The issues relating to coke circulation at the air tuyeres in high-productivity blast furnaces may be elucidated by systematic analysis of literature and production data and model experiments. Research on the forces associated with cavity formation and destruction in combustion ahead of the tuyeres indicates that three states are possible in the combustion zone: stability, instability, and collapse. In the stable state, when the uplift force of the gases from the cavity significantly exceeds the vertical pressure of the batch column, there will be no coke circulation. Coke circulation occurs in the unsteady state and at collapse. Rationalization of the terminology is proposed. In mechanical terms, it is expedient to divide the combustion zone into loose and dense sections, rather than into a circulation zone and a dense section.
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