In the process leading to improve burner design, small and semi-industrial scale experiments play an important role providing detailed diagnostics to guide the burner concept evaluation. A methodology of scaling of natural gas flames was developed at IFRF over the last ten years. The methodology was derived using a comprehensive set of experiments, which cover the thermal input span from 0.030 MW to 12 MW with intermediate scales of 0.3 MW, 1.3 MW and 4 MW. These experiments were carried out within the SCALING-400 project. In the present paper the data from the SCALING 400 study concerning the staged NOX flames are analysed.
A quite substantial NOX emission reduction is observed in the highly staged flames. The staged fuel jets immerge into hot combustion products. The mixing of the fuel gas with the combustion air takes place after the original fuel jet has been diluted with combustion products.
Scaling rules of staged-low NOX flames should aim to reach these conditions. To achieve similarity in the flow pattern the general conclusions are:
* The staged fuel-to-central-air momentum ratio must be maintained;
* The staged Natural Gas (NG) jet momentum and Re must be high enough;
* The effect of the furnace confinement is secondary for confinement ratio larger than 3 (the ratio between the furnace diameter and the quarl outlet diameter);
* The geometrical burner similarity should be maintained;
* The heat extraction in the furnace should be similar.