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Salina, KS -- The vast majority of conveying systems are of the dilute phase type since they are less expensive and more adaptable. Dilute phase conveying also provides less particle to particle interaction, which reduces particle size and shape degradation. Whenever degradation is a concern, its three primary causes must be addressed: velocity of material, angle of impact, and hardness of the material impacted.
Low Pick-up Velocity
Pick-up velocity should be as slow as possible while still maintaining a reliable and consistent flow. Testing of the material’s conveying characteristics is vital. As the material moves from the pick-up point to the destination, the transfer gas decompresses, expanding its volume, and thus increasing velocity. Therefore, transfer systems can be designed with larger line sizes that allow for overall lower decompression velocities.
With careful design, there may be enough decompression velocity to enlarge the cross sectional area of the convey line and thus reduce the material velocity. This is often referred to as a “stepped line size”. Dense phase systems can have greater decompression velocities since they operate at higher pressures, particularly during purge cycles and start-up sequences.
Elbows Count
Angle of impact interactions occur at the elbows and destination receiver. Reducing the number of elbows will greatly reduce degradation. This also helps lower system pressure and resultant decompression velocity. Long radius elbows are preferred because they provide a shallow angle of impact. At the destination, there are a variety of was to reduce degradation by reducing the velocity, impact angle, and hardness of impact.
There are some cases in which a soft walled hose works better than a rigid wall piping. Careful design is required due to the hose’s higher friction and greater pressure drop.
Sequencing
Vacuum sequencing type systems have also proven to reduce degradation with many friable materials. The average velocity is tempered by the cycling nature of these systems. Once the material enters the convey line, it may be several draw cycles before it reaches the destination.
Several other factors can affect degradation, such as temperature, humidity, and process equipment. However, the items mentioned above will go a long way towards choosing a system to reduce degradation.
About Our Author
Mr. Mahoney received his BS in Milling Science & Management from Kansas State University. Pat has been with Premier Pneumatics since 1993 and is currently a Senior Systems Engineer.
For more information about pneumatic conveying fragile and fiable materials, contact:
Mr. Pat Mahoney
Senior Systems Engineer
Premier Pneumatics, Inc.
606 N. Front St.
Salina, KS 67401
Telephone: (785) 825-1611
Fax: (785) 825-8759
Email: pmahoney@premierpneumatics.com
Web site: http://www.premierpneumatics.com/
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