Stabilizing Particles of Manganese-Iron Oxide with Additives for Thermochemical Energy Storage

Journal article, 2018

Manganese-iron oxide particles are a promising candidate for both chemical-looping combustion (CLC) and thermochemical energy storage. In CLC, the ability of metal oxides to oxidize fuels in an oxygen-free atmosphere and re-oxidize in air is addressed. Whereas, reaction enthalpy is the main focus of thermochemical energy storage for, e. g. concentrated solar power or an industrial process that requires high temperature levels. Sufficient mechanical strength of the particles while they endure chemical, thermal, or mechanical stress is a crucial factor for both concepts. Particle stability is investigated here by adding 20 wt.% of TiO2, ZrO2, or CeO2 as a supportive material to (Mn0.7Fe0.3)2O3. Thermal cyclization and temperature shock tests are conducted in a packed bed reactor to identify chemical stability as well as the effect of chemical and thermal stress. A subsequent particle size distribution analysis is performed to determine the relevant breakage mechanism. Attrition resistance is tested with a customized attrition jet cup to estimate the mechanical strength of particles. It is found that the high tendency of unsupported manganese-iron oxide particles towards agglomeration can be improved with any of the chosen additives. The particles with CeO2, and especially with ZrO2, as an additive indicate an increase in resistance towards attrition. However, adding TiO2 has a severe negative impact on the chemical reactivity of the manganese-iron oxide.