8th International Congress on Science and Technology of Ironmaking - ICSTI 2018

CO-H₂ mixture gas is often used for gas-based DRI process where carbon deposition reaction and Fe₃C metal dusting play serious roles for a stable reduction operation. Fe₃C decomposition leads to the formation of iron particles which is a catalyst for carbon fiber deposition. Because of the parallel occurrence of these reactions, kinetic analysis of them would be complicated. In the present study, to simplify the kinetic analysis, quantitative analysis was conducted by focusing on carbon fiber deposition using thermobalance. A powdery iron sample was prepared by reduction of Fe₂O₃ at 600℃ in 100vol%H₂. Carbon deposition on the iron sample was investigated at 500, 600 and 700℃ under flowing 100%CO, 90vol%CO-10vol%H₂, 75vol%CO-25vol%H₂, 50vol%CO-50vol%H₂, 25vol%CO-75vol%H₂ and 10vol%CO-90vol%H₂ mixture gases. Results showed that amount of the deposited carbon in the CO-H₂ mixture gas is larger than that in the pure CO gas. The largest amount of deposited carbon was obtained at 600℃ in the 75vol%CO-25vol%H₂ mixture gas. According to SEM observations and weight change measurements, carbon was deposited in fiber shape on the iron surface and amount of it was increased linearly with an increase in samples’ weight change. The rate constant of Carbon fiber deposition was calculated considering Rideal mechanism with focusing on elementary reaction steps. It was found that the rate constant of the hydrogen-oxygen reaction step was the largest indicating a significant effect of hydrogen on promoting carbon deposition. This would be due to the removing oxygen from CO by hydrogen on the iron catalyst.