A Kansas City area custom countertop manufacturer had a dust collector that was inadequate. They were getting fine dust particulate throughout their shop. They needed a machine that could keep up with multiple CNC routers and filter the fine dust.
The application involves processing a material called Solid Surface. This is a manmade material manufactured from a variety of resins. It is often used to manufacture customer countertop and other kitchen/bath products.
- CFM – 4600
- Static Pressure – 13”
Equipment Creating the Dust / Dust Source
- 2 CNC Routers
- 2 Chop saws
This customer had fine dust particulate bypassing their current dust collector. They were using an open bag style dust collector that was not designed to capture fine dust. The dust generated was potentially combustible, which had to be considered when designing this system. There were a few specific issues that had to be contemplated during system design. First, they had no way of putting the dust collector outside because they were land locked with other companies on every side. Second, they are leasing the building, so they could not put holes through the roof. Lastly, they needed to have a larger hopper to avoid emptying dust too often, and needed to keep the system under 19’.
The customer’s goals were to filter the dust and have a system that would effectively capture even the finest material. In their process they also had a small amount of wood that was used while cutting the Solid Surface.
Patrick Mulligan of Imperial Systems worked with the project manager on this plan to purchase a new system. They first started working with Imperial Systems when they found us on the internet. Patrick reviewed their application and concerns to start the development of this system and then scheduled a site visit to review. With the concern of the potential combustible dust Patrick created a system that included:
- EIV Explosion Isolation valve to protect return air in the event of a deflagration
- Flameless Explosion vent to protect the interior of the building from flame if there was an explosion. They did not go with a Chemical explosion suppression agent or a ducted vent to the exterior of the building because the cost was prohibitive.
- IDA Inline Deflagration Arrestor. The customer wanted to return the air to the building to save on utilities and in addition their lease caused issues venting outside. The Imperial IDA system stops a flame front in the event of a deflagration without the need for expensive secondary filters or other outlet isolation devices.
- DeltaMAXX Filters. Merv 15 rated Nanofiber Fire Retardant IDA filters. These filters are designed to capture the fine particulate
The beginning of the quoting process started in September of 2017 and the customer decided on Imperial Systems being the best partner for this project at the end of February 2018. After the order was received we designed, manufactured, and installed this turn key system by the middle of April.
There are many opportunities when working with cement for dust to start accumulating. Anywhere that the material is moved around, dust is produced. With companies facing new and stricter OSHA silica exposure laws, there is a tremendous need for filters in cement applications. Respirators may not be able to handle the high levels of dust produced, and even if they can, they are uncomfortable and often not used correctly.
OSHA’s hierarchy of hazard management considers the first line of defense as eliminating the hazard. Since it’s probably impossible for you to eliminate all the processes in your facility that produce dust, it makes sense to move to the next step, which is to use engineering controls to manage the hazard. A dust collector is an engineering control because it manages the hazard without the employees needing to actively do anything (like wear PPE) to be protected.
BAGHOUSE VS. CARTRIDGE COLLECTOR
While baghouses have dominated the cement industry in the past, they have many disadvantages. One major one is that very high airflow needs to be maintained to move dust-laden air from the various points of capture to the baghouse, requiring high energy usage and large fans. Also, baghouses often have a huge number of bags, which are very difficult and messy to change. A confined space procedure may be required to get into the air plenum where the filters are accessed. The bags often have to be pulled onto metal cages and there are a variety of complicated mechanisms for attaching them to the tube sheet.
Cartridge collectors are appropriate for almost all types of fine dust, as long as it is dry, and they are more efficient and much easier to change than bags in a baghouse. Cartridges are pleated, which allows them to have a much higher surface area than a bag and pack a lot more media into a smaller space. The ease of changing filters and overall maintenance is often a major factor in choosing a cartridge collector over a baghouse. Baghouses may still be preferred for certain applications; a systems engineer can help determine which will work best. High temperature applications, for example, often require a baghouse because the bag material can handle extreme temperatures better. Systems engineers are experts in system design and should always be consulted on a dust collection project.
Many applications, particularly those handling large amounts of bulk solids, have had excellent results with cartridge collectors. Grain and silica industries are two examples of applications where cartridge collectors are often in use. Especially where silica dust is involved, cartridge collectors are becoming increasingly popular because of the extremely high efficiency of the filter media, which helps companies make sure they are meeting OSHA’s new silica dust regulations.
Some companies have questioned whether cartridge filters are durable enough to handle tough applications like silica or cement dust. The answer is that yes, with a properly designed system they can definitely handle this material. Options such as overbags can help protect the filters if the dust stream contains some larger particles in addition to smaller ones. A cartridge collector will also have baffles that cause the air to slow down and larger material to drop out of the air stream before it reaches the filters, protecting them from damage.
CMAXX Spot Filter System
Another issue with a central system, whether it uses bags or cartridges, is that there may be very long runs of ductwork to access all of the points of dust capture. It may not be practical to run duct all the way down a very long conveyor, for example, or to a machine that’s a long way from the collector. You may even need dust collection on a mobile piece of equipment like a cement dust transport truck that moves material around the site. For all of these situations, spot filters are a great option to consider.
A spot filter is a small cartridge collector that is placed directly at the location where dust is being produced. Examples of good locations for spot filters include:
- Drying areas
- Conveyor belts
- Transfer points
- Dump pits
- Roller mills
- Blenders and mixers
- Bucket elevators
- Hammer mills
- Transport trucks
- Vents and openings in storage areas
- Material loading and unloading
Spot filters usually have two or four cartridges. Because of the pleated material, cartridge filters are perfect for applications where the collector needs to be small and compact. They are also self-contained, which means they do not need any ductwork run to them. They have their own fan and run independently, so you can put one a long way from your central dust collection system, or use them if you don’t have a central dust collection system. Spot filters sit directly at the point where the dust is generated, allowing them to capture the maximum amount of dust and prevent any of it from getting out into the air of your facility or exposing your workers to silica-containing dust.
An advantage of spot filters is also that they are very easy to maintain. In a well-designed collector, cartridges slide out easily on rails and new ones slide back in. This only applies to vertical collectors where the cartridges hang from a tube sheet at the top of the collector; horizontal collectors where the filters are inserted horizontally on a supporting yoke are much more difficult to change. The filters do not need to be cleaned; they clean themselves with compressed air according to their scheduled settings and maintain efficiency by pulsing excess dust off the filter surfaces.
Spot filters are perfect for those areas in a facility where fugitive dust escapes into the environment. This dust can accumulate around the area and cause a health and safety hazard. Certain pieces of equipment may be inconvenient or nearly impossible to reach with ductwork or attach to a central collection system. For these, spot filters can capture that fugitive dust before it gets loose to build up around the area.
A patented version of a spot cartridge collector is specifically designed to be mounted on trucks transporting and unloading bulk dust. Specifically designed for sand on hydraulic fracturing sites, these collectors are able to be mounted directly on a truck that’s used to load and unload cement dust. This is is a complete plug-and-play system. It can be mounted on sand transport trucks, at the points where material is being moved onto and off of transport belts, and over mixers and other equipment. The fans and airlocks are operated with hydraulics powered by the vehicle, and the compressed air is powered by a generator.
OSHA SILICA REGULATIONS
Because of the silica content of cement dust, new OSHA silica laws taking effect in 2018 will impact health and safety in the cement industry. These new laws strongly endorse engineering controls such as dust collection systems to prevent exposure to silica dust in the air.
In many places, we’ve seen a central baghouse removing dust from several main points of dust production. However, a lot of these places also have a number of other sites where fugitive dust is escaping and contaminating the area, accumulating around the facility. This dust can be easily stirred up and inhaled.
Health risks of inhaling silica dust include silicosis, a chronic lung disease where inhaled silica dust, such as the kind that is a component of cement, damages and scars the small air sacs of the lungs. This results in difficulty breathing and getting enough oxygen to the rest of the body.
Exposure can also cause an acute form of silicosis where the damage causes the lungs to swell and fill with fluid. This type of silicosis is uncommon but very dangerous. Chronic silicosis is very common among people exposed to silica dust. The scarring can progress to a condition called progressive massive fibrosis, where the lungs become stiff and full of scar tissue. When the disease is severe, people may need oxygen support to be able to breathe. Silicosis can cause death.
The health risks of silica include other deadly conditions. Silica is a known carcinogen, meaning it causes lung cancer. It also makes you more likely to get lung diseases like emphysema, tuberculosis or bronchitis. Because the cement industry has been targeted as one in which the dust includes silica, OSHA is likely to be very vigilant about dust management in cement handling applications.
Spot filters may be exactly the solution you are looking for if you have equipment such as conveyor transfer points, mixers, elevators, or other places where dust has a tendency to escape. If you don’t have a current dust collection system, or if it’s not practical to attach these pieces of equipment to the current system, a spot filter can be a very efficient solution. It sits directly on the area where dust is produced, captures it before there is any opportunity for it to get out into the air in the facility, and contains it safely.
Article featured in June 2018 issue of World Cement Magazine. https://www.worldcement.com
Sometimes it’s necessary to cut or weld, or hot work, in the vicinity of your dust collector. However, this can be extremely dangerous if your dust is explosive. A dust collector, after all, is an accumulation of dust, and if that material is combustible, careless hot work could lead to a catastrophic explosion.
“Hot work” is defined by OSHA as “welding, brazing, cutting, soldering, thawing pipes, using heat guns, torch applied roofing and chipping operations, or the use of spark-producing power tools, such as drilling or grinding”. While most of us would think twice about welding or cutting in the vicinity of the dust collector or any other combustible dust, using a spark-producing tool, even one that shouldn’t produce sparks but has faulty wiring, can lead to a fire or explosion.
No hot work should be done near the dust collector without the correct procedures (see NFPA 51B). This is the NFPA standard that specifically defines the procedures for conducting hot work anywhere that it might cause an explosion.
Hot work near or on a dust collector might include repairs, adding or removing a piece of equipment or ductwork, or any number of other projects. Before any of this kind of work is done around the dust collector, you must have a hot work procedure IN WRITING:
- Must be in writing and available to anyone conducting hot work in the area
- Must specify that an inspection of the work area is required before the work starts
- Must have a permit signed to show that all phases of the work have been inspected and approved
The program should assess safety equipment in the area. On a dust collector that might include a spark arrestor, spark detector, fire suppression or sprinkler system, abort gate, explosion venting, or other types of fire and explosion safety devices.
Hot work may require completely blocking the ductwork to the dust collector, or if the hot work is on or close to the collector, may require removing the filters, emptying or removing the hoppers, and thoroughly cleaning the entire dirty air side of the dust collector. It is strongly recommended that a fire suppression system be in place before hot work begins to suppress any fires that might start, and that if the dust is explosively combustible, as much of it as possible has to be removed.
NFPA 51B specifies that once the area has been inspected and determined to be safe for hot work, the company safety specialist will issue a permit for work to proceed. It’s the job of this designated safety specialist to inspect the area of hazards, make sure that all combustible dust has been removed or isolated from all sparks and heat, and establish safety procedures in the event of a fire.
No one should be allowed to perform ANY type of hot work, including the use of spark-producing power tools, in the vicinity of the dust collector without a permit. However, it happens all the time, and puts lives at risk if the dust is combustible. Take the time to assess this hazard in your own workplace. If the hazard exists, your safety professional should set up hot work procedures to make sure no one puts themselves or the facility at risk.\
Like many companies in the USA, Imperial Systems wouldn’t exist without our skilled tradespeople. Making a quality product comes from training and experience, and right now we’re lucky enough to have a young man who has come here for both of those things.
Garrett is a student at our local Mercer High School and participates in the Mercer County Career Center Vo-Tech trade school program. Every morning he comes to work at Imperial Systems, welding CMAXX and BRF’s, learning from our experienced team and getting great real-world experience.
Garrett knew about Imperial Systems from a friend who works here in the summer, and he chose us for his Vo-Tech worksite. He told us about how much he’d learned already, and the difference between welding in school and working from blueprints, working on projects that are actually going out to customers and have to be done right. Fortunately, he is eager to learn and enthusiastic about his work.
He’s also enthusiastic about welding in general, as shown by his artwork he created for a trade school skilled trades art show. He got to take his work as far as state competition in Hershey, PA. In school, he plays football, wrestles, and participates in show choir.
While show choir might seem like an unexpected hobby for a welding student, Garrett is an intelligent and well-rounded person, and our conversation ranged from his project on World War II propaganda to the deficit of skilled tradespeople and the over-abundance of college graduates with useless degrees. He has clearly thought a lot about his future and has a good understanding of the need for welders in the workforce and how it has affected his career choices.
He can also tell you from first-hand experience how under-funded trade schools struggle to attract and support students. The demand for skilled tradespeople dwarfs the budget that trade schools have to bring in and train these people. As a result, a future shortage of welders and similar skilled tradespeople looms, and trade schools continue to be neglected as a source of solid, well-paying careers for many young people who don’t see college (or the accompanying debt) in their future.
The school year is almost over, and Garrett has plans for his future in the skilled trades: he has enlisted in the army and plans to work in one of their metalworking divisions. He’s not sure whether he’ll stay in the military as a career, but he knows we have several veterans working here now, so he’d be in good company if he decides to come back.
1. What information do we need to start designing a system?
- First, you need to know about your dust. Important details: how it’s being generated, how toxic or hazardous it is, what exposure levels OSHA considers too high, whether it is combustible and/or explosive, particulate size, physical characteristics.
- Combustible dust will require special precautions to be worked into the system design to protect the facility and workers from deflagration or explosion. Dust testing can determine how explosive dust is and what precautions are needed.
- A general layout of the facility and each location where dust is being generated.
- A sketch of the duct layout, including the location of the dust collector, fans, and duct branches.
- A plan for the type of hood that will be used at each of the dust capture locations and how much CFM each one will require.
2. What are the basic components of a dust collection system?
- Hoods: must be correctly designed for each type of machine, and must be efficient at removing the dust produced by that machine.
- Ducts: must be correctly sized to allow proper airflow, keep air moving, and not have too many bends or elbows to slow down airflow; this can allow particulate to drop out of the airflow or can create a point for wear and tear on the ductwork.
- Fan: the fan must be powerful enough to keep air moving through all the ductwork at a high enough velocity. Drops in velocity or not enough velocity can allow dust to fall out of the air stream.
- Collector: must be correctly sized for the system, with an air to cloth ratio that makes it able to filter all the air coming into the collector. Must have correct filter material to handle the size and type of particulate (DeltaMAXX nanofiber for most applications, or spunbond, PTFE, or other specialized filters for particular applications). Filters must be fire-retardant if the dust is flammable.
- Fire Prevention: devices such as spark arrestors can help keep sparks from entering the dust collector. A water or chemical fire suppression system can extinguish sparks or flame when a sensor detects them.
- Venting/Exhaust: If air is being returned to the building, it must be clean enough to meet all health and safety standards. If dust is toxic, an extra layer of safety in the form of HEPA filters might be needed. A backdraft damper can prevent backdrafts from allowing dust back into the system. An abort gate with spark detector can sense a spark or flame and can divert the flame in a safe direction.
3. What is the process for designing a system?
- System design should start with identifying each place that a hood or other source capture point needs to go (anywhere that dust is generated).
- Use appropriate calculations to figure out how much CFM you need at each of these points
- Determine the minimum duct velocity. This is based on the transport velocity (the air flow needed to keep your particular dust moving in the air stream).
- Calculate the size of duct for each branch. This is based on the CFM and the transport velocity and will be different for different spots along the ductwork.
- Increase duct velocity at each branch to maintain transport velocity until all branches are connected to the main duct.
4. Will this be an ambient system or source capture system?
- Ambient system: removes air from the entire work area, filters it, and recirculates it back into the area, diluting contaminated air with clean air.
- Air changes per hour: the number of times per hour that the total amount of air in the area is changed from old/contaminated to new/clean. This is calculated by the cubic volume of the work area and the number of air changes required to maintain air quality.
- Source capture/close capture: captures dust at each point where it is generated throughout the facility.
- This type of system must have properly designed hoods at every capture point and properly calculated airflow. Specialty hoods can be designed for almost any application.
- Static pressure in these systems is an algebraic formula that includes loss at hoods, flex ducts, transitions, and straight runs. Minimal use of elbows and flex ducts will greatly improve system efficiency.
- For dangerous or toxic dust where exposure must be kept to an absolute minimum, a close capture system will keep the material from entering the air of the general workplace.
We hope this set of articles about ductwork help to answer some of your questions. Please thank the knowledgeable and experienced Charlie Miller for providing so much valuable information and sharing his wisdom.
1. What do the different types of air pressure measurements mean in ductwork?
- Basic behavior of air: it always flows through the past of least resistance, from higher pressures to lower pressures.
- STATIC PRESSURE: potential pressure exerted in all directions in the ductwork with no air flow, measures with a manometer. Can be positive (pressure outward on the duct) or negative (pressure pulling inward on the duct)
- VELOCITY PRESSURE: pressure necessary to move air through the ductwork at a certain velocity. This is kinetic energy, and the pressure is in the direction of the airflow.
- TOTAL PRESSURE: a calculation of system static pressure and velocity pressure (the formula is TP=SP+VP). It can be positive or negative. It is the overall energy content of the air stream.
2. When we calculate our fan size, what’s the difference between SCFM and ACFM?
- SCFM is Standard Cubic Feet per Minute. This is a measurement based on a standard temperature and air pressure.
- Temperature and air pressure can be significantly different in different areas (e.g. higher altitude, cold or hot climate, high humidity) or different applications (high/low temperature or humidity applications)
- ACFM is Actual Cubic Feet per Minute. This is a measurement of the actual air conditions that your system will be operating under.
- Fan manufacturers are able to make these calculations, but they need to be provided with accurate data about temperature and humidity conditions in your application.
3. What is conveying velocity and why is it important?
- Conveying velocity is measured in feet per minute (FPM). It is the velocity required to pick up dust in the air stream and move it through the ductwork.
- It is calculated by the CFM at the point of capture and the square foot cross-section of the ductwork.
- This is extremely important because if the conveying velocity drops too low at any point in the dust transport, the dust will drop out of the airflow.
- There are a variety of tables to help engineers calculate the minimum conveying velocity for different kinds of dust.
- Combustible materials might need a higher minimum conveying velocity because accumulation of this material in the ductwork could cause a deflagration or dust explosion.