Feed Mill Pneumatic Conveyors

Common types of pneumatic conveyors used in animal feed production include: Dilute phase, dense phase and airslide / aeration conveyors.

Dilute phase (lean or suspension) conveyors move material suspended in a gaseous flow (air) at high velocity. Almost any material can be conveyed in dilute phase regardless of particle size, shape or density. Equipment basically consists of a machine for generating air flow, a feed system (rotary valve, powder pumps, etc) which inserts the solid into the air stream, a conveyor line (pipe) and a solid-air separation system (centrifugal separator, reverse jet bag filter, etc). High velocities in these systems give rise to high degradation of solids (feed pellets) due to collision between the particles and between particles and the conveyor (pipe) walls. Not suitable where degradation of solids is undesirable.

Dense phase (non-suspension) conveyors move material at low velocity in a moving-bed flow or plug type flow. Moving bed flow conveys the material along the bottom of the pipe, like water in an open channel.  Typically limited to very fine powdered materials with good air-retention characteristics. Plug type flow conveys the material as full bore plugs separated by air gaps. Typically limited to materials that are essentially mono-sized and have good permeability (allow air to pass between). Pelletized materials and seeds are good candidates for this type of flow. Generally the low velocities in dense phase conveyors reduce the degradation of solids and can be used with fragile materials (feed pellets).

Airslide (aeration or fluidised gravity bed) conveyors are used to convey powders using gravity and low air pressure. Air at low pressure is passed through a porous membrane and into the bed of material. This air pressure and gravity essentially turns the material into a fluid. A large variety of materials can be conveyed with this method but typically the material must have a low moisture content (< 1%), temperature below 1200 degrees Fahrenheit and a particle distribution of 100% through a 20 mesh screen.

- Flexicon Corporation, DCL Inc images.