A review on experience feedback and numerical modeling of packed-bed thermal energy storage systems

Abstract

Solar thermal energy is a clean, climate-friendly and inexhaustible energy resource. It is therefore promising to cope with fossil fuel depletion and climate change. Thermal storage enables to make this intermittent energy resource dispatchable, reliable on demand and more competitive. Nowadays, most of the concentrated solar power plants equipped with integrated thermal storage systems use the two-tank molten salt technology. Despite its relative simplicity and efficiency, this technology is expensive and requires huge amounts of nitrate salts. In the short to medium term, packed-bed thermal energy storage with either liquid or gaseous heat transfer fluid is a promising alternative to reduce storage costs and hence improve the development of solar energy. To design reliable, efficient and cost-effective packed-bed storage systems, this technology, which involves many physical phenomena, has to be better understood. This paper aims to sum up some key aspects about design, operation, and performances of packed-bed storage systems. In the first part, most representative setups and their experience feedback are presented. The controllability of packed-bed storage systems and the special influence of thermal stratification are pointed out. In the second part, the various numerical models used to predict packed-bed storage performances are reviewed. In the last part, some useful correlations enabling to quantify the main physical phenomena involved in packed-bed operation and modeling are presented and compared. The correlations investigated enable to calculate fluid/solid and fluid/wall heat transfer coefficients, effective thermal conductivity and pressure drop in packed beds.

Flexibility and robustness of a high-temperature air/ceramic thermocline heat storage pilot

“…It is commonly accepted that decreasing particle size reduces the length scale for conduction, which is reflected by a lower value of the Biot number, limiting intraparticle thermal gradients, but at the cost of an increase in the pressure drop, requiring a trade-off between transfer quality and pressure drop [23]. These issues have been reviewed by T. Esence et al, providing a good insight into thermocline modelling [24]. The third aspect is focused on the influence of the operating conditions and industrial integration.…”

Experimental validation of steel slag as thermal energy storage material in a 400 kWht prototype

“…A huge research effort has been done in the last years in the search of high performing and low-cost filler materials, in the analysis of their stability in direct contact with the HTF and with thermal cycling, and in the understanding of the temperature stratification (thermocline) mechanisms that govern the thermal performance of the packed bed [1]. Despite all this work, there is still a lack of clear commercial implementation of this type of systems at real industrial scale.…”

Operation strategies guideline for packed bed thermal energy storage systems

“…Considering these boundaries, the search of technically high‐performing and cost‐effective TES solutions has become a priority for the industrial and scientific communities . Among other TES concepts, packed bed systems have been identified in the last years as a very promising technology . The high operation flexibility, the relative implementation simplicity together with its highly technoeconomic effective nature confer to this TES alternative a particular interest.…”

“…The packed bed storage concept has been widely investigated. 7 However, its full implementation at commercial scale is still unclear. Some works have associated poor thermal efficiency to this TES alternative.…”