Research On Additive Formula And Process Optimization Of Pellets Produced By Imported Iron Concentrate

At present,there is a problem that the proportion of bentonite is too high in the production of pellets in my country,which not only reduces the iron content of the pellets,but also increases the amount of blast furnace slag,resulting in an increase in the blast furnace coke ratio,CO₂ emissions and smelting costs,etc.Therefore,it is of great significance to develop new additives,reduce the ratio of bentonite,and improve the iron content and metallurgical properties of pellets.An additive with excellent pelletizing performance and high iron content was used to replace part of the bentonite in this paper.The influence of the additive on the performance of pellets at various stages under different ratios was explored and analyzed,and the optimal ratios of additive and bentonite and the pellet drying system were optimized through experiments.On the premise of meeting the performance requirements,the pellet grade was improved and the production cost was reduced finally.In the experiment,two kinds of imported magnet powders used in a steel mill were used as raw materials,and 4%,6%,8%and 10%of iron-containing additives with excellent spheroidizing properties were added to replace bentonite.Furthermore,the effects of iron-containing additives on green ball strength,burst temperature,calcined ball strength,reducibility and reduction expansion were investigated.The results showed that:as the iron-containing additive ratios increased from 4%to 10%,the compressive strength of green balls increased from 9.6N/P to 13.5N/P,and the drop strength increased from 3.7times/（0.5m）to 6.2 times/（0.5m）,the reduction degree of calcined balls increased from71.46%to 76.04%,the reduction expansion rate decreased from 11.3%to 8.1%,and the burst temperature of green balls decreased from 640℃to 560℃.When it was lower than8%,the burst temperature of green pellets would be higher than 600℃,which met the production requirements of pellets.Microscopic observation found that with the increase of iron-containing additives ratio,the degree of interconnection of pellets and the area of crystallites decreased,the uniform and fine pores between the crystals gradually became larger,resulting in the strength of calcined balls from 2425.5N/P down to 1890.6N/P.In order to improve the adverse effect of iron-containing additives on the strength of calcined balls,the effects of the ratio of bentonite and iron-containing additives and the drying section process system on the properties of green and calcined balls were investigated through orthogonal experiments.The results showed that 4.0%iron-containing additive and 1.5%bentonite were used to form pellets,the optimal blast drying temperature was 240℃and the time was 7 minutes,the air-drying temperature was 360℃and the time was 8 minutes.Compared with the existing pelletizing process with 2.5%bentonite,the optimized scheme increased the compressive strength and falling strength of green pellets and reduction degree of the roasted pellets by 9.7%,6.1%and 1.0%,respectively,and reduced the reduction expansion rate by 21.4%.The strength of preheating ball and roasting ball reached 866N/P and 3077N/P respectively,which fully met the quality requirements of blast furnace production for pellets.In this study,4%iron-containing additive was used to replace 1%of bentonite,which increased the theoretical iron-containing grade of pellets by 0.61%,and reduced the blending cost by RMB 22.37per ton.It is of great significance for reducing costs and increasing efficiency of blast furnaces as well as green and low-carbon smelting.