Due to the increasing importance of particulate products with a narrow particle size distribution smaller than 1 µm processes are needed to generate such particle systems. Conventional production processes like precipitation or wet grinding cannot guarantee, that all milled particles are smaller than 1 µm. Additionally conventional wet classification processes cannot separate fine particles in highly concentrated suspensions with a high selectivity. Therefore, in this work the crossflow classification is investigated as a method to classify particles in a particle size range from 0.1 to 1 µm.
The crossflow-classification utilizes the principles of the crossflow filtration. A suspension flows over a membrane tangentially. Due to a higher pressure on the concentrate side, pure liquid permeates through the membrane (permeate flux). The permeate flux creates a drag force on the suspended particles which transports them towards the membrane surface. The velocity gradient in the boundary layer of the crossflow creates a lift force on the suspended particles which transports them back into the bulk flow. Both forces depend on the particle size. By adjusting the crossflow rate and permeate flux, a separation size can be adjusted. The particles smaller than the separation size are deposited on the membrane, while the larger particles remain in the bulk flow. After rinsing the system with pure liquid the particles deposited on the membrane can be resuspended by backwashing and discharged from the system. For the initial experiments, a lab-scale experimental plant is constructed. With this setup, a parameter study for the influence of the mean velocity of the crossflow on the separation size and the selectivity is performed. The models for the lift force will be validated. An optimization of the resuspension and discharging of the deposited fine particles will be aimed at. The stabilization of the suspension of the resuspended particles is investigated, to inhibit re-agglomeration of the particles after the classification.
Session: M4 - Short Oral + Poster Presentations
Day: 14 March 2018
Time: 14:45 - 16:45 h