Computational fluid dynamics simulation of blast furnace hearth drainage

Iron and slag are the products from blast furnace and normally drained out as a mixture via taphole. Two tapholes are opening alternatively in the large-scale blast furnace hearth. After the taphole switches, molten iron is only tapped out at the first few minutes. This phenomenon is observed widely in the large-scale blast furnace and it is called the Slag delay. Due to the high temperature and high pressure inside the furnace, it is hard to execute real-time observations. A CFD model is developed to study the fluids of iron, slag, and gas inside the blast furnace hearth. This numerical simulation was performed by finite volume method that considers the key forces involved, including the gravity, buoyancy, and the drag between liquid-solid and liquid-liquid. The pressure difference between the liquid surface inside furnace and outside the atmosphere induces the pitting of the liquid surface during the liquids tapping. Consequently, when the bottom of pit reaches the taphole, the gas is drained out through the pit. The computational simulation results by liquid level model are consistent with the observations in the physical water model experiment. The gas is drained out at the water surface still above the taphole level. The pit cause by gas pressure forms a pathway of gas. The experiments show that it is possible to drain out the gas before liquid level attaches the taphole. Calculations are presented which suggest that under actual blast furnace conditions the gas can be drained out during the slag-iron interface is still above the taphole. This scenario in liquid level during the drainage successfully explains the slag delay in the research