Rate of Iron Carbide Formation from Reduced Iron in CO-H2-H2S Mixtures under Pressurized Conditions

Abstract

Under pressurized conditions up to 0.6 MPa, the rate of the iron carbide formation from completely reduced iron in CO-H 2 -H 2 S mixtures was measured by gravimetric technique. The fractional conversion for carbide formation, f θ , was defined as the weight gain divided by the weight of carbon for the complete conversion to cementite. First, the compositions of the partially reacted samples were analyzed by Mossbauer absorption spectroscopy. Then, the fractional conversion calculated from the composition, f M θ, was compared with f θ . The value of f θ agreed reasonably with that of f M θ in the range f θ <0.8, from which the gravimetric method is proved to be valid to the measurements for the rate of iron carbide formation. The carbide formation curves, f θ versus t relation, were not influenced by the weight of the sample and the flow rate of the reaction gas in the conditions; 50 mg, more than 3.33×10 -6 m 3 /s. Cross sectional view indicated the homogeneous distribution of cementite regions in the reduced iron particles partially converted to cementite. On the other hand, the rate was very sensitive to the conditions of the carburization reaction on the pore surface. The rate increased with increasing the content of carbon monoxide up to 80 to 90%, where the rate was the maximum, and then gradually decreased with further increasing the content. The rate increased with the total pressure, but decreased with the activity of sulfur. The rate controlling step of the iron carbide formation was discussed on the basis of the experimental results. The rate controlling step was assumed to be the carburization reactions on the pore surface of reduced iron particles.