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是平衡浓度差异并实现最大的均匀性。由于进料组分的各种物理材料性质，例如颗粒尺寸或固体密度，以及相关的不同颗粒迁移率，不能总是实现最大均匀性。通过添加少量的液体，这些不同的迁移率可以通过颗粒间液体桥力来补偿。然而，液桥力在很大程度上取决于液体的量和颗粒系统的润湿性质，这意味着液体添加不一定减少偏析。例如，如果亲水性组分需要与疏水性组分混合，则添加水可引起相反的效果。水选择性地积聚在亲水性组分中，使得形成不均匀的附聚物，其主要由具有良好润湿性能的材料组成。因此，通常不能假定液体的添加使分离最小化。这必须根据产品特性进行单独评估。本研究的主题是利用数值模拟来了解发生偏析机制与通过添加液体来减少偏析机制之间的关系。为此目的，应在离散单元法中开发和实施液桥力、液体分布和干燥颗粒接触的广泛模型。通过使用Fokker-Planck方程，可以根据分散和传输系数来评估由于液体添加而改变的混合和分离机制。这些系数，反过来，提供了适当的参数，可转移到技术上相关的材料系统与高粒子数，这是不能用数值模拟。最后，一个模拟工具将可用于数值研究分离，湿固体混合过程。这些结果可以通过使用适当的参数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.