SynopsisPrevious studies concerned with the drainage of the blast furnace hearth have assumed that the iron-slag interface remains horizontal and fixed at the level of the taphole during the outflow of the slag phase. As a consequence they have ignored the presence of the iron phase and its effect on the drainage characteristics of the slag phase.In this study we examine the validity of the above assumption using a novel two-dimensional experimental drainage apparatus which allows a clear visualisation o f the drainage behaviour of two immiscible f luids. The results of the study suggest that in most cases the iron and slag phases may be expected to flow simultaneously from the taphole and that the iron-slag interface will not remain horizontal and fixed at the level of the taphole as has been previously assumed.It is shown that the drainage process is characterised by a down-ward tilting of the gas-slag interface towards the taphole and a simultaneous downward tilting of the iron-slag interface away from the taphole. The experiments show that it is possible to drain the iron phase down to levels considerably below the level of the taphole. The volume of iron removed below the level of the taphole increases with increasing slag drainage rate. Calculations are presented which suggest that under actual blast furnace conditions this volume may be of the same order as the volume of residual slag remaining above the level of the taphole at the end of tapping.Finally, it is concluded that existing predictions of slag residual ratio based on studies which have neglected the presence of the lower iron phase may lead to a serious underprediction of the residual ratio particularly at higher slag drainage rates.

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A mathematical model for the four-phase (gas, powder, liquid, and solids) flow in a two-dimensional ironmaking blast furnace is presented by extending the existing two-fluid flow models. The model describes the motion of gas, solid, and powder phases, based on the continuum approach, and implements the so-called force balance model for the flow of liquids, such as metal and slag in a blast furnace. The model results demonstrate a solid stagnant zone and dense powder hold-up region, as well as a dense liquid flow region that exists in the lower part of a blast furnace, which are consistent with the experimental observations reported in the literature. The simulation is extended to investigate the effects of packing properties and operational conditions on the flow and the volume fraction distribution of each phase in a blast furnace. It is found that solid movement has a significant effect on powder holdup distribution. Small solid particles and low porosity distribution are predicted to affect the fluid flow considerably, and this can cause deterioration in bed permeability. The dynamic powder holdup in a furnace increases significantly with the increase of powder diameter. The findings should be useful to better understand and control blast furnace operations.

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