Dispersion of bubbles in molten iron and the nitrogen transfer in the bubble dispersion zone at 1 250.DEG.C.

Abstract

20 kg of pig iron was melted in a graphite crucible at 1 250 C. Nitrogen or argon was injected from the bottom. Bubbles in the molten iron were detected by electroresistivity probes, and simultaneously, the rate of nitrogen transfer between the bubble and molten iron was measured by chemical analysis. The radial distribution of bubble frequency at different heights could be represented by the two dimensional Gaussian curve. A plot of the three fold standard deviation against the height gave a clear edge of the bubble dispersion zone. Thermal expansion of the gas was not completed until the bubbles floated up 150 mm from the bottom. The bubble rising velocity had also the radial distribution with a peak at the center, ranging from 0.5 to 3.5 m/sec. The fractional size distribution of bubbles and the total surface area could be calculated by statistical treatments of the data. Using the calculated total surface area, the mass transfer coefficients in metal and gas phases could be calculated under the bottom injection. They were km = 0.82 and 1.28 X 10_3 cm/sec, and kg = 7.9 and 10.3 X 103 cm/sec.