All dry dust collectors have a hopper which temporarily collects the dust while it is moved out of the system. The hopper usually has a flanged outlet on bottom which allows the dust to fall outside of the dust collector vessel. When you are deciding what to put under the hopper it is important to make sure that air doesn’t flow out of or into the opening while still allowing the dust to empty from the hopper. An airlock (discharge valve) is used to prevent this.

An airlock comes in a variety of designs. The most common is the rotary airlock while the simplest design is a trickle valve (Aerodyne Vacu-Valve). What these valves do is prevent the higher pressure air from going to the lower pressure air. Generally dust collectors are designed to be under vacuum. This prevents dust from escaping the vessel and helps protect the exhaust fan from being damaged by dust loading. However, some systems do have pressured dust collectors for operational reasons. Either way it is important that there be some kind of airlock under the hopper.

Dust Collector Under Pressure

A pressurized dust collector will blow air out of the hopper if no airlock is installed on the hopper. This will create a dust cloud around the dust collector. If indoors this will coat the surrounding equipment and become a nuisance to employees in the area. Plus it’s pretty unseemly having a dust collector spewing dust out in a facility.

Dust Collectors Under Vacuum

A system under vacuum, however, is much more impacted by not having an airlock. The airlock prevents outside air from entering the system. So if you don’t have an airlock the exhaust fan will begin pulling air into the system through the hopper. This does two main things. For one, it lowers the airflow at the pickup points that are collecting the dust. Air will flow the easiest path (much like water). So if you have an opening allowing air to enter through the hopper then air will take advantage of this. And since your exhaust fan doesn’t care where the air comes from it will pull much of the air through the hopper. This airflow means that there will be less air coming from the pickup points. This could cause insufficient dust pickup at those points and even dust buildup in the ductwork. The second issue is that any dust collected in the hopper could get re-entrained by the air entering through the hopper outlet and then leave the dust collector. This will decrease the system removal efficiency and could cause violations of permits, increased fan maintenance, etc.

So when you are operating a dust collection system, make sure that the dust discharge flange is installed with an airlock, that way you will have the system operating at its peak efficiency.

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How Do Vacu-Valve Dust Valves Work?

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When you have a dust collector capturing valuable material, you often have to regularly clean the dust collector to remove the material and if it is perishable, remove it before it contaminates the other material. Some dust collectors are easier to clean than others.

Wet Scrubbers

Wet Scrubbers are pretty much self-cleaning. Since they use water to capture the dust, it pretty much washes the walls and internals regularly. The main issue with wet scrubbers are that if you are trying to use the material (whether in the process or as a product) then you will need to remove it from the water stream (unless having it in a water stream is desirable).

Cyclones

Cyclones are very low maintenance. Since they use centrifugal motion to remove the material, there isn’t much buildup inside the cyclone. So there really aren’t many places to build up. Designing the vessel with access doors will help keep the cleaning easy. Aerodyne’s horizontal cyclone has a unique design that allows you access to the whole cyclone through its back plate.

Fabric Filters

Fabric filters collect the material on the filters (bags/ cartridges). This builds up a layer of material which remains on it for the life of the filter. During cleaning, the material falling off might have recently been captured or material that has been on the filter for an extended period of time. This could contaminate the material being collected.

1. Baghouses require the bag to be removed in order to be cleaned or replaced. Often times this is a very time consuming process and can often require workers to enter the baghouse. If contamination is a serious concern, baghouses should not be used.
2. Cartridge collectors are much easier with replacing the cartridges. Often times this can be done in minutes compared to hours of a baghouse. So you can remove the cartridges, clean them and re-install. This will allow you to clean or replace the filters after each batch, thereby minimizing any contamination.

One option is to install a cyclone dust collector as a pre-filter before your baghouse or cartridge collector. The cyclone will capture the majority of the material without contaminating it for use in your process / product. While the smallest fines will then be captured in the baghouse / cartridge collector for disposal or treatment. This allows you to capture as much of your valuable material with minimal cleaning / contamination while also providing the high removal efficiency for the environment.

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5 Signs Your Dust Collection System Needs a Pre-Filter

Watch the video from the Dust Efficiency Clinic discusses how using a pre-filter will optimize your dust collection system. 

 

If you prefer this valuable information in white paper form, get our whitepaper, Top 5 Reasons to Use a Cyclone as a Pre-filter.

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Dust collectors can be used for a variety of reasons. Some dust collectors are placed around applications that create dust such as saws, grinders, lathes, etc. The dust collector system is used to pull air from the area producing the dust via a hood and through some ductwork until it gets to the dust collector. The dust collector then separates the dust from the air. The cleaned air is then vented out of the dust collector through an exhaust fan and either outside or back to the facility. Other dust collectors are used to clean the air in a facility. The dust collector collects air away from the equipment and processes generating the dust. Many times this air is collected up near the ceiling of the facility. The air is then sent through the dust collector and vented outside or back into the building.

Whenever possible, you should try to capture the dust as close to the process generating the dust as you can. The reason is it is easier to capture the dust closer to where it is generated. If you are collecting the air near the dust generation equipment you will not have to collect as much air, which allows you to size a much smaller system, thereby saving money on capital expenses and operational expenses. Whereas if you are trying to capture the dust away from where it is generated, you will have to process more airflow to capture the dust.

However, there are times that you cannot place hoods right by the dust generating equipment. In those situations you will need to design your dust collection system so that it is big enough to capture the dust while keeping it as small as possible. This might mean building special hoods, using curtains, etc. all to help minimize the airflow required while maximizing the dust entrainment.

Dust collectors can also be used in vacuum systems. A vacuum system allows you to vacuum up dust around the facility without using portable vacuums. This might be advantageous when dealing with explosive applications, since most portable vacuums aren’t rated for explosive applications. And with the NFPA specifications requiring housekeeping of the dust facilities as a main action item, having vacuum systems for explosive dust is desirable.

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What information do I need to size my dust collector?

The attached Questionnaire will provide most of the questions that would be asked for a dust collector. The information that absolutely must be provided for a dust collector to be sized and quoted are:

1. What is the airflow through the dust collector?
2. What is the temperature and pressure the dust collector will experience?
3. What is the dust being collected?
4. Is it explosive?
5. What removal efficiency do you require?

The five above will allow a supplier to provide a quote. However, with only the above information, the dust collector performance cannot be guaranteed.

See dust collector questionnaire.

Is my dust explosive?

To help answer this question, NFPA has released NFPA-652 and 654. A combustible dust is defined as a finely divided combustible particulate solid that presents a flash fire or explosion hazard when suspended in air or the process-specific oxidizing medium over a range of concentrations.

Basically, what this means is when the dust is in the air and its concentration is enough to cause a flash fire or propagate a deflagration or explosion if exposed to a spark or heat source, then it’s considered combustible. Continue Reading.

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Airlocks FAQ Volume 1

Airlock valves are important components in many dust collection and process systems, yet they are often overlooked. We hope this helps you choose your next airlock.

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5 Common Mistakes When Selecting a Dust Collector

The video presents a quick, do-it-yourself examination that helps identify symptoms of possible inefficient dust collection.

 

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A prominent coffee bean roaster is planning on building a new roasting facility in New Jersey. The head engineer contacted Aerodyne about trying to find equipment that could separate the coffee beans as they are pneumatically conveyed from one portion of the facility to the other. The engineer specified that the problem the facility was facing was space.

How Aerodyne GPC operates Differently in Coffee Industry

After sending over the specs of the application, Aerodyne concluded that the roasting facility could easily house a GPC-20 horizontal dust collector for the operation. The Aerodyne GPC Dust Collector operates differently than other dust collectors. A sloped spiral inlet directs the dirty gas stream toward a fixed ground plate and hopper of the dust collector.

The ground plate forces vortex reversal to occur in a much shorter space, eliminating the need for a long, tapered body. As the dirty gas stream strikes the convex ground plate, fine particulate that has not completely made it to the dust collector walls is deflected into the hopper. The ground plate also shields collected particulate from the forces of the vortex reversal, acting as a barrier between the separation chamber and the collection hopper. This innovative design enables a compact dust collector to operate at high efficiency, even when installed horizontally.

The GPC offers a unique dust collection solution. With the compact size and excellent removal efficiencies, it is an economical and low maintenance solution to removing dust and particulate from an air stream.

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Aerodyne GPC Used in Coffee Roaster's Process

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In dust collection one of the most important dust characteristics to define is the particle size of the dust. The larger the dust the easier it is to capture. While the smaller the dust particle the harder it is to capture and remove from the airflow. This applies to both heavy and light particles. What this means is that in order to accurately predict your removal efficiency, you need to know the particle size distribution.

Breakdown of Particle Sizes

The most useful particle size distribution includes a breakdown of the particle sizes under 50 microns in size. Most dust collectors will pretty much capture all or nearly 99% of particles greater than 50 microns, so it isn’t as important to know if you have 5% dust at 51 microns and 3% at 55 microns, a simple 8% over 50 microns would be effective.

However, when dealing with dust less than 20 microns, knowing the particle size distribution is very important. For example, some cyclones might get you around 85% removal of 10 microns dust but 60% of 5 microns dust and only 30% of 2 microns dust. So, if you have that 60% of the dust is less than 10 microns, it isn’t known how much of that is in the 2 microns ranger or the 10 microns range. This means that when calculating your removal efficiency, the estimated removal efficiency could range from less than 30% to 85%. The only way to know is to have a breakdown of the particle sizes.

Particle Size with Standard Deviation

Another way of providing a particle size distribution is to provide a mean particle size with standard deviation. This provides a decent approximation of the particle size. Personally, I would prefer the actual test data, because you are providing actual test data and not approximations. Depending on the process of dust generation, the approximation accuracy will vary. It also requires the person estimating the removal efficiency to calculate a particle size distribution. This takes more time and increases the chance of an error being introduced.

So, when you are looking to get your dust collector engineered, remember it is important to provide the equipment manufacturer with a particle size distribution. Often times you can send a sample in to a lab and within a week or so have a full distribution curve for a few hundred dollars. This will allow the manufacturer to better understand what they have to capture and select the best equipment for your application.

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How Do Horizontal Dust Collectors Work?

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When designing a dust collection system, the ductwork is like the highways of the system. They allow the dust to move from the area of production to the dust collector. The dust should move fast enough so it doesn’t fall out while not moving too fast to cause undue wear and pressure drop. What this means is when you are designing your dust collector ductwork, pay attention to the ductwork diameters. When picking the ductwork diameters throughout the system, make sure the velocities correlate with the design velocities shown below.

Low Velocity Causes Dust Build-Up

A velocity that is too low will cause major issues in your ductwork. Dust will fall out and begin to pile up in the ductwork. This will do three (3) things:

• The dust builds up, decreasing the area of the ductwork, until the open area is large enough to get the velocity back up within the range to prevent further dust buildup.
• Dust buildup will increase the weight of the ductwork, and could cause issues with the support of the ductwork.
• If the dust is explosive, the dust buildup creates fuel for an incident and could cause serious problems.

The table below is from the Industrial Ventilation Booklet (5-1) and gives the velocity ranges of various applications and dusts.

Nature of Contaminant	Examples	Design Velocity
Vapor, gases, smoke		Any desired velocity (1000-2000 FPM suggested)
Fumes, metal smokes	Welding	2000 – 2500 fpm
Very fine light dust	Cotton lint, wood flour, litho powder	2500 – 3000 fpm
Dry dusts & powders	Fine rubber dust, Bakelite molding, powder dust, jute lint, cotton dust, shavings (light), soap dust, leather shavings	3000 – 3500 fpm
Average industrial dust	Grinding dust, buffing lint (dry), wool jute dust (shaker waste), coffee beans, shoe dust, granite dust, silica flour, general material handling, brick cutting clay dust, foundry (general), limestone dust, packaging and weighing asbestos dust in textile industries	3500 – 4000 fpm
Heavy dusts	Sawdust (heavy and wet), metal turnings, foundry tumbling barrels and shake-out, sand blast dust, wood blocks, hog waste, brass turnings, cast iron boring dust, lead dust	4000 – 4500 fpm
Heavy or moist dusts	Lead dust with small chips, moist cement dust, buffing line (sticky), quick-lime dust	4500 fpm and up

 

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How Tough Dust Can Affect Your Dust Collection System

Watch this video from the Dust Efficiency Clinic and learn how to deal with all these tough dust issues.

As always the Dust Efficiency Clinic offers its ‘outside the box’ thinking and solutions to your tough dust problems.

 

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When protecting vessels from explosions, one of the most common ways is to install explosion vents. The explosion vent is an engineered weak spot in the vessel that fails when the internal pressure reaches a certain point. This failure allows the pressure to be released in a controlled way so that the entire vessel doesn’t explode. The explosion vent needs to be installed so that the venting is away from any equipment, walkways, roads, picnic areas, etc.

Explosion vents are primarily used when the vessels are located outdoors, however they can be used indoors, if certain criteria is met. To install an explosion vent indoors, the vessel has to be located by an exterior wall. The vent would then be ducted through the wall, so in case of an explosion it is directed outdoors. An indoor explosion vent will usually need to be larger than an outdoor explosion vent. This is due to additional combustion of material in the duct and the inertia of the air mass in the ductwork.

The following is an explanation taken from FM Global 7- 76 Section 3.1.8

During the early part of the venting process, unburned dust is ejected into the duct ahead of the flame front from the vessel. When the flame front moves into the duct, dust starts to burn within the duct and generate additional combustion products. Those combustion products expand in ALL directions, thus slowing down or even reversing the flow out of the vessel and the pressure builds up within the vessel.

Inertia of the air within the duct also increases explosion pressure within the protected vessel. When the explosion vent opens and combustion gases first start flowing into the duct, those gases must push all the air out of the duct. During the time required to eject the air, the pressure continues to grow within the vessel because the combustion gases are obstructed from reaching the open atmosphere. In a long duct, that mass of air can delay the venting of the combustion gases enough to significantly increase the pressure in the vessel.

So if you’re installing a vessel indoors and you want to vent it outside, keep it as close to the outside wall as possible.

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Are you in compliance with the 2018 version of NFPA 68?

Simply click the button for direct access to the webinar to learn more about how to these recent changes may require modifications to your system.

 

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To learn more about which dust collector, please contact our experts at 440-543-7400 or visit our website: www.dustcollectorhq.com.

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The saying goes that “Those who forget history are doomed to repeat it” and this is true of dust collection too.

Dust collections systems are often seen as an install and forget equipment. You turn it on and then do maintenance when you need to. However, the system was designed for a specific system or piece of equipment. This means the hoods, duct-work, airflow, dust collector, etc. are all taken into account in the design.

Then over time, equipment in the system is changed, repaired, optimized, etc. Additional pickup points are added and/or removed, filters are changed, process conditions change, new products are made and/or new components are used in the process. All of this can change the operation of the dust collector system. Anytime something changes in the dust collector system, the system should be reviewed to make sure it is still operating as required.

At this time, the change should be noted in the system manual so that in the future when another change is done or the system isn’t operating as required, the information is readily available. If the information isn’t noted on the system, history will be repeated in that the whole system will have to be re-designed to figure out what airflow is required and where the issues are. This will end up taking more time, and if the proper data isn’t available, could cause further issues down the line.

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Solutions Sourcebook

Learn how industrial dust collectors and material handling valves can help your application.

 

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5 Common Mistakes When Selecting a Dust Collector

The video presents a quick, do-it-yourself examination that helps identify symptoms of possible inefficient dust collection.

 

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Cyclone pre-filters offer multiple advantages to existing dust collection systems. They lower the dust loading going into the dust collector, thereby allowing them to concentrate on the smallest particles. Here we will discuss the benefits for both wet collectors and dry collectors.

Wet Scrubbers

Wet Scrubbers – cyclones remove the particulate before the particles see the liquid. Wet scrubbers use liquid (often times water) to capture the dust. The water droplet surrounds the particulate, thereby increasing the particle size of the particle so it is easier to collect. Once the particulate is in the water droplet, it falls into the scrubber sump and is removed from the air-stream. The problem is that as more and more droplets enter the sump tank, a slurry is formed and will require a blow-down to prevent plugging up the nozzles, pump and packing, etc. This requires adding additional liquid and removing slurry.

Benefits of Cyclone Pre-Filter on Wet Scrubbers

By installing the cyclone pre-filter, you are decreasing the amount of particulate entering the wet scrubber. This means less particles will be in the sump tank, lowering the amount in the slurry and requiring less blowdown. This decreases the amount of liquid you need to add to the system. Lowering the blowdown rate also decreases the cost to treat the blowdown liquid. The blowdown slurry is often sent to a waste water treatment facility (facility or municipal). Each gallon of blowdown must be treated so that it doesn’t contaminate the ecosystem. This additional cost is often forgotten about when evaluating a wet scrubber.

Fabric Filters

Fabric filters (baghouses, cartridge collectors, HEPA filters) – Cyclone pre-filters provide many benefits for fabric filters. Fabric filters work by building up a dust layer which then lets air pass, but not dust particles. As the layer gets thicker it is harder for air to pass through.   Baghouses and cartridge collectors often clean the filters periodically by blowing compressed air in them, causing the filters to expand and shake off the top layers of dust.

Benefits of Cyclone Pre-Filter on Fabric Filters

The cyclone pre-filter minimizes the amount of dust coming to the filters. They also collect the largest dust, only allowing the fine dust to get to the filters. The fine particles will then more evenly collect on the filters.   The lower dust loading mean that the filters will not require as much cleaning which extends the life of the filters. Since the filters are cleaned by blowing compressed air into them, the expansion will eventually cause tears. And over time, less and less particulate will fall off as dust works its way into the filter.

Filters also have issues with certain type of dusts. Dust that is sticky and hygroscopic can cause filters to plug up faster, especially if there is humidity in the area. Abrasive dust can cause premature holes in the filters and those holes in the filter allow dust to pass through the collector and out into the environment. Again, by minimizing the dust going to the filter, you extend the filter life and minimize the possibility of filters plugging.

The other big savings is that by installing a pulse-on-demand controller, with a cyclone pre-filter, you will be able to control your cleaning cycles. Therefore, you will only clean the filters when it’s needed. This will save your filters and minimize your plant air usage.

The other benefit that cyclones provide is that they capture the dust before it reaches the filters. Since the filters have a dust layer at all times, the dust that is collected is contaminated by all dust that it has seen before in the life of the filters. If the material you are collecting is expensive, perishables or are controlled substances (pharmaceutical manufacturing), then collecting in a baghouse could cause issues due to contamination from the filters. The cyclone will collect the material and can be easily cleaned between batches.

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Top 5 Reasons to Use a Cyclone as a Pre-Filter Whitepaper

Find out ow pre-filters help to extend bag or filter life, and improving removal efficiencies.

 

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How the Aerodyne SplitStream Cyclone Works

The SplitStream Cyclone Collector is designed for dust collection systems where tough dust like abrasive, sticky, fibrous, hygroscopic or granular persist. 

 

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