Effects and mechanism of composite binder on high-temperature consolidation of pellets
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摘要: 膨潤土是球團礦生產過程中的主要粘結劑,能顯著改善原料成球性、提升球團質量,但較高的SiO2和Al2O3含量會造成煉鐵生產渣量增加。添加少量有機粘結劑替代部分膨潤土已成為改善球團性能的必要手段。本文考察了有機粘結劑P替代部分膨潤土對球團高溫強度的影響,結合激光閃射法和熱重法(TG)研究了有機粘結劑對磁鐵礦球團內部結構及傳熱、傳質的影響。結果表明,復合粘結劑可以替代部分膨潤土,適量有機組分的增加有利于預熱球、焙燒球強度的提升和球團的氧化。主要原因是有機粘結劑P經過高溫后熱解,并在球團內部形成適量孔隙,球團熱傳導系數降低,內部升溫梯度減緩,避免了球團表層因過快氧化結晶而形成致密的氧化層。同時,細小的孔隙有利于氧氣進入球團內部,促進Fe3O4氧化成Fe2O3,氧化分數
$ f $ TGA隨著有機粘結劑P的添加而逐漸升高,由90.80%提至92.17%。Abstract: Iron ore pellets have several substantial advantages, such as high iron grade, low harmful elements, low smelting slag, and low pollution in the production process. Rapidly developing the pelleting process and improving the quality of pellet ores is crucial for achieving the goals of carbon peaking and carbon neutrality in the steel industry. Bentonite, a major binder in the pellet ore production process, can significantly improve the sphericity of raw materials and enhance the pellet quality; however, the higher SiO2 and Al2O3 content will cause an increase in the slag volume of ironmaking production. An organic binder has the advantages of low dosage and less harmful impurities, which can improve the pellet ore grade and the expansion rate of pellets. Thus, adding a small amount of organic binder to replace part of the bentonite is essential to improving the pellet performance. This study investigates the effect of organic binder P replacing part of bentonite on the high-temperature strength of pellets. The laser flash and thermogravimetric methods were employed to investigate the effects of organic binder on the internal structure, heat transfer, and mass transfer of pellets. The results indicated that bentonite was beneficial in reducing the porosity and high-temperature consolidation of pellets because it could promote the generation of a low-melting-point liquid phase. With increasing bentonite addition, the strength of preheated and roasted pellets increased, and the porosity decreased from 21.82% to 15.68% when bentonite addition increased from 1.1% to 2.0%. Thus, the composite binder could replace a part of the bentonite and significantly improve the strength of preheated and roasted pellets with increasing addition. Moreover, the organic binder P was pyrolyzed at a high temperature and formed pores inside the pellet, resulting in a lower thermal conductivity and a slower internal heating gradient. The thermal diffusivity reduced from 0.321 to 0.266 mm2·s?1, and the heat transfer coefficient decreased gradually from 0.551 to 0.454 J·g?1·K?1. Thus, the formation of a dense oxide layer on the surface of the pellets owing to rapid oxidation was avoided, and the oxidation of hematite inside the pellets was promoted, thus enhancing the pellet strength. Moreover, the tiny pores facilitated oxygen transfer to the interior of the pellets and promoted the oxidation of Fe3O4 to Fe2O3. The oxidation fraction$ f $ TGA gradually increased from 90.80% to 92.17% with the addition of organic binder P.-
Key words:
- pellets /
- bentonite /
- organic binder /
- oxidation consolidation /
- porosity
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圖 9 不同復合粘結劑添加量焙燒球團的氧化區域.(a)球團外層(1—1.2% F,2—1.2% F + 0.02% P,3—1.2% F + 0.04% P,4—1.2% F + 0.06% P);(b)球團內部(1—1.2% F,2—1.2% F + 0.02% P,3—1.2% F + 0.04% P,4—1.2% F + 0.06% P)
Figure 9. Oxidation zone of roasted pellets with different compound binder additions: (a) outer layer of pellets (1—1.2% F, 2—1.2% F + 0.02% P, 3—1.2% F + 0.04% P, 4—1.2% F + 0.06% P); (b) inner layer of pellets (1—1.2% F, 2—1.2% F + 0.02% P, 3—1.2% F + 0.04% P, 4—1.2% F + 0.06% P)
表 1 原料化學成分及配比(質量分數)
Table 1. Chemical composition and ratio of raw materials
% Iron ore TFe FeO SiO2 Al2O3 CaO MgO P2O5 Sx LOI Ratio ore-A 65.15 24.89 4.95 1.66 0.40 0.54 0.01 0.08 ?0.74 55 ore-B 65.46 25.83 3.76 0.63 1.02 1.62 0.10 0.20 ?1.91 25 ore-C 65.75 26.50 6.57 0.84 0.30 0.48 0.01 0.05 ?0.47 20 表 2 原料的粒度分布及比表面積
Table 2. Particle size composition and specific surface area of raw materials
Iron ore Particle size composition
(mass fraction)/%Specific surface area/(cm2?g?1) +74 μm ?74 μm~+45 μm ?45 μm ore-A 6.0 15.2 78.8 1408 ore-B 0.5 4.7 94.8 1466 ore-C 6.4 13.3 80.3 1568 表 3 膨潤土F物化特性
Table 3. Physical and chemical properties of bentonite F
Mass fraction of
montmorillonite/%Methylene blue adsorbed
(per 100 g)/gWater absorption
(2 h)/%Swelling coefficient/(mL·g?1) Colloid index
(per 15 g)/mL49.07 21.69 496 25 580 表 4 不同膨潤土F添加量的焙燒球團孔隙度
Table 4. Porosity of roasted pellets with different bentonite F additions
Mass fraction of Bentonite F/% Porosity/% 1.1 21.82 1.2 20.05 1.3 19.42 1.4 19.42 2.0 15.68 表 5 復合粘結劑添加量的焙燒球團孔隙度
Table 5. Porosity of roasted pellets with different composite binder additions
Mass fraction of composite binder /% Porosity/% 0.000 20.05 0.020 17.82 0.024 16.56 0.028 16.02 表 6 復合粘結劑對球團的傳熱性能的影響
Table 6. Effect of composite binder on the heat transfer performance of pellets
Mass fraction of
composite binderSample thickness/
mmSample density/
(g·cm?3)Thermal diffusivity/
(mm2·s?1)Heat transfer coefficient/
(W·m?1·K?1)Specific heat capacity/
(J·g?1·K?1)1.2% F 2.42 3.4 0.321 0.551 0.505 1.2% F + 0.02% P 2.46 3.3 0.309 0.530 0.504 1.2% F + 0.04% P 2.46 3.4 0.282 0.481 0.502 1.2% F + 0.06% P 2.46 3.4 0.266 0.454 0.502 259luxu-164 -
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