Impact comminution in jet mills

本计画的目的是对流化床喷射米尔斯磨中的两相流进行实验分析，并发展一个相关的流程模型，以应用于Dysol。流化床对置式气流粉碎机是一种特别有趣的设备，因为它将三个关键的单元操作，即冲击粉碎、气力输送和叶轮分级机的分级结合在一台设备中。在第一个资助期内，详细描述了多相射流中颗粒所经历的应力条件。为此，采用不同的实验装置来研究多相射流中的流体力学。采用粒子图像测速仪在实验室内测量了亚音速和扼流两种工况下的颗粒速度。以这种方式，计算颗粒破碎所需的动能。通过电容探针测量射流中的固体体积浓度。此外，流动模式可以分析非侵入性的X射线计算机断层扫描。附加粉碎动力学已确定在商业流化床对置式气流粉碎机。在此基础上，结合流体力学和物料破碎概率，建立了一个简单的磨削动力学模型。此外，建立了磨机内粉碎单元的简化模型。该模型将通过不同工艺参数和几何参数的进一步实验进行扩展。主要集中在两个最重要的参数：颗粒尺寸分布和持液率，这在动态过程中不断变化。通过一种基于球形金属颗粒的力学定义的新方法，实现了在搅拌介质磨机中对双面应力的应力数和应力能分布的实验表征，并将其转化为流化床磨机中的单面应力。机械上完全表征的金属颗粒将在磨机中受到应力。随后对受应力和变形颗粒的图像分析允许确定应力事件的数量和吸收的能量。结合SEM支持的压缩实验的有限元模拟可以将压缩颗粒的形状与体积比能量吸收相关联。单侧冲击应力的材料功能将由新建的单颗粒冲击装置测量。将系统地测量石灰石、玻璃和氧化铝颗粒（< 40 µm）的破碎概率和破碎函数。

The objective of this project is the experimental analysis of two-phase flow in fluidized bed jet mills and the development of a related flow-sheet model for implementation in Dyssol. The fluidized be opposed jet mill is particularly interesting because three key unit operations, namely impact comminution, pneumatic transport and classification with the integrated impeller wheel classifier, are combined into one apparatus. In the first funding period, the stressing conditions experienced by the particles in the multi-phase jets were characterized in detail. For this purpose, different experimental set-ups were used to investigate the fluid mechanics in the multiphase jets. The particle velocity in both the subsonic and choked flow regimes was measured in a semicircle plant using Particle Image Velocimetry. In this way, the kinetic energy required for particle breakage was calculated. The solids volume concentration in the jet was measured via capacitance probes. Moreover, flow pattern could be analyzed noninvasive by x-ray computer tomography.Additional grinding kinetics have been determined in a commercial fluidized bed opposed jet mill. Based on this, a simple model for the grinding kinetics was established, which combines fluid mechanics and material specific breakage probabilities. Furthermore, a shortcut model for the comminution unit within the mill was developed. This model will be extended by further experiments for different process and geometric parameters. Main focus is on the two most important parameters: the particle size distribution and the holdup, which continuously change during dynamic processes. The experimental characterization of stress number and stress energy distributions has been realized in a stirred media mill for two-sided stressing by a novel method based on mechanically well-defined spherical metal particles, and will be transferred to one-sided stressing in the fluidized bed mill. Mechanically fully characterized metal particles will be stressed in the mill. Subsequent image analysis of the stressed and deformed particles allows the determination of the number of stress events and the absorbed energy. Finite element simulations in combination with SEM supported compression experiments can relate the shape of the compressed particles to the volume-specific energy absorption. Material functions for one-sided impact stressing will be measured by the newly built single particle impact apparatus. The breakage probability and breakage function of limestone, glass and alumina particles (< 40 µm) will be systematically measured.