Powders, granules, and many other dry bulk materials can be transferred through enclosed pipelines with the help of a pressure differential and gas/airflow. Pneumatic conveying systems are designed to use this pressure differential to move bulk materials from one process area to another cost-effectively in Food and Beverage, Pharmaceutical, and Chemicals industries, and even in Additive Manufacturing.
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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 in the other hand are pneumatic conveyors that work with vacuum.
These systems are comprised of four basic elements:
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
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.
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 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.
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.
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.
Conveyed materials are transferred in a closed system, not being exposed to air.
Pneumatic conveyors can even be mounted right below the ceiling, taking up only a fragment of space compared to a mechanical conveyor.
The closed pipelines greatly reduce the possibility of material loss.
Pneumatic conveyors usually have an in-built filter cleaning system that prevents the filters from clogging.
Switching between materials and maintenance generally takes much less time compared to mechanical conveyors.
<p>There are several factors affecting the selection, like:</p> <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> <p>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.</p> <p>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.</p> <p>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.</p> <p>The application engineers of Piab are among the most knowledgeable professionals in this area, building on 70 years of experience in industrial automation.</p>
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