Effect of the Oil Injection Rate on Tuyere-Level Coke Characteristics

Two sets of tuyere drillings were carried out in a medium-size blast furnace operating with oil injection rates of 70 and 110 kg/thm. This study reports the effect of the oil injection rate on the modification of coke properties as it descends into tuyere-level regions. The changes in the mineralogy, the degree of graphitization, and the reaction rate of tuyere-level cokes with CO2 were characterized using SIROQUANT, X-ray diffraction, and a fixed-bed reactor, respectively. The effect of the injection rate was found to be most distinct in the bosh and raceway regions. High injection rate cokes were distinguished by a greater degree of graphitization, less amount of SiC, and complete absence of the mullite phase. Irrespective of the tested injection rates, the magnitude of ferro silicide phases in the tuyere-level cokes was found to be of similar range. During a higher injection rate, the apparent reaction rates of cokes were marginally lower because of a higher degree of graphitization as well as less amount of adsorbed potassium. The study suggests that the effect of injection rates on the coke properties is mainly influenced by their consequences on the changes in the associated temperature profile of various tuyere-level regions. In both operations, the proportion of -3.0 mm fines at various locations was found to be of similar range. However, a high injection rate campaign indicated a marginally higher proportion of -0.45 mm coke fines, which was attributed to a higher degree of the graphitization of cokes at various tuyere-level locations. The study has implications for improving coal selection criterion and coke performance in a working blast furnace.