Experimental and Kinetic Investigation of CH4 Hot Coflow-Assisted Combustion of Simulated Hydrogen-Rich Nuclear Off-Gas

Hydrogen-rich off-gas generated during nuclear fuel fabrication requires safe oxidation with limited nitric oxide (NO) formation. This study experimentally investigates the combustion of a simulated H2/N2 off-gas under open-air jet and CH4 hot coflow-assisted conditions with MILD-like characteristics. One-dimensional premixed flame calculations are further employed to examine the intrinsic kinetics of H2 oxidation and NO formation. Under the open-air baseline condition, the residual H2 and NO concentrations measured at the flame tip were 244.8 and 158.1 ppm, respectively. Introducing hot coflow elongated the visible reaction zone from 13.0 cm to 15.0–22.0 cm and reduced the flame temperature from 783.6 °C to 405–517 °C. The residual H2 concentration decreased to 30.7–104.3 ppm, while NO emissions decreased to 9.4–50.2 ppm. Kinetic analysis revealed that hydrogen oxidation was primarily governed by chain branching reactions involving H radicals and oxygen molecules. Increasing the hot coflow equivalence ratio altered the relative contributions of the Nitrogen–Nitrogen–Hydrogen (NNH) and Zeldovich-related NO formation pathways. Overall, the hot coflow was associated with an extended reaction zone as well as with reduced residual H2 and NO concentrations under the investigated conditions.