Generation of Nitrogen Oxides in Submerged Arc Furnace during the Production of Ferroalloys

The paper presents the method of selection of hard coals applied in reducing mixtures used in ferroalloy production technologies. The graphical relationship between reflectivity and reactivity towards SiO as well as reflectivity and the content of hard carbon Cfix has been presented. The use of hard coal in place of coke is associated with the release of significant amounts of volatiles contained in the coal. Increasing the amount of volatile matter may favor the increased generation of NOx from the fuel mechanism due to the nitrogen content in the organic matter of coal. The influence of the thermal mechanism of NOx generation may be limited due to contradictory phenomena. On the one hand, it is possible to have a higher calorimetric combustion temperature of post-reaction gases (due to the content of coal degassing products), and on the other hand, reducing the amount of energy released from SiO afterburning (less SiO due to higher silicon yields). The higher yield of silicon is related to the higher reactivity of appropriately selected hard coals. The mechanisms of NOx formation were presented together with measurements made during the production of the most popular ferroalloy FeSi75. Measurements were carried out along the two axes P1 and P2 in the furnace hood at three distances from the center of the pitch diameter of the electrodes.