Conversion of Stored Thermochemical Potential into High Quality Heat in a Continuous Flow Reactor/Heat Exchanger

Abstract

Thermochemical Energy Storage (TCES) offers a promising pathway to overcome the intermittency of renewable energy sources by storing excess heat as chemical potential. Among various high-temperature redox materials, manganese magnesium oxide (MnMgO) stands out for its favorable redox thermodynamic and kinetic properties, as well as its ability to retain its “charge” even under ambient conditions. Although prior work has demonstrated the feasibility of using MnMgO in both fixed and continuous reactors, integrating an independent heat transfer fluid (HTF) stream (other than the reacting gas) at high temperatures in a continuously operated system remains a fundamental challenge for scalable versatile TCES applications. Here, we present the design, operation, and performance of a kW-scale reactor/heat exchanger that continuously oxidizes MnMgO particles and transfers heat to an independent HTF. Reduced particles, processed at ~1500 °C in a separate reactor, are fed into the oxidation reactor at ambient temperature, preheated by the exiting oxidizing gas, and oxidized at ~1000 °C, yielding HTF outlet temperatures exceeding 900 °C. Strategic matching of oxidizing gas and particle flowrates ensures that both the feed and removal of solids occur near room temperature, simplifying solids handling and sealing. Steady-state trials under various conditions like differing HTF flowrates and external wall temperatures demonstrate stable reactor operation, with oxidation conversions above 60%, heat extraction efficiencies up to 55%, and continuous delivery of high temperature heat. These findings highlight the potential of MnMgO-based redox TCES for delivering firm, on-demand, high-quality heat in renewable intensive energy systems. By effectively decoupling heat generation (particle reduction) from heat utilization (oxidation), this particle-based reactor/heat exchanger design enables long-duration energy storage, flexible operation, and compatibility with different power cycles and industrial processes. Future research will focus on scaling up this technology, refining thermal management strategies, and investigating alternative HTFs for even higher efficiency and broader applicability.