Does Damage You Don't See Matter?
Plastic resin often passes through extensive pneumatic conveying systems during it's manufacturing and use. While those pneumatic systems are efficient and appropriate, they're not without complications to quality and throughput.
Two major problems frequently occur in the conveying of plastic resin:
- Degradation of the raw source material
- Damage to the conveying system and related components
Controlling Temperature and Abrasion
Friction is the chief source of all issues involving pneumatic conveying of plastic resins. As the resin pellets are conveyed within the duct, the contact between the pellets and the interior surface of the piping creates friction. The amount of friction increases around bends and other transitional sections of the piping or where the duct connects to storage tanks or other equipment.
Raw plastic resin materials are sensitive to the increase in temperature associated with friction in both dilute and dense phase pneumatic conveying. As temperatures rise, some materials begin to soften or even melt. The newly softened/melted material can then begin to coat or smear the inside of the conveying piping or create “streamers” or “angel hair” (long thin strips caused when the pellets melt). These can lead to blockages and cross contamination of other materials conveyed later in the same system. Still other compounds can break easily during conveying, leading to excessive dust, plugged filters, and waste.
Operators must also contend with damage to conveying piping and related equipment. Abrasive plastics can lead to excessive wear of conveying tubing, bends, and other equipment. Unexpected part failures can create costly repairs and unplanned downtime.
Both issues nearly always find their source in failure to control the pneumatic conveying velocity within recommended ranges. Increased velocity exponentially creates additional friction, heat and impact force causing the problems mentioned above. One report showed that even a seemingly minor increase in velocity from 2700 ft/m to 3300 ft/m resulted in 55% more “streamers”!
Yet simply reducing conveying velocity in pneumatic conveying systems often leads to downtime and production interruption due to conveyor blockages.
Process engineers face a challenge of optimizing particle velocity to minimize damage and optimize output. The barrier has traditionally been that particle velocity is calculated - since it couldn't be measured. And gas/air velocity, which is often used as a proxy, can vary substantially from the actual particle velocity in pneumatic conveying systems.
Monitor Particle Velocity in Pneumatic Conveying Systems with Auburn’s TRIBO.dsp Triboelectric Systems
By installing one of Auburn Systems’ triboelectric particle velocity monitoring systems, operators can monitor actual particle velocity in realtime as the material flows through the system. The instrument determines velocity by measuring the time it takes for material to pass by 2 triboelectric detectors. Depending on the application, the system can use either an intrusive style sensor with a standard triboelectric isolated probe or a non-intrusive flush-mounted ring sensor array. Most resin applications prefer the non-intrusive version as they avoid unnecessary friction in the system and eliminate the potential for contamination.
With accurate particle velocity measurements, operators can more effectively control input pressure and conveying velocity in the system to maintain the recommended minimum conveying velocity for the material. Additionally, some find it useful to monitor velocity at more than one point in the system, since velocity tends to vary significantly in longer systems. Further application variation arises since resin is received from different sources including trucks, rail, barge, etc., which may provide any number of different blower combinations. All this variety means that few of these operations will follow the exact same parameters. The constant change requires operators to pay close attention to particle conveying velocity (vs. air speed) to predict and prevent damage and downtime.
Having accurate velocity readings allows operators to strike a careful balance between conveying materials as quickly as possible without excess friction that creates problems due to temperature and abrasion. To learn more about how Auburn Systems’ triboelectric particle velocity monitoring systems provide operational improvements for pneumatic conveying systems, please contact us for a free consultation today!