Additionally, combustible dust pose a serious hazard to many industries. Numerous materials including otherwise harmless products like flour, iron powder, and wood are explosive and combustible in their dust form. These hazards pose a real danger to workers. Industrial fatalities are sadly common in combustible dust incidents and combustible dust incidents are destructive to plant structures, equipment, and other property. They often cause severe disruption to production and extensive and costly damage when one occurs.
Every health and safety issue is important – but this one has become much more so with the focus of OSHA guidelines, and NFPA 654 regulations on combustible dust. It’s time to understand the challenges and the range of instrumentation solutions that will help facilities stay safe and comply with rigorous regulatory requirements.
How Can Triboelectric Detectors Help Improve Industrial Health and Safety?
Controlling dust is key to eliminating or at least minimizing the aforementioned hazards in an industrial application. The key to controlling dust within a facility is an adequately designed, installed, operated and maintained dust collector system.
Triboelectric detectors help monitor, and often improve dust collector performance in multiple areas. Triboelectric detectors measure very small concentrations of dust particles in the airstream of an industrial process. For regulatory compliance these are often fitted on the end of the ductwork exiting the last pollution control devices (usually a baghouse) in order to measure the effectiveness of the collector. Triboelectric devices work by inserting an electrically isolated metal probe into the ductwork. When dust passes by or impacts the probe directly it creates a small AC or DC electrical signal (measured in pico amps). After processing by the controller this signal is displayed as a visual reading that corresponds linearly to dust concentrations in the airstream. A good triboelectric system is so sensitive that is can detect dust concentrations far smaller than any other monitoring system commonly in use today, down to 0.000002 gr/dscf. This level of sensitivity allows triboelectric detectors to be used in various ways beyond main stack compliance monitoring that other dust monitoring systems cannot.
Let’s consider some specific ways these systems can improve health and safety at your plant.
Improving Indoor Air Quality
Indoor air quality is one of the most serious contributors to employee disability and harm each year. Whether handling hazardous compounds or just working with benign materials in a very dusty application, dust concentrations inside a facility can easily rise to unhealthy levels. The key to controlling these hazards is an adequately designed, operated and maintained dust collection system. Accurate monitoring provides operational and maintenance information that’s important to proper operation.
Triboelectric monitoring provides plant operators and maintenance technicians the required insights into system operation to inform operational choices or maintenance allocations. For example, triboelectric detectors are sensitive enough to detect the incipient failure of a single filter inside a dust collector. By having such advance notice plant technicians can take quick corrective action to replace the leaking filter before it causes damage to others, and before it leads to a drastic rise in emissions from the stack. This also prevents the buildup of large amounts of dust within the unit that then requires extensive remediation often putting employees in direct contact with the collected dust. (See case study highlighting the difference in remediation work required between leak detected within minutes with triboelectric detectors and one identified days later by means of opacity monitoring.
Additionally, with accurate real time emissions data, operators can make informed operational decisions. This prevents problems with the system that could cause a lack of suction for example, which in turn might lead to backups elsewhere in the system that create accumulations of dust near pickup points, such as at machines or venting booths. It might also preclude inadequate venting of combustion areas, like furnaces, which could result in a dangerous and costly dust excursion.
Improve Combustible Dust Hazard Awareness
While there’s general awareness around the risks of combustible dust, there’s often a lack of knowledge about the amount of dust required to pose a hazard. Add the fact that dust collector malfunction or under-performance issues are often not easily observed and it’s easy to see how the circumstances arise that can lead to these devastating incidents. In most combustible dust incidents, large accumulations of dust in elevated spaces or within confined spaces (such as dust collection ductwork and dust collectors) provide the fuel for the conflagrations. Therefore, preventing the accumulation of dust throughout the facility is key.
Triboelectric detectors ARE NOT fire/explosion protection or prevention devices as defined by the NFPA and other regulatory agencies. However, they can be used effectively by plants to provide early warning of dust buildup and improve dust collection system performance. Simply keeping the dust collector in good working condition will prevent many common problems, but triboelectric offers other applications.
One particularly interesting use of triboelectric technology is to monitor conveying velocities within the ductwork. By installing two probes a short distance apart, operators can get a very accurate and reliable particle velocity reading within the ductwork.
Maintaining an adequate conveying velocity is crucial to prevent the buildup of dust within the ductwork. Every material has a certain airspeed that must be maintained in order to keep the materials suspended in the air. This is called the minimum conveying velocity for the product. If the speed begins to drop below this velocity the material will begin dropping out of the airstream and settling on the bottom of the ductwork. This product dropout effect then quickly leads to larger and larger accumulations of dust within the ductwork as conveying efficiency is compromised. It’s a vicious cycle that can quickly become critical.
These accumulations then provide ideal starting points for incoming sparks and embers to ignite fires and explosions within the ductwork. In addition, if any fire or explosion does enter the ductwork these accumulations provide ample fuel to continue the conflagration and allow it to propagate throughout the system, feeding itself on each new accumulation. Many of the most devastating combustible dust explosions have started this way and then spread throughout entire facilities leading to far greater destruction. By preventing the buildup of dust within the system, plants can minimize the risk that no such ideal conditions exist for a conflagration to start or propagate.
Another innovative use of triboelectric technology to help prevent combustible dust incidents involves the monitoring of ambient dust levels throughout a plant. As mentioned above, many combustible dust hazards come in the form of dust accumulations in elevated spaces throughout the plant such as tops of machinery, roof trusses, elevated walkways, etc. These usually form over time when elevated levels of dust are present inside a facility. Even if the dust levels are acceptable for respiratory reasons or workers are required to wear respirators, these elevated ambient dust levels will create these hazards if left unchecked. Even just a 1/4” of dust on an elevated space can pose an explosion hazard according to OSHA and result in fines and sanctions.
By installing ambient dust (or fugitive dust) monitors in various locations plants can be alert to any rise in fugitive dust levels. This serves as an early warning system in addition to careful monitoring of the dust collection system. If any of the alarms trigger, operators and maintenance technicians can investigate the cause of take corrective action to bring the levels back down.
Staying safe and staying ahead of regulations
Triboelectric detectors first and foremost serve as effective emissions monitoring devices. However, their capabilities to detect dust in such small concentrations means that they can provide additional assistance with regards to health and safety inside industrial facilities.
We don’t know exactly what any new regulations may require, but we do know how instrumentation can help you track dust levels within system components and in your general environment.
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