Cyclone Pre-filters can filter out 90% or more particulate before it reaches downstream filters, significantly reducing fabric filter wear and protecting other industrial dust collection equipment.

The Unique Dust Challenges In Foundries:

Foundries are hot, dusty places—factories where metal castings and other casting services come to life. Castings are produced by melting metal into a liquid, pouring it into molds, and allowing it to solidify. Sand, characterized as an abrasive, is used in metal casting for molding and core making, and silica is typically a key ingredient in molten metal shaping due to its uniform physical characteristics. Unfortunately, silica poses major health risks to humans if inhaled, and so the airborne dust created from sand molds and casting cleanups must be managed properly. The majority of manufactured goods rely in some way on the castings produced by foundries, and like other areas of manufacturing, the dust they produce must be managed via a dust collection system to keep the working environment safe and compliant.

Why Fabric Filters Struggle With Heavy Loading:

Baghouse and cartridge filter collectors are a core piece of many foundry dust collection systems, and are generally very well suited to filter dust from the air in these operations; situated towards the end of the dust collection system, they take on heavy loads of metal, sand, and silica. Depending on the particle size and loading rate of the dust particulate, these fabric filters can suffer from plugging or overloading, inhibiting the airflow of the dust collection system and allowing dust to escape and settle in work areas.

This is a serious concern for foundry personnel because of the increased risk of health hazards and potential explosions.

How Cyclone Pre-filters work:

Enter the cyclone pre-filter. Widely endorsed as a proactive measure for reducing filter loading and increasing dust collection system efficiency, they can be placed upstream of fabric filters to separate out the majority of particulate before it comes in contact with said filters. Cyclones also serve as spark arrestors, increasing the amount of time a spark has to travel before it reaches the filter, and helping to cool down sparks that touch the walls but are not captured—an added bonus for foundry applications.

Cyclones use centrifugal force to capture and remove dust from the airstream, and can often remove 90% or more particulate before it comes in contact with downstream fabric filters. They’re one of the simplest dust collectors available on the market: dirty air enters the cyclone’s inlet and swirls around the separation chamber, where centrifugal forces then force dust out towards the walls.

Once the mixture of air and dust gets down near the hopper, the air changes direction (called vortex reversal) and leaves through the center of the cyclone separation chamber. The solid particles that were concentrated near the wall fall into the hopper and are then removed from the hopper via the airlock.

Any small dust that makes it through the cyclone is then captured by downstream fabric filters, easing the load on the filters themselves and drastically changing the way that dust is managed in the system. Any sparks from the process and the majority of abrasive dust are removed before they can reach the filters, reducing filter cleaning requirements, fire risk, and the amount of compressed air required for cleaning (pulse jet type). Significant savings can be seen if the compressor loading can be downsized for a facility. Ultimately, less dust escapes into the surrounding work areas—lowering the risk of silica damage to employees, and decreasing the risk of explosions or fires.

Aerodyne’s GPC cyclones are compact models with removal capacities comparable to those of traditional cyclones; they differ from traditional cyclones in that they’re shorter, can be configured horizontally, and have an internal ground plate that acts as an integral vortex breaker. Cyclones can be installed in close proximity to areas where dust is generated, and where a larger, traditional cyclone may not fit, which allows the material to be collected and then directly re-entered into the process. This is critical in foundries, where much of the sand and casting materials are recycled heavily. An optional cleanout door can be configured on the cyclone’s backplate for easy access.

GPC Cyclone Specifications:

• proactive measure for reducing filter loading and increasing dust collection system efficiency by filtering majority of particulate ahead of filters
• serves as a spark arrestor
• designed to be installed vertically or horizontally with little effect on collection efficiencies
• utilizes centrifugal force + a ground plate to maximize collection potential
• handles abrasive materials
• eases filter loading to reduce cleaning cycles and increase filter lifetime
• can be installed in close proximity to areas where dust is generated and then directly re-entered into the surrounding processes
• optional “easy clean door”
• 7 sizes under 8 ft³ per NFPA 654
• Ideal for applications with limited space

Dust collection systems perform best in any industry when each of their components is optimized for its role in the system. When fabric filters like baghouses or cartridge collectors take the brunt of heavy dust loading by themselves, it’s a matter of time before efficiency becomes an issue. Implementing a high-efficiency cyclone pre-filter like the GPC shifts the heavy loading burden upstream, often capturing 90% or more of particulate, helping to intercept sparks, and ultimately stabilize airflow before it reaches the filters.

The GPC’s compact footprint and flexibility of installation make it particularly suited for space constrained foundry applications. Improving dust collection system performance doesn’t always translate to replacing the collector itself, but improving the system around the collector by evaluating upstream separation.

Dust collectors are used in many industries to improve air quality and remove harmful particles from the air. There are several types of dust collectors that are commonly used in industrial and commercial settings. Here are some of the most common types:

Baghouses

A baghouse consists of a vessel with many filters (bags) inside. The bags are located in rows and mounted on a tube sheet. The tube sheet separates the dirty air from the clean air. Dirty air enters the bag house near the bottom. The dirty air is forced through porous bags which have a built-up filter cake. Clean air goes through the filter/bag and leaves through the top of the vessel, while the dust falls down to be discharged through the hopper.

Cartridge Collectors

Cartridge collectors operate similar to baghouses except they use pleated cartridges to provide much higher surface areas in smaller filter volume than bag filters.  This means they are much smaller than baghouse for the same air volume.  However, the cartridges have lower temperature limits and can plug easily. They are used in the following applications: grinding, sandblasting, welding fumes, laser and plasma cutting fumes, graphite, pharmaceutical powders, acid fine chemical powders, and more. When dusts are difficult to handle, hygroscopic, or high temperature, a baghouse is a better alternative for trouble free dust collection and longer filter life.

Cyclone

The cyclone is the simplest design of all dust collectors. It is a mechanical way to remove dust from an air stream. The cyclone uses centrifugal and gravitational forces to force the dust to the vessel walls and then let gravity collect it. The cyclone requires only a discharge valve and fan for operation. Cyclones require very little maintenance. Cyclones are often used as prefilters for other dust collectors.  They can provide high removal efficiencies of larger dust particles, thereby decreasing the loading on the main dust collector, this can increase total removal efficiency, decrease system maintenance and extend equipment life, not to mention collect material before contamination.

ESP (Electro Static Precipitator)

ESPs use high voltage to electrically charge particulate in the air. The charged particulate is collected on charged plates as the air stream passes. ESPs use large amounts of electricity and can get collection efficiencies as high as 99% for many applications. ESPs provide good removal of sub-micron particulate. ESP are expensive and require high operating and maintenance costs.

Wet Scrubbers

Wet Scrubbers are available in a variety of designs including cyclones, venturi, packed towers, cloud chambers and fluidized beds. Wet scrubbers spray water into the dirty airstream allowing dust and water droplets to contact, thereby making them easier to collect.  Wet scrubbers have high removal efficiency but can be expensive to operate and treat the slurry leaving. The wet cyclone is just like a regular cyclone except that they spray water in the cyclone.

To improve efficiency and safety, there is no substitute for an on-site inspection by an experienced expert. Interested in connecting with a member of our engineering team to learn more about available dust collection solutions for your application? To speak directly with our applications engineer Dan, dial 440-543-7400 x 235 or reach out by email at dc@dustcollectorhq.com. For all other inquiries, click here.

The post What kind of dust collectors are available? first appeared on Aerodyne Environmental.]]> https://www.dustcollectorhq.com/dust-re-entrainment/ Thu, 31 Oct 2019 17:30:00 +0000 https://www.dustcollectorhq.com/dust-re-entrainment/ Dust Re-Entrainment

Surrounding areas

As mentioned above, the area surrounding the dust collector significantly affects where the dust collector can be installed.  Location of utilities such as electricity and compressed (plant) air all affect the dust collector location.  Baghouses and cartridge collectors usually require compressed air for cleaning, wet scrubbers often require makeup water and a drain to either local or plant water treatment facilities. 

Dust Collector Interference

The dust collector may interfere with surrounding equipment and operations, such as cranes and vehicle traffic.  Dust collectors are often tall pieces of equipment requiring large head room when indoors.  And the noise and explosion protection could affect personnel space such as break rooms, rally points, foot and vehicle traffic, etc.

So when looking for a space to install your dust collector make sure you take into account all the different factors such as explosion protection, utilities, operations, and workers safety and comfort. And install the dust collector as close as possible when conforming to the above requirements.

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

Humidity can cause problems in the process described above.  Humidity is a way to express the amount of water in the air, (the higher the humidity, the higher the amount of water in the air).  When high humidity air enters a dust collector with fabric filters, there is a chance that the water vapor will condense and create water droplets or the dust on the filters will absorb the water as the airflow passes through.  Many dusts change their physical properties when the water content increases.  Some become sticky, some become hard like concrete, etc.  When this happens to the dust cake, it affects the ability of the air to pass through and the ability of the dust to fall off during cleaning.

When dust becomes sticky, it will adhere to neighboring dust particles and not want to fall during cleaning.  Dust that becomes hard (like concrete) will prevent air from passing through.  When one of these issues develop in a dust collector the pressure drop across the dust collector will increase.  Over time, an increased pressure drop will lower the airflow being pulled through the system.  This will decrease the airflow being picked up at hoods, therefore lowering dust collection at where operators are located.

Humidity can also be introduced in the dust collector in the compressed air.  When air is compressed, the temperature of the air increases, thereby increasing the water content of the air.  The compressed air is at its saturation point.  As the air moves through the line, it cools, thereby condensing water in the system.  If additional drying technology isn’t installed, the compressed air will have water droplets in it as it is used in the dust collectors.  This will cause the filter cake to wet and cause issues as described above.  This is why it is important to dry compressed air when dealing with dust that is affected by water.

However, sometimes no matter how you treat your compressed air, you continue to have issues.  This could be because the airline travels outside and in winter time it gets very cold. It could be because you are located near a large body of water, and humidity is high.  One way to minimize the effect on your dust collector is to minimize the dust getting to your dust collector.  Cyclone pre-filters are ideal for these applications.  Cyclones collect dust and water droplets using centrifugal motion.  This means they aren’t affected by the changes to the dust as a filter is.  Cyclone pre-filters can often remove up to 80% of the dust before a dust collector with filters.  This means you can lower the number of water droplets going into your dust collector and minimize the cleaning required, thereby not getting as much water from the compressed air system.

To learn more about the different types of Dust Collection methods,  please contact our experts at 440-543-7400 or click on the button below to get our whitepaper, Top 5 Reasons to Use a Cyclone as a Pre-Filter.

To learn more about optimizing your system, request a dust collection system evaluation today.

At one time mechanical dust collectors were the industry standard in dust collection and air pollution control. However, with an ever increasing focus on air quality, EPA regulations regarding dust collection have steered the manufacturing world toward the higher efficiency capabilities of fabric filter baghouses, cartridge filters, and other dust collection equipment utilizing filter media. This change has undoubtedly helped to reduce the amount of harmful emissions released into the atmosphere in manufacturing processes. Unfortunately, the use of these fabric filter baghouse collectors is not without cost. The limitations of filter media such as moisture, heat, and high particulate volumes have added to the challenges of successful dust collection. Additionally, the high cost of bag or cartridge replacement, maintenance issues, and expensive pulse-jet controls to clean filter media can add up. The solution to these headaches for many has been the use of mechanical dust collectors before final-stage filtration.

Cyclonic Dust Collection

Mechanical dust collectors use a cyclonic air flow to separate particulate from an air stream. The centrifugal force created by the rotary flow throws the dust out of the air stream and toward the walls of the collector. In a typical cyclone, the particulate strikes the wall of the collector and falls to a hopper below for collection. Cleaned air is then vented through the top of the collector. While this form of collection can be highly efficient in dealing with large, dense particulate, extremely fine dust lacks the inertia to escape the air stream and is subsequently carried out with the cleaned air. Some high efficiency cyclones like the Aerodyne ‘S’ Series, use two air streams, to more efficiently separate the dust. The Aerodyne’s powerful secondary air stream intercepts the particulate before it contacts the side wall, reducing wear when handling abrasive materials. This secondary air stream also helps to sustain the cyclonic action inside the collector, thereby increasing its efficiency.

Filtration Struggles

Filter media dust collectors such as baghouses and cartridge filters use a fine filter media to remove dust from an air stream. The dust-laden air is drawn into the collector where it passes through the filter media and particulate is intercepted. Dust builds up on the filter until it is cleaned or replaced. Cleaned air is then vented out of the collector.

Many manufacturing processes involve circumstances that make it very difficult to rely completely on a baghouse. Heavy dust loading can be a maintenance nightmare for a filter media collector. A rock crushing operation based out of Minnesota realized the benefits of placing a cyclonic dust collector before its baghouse. The enormous amount of rock dust generated in the crushing operation was blinding the bags and causing frequent shutdowns. The decision was made to install a cyclonic dust collector to receive the dust before being sent through the bag house. The cyclone captured the vast majority of the rock dust, leaving only a small amount of fine particulate for the bag house to handle. The cost of the additional equipment was quickly recovered through fewer shutdowns and less frequent bag replacement.

Processes involving high temperature exhaust gas also plague filter media collectors. The hot air temperatures exhausted from foundries, glass making plants, and power plants can burn the filter media used by most baghouses. While high temperature filter bags and cartridge filters are available, they can be an expensive addition and are still not completely immune to the heat. Used as a spark arrestor, a cyclonic dust collector can be placed before a bag house to both reduce the temperature of the air stream and the particulate loading before it enters a final stage filter.

Conclusion

While a mechanical dust collector may not be necessary in every application, the benefits that can be gained from this proven technology are evident. As emission standards become more stringent and process costs continue to rise, any advantage that can be taken should be considered. By comparing process costs such as materials, labor, and downtime with the expense of a cyclone, a decision can be made as to the need for such equipment.

To learn more about the different types of Dust Collection methods,  please contact our experts at 440-543-7400 or click here to get our whitepaper, Not Your Grandfather’s Cyclone. 

The filters in a baghouse are the primary dust collecting component.  The filters build up an initial layer of dust, preventing dust from penetrating the filter while allowing air to pass through.  As the dust layer increases in thickness, it is harder for air to pass through.  This is measured by an increasing pressure drop.  Since most dust collection systems don’t use Variable Frequency Drives (VFDs) and airflow transmitters to control the airflow, the airflow through the system will decrease as the pressure drop across the bags increases.  Most baghouses use compressed air blown down the bag, to expand the bag off its cage to jar the most recent layers of dust off the filter. Other baghouses use a shaking cycle to remove the top layer of dust.

Over time, the constant expanding and contracting of the bag during the cleaning process could cause a hole to develop in the bag.  There are a few different ways for the bag filter to develop holes:

1. Gradual expansion of natural gaps in the filter during the cleaning process.
2. The bag being caught and ripped on the metal cage during the cleaning process.
3. High temperature causing localized failure of the filter.
4. Abrasive dust gradually wearing out filter materials.
5. High velocity of the air gradually wearing out the filters.

There are bag break sensors available on the market that will let you know when they detect a bag break.  Often, this is done by measuring the amount of dust particles after the baghouse and when the concentration suddenly jumps, an alarm is set.  Certain baghouse controllers will measure the compressed air used during the cleaning process.  From this, they can tell which row of bags have a hole so you can replace only a row of bags instead of all the bags in the baghouse.

A yearly maintenance inspection of the baghouse will help you avoid operational issues that could develop throughout the year.  This can prevent you from getting a fine or having to shut down the system in an emergency.

Timers and Clean-On-Demand

The two main controllers used are timers and clean on demand.  A timer is a simple controller which will turn on the cleaning cycle at a set time, such as every 5 minutes.  The timer can be changed, and a manual clean is usually available.  While the initial cost of this timer is less, it can end up wasting a lot of money if the timer is cleaning more often than required.  If the timer isn’t cleaning enough, then the dust collector is not operating at its optimal.  The other controller is clean on demand.  This controller uses a differential pressure transmitter to monitor the pressure drop across the bag.  When the pressure drop gets to a certain point, it will begin cleaning the bags until the pressure drop is lowered to a certain point.  This can save you a lot of money by minimizing the compressed air required.  However, if your bags are plugged, the cleaning can be continuous as the pressure drop will never fall below the cutoff point.

Reasons of High Pressure Drop On Filters

Filters will have high pressure drops due to a variety of reasons or even a combination of reasons working together.  These include heavy dust loading, wet or humid conditions, worn diffusers, humid compressed air, improper cleaning, and old filters.

• Heavy dust loading will plug filters faster than lower dust loadings. The faster dust covers the filters, the more the cleaning is required.  However, every cleaning doesn’t get 100% removal so over time the dust layer will get thicker and thicker; thereby, increasing the pressure drop.
• Wet or humid dust can cause pre-mature plugging. This is because when the dust gets wet it can form a mud.  This could prevent air from passing through, thereby increasing the pressure drop.  If the dust is hygroscopic and/or if the filter is pleated, the filter can plug up even faster.
• Dirty air entering a baghouse usually goes through a diverter, which directs the air evenly to each bag. Many times the diverter is some metal shape.  Over time, abrasive dust will wear away the diffuser changing the airflow.  This usually means some filters will get heavier dust loadings than others.  The filters getting the heavier dust loading will then plug faster, increasing the pressure drop through the system.
• Humid compressed air can cause major issues with certain dusts. If the dust is hygroscopic, then adding moisture to the system can cause problems.  Some dust becomes a mud while others form a concrete like substance.  Since the humidity is coming from the cleaning air, the humidity is meeting the dust in the filter holes, thereby plugging them up faster, and making it even harder for them to be cleaned.
• If the cleaning system isn’t operating properly, the bags will not clean effectively. This could be anything from stuck/broken air valves, misaligned venturi, bags stuck on cages, or too low compressed air.  Since the bags are cleaned by an expansion of the bag and losing the dust layer, if air isn’t delivered correctly, the bag may not fully inflate and not fully clean.  So any obstruction or barrier to full inflation would cause premature plugging.
• As mentioned above, over time all filters will plug up.

The best way to keep your dust collector working properly is to have a professional maintenance crew inspect and maintain your dust collectors.  Not only does this open your maintenance staff for other work, it allows them to use their experience to keep your baghouse operating at peak performance.

To learn more about finding the right dust collector for your application, please contact our experts at 440-543-7400 or visit our website: www.dustcollectorhq.com.

Baghouses and cartridge collectors are usually designed to handle a maximum of 6” W.C. of pressure drop.  When the baghouse pressure drop is 6” W.C., the airflow through the system is enough for proper operation.  When the pressure drop across the bags is greater than 6” W.C., the airflow through the system is less than it should be. The baghouse uses a control system to keep the pressure drop through the system to less than 6” W.C.  Most baghouses use compressed air to clean the bags, but shaking and sonic cleaners are also used. 

The two main controllers used are timers and clean on demand.  A timer is a simple controller which will turn on the cleaning cycle at a set time, such as every 5 minutes.  The timer can be changed, and a manual clean is usually available.  While the initial cost of this timer is less, it can end up wasting a lot of money if the timer is cleaning more often than required.  If the timer isn’t cleaning enough, then the dust collector is not operating at its optimal flow.  The other controller option is clean on demand.  This controller uses a differential pressure transmitter to monitor the pressure drop across the bag.  When the pressure drop gets to a certain point, it will begin cleaning the bags until the pressure drop is lowered to an acceptable point.  This can save you a lot of money by minimizing the compressed air required.  However, if your bags are plugged, the cleaning can be continuous as the pressure drop will never fall below the cutoff point.

Why does high differential pressure happen?

Filters will have high-pressure drops due to a variety of separate reasons or even a combination of reasons working together.  These include heavy dust loading, wet or humid conditions, worn diffusers, humid compressed air, improper cleaning, and old filters.

1. Heavy dust loading will plug filters faster than lower dust loadings. The faster dust covers the filters, the more the cleaning is required.  However, every cleaning doesn’t get 100% removal so over time the dust layer will get thicker and thicker; thereby, increasing the pressure drop.
2. Wet or humid dust are conditions that can cause premature plugging. When the dust gets wet, it can form a mud.  This could prevent air from passing through, thereby increasing the pressure drop.  If the dust is hygroscopic and/or if the filter is pleated, the filter can plug up even faster.
3. Dirty air entering a baghouse usually goes through a diverter, which directs the air evenly to each bag. Many times the diverter is some metal shape.  Over time, abrasive dust will wear away the diffuser, changing the airflow.  In this case,  some filters will get heavier dust loadings than others.  The filters getting the heavier dust loading will then plug faster, increasing the pressure drop through the system.
4. Humid compressed air can cause major issues with certain dusts. If the dust is hygroscopic, then adding moisture to the system can cause problems.  Some dust becomes a mud while others form a concrete-like substance.  Since the humidity is coming from the cleaning air, the humidity is meeting the dust in the filter holes, thereby plugging them up faster, and making it even harder for them to be cleaned.
5. If the cleaning system isn’t operating properly, the bags will not clean effectively. This could be anything from stuck/broken air valves, misaligned venturi, bags stuck on cages or too low compressed air.  Since the bags are cleaned by an expansion of the bag and losing the dust layer, if air isn’t delivered correctly, the bag may not fully inflate and not fully clean.  So any obstruction or barrier to full inflation would cause premature plugging.
6. As mentioned above, over time all filters will plug up. 

Why are system evaluations important?

The best way to keep your dust collector working properly is to have a professional maintenance crew inspect and maintain your dust collectors. Not only does this open your maintenance staff for other work, it allows them to use their experience to keep your baghouse operating at peak performance. Download our free guide on dust collection system evaluations to learn more.