Original Research PaperImprovement in the permeability of sintering beds by drying treatment after granulating sinter raw materials containing concentrates
Graphical abstract
Introduction
The typical iron ore sintering process supplies the main ferrous charge for blast furnaces in most steel mills. During sintering, first the sinter raw materials are intimately mixed and granulated to produce granules with a narrow size distribution, large mean size and sufficient strength. The resulting granules are then charged onto a moving strand to form a stacked bed with an ideal permeability [1]. The top of the bed is ignited by a gas burner. The heat transfer through the sintering bed depends on the air resistance provided by the bed or the ability of air to penetrate through the bed [2]. Hence, the permeability of the bed plays a very important role in sintering. An enhanced permeability of the sinter bed is desirable for transferring heat more quickly from the top to the bottom of the bed and for obtaining better productivity and quality from the sintering plant.
Due to the recent rapid development of China’s steel industry and the depletion of high-grade iron ore resources worldwide, concentrates have gradually been used as an alternative raw material for iron ore sintering [1], [2], [3], [4], [5]. These concentrates have demonstrated a notable impact on the sintering performance and sinter quality. On the one hand, magnetite concentrates are generally known for their high Fe grade and low impurity content and will release extra heat when oxidized to hematite, which means reducing the solid fuel consumption during the sintering process [5]. On the other hand, the concentrate powder is typically extremely fine. Therefore, more fine-sized concentrate powder can lead to additional challenges for sintering, for example, the worsening of the bed permeability [1], [2], [3], [4]. As a result, it is very important to improve the bed permeability when sintering with the introduced magnetite concentrate powder.
To take full advantage of magnetite concentrates, various additional countermeasures have been developed to improve bed permeability. Zhou et al. [1], [6] and Lu et al. [7] used hydrated lime (HL) as a binder to increase the permeability of the packed bed. Zhu et al. [8] improved the granulation performance of Brazilian specularite concentrate by damp milling pretreatment. After damp milling, the average particle size, granulation efficiency and permeability index of the material layer were improved. Yasuhide Yamaguchi et al. [9], [10] improved the permeability of the sintering bed by adding dry particles to granulated raw materials. At the same moisture content, the −0.25 mm ratio of pseudo-particle size was decreased by this technique. The bulk density decreased when dry particles were included in the mixture. These two reasons led to an improvement in the permeability of the packed bed. Zhu et al. [11] employed the pre-briquetting technique to improve the granulation of a sintering mixture comprising specularite concentrate. Compared with traditional granulation, granulation with pre-briquetted specularite concentrate increased the permeability of the sinter bed and average granule size by 12.69% and 11.17%, respectively, when the sinter blend contained 36% specularite concentrate. Huang et al. [12] studied the effect of pre-wetting treatment on the granulation behavior of iron ore fines. The granulation process reduced the ratio of small particles and increased the ratio of large particles, thus increasing the permeability of the stacked bed. Masaru Matsumura et al. [13] proposed that drying treatment after granulating the sinter raw materials can make the −0.25 mm ratio of pseudo-particle size decrease and ultimately improve the permeability of the stacked bed. The experimental results showed that the sintering permeability is related to the proportion of −0.25 mm quasi-particles. In addition, separated granulation [14], pre-balling, pre-granulation [15] and other technical measures have been used to increase the permeability of packed beds [5].
From the above, few studies have used drying techniques to improve the permeability of stacked beds [13]. The drying treatment method mentioned above has not been used in the granulation and packing tests of sintered materials comprising magnetic concentrate powder. Therefore, we conducted this study to verify whether the drying technique can improve the permeability of the stacked bed when the mixture contains magnetic concentrate powder. Considering that drying may cause the collapse of granules [13], [16], [17], we also tested the cases of adding a binder (HL).
In the present study, we conducted granulation and packing tests and studied the effects of the drying process on the granule characteristics and packed bed properties. Additionally, we tested the drying cases with HL addition to verify whether this process can further improve the permeability. Then, the mechanism affecting permeability was explained. Finally, the original sintering process was optimized.
Section snippets
Raw materials and sinter mixtures
All raw materials used contained iron ore fines, magnetic concentrate powder, coke, fluxes and return fines. Furthermore, hydrated lime was used as a binder. The hydrated lime is a high-grade, fine powder with a mean volume diameter of 12.66 μm (25% < 7.42 μm, 50% < 14.26 μm, 95% < 22.73 μm) [6]. The five kinds of iron ore used have a fairly widespread size distribution (0–9 mm). As fluxes, the sizes of limestone, dolomite and serpentine are below 3 mm while coke and the return fines are both
Comparison among the cases with equal moisture content after granulation
It should be mentioned that the cases in Table 2 are predetermined, and the experimental moisture may be slightly different from that in Table 2 due to the erratic weather and the differences in the batches of raw materials. The differences in the moisture content were generally less than 0.1%.
The comparison among the tests with equal moisture content after granulation (7.7%) is shown in Fig. 3. The results indicate that with more sufficient drying, the permeability of the stacked bed gradually
Conclusions
A technique of drying after high-moisture granulation is proposed to improve the bed permeability. The granulation and packing tests of sinter mixtures containing magnetic concentrate powder were conducted with and without this technique. The main conclusions are summarized below.
- (1)
This technique can dramatically improve the bed permeability. High-moisture granulation results in a bigger granule size and narrower size distribution, and drying before charging can improve the granule strength and
Acknowledgements
This work was supported by the National Science Fund for Distinguished Young Scholars of China (NO. 51825605).
References (28)
- et al.
Effect of pre-briquetting on the granulation of sinter mixture containing high proportion of specularite concentrate
Powder Technol.
(2018) - et al.
On the modelling of the packing of fine particles
Powder Technol.
(1997) - et al.
Voidage of ferrous sinter beds: new measurement technique and dependence on feed characteristics
Int. J. Miner. Process.
(1994) - et al.
3-D Transient conjugated heat transfer and fluid flow analysis for the cooling process of sintered bed
Appl. Therm. Eng.
(2009) - et al.
Energy and exergy analysis for waste heat cascade utilization in sinter cooling bed
Energy
(2014) - et al.
Characterization of granule structure and packed bed properties of iron ore sinter feeds that contain concentrate
ISIJ International
(2017) - et al.
Preparation of iron ore micro-pellets and their effect on sinter bed permeability
Trans. Indian Inst. Met.
(2018) - et al.
Effect of concentrate and micropellet additions on iron ore sinter bed permeability
Mineral Process. Extr. Metall.
(2016) - et al.
Relationship between iron ore granulation mechanisms, granule shapes, and sinter bed permeability
Miner. Process. Extr. Metall. Rev.
(2017) - et al.
Recent advances in sintering with high proportions of magnetite concentrates
Miner. Process. Extr. Metall. Rev.
(2018)
Influence of binder dosage on granule structure and packed bed properties in iron ore sintering process
ISIJ Int.
Strategies for efficient utilization of CRL magnetite pellet feed in sintering and pelletising
Improvement of sintering behaviours of Brazilian specularite concentrate by damp milling
Iron and Steel
Improvement of permeability of sintering bed by adding dry particles to granulated raw materials
ISIJ Int.
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2022, Powder TechnologyCitation Excerpt :Granulation moisture is also one of the critical factors affecting the structure of the green bed. The particle size of raw materials increases and its distribution narrows, the permeability of the green bed increases, thus the flame front speed increases [22], with the increase of granulation moisture within a specific critical value range, which is different for different iron ore materials [23,24]. The permeability of the green bed deteriorates under the condition of too high granulation moisture [25].