(303b) Segregation Behavior of Static Charged Systems - Measurement and Modeling

Segregation of powder and granular materials is a current problem with many industrial products. In order to mitigate segregation, one can modify the material or modify the process. However, in some cases the handling of product can induce electrostatic fields which charge particulate material prior to entering a process vessel. Such circumstances occur when material is transported by pneumatic transfer devices. Each particulate material has a different electrical permittivity and resistivity. Thus, each material generates different magnitudes of charge when subjected to the same charging stimulus. In addition, particles will lose charge when placed in process equipment. The rate of charge dissipation is partially dependent on the resistivity of the bed, which depends on the local concentration of each particle species along the pile surface. The induced charge causes incoming particles to follow modified trajectories during the filling process. These induced charges then initiate separation of particles based on the magnitude of static charge, resulting in radial segregation patterns. This paper discusses measuring techniques to measure segregation of charged material using spectral techniques and mathematical model development for predicting segregation patterns of material subject to static charge. The segregation tendencies are found to be a function of the rate of charge dissipation, as well as the fill rate and local charge intensity of each species. Small changes in trajectory can lead to large variations in segregation pattern. Thus, measuring the electrical properties of material gives an indication of segregation tendencies in some process systems.