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

• Applicant: Professor Dr.-Ing. Hermann Nirschl
• Subject Area: Mechanical Process Engineering
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 313759864

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.

• DFG Programme: Research Grants