Table 1. Values of friction factors of side tuyeres used for the 120 t AOD converter and its water model unit.And the gas side blowing rates of the main tuyere and subtuyere for the model corresponding to the gas blowing rates of the prototype during the practical refining process were determined in terms of the following two cases: 1) Considering only heating friction flow of the gas in the tuyere used for the real refining process.2) Taking both heating friction flow of the gas in the tuyere employed for the real process and heat expansion of the main tuyere gas after entering the bath into account. The results of theoretical calculations of the properties for the gas stream and evaluation of the heat transfer between the stream and liquid steel in the converter demonstrated that the outlet temperature of the subtuyere gas stream would have achieved or slightly exceeded the mean value of the gas in the bath, therefore, it would not be necessary to consider heat expansion of the subtuyere gas in the bath.The results obtained for the main decarburization period of the blowing process of 304 grade stainless steel in the 120 t AOD converter with the values of some related parameters are shown in Table 2, being markedly different from those given in the preliminary investigation, and having also much higher accuracies. Relevantly, the kinematic similarity between the model and its prototype is much better than that in the preliminary investigation.In addition, besides heating friction flow of the gas in the tuyere for the practical refining and heat expansion of the main tuyere gas after entry into the bath, an increase in the gas flow rate caused by formation of CO in side blowing process at a high initial carbon content of 3.5 mass% or so was also considered, and the corresponding gas blowing rate for the model was fixed.Since the hot metal employed for the practical refining in the 120 t AOD converter under consideration is all predesiliconized and the initial silicon concentration is very low, the influence of formation of solid and liquid oxides (especially SiO 2 ) during the side blowing process on the gas blowing rate of the main tuyere for the model was still ignored in the present work, like that done in the preliminary investigation.For the top blowing process with a gas-liquid two-phase system composed of a non-submerged gas jet and the bath liquid, the relevant r gp and r gm can be taken as (r g0 ) p and (r g0 ) m , and the gas flow rate for the top lance of the model at a given oxygen top blowing rate of the prototype can directly be attained from Eq. (2). Since the zone considered for a gas top blowing process is at the bath surface (which belongs to a gas-liquid system) and not at the lance outlet, the outlet March number of the gas jet from the lance for the model and the relevant gas supply pressure must be less than those for its prototype, in order to satisfy Eq. (2) thus ensure the kinematic similarity of the model with its prototype. Experimental MethodsExcept the tuyeres and top lance, the mo...

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 6 600 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.KEY WORDS: stainless steel; AOD refining; combined side and top blowing; fluid mixing characteristics; physical modeling.sults are reported in the paper. Experiments and ConditionsThe experiments were performed on a water model unit shown schematically in Fig. 1, which was entirely the same as that given in Ref. 1). The measurement method for mixing time of the liquid in the bath and experimental procedures were also the same as those used in the preliminary investigation.2,3) The electrical conductivity method was taken. After the gas blowing rate of a specified value was reached and stabilized, without changing the liquid flow pattern in the model bath, a saturated KCl solution of 150 mL was added to the liquid surface in about 1 s, and the adding point was fixedly located near the wall above the sector zone between the outer...

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