What Is a Pocket Filter?

Bag filter is a multi-purpose filtering equipment with novel structure, small size, easy and flexible operation, energy saving, high efficiency, closed work and strong applicability. The bag filter is a new type of filtration system. The inside of the bag filter is supported by a metal mesh basket. The liquid flows in from the inlet, flows out from the outlet after being filtered by the filter bag, and the impurities are trapped in the filter bag. After replacing the filter bag, it can be used continuously.

The bag filter is a pressure filter device. It mainly consists of the filter cylinder, filter cover and quick opening mechanism, stainless steel filter bag reinforcement mesh and other major components. The filtrate flows into the filter bag from the side inlet pipe of the filter housing. The filter bag itself is installed in the reinforced mesh basket. The liquid can penetrate the filter bag with the required level of fineness to obtain qualified filtrate, and the foreign particles are intercepted by the filter bag. The machine is very easy to change the filter bag, and the filter has almost no material consumption.

The bag filter has many advantages such as reasonable structure, good sealing performance, strong circulation ability, and easy operation. In particular, the probability of side leakage of the filter bag is small, which can correctly guarantee the filtration accuracy, and can quickly change the filter bag, which reduces the operating cost. The inner and outer surfaces of the filter are solved by mechanical sandblasting, which is average and easy to clean. We know that the filtering method adopted by the bag filter is the side-in and side-out method, and the side-in and bottom-out method can also be adopted. The filtering liquid medium is pressed into or drawn into the bag filter barrel through the pressure in the pipeline. The liquid medium to be filtered is filtered through the electro-polishing punching to support the filter bag supported by the filter blue, and the changed solid and liquid respectively reach the result of the liquid medium being filtered.

The structural design of the bag filter is that the top cover and the filter cartridge are sealed and locked by four sets of rocker ring bolts, so that the filter can withstand extremely high filtering pressure and water hammer pressure impact. The bag filter is composed of a filter cartridge, a filter basket and a filter bag. The structure is compact and simple; the liquid to be filtered enters through the filter inlet and flows into the filter bag. After being intercepted by the filter bag, it flows out from the filter outlet. . The inlet and outlet design of the bag filter generally adopts the side-in and bottom-out method to facilitate cleaning. ^[1]

There are the following types of bag filters: single bag filters, multi-bag filters, rocker bag filters, high-precision bag filters, etc. The filter accuracy is in the range of 1-10 microns. ^[1]

1) The probability of side leakage of the filter bag is small, which effectively ensures the filtration quality.

2) Bag filter can carry greater working pressure, low pressure loss, low operating cost, and obvious energy saving effect.

3) The filtration accuracy of the filter bag has been continuously improved, reaching 0.5 m.

4) The bag filter has a large processing capacity, a small volume, and a large dirt holding capacity.

5) Based on the working principle and structure of the bag filter system, it is convenient and quick to replace the filter bag, and the filter is free of cleaning, saving labor and time.

6) The filter bag can be used repeatedly after cleaning, saving costs.

7) Bag filter has a wide range of applications, flexible use and various installation methods. ^[1]

The bag filter is easy to operate. When using it, you only need to install the filter bag with the required level of fineness in the filter cartridge, check whether the O-ring seal is intact, and then tighten the ring bolt of the filter cap to start working. After the pump is started, the pressure gauge on the filter rises slightly. The initial pressure is about 0.05MPa. As the use time increases, the filter residue in the cylinder gradually increases. When the pressure reaches 0.4MPa, the cylinder cover should be stopped and the filter bag should be checked for residue In some cases, the replaceable filter bag can be used continuously (the filter bag can be reused by cleaning). The filter pressure is generally adjusted to 0.1-0.3MPa, which can be adjusted through the return line or the return valve on the pump. Excessive filter pressure will damage the filter bag and the protection net, which requires extra attention. Main uses: paint, beer, vegetable oil, medicine, chemicals, petroleum products, textile chemicals, photosensitive chemicals, plating solution, milk, mineral water, thermal solvents, latex, industrial water, sugar water, resin, ink, industrial wastewater, fruit juice , Cooking oil, wax, etc. China has many industrial chains, low concentration of production in the industry, low R & D capabilities supporting high-end products, and low level of manufacturing technology in the bag filter industry. The import and export trade deficit continues to expand. As a result, the trend of polarization in the brand camp has expanded.

First, daily use

The filtration system at work needs to constantly check the pressure difference between the inlet and outlet. When the pressure difference reaches 0.05-0.1Mpa, the filter bag should be replaced in time to prevent the pressure difference from breaking through the ambassador's filter bag and damage to the support net.

Second, open the filter cover properly

Warning: Do not open the cover under pressure in the bag filter, otherwise the remaining liquid may be ejected, causing liquid loss and personal injury.

So please do it in the following order:

1) Close the input valve; when there is pressure at the outlet, close the output valve.

2) After confirming that the pipeline connected to the exhaust valve has been connected to the safety place or the suction port (especially pay attention when filtering toxic and corrosive liquids), open the exhaust valve to prevent the liquid from causing harm to workers and the surrounding environment. Pollution.

3) Check the pressure gauge to make sure the internal pressure is 0. At this time, the bag filter should be separated from the pipeline system.

4) If there is a drain valve, confirm that the drain fluid is connected to the recovery place, and open the drain valve; wait for the remaining liquid in the bag filter to drain through the drain valve, and close the drain valve. This discharge can be done in conjunction with pressurization (refer to the pressurized discharge process).

5) Unscrew the upper cap and lift the upper cap. The multi-bag filter needs to be rotated through a certain angle.

Third, replace the filter bag

1) High-efficiency filter bags are made of fine fibers. These materials have weak hydrophilicity. The surface of the fiber will not be wetted with water, so like other filter elements using the same material, it must be wetted with another liquid with a lower surface tension before use. Before installation, you must immerse the filter bag in the pre-humid solution that matches the filter liquid for several minutes.

2) Open the upper cover of the bag filter.

3) Hold the cover firmly and carefully remove the filter bag.

4) Put in a new filter bag, please refer to the installation process.

Monitoring the quality of filtration

When the liquid input pressure is stable, the filtration quality is closely related to the pressure difference in the filter bag. If the pressure difference is too large, it means that the filter pore diameter of the filter bag is blocked and the filtration speed is reduced. Therefore, we recommend that when the bag filter starts to work, the pressure difference should be checked regularly, and the time for replacing the filter bag should be determined by the pressure difference displayed on the front and rear pressure gauges. Generally, the filter bag can withstand a pressure of 0.5-1Kg / cm2 0.1Mpa), when the pressure difference reaches this interval, the filter bag should be replaced in time to prevent the filter bag from rupturing and affect the filtering effect.

If the differential pressure drops suddenly, stop filtering immediately and check for leaks.

V. Pressurized discharge of residual liquid

When filtering high-viscosity liquids, compressed air can be passed through the exhaust valve to accelerate the discharge of residual liquid and shorten the waiting time. Its device is shown in the figure. Please note: The air used for pressurized discharge must be stable and the pressure should not exceed the working pressure of the filter.

The steps are as follows:

1) Close the input valve.

2) Open the intake valve.

3) The gas is introduced into the bag filter, and the remaining liquid is exhausted under pressure.

4) Check the outlet pressure gauge to confirm that the gauge pressure is equal to the pressure of the compressed air; confirm that no liquid flows out of the outlet.

5) Close the intake valve.

6) Open the exhaust valve slowly; the residual liquid at the outlet of the exhaust valve sprays out, it must be led to a safe place or the filter suction port.

7) After exhausting the compressed air, close the exhaust valve. At this time, there should be no pressure inside the filter, and the cover can be opened.

Six, cleaning bag filter

If the Shanghai Runhe bag filter continues to filter the same liquid, there is no need to clean it. However, if other types of liquids are filtered, the machine must be cleaned before use.

Maintenance and replacement of seals

Maintenance: The O-ring should be placed in the O-groove when used to avoid deformation of the O-ring. If it is not filtered, the O-ring must be removed and wiped clean, otherwise the residual liquid will adhere to it after solidifying. The surface causes hardening and poor sealing.

Replacement: If the O-ring is worn or damaged, please replace it in time. When replacing, select O-rings of the same model.

Special statement:

1. Under normal use, the filter and support net are guaranteed for one year. If it is damaged due to improper use, it is not covered by the warranty.

2. The maximum design pressure of a standard bag filter is 1.0Mpa, except for special specifications with a recommended maximum working pressure of 0.5Mpa.

3. The maximum design pressure in the jacket of the bag jacket filter is 1.0Mpa, and the maximum recommended working pressure is 0.6Mpa.

4. The design pressure of the multi-bag filter is 1.0Mpa, and the maximum recommended working pressure is 0.6Mpa. ^[1]

When installing, follow these steps:

1. Place the bag filter on the station to be filtered, connect it to the inlet or outlet flange or pipe, and fix it; block the exhaust port, or configure an exhaust valve. Jacket type connection heat insulation heat source.

2. Put the metal inner net into the bag filter gently so that the neckline of the inner net matches the mouth of the bag filter.

3. Place the filter bag so that the ring of the filter bag and the neckline of the metal inner mesh match.

4. Place the O-ring into the O-groove. The O-ring cannot be twisted or deformed. The multi-bag filter is fastened with the filter bag pressure ring.

5. Hold the handle of the upper cover with one hand, and grasp the other end of the upper cover with one hand (turn the top handwheel of the multi-bag filter)

6. After the upper cover is aligned, tighten the two diagonal caps at the same time, and tighten all the caps one by one (use a short stick to be inserted into the loop to tighten).

7. Close the exhaust valve installed on the top of the bag filter.

8. Please check whether the connecting pipes are firm; whether the working pressure is within the allowable range.

9. Open the output valve. When the heat source access valve is opened, the filter temperature rises to the specified temperature.

10. Open the input valve slowly to allow the liquid to slowly flow into and fill the filter, to prevent the liquid from suddenly hitting the filter bag, causing rupture, and then observe whether there is leakage. If no leaks occur, filtration can begin. ^[3]

The damage location of the filter bag is mostly at the bottom of the bag due to the accumulation of material at the bottom of the equipment, and the accumulation of material is mostly caused by the failure of the equipment at the bottom of the bag filter. When the system equipment fails, timely process should be made and the faulty equipment should be timely processed Overhaul, reducing the long-term accumulation of pulverized coal materials in the bag filter, minimizing the damage of the bag, and reducing the difficulty of replacing the bag, ensuring that the overhaul is completed in the shortest time and the production process is restored early. ^[3]

Damage location of bag filter bag

The damage location of the filter bag occurs in the bag and the burning of the bean bag is caused by the problem of material particle size and material distribution method. There are high-temperature particles of various sizes in the filtered high-temperature flue gas whose temperature exceeds 400 degrees or more, which cannot be detected by a general temperature detector. Most of them will settle in the gravity settling chamber, and some high-temperature particles will enter the bag filter through the flue gas pipeline at high speed with the air flow. If it is a polycondensation fiber such as polyester, polypropylene, PPS and other filter bags, when there is less dust on the surface of the filter bag, high-temperature particles will burn through the filter bag and form irregular round holes. When there is more dust on the surface of the filter bag, the high-temperature particles will not burn through the filter bag, and deep-color baking marks will be formed in the filter bag. This requires the operator to strictly control the relevant process indicators during the production process to ensure that the materials meet the relevant process requirements to ensure the stable operation of the equipment.

The damage location of the filter bag is mostly caused by the failure of the backflush system. Excessive backflushing pressure of the bag filter and eccentricity of the spray nozzle can cause this situation. After this happens, the spray system of the bag filter should be inspected in time, and the spray pressure and the spray port angle should be adjusted to ensure the stable operation of the bag filter. ^[3]

Method for judging shrinkage of bag filter bag

Each type of bag filter has its own special molecular composition and the use temperature is also very different. When the filter's use temperature limit is exceeded, the filter bag will shrink and cannot be filtered, and even the bag cage cannot be pulled out. There are several types of shrinkage of the filter bag:

(1) The bag cage in the dust collector is higher than the filter bag, sometimes on the top of the pipe, indicating that the filter bag is shrinking;

(2) The cage in the filter bag cannot be pulled out (except for deformation of the filter bag), indicating that the filter bag is contracted;

(3) The bottom of the filter bag is broken by the bag cage, indicating that the filter bag is shrinking;

(4) The filter bag becomes darker (except for corrosion). ^[3]

Blockage of bag filter and its countermeasures

(1) The main reasons for the clogging of the filter bag are too high filtration speed, too fine dust, sticky dust, poor cleaning of the filter bag, paste bag, dew condensation, and sclerosis. If the filtering wind speed of the dust collector exceeds the design standard of the filter bag, it is easy to cause the fine dust in the flue gas to enter the inside of the filter bag fiber, and the filter bag blocking resistance will increase. It is a better method to use coated filter material, coated filter material or pre-coating treatment on the surface of the filter bag. For sticky dust, you need to reduce the filtering wind speed, or increase the pressure of pulse blowing, or use offline pulse cleaning filter bag method, but the better method is to increase the filtering area, reduce the filtering wind speed, and extend the filter bag. Service life.

(2) Poor dust removal of the filter bag mainly includes frequent dust removal times and excessive dust removal time. Excessive frequency of cleaning and excessive pressure for cleaning can easily loosen the filter bag's fiber structure and increase the fine dust in the smoke to block the filter bag. If the cleaning time is too long, the initial powder layer on the surface of the filter bag will be washed away, which will cause the filtering accuracy of the filter bag to decrease. If the dust removal time is too short, the dust on the surface of the filter bag has not been completely dusted, and then the filtration starts. The dust gradually accumulates on the surface of the filter bag, causing blockage of the filter bag. To solve this problem, you can pass several times. Adjust the spray controller after trial operation.

(3) Moisture is the biggest cause of filter bag clogging. The reason for containing water is usually condensation at low temperatures, especially when dealing with high temperature flue gas. In this case, the following methods can be used to prevent: avoid improper startup; avoid Switch on when the resistance of the dust collector is large; switch on below the dew point. The dust collector operates below the dew point, which is prone to problems. If the air intake is unevenly distributed, it is easy to cause local corrosion of the dust collector housing. Therefore, the dust collector should be kept below the dew point. If startup at low temperatures is unavoidable, a thermal insulation device such as steam or electric heating should be used.

(4) Air infiltration. Air infiltration often occurs in the flange of the dust collector, the access door or the movable device of the dust collector. If the seal is not tight, the outside air enters the dust collector. When handling high-temperature flue gas, a low temperature zone will be generated inside the dust collector, resulting in low temperature Condensation everywhere can corrode the dust collector and cause paste bags or sintering of the filter bag. ^[3]