Reduction behavior of vanadium-titanium magnetite carbon composite hot briquette in blast furnace process

Abstract

The reduction behavior of a new type of blast furnace burden named vanadium‑titanium magnetite carbon composite hot briquette (hereinafter abbreviated as VTM-CCB), including fraction of reaction (f), reduction shrinking, crushing strength after reduction, phase transformation of valuable elements, and softening-melting-dripping behavior, were investigated with simulating blast furnace conditions in laboratory in this article. The reduction process of VTM-CCB could be divided into four stages. The devolatilization of the coal and the reduction of magnetite to wustite mainly occur successively in the first two stages. In the third stage, the reduction rate is much higher than that in the second stage due to the high carbon gasification rate. The reduction of Ti-bearing iron oxides occurs in the final stage. The shrinking of VTM-CCB samples is caused by the removal of carbon and oxygen and the suppression of the growth of iron whiskers during the reduction of wustite to metallic iron. The crushing strength of VTM-CCB after reduction is found to decrease from 1800 N to 600 N correspondingly with increasing temperature from 600 °C to 1100 °C. The loss of the crushing strength correlates to the pyrolysis of the coal, the carbon gasification, and the reduction of iron oxides. The phase transformation of valuable elements during reduction could be described as follows: Fe3O4 → FeO → Fe; Fe2.75Ti0.25O4 → Fe2.5Ti0.5O4 → (Fe2TiO4) → FeTiO3 → (FeTi2O5) → TiO2. The softening-melting-dripping behavior and permeability of mixed burden is improved obviously with charging a certain amount of VTM-CCB. However, the precipitation of Ti(C,N) would deteriorate the dripping behavior of packed bed when VTM-CCB charging ratio exceeds 20%.