Simulation and validation of multiphase flows in gas stirred vessels

The dynamics of buoyant flow due to oxygen injection inside a BOF vessel is very complex. It involves expansion of a compressible oxygen jet inside the liquid steel pool at high temperature. The local turbulence provides high rate of mixing and fast kinetics for preferential oxidation leading to rapid decarburization. As a first step, this work illustrates application of Computational Fluid Dynamics (CFD) in simulating the isothermal, non-reacting hydrodynamics of the oxygen-injected bath in the vessel. Following Guo, Gu and Irons, 2000[l], the high Mach number compressible oxygen jet is approximated with an equivalent jet of relatively higher density, lower velocity of same momentum to enable realizably big transient time steps. The method used is a transient Volume-Of-Fluid algorithm implemented in FLUENT that is successful in capturing the 'puffing' phenomenon. As the injection is continued, the gas stays trapped below a heavy mass of liquid steel and as the mass of trapped gas exceeds a critical limit, it explodes through the pool of liquid steel. This process repeats in time. While it allows good mixing, it is also prone to process instabilities and flame leak outs through the throat of the vessel. This study shows that CFD is successful in analyzing the possibilities, frequency and magnitude of such puffs.