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鐵礦氧化球團低溫還原粉化性能的影響因素評述

Review of influencing factors on the reduction disintegration performance of iron ore oxidized pellets

  • 摘要: 在高爐和氣基豎爐工藝中,為使爐況良好,應保證上升還原氣能快速且均勻地穿過料柱,而含鐵爐料的低溫還原粉化和還原膨脹是惡化料柱透氣性的兩大主要原因. 本文主要綜述了影響鐵礦氧化球團低溫還原粉化性能的因素,并在此基礎上討論了改善球團礦低溫還原粉化性能的主要措施. 影響球團礦低溫還原粉化性能的主要因素包括:球團礦的化學成分(堿度、SiO2、MgO、Al2O3含量等)、物相組成、微觀結構和碳沉積等. 在實際生產中,可以通過優化球團礦成分(適當提高堿度或MgO含量等)和固結形式(發展部分液相固結)、調控球團礦孔隙結構(噴灑或涂層降低球團孔隙率)等來降低還原速率,減少還原過程產生的內應力,從而改善球團礦的低溫還原粉化性能.

     

    Abstract: In countercurrent furnaces such as blast furnaces and gas-based shaft furnaces, ensuring smooth operation requires the rising reducing gas flow to pass through the charging materials promptly and uniformly. Two main factors lead to the permeability deterioration of the furnace charge: low-temperature reduction disintegration and reduction swelling of iron ore pellets. Generally, iron ore pellets exhibit good performance in low-temperature reduction disintegration. However, owing to the shortage of high-grade iron ore concentrates in China in recent years, the quality of pellet feeds has considerably declined, leading to a deterioration in the low-temperature reduction disintegration performance of certain types of iron ore pellets. Therefore, this paper comprehensively reviews the main factors affecting the low-temperature reduction disintegration performance of iron ore oxidized pellets under blast furnace and gas-based shaft furnace conditions. The mechanism behind the reduction disintegration of iron ore pellets at low temperatures, and the measures to improve their low-temperature reduction disintegration performance. The low-temperature reduction disintegration of iron ore pellets can be attributed to lattice expansion caused by the phase transformation from rhombohedral hematite to cubic magnetite during the reduction process. Additionally, carbon deposition occurs in the fine pores and crystal cracks of pellets, further increasing internal stress and exacerbating disintegration. As hematite is the dominant phase in iron ore oxidized pellets, phase transformation and internal stress generation during low-temperature reduction are unavoidable. The main factors influencing the low-temperature reduction disintegration performance of pellets include the type of pellet feeds, their chemical composition (e.g., basicity and SiO2, MgO, and Al2O3 content), phase composition, microstructure, pore characteristics of fired pellets, and carbon deposition reaction. In practical production, enhancing the low-temperature reduction disintegration performance of iron ore pellets involves optimizing preheating and roasting parameters based on the characteristics of raw materials, adjusting chemical composition by adding flux (such as increasing basicity or MgO content), modifying consolidation form (generating an appropriate amount of liquid phase consolidation), and regulating pore structure (by spraying or coating to reduce porosity) of iron ore pellets. The underlying principle of these measures is to strengthen the iron ore pellets matrix, increase the content of stable bonding phases during low-temperature reduction, and reduce the reaction rate during the initial reduction stage to mitigate severe expansion stress.

     

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