Formation and Control of Nitrogen Oxide in the Heating System of a Coke Oven

Formation of nitrogen oxides was investigated in the heating system of a coke oven during the combustion of enriched blast furnace gas (BFG). Due to the high temperatures in the heating system in situ measures cannot be taken. With the help of computational fluid dynamics (CFD) the combustion process can be investigated in order to predict the formation reaction of NO. For this problem a nonadiabatic simulation model composed of different models and submodels that described turbulence of flow, radiation, flame characteristics, species transport, and the formation of NO was used to calculate the thermal and prompt NO emission in a pseudo steady state. The simulation tool was applied to predetermined operating points of the coke plant. The goal of this study was to investigate the influence of a staged combustion of BFG that was enriched with natural gas, converter gas, and alternatively coke oven gas on NO emission. The NO emissions of the single-stage BFG combustion increased with rising air excess up to an O-2 offgas content of similar to 3%. After having passed this maximum the NO emissions decreased. Although the double-stage NO emissions show a slight increase with rising air excess, the CFD analysis demonstrated that a double-stage combustion of BFG produces lower NO emissions than a single-stage combustion.