铁矿氧化球团低温还原粉化性能的影响因素评述

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

在高炉和气基竖炉工艺中,为使炉况良好,应保证上升还原气能快速且均匀地穿过料柱,而含铁炉料的低温还原粉化和还原膨胀是恶化料柱透气性的两大主要原因.本文主要综述了影响铁矿氧化球团低温还原粉化性能的因素,并在此基础上讨论了改善球团矿低温还原粉化性能的主要措施.影响球团矿低温还原粉化性能的主要因素包括:球团矿的化学成分(碱度、SiO_(2)、MgO、Al_(2)O_(3)含量等)、物相组成、微观结构和碳沉积等.在实际生产中,可以通过优化球团矿成分(适当提高碱度或MgO含量等)和固结形式(发展部分液相固结)、调控球团矿孔隙结构(喷洒或涂层降低球团孔隙率)等来降低还原速率,减少还原过程产生的内应力,从而改善球团矿的低温还原粉化性能.

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 SiO_(2),MgO,and Al_(2)O_(3) 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.