The reduction of NO x formation in natural gas burner flames

Abstract

Natural gas is widely used in domestic and commercial central heating units because it is a clean fuel. However, some NO x is produced and because more stringent legislation on NO x emissions has been proposed, there is considerable interest in designing combustion chambers to give even lower NO x emission. The burners used in such units use multi-jets and the combustion zones and resultant temperature, composition and flow fields have complicated structures. NO x can be reduced by their optimization. Another low-NO x strategy involves the utilization of porous radiant surface combustors. In the present work these two systems have been investigated and experimental data are presented as an aid to understanding the controlling factors for thermal and prompt NO x . In both cases the NO x formation is modelled by a chemical reaction scheme for thermal and prompt NO. The gas flow and temperature fields were modelled by a commercial CFD package, FLUENT, and the NO x predicted with a post-processing package. The value of this method as a design technique is demonstrated. It also gives an indication of the strategies required for low-NO x combustion chambers.