Pneumatic conveyors are continuous conveyors for bulk material in which material is conveyed in an enclosed tube system by means of compressed air or by means of a vacuum. This type of conveyor is extremely flexible in terms of routing. Both compressed air and vacuum systems are based on the same principle, according to which solid particles—when the air velocity is fast enough—are picked up by the conveyor’s air flow and conveyed along the pipe.
There are three different conveying phases that are defined based on the material’s properties, the flow medium being used, the conveyor pipe, the volumes of both the flow medium and the material being conveyed, and the shape of the pipe route:
Dilute phase conveying (stationary lean phase) – when the proportion conformed by the material being conveyed is small. The material being transported is conveyed by means of comparatively large air volumes and low pressures at high air velocities (relative to the individual particles’ fall velocity). Dilute phase conveying is also referred to as “suspension flow conveying.”
Dense phase conveying (intermittent moving-bed and slug flow) – when the proportion conformed by the material being conveyed is average.
With this method of conveying, air no longer flows around individual particles and moves them aerodynamically. Instead, granular agglomerates in the shape of balls, dunes, and plugs are pushed by compressed air at relatively low velocities and higher pressures through the conveying pipe.
Dense phase conveying (stationary smooth slug flow) – when the proportion conformed by the material being conveyed is large.
High pressures are required, but the material will nevertheless be conveyed slowly.
Pneumatic conveyors are used primarily for granular and powdery materials. These bulk materials should not have adhesive properties or be pourable.
Small grain sizes are particularly suitable for this method of conveyance.
Pneumatic conveyors are characterized by their simple construction, low initial costs, the fact that they require little space, and their freedom from dust. Their disadvantages consist of high energy costs, a high level of wear, and the risk of becoming clogged.
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