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The choice of filter dust bag

 

Choice principle
Baghouse dust and gas is generally based on the nature of the nature and precipitator dust cleaning methods to choose, choose the following principles should be followed :
( 1 ) filter performance should meet the production conditions and the removal process in general, and special requirements .
( 2 ) In the above context, should be selected long service life of the filter , it is because long life can not only save operating costs , but also to meet the long-term gas discharge requirements.
( 3 ) Select the filter is to deal with a variety of filter sorting comprehensive comparison should not be used a so-called "good" filter to adapt to various working conditions occasions .
( 4 ) the nature of the gas , dust properties and cleaning methods , we should seize the main factors selected media, such as high temperature gases, combustible dust .
2, according to the nature of dusty gas selection
( 1 ) gas temperature . Dusty gas temperature is an important factor in the choice of media . Usually less than 130
the dusty gas as the gas at room temperature , greater than 130 dusty gas into hot gas , so the filter can be divided into two categories : that the room temperature is lower than 130 and above 130 high temperature filter media . This should be based on the appropriate choice of the flue gas temperature filter . Someone called 130 ~ 200 in the temperature gases, but the high temperature filter multiple choice .
Temperature filter media of " continuous long-term use temperature " and " short-term temperature two kinds of moments ." Continuous long-term use temperature "means the filter can be applied , the temperature of the long-term continuous operation , the temperature should be in order to use the filter ." Moment of temperature, short-term "means a filter which 10min not exceed the maximum daily temperature , time is too long , the filter will softening deformation .
( 2 ) the gas humidity . Dust-laden gas at a relative humidity divided into three states: the relative humidity is below 30% in dry gas at a relative humidity between 30% to 80% for the general condition , the relative humidity of the gas is above 80% humidity gas is . For humid gases, and high temperature state , especially dusty gas containing SO3 , the gas will produce cold and condensation . This will not only be the bag surface fouling , plugging , corrosion of structural materials and will therefore require special attention. The moisture in the gas filter is selected should note the following:
1> moisture trapped gas to the surface of the dust bag wet adhesion , especially for water absorption, and wet dust deliquescence will cause paste bag . To this end, should be used with glass fiber nylon surface smoothness , long fiber easy cleaning of the filter , and the filter in use for silicone oil, fluorocarbon resin for impregnation , or filter surface using acrylic , PTFE and other substances for coating process . Burning plastic plates and film material has excellent moisture resistance and ease of cleaning performance, as high humidity gas choice.
2 > When the presence of both temperature and humidity will affect the temperature resistance of the filter , especially for nylon , polyester imide poor hydrolytic stability of the material such as , especially, should be avoided .
3> on the moisture content of the gas in the dust bag should be used when designing a circular bag , try not to use complex shape, layout is very compact flat bag and diamond bag ( except plastic burn-in board ) .
4> precipitator dust gas inlet and the gas dew point temperature should be 10 ~ 30

( 3 ) chemical properties of the gas . In various furnace flue gas and chemical waste , often containing acid, alkali , oxidizing agents , organic solvents and other chemical components, and often affected by temperature , humidity and other factors affecting the cross . To this end , the choice of filter is to be thoughtful .
Polyester fiber at room temperature with good mechanical properties and acid and alkali resistance , but it is very sensitive to moisture , prone to hydrolysis , making a strong fall significantly. For this reason, polyester fibers in the dry flue gas temperature is less than the long-term operation 130
, but at high moisture content in the flue gas , can be reduced only to the long-term operating temperature 60 ~ 80 , Nomex fiber (Nomex) Good heat resistance, chemical resistance, but at high water the flue gas , its temperature will be reduced to 204 150 .
Nomex fibers than polyester fiber has good heat resistance, but in the high temperature conditions, chemical resistance worse. Polyphenylene sulfide (Ryton) with a high temperature and acid corrosion in a good performance for flue gas dust, but poor ability of antioxidants ; polyphenylene imide fiber although you can make up for its shortcomings, but hydrolytic stability is not satisfactory . As a " plastic" Teflon fiber has the best chemical resistance, but more expensive.
In the selection of the filter when Behe according to the chemical composition of dust and gas , to seize the main factors , comprehensive consideration .
3, according to the nature of selection dust
( 1 ) Dust wetting and adhesion . Dust wetting, infiltration is accomplished by capillary action is formed between dust completed , the atomic chain with the dust , the surface state and the liquid surface tension , etc. which can be used to characterize the wetting angle . Typically less than 60 ° by said hydrophilic , larger than 90 ° by hydrophobic . When the moisture absorbency of dust increases, the particle aggregation force , viscous force increases , fluidity, chargeability decreased, the adhesion to the surface of the bag , over time , cleaning failure , the dust cake compaction. Some dust such as CaO, CaCl, KCl, MgCl2, NaCO3 other after moisture further chemical reaction, the nature and morphological changes occurred , called deliquescence. After the dust deliquescence paste lived bag surface , which is the most taboo baghouse .
For wetting, deliquescent dust, in the selection of filter media should pay attention to smooth , lint-free and water-repellent , which the membrane filter media and plastic burn-in board for the best.
Many strong moist dust adhesion is strong, in fact, wet and sticky are inextricably linked . For baghouse If adhesion is too small, will lose the ability to capture dust and dust adhesion also caused excessive condensation , cleaning difficult. For the adhesive should be used equally strong dust filament lint fabric filter , or surface singeing, calendering , mirror handle needle felt filter , for impregnated, coated, coating technology should be fully utilized . Speaking from the filter material , nylon, fiberglass better than other varieties.
( 2 ) Dust flammability and electrical charge . Some dust concentration in a specific state in which the air in the case of spark- ignition or explosion . Flammable dust with a particle size , composition, concentration , heat of combustion and the combustion rate and other factors . The smaller the particle size , specific surface area , the more easily ignited . An important condition for dust explosion is a confined space , in this space, its LEL generally tens to hundreds of g / m 3 , dust and combustion heat of combustion higher the speed , the greater its explosive power . Dust fire or explosion fire is usually caused by friction sparks, static electricity sparks, hot particulate matter caused hazards which charge the maximum . This is because the fiber filter is usually easy to charge , if the dust simultaneously charge could easily produce sparks, so for ease of charged combustible dust such as coal , coke , aluminum powder and magnesium powder , etc., should be choose flame retardant filter and conductive media.
Generally believed that the oxygen index greater than 30, weaving fibers of the filter , such as PVC, PPS, P84, PTEF so is safe , and for oxygen index of less than 30 fibers, such as : polypropylene, nylon , polyester imide until the filter can be using fire retardant impregnation . Eliminate electrostatic filter is defined filter fibers mixed conductive fibers in the warp or weft filter conductive properties , the resistance is less than 10 9Ω. Commonly used conductive fibers are stainless steel fibers and modified ( carburizing ) chemical fibers. Comparison, the former stable and reliable electrical conductivity , which after a certain time conductivity Yi recession. Conductive fiber base fibers mixed with about 2% -5 % .
( 3 ) the flow and abrasive dust . Dust flow and friction resistance is strong, wear the bag directly and reduce service life. Surface roughness , surface area of the diamond particles of irregular friction smooth spherical particles greater than 10 -fold. The dust particle size of about 90μm maximum wear resistance , and when the particle size is reduced to 5-10um wear has been very weak . Wear and flow rate of 2-3 th power is proportional to particle size of 1.5 , thus μm, and the uniformity of air flow velocity must be strictly controlled . In common dust , aluminum , silicon , coke powder , toner, sintered ore , etc. are highly abrasive dust . For abrasive dust filter should use good wear resistance .
Dust filter wear parts and a variety of forms , based on experience , wear more in the lower part of the bag , this is because the upper bag filtration rate is low , gas dust concentration is small reason.
For strong grinding dust , the choice of filter media should pay attention to three points:
1 ) chemical fiber better than glass fibers, glass fibers extruded superior general fiberglass, thin, short , rolled fiber is better than thick, long , smooth fibers.
2 ) needle felting compound is appropriate ways to strengthen exchanges between networks of fibers , fabrics with satin fabric best, brushed fabric surface also improve the wear resistance of the measures , but felt material , satin fabrics and onwards cashmere filter will increase the value of the resistance .
3 ) For ordinary filter surface coating , calendering and other post-processing can improve the wear resistance . For glass fiber filter , silicone oil , graphite, PTFE resin treatment can improve the wear folding . But the membrane filter media for abrasion resistance and strong condition , the film will be prematurely worn , loss of coating effect.
4 . Press the dust cleaning mode selection
Baghouse cleaning method is to select the filter structure is another important factor varieties , different ways of cleaning bag filter cleaning due to the energy , the bag deformation characteristics of different varieties should use a different structure filter .

( 1 ) Mechanical Vibration class baghouse . Is the use of mechanical devices ( including manual , electromagnetic vibration , pneumatic ) generates vibrations of the bag cleaning baghouse . Such dust feature is applied to the kinetic energy of the dust layer less and more frequently , thus requiring the filter thin and smooth , soft texture , is conducive to transfer vibration wave in the filter surface to form a sufficient rapping force . Should be selected by the chemical fiber satin or twill fabric , thickness 0. 3-0. 7MM, mass per unit area 300-350G/M2, filtration speed 0. 6-1. 0M/MIN, for small units can be increased to 1.0 - 1. 5M/MIN. ( 2 ) sub-room cleaning class baghouse . Use of sub- chamber structure , the use of the valve chamber by switching to form reverse flow cleaning , or bulging of the bag deflated bag filter cleaning . It has two states and three state of the points, the number of cleaning 3-5 times / H, dust cleaning power comes from the capital with the main body of the pressure , it comes on special occasions anti-hair momentum. A low kinetic energy cleaning type filter should be used in light, soft texture , easily deformed and dimensionally stable thin filter, such as 729, MP922 filter. Filtration rate and mechanical vibration class dust fairly . Sub-room cleaning filter baghouse having inner and outer filter of the points, no difference in choice of filter media . Commonly used for medium-sized round dust bag, no frame , pocket diameter 120-300MM, bag long diameter of 15-40:1 , preferred satin ( or twill ) woven filter media, can also be used for special occasions base strengthen thin needle felt cloth filter, thick 1. 0-1. 5MM, mass per unit area 300-400G/M2; common flat for small dust bag, diamond bags or honeycomb -shaped bag, must take a supporting frame , the preferred anti- grindability , breathable thin needle felt filter , mass per unit area 350--400G/M2. Can also be used double or double weft fabric filter . ( 3 ) Vibration Blowback with class baghouse . Refers to both vibration and reverse flow cleaning dual role baghouse . Vibration loosening the dust cake , reverse air flow so that dust out . With each other in two ways , to improve the cleaning effect , especially for the fine particles sticky dust . Such dust filter selection principle is substantially the same sub-room cleaning dust category to choose satin ( or twill ) woven filter media based. With the needle felt the level of technology and product quality improvement, the development trend is the choice of fabric to enhance dimensionally stable thin needle felt. ( 4 ) Cleaning nozzle type baghouse. Cleaning dust blower to do is to use the power in the dust filter state, followed by moving the nozzle jet filter bag , forming a strong reverse flow of the baghouse filter bag cleaning , cleaning a moderate kinetic type . In the baghouse cleaning nozzle having rotary cleaning, reciprocating sliding blowback gas ring several forms. Reciprocating rotary cleaning and cleaning baghouse dust collector has adopted framed bags outside the filter flat form, structure compact. Such optional filter requires relatively soft, structural stability, good wear resistance filter, needle felt filter priority for medium thickness, mass per unit area of 350-500G/M2. Gas ring slide cleaning bag filter bag filter class belong nozzle cleaning a special form , using circular inner filter bag, slot-shaped nozzle for the ring , sleeve moves up and down outside the circle bags blowing . Requires selection of thick, abrasion resistance, good rigidity, lint filter, should use compressed felt and needle felt, because the bag badly worn, such dust rarely used. ( 5 ) Pulse jet baghouse class. Refers to the compressed air as power, the use of pulse jet institutions in an instant release compressed air flow speed induced secondary air injection multiples bag to rapid expansion, relying on shock and vibration, and reverse flow cleaning baghouse, is a high kinetic energy cleaning type. It is usually framed circular outer filter bag or flat bag. Requires selection of thick, abrasion resistance, Zhang Liqiang of the filter, the preferred fiber needle felt or compressed felt filter, mass per unit area of 500-650G/M2.

 

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