Granulation Behaviors of Specularite Fines in Ferrous Sinter Mixtures

Transcription

1 Granulation Behaviors of Specularite Fines in Ferrous Sinter Mixtures De-qing Zhu,Xiao-bo Li,Jan Pan,Ben-jing Shi (School of Minerals Processing & Bioengineering, Central South University,China)

2 Contents Instruction Materials and Methods Results and Discussion Conclusion

3 Instruction 28 billions tons reserved, main produced from Vale, Anglo, Cliffs, and Rio Tinto Be used or ever used in Baosteel, WISCO, Valin Group, Hansteel and Hebei steel,et.al. Fig1 Distribution of specularite in the world

4 Instruction Imported specularite fines in China High quality feed for sintering and pelletizing High iron grade Low impurity content Relative low price Utilization restricted by poor ballability Low specific surface area Unreasonable size composition Dense structure Blend ratio in sintering: no more than 20%

5 Instruction Granulation of the sinter feed mix is a key step in the overall sintering process. It is important to investigate the granulation behavior of specularite fines to increase its ratio in sinter mixtures. A compact system was established to research the granulation behavior of specularite fines. In which limonite fines acted as the matrix granulated with different ratios of specularite fines and burnt lime. The granulation behavior of specularite fines in this system was investigated comprehensively to provide guidance for improving their granulation performance.

6 Materials Materials and Methods Table 1 Chemical Composition of Raw Materials (mass %) Ores TFe SiO 2 CaO Al 2 O 3 MgO Mn P S LOI Specularite fines C Limonite fines A Limonite fines B Burnt lime % of the iron grade of the specularite fines and SiO 2 and Al 2 O 3 contents are lower than the other two limonite fines samples, which will increase the iron grade of the sinter and enhance the operation of the blast furnace.

7 Materials Materials and Methods Table 2 Size distributions of limonite fines samples (mass %). Size(mm) +8-8~+5-5~+3-3~+1-1~ Sum Limonite fines A Limonite fines B Table3 Size distributions of specularite fines and burnt lime samples (mass %) Size(mm) +1-1~ ~ ~ ~ Sum Specularite fines C Burnt lime % of mm particles in specularite fines C, and will affect the permeability of mixture then the productivity and quality of sinter.

8 Materials Materials and Methods Table 4 Molecular moisture content,capillary moisture content and ballability of iron ore fines samples Ores Molecular moisture content (%) Capillary moisture content (%) Ballability index (K) Specularite fines C Limonite fines A Limonite fines B When K<0.20, cannot be balled in a traditional granulator, when 0.20 K 0.80, possess mid-range ballability and when K>0.8,it means the ores granulate very well in a granulator. The molecular and capillary moisture contents of the specularite fines are much lower than those of the limonite fines, which means that the ballability of the specularite fines is quite poor.

9 Materials and Methods Methods Limonite Fines Specularite Fines Burnt Lime Measured Indexes: Granulation moisture level Pre-ignition permeability, J.P.U Permeability Blending Mixing Water Granulation kinetics (1) Adhering load of specularite fines (2) Microstructure of quasi-particles Granulating Size distribution FIG 1.Flowsheet for the experimental program Microstructure of quasi-particles

10 Results and Discussion Effects of the ratio of specularite fines and moisture on granulation 0.50 P/J.P.U Specularite fines ratio 0% 10% 20% 30% 40% 10% specularite fines has least effect on permeability The permeability of sinter bed get decreased with the increase of specularite fines Moisture(%) FIG2.Effect of moisture and specularite fines ratio on the permeability of granules (1.5% burnt lime and 5 min granulation time).

11 Results and Discussion Effects of the ratio of specularite fines and moisture on granulation FIG3.Granules for different ratios of specularite fines (9.5%moisture content, 1.5% burnt lime and 5 min granulation).

12 Results and Discussion Adhering kinetics of specularite fines The adhering load of specularite fines(%) Specularite fines ratio 10% 20% 30% 40% Granulation time(min) FIG4.Relationship between the total adhering load of specularite fines and granulation time (9.5%moisturecontent and 1.5%burnt lime). Adhering load of specularite fines climbs rapidly before 3 min for granulating then remains steady The adhering velocities of specularite ratios from 10% to 40% are respectively 2.28% min - 1, 4.01% min -1, 4.06% min -1 and 6.10% min -1

13 Results and Discussion Adhering kinetics of specularite fines TABLE 5 Distribution of specularite fines after granulation Specularite fines ratio in the mixture (%) Specularite fines adhering to quasi-particles (%) Specularite fines dispersed in the sinter bed (%) *(9.5%moisture content, 1.5%burnt lime and 5 min granulation). Although the more specularite fines in the mixture, the more fines adhering to nuclei, on the other hand the absolute value of specularite fines which are not adhering to nuclei increases rapidly too.

14 Results and Discussion The adhering behaviors of specularite fines Granulation conditions: 1.5% burnt lime, 40% specularite +60%limonite fines, 9.5% moisture and 5 min granulation). FIG5.Distribution of specularite in the adhering layers, (a)photograph of quasiparticles, (b)optical microscope image, (c)sem image 2000, a (d)the adhering layer of a quasi particle after sintering N-nuclei particles, L-adhering intermediary of fine limonite, S-specularite fines, G-gangue, H - holes.

15 Adhering load of specularite fines (%) Results and Discussion The adhering behaviors of specularite fines With limonite fines, 9.5% moisture Without limonite fines,6.5% moisture Granulation time (min) FIG6.Effect of adhering limonite fines on the specularite adhering load(1.5% burnt lime, 40% specularite, 60% limonite fines and optimal moisture level for each blend) The adhering load with unwashed limonite fines increased slower than with washed limonite fines ; However, these two curves go in opposite directions after granulating for 1 min.

16 Conclusion The conclusions from the study of the behaviour of specularite fines in ferrous sinter mixtures are as follows: (1)The permeability of granules deteriorated with increasing ratios of specularite fines in the mixture, although there was not much difference in adding only 10% specularite fines.

17 Conclusion (2) With increasing specularite fines ratios, the adhering speed accelerated, but longer granulation times were needed to reach balance. Therefore, the granulation time should be extended as specularite increase. (3) The specularite fines are dispersed in the adhering layer, bound by fine limonite particles, consequently, the granulation behavior of specularite fines can be improved by blending in other iron ore fines with high adhering properties.

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