20 methods to improve the performance of bag filter dust collector

As a result, plant operators and owners face one of three possible decisions about their inefficient baghouses:

1. Allow the bag filter to continue to operate without any modification.

2. Purchasing a new baghouse or upgrading the baghouse to a new, more efficient design, such as pulse jetting, can utilize high-efficiency pleated filter elements instead of filter bags and strainers.

3. Make minor modifications or use moderate equipment and tools to improve the operation of the existing bag filter.

These solutions all involve the mechanical part of the baghouse and suggest how to improve the performance of existing designs or upgrades to update the technology. Topics discussed included pipe configuration, rotary valve operation, and particle packing in the hopper. Each of these areas may inhibit overall dust collection efficiency and must be addressed in order to make additional modifications to the baghouse for maximum benefit.

The optimization guidelines are as follows:

1. Design new equipment correctly

Many of today's bag filters have been improperly designed from the outset, which may cause problems throughout the bag's dust removal process. Some of these devices are not well designed or designed to be too small to save money in budget decisions.

One of the most important aspects of a design that is sometimes overlooked is the proper air-to-cloth ratio. This ratio represents the amount of air being processed and the available bag area of the baghouse.

Pulsed bag filter with felt and in-line cleaning can operate at higher air to fabric ratios. The use of woven materials and off-line cleaning shakers and reverse air devices requires more filtration area. The ratio of air to fabric is a very important factor to consider in the design and operation of a baghouse. Inappropriate proportions can result in inefficient operation of the baghouse. Operating at high air ratios can cause many problems, including high pressure drop, insufficient cleaning, and inadequate ventilation at the draft point.

The size of the shaker and reverse air system should not be greater than the air to cloth ratio of 2.5 to 1. Most pulse jet systems should not exceed a 6 to 1 air to cloth ratio (and equipment with glass fiber filter media is much lower). The correct design for the initial installation will definitely save money over the life of the equipment.

2, optimize the pressure difference

The correct operation of the bag filter requires the use of a differential pressure gauge on the entire precipitator. The pressure gauge measures the differential pressure by installing a port on the clean side and installing a port on the dirty side of the baghouse or plenum. A system leak can be detected by indicating a sudden drop in pressure. A sudden increase in pressure means that the filter bag is clogged or the dust particles are agglomerated. The meter can be used for point-of-use or remote installation. U-tube pressure gauges can also be used for the same purpose as pressure gauges, but they are not technically advanced. These can also help identify problems with the damper and bag by indicating the pressure differential across the baghouse.

3. Use on-demand cleaning system

The differential pressure gauge should also be used with the cleaning system. The gauge is monitored using a pressure sensor to determine the cleaning cycle. The meter is manually set to operate between the high and low pressure points. When the differential pressure change of the bag reaches the high pressure point, the cleaning cycle is automatically started. When the low pressure point is reached, the cleaning stops. The ideal spacing between the high and low points should be no more than 1 inch, and the ideal spacing between the two points is 1/2 inch.

The continuous controller enhances the prevention of excessive and insufficient filter bags, thereby reducing airflow, increasing production levels and the life of the filter bag. The measurement sequence controller is used for automatic or manual activation, as well as aborting, using a pre-set bag filter chamber to clean the high and low pressure points. The cleaning cycle is automatically adjusted to match the bag filter load to prevent over-cleaning of the filter bag. The LED sequence controller works in the same way as the unit, but provides a 4-20 mA signal. This signal allows an external monitor or recording device to be used for remote monitoring or to connect to a programmable logic controller.

The reverse air/vibration table sequence controller automatically cycles through the closed damper and periodically opens the damper cycle. The cycle will repeat all cabins and eventually return to the first compartment. The active cleaning cycle is displayed on the timer panel. Cleaning can be scheduled for continuous or on-demand cycling.

All of these meters will help improve control of the system. They are fairly easy to install and cheaper than the benefits they achieve. They also help records the problem areas and how to correct them.

4, appropriate air intake design

The correct intake design is very important because it involves the operation of the bag filter. Many bag filters have a standard design and use "off the shelf" products. Deliver these products to end users who have installed an entrance in the hopper. Some of these designs have baffles on the inlet tube opening to direct the incoming air down to the funnel area.

Airflow into the bottom region of the hopper may cause the particles in the hopper to rotate upward and re-entrain in the filter media. When combined with the feed, the material re-carrying from the hopper produces a higher particulate load on the filter bag. If the feed passes directly through the narrow hopper, excessive wear can occur on the side wall opposite the feed port.

Enlarging the inlet duct before the hopper can reduce the inlet velocity at the inlet. Inside the hopper, the installation of the "trapezoidal blade" baffle produces a more uniform velocity profile in the hopper. Install trapezoidal vane baffles to evenly distribute airflow to the inlet chamber, reducing turbulence and uneven particle loading. Better distribution of the inlet air minimizes the possibility of re-entrainment and reduces the amount of material carried to the surface of the filter bag. These baffles are inexpensive and easy to install and are suitable for most bag filter designs.

5, do not use the hopper for material storage

Many problems occur when the hopper in the baghouse is used to store materials. The main purpose of the hopper is as an entry into the baghouse to facilitate moving the material into the silo or screw conveyor for further transport. When the material is stored in the hopper and has not been removed, serious problems can be caused by allowing the material to be re-entrained into the filter bag.

This re-entrainment may shorten the life of the filter bag due to wear on the lower portion of the filter bag. Material removed from the bag should be removed from the hopper as soon as possible to prevent re-entrainment problems. Material can be moved into the hopper by using a damper or discharge valve.

Even if the hopper is not used for storage, it is still possible to accumulate material on the side walls. These conditions may cause the same problem as previously listed, that is, when dust re-enters the filter bag, the material is completely emptied at one time instead of a stable and uniform flow.

Sound angles have proven to be an inexpensive method to prevent bridging and accumulation by using fluid waves that do not adhere the materials to each other to help fluidize the material. These acoustic devices can be easily installed through a throat or flange mounting system with minimal damage to the hopper and without causing deformation or cracking of the hopper wall at the seam.

6. Improve the operation of the pulse jet device by using the pleated filter element

The pleated filter element provides a simple retrofit for upgrading existing dust collection systems and problem solving systems. The pleated filter element is a one-piece pleated product of spunbonded polyester media that directly replaces traditional filter bags and pouches. This medium is resistant to surface penetration of particulate matter, significantly improving efficiency while operating at pressures significantly below the felt or woven material.

The media is folded and molded into a filter element that increases the filtration surface area on the bag by 100% to over 200%, depending on the size of the existing bag. The unique spunbond media used to make the pleated filter elements are different from conventional felt fabrics. It has a tight pore structure and rigid physical properties to maintain pleats without the need to support the backing material. Therefore, up to three times the filtration area can be installed in the same tubesheet hole to replace the traditional bag and bag cage.

Pleated filter elements offer a very economical alternative because of the enormous increase in filtration area within existing dust collection equipment, as new equipment has to be purchased or expensive. They also offer other substantial benefits that make this a very cost-effective way to improve the performance of existing equipment without major changes.

7, the correct slot hopper screw conveyor direction

At the dust collector with the trough hopper and hopper inlet, the high inlet gas velocity allows the dust to be re-entrained. On these devices where the screw conveyor moves the material to the hopper inlet, the possibility of dust re-entrainment is greater. By design, the material collected in the screw conveyor must be moved to a single discharge point, and as the collector loads the screw conveyor, the material depth in the screw conveyor increases.

When this material is moved to the dirty inlet (the highest speed point in the hopper), it often turns into air and is brought back to the filter bag. This increases the cyclic load in the precipitator and causes an artificial high pressure drop.

An easy way to solve this problem is to flip the screw conveyor and move the discharge point to the other end of the precipitator. The quality of the material now collected is removed from the gas inlet and the recycling of the collected material is eliminated. By not entraining the material, greater airflow and extended bag life can be achieved. The wear of the screw conveyor is also reduced, thereby reducing the maintenance required for the equipment.

8, screw conveyor leakage and emissions

Air locks on the funnel and screw conveyor are necessary. The air brake can be a double rotary valve design, a rotary lock air supply or other means. Rotary air brakes with a diameter of 8, 9, 10 or 12 inches should not exceed 20 RPM. The pocket of the rotary damper may move too fast to cause the material to fall out and be removed from the collection area. In this case, the effect of the rotary damper may be more like a fan than a true air brake.

The relationship between speed and capacity is linear for rotary air locks up to about 10 RPM. At 10 RPM, this relationship reaches 20 RPM at 93% efficiency. Above 20 RPM, this relationship will drop to 65% efficiency. In order to obtain the required 20 RPM, a drive or a double reduction drive via a sprocket must be used.

Screw conveyors that feed the rotary valve can also cause problems. Dust trapped in the hopper may be re-entrained and transported back into the bag. Any screw designed for the dust collector should be used as a feeder. The size of the screw should be 100%. Most problems occur when the screw size is 30-60%. Since the material agglomerates are removed from the compartment by cleaning, the screw can easily run 100%, complicating the dust removal system and overloading the airlock or rotary valve.

The conveyor spiral flight should be cut back to where it did not cross the airlock because it will drive the material directly through the gasket and seal. Flight should be reduced so that materials do not accumulate and accumulate.

9. Correct sealing of the access door

The access door allows maintenance personnel to enter the baghouse device for leak detection, replace the filter bag and properly identify operational problems. These doors require a reliable seal to reduce air bag leakage and heat loss. They also need to be properly sealed to reduce condensation that can cause bag failure and severe corrosion.

Care must be taken to ensure positive contact between the door seal and the door panel to prevent air ingress. Care must be taken to ensure positive contact between the door seal and the door panel to prevent air ingress. Door seal materials are used to help prevent ambient air from entering the baghouse causing metal corrosion and damage to the filter bag. There are a variety of designs to meet all of the specific needs of many applications based on gas chemistry, temperature and door configuration.

Proper use of the door seal is a very inexpensive and easy to install fixture that prevents many problems from occurring. All doors should be inspected and analyzed to determine the material needed to properly seal the door. It should be evaluated on a regular basis and repaired or replaced whenever the baghouse equipment is shut down.

10, adjust the damper installation

The dust cake collected on the filter bag has a variable static resistance to the ventilation system. As the dust on the bag increases, the resistance increases. After the filter bag is cleaned, the resistance is low. In many applications, grain loading quickly forms a powder on the bag, so the fan operates at high resistance and produces a small amount of air. When the load is completed and the dust load is reduced, the fan suddenly operates to resist the reduced resistance and the air volume increases. The resulting high velocity causes small particles to penetrate the fabric, resulting in clogging and venting.

A good advice is to install a damper on the fan that adjusts the pressure change. The damper maintains a larger adjustment volume to the baghouse to protect the fabric from impact. Control based on the static pressure measured at the inlet of the filter chamber will cause the damper to restrict airflow to compensate for the reduced resistance of the clean bag. As the static resistance increases, this will open up more space to allow for more trading volume.

The use of a modulated damper will help the operator of the equipment to better handle the process. This control results in a better filter bag life due to the constant airflow and dust cake on the bag. These dampers have different styles to choose from and should be evaluated based on specific aspects of the process.

11, correctly install the filter bag

Proper installation of the filter bag is important to extend the life of the fabric. The recommended procedure for installing a bag in a pulse jet cleaner is to point all the bag seams in the same direction. This provides a reference point to help identify problems caused by inlet wear. This can be a very useful troubleshooting technique that can provide a history of bag failures.

The edge of the bag with flanges or cuffs folded over the top of the support cage should be checked for smoothness to prevent leakage and bag wear. The seam on the bottom loading bag should be 180° from the crack or gap in the cage. The clips on these bags should be mounted 90° relative to the seams on the bag and in the pockets of the bag cage. The snap pockets that enter the pulse jet at the top should be mounted with the seams all facing the same direction. This identifies areas where problems occur and improves device troubleshooting.

The filter bag installed in the reverse air precipitator should have a seam at a 45° angle to the walkway and the access door, making it easy to verify that the seam is straight and vertical. This also ensures maximum distance between the bags, reducing the possibility of bag and bag wear.

Proper tension is also a key factor in bag performance. Loose, unsupported bags do not provide efficient collection, and the resulting bag and bag wear can lead to premature failure. Excessively stretched bags can cause pressure on the filter bag and shorten the life of the bag. The use of appropriate tensioning tools ensures that all bags are evenly and properly tensioned, eliminating the potential for damage during operation of the baghouse.

On the shaker precipitator, it is recommended to shake the shaker to one side so that all the bags in the row can be tightened. Once this line is installed, the vibrator should swing in the opposite position and the other row of bags should be mounted in a similar manner. This method does not cause any additional pressure on the rocking bearings, bushings or other parts, nor does it cause the bag to be too loose and the bottom bag to wear or the bag to close.

12. Clean air in the compressed air line

Moisture, oil and dirt problems in the compressed air line may affect the cleaning ability of the pulse jet dust collector. When the compressed air of the cleaning filter bag is contaminated, it causes many problems. Premature wear of pneumatic components may result, as these components are manufactured to be most efficient with clean compressed air.

Since the dirty air does not properly clean the filter bag, the pressure drop of the system will also increase. The contaminant pulse falls into the filter bag, which can cause the bag to become back blind and may increase the buildup of material on the bag due to moisture.

The problem of dirty compressed air can be eliminated by using a filtration system that is directly mounted on the compressed air line. Some of these systems can eliminate oil and water in the gas stream, with an efficiency of 99.97% of particles above 0.7 microns. With this type of production, equipment operation can be greatly improved with a small investment.

13, using a 1.5-inch pulse valve

In a pulse jet system, the pulse action used to clean the filter bag is a function of the filter bag impact, rather than a function of the amount of air. The instantaneous release of pulsed air creates a "shock wave" in the bag that must be strong enough to travel the entire length of the bag for complete cleaning.

The 1.5" double diaphragm pulse valve is more efficient than a single diaphragm valve or any small size valve. The first reason for this is that a single diaphragm valve must release all air that is held closed by the diaphragm. This is because the air travels along the length of the pilot duct and escapes through the small exhaust port in the first conductive magnetic valve, which slows the release of the pulsed air to the exhaust port.

The double diaphragm valve can only release a relatively small amount of air, and the small diaphragm is closed by the vent of the first conductive magnetic valve. At the same time, the air pressure that keeps the main diaphragm closed is released through the large exhaust port in the pulse valve, which allows the pulsed air to be immediately released into the blow pipe.

The second reason for the superiority is that the 1.5-inch pulse valve and the blow tube contain a cross-sectional area of 1.76 square inches. The 1 inch pulse valve and blow tube contain a cross-sectional area of 0.88 square inches. In contrast, 15 3/8 inch diameter blowpipe holes contain a combined cross-sectional area of 1.65 square inches. This means that the 1.5-inch pulse valve will provide enough space for the pulsed air to flow unimpeded to all of the blowholes. In contrast, a 1-inch pulse valve or smaller restricts the area that prevents air from flowing into the blow tube bore.

The dual diaphragm valve produces a crisp transient pulse and creates a stronger shock wave in the filter bag. This, in turn, provides more effective cleaning. This change to a 1.5 inch pulse valve is fairly easy to achieve and should save a significant amount of bag replacement costs and possible production losses due to insufficient cleaning of the filter bag.

14, pulse backflush setting

In the pulse jet dust collector, the cleaning function not only removes the collected dust, but also rearranges the bag structure on the remaining dust cake, thereby causing a change in the pressure difference. In devices with high gas velocities, mechanical separation of fine submicron dust may occur, resulting in a very dense powder structure. Dense powders cause airflow resistance and high pressure differentials.

The cleaning sequence can play an important role in reducing material re-entrainment. Pulsating a row (in order) next to another row may result in a fine submicron material migration to the cleaned row. The staggered pulse sequence improves the filtration of the filter cake. An example is pulse line 1, then lines 4, 7, 10, 13, 16, 2, 5, 8, 11, 14 etc. until the entire system has been cleaned up.

The cleaning cycle of the pulse jet dust collector should be designed to produce short, brittle pulses of pulse duration to create an effective shock wave in the bag. This duration is usually set to 0.10 seconds. The frequency of pulse jet cleaning is also critical to proper powder holdup. This frequency can range from 3 seconds to 30 seconds or longer and is adjusted by a potentiometer on the timer panel. The frequency should be adjusted so that the pressure difference across the precipitator ranges from 3 to 6 inches in the water column (75-150 mm).

On a pulse jet precipitator, the pulse frequency can be increased, but the next pulse should wait until the compressed air pressure in the precipitator recovers. This will clean the same pulse force for each row. The recovery of air pressure depends on the ability of the compressed air system connected to the baghouse and the size of the compressed air duct.

15, cloth bag and bag cage

The main cause of the failure of the pulse injection system is the improper cooperation of the filter and the support cage. In order to ensure the normal operation of the pulse jet filter, the fit between the bag and the skeleton is crucial. Too loose or too tight a filter can severely limit collection efficiency and lead to premature failure.

There are many types of bag cages on the market, but care must be taken to ensure that the bag cage structure properly supports the filter bag and optimizes cleaning and efficiency. Variables that are important for review include the number of vertical wires used and what type of annular spacing should be used for proper operation in the dust collection equipment.

16, the blowpipe arrangement

One of the main reasons for the failure of the filter bag in a pulse jet cleaning dust collection unit is the misalignment of the purge tube in the cleaning system. The blow tube is used to provide compressed air cleaning that feeds air into the top of the filter bag and bag cage assembly. If the blow tube holes are not properly aligned with the filter bag, no high-efficiency filter cleaning will occur.

If the blow tube hole is not properly centered, the fabric is subjected to excessive force and a hole may be formed in the top of the filter bag. These holes will eventually cause the bag to fail and need to be replaced. Another potential problem is that the pulse jet cleaning energy is reduced and the filter bag may not be cleaned due to the impediment of the pulse gas at the bottom of the filter bag.

The blower installation and its alignment with the filter should be thoroughly reviewed and changed to ensure proper operation of the equipment. This is a very quick fix that can be easily changed, and it can also produce significant improvements in the system.

17. New filter bags and coatings

A coating is injected into the baghouse to create a porous control layer on the surface of the filter bag. This prevents particle leakage, clogging and problems due to hydrocarbon and moisture carryover. After the entire replacement, the coating should be used to pre-coat all the filter bags, and even the coating can be used continuously to improve the operation of the baghouse.

The best coating available consists of polymorphic particles used to form the initial control layer on the filter bag. The different particle sizes allow the air passage to remain open, keeping the pressure drop to a minimum and maximizing the air flow. A suitable coating can also improve the release of the cake by detaching the dust cake from the bag during the cleaning cycle rather than compressing it into a permanent material. The result will extend the life of the bag, higher airflow, and reduced emissions and pressure drops.

Spark propagation can cause a bag filter to fire. The composition of these coatings is similar to the standard coating, but with the addition of flame retardant chemicals. When the spark comes into contact with the coating, a chemical reaction takes place and the flower is extinguished.

18, using leak detection powder

Many factories in the past and today have taken the time to manually inspect the holes, holes and leaking seams on each filter bag, which takes a long time and is often inaccurate. In addition, structural air leaks in the system (such as weld cracks and improper metal casing covers) cannot be detected unless clearly visible.

A better way to test all of these possible leaks is to use a leak test powder. The leak detection powder is an inexpensive, lightweight phosphor that is directly injected into the baghouse. Since the powder uses the least resistant path, the tracer will accumulate around the source to determine the location of the leak and its severity. Monochromatic light is then used to locate the area where the powder is accumulated. When a leak is found, the phosphor will illuminate under the light. Once the leak is discovered and repaired, the second test should be run in a different color to determine if all leaks have been eliminated.

It should be noted that leak detection powders containing different particle sizes should be used to minimize fabric penetration. This ensures that all leaks will be discovered, regardless of their size, for proper leak identification. There are usually four colors that work better to varying degrees, depending on the application and the dust collected. It is important to choose the right color for each specific application.

19. Maintenance and record keeping

Proper maintenance and recordkeeping play a vital role in the operation of the baghouse. The information collected can help implement an effective preventive maintenance program. Inspection, observation and maintenance documentation will help to improve the efficiency of the baghouse and prevent the plant from becoming non-compliant.

Areas that need to be monitored and carefully recorded include bag filter operation, production processes, food loading or fuel changes. All these variables will have a significant impact on the performance of the bag filter. Pressure drop fluctuations, wash cycle adjustments and emission levels should be monitored and recorded.

Record keeping includes information recorded on a regular basis and information recorded in a specific event. Records that should be kept on a regular basis include a chart record that tracks the pressure drop of the baghouse and the inlet temperature. The system should maintain a chart recorder is compared with the current data baghouse. The system operation report can be maintained every hour during the original system startup to establish initial operational criteria. After the system has been running for a while, its operation is more familiar, and these reports can be reduced to one or two times per shift. Event records are kept at specific times, such as startup, shutdown, baggage check and failure.

All of this information is readily available and is very inexpensive to maintain in the factory. Some useful specific documents include bag filter cloth live reports, bag filter maintenance reports and emergency worksheets.

20, filter bag testing and analysis

The only way to accurately analyze the filter bag during operation is to perform a filter bag analysis by a reputable test facility. The bag removed from the dust collector must be kept in the state it has just been taken out in order to be able to complete accurate test results. The used filter bag is then completely sealed in a suitable container and sent to the test laboratory.

Properly equipped laboratories will provide complete laboratory testing for fabric and dust weight, breaking strength, permeability, batt burst, flexible circulation and chemical analysis to provide troubleshooting for fabric filters. Test reports should also be written in clear and concise language with complete conclusions and recommendations. This information will need to be evaluated based on the device's current operating parameters for proper adjustment.

Some laboratories also provide test program to help select the appropriate filter media bag filter. Baghouse dust particles from a sample can be fully evaluated microns distribution, dust mass volume, and surface area expansion of the overall number of sub-micron and micron size.

The test chamber can then be used to generate accurate inlet concentrations and run a variety of fabrics according to the air cloth ratio of the system design. Collection efficiency and operating differential pressure performance were continuously monitored throughout the test. This evaluation, together with chemical analysis, allows the selection of a suitable filter medium and does not require extensive testing.

in conclusion

There are many variables to consider when optimizing a bag filter. Each bag filter should be designed and installed according to its application, temperature, dust load, micron distribution, chemical composition, air cloth ratio, tank speed and other factors.

When determining the system size or evaluating the system, it is important to consider all parameters. Collecting data over time and recording it is useful for troubleshooting systems as they arrive.