Effects of liquid dripping on drainage behavior of blast furnace hearth

Abstract

Among many ironmaking devices, the blast furnace still dominates over the past centuries. In this research area, the understanding of the blast furnace hearth is relatively insufficient because of its complicated environment from which all the accumulated final products are removed. The removal of the liquid iron and slag from the hearth is usually called drainage, tapping, or casting. The drainage in the hearth has been appreciated crucial in avoiding overflood- ing or gas leak, which can either cause damage or disturbance to the blast furnace operation. For example, a Flow-out coefficient (FL) was derived from the Fluid Dynamics theories to qualitatively predict the drainage behaviour, followed by a series of modifications to tweak this number for different tapping conditions. However, the physical approaches do not provide sufficient flow details for a better understanding of this phenomenon. Instead, to track the slag-gas surface during the drainage, Pinczewski et al. used the Finite Difference Method (FDM) to establish a two-dimensional numerical model. More numerical models were developed afterwards with more advanced discretisation and surface track methods. However, while modelling the tapping process, the dripping pattern has been constantly assumed uniform and even neglected particularly in evaluating the drainage efficiency. Even though, it was proven that gas drag can significantly bias the dripping pattern. In order to understand the effects of the descending slag on the drainage behaviour, a Computational Fluid Dynamics (CFD) model was created within acommercial software package. Then, it was used to validate a latest modification of FL. Secondly, the current study extensively investigated the influences of various dripping patterns on the slag-gas interface and the slag flow in the hearth. In agreement with the previous assumption that the uniform dripping pattern has limited effects on the drainage behaviour, the results of this study demonstrate that a wall-biased dripping pattern can effectively reduce the residual ratio by 25% and the accompanying changes in the slag flow. In conclusion, this study offers the prerequisite for a new guideline in improving the drainage efficiency for the real operation given that the dripping pattern can be significantly biased by gas drag.