Air Current Segregation in Insutrial Silos – a Design Challenge for Filters in the Air Extraction System

The loading of storage silos with fine powders (such as carbon dust) requires a profound understanding of the segregation behaviour of the material in the silo. When the silo is being filled settling particles accelerate the air through transference of drag effects.The air starts circulating, creating local areas with different velocity and pressure characteristics within the silo. Fines entering a zone with higher air velocities are accelerated and carried away from the main bulk and often are sucked out of the silo by the extraction system. This results in a significant pressure drop across the filter. The pressure drop is strongly influenced by the filter material and the properties of the filter. Fines build up until the filters reach saturation and require cleaning. Experiments were conducted using different filter types. The filter was loaded and cleaned in a continuous process, and filter efficiency analysed.