Design and Scale-Up of Direct-Contact Continuous Oxidation Reactors for High-Temperature Thermochemical Storage Using Concentrated Solar Energy

Thermochemical energy storage (TCES) is a promising solution for long-duration, high-temperature heat storage in concentrated solar power (CSP) systems. This study presents a comprehensive analysis of the design and scale-up of direct-contact continuous oxidation reactors using manganese–magnesium oxide (MnMgO) as the redox material. Operating in the 1000–1500 °C range, MnMgO offers high energy density (>1600 MJ/m3), favorable kinetics, and excellent redox stability. A moving bed reactor regime was considered to estimate the required reactor volume and assess the influence of key parameters, including the temperature, particle size, and gas flow rate. Experimental thermogravimetric analysis (TGA) validated a kinetic model across multiple temperatures and oxygen partial pressures, identifying an optimal operating window between 1000 and 1200 °C for effective oxidation. A time-scale analysis revealed that oxidation kinetics dominate at particle sizes <6 mm, while diffusion becomes rate-limiting at larger sizes. Computational fluid dynamics (CFD) simulations of a 1 kW-scale reactor demonstrated stable temperature profiles, with heat transfer fluid (HTF) outlet temperatures reaching >1300 °C and chemical-to-thermal efficiencies exceeding 70%. Design guidelines were derived for scale-up to 100 kW, highlighting the importance of maintaining gas velocities below minimum fluidization thresholds to avoid entrainment, and of minimizing pressure drop and pumping power through particle size selection. The results indicate that 6 mm particles and a reactor diameter of ∼50 cm are suitable for 100 kW operation. This study provides a validated framework for the practical design of continuous TCES oxidation reactors and supports the integration of MnMgO-based systems into next-generation solar thermal applications.