高炉焦炭微观结构演变的多尺度表征及应用

 焦炭是高炉冶炼的重要原料,其微观结构演变的多尺度表征对焦炭质量的合理评价和高炉顺行起着至关重要的作用。溶损过程中,焦炭多孔结构内部会产生不同程度的劣化梯度,这对焦炭行为会产生十分重要的影响,但目前的焦炭评价体系并未能考虑到这一因素。以反应速率常数k_rea和扩散系数D_eff的比值(k_rea/D_eff)表征溶损反应对焦炭空间结构劣化的影响,可为进一步准确表征和预测焦炭内部的劣化梯度从而优化焦炭质量提供基础。对不同粒级尺度的焦炭进行了高温溶损试验,并研究了溶损过程中焦炭的基质反应特性和孔结构演变特征。通过傅里叶变换红外光谱、光学显微镜、SEM-EDS和BET比表面积孔径分布仪对不同溶损焦炭的成分、孔结构参数等进行了分析。结果表明,随着焦炭溶损程度的加深,矿物质在焦炭表面逐渐析出,并对溶损过程起到一定的催化作用,导致反应活化能Ea降低、k_rea增大;此时焦炭内部的微孔扩大并合并成中孔和大孔,CO₂分子的扩散路径减少,扩散活化能E_D降低、D_eff逐渐增大。进入溶损反应中后期,焦炭中的活性组分被大量消耗,且其内部的灰分大量析出,使得反应活化能Ea升高、k_rea减小;而焦炭内部的大孔数量也进一步增加,多孔结构的曲折度大幅降低,使得扩散活化能E_D继续降低、D_eff增大。通过研究焦炭k_rea/D_eff发现,随着溶损程度增加,k_rea/D_eff呈快速减小的趋势。且k_rea/D_eff越大,焦炭内部的劣化梯度越大,容易从焦炭表面产生焦粉,不利于高炉实际生产。因此,在降低焦炭溶损率或反应后强度CSR的基础上,控制k_rea/D_eff在合理范围内是进一步提高焦炭质量的有效措施。

Multiscale characterization and application of microstructural evolution of blast furnace coke

Coke is an important raw material for blast furnace smelting, and the multi-scale characterization of its microstructural evolution plays a crucial role in the rational evaluation of coke quality and blast furnace operation. During carbon loss reaction, different degrees of degradation gradients generate inside the porous structure of coke, which have a very important impact on coke behavior, but the current coke evaluation system fail to take this factor into account. The ratio of the reaction rate constant k_rea to the diffusion coefficient D_eff (k_rea/D_eff) was proposed to characterize the effect of the carbon loss reaction on the deterioration of the coke's spatial structure, it could provide a basis for further accurate characterization and prediction of the degradation gradient inside the coke, thus optimizing the coke quality. The matrix reaction characteristics and pore structure evolution characteristics of coke with different particle size were studied. The composition and pore structure parameters of different carbon loss cokes were analyzed by Fourier transform infrared spectroscopy, optical microscope, SEM-EDS and BET specific surface area pore size distribution analyzer. The results show that with the deepening of coke's carbon loss, minerals gradually precipitate on the surface of coke, and play a catalytic role in the process of carbon loss, resulting in a decrease in activation energy Ea and an increase in k_rea. At this point, the micropores in coke expand and merge into mesopores and macropores, the diffusion path of CO₂ molecule decreases, the diffusion activation energy E_D decreases, and D_eff increases gradually. In the middle and late period of carbon loss reaction, the active components in coke are consumed and a large amount of ash in coke is precipitated, which increases the activation energy E_a and decreases the k_rea. Moreover, the number of macropores in coke is further increased, and the tortuous degree of porous structure is greatly reduced, which leads to the decrease of diffusion activation energy E_D and the increase of D_eff. Sudying the ratio of coke k_rea and D_eff shows that k_rea/D_eff decreases rapidly with the increase of carbon loss reaction. And the larger the k_rea/D_eff is, the larger the deterioration gradient inside the coke is, and the coke powder is easily generated from the coke surface, which is not conducive to the actual production of the blast furnace. Therefore, on the basis of reducing the coke dissolution loss rate or CSR, controlling k_rea/D_eff within a reasonable range is an effective measure to further improve the coke quality.