Particle flow in dust collection systems is frequently ignored. Once the product enters the dust collection pickup point operators receive no new information until it exits at the dust collector, which could be hundreds or even thousands of feet downstream.
In many applications, changes in particle velocity within the ductwork can indicate problems, and even cause significant issues. Let's look at just two reasons
Prevent Product Drop Out
Every conveyed material, whether metals, ceramics, food stuffs, or any other, requires a specific airspeed in order to keep the the particles suspended in the air and carried along. This is called the material’s minimum conveying velocity. A dust collection system must keep its airspeed above this level at all times. If the airflow ever drops below its minimum conveying velocity the dust will begin to fall out of the airstream and settle at the bottom of the ductwork. This is called product dropout.
When product dropout occurs it causes problems. Besides the obvious housekeeping issues associated with reduced suction at the collection points, it also can disrupt the system’s efficiency and create health and safety hazards.
As dust settles in the ductwork, over time large accumulations begin to form, eventually restricting the airflow by blocking off more and more of the duct. This will lead to a reduction of vacuum and airflow (CFM). Additionally, these large accumulations can cause the eventual collapse of the duct under their increased weight, which can damage the surrounding area and potentially injur employees in the area.
Most seriously, product dropout and the reduction in dust collection system efficiency directly contribute to creating dangerous combustible dust hazards. Any accumulation of dust within the ductwork (even tiny ones) can provide a starting place for a primary combustible dust fire/explosion. Worse yet, once a small fire or explosion has occurred, dust accumulations present throughout the ductwork system can provide fuel for a self-propagating secondary dust fire/explosion. These secondary conflagrations are far more destructive and can cause catastrophic damage to entire plants and frequently result in fatalities.
By monitoring particle velocity, operators can stay alert to any drop in air velocity that requires immediate attention. Taking quick corrective actions prevents small collector issues from causing reductions in system capacity and efficiency as well as eventual health and safety issues cited above.
Avoid Damaging Conveyed Product
In many process applications, triboelectric systems from Auburn System can be used to monitor flow rates. These include ensuring flow in a system (Flow/No Flow) and monitoring and measuring flow volume (More Flow/Less Flow) and even particle velocity (vs. simply observing air velocity.)
Plants can also use triboelectric particle velocity monitoring systems to control product velocity to prevent damage to fragile conveyed goods. For example, during the manufacturing process of baked products, the food items are fragile and need to be protected from damage in the conveying system as they are moved to packaging. Using TRIBO system from Auburn Systems operators monitor the velocity of the product being conveyed vertically before moving to final product stages. The purpose is to convey the product at a minimum velocity to prevent damage without causing backups and other conveying difficulties. The non intrusive sensor is placed flush on the duct wall.
Above we have discussed briefly only two specific applications that benefit from particle velocity monitoring - one in the dust collection system and one in the product manufacturing/processing/packaging area. Chances are that your facility can also see benefits from monitoring this often overlooked data metric and process control.