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The key points of design of bag type dust collector
2014/5/9 閱讀次數:[1214]
The working mechanism of bag type dust collector is dust containing flue gas through the filter material, the dust is filtered, the filter material to trap coarse dust mainly depends on the inertial collision, collecting a fine dust mainly by diffusion and sieving effect, the dust filter layer also has a certain degree of filtration.
The merits of bag filter design involves many factors, this paper introduces the design of bag type dust collector from the following factors.
1, volume
Air volume determines the sizes of bag type dust collector. The general air volume in air condition. Design must pay attention to the use of the duster places and flue gas temperature, if the temperature of flue gas treatment of bag type dust collector has been determined, and the gas and take dilution cooling, air volume but also consider the increase the quantity of air dilution; consider the future technological change, air volume design refers to the value to increase the insurance factor of 5% ~ 10% in normal air basis, otherwise the future once the adjustment of process increases the air volume, the filtration rate of bag type dust collector will increase, so that the device resistance increases, or even shorten the service life of the filter bag, also will become the other fault frequency sharply rising reason, but if the insurance coefficient is too large, will increase the cost of investment and operation of dust collector; filtration velocity the types and characteristics of bag type dust collector, filter different have the very big difference, air volume is determined, the filter area can be determined according to the filtration velocity to determine the required.
2, the use of temperature
Using the temperature of bag type dust collector is an important basis for the design, the use of the designed temperature and the deviation, will lead to serious consequences, because the temperature under the following two conditions: one is to allow different filter material the highest temperatures (instantaneous temperature and long period running temperature) are strictly limited; two is for to prevent condensation, gas temperature must be kept above the dew point of 20 ℃. The high temperature gas, must take the cooling to the filter material can withstand temperatures, there are a variety of ways of cooling, more typical of a natural wind cooling, forced air cooling, water cooling, the concrete can be design according to different process and cooling temperature, layout size requirements.
3, the gas composition
Except in special circumstances, gas treatment of bag type dust collector, mostly air or flue gas, usually under the design of bag type dust collector according to calculation of air, only in the design calculation and cooling device density, viscosity, specific heat parameters related to wind power performance and pipe resistance. When, before considering the gas composition. In many cases the flue gas in the flue gas contains water, with the increase in water, the resistance of the equipment bag type dust collector and fan energy change. Water content in dust contained gas, can be determined by the measured, can be calculated according to the combustion, material balance cooling. There is no corrosive gas in the flue gas is the factors to be considered in decisions filter, dust collector shell material and anticorrosion selection. In addition, if the toxic gases in flue gas, generally is the trace, the performance of the device does not have much impact, but in dealing with such dust, bag dust remover must use the structure does not leak, but also to regular maintenance, regular maintenance, avoid the toxic gas leakage accident.
4, entrance dust concentration
Entrance dust concentration is often expressed as standard state volume dust quality, on the entrance dust concentration, the design of bag type dust collector should be considered as follows
(1) the resistance of the equipment and the cleaning cycle. Entrance dust concentration increased filter area, the same case, the resistance of the equipment is also increasing, in order to maintain the resistance of the device is certain, the cleaning cycle is shortened correspondingly;
(2) wear filter and box. With a high concentration of strong wear in the dust, the wear volume and the dust concentration is proportional to, in the precipitator entrance should guide wear processing technology, such as sintering dust, alumina, silica powder etc.;
(3) the pre filter and filtration velocity. In the entrance dust concentration under the condition of high filtration velocity, should design and pre filter design is relatively low, but if the design has the structure of primary settling function, also can cancel the pre dust remover;
(4) and ash discharging device. The ash is discharged all dust collected by energy as the standard, the amount of dust exhaust, is equal to the entrance, outlet dust concentration and the difference of air volume product, design of multistage ash discharge device capability should be more than a one level below the ash discharge capacity shall prevail.
5, the outlet dust concentration
Outlet dust concentration must be below the laws and regulations and national hygienic standard for environmental protection of the specified value. Bag type dust collector outlet dust concentration, according to the structural form, dust collector, dust filter types vary according to the nature, commonly between 1 ~ 50mg/m3. To contain lead, cadmium and other hazardous substances under the requirements of export concentration, particularly low, according to the purpose and characteristics of different process design, selection of different bag type dust collector structure and filter material.
6, the dust properties
Have a great influence on the properties of design of dust bag filter for dust, some special nature, effective measures should be taken according to the design experience.
(1) adhesion and cohesion. Adhesion and cohesion of dust into the bag filter, dust slightly agglomerated will particles become larger, the accumulation in the surface of the filter bag dust to be shaking in the process, can also continue to be condensed, cleaning efficiency and the amount of dust filter and dust adhesion and cohesion of. Therefore, the design of adhesion and cohesion of dust is very significant, or almost no adhesion and cohesion of dust, dust species, according to different purposes, take different measures according to design experience.
(2) tube blowing and box blowing. Tube type injection is a blowing pipe at the top of each row of filter bag, belonging to the order that is blowing, blowing air to each bag injected through the nozzle pipe, blowing the aperture of each are not identical, ensure that the dust cleaning strength uniform, for large long bag pulse dust collector tube blowing structure is much better than that of box type injection. Box type injection without blowing pipe, belonging to the disordered blowing, cleaning air by pulse valve is directly injected into the upper box and the pressure, then the energy transfer to the chamber to realize each bag cleaning; box type pulse jet dust catcher, in different parts of each bag, ash deposit in the larger strength the difference, and the general gas consumption amount is larger, the bag length is restricted, airtight dust cleaning effect of the off-line valve on the larger, so the box blowing for small dust collector.
11, the ascending velocity
In the dust collector bag inside, the actual speed of low-end dust containing gas will rise, is the ascending velocity. The ascending velocity of gas containing dust filter bag filter and dust by abrasion due to pulse cleaning out along with the air return filter bag dust bag surface has an important influence. The ascending speed is the maximum speed in cyclone flue gas should not exceed, meet and exceed the speed, particulate matter in flue gas will be worn away bag or dust, and even lead to equipment running resistance is too large.
Bag type dust remover filtration time for inner filter and filter two kinds, the former the dusty gas flows from internal to external bag, the latter the dusty gas flows from external to internal bag bag.
The filter bag filter air rising velocity calculated:
Vk = Sa Vc/S
Type Vk -- precipitator air velocity, m/min;
Sa -- a single bag filter area, m2;
Vc -- the filtration rate, m/min;
S -- the bag mouth of the cross-sectional area, m2.
External filtering bag type dust collector airflow rate calculated:
Vk =Qv/ (SA-nS)
Type Vk -- precipitator air velocity, m/min;
Qv -- volume bag room, m3/min;
SA -- the bag chamber bag lower section area, m2;
N -- the baghouse filter bag number, a.
Filtration velocity and flow rate two in the bag type dust remover everywhere should be maintained in a certain range. If the filtering velocity selection or compartment distributing not all, will affect the life of the filter bag, the same air updraft quickly, improper selection or chamber rise speed is not uniform, will also affect the service life of the filter bag. Therefore, in the design should not only reasonable design, filtration velocity in the design not only to design a reasonable and diversion technology makes the air distribution uniformity, but according to the dust particle size, concentration, working conditions of reasonable selection of design flow rate, to ensure that lengthen the life of bag filter.
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