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Pneumatic Conveying Is A Common Way Of Moving Materials

Pneumatic conveying is a common way of moving dry bulk materials such as powders and granules from point A to point B. This transfer technology is frequently used in the plastics and compounding industries as well as in the processing of chemicals and food. Systems of this kind lend themselves to the transport of substances such as plastic pellets, cement, sand, flour and a long list of other dry materials. The technology is ill-suited for pasty, sticky or doughy substances.

The word “pneumatic” is of Greek origin and means air or wind
. Pneumatic conveying systems are so-called because they are essentially powered by gas pressure (usually oxygen or nitrogen). The system is generally comprised of an air mover (such as a blower or fan), a feeder, a conveyor, a material receiver and a dust collector. If the air mover is positioned at the start of the line, it pushes out air to activate the transport system. If it is located at the end of the line, it sucks in air and creates a vacuum that in turn triggers mobilization. Most people know pneumatic conveying systems from banking institutions, where pressurized tubes are often utilized to push and pull canisters containing cash or checks during drive-through transactions.

A pneumatic conveying system has several advantages over more traditional mechanical transport methods. Because it is usually fully enclosed, it generates minimal dust on the factory floor, enhancing the longevity of other equipment located in the plant. In addition, the enclosed tubes feature superior flexibility as they can be arranged around existing machinery and bend in multiple directions. Maintenance and durability are yet another advantage, as the system incorporates few moving parts. On the downside, an air pressure system requires a lot of horsepower and consumes more electricity than its mechanical counterpart.

There are two basic types of pneumatic conveying systems: dilute-phase and dense-phase.

Dilute-phase (also known as stream-flow) systems operate on a principle of high velocity/ low pressure differential
.  This means that the air mover predominantly uses high acceleration to propel the substance forward and through the tubes. An analogy could be a child blowing a paper wad through a straw. The initial effort is the most crucial because the air flow must move the paper wad from a static position.

A dense-phase system works the opposite way: high pressure differential/low velocity. Once again using an analogy, this method could be compared to a butcher forcing meat into a sausage casing. The butcher’s sausage stuffer exerts immense pressure on the meaty paste, but at a relatively slow speed.  

When choosing a type of conveying system, or deciding between dilute-phase or dense-phase technology, it is important to consider the following:

•    The particle size, shape and weight of the material to be transported; small particles are more easily moved by air pressure than larger ones.
•    The material’s bulk density, moisture content and cohesiveness; very sticky or pasty substances are generally more suitable for mechanical transport.
•    The desired transfer rate of the material.
•    Space availability and constraints; which system delivers the best fit for the existing setup?
•    Dilute-phase systems usually require a lower initial investment than dense-phase systems.
•    Long line runs are better served by dense-phase systems.
•    A vacuum system may be safer for moving toxic or explosive materials.

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