Fabric filtration is a common way to separate dry particles from a gas stream. A baghouse is the term used to describe the collection of many fabric filters contained within the same housing. Baghouses are utilized in gas stream or air filtration in industrial and commercial applications.
The fabric filters used in baghouses are a useful method of air filtration when particle size classification is not desired, operating temperatures are low to moderate, high efficiency is needed, the particulate needs to be recovered, or relatively low particulate volumes are encountered. Baghouses are used in fossil fuel power plants, fertilizer plants, steel mills, food processing, hospital waste incinerators, cement manufacturing, paper mills, mining plants, industrial waste incinerators and pharmaceutical production.
Function of the Baghouse
In a baghouse, dirty air flows into and through a number of cloth filter bags that are placed in parallel. The filters remove the particulate from the gas stream while the cleaned gas passes thorugh the cloth and is exhausted to the atmosphere. The fabric filters do some filtering of the dust particles; however, their more important role is to act as a support for the layer of dust (filter cake) that quickly accumulates on it. This layer then acts in a highly efficient manner to filter both the large and small particles from the gas stream and becomes the main filtration mechanism throughout the process.
Types of Baghouses
The baghouses are named after the method used for cleaning the dust and filter cake from the bags. These include the shaker baghouse, reverse-air baghouse, pulse-jet baghouse, and sonic horn baghouse. In the shaker baghouse, the dusty air flow is taken offline and the isolated bags are shaken to knock off the dust. In the reverse air baghouse, the dusty air flow is blocked from the compartment to be cleaned and the clean air is forced to flow gently backwards through the bags thus dislodging the particles. In a pulse jet baghouse a blast of compressed clean air flows brieftly into the bags, while they are still filtering dusty air. In a sonic horn baghouse, a pulse from a sonic horn is sent through the bags to dislodge some of the dust. In all of these baghouses, the particlulate falls down from the filters and is collected in a hopper where it can be removed.
Baghouse Fabric Filter Material
The fabric filters utilized in a baghouse depend on operating temperatures, physical resistances such as abrasion, shaking and flexing, and chemical resistances such as acids, oxidizers and solvents. Examples of fabrics utilized include cotton, wool, nylon, polypropylene, dacron, orlon, nomex, teflon, vycron and glass.
Size of Baghouses
Baghouses typically have a large footprint. This is due to the large numbers of bags utilized to filter the volumes of air required. If too few bags are used and large volumes of air are required to be filtered, the pressure drop thorugh the baghouse significantly increases. Industrial baghouses typically have many compartments that each may contain hundreds of individual filter bags.
Advantages of Baghouses
Baghouses have a very high collection efficiency for both large and small particles, they are modular in design, and they can operate on a wide variety of dust types and wide range of flow rates with reasonably low pressure drops.
Disadvantages of Baghouses
Baghouses require a large floor areas to operate, need frequent cleaning, have the potential for fire/explosion hazards, and need bag replacement. The fabric filters have the potential to degrade from high temperatures or corrosive environments. The filters may also become clogged in highly humid or moist environments.
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