Research On Preparation Technology Of High-titanium BF-protecting Pellet

The use of high-titanium pellets is one of the important technologies for blast furnace protection.So far,the TiO₂ content of titanium-bearing oxide pellet generally less than 13%.The increasing of TiO₂ in the protection pellet can reduce its addition,stabilize the smelting of the blast furnace,and reduce the transportation cost of BF-protecting pellets.Limited by the properties of raw materials and production costs,two key problems in the production of BF-protecting higher than 15%TiO₂ arising:difficulty in pelletizing and poor strength of roasted pellet.The ball-forming performance test and balling test have shown that the balling property order of single ore is:Baima concentrate>Titanium concentrate>Medium titanium concentrate.Medium titanium concentrate with coarse particle size and small specific surface area is unsuitable for preparing pellet,Baima concentrate has good ball-forming performance,when mixed with Titanium concentrate balling,as the ratio of Titanium concentrate increases,the drop number and crushing strength of green ball decrease significantly.The appropriate Titanium concentrate ratio should be less than 41.3%,that is,the pellet TiO₂ content is less than25%.The results of the tube furnace roasting test shown that reducing the preheating temperature and extending the preheating time are the keys to improving the strength of the high-titanium pellet.The preheating time is a key thermal parameter affected by the TiO₂ content of the pellet;the oxidation of high-titanium pellets during preheating process involves two reactions:（a）the oxidation from titanomagnetite（the solution of magnetite and ilmenite）to titanohematite（the solution of hematite and ilmenite）,（b）the oxidation from ilmenite to brookite.Fact Sage7.3software was used to study the oxidation process of pellet,the results shown that the increase of the TiO₂ content in the pellet is beneficial to the oxidation process,and the oxidation process release more heat.the results of oxidation kinetics study shown that the oxidation rate of the pellets first increases and then decreases with the preheating time,the average oxidation rate is 0.108 mm/min at 875℃,and the oxidation rate indicated a linear upward trend with the increase of preheating temperature,relational formula is v=3.20*10^-4（T-556）（mm/min）;due to reaction（b）produce dense brookite（Fe₂TiO₅）,hinder the internal oxidation of the pellet,the pellets form a layered structure,reduce the strength of the roasted pellet.The increasing of TiO₂ content is actually not conducive to improving the pellet consolidation strength,and the increasing temperature will accelerate the rate of reaction（b）,and go against improving the strength of pellet.Research on strengthening technology for balling and consolidation of high-titanium pellet shown that wet grinding can effectively increase the specific surface area of the raw materials,increase the green ball strength without reducing the shock temperature of the green pellet,and improve the consolidation performance of the pellet.Increasing the addtion of bentonite and adding Na OH can also increase the strength of the roasted ball.Other strengthening technologies for raw material has little improvement effect for balling or pellet consolidation.Grate-kiln simulation test results shown that for pellets with a TiO₂content of 21%,under the optimized process parameters:the raw material moisture is 6%and humidifying grind for 6 min,with addition 2.0%bentonite and 0.1%Na OH,under 150mm bed height,170℃blast wind temperature and 1.3m?s^-1speed,2min duration,300℃suction wind temperature and 2.1m?s^-1 speed,5min duration,875℃preheating wind temperature and 2.4m?s^-1 speed,16min duration,1250°C roasting air temperature and 2.4 m?s^-1 speed,14 min duration,qualified roasted pellet was obtained.Increasing the addition of bentonite or adding a small amount of Na OH are beneficial to the strength of roasted pellet,the addition of Na OH will reduce the RI of the pellet and reduce the softening and melting range of the pellet.There are 32 figures,69 tables and 54 references in this dissertation.