Many industrial workplaces require dust collection systems that clear away any filter airborne dust, along with other debris, during production. Dust collectors work on the basic premise of catching, transporting, and gathering dust and other particulates. A good dust collector design is one that does all these things well, and safely. As a key part of this system, dust collection ductwork works by helping transport airborne particulates away from people and machinery, before gathering them where they will not damage expensive equipment, harm workers, or otherwise disrupt operations.
Without proper ductwork, things can go horribly wrong. In 2012, a newly installed but poorly designed dust collector system at a US Ink plant in New Jersey caused an explosion just four days after installation. The US Chemical Safety Board found that the explosion occurred due to the accumulation of combustible dust and hydrocarbons in the ductwork, which then overheated, causing a spontaneous explosion in a rooftop dust collector. Seven plant employees experienced burn injuries from a blowback explosion, which enveloped them after they gathered at the entrance to the ink mixing room to investigate a loud thump coming from the system, along with signs of a flash fire at the bag dumping station.
Besides explosions, dust and other particles can also lead to other health conditions, exacerbating asthma, bronchial infections, and other breathing conditions while also heightening the risk of developing certain types of cancers. A dust collector designed properly will ensure worker safety while keeping production moving, while customizing dust collection ductwork can help meet certain industry or material specifications.
Steps to Dust Collection Ductwork
There are six basic steps for designing dust collector systems. Careful measurements and calculations should be made to ensure the dust collector design’s meet the needs of the operation.
Dust collector design steps should go as follows:
- Determine the system’s ability to handle the transport velocity, taking into consideration the type of dust being used.
- Establish diameters for each branch line of ducts.
- Verify the volume each branch can handle.
- Identify which machines are primary or used most, and which operate regularly together, in order to size the system to prepare it for situations where they will receive the heaviest use.
- Size the main trunk line, beginning with the primary machine furthest from where the dust will be disposed.
- Calculate static pressure or resistance in the system that requires overcoming.
Planning Dust Collector Ductwork
As a key part of the dust collection system, ductwork needs to be appropriately sized and capable of extracting dust from the air before conveying it to a place where it can be gathered for disposal. Dust collector design must keep the air velocity at a constant minimum speed throughout the ductwork in order to keep particulates suspended and moving. Dust collector ductwork fails when this is not achieved, sometimes leading to material settling at the bottom of ducts and clogging them, a.k.a. saltation.
The size and complexity of ductwork needed for dust collection systems depend upon the type of dust generated, along with the volume, density, shape, and velocity of the particles moving through the system. Dust collector designs normally seek to limit the complexity of the ductwork, minimizing curves and other transitional elements while using straight lines as much as possible. This ensures a more efficient dust collection system.
Some basics to keep in mind for dust collector ductwork projects:
- Keep ductwork straight to reduce resistance and issues of wear.
- Larger diameter pipes allow more movement through them and reduce static pressure.
- Long horizontal runs for ducts can increase the threat of dust buildup and heighten static pressure.
- Lower static environments require exhaust blowers with lower horsepower that also consume less energy and tend to be less expensive.
- Since suspended dust can explode, duct runs should be grounded.
- When curves or bends are required in dust collector ductwork, making them gentler and more gradual will reduce static pressure and improve airflow.
Dust density can also affect carrying velocities and may require professional engineering assistance to avoid poorly conceived dust collection ductwork. Particle density depends on its structure, properties, temperature, level of moisture, size, combustibility and other considerations. Knowing how much dust to remove from the air also factors into ductwork design.
Mechanisms for Dust Removal
A variety of mechanisms are used within dust collector systems. Choosing the ideal dust removal mechanism depends upon the type of dust collected, the type of dust collector used and the rate at which dust enters the system.
Dust removal mechanisms include:
- Drums or bags that allow workers to remove, empty and replace them once full, which normally are used for easily handled, non-toxic dust.
- Enclosed boxes that employ pipes to funnel dust into them, which are typically used with light dust loads and non-hazardous dust.
- Rotary valves – also known as airlocks, airlock feeders or rotary feeders, which typically are used in larger systems; these operate between the collector and the drums or bins to minimize loss of product. Rotary valves are typical in systems that handle combustible dust.
- Screw conveyors handle heavy dust loads and are used with larger dust collector systems to carry dust to designated disposal areas, often used with hazardous materials from industries working with materials that include agricultural products, minerals, metals, wood and chemicals.
Explosive Dust & Moving Air
As per the US Ink accident, an important thing to consider is whether material traveling through a dust collector’s ductwork can easily catch fire or explode. Appropriately mitigating potential detonation or combustion means using devices such as explosion panels or vents, spark detectors and flameless venting into the dust collector design.
When it comes to combustible dust, ensuring the correct carrying velocity with dust collector ductwork is imperative. Air moving too slowly through ducts allows dust to settle inside them, which can lead to clogging and reduction of duct diameter size. It also increases the risk of fire or explosion. However, if air moves too quickly through the ductwork, the particles can damage the interior walls of the ducts.
Working with CPE Filters
Systems for collecting dust depend upon well-thought-out designs put together by experts in the industry. The variables involved in good dust collector design require ductwork experience that CPE Filters can provide.
Industries served by CPE Filters include but are not limited to:
- Consumer goods
- Food processing
- Mineral processing
- Solid waste
- Water treatment
- Wood processing
CPE Filters offer a variety of services, equipment and systems related to the collection and containment of industrial dust, including manifolds, exhaust ductwork, pick-ups, stacks and hoods. We also offer scheduled and preventative maintenance, along with installing baghouse replacement parts. Contact CPE Filters today to learn more about how we can help with your dust collection needs.