VOIDAGE OF FERROUS SINTER BEDS - NEW MEASUREMENT TECHNIQUE AND DEPENDENCE ON FEED CHARACTERISTICS

A new technique for measuring the voidage of a packed bed of wet deformable granules is described. Rather than attempt to measure voidage in situ, the voidage is calculated from accurate measurements of bed bulk density and separate measurement of granule apparent density by kerosene displacement. The technique is reproducible to +/- 0.005 void fraction. This technique is used to study in detail the factors which determine the voidage of packed beds of granulated ferrous sinter feed. 10 sinter feed blends are used varying the type of ore (7 ores), feed size distribution and moisture content (3.5% to 8%). As moisture content increases, bed voidage passes through a maximum. At low moisture contents, added water reduces the spread of the granule size distribution and increases the voidage. At higher moisture contents, granule deformation becomes important. Granules become more deformable as moisture content increases and the bed voidage drops. The key parameter which affects granule deformation is the granule layer mass to nuclei mass ratio (R). All blends show the same relationship between R and voidage. Voidage decreases with increasing R before approaching an asymptotic value for large values of R. The effect of feed particle size distribution, moisture holding capacity and moisture content on voidage can be explained by their effect on the layer mass to nuclei mass ratio during granulation. Hence, with the aid of a suitable granulation model, the effect of feed blend properties and granulation conditions on bed voidage can be predicted.