Dust Collection Equipment Webcast: Your questions answered

A recent Plant Engineering Webcast featured Kirt Boston and Chrissy Klocker of Donaldson Company discussing strategies and best practices around dust collection equipment. The Webcast produced more viewer questions that time allowed to be answered. Boston and Klocker agreed to respond to additional viewer questions.

The archived Webcast can be viewed here.

Q: What industries use dust collection systems?

A: Dust collectors are typically required where dust generated in a process creates issue for the process or where the dust impacts employee safety. Dust collection may also be applied to retain dusts that have market value, or to avoid discharging hazardous dusts to the environment or workplace. Examples of hazardous dust properties might include toxic, corrosive, abrasive, or combustible dusts.

Q: What are the particle removal efficiencies of your various filters?

A: Effective particle removal efficiency and the resulting filter emissions for a filter will vary by media type, dust load, particle size, and collector design. As discussed in the webinar, media styles offer different emission performance and to understand emission capabilities for a filter you should discuss your application with the filter and collector supplier.

Q: Do we need to give slide gate or orifice in duct network for better balancing? What are the best options?

A: Balancing total airflow and airflow distribution in duct systems is critical to ensure dust is controlled at each pick-up point in the system. Controlling total airflow also can extend the operational life of filters and reduce the downtime for your collector. Blast gates and orifice plates have traditionally been used to control air distribution in duct systems and to control total airflow. Current duct system design uses duct selection to balance air distribution (balance by design) with a reduced total energy cost for running the system. The Industrial Ventilation, a Manual of Recommended Practice for Design published by the ACGIH is often referenced as a good resource on duct system design practice. The use of a variable frequency control on the fan rather than an outlet damper can also offer energy savings for the system.

Q: Is there an estimated life or hours of use on a standard filter cartridge before it needs to be changed?

A: Reasonable expectations for filter life are again influenced by many variables. For many applications, the filter life expectation may be several thousand hours. For other applications it may be longer or shorter depending on variables such as oil content of the dust, abrasive character of the dust, type of collector, operational pattern for the collector, and the relative size of the collector for the airflow being filtered. Contact your collector supplier if you questions on filter life expectation and performance.

Q: I am looking at using one of your units as a bin vent, but instead of picking up the dust, I want to mainly just pick up the air to keep a negative on my conveyor system. Do you have any suggestions for this?

A: Collectors without hoppers or legs are sometimes mounted directly on a process or bin, and are often referred to as "Bin Vents". Such collectors can be very effective in managing dust directly at that point in the process where the dust is generated. In the situation described a bin-vent collector mounted on the enclosure of the belt conveying system could contain dust generated at the tranfer point and return the dust back to the belt. This approach keeps the dust in the commodity stream, eliminates ducts, and reduces the fan power required. As with any project the process owner should assess the properties and risks associated with the dust before making a decision on dust collector strategy.

Q: Could I expect to cut operation expenses noticeably by adding a second dust collector and cutting a long run length by, say, half?

A: Reconfiguring a duct system by splitting the system between two collectors may offer operational cost savings if the reconfiguration offers one or more of the following features:

• Will the system change allow idle portions of the system to be routed to one collector while active portions are routed to the other collector? This would reduce the total air volume and fan power required.
• Will changing the system eliminate long duct runs? 100-ft of duct in a wood shop adds around an of fan static to a system.
• Does the proposed change allow for two smaller collectors, which will reduce total maintenance efforts?
• Will the new layout allow different collector selections?

The impact of duct layout changes can be complex so talking with your dust collector supplier before considering any changes may prove helpful.

Q: Using a VFD, what needs to be monitored to adjust the speed of the fan? Would it better to monitor static pressure or velocity pressure or something else for doing this via a PLC?

A: Variable frequency drive (VFD) control is becoming a more common strategy for maintaining design flow in dust collector applications. A common strategy is to identify inlet static to the collector, hood static pressure at a critical hood, or velocity pressure in a clean air duct as a control variable. The control logic is then established to ensure the variable is maintained at the desired value to ensure consistent design flow is going through the collector. Each strategy mentioned above has both advantages and disadvantages, so you should talk to the supplier of your dust collector and fan before settling on a strategy.

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