In blast furnace operation, metal/slag drainage rate sometimes differs among tap holes, that is, higher slag fraction fluid is drained from one tap hole and lower slag fraction fluid is drained from the other. To analyze the difference, the mathematical tapping model assuming the hearth includes vertical low permeability zone is introduced. In the model, hearth is divided in two parts by vertical low permeability zone in which molten metal can permeate and molten slag can’t permeate due to their viscosities. During tapping, slag height of the tapping side is lowered and only metal is supplied from the other side to maintain the static pressure in the furnace resulting in the difference of slag fraction in drained fluid. The calculated results can trace the observed value. Furthermore, influence of differences in initial tap hole diameters and tap hole mix durability are examined by calculation.

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