks which are not taken into account in the Ergun equation.

Experimental and numerical analysis of a packed-bed thermal energy storage system designed to recover high temperature waste heat: an industrial scale up

“…Globally, numerical results fitted well experimental points which indicates that the TES performances were consistent to the design. During the first hours of charging, the thermocline entirely occupied the tank, similarly to the observation of Esence et al [13]. At the end of the charge, the temperature was constant at 525°C (feeding temperature) in the first meter length of the tank.…”

“…Esence et al observed a thermal discrepancy of 250°C in the corner of the tank, indicating high velocities due to the channeling effects [13]. This phenomenon is absent in this study, since the thermocouples temperature is relatively homogeneous, meaning an equal distribution of the fluid velocity along the cross section.…”

“…However, thermal alterations would be likely to appear on an industrial storage unit because of longer charging periods. Moreover, Esence et al showed the issues related to thermal ratcheting [13]. These can be solved by using a horizontal geometry which would decrease the pressure on the walls, by increasing the ground area.…”

“…Air leakage has been detected due to flow channeling in the corner, causing large heterogeneities in the transverse sections. The rectangular geometry was strongly affected by the mechanical stress, with the fracture of 97% of the structured material and a rupture of the edge of the internal walls for the packed bed storage [13].…”

Thermal Storage and Release Features of Electric Thermal Storage Heating Systems with Solid Storage Material

“…Doppiu et al [2] put forward an alternative material for thermal storage, analyzed different components theoretically, and measured the reversibility and stability of the material under experimental conditions. Esence et al [3] compared the thermal performance between two regenerators, and evaluated their operating errors. Tian et al [4] simulated the effective thermal conductivity of an autoclave aerated concrete (AAC).…”