Particle stability investigation of Mn-Fe oxides supported by TiO2, ZrO2 or CeO2 as thermochemical energy storage materials

Abstract

Thermo-chemical materials have a higher energy density for heat storage applications compared to latent or sensible storage materials. The reversible gas-solid redox reaction of metal oxides offers the advantage that oxygen from ambient air can be used as reactive gas, thus there is no need for a separate storage of the gaseous reaction partner. Depending on the selected reaction system of metal oxide, the equilibrium temperature under atmospheric pressure is in the range from around 700 °C to over 1300 °C. Therefore solar thermal power plants with receiver temperatures up to 1000°C represent one promising application for metal oxides as thermal energy storage material since it allows for a dispatchable renewable power generation. By using the concept of a continuously operated reactor, e.g. a moving bed system, the storage capacity and thermal power output of the storage can be defined separately. However, attrition processes are positively correlated to the particle velocity, leading to increased requirements towards particle stability for a moving bed reactor. Manganese iron oxides are promising candidates for heat storage devices, with an equilibrium temperature between 900 °C and 1350 °C in air depending on the manganese-to-iron ratio. These reaction systems have been already investigated in fixed beds and fluidized beds, where in addition to particle attrition, agglomeration and sintering effects could be observed as well, representing the main issues of particle stability. Since support materials can have a positive effect on attrition resistance and agglomeration processes, the influence of support materials on the stability of manganese iron oxides is examined by measuring the attrition rate and the agglomeration tendency under fixed bed and fluidized bed operating conditions.