Solving the microwave heating uniformity conundrum for scalable high-temperature processes via a toroidal fluidised-bed reactor

• Published in: Chemical engineering and processing Vol. 202; p. 109838
• Main Authors: Rodriguez, Jose, Morona, Lorena, Erans, Maria, Buttress, Adam J., Nicholls, Matt, Batchelor, Andrew R., Duran-Jimenez, Gabriela, Kingman, Sam, Groszek, Daniel, Dodds, Chris
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.2024
• Subjects: Electromagnetic modelling; Fluidised bed; High temperature; Hybrid heating; Microwave heating; Thermal processing; Hybrid heating; Electromagnetic modelling; High temperature; Thermal processing; Microwave heating; Fluidised bed
• ISSN: 0255-2701; 1873-3204
• DOI: 10.1016/j.cep.2024.109838

•Heating uniformity is a major challenge to scale-up of microwave processes.•Novel hybrid convective-microwave heated toroidal fluidised bed reactor presented.•Rapid uniform volumetric heating of process material is achieved.•Robustness, scalability and high-temperature operability built in reactor concept.•Flexible platform technology for development of sustainable processes. Challenges exist to implementing high-temperature microwave processes with changing dielectric properties that achieve uniform processing. This paper presents a new high-temperature hybrid microwave processing system which overcomes these challenges in a robust, scalable way, integrating a slotted waveguide ring microwave feed into a toroidal fluidised bed reactor and maintaining its fluidisation behaviour. The prototype operates at a frequency of 2450 MHz with a maximum power of 10 kW and within a temperature range of 50–300 °C, though it is scalable to industrial levels. Electromagnetic simulations of the system were experimentally validated using a range of agri-crop feedstocks. Hydrodynamic and thermodynamic reactor characterisation was performed, and treatment performance was quantified regarding surface bed temperature variation. Excellent treatment uniformities were found under microwave and hybrid regimes, with a temperature coefficient of variation (CoV) across the bed's surface below 2 %, an order of magnitude better than existing microwave processes, generally regarded as highly uniform with CoV of approximately 20 %. The integration of microwaves and toroidal fluidised beds, without exposed moving parts, potentially unlocks a range of applications previously inaccessible to microwave technology or fluidised bed technologies on their own. Future work involves process development, techno-economic studies, and large-scale pilot trials. [Display omitted]