多尺度焦炭在高炉炉缸溶解及劣化基础研究

Under the driven of cost orientation in the current blast furnace (BF) ironmaking process, it is increasingly important to maintain the coke functions as a structural material owed to the lower coke rate operation. Therefore, deeply understand the dissolution and degradation process of multi-scale coke particles in BF hearth for guiding production has become the prior focus of ironmaking researchers. Hot metal carburization and graphization are the main process coke experienced in hearth. In this project, the carbon dissolution experiments will be carried out under multi-scale conditions. The formation mechanism of the mineral layer between coke and liquid iron during carbon dissolution can be characterized. Meanwhile, the rate-determining step and dissolution rate will be determined. The influence of coke ash, the microcrystalline structure order and liquid iron content on the dissolution process will be expored. The changes of microstructure and optical texture can be deduced. By comparing the experimental results under different multi-scale conditions, the effect of macroscopic cracks and pore structure on the dissolution process will be clarified, which could provide theoretical basis for clearing the coke dissolution mechanisms in BF hearth. Besides, the graphitization tests of cokes will be carried out at high temperature. The relationship between the microcrystalline structure, graphitization degree and coke strength after degradation, pulverization rate will be investigated, by which the catalysis mechanism of mineral on coke degradation will be revealed and simultaneously the degradation and pulverization mechanism of coke under high temperature can be clarified. Based on the above research results, cokes with proper quality could be selected for BFs.

在当前高炉炼铁“成本导向”的驱使下，低焦比操作使得焦炭在高炉内的料柱骨架作用愈发突出，因此深入认识高炉炉缸高温区多尺度焦炭颗粒的溶解及劣化过程，指导高炉冶炼已成为炼铁工作者关注的焦点。焦炭在炉缸内主要经历铁水渗碳和石墨化过程，本项目拟通过开展多尺度条件下焦炭的渗碳溶解试验，掌握铁水渗碳过程中焦炭与生铁界面灰层的形成机理，确定焦炭溶解的渗碳速率及控速环节，探索焦炭灰分、碳素微晶结构有序性、生铁成分等因素对渗碳过程的影响，揭示焦炭的微观结构、光学组织等形貌的变化规律，对比不同尺度下的试验结果，明晰焦炭宏观裂纹、气孔结构等因素对焦炭溶解过程的影响，为探索焦炭在高炉炉缸的溶解机理提供理论基础；拟通过开展焦炭在高温下的石墨化试验，阐释焦炭的微晶结构、石墨化度与焦炭劣化后强度、粉化率之间的关系，揭示灰分矿物质对焦炭劣化的催化机理，明晰焦炭在高温下的劣化及粉化机制，为高炉选择适宜质量的焦炭提供理论支持。

当前低碳高炉冶炼条件下使得炉内焦炭层变薄，恶化了料柱的透气透液性，焦炭在炉缸高温区石墨化过程中产生的焦粉是导致该现象出现的主要原因之一。本项目深入开展了焦炭的石墨化过程、孔隙结构演变过程、光学组织演变过程、焦炭气化反应过程以及铁-碳界面润湿及反应行为研究，揭示了焦炭在炉缸区的劣化机制，为高效利用、合理评价焦炭质量提供了理论依据。研究结果表明随着温度的升高，焦炭石墨化程度加深，且温度每升高100 ℃，焦炭石墨化度约提高1.8 倍，层间距d002值约降低2 %，微晶结构层片直径La值约提高3 %，层片堆积高度Lc值约提高15 %；焦炭的表面气孔减少，特别是大气孔减少，焦炭表面镶嵌组织结构减少，各向同性组织增多，焦炭的结构有序化程度增强。随着焦炭石墨化程度的加深，焦炭的反应性逐渐减小、反应后强度逐渐提高，焦炭表面的劣化情况减弱，生成的大气孔减少，气孔壁破坏趋势减弱。焦炭的石墨化对焦炭的碱侵害具有一定的抵抗作用，降低了焦炭表面的劣化程度。焦炭的孔隙演变也随着二次加热温度的提升有着规律性变化，焦炭的灰分大概在1400℃左右完成迁移。焦炭光学组织对其气化反应的促进作用较孔隙结构发达程度对气化反应的促进作用明显。石墨基板与未饱和铁液在高温下发生渗碳溶解反应，使得润湿界面形成一定的凹陷体积，且石墨基板碳原子溶解渗透进入铁液的量随着铁液的初始碳浓度的增大而减小，渗碳效果越差；良好的润湿性可以促进碳的传质，在铁粒的熔化过程中，石墨基板中的碳原子渗透进入铁液，减小了铁液与基板间的表面能，导致表面张力减小，铁液慢慢铺展，所以接触角在熔化过程中慢慢递减。