基于CT显微图像的烧结矿孔隙特征分析及有效热导率预测

Characterization of pore structure and effective thermal conductivity of iron ore sinter using micro CT images

全面了解获取多孔烧结矿的热物理特性对于在钢铁企业中相关过程的运行优化和节能减排具有重要意义。在此前景下,无损的高精度X射线显微断层扫描技术被应用到表征烧结矿的孔隙结构并结合数值模拟来预测烧结矿的有效热导率。以40μm的分辨率扫描了3个熟石灰添加水平下的烧结杯试验中获取的烧结矿样品。三维重建后的烧结矿可观测到各向异性的非常复杂的孔隙分布,导致其有效热导率也各向差异较大,形成复杂的内部温度场分布。烧结矿中0~300μm的小孔隙在数量频率上占据大多数(约45%~50%),但仅占小部分的大于1 mm的大孔隙则贡献了约95%的孔隙体积占比,并主要决定了烧结矿的导热行为。3个烧结矿样品的有效热导率分别为0.645、0.682和0.784 W·m^(-1)·K^(-1),对应的孔隙率分别为53.8%、53.1%和49.7%。通过与文献中的类似铁系聚合物的导热值,典型的经验式预测方程和结构分析模型等比较,证明了CT三维重建结合数值模拟的技术手段可有效捕捉烧结矿真实的多孔结构,从而比简单的经验式方程或结构分析模型能获取更精确的热物理行为的预测效果。

Understanding of the thermophysical properties of porous sinter is especially important for operation optimization and energy saving in integrated steel mills. Under this prospect, nondestructive X-ray microtomography was applied to characterize the pore structure and the simulations for estimating the sinter effective thermal conductivity were performed. Three sinter cakes produced from pilot-scale sinter pot tests under three hydrated lime addition levels were scanned with resolution ratio of 40 μm. The reconstructed sinter cakes have various complex pore distributions, leading to remarkable anisotropic thermal conductivities and complicated temperature field. The pores smaller than 300 μm dominate the number frequency in sinter cake（around 45%—50%）, while a small amount of pores larger than 1 mm account for around 95% of the total pore volume, which determines the thermal behavior greatly. The estimated effective thermal conductivities of three samples are 0.645, 0.682, and 0.784 W·m^-1·K^-1, corresponding to the porosity of 53.8%, 53.1% and 49.7% respectively. Comparing these values with values of similar iron agglomerates in the literature, some empirical correlations and analytical models, the results proved that CT-simulation is a valid approach for capturing the peculiar details of the real sinter porous structure, thus to predict thermal behavior with higher accuracy than the simplified geometric models.