Conveyors

Conveyors and elevators are used to transport solids. An industrial plant typically contains more than one type of conveyor or elevator.

(Copyright Astec, Inc., Chattanooga, TN)

Mechanical Conveyors

Belt

Belt conveyors are the most popular type of mechanical conveyor. Mechanical conveyors use moving parts to transport material.

(Copyright PRAB, Kalamazoo, MI)

General Information

Belt conveyors can be used for almost any material. They come in many sizes and can be inclined. Typically they are connected in series to form a long belt conveying system.

(Copyright PRAB, Kalamazoo, MI)

Equipment Design

The main component of a belt conveyor is a continuous belt. It can be made of polyester coated with rubber, plain or coated canvas, woven wire, or a steel ribbon. Belt conveyors are usually flat but in bulk solids handling they are typically troughed to prevent material from falling. Belt conveyors are driven at one end by a motor, not shown, that rotates the drum to move the belt. At the other end of the conveyor there is an idle drum.

Usage Examples

Belt conveyors are typically used for transporting, proportioning , feeding, discharging, and metering bulk solid materials. The picture below shows a series of belt conveyors that are used in an asphalt plant.

(Copyright Astec, Inc., Chattanooga, TN)

Advantages

Disadvantages

  • Can be developed to convey almost any type of solid material.
  • Easy to adapt to plant layout.
  • Inclination angle must be less than 22°.
  • Cannot transport anything at temperatures greater than 120 °C.
  • Small scale experiments needed to determine operating parameters.

Drag Chain

General Information/Equipment Design

Drag chain conveyors are a type of mechanical conveyor that can transport solids horizontally, vertically, or on an incline. Drag chain conveyors use a hopper to feed the material onto the ledges of a single or double chain. After the material is loaded onto the chain, it is conveyed through a tube until it reaches the discharge point. It is possible to have many inlet and outlet points along the chain.

(Animation based on picture Copyright Hapman Conveyors, Kalamazoo, MI)

Usage Examples

Drag chain conveyors are used to convey pieces of particle board in a wood processing facility. They are also used to convey wet and dry solids in the chemical and food industry.

Advantages

Disadvantages

  • Flexible in loading and unloading
  • Self-loading
  • Many possible discharge and loading points
  • Product build-up on walls
  • Large amount of solid needed for effective transport

Screw

General Information/Equipment Design

Screw conveyors are the simplest and cheapest for transfer of materials at rates of up to 40 ton/hr over distances of up to 65 ft. Screw conveyors are flexible; depending on their diameter, they can be curved to some extent. Screw conveyors consist of a special heat-treated and tempered carbon or stainless steel spiral that rotates with an ultra-high-molecular-weight polyethylene (UHMWPE) food-grade tube. The transport of material in a screw conveyor occurs by the turning of a helix screw in a trough casing. The particles should be smaller than the screw pitch. The screws can have constant, variable, or tapered pitch. In tapered pitch, the distance between the grooves gradually decreases down the length of the conveyor.

(Copyright PRAB, Kalamazoo, MI)

Screws with round cross sections are flexible and strong, and screws with flat cross-sections are more suited for high velocity applications. The trough casing can be round, rectangular, or U-shaped. The picture below to the left shows a single helical screw conveyor, and the picture below to the right shows a dual auger design.

(Copyright PRAB, Kalamazoo, MI)

Usage Examples

Screw conveyors are used in pharmaceutical , food, and dairy production applications. The screw conveyor below to the left is used in an asphalt plant, and the one to the right is used as a feed for a metal turnings shredder.

(Copyright Astec, Inc., Chattanooga, TN)

(Copyright PRAB, Kalamazoo, MI)

Advantages

Disadvantages

  • Closed tube prevents product contamination
  • Inexpensive to purchase and operate
  • Quick installation
  • Flexible conveyors can be routed around obstacles
  • Product handled gently
  • Product is usually very accurate and highly repeatable batches are possible
  • Conveyor can be easily emptied at the end of a batch operation
  • Particles must be smaller than the pitch
  • Abrasive materials will most likely cause wear
  • Small scale experiments needed to determine operating parameters
  • Need to run full of products

Vibratory

General Information/Equipment Design

Vibratory conveyors have a single trough design. This single trough vibrates on springs to produce an upward, forwards flow of the material. This type of flow creates a forward hop. The capacity of a vibratory conveyor is determined by the cross-sectional area and slope of the trough. A vibratory conveyor should be used when the material has a high friction factor on steel.

(Copyright PRAB, Kalamazoo, MI)

Usage Examples

Vibratory conveyors are used in a variety of industries. In the chemical industry, they are used to transport fertilizer, detergent powders, and plastic pellets or powders. In the food industry, they are used to convey corn kernels, instant coffee, and cereal flakes. The video below shows a vibratory conveyor used to handle scrap aluminum.

ConveyorVibr.gif

(Copyright PRAB, Kalamazoo, MI)

Bucket Elevators

General Information/Equipment Design

Bucket elevators are usually used when there is not enough space for a horizontal conveyor. Bucket elevators consist of buckets mounted on a single or double chain. The buckets are loaded at the bottom of the apparatus and dumped through a chute at a higher level. From the chute, the materials are usually loaded on a conveyor or stored in a silo.

(Copyright Astec, Inc., Chattanooga, TN)

Advantages

Disadvantages

  • Can operate at speeds of about 1.5 m/s.
  • Can handle large capacities of material in a short time.
  • Buckets undergo wear and tear.
  • No universally accepted design.

Non-Mechanical Conveyors

Pneumatic

Pneumatic conveying uses a gas to convey solid material.

(Copyright MAC Equipment, Inc., Kansas City, MO)

General Information

Pneumatic conveying is not a type of mechanical conveying. Instead of using moving parts to convey material, gas flow is used to transport materials horizontally, vertically, or on an incline.

(Copyright Kaeser Compressors, Inc., Fredericksburg, VA)

Equipment Design

The two types of pneumatic conveyors are dense phase and dilute phase. In dense phase pneumatic conveying the particle concentration is very high, as shown in the left picture. Dilute phase pneumatic conveying, shown on the right, has a small solid concentration

(Copyright MAC Equipment, Inc., Kansas City, MO)

In dense phase pneumatic conveying, the material is first placed in a hopper. The hopper feeds the material into a dense phase transmitter, which mixes the feed with a gas, usually air. The material travels by plug flow to its destination.

giphy (7).gif

(Copyright MAC Equipment, Inc., Kansas City, MO)

In dilute phase conveying, the material is fed into an airlock feeder. The solid material is suspended into air at a ratio of about 3 to 5 kilograms of feed to 1 kilogram of air. The material is then conveyed as a suspension along the pipe line. Throughout the entire process air penetrates through the feed stream. If chemical reactions with air are a concern, other gases can be used.

Usage Examples

The pictures below exemplify a pneumatic conveying system used to transport metal chips for processing. The upper picture shows the inlet receiving hopper and pick up pneumatic piping. The lower picture shows the overhead pneumatic transfer system from the pick up lines to the main pneumatic line.

(Copyright PRAB, Kalamazoo, MI)

Advantages

Disadvantages

  • No dust contamination
  • Flow direction can be varied
  • Low maintenance costs
  • Can handle multiple products with one system
  • Virtually no limitation in capacity, product type, distance, or routing
  • Particles must be dry
  • Possibility of product breakage
  • Wear and tear on the pipes
  • High cost compared to other systems
  • High amounts of filtration required

Acknowledgements

Astec, Inc. , Chattanooga, TN

Hapman Conveyors , Kalamazoo, MI

Kaeser Compressors, Inc. , Fredericksburg, VA

MAC Equipment, Inc. , Kansas City, MO

PRAB , Kalamazoo, MI

References

Degirmencioglu, A. and A.K Srivastava. "Develoment of Screw Conveyor Performance Models      Using Dimensional Analysis." Transactions of the ASAE Vol. 39 September-October 1996:      1757-1763.

Gager M. and S. Tappeiner. "Additional Strain in Conveyor Belts Caused by Coarse and      Transition Geometry." Bulk Solids Handling . Vol.13 November 1993: 695-703.

Kimbel, Kirk W. "Troublefree Pneumatic Conveying." Chemical Engineering April 1998: 78-83.

Kolhe, P.P. and D.J. Tidke. "Belt Design and Load Capacity Estimation for Air Supported Belt      Conveyors." Bulk Solids Handling . Vol. 14 Oct-Dec 1994: 755-758.

Mainwaring, Nigel J. "Characterization of materials for pneumatic conveying." American Ceramic Society Bulletin . Vol.72 August 1993: 63-71.

Perry, Robert H. and Don W. Green. Perry's Chemical Engineers' Handbook . 7th ed. New      York: McGraw-Hill, 1997: 21-14, 21-6 - 21-10, 21-13 - 21-14, 21-19 - 21-21.

Podevyn, Michel. "Selecting a Conveyor" Chemical Engineering February 20089 27-29.

Roberts, A.W. "Advances in the Design of Mechanical Conveyors." Bulk Solids Handling Vol.14      April-June 1994: 255-281.

Shamlou, P. A., Handling of Bulk Solids: Theory and Practice . Boston: Butterworth & Co.      Ltd., 1988.

Stewart, Gordon. Modern Steam Traps: Their Construction and Working . New York: D. Van      Nostrand Co., 1907.

Developers

Julie Messacar

Joseph Palazzolo

Steve Wesorick

Abigail Nalbandian

Steve Cotton