Ichiya Endo1, Yasuaki Morioka1 and Shunji Itoh1
1Research Laboratories, Kawasaki Steel Corporation, Chiba
In the manufacturing process for obtaining reduced iron powder from mill-scale of rimmed steel strips, the production of iron powder is strictly controlled by the pre-reduction process of the packed mill-scale bed by coke. Consequently, for the increase of this product, the fundamental knowledge of a reduction mechanism of the packed bed has to be reviewed.
In this paper, time dependences of fractional reduction R for a packed columnar iron oxide bed at 1100°C were measured for various kinds of iron oxides with various particle sizes, using several reducing agents different in reactivity. Then, these results were analyzed by applying an unreacted core model.
The results obtained are as follows:
(1) An unreacted core model is applicable to the reduction mechanism analysis.
(2) The reactivity of a solid reducing agent has a considerable effect on R. The reactivity above about 20 vol% (critical value) is necessary for an increase of the reduction rate.
(3) When a reducing agent with a reactivity above this critical value is used, for the reduction of -80\# mill-scale, both R and apparent density of the reduced sponge iron increase with decreasing mill-scale particle size. Below this critical value, on the other hand, the particle size dependences of both R and this apparent density are entirely reversed. However, for the reduction of +80\# mill-scale, those dependences are not recognized at any reactivity values.
(4) The reduction of a packed ore bed containing much Fe2O3 is mainly controlled by an interfacial reaction. On the other hand, the reduction of a packed mill-scale bed containing much FeO is controlled both by a diffusion of CO gas through sponge iron and by an interfacial reaction.
Please do not copy without permission.