【作者】 何国强；

【导师】 姜涛； 范晓慧；

【作者基本信息】 中南大学 ， 钢铁冶金， 2011， 博士

【摘要】 氧化球团矿是优质的高炉炼铁炉料。我国目前主要以磁铁矿为原料采用链箅机—回转窑工艺生产普通酸性氧化球团矿。但随着炼铁生产对球团矿质量和品种要求的不断提高以及我国铁矿资源日渐贫杂化、多样化,拓宽球团生产的原料范围、提高球团矿品质是成为氧化球团矿生产重要而紧迫的课题。与磁铁矿相比,全球赤铁矿资源储量丰富,且价格相对较低,但是由于其赤铁矿球团的焙烧温度高、高温固结温度区间窄等原因,目前还无法大量用于氧化球团矿的生产。本文以巴西产赤铁矿为主要原料,在系统研究氧化球团制备特性的基础上,从改善赤铁精矿表面性质、促进固相扩散、活化晶格、调控液相量等方面改善赤铁矿球团的造球、焙烧性能,并通过实验室试验研究和扩大试验,开发赤铁矿球团制备的工艺技术,实现以全赤铁矿为原料制备优质氧化球团矿。论文首先研究了赤铁矿制备氧化球团的基础特性。研究表明,虽然所用赤铁精矿的铁品位高,但微细粒含量少,比表面积仅为644cm2/g,成球性能很差；仅当预热温度达到1100℃、预热时间8-14min,焙烧温度1300-1320℃,焙烧时间10-18min,才能获得预热球强度400N/P、焙烧球强度2500N/P的产品,采用常规的链箅机—回转窑工艺难以生产出优质球团矿。研究了铁精矿预处理改善造球和球团焙烧性能的方法和机制。结果表明,采用高压辊磨和球磨对赤铁矿精矿进行预处理均可以降低铁精矿的粒度,提高铁精矿的比表面积。高压辊磨主要作用是改变了铁矿颗粒的形状和结构；而球磨后细颗粒明显增多,主要是起到了细磨的作用。采用球磨-高压辊磨预处理方式可显著改善赤铁精矿的成球性能。与不预处理相比,预处理后比表面积达1600cm2/g以上时,造球膨润土用量可降低0.75个百分点,适宜的预热温度可降低100℃,在焙烧温度相当的条件下,球团矿强度可提高500N/P以上。研究了内配适量的碳(无烟煤)改善赤铁矿的焙烧性能的可行性和作用机理。研究表明,与未配碳球团相比,内配少量无烟煤可降低焙烧温度20℃～50℃,缩短焙烧时间5min～10min,同时焙烧温度区间范围扩大了50℃。研究发现：①无烟煤在预热阶段会着火燃烧,释放热量,可降低赤铁矿球团的预热温度；②无烟煤中的碳燃烧产生的CO气体可使赤铁矿在预热阶段部分转化为磁铁矿,这部分磁铁矿在焙烧阶段再氧化放热,转化为活性较高的次生赤铁矿,从而降低赤铁矿球团的焙烧温度,改善球团矿固结强度。研究了添加剂对赤铁矿球团的影响和以赤铁矿为原料制备熔剂性球团矿的可行性。试验表明：石灰石和白云石在预热阶段由于分解吸热,降低了球团内部的温度,致使预热球强度降低。CaO在预热阶段与Fe2O3发生固相反应,生成铁酸钙等低熔点矿物,在焙烧阶段形成少量液相,促进了铁氧化物的微晶连接,提高了焙烧球团的强度。添加少量的白云石可降低球团矿的还原膨胀率。论文最后采用实验室扩大化试验装置研究了以全赤铁矿为原料生产氧化球团矿的工艺技术,获得了最佳的工艺参数。试验表明,内配适量无烟煤和熔剂,采用链箅机-回转窑工艺和带式焙烧机工艺,均可制备出质量优良的熔剂性球团矿。相比而言,链箅机-回转窑生产出的球团矿质量更均匀、转鼓强度高、耐磨性能好。更多还原

【Abstract】 Oxide pellets are quality burden for blast furnace. At present, grate-kiln is the main process for oxide pellet production in China. Acid pellet production by grate-kiln process with magnetite as the main raw material is becoming mature. However, diversified oxide pellet is required by the complex raw material structure in China, so that impoverishment and diversification problem of iron ores can be solved and higher demand of pellet quality by high coal injection and high-intensity smelting can be met. Therefore, it is an important subject of pellet technology to broadening the range of raw material and improving pellet quality.Compared with magnetite, though with resource reserves and price advantage, utilization of hematite is limited by poor induration performance, higher preheating and roasting temperature demand, as well as higher reduction swell index of hematite pellet. In this study, a certain hematite from Brazil is taken as the main raw material. Based on the systematic study of hematite oxide pellet, mineral composition and microstructure of hematite pellet are reconstructed by improvement of surface properties, control of solid diffusion conditions, activation of crystal lattice, control of liquid phase quantity, etc. to improve the quality of hematite pellet according to the poor strength of green pellet, high induration temperature, and high reduction swell index.The research on basic characteristics of hematite oxide pellet indicates that the iron ore concentrate used in this test has high iron grade, but little fine particles and small specific surface area (644cm2/g), thus it has bad balling capability. It requires a thermal regulation of preheating temperature 1100℃, preheating time 8-48 min, roasting temperature 1300-1320℃, and roasting time 10-18 min to obtain the preheated strength of 400 N/P and roasted strength of 2500 N/P. The thermal regulation above is hard to realize with regular grate-kiln process.Both high pressure roller grinding and ball milling are able to micronize iron ore concentrate particles, increase its specific surface area. The main effect of high pressure roller grinding is shape change while the main effect of ball milling is ore grinding. The balling capability of hematite concentrate can be remarkably changed by pretreatments of ball-milling and high pressure roller grinding. After the pretreatment, when the specific surface area is over 1600cm2/g, the dosage of bentonite can reduce 0.75%, the feasible preheating temperature is 100℃lower, the roasting temperature is analogous while the pellet strength increases to higher than 500N/P.Compared with carbon-free pellets, hematite pellets with proper amount of carbon burden require a 20℃～50℃lower roasting temperature,5min～10min shorter roasting time, and the feasible range is 50℃larger. The main effects of anthracite on induration process of hematite pellet include:①heat supply:anthracite catches on fire during preheating, and a certain amount of heat is released, therefore, the preheating temperature can be lower;②reduction:the carbon in anthracite, as well as the gas product of combustion, CO, can reduce the hematite. The hematite is partially transformed into magnetite which is reoxidized with heat releasing out during induration process. These magnetite are then transformed into secondary hematite with higher activity. Therefore, roasting temperature of hematite is lower, and indurated strength of pellet is better.The research on flux adding indicates that limestone and dolomite are mainly composed with carbonate minerals. A certain amount of heat is absorbed by decomposition during preheating, therefore, pellet temperature falls as well as the strength of preheated pellet. Solid state reactions take place between CaO and Fe2O3 during preheating. The low melting point reaction products, such as calcium ferrite, are produced. These low melting point materials form the liquid phase during roasting which promotes microcrystalline connection of iron oxides and pellet strength improvement. Moreover, reduction swell index can be decreased by addition of dolomite.Optimizing technological parameters are obtained by pilot experiment. The research on process of carbon burden fluxed pellet indicates that fluxed pellet with high quality can be produced by grate-kiln or straight grate process. And grate-kiln pellet is more uniform in quality, has higher tumbler strength and better abrasion resistance comparing with the latter process.更多还原