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Partic. vol. 41 pp. 11-19 (December 2018)
doi: 10.1016/j.partic.2018.03.001

Evolution of deposited carbon during multi-stage fluidized-bed reduction of iron ore fines

Zhan Dua, Qingshan Zhua,b,*, Feng Pana, Zheng Zoua, Zhaohui Xiea, Hongzhong Lia

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qszhu@ipe.ac.cn

Highlights

    • Effects of reduction conditions on carbon deposition of iron ore fines was investigated. • Addition of H2 in CO–CO2 in pre-reduction step promoted the formation of graphite filaments. • Graphite could inhibit the formation of fibrous iron and decrease the surface viscosity. • Graphite was more reactive than Fe3C during gasification and solid-state reduction. • Carbon deposits acted as efficient reductant for the reduction of FeO to Fe above 950 °C.

Abstract

The influence of reduction conditions on carbon deposition during fluidized-bed pre-reduction of iron ore fines was investigated experimentally. The results showed that reduction temperature and the composition of reducing gases had a significant effect on the rate of carbon deposition and the type of carbon deposits (graphite and Fe3C). Low reduction temperature, high CO content, and addition of H2 favored the deposition of carbon, especially graphite. The reduction conditions also significantly affected the surface morphology of the as-reduced iron ore fines. As the amount of deposited graphite increased, the formation of fibrous iron disappeared and graphite filaments were observed. The pre-reduced iron ore fines were further fluidized in pure CO at 850 °C for final reduction. The results showed that graphite could suppress the formation of fibrous iron and decrease the surface viscosity, thereby inhibiting agglomeration during the final high-temperature reduction stage. Reactions that consume the deposited carbon during the final high-temperature reduction were identified and graphite was shown to be more reactive than Fe3C. To enhance the application of fluidization technology in producing sponge iron, a novel solid-state high-temperature reduction method via deposited carbon was proposed and demonstrated to be feasible.

Graphical abstract

Keywords

Carbon deposition; Multi-stage fluidized-bed reduction; Carbon deposits; Surface morphology