July 2016

Baghouses: How They Work

by Imperial Systems | Jul 13, 2016 | Uncategorized

People often use baghouses and dust collectors as synonyms. What is a baghouse? It is a system in which bags made of various materials filter the air. The system periodically cleans the bags to remove accumulated dust.

Today, cartridge dust collectors are increasingly popular in many industries, and for good reason. Cartridge filters can pack a lot of surface area into a small space. They can also filter very small (sub-micron) particulate very efficiently. For some industries, this is essential. This includes metalworking, which generates smoke and fumes that contain potentially toxic materials.

The baghouse, however, has been a workhorse for industrial dust control for many years and continues to serve its role today. While the basic concept remains the same, today they are more adaptable than ever. This is due to new filter materials and new ways to solve problems. Not every industry produces dust that’s fine enough to need the high efficiency of a cartridge collector. The baghouse efficiency is sufficient in plenty of cases.

Types of Baghouses

So how does a baghouse dust collector work? Generally, all baghouses have a tube sheet to which the bags attach. They also have an inlet for dirty air and an outlet for clean air. Then there’s an opening at the bottom for collected dust to drop out. The location of these features depends on the type of baghouse. The main differences between types of baghouses are how they clean the bags.

Shaker Baghouses

A shaker baghouse cleans the bags by mechanically shaking them. The bags usually hang from the top of the unit and attach to the tube sheet at the bottom. In this type of system, air typically enters from the bottom. The system pulls the air through to collect dust on the inside of the bags. Clean air then exits at the top while collected dust remains inside the bags.

To clean the bags, the airflow must first be shut off. Then the hanging mechanism shakes the bags to get rid of the dust, which drops out the bottom. These are not the most efficient types of baghouses and can be high-maintenance. Yes, the design is simple and does not require compressed air or complicated supports for the bags. However, damage to the bags can occur from the mechanical shaking mechanism.

Reverse Air Baghouses

In a reverse air filter bag house like our BRF, dirty air enters the collector and dust collects on the outside of the bags, which are supported by a metal cage to keep the air pressure from collapsing them. Steady air circulation continuously pulls air through the filter bags. For cleaning, a fan rotates over the bags, blowing reverse air into them to remove dust.

This type of reverse air baghouse generates a lower pressure than the compressed air pulses of a pulse jet. This decreases wear and tear on the bags and saves on the cost of compressed air. They are usually very cost-efficient and when using within the design parameters, they are also very effective. Also, this type of reverse air baghouse can continue running while cleaning occurs.

An older type of baghouse, also sometimes referred to as reverse air, collects dust on the inside of the bags. Then it cuts off the inflow of dirty air and uses a reverse flow of clean air. This partially collapses the bags, which also removes the dust. These types of bags have rigid rings that allow them to flex but not collapse completely, or “pancake”.

These types of reverse air baghouses have to be taken offline for cleaning. But sometimes they are divided into compartments so one section at a time can be cleaned. So, you can see that the reverse air baghouse working principle can vary from brand to brand.

Pulse Jet Baghouses

A pulse jet baghouse design is somewhat similar. Metal cages support the bags and hang from a tube sheet at the top of the baghouse. Dust and air enter and dust collects on the outside surface of the bags, not the inside. Bursts or pulses of compressed air clean the bags. These travel down the length of the bag and dislodge the dust.

Because the pulse of air travels very quickly down the bags, the baghouse is cleaned without taking it offline. This allows them to operate more efficiently since the system removes dust from the bags at more regular intervals. The downside to the pulse jet bag filter design is the higher pressure and expense of compressed air. These both add to operating costs.

Operation and Maintenance Costs

The EPA provides information (link: https://www3.epa.gov/ttncatc1/dir1/cs6ch1.pdf) to help you make a general calculation of the capital costs of a baghouse dust control system. Their calculations include the cost of the collector, the bags (and cages if necessary), measurement instruments, installation costs, and the annual operating costs (electricity, compressed air, labor, and materials).

These costs will obviously vary widely. A pulse jet baghouse requires compressed air, which other types of baghouses do not need. But it may require fewer filters since they are more efficient.

Filter Replacement

One thing that is a major headache for owners of any type of baghouse: replacing the bags. This is usually a dirty, messy, and time-consuming job. It also requires the collector to be offline for a considerable period of time. It often involves working in an enclosed space. Mechanisms for attaching the bags to the tube sheets vary widely. It can be a very involved process, especially when using cages. Some companies installing new dust control equipment choose a cartridge filter collector. This is because vertical collectors like our CMAXX™ are easy to change and do not involve issues with confined spaces.

For existing baghouses that need frequent bag changes, a pleated filter bag is an option that should be considered. These have a much larger surface area and last much longer than traditional bags, which means less frequent changes. Also, pleated filter bags do not require cages, which greatly simplifies the changing process.

Conclusion

Yes, there’s a lot to know about baghouses! Call us today at 800-918-3013. Our helpful, knowledgeable team members can answer any questions you may have about them. Our goal is to provide the right dust collection solution for your application. Learn more about Imperial Systems’ baghouses.

Toxic Metal Dust Danger

by Imperial Systems | Jul 7, 2016 | Uncategorized

What Makes Good Chromium Go Bad? How This Anti-Corrosion Wonder Metal Can Turn Into an Occupational Health Disaster

Chromium is an amazing metal. Polish to a brilliant shine and will keep that shine without tarnishing or corroding. When allowed with other metals, it makes them harder and more corrosion-resistant. Also, electroplating with chromium gives a durable, high-polish coating. However, chromium can produce toxic metal dust.

Chromium didn’t get its name by being shiny, though. “Chroma” is the Greek word for “color.” Many chromium compounds come in bright, beautiful colors including purple, yellow, and green. For many years, chrome yellow was used to create the familiar yellow school bus. The military uses chrome pigments that reflect infrared rays to conceal vehicles. Some treated wood and tanned leather use chromium salts.

What turns this incredibly useful item into a toxic metal dust health hazard?

Metals exist in a variety of oxidation states, depending on the compounds they are part of. Metals are good at sharing electrons, so chromium, like many other metals, can exist in several different oxidation states. Hexavalent chromium or chromium (VI) is a chromium compound at the +6 oxidation state. In this form, it mimics other essential elements and tricks cells into taking it in. Depending on the site of exposure, the results can be skin damage, stomach, and intestinal injury, lung damage, and eventually lung and kidney cancer.

Many dyes, pigments, and primers contain hexavalent chromium in its direct form. Most exposure, though, occurs when stainless steel or other metals alloyed or coated with chromium are heated by welding, grinding, or cutting. The heat involved in these processes causes previously stable and harmless chromium to oxidize to its dangerous hexavalent form.

Welding fumes, grinding or metalworking dust, and fumes from plasma or laser cutting tables can all contain this form of chromium as a toxic metal dust. So can dust or smoke from treated wood, dust left over from leather tanning and residues from electroplating with chrome or from heat-treating materials with a chromium anti-corrosion coating.

Awareness Is the Key to Prevention

Remember Erin Brockovich? She made a name for herself fighting a facility in southern California. They had been using hexavalent chromium in their systems as a corrosion prevention agent and then allowed it to contaminate the groundwater. She has since gone on to participate in several other high-profile lawsuits involving the contamination of groundwater with hexavalent chromium in Missouri and Texas.

OSHA and environmental groups including the EPA closely monitor all forms of toxic metal dust including hexavalent chromium. If your facility’s dust collection equipment isn’t up to the job of handling this byproduct, your workers are at risk of health problems. Which means you could be at risk of fines. Many companies don’t know that their processes are producing hexavalent chromium. This dangerous version of a common and useful metal is found in more types of dust, smoke, and fumes than you may realize.

Check out our infographic on hexavalent chromium!

Dust Testing FYI

by Imperial Systems | Jul 1, 2016 | Uncategorized

The Mechanics of Deflagration: Dust Testing Research

Some dusts are more dangerous than others. The organizations that set standards for combustible dust management, like OSHA and the National Fire Protection Association, run dust testing on many types of dust to determine how dangerous they are and what conditions make them explode.

In many cases, these formal tests replicate what common sense would already tell you. Combustion chambers are often used to measure the amount of pressure that’s produced when a measured amount of a dust is ignited. They are used to measure the minimum concentration of the dust that’s needed to start a deflagration. This is an important number, because even if you don’t normally produce enough dust to reach the concentration that could ignite, a heavy day of fabrication or dust dislodged from overhead surfaces could raise that into the danger zone.

Methods of Dust Testing

A combustion chamber is also used to test another key component of an explosion: the amount of oxygen needed to fuel it. Fire requires oxygen, but depending on how flammable a material is, it may burn even in an environment with low oxygen.

A spark igniter creates sparks to test the minimum amount of energy needed ignite a deflagration. Materials that are very easily ignited by even a small spark are a hazard in any situation where there is static discharge, even in the absence of any heat or flame.

A furnace is used to test how hot a material has to get before it will spontaneously ignite without a direct heat source. A cloud of dust may not burn even in very, very hot air unless there is a spark or flame to ignite it. If the dust ignites in the furnace, it means that temperature control is a key factor in handling this dust safely.

Some dust testing use a hot surface to test whether dust will ignite when a surface with a layer of dust on it is heated. Again, some types of dust may not ignite even when exposed to very high temperatures unless there is a spark or flame, but some types of dust may ignite from being in contact with a hot surface, and this type of dust is dangerous anywhere that it could come into contact with hot materials.

Conclusion

These factors together are used to calculate a deflagration index, which is an overall rating of how likely that type of dust will produce a deflagration. This index is used to group dusts into explosion classes: Class 0 in non-explosive (silica), Class 1 is weakly explosive (charcoal, zinc, many food products), Class 2 is strongly explosive (wood flour, many plastics) and Class 3 is extremely explosive (aluminum and magnesium dusts, some plastics and other chemicals)