Reduction kinetics of iron oxide pellets with H2 and CO mixtures

Abstract

Reduction of hematite pellets using H 2 -CO mixtures with a wide range of H 2 /CO by molar (1:0, 3:1, 1:1, 1:3, and 0:1) at different reducing temperatures (1073, 1173, and 1273 K) was conducted in a program reducing furnace. Based on an unreacted core model, the effective diffusion coefficient and reaction rate constant in several cases were determined, and then the rate-control step and transition were analyzed. In the results, the effective diffusion coefficient and reaction rate constant increase with the rise in temperature or hydrogen content. Reduction of iron oxide pellets using an H 2 -CO mixture is a compound control system; the reaction rate is dominated by chemical reaction at the very beginning, competition during the reduction process subsequently, and internal gas diffusion at the end. At low hydrogen content, increasing temperature takes the transition point of the rate-control step to a high reduction degree, but at high hydrogen content, the effect of temperature on the transition point weakens.

Reduction of Iron Oxides with Hydrogen—A Review

“…Many kinetics studies show that hydrogen always acts as a better reducing agent. Zuo et al investigated the reduction behavior of iron oxide pellets with different gas mixtures containing H 2 and CO. Figure a shows the reduction progress for different gas mixtures at 800 °C.…”

“…With the increasing ratio of CO to H 2 , the reduction rate slows down. This happens because the diffusion behavior of hydrogen is much better than that of carbon monoxide . Thus, the diffusion rate is more important than the thermodynamic driving force.…”

Reduction Behavior and Kinetics of Iron Ore Pellets under H₂–N₂ Atmosphere

“…Kazemi et al 14) studied the mechanisms of different hematite pellets reduction by hydrogen gas at 800°C and 850°C, it was found that the rate of reduction increased at higher temperatures, but the reduction mechanisms of pellets from industry and laboratory were different. Zuo et al 15) found the reaction rate constant increased with the rise in temperature or hydrogen content through kinetics analysis of hematite pellets reduction using gas mixtures with a wide range of H 2 /CO ratio.…”

“…It takes about 24.5 and 30 min to reach steady state at 1 000°C and 900°C, respectively, which are 5 minutes more than the results under pure hydrogen condition. 15) …”

“…[9][10][11] Reduction process of iron oxides by hydrogen has been widely investigated by numerous researchers. [12][13][14][15][16][17][18][19] EL-GEASS et al 12) found that reduction rate of iron oxide compacts was greater for H 2 reduction and lower for CO reduction, while using gas mixtures showed intermediate rate values with 50%CO-H 2 reduction faster than that of reformed natural gas. Costa et al 13) studied reduction of iron ore by pure hydrogen using small haematite cubes shaped from industrial pellets.…”