Influence of Coke Combustion on NOx Emission during Iron Ore Sintering

Abstract

This paper explores NOx emission during iron ore sintering on a pilot-scale pot. A novel technique of using a three-layered bed structure was adopted to study the role of coke level, properties and combustion behavior on NOx emission. In addition, the lime content of the mix was also altered to understand the effect of the melt formation process. Thirteen sinter pot tests were employed to analyze the influence of coke combustion on NOx emission. As the flame front descended down the pot, NOx emission decreased because of increasing bed temperatures. For this reason, it is to be expected that increasing coke rate will result in higher sinter bed temperature and lower conversion of coke-N to NOx. However, overall NOx emission is little changed because more coke means higher N availability. Increasing basicity (CaO/SiO2) from 1.9 to 2.4 in raw mix results in the decrease of NOx emission, about 5%. Increasing coke size may result in the decrease or increase of NOx emission. Placing coke particles on the outside of granules can lower NOx emission in the middle and bottom layers, by 4–15%. NOx emission in the iron ore sinter process is determined by the conversion of coke-N to NOx and nitrogen source in sinter mix. The atmosphere around coke particles is very important for NOx reduction, and NOx emission will increase by around 15% when oxygen increases by 1 vol.%. During iron ore sintering, temperature has great influence on NOx emission, with levels decreasing by 15–25% for a 100 K temperature increase.