Softening–melting–dripping characteristics and evolution mechanism of vanadium-bearing titanomagnetite carbon composite briquette used as novel blast furnace burden

Vanadium-bearing titanomagnetite carbon composite briquette (VTM-CCB) was proposed as an innovative and promising blast furnace burden to realize low-carbon and high-efficiency ironmaking. To optimize the compositions of VTM-CCB based on its softening–melting–dripping characteristics, the evolution behavior and mechanisms of VTM-CCB in cohesive zone and dripping zone were investigated by conducting softening–melting tests under blast furnace conditions. The results show that the structure evolution of VTM-CCB in softening–melting process is correlated to the molten slag, metallic iron, liquid iron, and residual carbon. With the molar ratio of the fixed carbon to the reducible oxygen in iron oxides (FC/O ratio) ranging from 0.8 to 1.0, the VTM-CCB tends to form dense structure and accelerate the softening and melting. With increasing the FC/O ratio to 1.2 and 1.4, the VTM-CCB tends to form concentric circular structure, which could suppress the collapse of packed bed, shift down the location of core cohesive zone, and improve the gas permeability. Although the appropriate increase in FC/O ratio could improve the softening–melting performance of VTM-CCB, a higher FC/O ratio could also promote the precipitation of Ti(C,N), thereby thickening the molten mixtures and deteriorating the dripping behavior. Fully considering the softening–melting–dripping characteristics and permeability, the appropriate FC/O ratio of VTM-CCB should be controlled in the range of 1.0–1.2.