Hard-particle methods characteristics

If the extrusion is performing well the particles formed are very regular, hard and uniform. The extruder can produce great quantities of variously shaped products and, as a consequence, the extrusion process is relatively cheap in comparison with the pelletization method of making catalyst shapes. The mechanical strength is less than that of the pellets so the extrudates are less resistant to abrasion, but they do have better characteristics from the standpoint of porosity and freedom from lubricant. Furthermore, many different shapes and sizes are possible. 

Particles in gas streams vary so widely in terms of size, density, shape, stickiness, friability, erosiveness, surface charge, and other characteristics that no one method of separation, and not one type of separator, is suitable for processing the entire spectrum of materials. Thus the separation equipment must be capable of processing a very wide variety of material—from pellets to sub-micron powders, from hard minerals, like garnet sand, to soft food products like rolled oats. Some of these materials are very free-flowing, others tend to compact or cake. The products and types of particles shown in Figs. 1.2.1 and 1.2.2 are rather typical of the myriad of substances that can, and have been, successfully conveyed and subsequently classified or separated in modern separation equipment, including cyclones, bag filters and electrofilters. 

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