Experimental and numerical analysis of blast furnace drainage

The thesis studies slag and iron flow in the blast furnace hearth and the complex hearth drainage phenomena by both experiments and numerical simulation. It also presents a mathematical model by which the asymptotic state of the hearth lining can be estimated. The main points of the work were to undertake a quantitative analysis to shed further light
on blast furnace hearth drainage and the corresponding flow and behavior of the interfaces. A transparent Hele-Shaw (H-S) slot model was constructed and experiments were undertaken with it. To gain quantitative tapping information from the experimental model, an image analysis algorithm was developed to treat and refine the experimental results. The H-S model has inherent merits for the application of image analysis, such as low optical distortion. Based on the developed image analysis method, the role of the blast pressure, slag viscosity, and initial accumulated liquid amounts on the tapping duration and residual liquid ratios were examined. Some results were processed to dimensionless form to employ the findings in the practical BF system. In addition, the influence of the operational conditions on the tapping end state was studied. The evolution of liquid levels and volumes, liquid outflow rates and oil ratio, as well as interface angles was studied to characterize the hearth draining.
Since it is not easy to use the H-S model to study certain factors, like the coke-free zone or bed permeability, a simulation model of the H-S was developed to mimic the experimental counterpart. This computational fluid dynamics (CFD)-based model was first validated by experimental data and then applied to analyze the evolution of key process variables. Even though the real furnace hearth experiences continuous inflows of iron and slag, the experiments and computational models developed in this thesis for the sake of simplicity only considered the drainage. To gain an understanding on how the hearth lining design and boundary conditions affect the inner profile of the hearth, an asymptotic erosion model was also developed. The model considers hot metal flow, heat transfer, lining erosion, and possible skull formation and can be used to estimate the durability of the hearth. A number of cases were studied to illustrate the applicability and versatility of the model.