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Bucket elevators : an overview

Bucket conveyors design, safety, application

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Page summary
1. Definition of bucket elevator
2. Bucket elevators design
3. Bucket elevator applications
4. Bucket elevator manufacturers


1. Definition of bucket elevator

What is a bucket elevator ?

Bucket elevators are mainly used for vertical (elevation) conveying, although some manufacturers are also proposing designs allowing to cover horizontal sections. In bucket elevators, buckets, that are filled with material in order to convey it, are mounted on a belt, driven by a motor. The buckets are first loaded, travel (up) full, are discharged automatically by tilting, then travel back empty to be loaded again. One of the advantages of bucket elevators are that they can convey vertically over relatively large distances without breaking the powder or granular material handled.

2. Bucket elevators design

How does a bucket elevator work?

Bucket elevators are particularly used in heavy industries : mining, cements, power plants or in grain industries. They allow to bring up at high capacity materials that would not be possible to convey otherwise.

Bucket elevator working principle

Capacity of bucket conveyors

  • Up to 200 m3/h, depending on the size and speed of the buckets
  • Some very large design up to 1600 m3/h

Size

  • Up to 0.5 m wide buckets

Conveying distance

  • Conveying is always upwards, up to 50 m

Drive

  • Chain or direct coupling drives

Specificity of design

  • Buckets are mounted on a rubber belt or on some drive chains. When full of product, the system is always maintaining the buckets leveled during up of sideways movement to avoid that product falls from the bucket. The bucket is only tipped when arriving at the product chute. Buckets are also designed to overlap in order to reduce the risk of product spillage.
  • Some manufacturers are applying small venting holes at the bottom of the buckets (also called cups) so that the discharging is easier thanks to the air getting in the venting hole to compensate the vacuum created by the moving bulk solid. Others are using knockers to help the product flow out of the buckets.
  • The product pick-up point, at the bottom of the elevator can be a point of product accumulation and some product may fall from the buckets when they are conveyed up. In order to provide an easy cleaning of the materials, the base of the elevator is often mounted on a stand, a hatch of gate valve positioned at the bottom of the casing, to allow for the accumulated product to discharge by gravity to the floor, collecting the products in buckets or bags positioned there.
  • Hatches must be located at regular intervals on the casing of the bucket elevator in order to allow an inspection, maintenance and cleaning point. The lids can be designed for a quick access but safety must be ensured with interlocks so that belt cannot run while someone inspects. The access to the lid through stairs or ladders should also be foreseen.

Bucket elevator Safety

One of the key safety aspects of bucket elevators is to manage dust explosion hazards. Since already several years a dust explosion risk analysis must be done in Europe for all processes handling particulate solids and it is now also a mandatory exercise in US following the issue of NFPA standard 652 which is requesting a Dust Hazard Analysis. When designing a new bucket elevator or reviewing an installed one, the following points must be considered to ensure a safe operation in the presence of dust :

  • Bucket elevators were in the past the source of several explosions, thus a strong dust hazard analysis must be performed for every unit. If not possible to prevent explosions, most manufacturers are now proposing to include explosion vents.
  • To prevent explosions, manufacturers are using a fully conductive drive assembly with a continuous electrical grounding. They also use antistatic belts, a monitoring of the temperature of bearings, dedusting systems, or even apply inerting.
  • Dust aspiration points must be installed all along the conveyor and more specifically at product pick-up and discharge where the material is flowing and generating the more dust.
  • Electrical equipment in the vicinity of bucket conveyors must be rated for dust explosion area and the max temperature of the motor must be lower than MIT and SIT of the materials.

Bucket elevator hygiene

  • The installation of a Cleaning In Place (CIP) system in one section of the bucket elevator is possible when using this equipment in industries requiring sanitary conditions. The cleaning section is followed by a drying section to make sure no water is remaining in the bucket, which could cause issues in terms of material flowability, hygiene and food safety.

3. Bucket elevator applications

Bucket elevators are often found in large industries that require quite a high capacity of conveying without having much constraints in terms of hygiene or toxicity of  the materials conveyed. Therefore, industrial bucket elevators main applications are the following :

  • Grain bucket elevators : those equipment are typically found in large agricultural exploitation, to transfer and pile grain, or in silos.
  • Fertilizers
  • Plastic pellets
  • Cement
  • Coals handling
  • Minerals
  • Ships unloading

4. Bucket elevator manufacturers

In order to get quotes, prices of bucket elevators, the reader can refer to the following companies :

https://www.denis.fr/en/company/

https://www.lessine.com/en/solutions/handling/bucket-elevator

http://www.stolz.fr/en

(Note that PowderProcess.net has no link with those companies)