The Cohesive Behavior of Granular Solids at High Temperature in Solar Energy Storage

Abstract

Solar technology has shown a keen interest in thermochemical storage to extend its operational timespan beyond a daily basis. Thermochemical solutions are operated by fine powders. Unlike regular granular media, fine powders become cohesive. However, despite the paramount importance of controlling powder flowability to integrate these solutions in solar technology, little research has focused on how powder cohesiveness shapes the flow regime through the storage circuit. This paper investigates two critical factors governing the granular flow through the storage route: temperature and consolidation. The experimental setup emulates the transition powders undergo from silos to reactors. Powders were consolidated before being fluidized at a given temperature, ranging from ambient to 500oC. Tensile yield strength was then measured for different powders. The results exhibit the expected rising trend in the tensile yield strength of powders as temperature increases. But, interestingly, tensile yield strength skyrocketed when powders were subjected to higher consolidations. Backed by theoretical estimations based on mechanical models, the analysis unveils a cross-effect between temperature and consolidation. A combined action that reinforces cohesion by promoting a plastic deformation; worsening, thus, powder flowability. In conclusion, consolidation introduces a multiplying effect on the powder cohesiveness as temperature increases, which represents a serious caveat to solar energy storage technology. To mitigate potential flowability issues, this work explores the use of nanoparticles of silica to layer limestone (calcium carbonate, CaCO3) particles. The nanosilica coatings turned out to be a very promising solution to preclude the enhancement of cohesion induced at high temperatures. Coated samples showed powder cohesiveness at high temperatures similar to the values obtained at room temperature. A solution that offers a simple and reliable alternative to smooth the flow regime in solid-based energy storage technologies at production environments.

Versión aceptada del artículo. La versión final puede consultarse en: https://doi.org/10.1016/j.enconman.2021.114217