Absorption and Desorption Rates of Nitrogen in Molten Iron by Bottom Injection of Gases

Abstract

Argon and/or nitrogen was injected into molten pig iron through the bottom orifice.The experimental conditions are as follows : gas flow rate, 10-25Nl/min ; melt depth, 9-28cm temperature, 1400-1600°C.
The absorption rate from pure nitrogen was controlled by the mass transfer in metal phase.When Ar-N₂ gas mixture was injected, however, the absorption rate was controlled by the mass transfer in gas phase.The desorption rate of nitrogen by pure argon was controlled by the gaseous mass transfer.
The volumetric rate constant, which is defined as the mass transfer coefficient multiplied by the total interfacial area between bubbles and molten iron, was obtained in different conditions.The rate constant for the gaseous mass transfer, Ak_g, increased linearly with the gas flow rate and the melt depth.The apparent activation energy was 64kcal/mol.The rate constant for the mass transfer in metal phase, Ak_m, increased proportionally to 0.65 power of the gas flow rate, and linearly with the melt depth.The apparent activation energy was 43kcal/mol.Ak_m/H obtained in the present work was compared with the published data, including not only those of nitrogen transfer, but also of oxygen transfer between bubbles and molten copper and silver.