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.
The flow patterns of the chromium converter (CRC) during top and side-wall blowing have been studied using a physical model (1:7). The dynamic similarity between model and real system has been determined by the Froude number and specific mixing energy. This ensures reliability of model studies, although some simplifications have had to made. The model tests demonstrated clearly that mixing was not sufficient to form slag-steel emulsion by the old blowing practice. Furthermore, the mixing time was 27% shorter in the model by the new practice according to conductivity measurements. Calculations and process tests indicated that back-attack diminished and penetration of gas jets to the steel bath increased. The blowing practice of the CRC has been changed, based on the model tests and semi-empirical calculations. The portion and amount of inert gas from the sidewall tuyeres have been increased and oxygen is brought mainly with Sidewall blowing converters have traditionally used for stainless steel producing. Often a short lining life of the tuyere area has became problematic because of thermal, chemical and mechanical stress during blowing. Minor penetration of gas jets, back-attack of tuyeres and locally high temperature and low mixing have increased wearing of refractory material at the tuyere area.Flowing patterns and sidewall blowing have been researched in several studies by numerical and physical models. The early work of Themelis et al. [1] for modelling jet trajectories has been well proven for the air-water system. According to research of Oryall & Brimacombe [2], physical properties of the liquid exert considerable influence on the jet behaviour. The penetration of jet in the mercury-air system was clearly reduced and expansion angle of the jet was changed from 20ae for the water-air system to 155ae. Igwe et al. [3] have researched the maximum penetration of the nitrogen jet in water and the effect of the liquid density on jet penetration. They have discovered that the penetration of the jet in the liquid steel would be related to that of nitrogen in water by a ratio of 1:1.25 to 1:1.4. According to Hoefele & Brimacombe [4], penetration of the jet increases with the modified 57 a lance to liquid steel. In the previous practice, minor penetration of gas jets and hot reactive oxide mass effected an uneven wearing profile of tuyere area. The addition of an inert gas volume rate prevented forming of 'hot spot' areas near uyeres. As a result of practice change, the lining life in the tuyere area has increased by 12%. The processing time has decreased by 13% because of a more effective mixing and increased oxygen flowrate.Froude number N Fr and the density ratio r g /r l . Experimental measurements of the AOD water model has indicated that penetration distribution of the gas jet is large, and the jet angle varies between 20-155ae [5]. Furthermore, competent mixing has been achieved by horizontal blowing. Mixing has been studied in several works by numerical and physical models [6][7][8][9]. Many parameters (diame...
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