Mixing Time in a Side-Blown Converter

Abstract

3/s and 800 cm 3 /s as well as bath heights ranging from 106 to 314 mm. The mixing times were also calculated based on an expression involving the Strouhal and Reynolds numbers. The experimentally determined mixing times were found to be within Ϯ20 % of the theoretical values, which is considered to be good in physical modelling. Overall, the mixing time was found to be influenced by the gas flow rate and the vessel diameter, but not by the bath height.KEY WORDS: physical modeling; mixing time; converter; side-blown; conductivity measurements. 663© 2010 ISIJ used to simulate steel and air to simulate argon/oxygen. The gas flow rates were determined by using the Froude number to scale the rate from a full scale converter to a physical model.The different flow rates were calculated by using the Froude number similarity criteria: (2) where r g is the density of air, Q g is the gas flow rate, r l is the density of water, g is the gravitational constant and d i is the nozzle inner diameter. In addition the following Froude number was used to scale the gas flow rate: Equation (3) was used to scale the gas flow rate, compared to a real converter. When this is determined, Eq. (2) was used to scale the size of the nozzle. The size of the nozzle was determined to be 3.2 mm for the smaller physical model. From experience it was determined that the nozzle size has a very small influence on the mixing time in the same manner as observed in a bottom blown bath. The mixing time is mainly governed by the gas flow rate, although the penetration depth of bubbles in the horizontal direction is affected by the nozzle size as well as the gas flow rate. Thus, the same nozzle was used in the larger physical model.A mass flow controller was used to regulate the gas flow rate during the experiments. Also, a conductivity probe was used to measure the change in conductivity. The probe was placed 30 mm from the bottom of the bath and near the side wall, as illustrated in Fig. 1. The output of the probe was fed to a conductivity meter and provided a 0 to 1 V DC output to a computer interface. In addition, the fluid flow was fully developed before the tracer injection of the KCl-solution was made. The solution had a concentration of 1 M KCl, and the amount added was 1 mL solution per 1 000 mL of liquid in the bath. Furthermore, the injection was made by a syringe close to the wall of the vessel. The conductivity of the bath was measured with an interval of 100 ms.The experimental mixing time was defined as the period required for instantaneous tracer concentration to settle within Ϯ5 % deviation around the final tracer concentration in the bath. Results and DiscussionExperiments were done using two vessel diameters of 200 mm and 300 mm, respectively. In addition, experiments were done for bath heights varying from 106 to 314 mm.Air was injected at the bottom of a side wall, as illustrated in Fig. 1. Flow rates between 30 cm 3 /s and 800 cm 3 /s were tested during the trials. Based on Eq. (2) the inner diameter of the side nozzle was determi...

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