Role of magnetic fields and flue gas recirculation (FGR) in a practical MILD heat treatment furnace: Mitigating CO and NO emissions

Flue gas recirculation (FGR) mitigates remarkably NO formation and emission while it unintentionally increases CO emissions as CO₂ oxidation increases in the recirculated gases. Thus, this study investigates the combined effects of flue gas recirculation (FGR), ranging from 0 % to 60 %, and a 6 T applied magnetic field on temperature uniformity and both pollutant emissions in a MILD combustion furnace. A novel FGR modeling approach is developed, and the location and flux densities of the magnet are investigated. A furnace with CO emissions exceeding EPA regulatory limits is selected to ensure the applicability of the current approach. Magnetic fields influence combustion through the Lorentz force and Joule heating, enhancing flow mixing and improving temperature uniformity. Results indicate that FGR effectively reduces NO emissions by lowering peak temperatures and increasing temperature uniformity. Increasing the FGR ratio from 0 % to 40 % reduces NO from 2.5 ppm to 2.15 ppm under the magnetic field, below the U.S. Environmental Protection Agency (EPA) limit. However, FGR significantly increases CO emissions from 382 ppm to 3107 ppm, in a case without the magnetic field. The applied magnetic field mitigates this issue, reducing CO by 96 % to 119 ppm at 40 %FGR and reaching the EPA standard limit. Additionally, MILD combustion criteria analysis confirms a higher MILD quality by combining FGR and magnetic field. Consequently, applying a 6T magnetic field with 40 % FGR optimally reduces emissions, enhances MILD quality, and improves thermal efficiency for cleaner combustion. These findings establish magnetic field-assisted MILD combustion as a promising pathway for high-efficiency, low-emission industrial heating applications.