焦炭在高炉内结构演变行为及多相反应机制

发布时间：2018-01-12 07:23

本文关键词：焦炭在高炉内结构演变行为及多相反应机制　出处：《北京科技大学》2017年博士论文　论文类型：学位论文

【摘要】：随着低碳经济时代的到来,以碳(焦炭)作为能量流和物质流主要载体的高炉炼铁工艺面临前所未有的挑战。一方面,大喷煤技术的广泛推广以及高炉大型化对焦炭质量提出更加严格的要求;另一方面,优质炼焦煤资源的枯竭以及对焦化行业污染物排放的严格控制使得生产优质焦炭面临前所未有的压力;此外,捣固焦和顶装焦的同时使用,以及高炉内有害元素量的增加,为焦炭质量评价带来困难。因此,亟需深入理解高炉内焦炭行为,为焦炭质量和性能评价提供参考依据,有效地为炼铁和炼焦行业的衔接提供理论结合点。本文采用模拟实验、理论计算以及工业取样分析等多种研究手段,依据焦炭在高炉内不同区域的反应条件,从微观层次揭示了焦炭在高炉内不同位置的结构演变行为及多相反应机制,完善了焦炭在高炉内的行为理论。本文通过热力学计算及热重实验研究了在C-CO_2-Na_2CO_3/K_2CO_3体系下焦炭和石墨碳的气化动力学规律。结果表明,碱金属碳酸盐对石墨碳和焦炭气化反应均有着催化作用,其对石墨碳的催化作用比对焦炭的催化作用明显。催化效应对于石墨碳和焦炭气化过程都有一个极限,由于焦炭中碳为非均匀乱序结构以及内生矿物的催化作用,导致碱金属碳酸盐的催化极限值低。动力学研究表明石墨碳和焦炭的气化反应均存在动力学补偿效应。石墨碳气化过程的活化能能够被碱金属碳酸盐明显地降低,而焦炭气化过程很难被进一步降低,这主要是由于焦炭的杂乱碳结构以及内生矿物的催化已经使得焦炭中碳反应的活化能处于较低水平。采用碱化实验系统地研究了碱金属蒸气对焦炭碳结构、矿物结构以及高温性能的影响规律。被钾蒸气碱化后的焦炭组织受到严重破坏,伴随着有碎屑和焦粉的产生,表明钾蒸气对焦炭有很强的直接破坏作用,这种现象被称为"剥落效应",而钠蒸气不具有这种直接破坏作用。X射线衍射及元素面扫描实验证实了被钾碱化后新生矿物相为六方钾霞石或者钾铝硅酸盐(KAlSiO_4),被钠蒸气碱化后的新生矿物相为钠铝硅酸盐(Na_6Al_4Si_4O_(17)),并且钾钠均可以与碳基体产生层间化合物导致碳基体体积膨胀。含钾矿物和含钠矿物对焦炭气化反应的催化程度相近。由于钾蒸气的直接破坏作用比钠蒸气强很多(钾蒸气对焦炭有"剥落效应",而钠蒸气没有),因此钾蒸气在高炉内对焦炭性能的破坏能力更大。通过分子动力学研究了熔融焦炭灰分体系(SiO_2-Al_2O_3-CaO)结构和性能随着SiO_2含量的变化情况。结果表明熔体中[AlO_4]四面体结构不如[SiO_4]四面体结构稳定,并且存在配位数高于4的铝氧多面体结构。化学成分对键长和键角的影响非常小,这也表明了体系网络结构局部的稳定性。随着SiO_2的还原(减少),体系中桥氧含量降低,而三配位氧的比例增加。随着SiO_2含量从体系中的减少,Si、Al、Ca和O原子的扩散系数均明显增加,这主要是由于Si-O键的减少削弱了网络结构的稳定性。分子动力学和FactSage计算的粘度值非常接近,且均随着SiO_2含量的降低而降低,这与实验结果一致,这也验证了本模拟计算方法的可靠性。采用分子动力学研究了 K_2O和Na_2O两种碱金属对熔融焦炭灰分结构和流动性的影响,结果能够重现相似体系的实验结果并且区分两种碱金属对体系影响的核心差别。两种碱金属对局域结构的影响非常微弱,均没有使得体系中原子间的近邻距离、次近邻距离以及配位数发生明显的变化。和预期的一致,Na~+的扩散能力高于K~+,并且含有Na_2O的体系中的原子扩散能力普遍比含有K_2O的体系中的原子扩散能力要高。体系中原子的总扩散系数随着Na_2O含量的增加而增加,从而使得体系的粘度降低;但是体系中原子的总扩散系数随着K_2O含量的增加而降低,从而使得体系的粘度增加。通过对风口焦炭和炉缸焦炭的分析,揭示风口区域焦-渣-铁的界面特征,诠释了炉缸焦炭的石墨化及其与炉渣的交互作用。焦炭内的灰分在风口位置的高温区将会熔融并迁移到焦炭表面,熔融灰分包裹焦炭表面会阻碍焦炭与其他物相(气、固、液)的反应。炉腹渣中的FeO的还原在焦-渣界面发生,反应先在焦炭表面形成一个铁液层。焦-渣之间的反应将通过侵蚀反应作用对焦炭的结构和组织产生破坏。所有的炉缸焦炭样品,无论尺寸大小,均已经被严重的石墨化。焦炭尺寸越小,其石墨化程度越高,这表明了焦炭在高温区的石墨化从表层开始,且石墨化的过程伴随焦粉的产生。产生的焦粉很容易与渣铁形成复杂混合物,这会影响到高炉高温区的透气透液性。炉缸的多孔焦炭内部被发现充满了炉渣,而焦炭内部原始的灰分已经完全融入炉渣中。综上所述,关于焦炭在高炉内的演变行为,本论文在前人研究基础上,针对几个尚不清楚的问题展开了系统和全面的研究。深入研究了不同形式碱金属对焦炭的影响机理,从原子尺度揭示了焦炭熔融灰分的结构演变机制,对工业解剖高炉的风口焦炭及炉缸焦炭进行了全面表征,为合理评价及高效利用焦炭提供了理论基础。
[Abstract]:With the era of low-carbon economy, carbon (coke) blast furnace ironmaking process as the energy flow and material flow are the main carrier of the hitherto unknown challenge. On the one hand, pulverized coal injection technology is widely promotion and the large-scale blast furnace, puts forward more strict requirements on the quality of coke; on the other hand, high-quality coking coal resource depletion and coking industry emissions to strictly control the production of high quality coke making faces the hitherto unknown pressure; in addition, at the same time stamping and top charging coke, and increase the amount of harmful elements in the blast furnace, coke quality evaluation difficult. Therefore, to understand the behavior of coke in the blast furnace, to provide reference for the evaluation of the quality and performance of coke. Effective convergence for the iron and coking industry to provide the theory. This paper uses the simulation experiments, several research methods theoretical calculation and industrial sampling analysis etc., On the basis of coke in the blast furnace in different regions of the reaction conditions, reveals the structure of coke in the blast furnace in different positions and evolution behavior of multiphase reaction mechanism from the micro level, improve the behavior theory of coke in the blast furnace. Through thermodynamic calculation and experimental study on the thermal gasification kinetics of coke in the C-CO_2-Na_2CO_3/K_2CO_3 system and the law of graphite. The results show that the alkali metal carbonate on the graphite and carbon gasification reaction of coke has a catalytic effect, catalytic effect of its catalytic effect on the graphite ratio of coke catalytic effect obviously. There is a limit for graphite and coke gasification process, the catalytic effect of carbon in coke for non uniform structure disorder and endogenous minerals the limit leads to the formation of alkali metal carbonate value low. Kinetic studies showed that there were kinetic compensation effect of graphite carbon gasification reaction and coke stone. The activation graphite gasification process can be alkali metal carbonate significantly decreased, and the coke gasification process is difficult to be further reduced, this is mainly due to the catalytic promiscuity carbon structure of coke and endogenous minerals have made carbon in coke reaction activation energy at a low level. The experimental system of alkalization of coke carbon the structure of metal vapor by alkali, influence of mineral structure and high temperature performance. By coke tissue potassium vapor after alkalization was severely damaged, with debris and coke powder, showed that potassium vapor direct damage with a strong effect on coke, this phenomenon is called "peeling effect", and the sodium vapor this is not directly damaging effects of.X ray diffraction and element scan experiment confirmed by alkaline potassium after new mineral phases for the Six Party of kalsilite or potassium aluminum silicate (KAlSiO_4), is after the new alkali sodium vapor Students for the mineral phase of sodium aluminum silicate (Na_6Al_4Si_4O_ (17)), and potassium sodium could produce intercalation compounds resulted in volume expansion of carbon matrix and carbon matrix. Its catalytic extent of potassium bearing minerals and sodium containing minerals on the gasification reaction of coke is similar. Due to the direct damage of potassium vapor than sodium vapor (potassium vapor on many strong coke has "peeling effect", and therefore no sodium vapor), potassium vapor in the blast furnace capacity of coke performance more. Through molecular dynamics study of molten coke ash system (SiO_2-Al_2O_3-CaO) structure and properties change with the SiO_2 content. The results show that the melt [AlO_4] tetrahedral structure as [SiO_4] tetrahedral structure stability the structure and coordination number of aluminum oxide polyhedron are higher than 4. The influence of chemical composition on the bond length and angle is very small, it also shows that the stability of the network structure system with the SiO_2 local. Reduction (reduce), reduce the oxygen content in system, and the three ligand oxygen ratio increased. With the content of SiO_2 from the system reduced, Si, Al, Ca and O atom diffusion coefficient were significantly increased, this is mainly due to the decrease of Si-O bond weakens the stability of network structure. Molecular dynamics and FactSage the calculation of the viscosity is very close, and with the decrease of SiO_2 content decreased, which is consistent with the experimental results, which verifies the reliability of the simulation calculation method. The effects of K_2O and Na_2O of two alkali metal to melt coke ash structure and mobility by using molecular dynamics, the results can reproduce the core difference between similar systems the experimental results and distinguish the effects of two kinds of alkali metal on the system. The influence of two kinds of alkali metal on the local structure is very weak, are not made of neighbor atoms system in distance, the second nearest neighbor distance and the coordination number. Changed significantly. And the expected, the diffusion ability of Na~+ is higher than K~+, atom diffusion and contains Na_2O system in general than the K_2O containing system in atom diffusion is higher. The total diffusion coefficient of atoms in the system increases with the increase of Na_2O content, the viscosity of the system decreased from that; but the total diffusion coefficient of atoms in the system decreases with the increase of K_2O content, which makes the viscosity of the system increased. Through the analysis of tuyere coke and coke hearth, tuyere coke - interface to reveal the characteristics of slag and iron, the interaction of the interpretation of the graphite and coke hearth slag ash in coke. The outlet position in the high temperature zone will melt and migrate to the surface of coke, coke ash melting inclusions surface will hinder the coke and other phases (gas, solid, liquid) reaction. The bosh slag in the FeO reduction in coke slag field The surface reaction occurred before the formation of a molten iron layer on the surface of coke. The coke slag will be produced by the reaction between erosion reaction of coke structure and tissue destruction. All the hearth coke samples, regardless of size, have already been graphitization serious. The coke size is smaller, the higher the degree of graphitization this shows that, the coke in high temperature area of graphite from the surface, and the process of graphitization with coke. Coke powder produced easily with iron slag forming a complex mixture, which will affect the air permeability of blast furnace hearth temperature areas. The internal porous coke was found filled with slag, and coke inside the original ash has been fully integrated into the slag. In summary, on the evolution behavior of coke in the blast furnace, this paper on the basis of previous research, aiming at some unclear issues in a systematic and comprehensive study. Deep research The influence mechanism of different forms of alkali metals on coke is revealed. The mechanism of the evolution of coke ash is revealed from the atomic scale. The anus, coke and hearth coke of the industrial anatomic blast furnace are comprehensively characterized, which provides a theoretical basis for reasonable evaluation and efficient utilization of coke.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TF526.1

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