Full scale testing and CFD analyses of a 35 MW heavy duty MILD burner

Experimental and numerical analysis of a 35 MW semi-industrial Ultra-Low NOx burner, operating in Moderate or Intense Low-oxygen Dilution (MILD) combustion regime, are illustrated. The first part of the study presents the experimental investigation of the heavy-duty burner designed for steam generators, embedding steam injection and external flue gas recirculation (EFGR) strategies to mitigate NOx emissions. Tests conducted by Centro Combustione Ambiente (CCA) show NOx level of 26 ppm with 1.3 % residual oxygen (dry basis) under baseline conditions (natural gas as fuel), maintaining stable combustion down to 5 % excess air with CO emissions below 25 ppm. Steam injection by 26 % of fuel mass flow rate results in a 40 % reduction in NOx emissions; then adding EFGR up to 32 % of combustion air reduces NOx emission below 10 ppm, corresponding to a 60 % reduction relative to baseline operation. In the second part, CFD simulations are used to give insight into flow and combustion, assessing the suitability of the Flamelet Generated Manifold (FGM) and the Perfectly Stirred Reactor (PSR) modelling approaches coupled with Gri-Mech 3.0 mechanism. Numerical analyses show the high degree of internal flue gas recirculation already under baseline conditions, which contributes to dilution of the reactive mixture, confirming typical MILD combustion behavior. The implementation of steam injection and EFGR further suppresses peak flame temperatures and enhances the dilution of the fuel-oxidizer mixture. Comparison against experimental data shows that FGM and PSR models quite reliably predict NOx emissions, while CO estimates remain inaccurate, highlighting the need for further model refinement.