Baghouse, also known as bag filters or fabric filters, are a type of dust collector, which is any system or machine that draws dust out of the air into a filter or separator. In this same group are equipment like air scrubbers, electrostatic precipitators, wet scrubbers, unit collectors and inertial separators.
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Advantages of Baghouses
By removing contaminated air particles from the environment around them, baghouse and dust collecting systems like them improve air quality and worker health and safety. Baghouses, which trap dust particles using fabric filters, are popular for a number of reasons. For starters, they are easy to use and cost-effective; they typically exhibit a fine particulate capture rate of up to 99.9%. In addition, rather than disposing of the dust after collection, as scrubbers do, baghouses return it to the mix. There, the dust can be reused. Another advantage of baghouses is the fact that they are more portable and flexible than other devices. Also, they require less horsepower than others to operate.
Purpose of Baghouses
In addition to simple dust, baghouses commonly capture particles such as: concrete dust, wood dust, welding fumes and incinerator smoke. They can also separate and filter toxic media, explosive media and metalworking chips. They are popular in work environments including manufacturing facilities, workshops and plants. In particular, they are the preferred method of particulate emission control in hot mix asphalt plants. They are also useful to companies seeking to comply with OSHA regulation pollution codes without breaking the bank. Typical industries in which companies like these are involved include: agriculture, cement fabrication, chemical processing, coal handling, metal fabrication, pharmaceutical processing, recycling, waste incineration and woodworking.
Design of Baghouses
Baghouses consist of ducts, a fan, a hopper, fabric filters, an outlet and an airlock. To pull contaminated air through the fabric filters, or bags, the fan creates a vacuum. The air enters through the ducts into the hopper, where the filters are housed. Here, the filters capture smoke, dust and other particles and let the clean air move freely through and out of an outlet at the top of the baghouse. The captured particles eventually settle into a routinely emptied airlock, found at the bottom of the hopper. As they settle, the dust particles accumulate on the fabric filters and build up to form a layer known as a filtering cake, filter cake or dust cake. The filter cake is an important and unique feature of the baghouse; it is used as a barrier that can catch extremely fine particulates. The filter cake must be carefully maintained, though, because if it is allowed to build up too much, it will clog the airway and become ineffective.
Types of Baghouses
There are three main types of baghouses, each which maintains the filter cakes in different ways.
- Reverse-Air Baghouses
- To work, filtration is paused in a compartment about to be cleaned. (Reserve-air baghouses are compartmentalized so that filtering can continue in most areas, even if it is halted in one compartment during cleaning.) Then, clean air is injected into the baghouse in reverse direction, thus pressurizing the compartment and causing the filter bags to partially break down. This breakdown causes the filter cake to crack and fall into the hopper.
- Reverse-Jet Baghouses
- Permit unbroken filter operation during cleaning, but they do not usually have compartments. In this case, the filter bags are cleaned when compressed air is sent through in short bursts via a compressed air manifold.
- Mechanical Shaker Baghouses
- Clean themselves using vibrations that shake the filter cake off of the filter and into the hopper. These vibrations are generated by a motor-driven shaft and cam. In addition, this cleaning process may be supplemented by a device known as a sonic horn. Sonic horns work by emitting low frequency, high intensity sound waves; these sound waves help sever the bonds between particles sitting on the filter media surface, and they also help with dust removal.
Materials Used for Baghouses
Baghouses are most often made from fiberglass materials, cotton, or various other synthetic materials. To determine the best baghouse materials and configurations for your application, call a trusted dust collection professional today. Once you have your baghouse, make sure to care for it properly by paying attention to the following factors of its performance: gas temperature, pressure drop, opacity and gas volumetric flow rate. Provided all of these elements are watched and corrected when wrong, you can count on your baghouse to clean your air efficiently for many years to come.