Session: 05-01 Thermochemical Energy Storage for CSP Applications

Paper Number: 114799

114799 - Design, Construction and Testing of a Combined Moving-Fluidized Bed Oxidation Reactor for High Temperature Discharge of Solid-State Thermochemical Energy Storage Particles 

Thermochemical energy storage (TCES) using metal oxide particles has the potential to enable renewables dispatchability by storing energy as chemical bonds for short or long-terms. Other advantages of TCES include high energy density, decoupled charging and discharging steps for long term storage, and delivery of high temperature heat (~1000 °C). TCES converts heat from renewable excess energy into chemical energy undergoing a reduction reaction, then, high temperature heat is released during the reverse oxidation reaction. The oxidation reaction involves the interaction of solid particles and oxidizing gas, which inherently creates mass and heat transfer limitations. The design space for the oxidation reactor is vast; solid-gas contacting patterns can take on forms of moving beds, fixed beds, and fluidized beds. However, an effective decoupled oxidation reactor design for different heat transfer fluids has not been presented so far. 

To enable effective extraction of high temperature heat from TCES, we present here a reactor concept in which a counter-flow fluidized bed with heat exchanger is located between two moving beds. The operation of the reactor involves introducing reduced magnesium manganese oxide particles into the reactor. The particles undergo an exothermic oxidation reaction under air. The moving beds will enable sensible heat exchange between gas and solids to completely preheat and cool down gas and particles, whereas the fluidized bed will facilitate the oxidation reaction and heat extraction. The heat transfer fluid (HTF) destined for the high temperature application will pass through the heat exchanger removing the reactive heat from the fluidized bed. The advantages of the proposed design include: feeding and removal of particles at ambient temperature to avoid handling of hot materials, enabling the integration of different HTFs such as air or sCO2, preventing the carriage of fines downstream, and enhancing heat transfer between reactive particles and HTF.

Low order mathematical models were developed to aid the design and to estimate the effect of operating parameters such as solids and gas flowrates, particle size, final extent of oxidation and HTF type on the performance of the moving beds, fluidized bed, and heat exchanger plates. The design calculations indicate that a heat output between 0.8W to 1.2W from the particles undergoing oxidation can be produced with a particle flowrate between 1 to 2 g/s, achieving conversions between 0.7 to 0.9 using air as process gas. Furthermore, due to the counterflow nature of the operation, the top and bottom moving beds have the potential to completely preheat from 25 °C to 1000 °C the particles and the incoming process gas respectively in a short distance. A finned, narrow channel heat exchanger is employed to accommodate different heat transfer fluids and to maximize heat transfer from the particle bed to the HTF to achieve high temperatures at the outlet.   

Additionally, a 1kW reactor was constructed in high-temperature resistant materials such as superalloy Hastelloy X for the heat exchangers and fluidized bed, and non-porous alumina for the top and bottom moving beds. The reactor is modular, so it enables easy access for maintenance and potential scalability to test larger reactive beds. The system includes an “L-valve” particle pneumatic conveying mechanism for particle flowrate control. Initial testing using N₂ as heat transfer fluid indicates that HTF outlet temperatures between 800 °C to 1000 °C can be obtained in the heat exchangers from ~1kW of heat produced on the particle side. The reactor concept has the potential to be used in several applications such as concentrated solar power plants storing chemical energy during the day and releasing thermal energy at night. It can also be used in waste heat recovery systems storing energy for short or long-terms. 

Presenting Author: Juve Ortiz-Ulloa Oregon State University

Presenting Author Biography: Juve is graduate student pursuing a Doctoral degree in Chemical Engineering at Oregon State University. He also works as a Graduate Research Assistant in Dr. Nick AuYeung's lab. His research focuses on high temperature thermochemical energy storage, reactor engineering and fluidization. Juve has collaborated with leading researchers from Michigan State University, Mississippi State University, Purdue University Northwest and RedoxBlox. He has worked on projects funded by the U.S. Department of Energy focused on developing and scaling up thermochemical energy storage solutions using metal oxides. He was awarded a Fulbright fellowship during the period 2020-2022.