Physical Modeling Study on Combined Side and Top Blowing AOD Refining Process of Stainless Steel: Fluid Mixing Characteristics in Bath

摘要

Based on water modeling of the gas stirring and fluid flow in the bath, the fluid mixing characteristics in the bath during the combined side and top blowing AOD refining process of stainless steel were studied on a water model unit of a 120 t AOD converter. The influences of the angle included between each tuyere, the side tuyere number and the gas flow rates for both side and top blowing on the characteristics were examined. The results illustrated that the combined side and top blowing process possessed a good mixing effectiveness. The gas flow rate of the main tuyeres had a key role on the liquid mixing in the bath. With a physical shielding effect of the gas streams from the subtuyeres on the gas streams of the main tuyeres, increasing suitably the gas flow rate of the subtuyeres could enhance mixing efficiency; and the gas jet of the top lance could prolong the mixing time. For a simple side blowing, at a given tuyere number and gas side blowing rate, an increase in the angular separation between each tuyere could be advantageous for shortening the mixing time. At a given angle between each tuyere and gas side blowing rate, increasing the tuyere number could not necessarily reach definitely a similar result. Moreover, it could make the high temperature zone move towards the sidewall around the tuyere outlets and lower the life of the refractory lining due to reducing the gas flow rate of single tuyere and the horizontal penetration of the gas stream. Relevant to the oxygen top bowing rate of 6600 Nm~(3)/h used in the practice, taking 5 tuyeres with 22.5° or 6 tuyeres with 27° could offer a roughly equivalent and good mixing result. As far as only the mixing in the bath is concerned, for the 120 t AOD converter, the existing 7 tuyeres with 18° would not be a proper equipment and arrangement of tuyere under the blowing operations employed for the practical refining. Using 6 tuyeres with 27° could give a perfect mixing in all the various refining periods. The relationships of the mixing time with the gas blowing rates of main tuyeres and subtuyeres and top lance, the angle between each tuyere, the tuyere number, the agitation power densities, and the modified Froude numbers were determined.