Effect of titanium on the sticking of pellets based on hydrogen metallurgy shaft furnace:Behavior analysis and mechanism evolution

Direct reduction based on hydrogen metallurgical gas-based shaft furnace is a promising technology for the efficient and low-carbon smelting of vanadium-titanium magnetite.However,in this process,the sticking of pellets occurs due to the aggregation of metal-lic iron between the contact surfaces of adjacent pellets and has a serious negative effect on the continuous operation.This paper presents a detailed experimental study of the effect of TiO2 on the sticking behavior of pellets during direct reduction under different conditions.Results showed that the sticking index(SI)decreased linearly with the increasing TiO2 addition.This phenomenon can be attributed to the increase in unreduced FeTiO3 during reduction,leading to a decrease in the number and strength of metallic iron interconnections at the sticking interface.When the TiO2 addition amount was raised from 0 to 15wt%at 1100°C,the SI also increased from 0.71%to 59.91%.The connection of the slag phase could be attributed to the sticking at a low reduction temperature,corresponding to the low sticking strength.Moreover,the interconnection of metallic iron became the dominant factor,and the SI increased sharply with the increase in re-duction temperature.TiO2 had a greater effect on SI at a high reduction temperature than at a low reduction temperature.

Direct reduction swelling behavior of pellets in hydrogen-based shaft furnaces under typical atmospheres

Hydrogen-based shaft furnace process is gaining more and more attention due to its low carbon emission, and the reduction behavior of iron bearing burdens significantly affects its operation. In this work, the effects of reduction degree, temperature, and atmosphere on the swelling behavior of pellet has been studied thoroughly under typical hydrogen metallurgy conditions. The results show that the pellets swelled rapidly in the early reduction stage, then reached a maximum reduction swelling index (RSI) at approximately 40%reduction degree. The crystalline transformation of the iron oxides during the reduction process was the main reason of pellets swelling. The RSI increased significantly with increasing temperature in the range of 850-1050℃, the maximum RSI increased from 6.66%to 25.0%in the gas composition of 100%H_(2). With the temperature increased, the pellets suffered more thermal stress resulting in an increase of the volume. The maximum RSI decreased from 19.78%to 17.35%with the volume proportion of H_(2) in the atmosphere increased from 55%to 100%at the temperature of 950℃.The metallic iron tended to precipitate in a lamellar structure rather than whiskers. Consequently, the inside of the pellets became regular, so the RSI decreased. Overall, controlling a reasonable temperature and increasing the H_(2) proportion is an effective way to decrease the RSI of pellets.