Experimental study on crushing strength and Young's modulus of granules in iron ore sintering using Taguchi method

The contributions of three operating parameters(moisture content,hydrated lime addition,magnetite concentrate substitution)to the crushing strength and Young's modulus of granules in each stage of iron ore sintering were studied by applying the Taguchi method.The results indicated that the strength properties of the iron ore granules were greatly affected by its structure,which is composed of inner nuclei and an outer adhering layer.The granules with a thick adhering layer showed a clear changing trend in strength with increasing temperature,whereas those with a thin adhering layer showed additional fluctuations as their force-displacement responses were greatly determined by the nuclei.The granules with a thick adhering layer were gen erally more deformable and easier to break than that those with the thin adhering layer in most states.The signal-to-noise ratio and variance analysis indicated that moisture was the dominant parameter affecting the strength properties of the iron ore granules,as this factor controls the primary granule structure and material distribution.With the progress of sintering,the contribution of moisture to the quality characteristics gradually decreased(from〜80%to 50%),whereas the contributions of hydrated lime and magnetite concentrate increased correspondingly(from〜5%to 20%).

Direct reduction of hematite powders in a fluidized bed reactor

Ultrafine hematite powder was reduced to produce ultrafine iron powder in a 50%Ar-50%H2 atmosphere at 450-550 ℃ in a fluidized bed reactor. The ultrafine hematite powder shows the typical agglomerating fluidization behavior with large agglomerates fluidized at the bottom of the bed and small agglomerates fluidized at the upper part of the bed. It was found that defluidization occurred even at the low temperature of 450 C with low metallization rate. Defluidization was attributed mainly to the sintering of the newly formed iron particles. Granuation was employed to improve the fluidization quality and to tackle the defluidization problem, where granules fluidized like a Geldart＇s group A powder. Granulation was found to effectively reduce defluidization during reduction, without however sacrificing reduction speed. The asreduced iron powders from both the ultrafine and the granulated hematite exhibited excellent sintering activity, that is, fast sintering at temperature of as low as ~580℃, which is much superior as compared to that of nano/ultrafine iron powders made by other processes.