MASS-TRANSFER IN GAS-PHASE FOR DECARBURIZATION OF LIQUID-IRON BY CO2-CO GAS-MIXTURES

The rates of decarburization of liquid iron by CO2-CO gas mixtures were measured to discuss the mass-transfer characteristics in the gas phase for a system of reaction between an impinging jet of gas and liquid iron stirred inductively in a crucible under various conditions (concentration of carbon in liquid iron greater-than-or-equal-to 0.2 mass%, gas flow rate = (0.83 approximately 4.17) x 10(-5) m3 NTP.s-1, mol fraction of CO2 = 0.1 approximately 1.0, diameter of nozzle = (0.66 approximately 1.32) x 10(-2) m, temperature = 1773 approximately 1973 K, and frequency of furnace = 9.0, 480.0 kHz). Results obtained are as follows: (1) The decarburization rates under the above experimental conditions depend upon factors such as the gas flow rate, the concentration of CO2 in gas phase and the nozzle diameter which affect the gas-phase mass transfer. While the rates are affected hardly by the temperature which affects the chemical reaction, and also are independent of the concentration of carbon in liquid iron and the frequency of furnace which affect the mass-transfer rate in liquid. From these, it is shown that the decarburization is controlled by the mass transfer in the gas phase. (2) Sherwood numbers Sh (= k(G)d/D(AB)) obtained from observed values of rates and a rate equation of the gas-phase mass transfer are correlated by an equation, Sh = alpha(r(s)/d)-1.5(v/D(AB))0.5(du(G)/v)0.76 (alpha = 0.27 +/- 0.05), where k(G) is the mass transfer coefficient for gas phase, d the diameter of nozzle, D(AB) the diffusion coefficient, r(s) the radius of crucible, v the kinematic viscosity of gas, and u(G) the velocity of gas in nozzle. (3) The Sherwood numbers Sh obtained from reported values of decarburization rates are roughly consistent with those given by the above empirical equation.