Real World Complications
When unloading bulk material, sudden changes in air flow can create complications for material conveying systems. Rapid increases in material flows, or high volume air flow as material flow suddenly slows, can damage filters within the system filter receiver. Often this change occurs quickly, and even if operators are diligently observing, they may not react quickly enough to prevent damage.
How can plants avoid these issues and prevent damaging their filters?
Common Causes of Sudden Increases in Flow Rates
In most cases, there are several causes of sudden increased material flow.
1. A rush of material at end of unloading due to uneven emptying of the material from the storage container. Bulk materials stored in a hopper or bin can sometimes have problems emptying from their storage container. The material could experience bridging or arcing of the material over the outlet. In other instances the material can flow in funnels (sometimes called ratholing) over the outlet. In both cases, the effect can slow the material flow rates followed by a sudden rush of more material. When not accounted for by operators this can create a sudden increase in conveying velocity, pressure or wear on the system.
2. An increase in pressure at source in an attempt to speed up product flow. Time pressure and delivery schedules may encourage some to increase pressures to speed up the unloading process. Gradual increase in PSI at the source will move more product faster but increase the likelihood of damage to various system components when suddenly material slows and air pressure overwhelms separator media not designed to accommodate large volumes of air.
Using Triboelectric Devices to Control Material Flow
Using Auburn Systems’ TRIBO.hs 5000 series of particle velocity monitors plants can monitor actual particle conveying speed and carefully control product flow rates in material conveying systems. A typical system which relies on operators for continuous adjustment can have real time reading of velocity within the system to enable them to make adjustments to keep the flow rates within specified parameters.
In more advanced installations, companies seeking to automate the process have begun exploring interfacing the TRIBO.hs 5000 series directly with their conveying controls. This eliminates the risk of excessive pressures potentially causing damage to system components.
With careful monitoring of material flow rates and material velocity, plants can ensure that they operate their conveying systems within the recommended pressures and flow rates to avoid damage to the pneumatic conveying system, filter receiver and its filters or the bulk goods themselves.