Head to Head: Bucket conveyors and Pneumatic conveyors
September 18, 2015
Highlighting when bucket conveyors have the edge
A question we are often asked is, “Do pneumatic conveying systems outperform bucket conveyors?” The short answer is that while pneumatic conveying systems have some advantages, for certain applications bucket conveyors still remain the equipment of choice.
To avoid confusion, this blog contrasts pneumatic systems with continuous bucket conveyors – the equipment type manufactured by UniTrak. In contrast to centrifugal bucket conveyors, continuous bucket conveyors are slower-speed conveyors, where the buckets are spaced continuously to permit discharge under the force of gravity. Continuous bucket conveyors are ideal for handling friable and fragile materials, or those materials where aeration of the product must be avoided.
Understanding Pneumatic Conveying Systems
Pneumatic conveying systems are classified by their operating principle into two basic types: dilute phase and dense phase. In dilute phase conveying, particles are fully suspended in the conveying air and transported at low pressure and high velocity. In dense phase conveying, particles are not suspended in the conveying air and are transported at high pressure and low velocity. Both dilute and dense phase pneumatic systems can be further subdivided into two types: pressure or vacuum.
Dilute phase conveying
Dilute phase pressure conveying is one of the more common conveying methods for powders or granules. This method is most often used with non-abrasive, non-fragile materials that have a light bulk density, such as flour, sugar, corn starch, plastic granules, sodium bicarbonate, etc. In contrast, dilute phase vacuum conveying is suitable for conveying materials that tend to pack or compress under pressure, such as fibrous materials, and for toxic materials that be fully contained within the conveyor. Dilute phase vacuum conveying is typically used to convey materials over short distances at low capacities.
Dense phase conveying
Dense phase pressure conveying is suitable for gently conveying fragile or abrasive materials comprised of small particles over long distances. This method conveys materials at a relatively low speed to reduce material degradation, air consumption, and abrasion on contact surfaces. Dense phase vacuum conveyingis ideal for gently conveying fragile or abrasive materials over short distances. This method is typically used to transfer powder and granules at a low rate in applications such as truck or railcar unloading.
Four ways Bucket Conveyors Consistently Outperform Pneumatics
While pneumatic conveyors are a viable choice to consider for some applications, bucket conveyors still retain some primary advantages. These include the following:
#1: Product integrity
Continuous Bucket conveyors are unsurpassed for preserving and ensuring product integrity during conveyance. This is particularly critical when transporting friable materials and products. Well-designed bucket conveyors, such as UniTrak’s TipTrakTM line, can outperform pneumatic systems by gently handling and protecting friable materials from degradation during conveyance.
#2: Mix and blend integrity
Mixes and blends need to be conveyed without loss of consistency or separation of the constituent ingredients. Unlike pneumatic systems, what comes out of a bucket conveyor is exactly what went in, thus ensuring that mix and blend integrity is preserved.
#3: Difficult-to-handle products
Pneumatic conveyors can become blocked when sticky materials accumulate within the system. These systems can also have problems in successfully conveying products with a large particle size and high bulk density, such as gravel and very coarse materials. Continuous Bucket conveyors can handle these challenges in stride and ensure a successful transference or product.
#4: Energy consumption
Pneumatic conveyors typically require greater horsepower to operate than a bucket conveyor. In addition, pneumatic systems often require much larger dust collection systems than a bucket conveyor, with commensurately higher energy consumption.
While there is sometimes no clear-cut answer as to whether a bucket or pneumatic conveyor is best for any given application, reputable equipment vendors can provide sound guidance. However, equipment buyers should not discount bucket conveyors from their procurement list – there are still many applications in which this technology outperforms pneumatic systems.