FORMATION OF H2S IN THE BATH SMELTING PROCESS

With the direct utilization of coal to produce hot metal, impurities i n the coal, such as sulfur, enter into the process. The amount of sulf ur in each phase (metal, slag and gas) depends on the operating condit ions. Trials at American Iron Steel Institute (AISI) Direct Steelmakin g and Japan (DIOS) indicate that much of the sulfur enters the gas pha se and the thermodynamics indicate that H2S will be the predominant sp ecie. The sulfur can enter the gas phase by a reaction of the smelting gas with the slag or during the devolatilization and combustion of th e coal. The rate of formation of H2S by the reaction of an Ar-H-2-H2O gas with the slag was measured. It was found that the initial rate is dependent on P(H2O) and the sulfur content of the slag. Under present experimental conditions the rate is controlled by liquid phase mass tr ansport. The diffusion coefficient of the sulfur in liquid slag, assum ing mass transfer control, is estimated to be 6.65 x 10(-7) cm2/s at 1 723 K which is in agreement with published values. The rate of H2S fo rmation was also measured when gas was bubbled through the slag. A rat e expression was derived for desulfurization with a foamy slag. The su lfur content of the slag as a function of time was calculated from the derived rate expressions for different circulation rates of slag from bulk to foam. The sulfur content of the bath smelting gas was estimat ed based on experimental results. Some coal samples were devolitilized and partially combusted with simulated bath smelting gas. The experim ental results indicate that a large portion of the sulfur enters the g as phase during devolatilization and combustion of the coal.