Processes 2022, 10, 1680. https://doi.org/10.3390/pr10091680 www.mdpi.com/journal/processes Article Development of a Moving Bed Reactor for Thermochemical Heat Storage Based on Granulated Ca(OH)2 Aldo Cosquillo Mejia 1, *, Sandra Afflerbach 2 , Marc Linder 3 and Matthias Schmidt 1 1 German Aerospace Center—DLR e.V., Institute of Engineering Thermodynamics, Linder Höhe, 51147 Cologne, Germany 2 Chair for Environmental and Process Engineering, University of Siegen, Paul‐Bonatz‐Str. 9–11, 57076 Siegen, Germany 3 German Aerospace Center—DLR e.V., Institute of Engineering Thermodynamics, Pfaffenwaldring 38–40, 70569 Stuttgart, Germany * Correspondence: aldo.cosquillo@dlr.de Abstract: Calcium hydroxide is promising for thermal energy storage due to its low cost and high energy density. Nevertheless, the powdered material is cohesive and has low thermal conductivity which is a major challenge for the operation of moving bed reactors. One approach to facilitate the movement of the reaction bed is the stabilisation of the particles through the coating of Ca(OH)2 granules with Al2O3 particles. In this work, a newly designed reactor concept was specifically de‐ veloped for testing coated Ca(OH)2 granules. The design allows for the movement of the reaction bed by gravity assistance and direct heating of the particles by a counter current gas flow. The op‐ eration was successfully demonstrated and proved to achieve high heat transfer between gas and granules. Furthermore, the movement of the reaction bed was achieved after the discharging phase. Two batches of uncoated and coated Ca(OH)2 granules were subject of 10 thermochemical cycles in this reactor. The cycling stability, structural integrity, mechanical stability, morphology and phase composition of the granules were analysed. Full conversion of both samples was demonstrated for the entire experimental series. It was found that the alumina coating enhances the mechanical sta‐ bility of the granules under reaction conditions. Keywords: reactive moving bed; calcium hydroxide; nanocoated particle stabilization; thermochemical storage 1. Introduction A major challenge for the transition to a zero‐emission energy system is the intermit‐ tent availability of the renewable energy sources [1] (e.g., solar and wind power). In order to match the supply and demand, energy storage solutions can be implemented [2]. The thermochemical storage system based on the gas‐solid reaction: CaO + H2O ⇌ Ca(OH)2 + 104 kJ/mol is considered promising due to the number of advantages it features such as high energy density, non‐toxicity, multiple cyclability [3], general availability and low cost [4]. The applications of this storage system have been analysed for concentrated solar power (CSP) plants, conventional power plants and waste heat recovery [5,6]. It is also free of heat losses during the time of storage and therefore suitable for seasonal long‐term storage. For all these reasons, multiple studies have been carried out to characterise the reaction, determine the thermodynamic equilibrium and reaction enthalpy [6–8]. This storage system has been tested in different reactors concepts. For example, fixed bed reactors were demonstrated in several investigations [5,9–14] and served successfully for the thermodynamic characterisation of the reaction process in technical scale. How‐ ever, as in this concept the storage material is attached to the reactor, large heat exchange surfaces are necessary for large storage capacities in industrial‐scale applications which Citation: Cosquillo Mejia, A.; Afflerbach, S.; Linder, M.; Schmidt, M. Development of a Moving Bed Reactor for Thermochemical Heat Storage Based on Granulated Ca(OH)2. Processes 2022, 10, 1680. https://doi.org/10.3390/pr10091680 Academic Editor: Andrea Petrella Received: 19 July 2022 Accepted: 19 August 2022 Published: 24 August 2022 Publisher’s Note: MDPI stays neu‐ tral with regard to jurisdictional claims in published maps and institu‐ tional affiliations. Copyright: © 2022 by the authors. Li‐ censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con‐ ditions of the Creative Commons At‐ tribution (CC BY) license (https://cre‐ ativecommons.org/licenses/by/4.0/).