Biomass reducing agent utilisation in rotary hearth furnace process for DRI production

Abstract

This study aims to provide a theoretical and technical basis for utilisation of biomass (bamboo char, charcoal and straw fibre) in the rotary hearth furnace process to produce direct reduced iron. Each biomass material has strengths and weaknesses. The bamboo char pellets possess high fixed carbon content, but the lower strength and the expansion rate of pellets make it difficult to reach production requirements. Although the charcoal based pellets are similar to coal based pellets, their strength is the lowest of these reducing agents. The straw fibre based pellets possess high strength and large volume shrinkage, but the low fixed carbon content results in low productivity. Using biomass in a combination of these alternatives can enable coal to be replaced and produce pellets with a higher metallization than with coal.     

转底炉对转炉污泥的处理

 为了合理利用转炉污泥,减少炼铁流程中有害元素的富集,对转底炉处理转炉污泥进行了研究。结果表明,转炉污泥配入混合料后对生球质量影响较小,但可以提高干球的强度,因此可以减少球团在转运和预热阶段的破裂、粉化情况。混合料的碱度和碳质量分数是影响金属化球团质量的关键因素,而转炉污泥配入混合料后会对它们产生较大影响。将混合料的碱度控制在0.75~0.85,碳质量分数控制在11%~12%,可以保证金属化球团具有所需的强度和金属化率。工业试验过程中,转炉污泥配比从8%逐渐提高至24%,通过控制各原料配比来调节碱度和碳质量分数,金属化球团的质量能够满足生产需要。     

厚料层转底炉含铁尘泥直接还原模拟

转底炉工艺是目前处理含铁尘泥最有效的工艺之一,但传统转底炉处理尘泥需要造球且只能铺设1~2层球团以致生产效率较低。针对该问题,料层厚度是传统工艺10~30倍的新型厚料层转底炉技术应运而生,同时无需造球并取消了燃烧装置,极大提高生产效率。基于计算流体力学(CFD)方法建立了新型厚料层转底炉工艺多孔介质异相反应直接还原数学模型,研究厚料层转底炉的工作特性,分别对厚料层转底炉内的还原性气氛、脱锌、金属化率进行分析与讨论。研究表明,厚料层转底炉物料出炉时脱锌率超过99%且金属化率达到90%以上,能够有效提升生产效率。研究结果丰富了转底炉工艺理论,并为新型厚料层转底炉工程化提供理论依据。     

环形加热炉电气控制策略的优化

环形加热炉是无缝钢管热轧生产线上的管坯加热设备,其电气控制水平高低直接影响环形加热炉的加热过程和轧线的生产情况.根据多年从事环形炉的设计经验,对环形炉在电气控制方面存在的缺陷及使用中的不足之处进行了探讨,对环形加热炉机械设备的电气控制在实践过程中做了改进.经实际验证,从投资造价和使用性能上都取得了较好效果.     

转底炉工艺处理含铁尘泥关键技术

 转底炉是当前用于处理钢铁厂含铁锌尘泥工艺的典型代表,能有效利用尘泥中的铁、碳和氧化锌等物质,生产金属化球团,同时产生副产物氧化锌粉,具有较好的处理效果和经济效益,是未来钢铁企业含铁尘泥处理技术发展的趋势之一。基于转底炉处理含铁尘泥工艺,对转底炉工艺涉及的诸多关键技术进行分析和讨论,结合转底炉生产实践和实验室研究成果,在转底炉原料选择、成型技术、优化配矿、渣系优化以及锌的控制等方面提出建议,以期为转底炉处理含铁尘泥工艺的改进和创新提供参考。     

含碳球团转底炉直接还原的关键技术

介绍了国内外转底炉直接还原工艺发展现状,提出含碳球团造块技术、转底炉装料机设计、转底炉出料机设计、转底炉炉温、炉压及炉内气氛的控制以及金属化球团防氧化技术等是保障转底炉连续稳定顺行的关键技术。合理的水分、压力及粘结剂种类可以获得较好的压球效果;振动给料机和装有硬质耐磨合金的螺旋出料机是目前转底炉装、出料机的主流;根据原料的不同,各厂家已摸索出适宜的炉温、炉压等工艺参数,并对金属化球团采取冷却或隔绝空气的保护措施。     

基于转底炉直接还原工艺的钒钛磁铁矿综合利用试验研究

通过大量试验研究,提出了＂钒钛磁铁矿转底炉直接还原—电炉深还原—含钒铁水提钒—含钛炉渣提钛＂工艺流程。铁、钒、钛元素回收率分别达到90.77%、43.82%和72.65%。通过试验室和工业试验研究,解决了钒钛磁铁矿直接还原金属化率低、电炉深还原钒还原率低、高硅铁水提钒、高镁铝含钛炉渣提钛等技术难题,获得了直接还原金属化率大于90%,电炉深还原钒还原率大于80%,钒渣提钒钒回收率大于65%,钛渣提钛钛回收率大于75%的良好效果,分别获得了符合电炉炼钢要求的低碳生铁、符合YB/T5304-2006要求的片状V2O5和达到PTA121质量要求的钛白产品。     

转底炉分区域供热研究

基于国内转底炉直接还原炼铁在起步阶段亟待解决的热工系统问题,分别以系统分析、热模拟实验和数值模拟为手段,对转底炉分段热工参数进行了研究.建立了转底炉冶金模型和热模型（涉及变量83个、参数20个）,模拟计算结果表明,每生产1t金属化球团,需铁精粉1213kg,消耗煤粉283kg、煤气615kg.基于转底炉分区域系统分析,分别进行了预热段、加热段、还原段条件下的热模拟实验研究,确定出不同工况下（n_C：n_O=0.8~1.2）含碳球团于各段的实时还原进度,并依据含碳球团自还原吸热与热工参数的匹配,确定出各段燃料供应参数.使用Fluent模拟软件对分段热工参数进行了验证,结果表明分段热工参数设计合理,能有效实现转底炉的分段职能,为转底炉的优化设计提供了基础.     

Gaseous reduction of ultrafine metallurgical dust in rotary furnace

A laboratory scale rotary furnace has been developed for gaseous reduction of ultrafine metallurgical dusts to produce iron, zinc and other metal resources at submelting point temperatures. The kinetics of this process is much higher than say static or moving bed systems. By way of example, using dust with 38%Fe and 10%Zn, a 17?min treatment at 900°C produces an iron product of ～92%Fe and a zinc product of ～86%Zn.     

The reduction of iron oxides by volatiles in a rotary hearth furnace process: Part III. The simulation of volatile reduction in a multi-layer rotary hearth furnace process

For reduction of iron oxides by volatiles from coal, the major reductant was found to be H₂, and it can affect the overall reduction of iron oxides. In this study, the reduction by actual volatiles of composite pellets at 1000 °C was studied. The volatile reduction of the hand-packed Fe₂O₃/coal composite pellet as it is devolatilizing out of the pellet was found to be negligible. However, the reduction of iron oxide pellets at the top layer by volatiles from the bottom layers of a three-layer pellet geometry was observed to be about 15 pct. From the morphological observations of partially reduced pellets and the computed rates of bulk mass transfer, volatile reduction appears to be controlled by a mixed-controlled mechanism of bulk gas mass transfer and the limited-mixed control reduction kinetics. Using the reduction rate obtained from the single pellet experiments with pure hydrogen and extrapolating this rate to an H₂ partial pressure corresponding to the H₂ from the volatiles, an empirical relationship was obtained to approximately predict the amount of volatile reduction up to 20 pct.     

转底炉用蓄热式烧嘴的模拟

运用Fluent软件对转底炉加热设备(蓄热式烧嘴)进行模拟,确定仿真计算所需的最佳网格精度,并分析空气-燃料比(以下简称空燃比)对燃烧温度和燃烧生成组分摩尔分数的影响.结果表明:当网格精度Interval=1.5,燃烧温度为2 220 K(1 947℃)时,较为接近丙烷理论燃烧温度,此时网格数为23 724个,完全达到仿真要求;当空燃比处于18~38时,丙烷能充分燃烧,燃烧温度可稳定保持在2 110 K(1 837℃)以上;当空燃比低于18或者高于38时,燃烧温度降至2 080 K(1 807℃)左右;当空燃比发生变化时,烧嘴内各组分的摩尔分数会发生变化,O2的摩尔分数所占量小,N2的摩尔分数较高,CO2的摩尔分数最高约0.1,并且当空燃比为15时,CO产生的总量相对高.     

转底炉处理赤泥工艺技术

为了综合利用氧化铝冶炼产生的赤泥,探索在转底炉中直接还原赤泥、磨矿磁选获得高品位直接还原铁。通过实验室试验摸索了转底炉还原工艺参数,并在转底炉工业试验线进行了工业试验。实验室结果表明,赤泥还原后的直接还原铁(DRI)金属化率可达88.6%,磁选后的铁品位可达82.1%,磁选后的铁回收率可达88.9%。工业试验中,转底炉还原后,产品金属化率平均为69.2%,将还原后的DRI磁选获得高品位的DRI产品,磁选后DRI的铁品位为72.8%,磁选后铁回收率达到了85.2%,初步打通了在转底炉中还原赤泥、磁选的工艺路径。     

Carburizing performance and kinetics of carbon sources in blast furnace hearth

It is of great significance to improve the carbon saturation of molten iron which weakens the erosion of sidewall carbon bricks, so as to realize the hearth longevity. Carburizing properties of various carbon sources in molten iron by static method was systematically investigated. The apparent reaction rate constant K of samples was calculated. The results show that the carburizing properties of different carbon sources from strong to weak are NMA carbon brick > carbon rod > pulverized coal > coke > 9RDN carbon brick. The carburizing performance of carbon sources decreases with the increase in its graphitization degree. Ash has a negative effect on the carburizing performance of carbon sources, but ash in the form of agglomerated large particles cannot weaken the carburizing performance of carbon sources. The Al2O3 phase can obviously degrade the carburizing performance of carbon sources. The 9RDN carbon bricks with low carburizing properties can be adapted to more complex furnace conditions. The carburizing properties of pulverized coal and coke are relatively weak. When the pulverized coal and coke powder formed in the tuyere raceway enter the hearth, the porosity of the deadman will be reduced, resulting in hearth inactivity and frequent fluctuation of furnace condition, and it is not conducive to the carburization of the deadman. Therefore, it is necessary to properly improve the coke particle size and increase the air volume for weakening the negative effects of unburned coal powder and coke powder on the longevity of the hearth sidewall carbon bricks.     

高炉炉缸碳源渗碳性能及动力学

摘要：提高铁水碳饱和度,减弱侧壁炭砖侵蚀,实现炉缸长寿对高炉炼铁具有重要意义。利用静态法系统地研究了高炉系统中进入炉缸铁水的碳源的渗碳性能,并计算了表观反应速率常数K。研究结果表明,不同碳源的渗碳性能由强到弱为：NMA炭砖>碳棒>煤粉>焦炭>9RDN炭砖。碳源的渗碳性能随其石墨化程度的升高而降低。碳源中的灰分会极大影响其渗碳性能,但以团聚大颗粒形式存在的灰分并不能减弱其渗碳能力,同时Al2O3可明显降低碳源的渗碳速率。9RDN炭砖的渗碳性能低,预示着其可适应更加复杂的炉况条件。煤粉和焦炭渗碳性能偏差,煤粉以及炉料下行过程形成的焦粉进入炉缸会降低死料柱空隙度,造成炉缸不活跃,使得炉况波动频繁,并不利于死料柱渗碳和侧壁保护层的稳定。因此,要适当提升入炉焦炭粒度,增大风量,减弱未燃煤粉及焦粉对炉缸侧壁炭砖长寿的负面影响。     

高炉炉缸凝铁层物相分析

在高炉炉缸破损调研的基础上对高炉炉缸耐火材料热面凝铁层进行取样,利用扫描电子显微镜、物相分析等分析手段揭示了凝铁层的物相组成,并运用Thermol-calc热力学计算软件结合TCFE8数据库对铁水中石墨碳的析出温度及析出相分数进行了计算,最后揭示了炉缸凝铁层物相的形成机理.结果表明,高炉炉缸凝铁层主要由Fe相和石墨碳相交替分布组成,铁水成分对石墨碳析出温度影响较大,石墨碳析出温度远高于铁水凝固温度,铁水中C、Si元素含量对石墨碳析出相分数影响较大,而石墨碳析出相可增大铁水黏度11.9%.凝铁层中石墨碳的析出主要是由于Fe-耐火材料界面温度低于石墨碳析出温度,使得铁水中C不断向耐火材料热面迁移,进而形成Fe-C交替的分层结构.     

高炉炉缸凝铁层的组成分析与导热系数测定

摘要：高炉炉缸内衬表面形成稳定的凝铁层将保护高炉炭砖并延长高炉寿命。利用光学数码显微镜观察统计分析高炉凝铁层生产样品,探究不同焦炭体积占比对凝铁层导热系数的影响。利用元素分析（XRF）、X射线衍射分析（XRD）、扫描电镜(SEM-EDS)等手段分析凝铁层的组成,并观察其微观形貌。利用瞬态平面热源法（TPS）测定凝铁层的导热系数,进一步分析其组成与导热系数之间的关系。结果表明,凝铁层由铁、充满铁水的焦炭、石墨碳、少量渣相组成,凝铁层内部没有气隙。凝铁层生产样品的导热系数测定范围为27.21～97.38W/(m·K),导热系数（λ）与其组成的焦炭面积比（Sc=22%～48%）之间的线性关系为：λ=-257.47Sc +157.65。模拟实验凝铁层的导热系数范围为30.54～53.95W/(m·K),该值远大于目前数学模型中采用的凝铁层导热系数（2～4W/m·K）,随着焦炭粒度的增加,凝铁层的导热系数先增加后减小。凝铁层中导热系数（λ）与焦炭体积分数Vc（Vc=39%～50%）的线性关系为：λ=-80.50Vc +78.56。研究结果进一步明确了凝铁层的物相组成及其导热系数,为高炉长寿的研究指明了方向。     

炉缸复合棕刚玉砖蚀损机理的探讨

采用实验模拟和现场取样的方法研究了有害元素对复合棕刚玉砖的蚀损机理,研究表明:复合棕刚玉砖具有较好的抵御渣、铁和Pb、Zn侵蚀渗透的能力,而对碱金属K、Na的抗渗透能力较差,炉缸复合棕刚玉砖蚀损是有害元素共同作用的结果,侵入砖体的顺序依次是K、Na、Zn、Pb.     

高炉炉缸死焦堆受力分析与计算

建立了一个特殊情况下死焦堆在炉缸中的受力模型,推导出了最小死铁层深度的计算公式,并用某高炉解剖数据进行了验证,结果表明该模型可靠.在此基础上提出了一般条件下的死料柱受力模型,推出了一个用于估算一般情况下死焦堆浮起高度的公式,并讨论了死焦堆浮起高度与炉渣液面高度的关系.     

高炉炉缸死焦堆对渣滞留率的影响

采用三维动量守恒方程、标准k-ε双方程模型、VOF多相流模型以及多孔介质模型模拟计算了不同死焦堆状态下炉缸内的渣滞留量.结果表明:炉渣滞留主要集中在死焦堆中,死焦堆外围焦炭分布是决定渣滞留率的关键;最低渣-铁界面以下区域的状态对总渣滞留率影响很小.由于铁口附近渣铁水流速远大于死料柱中流速,形成了向铁口倾斜的气-渣界面,当铁口来风时需停止出铁,导致部分炉渣来不及排出炉缸,因此改善死料柱透液性是减少渣滞留量的有效手段.     

The reduction of iron oxides by volatiles in a rotary hearth furnace process: Part I. The role and kinetics of volatile reduction

With iron ore reduction processes using coal-ore pellets or mixtures, it is possible that volatiles can contribute to reduction. By simulating the constituents of the individual reducing species in the volatiles, the rates for H₂ and CO were investigated in the temperature and reduction range of interest; hydrogen is the major reductant and was studied in detail. The kinetics of the reduction by H₂ has been found to be a complex mechanism with, initially, nucleation and growth controlling the rate. There is a catalytic effect by the existing iron nuclei, followed by a mixed control of chemical kinetics and pore diffusion. This results in a topochemical reduction of these iron oxide particles. Up to 1173 K, reduction by H₂ is considerably faster than by carbon in the pellet/mixture or by CO. It was also found that H₂S, which is involved with the volatiles, does not affect the rate at the reduction range of interest.