Solid fuels, such as coal or biochar, can be injected into a blast furnace for low-carbon ironmaking. However, unburnt coal or biochar powders may accumulate in the coke bed, potentially reducing bed permeability and compromising furnace stability. Current CFD-DEM methods struggle to simulate systems with significant size differences between coke particles and coal or biochar powders, where the diameter ratio d_ck/d_cl is 100–200 times. In this work, a novel multi-resolution hybrid CFD-DEM model is developed to simulate gas-unburnt powders-coke particles flow dynamics within and around the raceway with high fidelity. The model’s accuracy is validated by comparing the simulated evolution of the raceway cavity shape with experimental results. Subsequently, the hybrid model is used to simulate unburnt powder flow through the raceway and the adjacent coke bed (d_ck/d_cl = 100), comparing its performance with the conventional smoothed CFD-DEM model. The effects of gas inlet velocity and powder wettability are also analysed. Results show that the hybrid CFD-DEM model effectively simulates detailed pore fluid flow in the coke bed, which the smoothed model fails to capture, demonstrating the hybrid model’s superiority. Increasing gas inlet velocity enlarges the raceway cavity, intensifies high-speed pore flows, and accelerates powder transport into the coke bed. Additionally, higher cohesion energy density (k_CED) reduces powder penetration, aligns the peak holdup position and penetration angle, and decreases permeability at key probe positions. This work provides an effective and efficient numerical tool to help understand and optimise the injection operation in blast furnaces.

中文翻译：

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使用混合 CFD-DEM 方法对工业规模高炉中未燃烧的煤流进行高保真建模


固体燃料，如煤或生物炭，可以注入高炉进行低碳炼铁。然而，未燃烧的煤或生物炭粉末可能会积聚在焦床中，可能会降低床层渗透性并损害炉子稳定性。当前的 CFD-DEM 方法难以模拟焦炭颗粒与煤或生物炭粉末之间尺寸差异显著的系统，其中直径比 d_ck/d_cl 为 100-200 倍。在这项工作中，开发了一种新的多分辨率混合 CFD-DEM 模型，以高保真度模拟管道内部和周围的气体-未燃烧粉末-焦炭颗粒的流动动力学。通过将滚道型腔形状的模拟演变与实验结果进行比较，验证了模型的准确性。随后，使用混合模型模拟通过滚道和相邻焦床的未燃烧粉末流动 （d_ck/d_cl = 100），将其性能与传统的平滑 CFD-DEM 模型进行比较。还分析了气体入口速度和粉末润湿性的影响。结果表明，混合 CFD-DEM 模型有效地模拟了焦床中详细的孔隙流体流动，而平滑模型无法捕捉到这些流动，证明了混合模型的优越性。增加的气体入口速度会扩大滚道腔，增强高速孔隙流，并加速粉末向焦床的输送。此外，更高的内聚能密度 （k_CED） 降低了粉末的穿透力，对齐了峰值保持位置和穿透角，并降低了关键探针位置的渗透率。这项工作提供了一种有效且高效的数值工具，有助于理解和优化高炉中的喷射操作。