The choice of the felt

Filter bag is the core of the filter assembly , bag making material directly determines the bag house performance parameters , such as the size of dust removal equipment , dust removal efficiency , emission concentration , running resistance , the use of life and other indicators. Therefore , when choose the needle felt , some factors must be considered (such as dust concentration , temperature, humidity , pH ) and the nature of dust ( such as particle size , viscosity, abrasive ) , etc. , correctly and appropriately to choose needle felt , in order to meet the needs of dust removal equipment .

1.1 Principles of selection

Felt is generally based on gas and dust filter bag nature and way of cleaning bag choices, options, should follow the following principles:
( 1 )Reasonable structure , trapping rate
( 2 ) Peeling , easy cleaning , easy to scale
( 3 ) Suitable permeability , low resistance, high filtration precision
( 4 ) Have sufficient strength, dimensional stability
( 5 ) Has good heat resistance , chemical resistance , resistance to oxidation , hydrolysis resistance and wide adaptability and other properties
( 6 ) A wide range of sources of raw materials , stable and reliable performance
( 7 ) Low price , long life.

1.2 According to the filter characteristics to select the felt

1.2.1
Polyester: Polyester filter is usually applied to the lower temperature of the occasion , no coated in normal circumstances, only when the discharge requirements of less than 30 mg / Nmm³, or very fine dust , humidity when considering coated .
1.2.2
PTFE: Polytetrafluoroethylene (PTFE) , also known as Teflon , stretched into a powerful multi- microporous material , pore size 0.1μm ~ 2.0μm, porosity of greater than 80% , with excellent resistance to chemical corrosion in sulfuric acid , sodium hydroxide and atomic industry strong corrosive uranium pentafluoride will not corrode and can be cold and heat , prolonged use at -200 ℃ ~ 250 ℃, there are very good electrical insulating properties and surface smoothness characteristic. PTFE coating and other media tend to be technical or acupuncture treatment , in order to improve collection efficiency and extend using life.
1.2.3
Nomex:Nomex felt can be used in high temperature , dust particles coarser occasions. Nomex high temperature resistance than glass bending, high injection pressure can be used , with a pulse valve can jet more bag .
1.2.4
Fiberglass High temperature performance glass fiber , tensile strength , acid and alkali and water-repellent are good, but there is no bending glass fiber filter , installation and operation of the easily damaged , can not be subjected to high pressure cleaning of the bag cage higher and other shortcomings.But under the current conditions of glass science and technology through good handling and application of coating technology plus , making filtration performance is excellent , especially in foreign countries has been widely used in Europe and America .
1.2.5
P84 :P84 filter bag is an Italian company developed a comprehensive performance are superior fibers woven into the filter. Its high temperature performance slightly inferior to glass fiber, a good anti- acid-base properties . However, due to its special fiber structure is usually not coated , and therefore less efficient than filtration membrane bag .

1.3 Selected in accordance with the dusty gas properties

1.3.1
Gas temperature Dusty gas temperature is an important factor in the choice of felt . Usually less than 130 ℃ of dust and gas called ambient gas , dust and gas more than 130 ℃ called high temperature gas , so the felt can be divided into two categories : the felt below the normal temperature of 130 ℃ and 130 ℃ higher than the high temperature felt Bag temperature of the ” long-term continuous use temperature” and ” instant short-term temperature .” ” Long-term continuous use temperature ” means the felt can be applied to long-term continuous operation temperature , the temperature should be in order to choose the bag . ” Short-term instantaneous temperature” means a bag which must not exceed the maximum temperature of 10 min per day , for too long, the bag will soften deformation.
1.3.2
Gas Humidity Dusty gas in relative humidity divided into three states : the relative humidity at 30 % or less dry gas , relative humidity between 30% to 80 % of the general state of the gas relative humidity is above 80% humidity gas. When the gas humidity , and in the high temperature state , especially dust containing SO2 gas , the gas cooling will produce condensation . This not only makes the bag surface fouling , clogging and corrosion of structural materials , and therefore need special attention.
For moisture gas bag should be chosen in the following in mind:
( 1 ) Moisture trapped gas to the surface of the dust bag wet adhesion , especially for water absorption, deliquescence and wet dust can cause paste bag . For this purpose, it should be used in nylon with smooth surface such as fiberglass , long fibers easy cleaning of the bag , and the bag should be for the use of silicone oil , fluorocarbon resin for impregnation treatment , or acrylic surface in the bag , polytetrafluoroethylene a coating treatment and other substances . Burning plastic plates and film material has excellent moisture resistance and ease of cleaning performance , it should be preferred as the humidity gas.
( 2 ) When the presence of high temperature and humidity will also affect the temperature of the bag , especially for nylon, polyester , imide and other poor hydrolytic stability of the material .
( 3) filter dusty gas inlet temperature should be above the gas dew point 10 ~ 30 ℃.
1.3.3
Chemical properties gas.In various furnace flue gas and chemical gas , often contain a variety of chemical constituents acids, bases, oxidizers , organic solvents, etc. , and often subject to cross many factors temperature and humidity .Therefore , in the selection of the felt, it must be based on the chemical composition of dust and gas , to seize the main factors were considered.

1.4 Selected according to the property of the dust

1.4.1
Dust wetting and adhesion Dust wetting, infiltration can be used to characterize the wetting angle , typically less than 60 ° are called hydrophilic , of greater than 90 ° are hydrophobic . Hygroscopic dust when after increasing its moisture , particle cohesion , viscous force increases , flow-ability, charge ability decreases , adhered to the surface of the bag , over time, cleaning failure , dust cake compaction. Some dust as further after CaO, CaCl, KCl, MgCl2, NaCO3 moisture and other chemical reaction, deliquescence paste bag , this is the most taboo felt .Therefore, wettability , deliquescence dust , the choice of the bag should pay attention to the felt smooth , lint-free and water-repellent , which the coated and plastic burning plate for the best. For adhesion strong dust should also not selected filament pile fabric bag , or surface singeing , calendering , mirror -treated felt for dipping , coating, coating technology should be fully utilized .
1.4.2
Flammable dust and chargeability Some dust concentration in a particular state , in the air in case of fire or explosion spark occurs . Dust combustion or explosion ignition source is usually caused by friction sparks, static electricity spark , caused by hot particles , wherein the charge of damaging. This is because the synthetic bag is usually readily charged , if the dust is charged at the same time and it is easy to produce sparks. So for combustible dust and easy to charge as coal, coke , aluminum powder and magnesium powder , etc. , should choose flame retardant felt and a conductive felt . Such as PVC, PPS, P84, PTEF and other oxygen index greater than 30 fiber woven bag , and for fiber oxygen index of less than 30 , such as: polypropylene, nylon , polyester , imide . For easy charge of the bag can also be mixed with conductive fibers in one fiber filter bag , filter bag in the warp or weft having conductive properties , the resistance less than 109 Ω. Commonly used conductive fibers are stainless steel fibers and modified ( carburizing ) chemical fibers.
1.4.3
Dust flow and friction .When the dust flow and strong friction , wear felt will directly reduce the service life . Rough surface , irregular diamond particles smooth spherical surface area 10 times larger abrasive particles . Particle size of 90 μm dust particles of maximum wear resistance , and when the particle size decreases to 5 μm ~ l0 μm wear has been very weak. Abrasion resistance and airflow velocity of 2 to the third power , power is proportional to the particle size of 1.5 , so that the airflow velocity and uniformity must be strictly controlled . In common dust , aluminum powder, silicon powder , coke powder , carbon , a high sintering ore and other abrasive dust . For wear dust bag should use good wear resistance . Dust bag of wear parts and a variety of forms , based on experience , mostly in the lower portion of the bag to wear , so the choice of the bag should be noted:
( 1 ) Chemical fiber better than glass fibers , expanded glass fiber glass fiber superior general , thin , short, curly fibers better than thick, long , smooth fibers.
( 2 ) The feed is appropriate acupuncture felt the way to strengthen the entanglement between the fibers , the best fabric to satin fabric , brushed fabric surface also improve the wear resistance of the measures, but felt material , satin fabric and Fleece bag will increase the resistance value.
( 3 ) For ordinary felt surface coating , calendering , etc. can also be treated to improve wear resistance. For the fiberglass filters were silicone oil , graphite, polytetrafluoroethylene resin folding process can improve the wear resistance . However, when the film bag for extremely abrasive conditions, the film will wear out prematurely , losing film role.