The Determination of the Minimum and Operational Gas Flow Rates for Sidewall Blowing in the AOD-Converter

Abstract

Gas flow rates from the sidewall tuyeres in the AOD-converter can vary within large range during processing. Back-attack phenomenon, blocked tuyeres, uneven wear of refractory lining and oscillation of the bath set inconsistent demands for the optimum tuyere diameter, number of tuyeres and the angle between each tuyere. Oscillation of the liquid bath, mixing and the penetration of the gas jets with different sidewall blowing procedures were studied by a physical model. The aim of the present study was to determine the criteria for minimum and operational gas flow rate in the actual AOD based on the studied physical phenomena. According to the tests, minimum and operational gas flow rates through the different sized sidewall tuyeres can be defined by modified Froude number based on the appearance of the tuyere blockage (or back-attack) and oscillation. In sidewall blowing, the main reason for the oscillation of the bath is the symmetry of the plume on the vertical axis of the vessel caused by deep penetration of the gas jets. The nominal frequency of the oscillation of steel bath in the actual AOD was determined by dimensional analysis. The gas flow rate, which should be avoid is limited by appearance of oscillation of the bath. Penetration of the molten steel into the tuyeres determines the minimum gas flow rate from sidewall tuyeres. Smaller number of sidewall tuyeres and also a smaller diameter of tuyeres provide larger operational area as far as gas flow rate is considered.