Pneumatic conveying systems by Piab

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What is pneumatic conveying?

Pneumatic conveying systems are designed to use pressure differential to move bulk materials from one process area to another. Powders, granules, and many other dry bulk materials can be transferred through enclosed pipelines with the help of a pressure differential and gas or airflow.  Pneumatic conveyors work best with fine, fluidizable, dry powders that can easily “fly” through the conveying line. The systems find applications in a variety of industries, including food processing, pharmaceuticals, chemicals, or metal additive manufacturing. There is a long list of different powders that can be conveyed with pneumatic conveying, including flour, cement powder, carbon black, sugar, plastic pellets, small food particles, tablets, sands, metal powders, and many more. Moist or heavy, granular materials, such as crushed rock, large food particles, wet sand, and gravel, are – on the other hand - not suitable for pneumatic conveying, for example, products with particle sizes larger than 30mm/1.2" and bulk densities over 8kg/l / 500 lb/ft³.

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How does the pneumatic conveyor work?

Pneumatic conveyors either work with positive pressure, when bulk materials are blown by the equipment from one point to another. Vacuum conveyors on the other hand are pneumatic conveyors that work with vacuum.

These systems are comprised of four basic elements:

a vacuum source,
a material feed device,
a conveying line and
an air-material separator.

Cyclic operation

It generates a vacuum, and the conveyed material is transferred from the feeding point into the conveying line and then to the container.

During the conveying process, the filters protect the pump and the surrounding area from dust and small particles, and the air shock tank is filled with compressed air.

After each cycle, the bottom valve opens, and the material is discharged into a hopper or any other piece of equipment.

At the same time, the filters are cleaned with a filter shock or similar cleaning method in each cycle.

Pneumatic conveying

Types of pneumatic conveying systems to choose from

Dense phase pneumatic conveyor

In dense phase conveying, the material is conveyed in a more concentrated, slower-moving plug or slug within the pipeline. This method is suitable for heavier or more fragile materials, as it reduces the risk of material degradation. Dense phase conveying is often used for shorter distances and in situations where gentle handling of the material is critical.

Medium phase pneumatic conveyor

Medium phase conveying falls between lean phase and dense phase conveying in terms of material concentration. The velocity is higher than that of dense phase conveying but lower than dilute phase conveying. Medium-phase conveying represents a compromise between the extremes of dilute and dense phase and offers a versatile solution for materials that are in the middle of the spectrum in terms of material characteristics.

Dilute phase pneumatic conveyor (lean phase)

In dilute phase conveying, the material is transported in suspension within a stream of air or gas. The terms "dilute phase" and “lean phase” are thereby often used interchangeably. The material is generally conveyed at high velocities, and the concentration of the material in the conveying air is low. Dilute phase or lean phase conveying is suitable for lighter materials and is often used for longer-distance transport.

Cog wheels

How do mechanical conveyors work with bulk powders?

The basic components of a mechanical conveying system include a drive motor through a gear and/or chain reducer  connected to a drive device, such as a roller or a sprocket. The motor's energy is transferred directly to the conveyor, which is in direct contact with the conveyed material. Mechanical conveyors can be open or closed to the atmosphere, with hundreds of moving and working parts.

Types of mechanical conveyors

Bucket elevators

Bucket elevators have an open, uncovered top and a rotation belt. When the product material is undischarged in a cycle, then it usually disperses into the production area.

Installation of a bucket elevator requires civil engineering which is time consuming, expensive and entails high maintenance costs. It is also a rigid system which can only work on the capacity that it was planned for. It is not fulfilling the highest hygienic standards as it has big contact areas with the conveyed product, and it is also hard to sanitize it.

Belt conveyors

Belt conveyors consume a lot of floor space. These are bulky pieces of equipment that have a high risk of spillage.

Belt conveyors have high maintenance costs, especially if they are used to convey abrasive materials. Apart from spillage, sanitization is also a major issue, and the conveyed material can easily get into the air, causing health issues and the risk of dust explosions.

Screw conveyors

The friction caused by screw conveyors can lead to significant damage as well as temperature change in the conveyed material.

Screw conveyors don’t allow curves or direction changes, they are bulky and can’t convey in a vertical line which makes their application areas limited. They are also difficult to clean.

Why choose pneumatic conveyors with vacuum over mechanical conveyors?

The safest option to convey powders

There are no moving parts that can shear objects or need to be lubricated, pinch points that would grab a piece of clothing or nip points where the gears would meet.

Eliminates the risk for contamination

Conveyed materials are transferred in a closed system, not being exposed to air.

Saves space

Pneumatic conveyors can even be mounted right below the ceiling, taking up only a fragment of space compared to a mechanical conveyor.

Eliminates spills in the production line

The closed pipelines greatly reduce the possibility of material loss.

Easy to clean and sanitize

Pneumatic conveyors usually have an in-built filter cleaning system that prevents the filters from clogging. 

Flexible and easier to maintain

Switching between materials and maintenance generally takes much less time compared to mechanical conveyors.

How to choose the right conveyor type?

There are several factors affecting the selection, like: <ul> <li>Material characteristics, such as particle size, distribution and shape, hardness, the tendency to get hygroscopic and fluidize, moisture content, concentration, and bulk density</li> <li>Environmental factors, such as temperature, humidity</li> <li>Connected equipment characteristics, such as system distance and throughput, height, and angles.</li> </ul> The most important factor is material characteristics. Pneumatic conveyors work best with fine, fluidizable, dry powders which can easily “fly” through the conveying line. There is a long list of different powders that can be conveyed with pneumatic conveying, including flour, cement powder, carbon black, sugar, plastic pellets, small food particles, tablets, sands, metal powders, and many more. Moist or heavy, granular materials, such as crushed rock, large food particles, wet sand, and gravel, are – on the other hand - not suitable for pneumatic conveying. Humidity often affects conveying as certain materials, like sugar, become hygroscopic (sticky) in tropical climates. The size of the conveyor, the optimal pump, pipes, and other accessories are determined by the required throughput, height, and the number of angles the pipes must have. These parameters must all be considered when the optimal way of conveying is planned, so it is extremely important to choose the right provider with extensive know-how. The application engineers of Piab are among the most knowledgeable professionals in this area, building on 70 years of experience in industrial automation.

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