Carbon Formation on the Surface during the Reduction of Iron Oxide Particles by CO and CO/H2 Mixtures

Abstract Carbon deposition on the iron surface is of great interest due to a good performance to prevent sticking during the direct reduction (DR) in the fluidized bed. The promising routes of carbon formation were investigated by the density function theory (DFT). An innovative kinetic model, which considers adsorption and decomposition of CO, is applied to control the carbon content of direct reduction iron in the two-stages reduction process. The results show that the C O bond of CO is stretched due to the attractive force of surface iron atoms on the C and O atoms. The added H 2 can significantly improve this C O bond stretch to decrease the barrier energy of CO decomposition. The formation of carbon is sensitive to the temperature and the added H 2 can extend the temperature range for carbon formation and reduce the temperature of the maximum rate of carbon formation. Besides, the proper concentration of H 2 added in the CO/H 2 mixtures can improve the formation of carbon shell. However, the carbon shell will not be formed under a condition of extremely high mole fraction of H 2 because H 2 increases the adsorption energy of CO on the iron surface.