Numerical Investigation on Flow-Combustion Coupling and NO Evolution Mechanisms of coal-NH 3 Co-Firing in a Radial Air-Staged Burner with a Pre-Combustion Chamber

A 3D CFD model of a 0.3 MW burner was established to investigate NH3 blending (0–25%) in coal combustion. Arrhenius parameters were adapted to characterize the thermal and chemical promotion induced by coal-NH3 co-firing. Results show that increasing NH3 shifts the combustion mode from recirculation-dominated to jet-dominated. In 0–15% cases, the central recirculation zone ensures rapid near-field NH3 consumption. At 25%, the enhanced jet inhibits recirculation, shifting the reaction zone downstream and delaying NH3 consumption. Tail NO increases at every NH3 blending ratio tested relative to pure coal (335 mg/m3): it reaches 829 mg/m3 at 5%, 386 mg/m3 at 15% and 490 mg/m3 at 25% (O2 = 6%). Among the co-firing cases, the trend is non-monotonic (“increase-decrease-increase”): 15% NH3 yields the lowest co-firing NO (386 mg/m3) due to optimal reduction, whereas 25% triggers a rebound via NH3 slip and downstream re-oxidation. The study highlights that NO evolution is governed by the flow-mixing-reaction coupling within the pre-combustion chamber.