The pneumatic conveyor moves granular materials in a closed duct by a
high velocity air stream. Pneumatic conveying is a continuous and flexible
transportation method. The material is carried in pipelines either by suction or
blowing pressure of air stream. The granular materials because of high air
pressure are conveyed in dispersed condition. For dispersion of bulk material, air
velocities in the range of 15-30 m/s is necessary.
The pneumatic conveying system needs a source of air blowing or
suction, means of feeding the product into the conveyor, ducts and a cyclone or
receiving hopper for collection of product. There are three basic systems of
pneumatic conveying. These are pressure or blowing system, suction or vacuum
system, and combined push-pull or suck blow system.
In blowing or positive pressure systems, the product is conveyed by using
air pressures greater than the atmospheric pressure.
The selection of air mover is the most important aspect of the design of a
pneumatic conveying system. In design, the two factors, (1) supply air pressure
and (2) the volumetric flow rate of air should be considered.
For separation of product particles from air, air-product separators are
used. Cyclones are mostly used to collect the particles. Cyclone is a device
which removes the bulk of the product particle from the conveying air stream by
centrifugal force. In some cyclone, a fabric filter is attached to remove residual
dust and fine product particles from the air stream (Figure 4.1).