Formation of H2S in the Bath Smelting Process.

With the direct utilization of coal to produce hot metal, impurities in the coal, such as sulfur, enter into the process. The amount of sulfur in each phase (metal, slag and gas) depends on the operating conditions. Trials at American Iron Steel Institute (AISI) Direct Steelmaking and Japan (DIOS) indicate that much of the sulfur enters the gas phase and the thermodynamics indicate that H2S will be the predominant specie. The sulfur can enter the gas phase by a reaction of the smelting gas with the slag or during the devolatilization and combustion of the coal. The rate of formation of H2S by the reaction of an Ar-H2-H2O gas with the slag was measured. It was found that the initial rate is dependent on PHO and the sulfur content of the slag. Under present experimental conditions the rate is controlled by liquid phase mass transport. The diffusion coefficient of the sulfur in liquid slag, assuming mass transfer control, is estimated to be 6.65×10-7 cm2/s at 1723 K which is in agreement with published values. The rate of H2O formation was also measured when gas was bubbled through the slag. A rate expression was derived for desulfurization with a foamy slag. The sulfur 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 estimated based on experimental results. Some coal samples were devolatilized and partially combusted with simulated bath smelting gas. The experimental results indicate that a large portion of the sulfur enters tha gas phase during devolatilization and combustion of the coal.