Clarification of segregation behavior of polydisperse, moist bulk materials with different wetting properties in discontinuous mixing processes

每个固体混合过程的目的都是平衡浓度差异和实现最大的均匀度。由于进料成分的各种物理材料属性，例如颗粒大小或固体密度，以及相关的不同颗粒迁移率，并不总是能够达到最大的均匀度。通过加入少量的液体，这些不同的迁移率可以通过颗粒间的液桥作用力来补偿。然而，液体桥力在很大程度上取决于液体的数量和颗粒体系的润湿性质，这意味着液体的加入不一定会减少偏析。例如，如果亲水性成分需要与疏水性成分混合，则添加水可能会产生相反的效果。水选择性地聚集在亲水性成分中，从而形成不均匀的团聚，这些不均匀的团聚主要由具有良好润湿性的材料组成。因此，一般不能假定加入液体就能使偏析最小化。这必须根据产品特性进行单独评估。通过数值模拟了解偏析的发生机理与添加液体减少偏析的关系是本研究的主题。为此，应建立广泛的液桥力、液体分布和干湿颗粒接触模型，并在离散元方法中实施。利用福克-普朗克方程，可以根据弥散系数和输运系数来评估由于液体加入而改变的混合和分离机制。这些系数反过来又为转移到技术上相关的高粒子数材料系统提供了合适的参数，这是无法用数字模拟的。最后，将使用模拟工具对混合过程中分离的湿固体进行数值研究。通过使用适当的参数，这些结果可以转移到技术混合过程中。

Each solid mixing process is aimed at balancing concentration differences and achieving maximum homogeneity. As a result of various physical material properties of the feed components, e.g. particle size or solid density, and the related different particle mobilities, maximum homogeneity cannot always be achieved. By adding small amounts of liquid, these different mobilities can be compensated by interparticle liquid bridge forces. However, liquid bridge forces depend largely on the amounts of liquid and wetting properties of the particle systems, which means that liquid addition does not necessarily reduce segregation. If hydrophilic components need to be mixed with hydrophobic components, for example, the addition of water can cause the opposite effect. The water accumulates selectively in the hydrophilic component, such that inhomogeneous agglomerates are formed, which are mainly composed of material with good wetting properties. Accordingly, it cannot generally be assumed that the addition of liquid minimizes segregation. This has to be assessed individually depending on the product characteristics. It is the subject of this research to understand the relationship between occurring segregation mechanisms and their reduction by the addition of liquid using numerical simulation. For this purpose, extensive models of liquid bridge force, liquid distribution, and moist-dry particle contact shall be developed and implemented in the discrete element method. By using the Fokker-Planck equation, the mixing and segregation mechanisms changed as a result of liquid addition can be assessed on the basis of dispersion and transport coefficients. These coefficients, in turn, provide suitable parameters for transferability to technically relevant material systems with high particle numbers, which cannot be simulated numerically. Finally, a simulation tool will be available to numerically investigate segregating, wet solids in mixing processes. These results can be transferred to technical mixing processes by using appropriate parameters.