Dust Collectors From China

In recent years there has been a marked increase of dust collectors, built in China or India, coming on the market. Some manufacturers, who claim and/or imply to be USA or Canadian built, are actually branding Chinese built dust collectors. At Quality Air Management, we were approached to enter into such a branding arrangement with a Chinese firm. We turned it down flat.

You can purchase NEW Advanced Technology dust collectors, such as the Ultra-Flow, on the North American market that run with a fraction of the maintenance, operating cost and power consumption. China is producing a copy of OLD conventional technology dust collectors. That technology was obsoleted over 30 years ago in North America.

Read more about... Advanced Technology dust collectors

No doubt, that due to cheap labor, a Chinese built dust collector will have an attractive price. However, price isn't everything! Who do you turn to for warranty problems, and, there will be plenty of them? The North American company will fight it out with the Chinese fabricator, and you will be left holding the bag. Should you buy directly from China, your goose is completely cooked.

The news is full of reports on cheap, poor quality products and a total disregard for quality control, poor labor standards, and environmental issues coming from China. Do you want to take the risk? Then again, when will you receive the dust collector? Delivery is an issue also.

Read more about... Quality Air Management

Dust Collectors; Old vs New Technology

OLD TECHNOLOGY

•85-90% of the market, sold by all the big conventional suppliers.

•Handle most dust loadings, high temperature.

•Circa 1963; compressed air powered cleaning by rows of bags, venturi accelerated the jet to project to bottom of bag. Filter ratio 10:1 or less, dependent on application. Dust penetration (puffing) unacceptable for re-circulation to the work area.

•Circa 1971; “generic” design, modified to use 10-foot bags. Major design flaws led to selection strictly by filter ratio. Most operated at 4-6:1 ratio. Pressure drop is 6-8”wc. High compressed air consumption with higher cleaning frequency.

•High velocity dust impinges on adjacent bags which are too close together.

•The entire industry copied the same design and very little has changed to this day.

NEW ADVANCED TECHNOLOGY

•Ultra-Flow  by  QAM, circa 2003, are the 6th evolution of the advanced technology.

•Circa 1979; “Advanced Technology” first appeared. Proven technology but little known.

•95% less dust emissions, allows for re-circulation to work area.

•25-40% lower power consumption.

•50-80% lower operating and maintenance cost.

•30-40% smaller footprint.

•No venturi to restrict flow, low velocity - high volume jet = gentle but powerful cleaning pulses = no penetration & complete cleaning. 200% increased bag filter life & uses half as many bags.

•High, side inlet eliminates “can velocity”.

•Supersonic nozzles; very high energy cleaning pulse and only 1/4 compressed air consumption.

•Runs at 18-24:1 filter ratio, independent of process & dust loading.

•Runs at 1.5- 3”wc(max) pressure drop. 

Read more about... Advanced Technology dust collectors

Check out our... Dust Collector Selection Guide and Correspondence Course 

Blinded Filter Bags

This is an Ultra-Flow 60 bag advanced technology baghouse dust collector, collecting rubber, fiberglass fiber and metal slivers from two hammer mills, in a tire recycling plant.

Problem: Dust bags started out at 1-1.5”wg pressure drop, then, rose to 7-7.5” in a short space of time. Cleaning off-line only reduces the pressure drop to 5-5.5”wc. Then a third set of bags, installed a year later, started at 4”wc and clogged (7-8”wc) in 2-3 hours.

Observation (first set of bags, June 2, 2009):

        I.      There was no indication of leakage from the dirty side to the clean side of the collector.

      II.      A bag was sent to our testing lab for analysis. The findings were;

a.       Confirmed no leakage of the bags.

b.     The bag was totally blinded on the dirty side. It was a paste-like dust cake. It is also an indication of moisture in the process getting onto the bags.

c.        The bag was cleaned well but permeability was still low at 2-4 CFM. This indicates chemical attack of the media, likely from some kind of solvent. That renders the bags not recoverable.

   III.      Further very deep laundering of the bag with a surfactant started recovering the bag and increased the permeability to almost the “as new” state. This revealed that instead of chemical attack, the pores of the media were being “painted” making the bag coat with a sticky substance. No dust collector cleaning system can handle paint, blinding the bag media. There is likely rain, snow, road tar and solvent coming in with the tires. This moisture, when heated by the action of the hammer mill, would create latex and/or solvent based paint that got onto the bags. This situation would be intermittent. Once the moisture got through and the process dried up, the paste/paint on the bags would dry out also, leading to the false conclusion that the dust collected was dry.

  IV.  A subsequent squeeze test of the dust collected, alone, revealed no presence of oily substance, leading us to conclude that the painting is caused by moisture (water or snow remaining in the tires when put through the hammer mill.

Solution:

      II.      Teflon bags would resist solvents. We would advise Teflon impregnated bags, not membrane (i.e. Gortex), to keep the permeability at a manageable level. The use of Teflon membrane would require de-rating the dust collector performance by 50%.

   III.      Too much heat may be generated at the hammer mill which can be corrected by using a current controller (instead of a voltage limiting speed limiting controller) on the drive, producing a powder instead of paint. Also an inert dust could be fed in as pre-coat to make it a powder cake instead of a gooey coating.

    IV.      Same as III.

Observation (third set of bags, April 2010):

3. These bags no longer displayed the wetting and hydrocarbons of the first set, due to corrections in the process. The polypropylene bags, from a new supplier, appeared heavier and glazed on both sides of the bag material.
4. The snap band collar was uniformly dirty, not just the part below the tube-sheet groove, and there was dirt on the inside of the bag. This was an indication that the bags were installed wrong. Instead of snapping the band’s groove into the tube-sheet edge, they laid the snap band on top of the tube-sheet. That created a loose fit and a large leak of air from the dirty chamber to the clean air chamber. Each pulse would blow dirt back down into the bag, coating the clean side with dirt. This negated the cleaning system by blinding the bags.
5. The hopper was being discharged into a porous bag instead of the original sealed bin. This results in the air being drawn up through the discharge into the collector. The upward “can velocity” hangs up the dust into the collector and causes the dust to be re-entrained onto the bags during a cleaning pulse and will not drop to the hopper and bag below. When we opened the access door on the hopper a large amount of dust would drop to the bag when the suction was released at the discharge.
6. A replacement set of polyester bags had a high 4-5”wc initial pressure drop when installed.

Solution:

1. Our testing laboratory confirmed that the bags, when clean, were 5-10 cfm permeability instead of 25-35 as specified for those bags. That accounted for the high initial pressure drop. The test also confirmed that we now have normal dry rubber dust and none of the sticky stuff from before. A new set of bags was supplied, under warranty, switching back to the standard singed polyester material since moisture was no longer an issue. Polypropylene was supplied for the second set to account for the moisture getting in the process, at the time.
2. The new set of bags was supplied with our standard o-ring seal. In this way, the bags could not be installed improperly, creating a reliable seal at the tube-sheet.
3. The hopper discharged was sealed by a rotary air-lock which prevented dust hanging up in the hopper and filter bags.
4. The new set worked well. The initial high pressure drop reading was the result of a clogged air line filter to the magnehelic gauge. After cleaning out the filter and air line, the false reading came back to the normal 1.5”wc.

Read more about: Troubleshooting dust collector problems,

Sound Engineering Basis for New Technology

Design flaw #1 for conventional designs:

Conventional designs with cylindrical bags propel the dust from the rows of bags in process of being cleaned toward the adjoining rows in the filter mode. This high speed jet (between  350 and 400 ft/sec) drives the dust through the filter and filter cake, partially blinding the bags and reducing dust holding capacity by 80-90 percent with dense dusts. To operate at reasonable pressure drops, the potential filtering capacity of the bag is reduced by up to 80%. This high velocity dust also raises outlet loading above 100x10^-4 grains per cubic foot.

The new technology design reduces the exit velocity from the bag to between 190 and 250 ft/sec depending on gas density. This keeps the permeability of the media plus filter cake to a few percentage points higher than a new bag. It typically holds several times more dust between cleanings, even at filter ratios of 15 to 20, compared to conventional designs.

Design flaw #2 for conventional designs:

The filtering capacity of the filter element is limited by the reverse air volume generated by the cleaning system. The reverse air volume is also based on the diameter of the venturi at the entrance of the bag. This, for a four inch by 1.875 diameter throat bag is only 20% of the area of the opening at the top of the bag.

The new technology removes the restrictive venturi used in conventional designs and opens up the opening by 4 to 5 times. This increases the cleaning volume while reducing the pulse jet speed by 3 to 3.5 times. Half of the bags are removed and replaced with new bags and cages with the venturi eliminated. The rest of the bag openings are plugged and no longer used.

Other considerations

When these changes are made, the fine dust which formerly bled to the outlet is collected on the bags and ejected to the hopper. Because it is so fine, the vertical flow entering to the bag compartment, from a hopper inlet, would prevent this dust from falling into the hopper. This is the effect of upward “can” velocity.

The retrofit design removes half the bags from the collector. The dusty air enters from the bottom and also through the opening in the center of the bag compartment. This reduces the upward can velocity coming from a hopper inlet to a level 70 - 80% less than before the modification. Now the fine dust falls into the hopper unimpeded. It is equivalent to putting a high inlet in the center of the collector.

95% of the time, the collector will pass the initial engineering review. A report will be issued for your approval, before any fabrication of components begins.

A normal compressed air requirement, for contemporary designs, is 0.9 to 1.2 SCFM of compressed air per 1000 CFM of filtered air. Predicted for advanced technology designs is only (0.328 x (0.9 to 1.2) = 0.3 to 0.4 SCFM per 1000 CFM of filtered air.

Based on an average system requirement of 10 inches water column, a two inch reduction in pressure drop across the dust collector would reduce power consumption in the exhaust fan by 20%. 

Read More... New Advanced Technology Dust Collectors

Welding Fumes

Venting welding fume operations poses some difficult application decisions. Welding is different now than it was even five years ago. Welding is welding, the difference primarily is the coating or lack of it on the metal to be deposited. Anti-spatter is putting the coating on the welding rod from the bottom.

In fact, many suppliers refuse to bid fabric or cartridge collectors for this application.

Electrostatic Precipitators:

Years ago, the preferred method of collecting weld fume was with two stage electrostatic precipitator dust collectors. These had several advantages, they were relatively compact and were generally very effective on general ventilation applications. They could handle relatively large gas volumes through the collectors and generally were located near the roofs of buildings. The collection efficiency was variable depending on the velocity going through the collection plates. The same unit could run at 98%, 90% or 80% collection efficiency at volumes that would vary as much as a ratio of 3:1. The higher the volume would produce the lowest efficiency. On general ventilation lower the efficiency did not cause any problems. The cleaning of the precipitators was accomplished by a detergent wash system. The loading for general ventilation units were from 0.5 to 1 grain per thousand cubic feet per minute. The washing frequency was typically once a week or once every two weeks. The presence of condensed hydrocarbons along with the fume was not a problem. Generally these would be oxidized into solids by time that they were collected. These collectors were generally the same ones that were applied in HVAC systems. The washing mechanisms were designed for 1000 cycle life which would translate to over ten years of life under these general ventilation loading conditions. As the welding operations generated heavier loads, especially in high production facilities, the trend was to hood the welding operations. This venting of the hoods had some pronounced effects on the application of these precipitators:

Effects of hooded systems

1. The load to the precipitators was increased to levels that varied from 5 to 20 grains per 1000 cfm. This was 10 to 40 times as high as the general ventilation requirements.
2. The distribution of air across the intake of the precipitators became critical.
3. Lower efficiencies; The precipitators, because of competitive pressures, were sized for the higher volumes and lower efficiencies

The increased loading meant that the life of the washer systems became 1/10 to 1/40 of that of the general ventilation units. The translated into washer units that had less than six months service life. These HVAC service designs also had problems with coatings building up on the high voltage insulators so they required replacing at about the same frequency as the washers.

The gas distribution across the collection plates radically affected the collection efficiency. If we had a gas stream that averaged 100 fpm that would be designed to operate at 95% collection efficiency and the real velocities entering the plates varied from 50 to 150 fpm, the section at 50 fpm might have a collection efficiency of 98% and the section at 150 fpm would be running at 80%. This would mean that the overall efficiency might operate at close to 85%. Lower efficiency caused by running at higher average velocities were common. In the example above, the collector might be selected to run at 125 fpm and an average efficiency of 85%.

The electrostatic precipitator ionizes the gas molecules and in the process places a charge on all of the dust particles. The charge attracts the dust to the grounded plates. Later these collecting plates are cleaned to remove the dust from the unit.

Running the collectors at these higher loads and decreased efficiency allowed some dust to pass through the precipitator while the dust still retains its charge. As the exhaust gas mixes with the ambient air the dust usually loses its charge and the gas stream loses it’s ionization. The length of time required to lose its charge depends on the dust loading in the exit gas stream as well as the humidity of the ambient air. Dry air will allow the charge to be retained longer. Under certain conditions of low humidity and higher dust concentrations, the dust will hold the charge indefinitely. Suddenly the whole room will be ionized and the charged dust will be attracted to all the neutral surfaces in the room including walls, eyeglasses worn by personnel, windows and even light bulbs. This phenomenon is known as “plating”. There have been occasions where a newly painted plant was coated with black soot within minutes. It is because of these circumstances that welding fume collection was changed to pulse cleaned dust collectors.

Cartridge Dust Collectors:

There are thousands of cartridge collectors in service on these applications

However, there were big differences in power requirements, cartridge life and penetration of dust through the collectors: These were due to the following :

1. Cleaning controls: The much used pressure drop actuated cleaning control has some serious flaws. It is impossible to predict the pressure drop at which the most effective filter cake is formed. It is likely, that this pressure drop may be just slightly higher than the initial pressure drop. If the cartridges are not cleaned early enough the result is that the dust will bridge across the pleats and a large percentage of the filter media in the cartridge (that which is below the bridge) will be unclean able. Initially, the collector should be cleaned by a timer control until the pressure drop stabilizes. The control can be extended until the pressure drop starts to rise and then the timing speeded up slightly. Alternatively, the pressure control can be set slightly above the stabilization point. The best operation occurs when the collector runs at the lowest possible pressure drop. Penetration of dust, cleaning frequency and cartridge replacement time, increase with pressure drop, usually related to the square of the increase in pressure drop.
2. The filter area of the cartridge can be and often is excessive. The media that can be cleaned by the cleaning system is the only media that is useful. Often, suppliers cram more media into a given size cartridge by inserting closely spaced pleats. This cramming of media provides useless media and causes operational and structural defects. If pleats are close together, the adhesive that holds the cartridge together will not wet the media and a strong bond cannot be developed between the end caps and the filter media. A poor bond may allow leakage between the media and the adhesive. If the filter cake is deeper than the open distance between the pleats the cartridge will bridge. Typically cartridge filtering ratios should be no less than 3 FPM, and generally will operate at 4-7 FPM. Most systems operate at lower filter ratios where pressure actuated controls do initiate frequently enough to clean the cartridges effectively. Conventional cleaning systems may not allow for recommended filter ratios of 4-7 FPM. Advanced technology collectors will run at even higher filter ratios and clean the media more effectively, promoting higher efficiency and longer cartridge life.
3. The cartridge shape should be flat and cylindrical. Truncated cone bottoms, formed into the closed end cap, causes damage to the filter cake allowing excessive penetration through the dust collector. The cone develops more cleaning pressure near the bottom than in the rest of the cartridge. Premium construction cartridges are often necessary to develop maximum cartridge life and improved collection efficiency.

Oil-Smoke:

The above applies to welding of clean parts. Recently, there has been a trend to vent from welding operations where the parts are coated with a light film of oil.

A mixture oil and powder can produce oil based paint. This oil/powder mixture can progressively blind the cartridges and produce premature cartridge failure. When you collect oil on the cellulose cartridge, it acts like a blotter and the media swells, permeability and available collection media is reduced. This latter phenomenon is in at edition to the painting action. With some hydro/oleo phobic media, that is specially coated, the oil will not wet the fibers and the media will not swell. Some of these cartridges can be recovered by washing them in detergent, but over a period of time the oil starts to dry and a solid is formed which cannot be washed. Typically after two or three washings the cartridges must be replaced, as there will a creeping higher initial pressure drop.

Usually, the welding fume load is extremely light and with the special fibers, the cartridges can last for several months before they need to be washed or replaced. Actually even cellulose based fibers can be washed successfully two or three times, but the time between washing goes down for each wash as the residual permeability decreases after each washing.

There is some promise in using a precoat (filter aid) of some dust on the media to blot some of the oil so a paint will not form. There are some commercially available coatings that are promising. The choice will be empirical.

Stainless Steel

This is one of the most deceptive applications we can deal with. Most of the time, you will believe that the material has not been pickled with oil or another preservative. The metal looks perfectly dry. Some manufacturing processes will prewash the stainless, thinking they are removing any residue that may be there. When you well donned the material, to everyone's surprise, a residue appears at the dust collector filter elements. A way to determine this is to soak the filter elements in a tank and observe a film of oil form on the surface of the water. Another test would be to take a folded piece of tissue paper and squeeze it between the pleats of the filter element for 24 hours. Automatic pre-coating, or seeding, of the filter elements is a solution to this problem.

Weld-aid (anti-spatter)

Welders often use “weld aid” type of substance to prevent spatter from adhering to the work piece. It is mostly water with a 15% fatty substance. It is usually sprayed on the work piece before welding. This is a very greasy substance that is difficult to remove from the cartridge media and fills in the pores. You should have a washable media, such as polyester spun bond, preferably with a non-stick surface. All paper, cellulose formulations are unacceptable media selections because water gets absorbed and the media swells. Do not use exotic medias that have low permeability. It is recommended to install an automatic filter-aid feeder, such as the one designed and sold by QAM. You also should consult a welding expert to change the welding process, which will eliminate the necessity of using weld-aids or change to a powdered version.

Automatic seeding system

With a special design and a seeding system, it can last indefinitely. A layer of inert absorbent dust is fed into the collector. The collectors not pulsed except twice a day. The inert layer blots up the oil fume and the oxides from the welding are also mixed on the surface. There is an airlock, usually the smallest kind available which feeds the dust back into the bags after the collector is restarted or even pulsing is done while the collector is operating. The ULTRA-FLOW bag-house can run at 18:1 ratio and is probably less costly than the cartridge collector for the application.

Read more on ... Ultra-Flow Baghouse dust collectors

SPARKS & FIRES

Sparks are a very common occurrence in the welding process. These sparks are swept up into the collection hood or device and are transported to the collector. Fires can occur in exhaust ducts as well as inside dust collectors. Requirements of fires or any combustion process are: a) Fuel, in gas, liquid or solid form. b) Oxygen (Atmosphere consists of 20 per cent oxygen) c) Fuel must be raised to the ignition temperature to start burning.

Transport of sparks through ducts.

There is a glowing ember surrounded by some hot air which gives the sparks buoyancy. This spark and the hot gas associated with the spark can travel hundreds of feet in a duct. The ductwork is designed to give laminar (smooth) flow. Spark suppressors are placed in the duct to change the flow to turbulent (coarse) flow. This agitation or turbulence strips the air from around the ember removes the fuel (oxygen), therefore extinguishing and cooling the spark below ignition temperature.

Read more about ... Spark Arresters and Coolers

Prevention depends on eliminating the causes of ignition. Spark traps can change laminar to turbulent flow and extinguish any sparks in a duct. Design for proper dust transport velocities. Install pneumatic actuated duct booster to flush dust into dust collector. Use air jets to remove electrostatic charges on the duct surfaces.

View and print... fires and explosions

Cartridge Collector on ARC SPRAY

The first suspicion for pressure drop problems on arc spray is that the spray is coating the cartridge, since the compounds have not lost there coating characteristics before they reach the surface of the media and seal or partially seal the surfaces. This is referred to as “painting effect”.

The symptom of this is that the pressure drop goes up quickly within 20 minutes. It does not recover from on line cleaning. The pressure drop for off-line cleaning quickly ratchets until the you get to the top of the hump in the fan curve.

We ran some tests on an operation in Atlanta about five years ago where we installed a pilot unit with varying lengths of pipe and found on that operation that it required 0.8 seconds of transit time from the spray gun to the surface of the cartridge filter elements, to prevent “painting”. Other reports that we received from Torit installations reinforced our conclusions. They sprayed aluminum, titanium, nickel, and ceramics. They were coating turbine blades for jet airplanes.

The observation of very fine dust floating in the collector, when the fan was off, can be very significant. It would be important to observe whether the same was evident in the clean air plenum. If it was, I would want to question the efficacy of the filter seals. The next possibility that this observation raises is whether the dust agglomerates on the media surface and/or stays agglomerated during the cleaning cycle. If it does not stay agglomerated during the cleaning cycle the coarser agglomerates will fall into the hopper and the finer fractions will return to the surface of the filter media. This will cause a ratcheting of the pressure drop at each cleaning cycle.

It was also observed a gradual increase in pressure drop. This can be caused by the lack of agglomeration as described above. However if this is the cause, the collector should return to initial pressure drop after an extended cycle of off-line cleaning. We would say that you need to put fifteen minutes off time and pulse the collector four times.

There are other processes that might have some of the symptoms. Among them:

Oil in the compressed air. If they have a screw compressor there is a filter that comes with the compressor. Sometimes the installer forgets to put it in. With pneumatic cylinders, the air line cleaners are sufficient to allow suitable operation.

Moisture in the compressed air line. Here again they should have a refrigerant or a desiccant dryer.

Condensation on the media surfaces because of the cooling of the cleaning air jet. If the latter is the case, the pressure drop increase will generally be apparent more likely in the morning when the difference between the dry and wet bulb temperatures are most likely to occur.

Replacing a third of the cartridges is generally not a good idea. It is also important which ones you replace. If they are tandem cartridges I would replace one on each tandem set. Personally, if I were to replace cartridges to run a test I would replace the ones furthest from the pulse-jet orifice/nozzle. When you do that, you do not even need to initially clean off-line. I figure you are wasting most of your media in a tandem configuration so when you replace cartridges on a trouble job, it is smart to replace only the outer one.

We need to determine if the cartridge is plugging from the dirty side or the clean side. We assumed it was from the dirty side but the clean side is a possibility. We usually check to see if there is any dust in the clean air plenum. If there is, the problem may be the seals. You may need special seals for this fine submicron dust.

You can always send us a used cartridge for a lab test. Make sure you seal the opening(s) to the clean air side. I usually use good ol' duct tape.

For assistance with a trouble job... Technical assistance with dust collectors

Pleated Bag, Cartridge Dust Collectors

Pleated bags and cartridge collectors have been applied to collecting spice dust with mixed results. The first cartridge collectors were offered in 1976. They were an immediate success on applications where contemporary fabric pulse jet collectors were marginal. (e.g. Welding fume, arc furnaces with low temperature canopy hooded vent systems, and electrostatic powder coating vent systems.)

The 1978 American Foundry Society's test, at an automotive foundry, was to ostensibly find out if collectors could be used for recirculation provided an impetus to the cartridge collector's wide acceptance. The test report was widely circulated on a system that had shot blast and sand recovery systems. The results were very outstanding for dust emissions:

Standard Pulse Jet Collectors Penetration 600 to 800 x 10^-5 grains per cu. ft.

Shaker Collectors Penetration 60 to 80 x 10^-5 grains per cubic ft

Pleated filter / Cartridge Collectors Penetration 4 to 4.5 x 10^-5 grains per cu. ft.

The reasons for this astounding increase in collection efficiency was not discovered for another ten years.

1. The media was similar (identical permeability and collection efficiencies before formation of a filter cake) to the felted media but thinner.
2. The ejection of the dust towards adjacent rows of filtering elements was halted. During cleaning the gas and dust leaves the filter media perpendicular to the surface. In a pleated filter element, the dust is hurled toward the surface on the other side of the valley in the pleat. But this surface is also pressurized, blowing dust and gas towards the middle of the pleats. The dust laden gas is slowed down and directed toward the wide part of the pleat. The agglomerated dust then falls into the collection hopper below.

Read more on different dust collectors ...  QAM dust collectors

The belief was that more filter media (and associated filter ratio) made the selection more conservative. This is generally true with pulse jet fabric collectors with high velocity cleaning jets in that it extends bag life. The fact is that the opposite is true in cartridge collectors because of bridging across the pleats. If the media is not cleaned, bridging occurs. As dust accumulates in the valley of the pleat, it bridges. During the cleaning cycle the cleaning air looks for the easiest path from the inside to the outside of the filter cartridge. That path is above the bridge. What contributes even more to this phenomenon, is the fact that a certain volume of air can only clean a certain amount of media. Because the cartridge may contain huge amounts of media that cannot be cleaned, the media not cleaned plugs. In most designs running at filter ratios of less than 2:1, an operating cartridge may contain 10 to 40 pounds of dust. Table 1 illustrates the area of media that can be cleaned with various orifices and /or converging diverging supersonic nozzles.

Table 1

Orifice or      ON Line        OFF Line        ON Line           OFF line

Nozzle dia   Sq.ft.(Orifice)  sq.ft. (Orifice)  sq.ft. (Nozzle)  sq.ft. (Nozzle)

0.25 in.           5.5              6.8                 8.8                   11

0.312 in.         8.6             10.7               13.75                 17.2

0.375 in.       12.3             15.4               19.8                   24.7

0.50 in.         22               27.5                35                     43

0.75 in.         49.5            61                   79                     98.7

1.0 in.           88             110                  132                   165

1.5 in.         198             247                  376                   395

Advanced Pleated filter technology has allowed us to increase filter flow per size of cartridge. Formerly the limitation on application was to be able to use all of the filter media to filter the dust. Even spreading the pleats widely apart was only an improvement rather than a solution. When a pleat with conventional media is placed under pressure across the filter element, the pleat collapses and squeezes together so that media on the filtered side and is no longer in service. This squeezing has several direct and indirect effects:

1. The pressure drop goes up and squeezes even more of the media and the additional pressure drop disables a larger percentage of the media in the filter element. 
2. This decrease in effective media decreases the quantity of dust that can be stored in the element between cleanings. To compensate for this effect the cleaning frequency is increased to keep the pressure drop stable. 
3. Since the dust penetration through the filter element is a direct function of the cleaning frequency, the collection efficiency will  be reduced  by up to 90%, especially with applications with varying dust loading. 

The latest advanced technology, we have developed, is the media that is applied has sufficient resiliency (or springiness) to prevent any squeezing or pinching of the pleats. The new media allows the cartridges even to recover from failures of the cleaning system where a presumably plugged filter element can recover completely within a few off-line cleaning cycles. Another innovation is a tandem pleat with a stiff backing, to prevent pinching. This in effect allows us to have a permanent re-cleanable filter that can be washed manually in a laundry tub. Be the first in your company to take advantage of this technology. We can usually supply retrofit cartridges to bring an older conventional dust collector into the 21st century. This approach eliminates disposal problems, lowers operational costs.

Analysis of 2 tandem cartridge (Torit style) design

This typical contemporary design can be analyzed.

Valve: 0.75 inches Cartridge media (two cartridges) 450 sq. ft.

Approximately 550 grains per sq. ft. of dust loading

From Table 1; 49.5 sq. ft. cleaned on line 61 sq. ft. off line

Plugged media area 400 sq. ft. / 389 sq. ft (on-line / off-line cleaned),

When media is plugged, 550 gr./ sq. ft x 400 sq. ft. = 220,000 grains is imbedded in cartridge.

Therefore, 220,000 / 7000 gr./lb. = 31.5 Ibs per tandem set weight.

Another factor is that the cleaning action is generally initiated by a pressure switch. The most prevalent pressure switch setting is about 3 1/2 inches. For most applications the pressure should be about 3/4 -11/2 inches WC above the initial pressure drop. Typically, initial pressure drop through the cartridges is 0.3 - 0.5 inches of water column. At 3 1/2 inches WC, over 80% of the available media is generally plugged and the cartridge must be cleaned three times more frequently than if the switch were set in the proper range.

Dust Collector Selection

The best desiqn for a pulse jet collector with fabric media on these applications are those offered by ULTRA-FLOW/QAM; with low jet velocities and higher filter ratios. The characteristics of these designs are listed below:

Average velocity at bag opening    10,000 feet per minute

Bag opening (no venturi)               4"diameter

Jet volume                                  740 CFM

Bag diameter and length              4 inches x 96 inches

Bag area                                    10 sq.ft.

Filter volume rating per bag          190 CFM

Nominal filter ratio                       20 FPM

Average pressure drop                 2.5 inches water column

Average Air Consumption             0.5 SCFM/1000 CFM of flow

Average dust penetration             5 x 10^-4 gr. / cu. ft. (at 5 gr./ cu. ft. load)

Of course, as stated above pleated filter elements can be a collection option. However on many applications, such as low density spice dust, the operating cake can be relatively thick as much as 1/8th of an inch thick and the pleats bridge and cause operating problems.

Advanced Technology Cartridge Collectors :

You will note that our collector is somewhat different in appearance and design than those offered by the other bidders. However we are convinced that our design has a much more suitable dust service than the other offerings. We will briefly outline these differences and the advantages for your service.

1) Cartridge Mounting You will note that in our CV Series, cartridges are mounted vertically instead of horizontally. This allows the dust to fall unobstructed into the hopper. We have noted that at the trade shows several of the suppliers exhibiting their horizontally mounted cartridge dust collector units have a common problem. On these units, when you look through the Plexiglas view ports, there is a pile of dust on the upper surfaces of every cartridge except the top one in the vertical rows. This dust blocks the media and provides an undesirable inventory of dust. This is especially serious when handling dusts that are toxic or flammable.

2) Air to cloth ratio; It is often forgotten by cartridge dust collector specifiers and designers that the quantity of media that can be cleaned by a reverse jet pulsed cleaning system is a function of the reverse air volume of the cleaning jet. While the design of the cleaning system is relatively complex, we can relate this to the valve size. The other pertinent relationship is that the maximum air flow through a filter (or set of filters in the case of a tandem filter) is related to the maximum compressed air flow in the valve or orifice (in case of a blow pipe unit). Both of these relationships are listed below. (Note these values change depending on the efficacy of the cleaning system design).

Orifice         Flow in      Media Area

or valve dia.   scfm        cleaned

1/4”               90           12-17 sq. ft.

3/8”             200           30-40 sq. ft.

1/2”             360           50-70 sq. ft.

3/4”             810          115-155 sq. ft.

1”              1440          205-265 sq. ft.

1 1/2”         3240         450-619 sq. ft.

2”               5760        820-1100 sq. ft.

What happens to the media not cleaned? It bridges and plugs. Once plugged and bridged, the dust in the folds of a cartridge filter element cannot be removed by the cleaning system. The cleaning air will look for the path of least resistance so it renews some of the media until it reaches the areas listed above. In the typical tandem design with one 3/4” valve to clean a tandem set of two cartridges and with 530 sq. ft. of total media, approximately 135 sq. ft. of media get cleaned and 395 sq. ft are plugged. The uncleaned media eventually holds about 20 lbs of dust. The dust piling on the upper surfaces may amount to another 4 or 5 pounds.

3) Cleaning Controller Many designers advocate and supply a pressure switch to start the cleaning system pulse timer. Although this is a possibility for controlling the cleaning, the difficulty lies in determining the proper pressure drop at which to activate the controller. Selecting an arbitrary number such as 3.5” w.g., the dust build up in between the pleats will be four times as much, similar to the calculations above.

4) Clean Side Access If the power to the controller or the compressed air system drops below the necessary cleaning pressure, the pleats will bridge and the cartridge filter elements will not recover by reverse jet cleaning. Cartridges can be recovered to near new condition by blowing them clean with a modified blow gun.

5) Seals and cleaning system design. Many suppliers have inadequate seals and poorly designed cleaning system. The cleaning jet grows at a relatively narrow angle until it encounters a venturi wall, an orifice or a wall of filter media. Many collector cleaning systems locate the blow pipes (or valve) too close to the opening in the cartridge. The net result is that the media nearest the pulse pipe or valve is not cleaned. The additional storage of dust in the pleats is often considerable. There are some suppliers who use inadequate or improperly designed seals. If seals leak premature cartridge replacement and high pressure drop operation will become the norm. A proper dust tight seal needs to maintain proper pressure on the sealing surface. Too high of pressure will harden the seals and cause leaks. Too low a pressure will allow dust to pass through, when the pressure drop exceeds the pressure on the seal. Our ULTRA-FLOW normal cartridge life can exceed 30 months.

Conclusion

The best dust collection choices are a fabric collector with low jet velocities and a manifold heater. The next best selection, only with light density powders, is cartridges or pleated bags with very wide pleats and a manifold heater. We trust that you will take the above into consideration when evaluating your needs for a cartridge dust collector. Advanced Technology cartridge collectors have been supplied since 1987 with hundreds of installations on a wide range of applications including a large portion on a brace of blast and grinding applications. Their performance has been outstanding with high efficiency, low pressure drop and long cartridge life being the normal expectancy.

Read more on ...  Quality Air Management dust collectors

Major Design Flaws and New Technology Baghouse Dust Collector

Design flaw #1 for conventional designs:

Conventional designs with cylindrical bags propel the dust from the rows of bags in process of being cleaned toward the adjoining rows in the filter mode. This high speed jet (between  350 and 400 ft/sec) drives the dust through the filter and filter cake, partially blinding the bags and reducing dust holding capacity by 80-90 percent with dense dusts. To operate at reasonable pressure drops, the potential filtering capacity of the bag is reduced by up to 80%. This high velocity dust also raises outlet loading above 100x10^-4 grains per cubic foot.

The new technology design reduces the exit velocity from the bag to between 190 and 250 ft/sec depending on gas density. This keeps the permeability of the media plus filter cake to a few percentage points higher than a new bag. It typically holds several times more dust between cleanings, even at filter ratios of 15 to 20, compared to conventional designs.

Design flaw #2 for conventional designs:

The filtering capacity of the filter element is limited by the reverse air volume generated by the cleaning system. The reverse air volume is also based on the diameter of the venturi at the entrance of the bag. This, for a four inch by 1.875 diameter throat bag is only 20% of the area of the opening at the top of the bag.

The new technology removes the restrictive venturi used in conventional designs and opens up the opening by 4 to 5 times. This increases the cleaning volume while reducing the pulse jet speed by 3 to 3.5 times. Half of the bags are removed and replaced with new bags and cages with the venturi eliminated. The rest of the bag openings are plugged and no longer used.

Other considerations

When these changes are made, the fine dust which formerly bled to the outlet is collected on the bags and ejected to the hopper. Because it is so fine, the vertical flow entering to the bag compartment, from a hopper inlet, would prevent this dust from falling into the hopper. This is the effect of upward “can” velocity.

The retrofit design removes half the bags from the collector. The dusty air enters from the bottom and also through the opening in the center of the bag compartment. This reduces the upward can velocity coming from a hopper inlet to a level 70 - 80% less than before the modification. Now the fine dust falls into the hopper unimpeded. It is equivalent to putting a high inlet in the center of the collector.

95% of the time, the collector will pass the initial engineering review. A report will be issued for your approval, before any fabrication of components begins.

Normal compressed air requirements, for contemporary designs, is 0.9 to 1.2 SCFM of compressed air per 1000 CFM of filtered air. Predicted for advanced technology designs is (0.328 x (0.9 to 1.2) =0.3 to 0.4 SCFM per 1000 CFM of filtered air.

Based on an average system requirement of 10 inches water column, a two inch reduction in pressure drop across the dust collector would reduce power consumption in the exhaust fan by 20%.

Read more about ... Baghouse retrofits
Read more about ... New advanced technology baghouse dust collectors