The 5 Cs of Dust Collection

A well-engineered dust collection system considers what we refer to as the 5 “C’s” of dust collection. Each is equally important and must be given adequate consideration.

Capture (type of hoods and capture devices)
Convey (size and type of duct)
Collect (dust collection or air filtration technology)
Clean (maintenance of the system)
Combustibility (explosiveness and/or flammability of the material)

For each type of process and contaminant, there are various technologies that can be used to successfully collect the contaminants.

• Electrostatic precipitators are ideally suited for collection of submicron contaminants
• Media filtration units are ideally suited for the collection of dusts and mists in low concentrations
• Dust collection equipment is ideally suited for a wide variety of contaminants.
• Cartridge units
  • Cyclone collectors
  • Oil mist collectors

Capture

The goal of a source capture system is to contain the dust/smoke prior to entering the ambient air.
The first step in designing a source capture system is to determine the most effective type of hood design and then decide where to place the hood relative to the location of the contaminant source. Important things to keep in mind are:

1.  Thermal air currents
2. How the machinery moves- for example grinding wheels, belt conveyors, arc cutting equipment
3. How the material is contained/handled- for example dumped, filling a container, etc
4. Movement of the operator.
5. Natural room air currents and ones that are changed due to heating/air conditioning

However, in all instances, the same basic principle applies in that a hood placed closer to the source will result in a lower air volume requirement.

Convey

Often, the duct system on a dust collector/air filtration system is overlooked. The duct system is like arteries that carry the dust from the source to the collector. If not sized properly, dust/mist/smoke will settle resulting in duct blockage, fire hazards, and in combustible applications, explosion hazards. The duct design (branch entries and elbows) needs to be carefully considered and engineered to minimize resistance to the air stream. How this system is designed will have a direct effect on the horsepower of the fan.
There are many different types of ducts including the following:

• Nordfab clamp together duct is simple and easy to install is one of the more common ducts utilized. It provides flexibility should changes need to be made at a later date.
• Spiral pipe is an economical duct for light dust collection projects. It should not be used for oily applications as it will leak.
• Welded duct with flanged ends is commonly used on heavier and abrasive dust applications. While the most expensive it is also the most durable duct system.

Collect

There are many dust collection and air filtration technologies available today including baghouses, reverse pulse cartridge-style, cyclones, ESP’s, media systems, centrifugal mist collectors, and wet collectors to name a few. When selecting a technology we consider the type of contaminants (and all the characteristics such as particle size), the loading (how much of the contaminant is generated), and the desired/necessary filtration requirements. With each collector there are various options such as silencers, cleaning controls, dust disposal, and many more that must be considered.
Experience plays a large role in determining which technology is best suited for a given application. This experience is available to you through our manufacturers and our personnel at Dynacom, Inc.
Parameters that go into determining which technology is best:

• Loading: how much is generated in a given time (cubic feet in a day)?
• Hours of operation: how many shifts are they operating?
• Characteristics of the dust: What is the dust? Is it abrasive? Is it sticky? Is it granular or fibrous? Etc.
• The process: What is their process/operation (i.e. dry grinding, welding, plasma cutting, wet grinding, machining, etc. etc. etc.)
• Temperature of the airstream: Most often, the temperature will be close to ambient temperatures and is not an issue.

Clean

How the collector is maintained is critical to any system. There is no such thing as a maintenance-free air filtration or dust collection system. However, there are ways to automate the cleaning which are considered based upon the requirements of the end user.

The maintenance of any system is a key factor. If the system is not maintained it will not function properly.
Electrostatic precipitators require manual water wash cleaning. Media systems require filter change-outs and potentially expensive replacement filters. Cartridge-type dust collectors reverse pulse the filters to keep them clean continuously and online during operation.

Combustibility

It is critical that the generator of any dust determines whether or not it is combustible and/or the flammability of such materials. In many instances, this may require that the producer of the dust or contaminants will have to have the material tested to determine the Kst value (how combustible the dust is). Per the OSHA standards as set by the NFPA, anything over a Kst value of zero (0) should have proper explosion venting and all other applicable controls.
It is the sole responsibility of the client to determine whether or not these controls are necessary.
When discussing “dust collection systems” ALWAYS determine if the dust is combustible.
If the dust is combustible this can have a significant impact on the design and cost of the system. Controls and limitations for dust collection systems collecting explosive (different than flammable) dusts can include, but are NOT limited to the following:

• Explosion venting on the dust collector
• Explosion suppression systems
• Isolation gates (on the inlet and possibly on the outlet duct)
• Fire suppression systems
• Location of the collector (may need to be located outside and may need to follow certain parameters relative to personnel traffic such as parking lots, exit doors, etc.)
• Duct design and velocities (i.e. duct systems collecting explosive dusts technically should NOT have slide gates at branches and typically have minimum duct velocities they must maintain.
• The ability to return the exhaust air back within the building.

Summary

As you can see, there are a lot of steps involved in designing a dust collection system. The key is to ask the right questions in order to understand the problem and recommend the best solution. Only once there is a full understanding of the problem and the resources available to help address the issue can a true solution be recommended.