Triboelectric Detectors - Beyond the Baghouse 2

Posted by Justin Dechene on Sep 3, 2015 9:00:00 AM

Triboelectric dust detection systems are widely used for monitoring particulate emissions from dust collectors. However, part 1 of this article showed how their use is not limited to dust collector monitoring. Ambient (or fugitive) dust monitoring as well as flow/no flow indicators are other applications for triboelectric detection technology. In part 2 of our article, we will discuss another area where triboelectric technology can be used to the benefit of a facility.

First, lets talk about a common dust collection system problem that many industrial facilities face: Product dropout and buildup.

triboelectric_detectors_for_dust_velocity_monitoring

What is Product Dropout and Why is it so Serious?

In order to move powders in an airstream (dilute phase conveying) the airspeed must stay above a certain speed to keep the dust fully entrained. When the air in the ductwork drops below its minimum conveying velocity the dust will begin to drop out of the air and settle in the ductwork. (For reference list of minimum conveying velocities see Industrial Ventilation: A Manual of Recommended Practice for Design (28th ed.). (2013). Amer Conf of Governmental)

Over time, large amounts of dust can build up, which then negatively affect the entire dust collection system. Eventually, ductwork can collapse under the immense weight of dust accumulations. Large accumulations of dust also reduce the total cross-sectional area in the duct( i.e. block off part of duct), forcing the air to speed up significantly. The now accelerated dust-laden air will quickly erode parts of the ductwork (similar to sandblasting), especially near corners and bends.

Most seriously, large accumulations in the ductwork pose a serious hazard in applications that handle combustible dusts. Piles of dust provide ideal fuel sources for sparks and embers, which can start fires or cause explosions within the ductwork. If an explosion or fire does occur within the ductwork dust accumulations throughout the system can provide ample fuel for propagating the conflagration further downstream, eventually reaching the dust collectors (which can then violently explode) or exhausting out of the system (where it can ignite further fires or directly harm workers or damage property).

Particle Velocity Monitoring

In view of the foregoing, plant operators should carefully monitor particle velocity as part of a comprehensive effort to prevent product dropout in the ductwork system. To assist them, Auburn Systems has worked hard to develop equipment configurations for monitoring particle velocity.

By combining two triboelectric detector probes spaced a few inches apart, the unified triboelectric system can measure particle flow speeds. These systems have proved durable and reliable in this application as they provide very accurate particle velocity readings (as opposed to just relative airspeed) and are not as susceptible to dust buildup compared to the main alternative (pitot tube systems).

With advanced warning of dropping particle velocities in the system plant operators can be alert to problems before they cause large accumulations to form. (See Footnote)

Conclusion

The evidence we have considered in these two articles clearly shows that value of triboelectric dust monitoring technology extends beyond emissions monitoring. Would you like to know more about how Auburn Systems’ solutions can assist your facility? If so, please read more about our products here or contact us for a free consultation.

Footnote: Why Airspeed May Drop In a Baghouse System

Low airspeed in the ductwork indicates a problem with the dust collection system, usually an overloaded system. Many times outside vendors will undersize a system in order to make their bids more attractive. Other times, plant decision-makers decide to add additional drop points to a system without increasing overall capacity (even small additions such as vacuum hose attachments can use up a large portion of a system’s capacity). Additionally, when the baghouse filters become overloaded and blind off, the resulting increase in pressure drop across the baghouse will result in lower vacuum pressure throughout the system eventually causing lowered velocities towards the furtherest drop points.

 

image - Kice Industries