Decarbonization of the world's grid-scale electricity infrastructure will require the implementation of a variety of energy storage technologies. One such technology is thermochemical energy storage with reactive packed beds of metal oxide materials that undergo cyclically stable reduction/oxidation (redox) reactions at high temperatures. These materials store energy via an endothermic reduction reaction that releases oxygen gas, then discharge energy by a coupled exothermic oxidation reaction and interstitial convective heat transfer process, with atmospheric air as both the reactant and heat transfer fluid.Magnesium-manganese oxide is a candidate redox metal oxide material that has demonstrated cyclical reactive stability between 1000-1500 ℗ʻC for several compositional variants. In order to build an energy storage reactor based on a packed bed of these materials, it's critical that the overall energy storage capacity, the optimal operating conditions, and the rate of energy release during the discharge step are quantified.The first half of this work develops a calorimetric method for determining the energy storage densities of magnesium-manganese oxides of five Mn/Mg compositional variants between 1000-1500 ℗ʻC. Drop calorimetry measures the total enthalpy of the phases that exist at the drop temperature, from which the energy stored as sensible heat is computed. Acid solution calorimetry of samples rapidly-quenched in inert gas measures the standard enthalpy of formation at room temperature of the compounds that exist at high temperatures, from which the energy of the redox reaction is computed. The total energy density is then summed from these measurements. The further gains in energy density that can be achieved by lowering the partial pressure of oxygen during reduction are also examined. The Mn/Mg variant of 1/1 is found to have the maximum energy storage capacity when reducing under a low oxygen partial pressure and cycling between 1000-1500 ℗ʻC. A bulk oxidation kinetic model is also presented as part of the energy discharge step.The second half of this work quantifies the convective heat transfer within a packed bed of magnesium-manganese oxide particles. Porous medium heat and mass transport theory for geometrically homogenous and isotropic packed beds is summarized. A collection of similar studies from the literature are selected for comparison with this work. Both a steady-state and a transient method are considered for measuring the interstitial convective heat transfer coefficients. The transient method is found to be more suitable, and a general particle-diameter based convection correlation is proposed for packed beds of spheres. Unique correlations are developed with the transient method for two beds of 1/1 Mn/Mg particles, one granular and one cylindrical. A parametric analysis of the effect of transient wall-to-fluid convective heat transfer on the accuracy of the measured interstitial heat transfer coefficients is performed, finding that a minimum bed radius-to-bed length (R/L) ratio between 1 and 2 should be chosen for any similar experiments and that a lower minimum Reynolds number requires a larger minimum R/L ratio in order to minimize the measurement error. Finally, a 1D coupled oxidation-convection model combines these measurements in a parametric study of the outlet behavior of a reactive 1/1 Mn/Mg packed bed for different inlet Reynolds number and length-to-radius ratios and determines the scenarios in which accurate interstitial convective heat transfer coefficient measurements are important for modeling and controlling the discharge step of a magnesium-manganese oxide energy storage reactor.
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