Cyclone Dust Collector Bridging & Other Hassles
Triboelectric dust detection systems can be used effectively to monitor a cyclone dust collector just as well as a fabric filter collector. In the same way that triboelectric systems can monitor baghouses for collection efficiency, operational output and maintenance needs, so to can they monitor cyclone dust collectors. In this article we'll take a quick look at common applications for cyclone collectors and then dig into two common operating problems that triboelectric detectors can assist with.
What are Cyclone Dust Collectors Used For?
Cyclone collectors are the simplest style dust collectors in use today. As the dirty air enters into the cone shaped collector it begins swirling around at high speeds. As the air passes through the carefully shaped collector the spinning air column creates immense centrifugal force that flings the particulates out of the air. The particles then collect at the bottom of the unit in the hopper for temporary storage before removal.
In this manner they can remove 90%-95% of particulate matter from the air stream. They are especially good for removing large particles from the air stream. In many cases these are actually product being accumulated. In others, they are large pieces of debris such as shavings and cuttings from wood or metal milling applications. While they lack the collection efficiency needed for most modern emissions control or health and safety applications, cyclone dust collectors find extensive use as pre-cleaners to help lighten dust loading on primary dust collection systems (e.g. fabric filter collectors). Removing the vast majority of the dust, especially larger more abrasive particles, extends the life of the filters and increase collection efficiency and helps maintain a lower differential pressure over time. Finally they are sometimes used as part of bulk transportation system or as part of processes to sort different sized materials.
What is Hopper Bridging and How Can Triboelectric Monitoring Help Prevent This?
Hoppers on dust collectors refer to the bottom portion of the unit where the dust lands after being separated from the air stream. In a cyclone this occurs when the particles are spun out of the twisting air column and they hit the sides of the unit and drop down. Dust collector hoppers are for temporary storage only. Hoppers filled with dust create operational problems as well as pose a severe fire hazard. Therefore, the hopper must be continually emptied as dust fills the hopper, either with a rotary airlock or a manual slide gate.
However, at times even units with automatic discharges may encounter problems from what's called hopper bridging. As product flows out the bottom, dust above the discharge may stick together and form a bridge over the discharge thus preventing the free flow of dust into the discharge and out of the unit. If left unchecked, this can cause the hopper to overflow with dust and affect the operation of the unit (frequently called “plugging up the unit”) all while operators think the discharge system is functioning correctly.
Thankfully, these problems can be avoided by using a tribo dust monitoring system on the cyclone. By monitoring the total emissions coming out of the cyclone, operators can see any sudden spikes in emissions levels that may occur when hopper bridging or overflow occurs. Additionally, systems equipped with Auburn’s particle velocity monitoring systems can note any decrease in airflow velocity upstream of the baghouse that could occur as a result and take swift corrective action.
With the problem detected, maintenance personnel can clear the bridging by gently striking the hopper with a rubber mallet or with the use of handheld or pre-installed vibrators. (if using mallets take care to avoid denting the hopper which can cause further problems).
Tracking particles across applications
Auburn's triboelectric instruments are well suited to detecting the very small particles in very dilute concentrations in baghouse and stack monitoring, as well as ambient dust detection situations.
Although less widely known, the instruments have also been adapted to observe particles in much more concentrated streams - such as flowing out of the bottom of the hopper or even in pneumatic conveyors.
So triboelectric particulate monitors offer another potential instrumentation solution to the bridging challenge with cyclone collectors - the ability to check for flow of product out of the hopper when the airlock or slide gate is open. This is a simple flow/no flow observation, but one that could provide early warning of a bridging problem.
All dust collectors can be affected negatively when hopper bridging occurs. Prevent this production disruption, or even possible fire hazard by using triboelectric monitoring to detect the problem during its earliest stages and take corrective action.
Photo Credit: http://unitedstatessystems.com/hoppers-bins-tanks-vessels-silos/