| Blast furnace gas (BFG) and coke oven gas (COG) are exhaust gases from primary operations in steel making that are almost exclusively utilized as supplemental fuels within the steel plant. These by-product fuels contain mixtures of H2, CO, CH4, CO2, and N 2. They are burned alone or in combination with natural gas (NG) to fire the coke ovens, blast furnace stoves, utility boilers and metal working furnaces. The utilization of these by-product fuels reduces the waste gas emissions at the steel mill and reduces the requirements for outside fuel sources. However, the combustion of these by-product fuel blends does produce hazardous pollutants, which, due to the variable composition, is not well understood. The objective of this research was to develop an understanding of the mechanisms controlling the formation of nitrogen oxides (NOx) and investigate process modifications to minimize NOx emissions.; Combustion experiments were performed on a 100,000 Btu/hr, U-shaped furnace and on a 15,000,000 Btu/hr tunnel furnace utilizing a variety of fuel blends under various conditions. NOx formation was found to be the greatest when utilizing COG and COG blends, indicative of the thermal dependence on NO formation as COG contains significant amounts of H2 and CO, both of which liberate more heat than NG when combusted.; The NOx emission data for the by-product fuel blends correlate strongly to theoretical, adiabatic flame temperature, despite the wide variation of mixtures investigated and different combustion environments. NOx emissions were characterized by the extended Zeldovich reactions. However a single expression for the rate of NO formation based on these reactions failed to account for the rapid formation rate.; Process modifications in the form of fuel blending and fuel reburning were evaluated experimentally and in chemical kinetics modeling. BFG blends with COG effectively reduced NOx emissions, mainly as a result of thermal dilution, similar to the proven reduction strategy of flue gas recirculation. COG was shown to be an effective reburning fuel, similar to the proven reburning fuel NG, despite having a majority composition of nonhydrocarbon fuels. Chemical kinetics modeling confirmed the effectiveness of these strategies in reducing NOx emissions. |
