Suppression of nitrogen oxides emission from the sintering process of iron ores by optimizing the structure of coke granules

Various types of coke granules were prepared with different powders of reagent, such as SiO₂ Ca(OH)₂ and Fe₂O₃ silica sand, limestone and their mixtures. Combustion experiments were carried out using packed beds of mixtures of the coke granules and alumina spheres in a laboratory-scale sintering simulator under different conditions, e.g., preheating temperature, initial gas composition and so forth. Composition of outlet gas was determined with a lapse of time by conventional infrared gas analyzer and an FT-IR gas analyzing system developed by the authors. Rate of coke combustion and conversion factor from organic nitrogen in coke to nitrogen oxides, i.e., NO, NO₂ and N₂O in outlet gas were calculated using the measured data. Moisture content in the introduced gas considerably affected the formation of nitrogen oxides during coke combustion. Certain types of coke granules, especially those made from the mixtures of CaO and Fe₂O₃ bearing powders gave extremely low amount of nitrogen oxides formation. This phenomenon can be explained by the physical and chemical behavior of calcium ferrites formed by the reaction between CaO and Fe₂O₃ in high temperature.On the basis of these results, a method to reduce the nitrogen oxides emission from the sintering process of iron ores without any serious process change was proposed and the validity of the method was verified by sinter pot tests.