SITE MAP          CONTACT US           ABOUT US          DUST COLLECTOR (HOME)   

Technology of the Dust Collectors Cartridge Filter

Dust Collection Via Cartridge Filtration Both shaker collectors and fabric pulse jet collectors had limited dust collection efficiency when it came to applications such as high density dust from powder coating booths. The high-density dust from these powder-coating booths caused the fabric pulse jet collectors to operate at a high pressure drop and thereby increased compressed air requirements for cleaning. Another problem was that exhaust air could not be recycled into work areas due to high amount of dust penetration into adjacent bags. Cartridge dust collectors overcame the above problems effectively.

Do You Think You Need a Cartridge Dust Collector? Are you sure its what you need? How do you really know? Find out for sure. Ask an expert. Just click the orange button and answer a few questions.  An expert will review your responses and contact you.  Call Toll Free 1-877-688-2703 Serious Inquiries Only!

The Cartridge dust collector uses a perforated metal cartridge with a cellulose filter pleated, non woven filter media, bound by steel caps at the top and bottom. The end caps were joined with the cellulose media and outer and inner cores by an adhesive. Cellulose media was used because it has pressure drop qualities similar to those of felted media in pulse jet collectors. Pleated media filter elements with narrow pleat spacing (8 pleats per inch) are efficient for filter cakes (formed with fine dusts) that are less than 0.02 inch thickness. Narrow pleat spacing loses its relevance when dust particle size is beyond 0.03 inch. The pleated design provides greater amount of filtering area while occupying lesser space. Consequently the air - filter media ratio, pressure drop and cartridge collector size reduce considerably.

Are you looking for a Cartridge Dust Collector?
Contact Dust Collector Experts

Dust Collector Cartridges Use

Cartridge collectors are highly efficient in collection of dust with high bulk densities and fine dust particles. Filter cake forms well at low pressure drop and has high filtration efficiency. In a study conducted by the American Foundry Society it was found that the outlet dust flow in cartridge collectors was the least in comparison with other dust collectors in foundry operations as shown below:

At an inlet load of 1-2 grains/cubic foot

A version of the filter media elements of the cartridge collectors was used as intake air filter cartridges for trucks. The pleats were pushed deep into the media surface, 0.014 inch deep, and tightly spaced. These truck filters had a long life since inlet loads were only 0.0002 grains per cubic feet. The fine dusts collected on the top of the filter media or on adjacent pleats and the filter operated on the principle that more media contributes to longer filter life.

Main differences between truck engine filter and dust collector:

1. Loads: Dust collector loads are 1-20 grains per cu. ft whereas dust loads for truck filters are 0.0002 grins per cu.ft (5000 to 100000 times more than engine filters)
2. Dust cake: Dust cake in dust collector forms on the filter media surface as well as within the media. The dust cake in truck filters forms only within the filter media.
3. Pressure drop: Pressure drop in the dust collector is 2-3 times more than the pressure drop in the truck filter.

Cyclic Pulse Cleaning Increases Cartridge Efficiencies

Thicker dust cakes on filter elements that were cylindrical were found to be efficient and reduced the requirement of compressed air. An efficient solution to clean coarse dusts was by introducing a cleaning ‘cycle’ (as opposed to continuous cleaning) that activated on pressure setting. A pressure switch such as a photohelic gage was used for this application and pressure switch setting was at 3 ½ inches water gage. By operating the collector at a pressure of ¼ inch water column above the initial pressure drop, the pressure actuated cleaning system is best utilized. By shortening off time cleaning interval, the pressure drop can be stabilized. The frequency of the cycles can be reduced if greater amount of dust can be removed in each cycle. The lower pulsing frequency in cylindrical cartridges implies that dust penetration to adjacent filter media is reduced since dust penetration is directly related to pulsing frequency.

Though pleated filter elements can also operate with a pressure switch actuation system, we must understand that the pressure drop setting in these elements is normally limited by pleat spacing. The dust loading could be minimal in applications such as fume dusts and welding operations that may require only one or two cleaning cycles per day. Further compressed air utilization increases with narrow pleat spacing.

Eg. Considering the initial pressure drop across a pleated filter media to be 0.1 inches water gage, we can see that if ‘bridging’ (filling up) of pleat groove with dust occurs, then cleaning air flow is obstructed in the portion below the dust bridge. In such a case cleaning air has no option but to take the path of least resistance that makes all the media below the bridge ineffective. In such cases pressure switches can be set for dusts that can filter effectively at a wide range of pressure settings.

Assuming a dust load of 2 grains per cubic foot and pressure switch settings are provided at 1 ½, 2 ½ or 3 ½ inches water column, we get the following results:

If pleats are spaced narrowly, compressed air usage would increase. From the table we can see that the air usage is higher initially (due to shallow cake) and reduces despite bridging. As bridging increases so does the cleaning cycle and compressed air usage.

Cleaning Action in Cartridge Collectors

Cleaning action is achieved by compressed air jet. The jet enters the top of the filter element and expands at an angle of 14-16 degrees, drawing clean air from the clean air plenum. When this expanding air flow enters the filter element, it loses its capability to draw more clean air because the filter and the dust cake offer resistance to the flow. The air jet starts compressing the clean air in the filter element causing a pressure wave that expels the fan air present in the filter element. Once fan air is expelled, a positive pressure is created which sweeps out accumulated dust that has collected on the outside surface of the filter media in the dirty air chamber.

In pleated design, dust is displaced at the speed of cleaning air jet in a perpendicular path from the filter media surface. This prevents dust from striking the adjacent media, which is also ejecting dust at an angle. This advantage is lost in cylindrical and envelope bag pulse collectors where dust is thrown on to the adjacent rows during cleaning action. Pleated cartridge filter design has one of the better collection efficiencies due to this factor of not propelling dust to the adjacent bags.

Drawbacks

One drawback of pleated filter elements is that dust leaks through the filter media during cleaning cycles. This happens before the dust cake is properly formed. This dust then leaks on to the clean air chamber. Over a period of time, it can cause problems such as creating high pressure drop, frequent need of cleanings and reduced filter element life.

Cartridge Filter Placement

The old method of filter placement within the cartridge was in vertical rows. By virtue of the vertical placement of these elements in the polluted air section of the collector, they posed a health hazard to workers who had to enter the polluted section to change the filter elements. To counter this hazard filter placement was designed such that they could be removed from the outside of the collector. An efficient variation of filter placement from the outside is the horizontal placement of filter elements in vertical rows. Cleaning sequence was from the top to the bottom row.

Dust Collection Considerations

• Fine dust normally adheres to surface of filter element and accumulates other fine dust particles as well
• When accumulated dust cake formed properly and is large enough and unaffected by upward air streams, it falls into the hopper

Drawbacks of Cleaning Action in Horizontal Rows

During cartridge cleaning in horizontal rows, dust falls from the filter elements in the top rows (that are cleaned first) on to the filter elements in rows below. Accumulation of dust in this fashion on the rows below makes the cleaning action in the affected rows inefficient.

This problem can be countered by using a baffle arrangement at the inlet. The baffle arrangement splits the incoming polluted air into smaller channels and distributes dusty air evenly to the filter elements and helps the down flow of process air. This arrangement reduces dusty air flow speed and mitigates problems of dust particles settling on other rows.

Filter Ratio Design

Cartridges with large amount of filter media require greater cleaning jet speed. Cartridges with less filter media however, stand to benefit by the advantage of a greater cleaning jet speed since it promotes effective cleaning – an advantage that cannot be enjoyed conversely.
Normally the cleaning air to process air ratio is between 4:1 or 6:1 (which means that the cleaning flow of 1600 and 2400 CFM is required for a cartridge filter that is rated for 400 CFM). However, in spite of the high cleaning air flow rate, cartridges collect dust and get plugged. This causes active filter media to be plugged and thus the inactive filter media are activated.
The operating pressure drop across the filter media remains constant as long as there are inactive filter media in reserve. But when all the filter media get plugged and there are no more inactive filter media left, pressure drop rises and consequently cleaning frequency must be increased. When pressure drop increases to a point where it is difficult to sustain required fan air flow in the system, the cartridges must be substituted. In circumstances when dust accumulates in uncleaned pleats and bridges the system undergoes mechanical stresses on the structure and the seals.

Cartridge Cleaning System Improvements

The cleaning action in cartridge collectors can be made more efficient by the use of an appropriately designed nozzle that increases speed of compressed air jet from 1000 fps to 1750 fps. This increased speed of the air jet now enables it to draw more clean air (when it expands in an angle) and gives cleaning air jet good cleaning characteristic.

Venturi is placed at inlet to filter media to improve cleaning efficiency of cartridge. It also helps in

• blocking fan air from escaping the cartridge
• pushing out fan air when cleaning air jet is off with less instability

By increasing space between cartridges, the problem of dust falling on adjacent cartridges is reduced.

It must be remembered that the system efficiencies of cartridge collectors depend upon good cleaning of the cartridge and not by adding more filter media in the cartridge. Additional filter media neither improve function nor life of the cartridge. By merely adding filter media it is likely that even the initial advantages in terms of airflow and pressure drop may be lost. The amount of filter media should be decided based on nature and size of dust particle.

Proper Seal Design

Seals are useful for separating dusty air from cleaned filter air. They are also used to maintain differential working pressures (separating atmospheric pressure from system pressure). If the seal design is flawed, cartridges could quickly get plugged and system loses efficiency.
The use of a compression spring mitigates seal deflection problems. Seal design must take into account an appropriate size of seal as well as material strength such that it is robust and does not get crushed. The cartridge opening is sealed by an inner door cover, an outer door plate that separates the dust chamber from the atmospheric pressure and washers that seal outside door handle from internal dirty air chamber. The door parts are attached to one another and installation or dismantling of the door assembly is easy.