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In order to enhance the dispersion of desulfurizing agents into hot metal, the injection of nitrogen gas has been used together with the revolutional stirring by an impeller of a gate type. At the both ends of the impeller, a nozzle is embedded and used for the injection of nitrogen gas into hot metal toward the direction opposite to the movement of the impeller.Water model experiments show that the gas injected efficiently breaks up a cone shaped agglomerate of desulfurizing agents at the bottom of the rotational vortex formed around the impeller shaft and makes it disperse homogeneously into the bath. This suggests that the chemical efficiency of desulfurization will be improved to a greater extent than that without the gas injection.The plant scale equipment has been constructed to desulfurize 60t of hot metal in a ladle. Under the condition of 77 rpm in revolution rate and 3 Nm3/min of nitrogen gas, sulfur content of 0.05% is reduced to 0.012% after the treatment of 1 1 min with calcium carbide of 3kg (75% in purity) per ton of hot metal.The observed rate of desulfurization is reasonably interpreted in terms of the rate controlled by sulfur transfer in hot metal.

SynopsisBubble dispersion and mass transfer between gas and liquid in a gasstirred system have been studied experimentally and theoretically.Nitrogen gas was injected into water through a nozzle located at the bottom center of a cylindrical vessel. Local gas-holdup distributions were measured by an electrical resistivity probe . The volumetric coefficient in the bubble-dispersion zone for the absorption of C02-water system was measured. Experimental conditions were as follows: gas-flow rate (qG) =(16.7-167) X 10-6 m3/s, radius of vessel (r1)=O.055-.'0.50m, height of water (z1) = 0.1-0.4 m and diameter of nozzle = 6 mm.A mathematical model based on the boundary-layer theory is proposed. The model consists of equation of flow with uniform effective kinematic viscosity ve and equations of bubble and solute diffusion with uniform effective d fusivities, De ,B and Dens, respectively. Equations were solved numerically assuming ve=De ,B=Dens, and the theoretical distribution of local gas holdup, axial velocity, and solute concentration were obtained. By comparing the theoretical distributions of local gas holdup with the measured ones, values of ye could be obtained for various qG, rl and z1. The values of ve were correlated with qG on the basis of dimensional analysis. This correlation was consistent with related data available in the literature. Volumetric coefficients, calculated by the present model, were in agreement with the observed ones.

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