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Difference between revisions of "Baghouses"
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[[Category:Filtration]]{{Knoppen}} | [[Category:Filtration]]{{Knoppen}} | ||
[[File:Baghouses_01.gif|thumb|right|Baghouse]] | [[File:Baghouses_01.gif|thumb|right|Baghouse]] | ||
[[File:Baghouses_03.jpg|thumb|right|Baghouse model]] | [[File:Baghouses_03.jpg|thumb|right|Baghouse model]] | ||
[[File:Baghouses_04.jpg|thumb|right|Industrial baghouse]] | [[File:Baghouses_04.jpg|thumb|right|Industrial baghouse]] | ||
A '''baghouse''' (BH, B/H) or fabric filter (FF) is an air pollution control device that removes particulates out of air or gas released from commercial processes or combustion for electricity generation. Power plants, steel mills, pharmaceutical producers, food manufacturers, chemical producers and other industrial companies often use baghouses to control emission of air pollutants. Baghouses came into widespread use in the late 1970s after the invention of high-temperature fabrics (for use in the filter media) capable of withstanding temperatures over 350°F. | |||
A baghouse (BH, B/H) or fabric filter (FF) is an air pollution control device that removes particulates out of air or gas released from commercial processes or combustion for electricity generation. Power plants, steel mills, pharmaceutical producers, food manufacturers, chemical producers and other industrial companies often use baghouses to control emission of air pollutants. Baghouses came into widespread use in the late 1970s after the invention of high-temperature fabrics (for use in the filter media) capable of withstanding temperatures over 350°F. | |||
Unlike electrostatic precipitators, where performance may vary significantly depending on process and electrical conditions, functioning baghouses typically have a particulate collection efficiency of 99% or better, even when particle size is very small. | Unlike electrostatic precipitators, where performance may vary significantly depending on process and electrical conditions, functioning baghouses typically have a particulate collection efficiency of 99% or better, even when particle size is very small. | ||
==Operation of Baghouses== | ==Operation of Baghouses== | ||
Most baghouses use long, cylindrical bags (or tubes) made of woven or felted fabric as a filter medium. (For applications where there is relatively low dust loading and gas temperatures are 250°F or less, pleated, nonwoven cartridges are sometimes used as filtering media instead of bags.) Dust-laden gas or air enters the baghouse through hoppers (large funnel-shaped containers used for storing and dispensing particulate) and is directed into the baghouse compartment. The gas is drawn through the bags, either on the inside or the outside depending on cleaning method, and a layer of dust accumulates on the filter media surface until air can no longer move through it. When sufficient pressure drop (delta P) occurs, the cleaning process begins. Cleaning can take place while the baghouse is online (filtering) or is offline (in isolation). When the compartment is clean, normal filtering resumes. | Most baghouses use long, cylindrical bags (or tubes) made of woven or felted fabric as a filter medium. (For applications where there is relatively low dust loading and gas temperatures are 250°F or less, pleated, nonwoven cartridges are sometimes used as filtering media instead of bags.) Dust-laden gas or air enters the baghouse through hoppers (large funnel-shaped containers used for storing and dispensing particulate) and is directed into the baghouse compartment. The gas is drawn through the bags, either on the inside or the outside depending on cleaning method, and a layer of dust accumulates on the filter media surface until air can no longer move through it. When sufficient pressure drop (delta P) occurs, the cleaning process begins. Cleaning can take place while the baghouse is online (filtering) or is offline (in isolation). When the compartment is clean, normal filtering resumes. | ||
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Baghouses are classified by the cleaning method used. The three most common types of baghouses are mechanical shakers, reverse gas, and pulse jet. | Baghouses are classified by the cleaning method used. The three most common types of baghouses are mechanical shakers, reverse gas, and pulse jet. | ||
===Mechanical Shaker Baghouses=== | ===Mechanical Shaker Baghouses=== | ||
In mechanical-shaker baghouses, tubular filter bags are fastened onto a cell plate at the bottom of the baghouse and suspended from horizontal beams at the top. Dirty gas enters the bottom of the baghouse and passes through the filter, and the dust collects on the inside surface of the bags. | In mechanical-shaker baghouses, tubular filter bags are fastened onto a cell plate at the bottom of the baghouse and suspended from horizontal beams at the top. Dirty gas enters the bottom of the baghouse and passes through the filter, and the dust collects on the inside surface of the bags. | ||
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===Reverse Air (R/A) Baghouses (aka Reverse Gas)=== | ===Reverse Air (R/A) Baghouses (aka Reverse Gas)=== | ||
In reverse-air baghouses, the bags are fastened onto a cell plate at the bottom of the baghouse and suspended from an adjustable hanger frame at the top. Dirty gas flow normally enters the baghouse and passes through the bag from the inside, and the dust collects on the inside of the bags. | In reverse-air baghouses, the bags are fastened onto a cell plate at the bottom of the baghouse and suspended from an adjustable hanger frame at the top. Dirty gas flow normally enters the baghouse and passes through the bag from the inside, and the dust collects on the inside of the bags. | ||
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Space requirements for a reverse-air baghouse are comparable to those of a shaker baghouse; however, maintenance needs are somewhat greater. | Space requirements for a reverse-air baghouse are comparable to those of a shaker baghouse; however, maintenance needs are somewhat greater. | ||
===Pulse Jet Baghouses (aka Reverse Jet)=== | ===Pulse Jet Baghouses (aka Reverse Jet)=== | ||
In reverse-pulse-jet baghouses, individual bags are supported by a metal cage (filter cage), which is fastened onto a cell plate at the top of the baghouse. Dirty gas enters from the bottom of the baghouse and flows from outside to inside the bags. The metal cage prevents collapse of the bag. | In reverse-pulse-jet baghouses, individual bags are supported by a metal cage (filter cage), which is fastened onto a cell plate at the top of the baghouse. Dirty gas enters from the bottom of the baghouse and flows from outside to inside the bags. The metal cage prevents collapse of the bag. | ||
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| || Have low pressure drop for equivalent collection efficiencies || | | || Have low pressure drop for equivalent collection efficiencies || | ||
|} | |} | ||
==Baghouse Cleaning Considerations== | ==Baghouse Cleaning Considerations== | ||
===Sonic Horns=== | ===Sonic Horns=== | ||
Some baghouses have sonic horns installed to provide supplementary vibration cleaning energy. The horns, which generate high intensity, low frequency sounds waves, are turned on just before or at the start of the cleaning cycle to help break the bonds between particles on the filter media surface and aid in dust removal. | Some baghouses have sonic horns installed to provide supplementary vibration cleaning energy. The horns, which generate high intensity, low frequency sounds waves, are turned on just before or at the start of the cleaning cycle to help break the bonds between particles on the filter media surface and aid in dust removal. | ||
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Two main sequence types are used to clean baghouses: | Two main sequence types are used to clean baghouses: | ||
*Intermittent (periodic) cleaning | *Intermittent (periodic) cleaning | ||
*Continuous cleaning. | *Continuous cleaning. | ||
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==Baghouse Performance== | ==Baghouse Performance== | ||
Baghouse performance is contingent upon inlet and outlet gas temperature, pressure drop, opacity, and gas velocity. The chemical composition, moisture, acid dew point, and particle loading and size distribution of the gas stream are essential factors as well | Baghouse performance is contingent upon inlet and outlet gas temperature, pressure drop, opacity, and gas velocity. The chemical composition, moisture, acid dew point, and particle loading and size distribution of the gas stream are essential factors as well | ||
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==Baghouse Design Variables== | ==Baghouse Design Variables== | ||
Pressure drop, filter drag, air-to-cloth ratio, and collection efficiency are essential factors in the design of a baghouse. | Pressure drop, filter drag, air-to-cloth ratio, and collection efficiency are essential factors in the design of a baghouse. | ||
*Pressure drop is the resistance to air flow across the baghouse. A high pressure drop corresponds with a higher resistance to airflow. Pressure drop is calculated by determining the difference in total pressure at two points, typically the inlet and outlet. | *Pressure drop is the resistance to air flow across the baghouse. A high pressure drop corresponds with a higher resistance to airflow. Pressure drop is calculated by determining the difference in total pressure at two points, typically the inlet and outlet. | ||
*Filter drag is the resistance across the fabric-dust layer. It is the pressure drop per unit of velocity. | *Filter drag is the resistance across the fabric-dust layer. It is the pressure drop per unit of velocity. | ||
*An understanding of the term air-to-cloth ratio is vital to understand the mechanics of any baghouse system regardless of the exact type used. This ratio is defined as the amount of air or process gas entering the Baghouse divided by the sq. ft of cloth in the Baghouse. Units of measure are (ft3/min)/ft2 or (cm3/sec)/cm2. | *An understanding of the term air-to-cloth ratio is vital to understand the mechanics of any baghouse system regardless of the exact type used. This ratio is defined as the amount of air or process gas entering the Baghouse divided by the sq. ft of cloth in the Baghouse. Units of measure are (ft3/min)/ft2 or (cm3/sec)/cm2. | ||
*Commonly, baghouses are designed with 99.9% collection efficiency. Oftentimes, cleaned air is recirculated back into the plant for heating. | *Commonly, baghouses are designed with 99.9% collection efficiency. Oftentimes, cleaned air is recirculated back into the plant for heating. | ||
===Baghouse Filter Media=== | ===Baghouse Filter Media=== | ||
Fabric filter bags (sometimes referred to as envelopes) are oval or round tubes, typically 15–30 feet and 5 to 12 inches in diameter, made of woven or felted material. Depending on chemical and/or moisture content of the gas stream, its temperature, and other conditions, bags may be constructed out of cotton, nylon, polyester, fiberglass or other materials. | Fabric filter bags (sometimes referred to as envelopes) are oval or round tubes, typically 15–30 feet and 5 to 12 inches in diameter, made of woven or felted material. Depending on chemical and/or moisture content of the gas stream, its temperature, and other conditions, bags may be constructed out of cotton, nylon, polyester, fiberglass or other materials. | ||
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Some baghouses use pleated cartridge filters, similar to what is found in home air filtration systems. | Some baghouses use pleated cartridge filters, similar to what is found in home air filtration systems. | ||
==Components of a Baghouse== | ==Components of a Baghouse== | ||
*Bags, fabric & support | *Bags, fabric & support | ||
*Housing or shell | *Housing or shell | ||
*Collection hoppers | *Collection hoppers | ||
*Discharge devices | *Discharge devices | ||
*Filter cleaning device | *Filter cleaning device | ||
*Fan | *Fan | ||
==Related topic== | ==Related topic== | ||
[[Electrostatic Precipitators]] | |||