Cross effect between temperature and consolidation on the flow behavior of granular materials in thermal energy storage systems

Abstract

Calcium looping (CaL) process offers a promising option to boost the energy efficiency and dispatchability in concentrated solar power (CSP) plants. Backed by ample experience on lime and cement industry, the CaL integration in CSP plants could be not only a feasible and reliable technology for energy storage but also a low-cost choice based on the abundance and cheap price of limestone (CaCO3). However, to date, there is no deep fundamental understanding about how different conditions through the pipes and in storage silos affect the flowability of the granular medium. This is a critical issue, therefore, concerning the ease with which the granular medium is transported, fluidized or stored. Our present work challenges the status quo on the granular-based energy storage systems in which many central questions about powder dynamics through the circuit have been dodged. To deeply explore and figure out optimal settings, we have investigated the potential side effects that changes in temperature and consolidations can induce in the powder flowability. In so doing, we analyze the variation of the tensile strength of the powder while it is being fluidized in a wide range of temperatures and consolidations. The powder, CaCO3 with a particle size around 50 μm, was chosen to mimic the actual conditions in CaL-CSP pilot plants (currently under development). The results show a severe impact on cohesion when the CaCO3 granular medium is exposed at different temperatures ranging from ambient to 500 °C, and consolidation stresses up to 2 kPa. With cohesion increasing up until an order of magnitude in this range of relatively low consolidations, it is a foregone conclusion that those changes uncover a scenario that has not been brought up so far.