Simulation of flow and heat transfer in blast furnace hearth

Abstract

The erosion of hearth refractories is the main limitation for a long campaign blast furnace life. An in-depth understanding of the flow and heat transfer is essential in order to identify the key mechanisms for the hearth erosion. In this study, a comprehensive computational fluid dynamics model is described which predicts the flow and temperature distributions of liquid iron in blast furnace hearth, and the temperature distribution in the refractories. The model addresses conjugate heat transfer, natural convection and turbulent flow through porous media, with its main features including three-dimensional, high grid resolution and a wide range of geometrical and kinematic scales (from taphole diameter to hearth outside diameter). The melt flow was simulated using improved transport equations, including a modified k-ε turbulence model and a thermal dispersion term. The predicted results show a well-organized flow pattern: two large scale recirculation zones are separated vertically at the taphole level. This flow pattern controls the temperature distribution in the liquid phase, so that the temperature remains nearly uniform in the upper zone, but changes mainly across the lower zone. The effects of several important factors are examined, such as the fluid buoyancy vs constant fluid density, and the shape and position of coke free zone (different shapes of coke free zones were assumed in connection with the reported dissection study). The inclusion of fluid buoyancy was found to be most important for the flow pattern observed. Comparison with the plant data from BlueScope Steel's Port Kembla blast furnaces shows that the pad temperature is most sensitive to the thickness of protection layer in the hearth lining.