Safety Issues with Venting Dust Producing Operations

Typical manufacturing, mining and material handling operations produce various types of dust and other contaminants. These contaminants may be quite toxic when they enter the workers’ lungs. Protection systems involve either suppressing the mostly solid particulate contaminants generated or the venting and collection of the contaminants.

Dust Suppression

The first approach is to prevent the generation of these toxic contaminants before they enter the work environment. This can be accomplished by dust suppression systems. An example of this would be a rock quarry or coal mine. As the gravel or coal is processed into smaller usable sizes by crushing and placed on belt conveyors to be delivered to trucks or railroad cars, and then delivered to further processing. All of these operations produce large quantities of dust if they are not controlled in these operations. Dust suppression is achieved by spraying liquid over the rocks and coal so that the operations do not produce dust. In dust suppression technology, compounds are added to the water that eliminates the surface tension of the water so that the liquid coating is spread over a much larger surface area. The dust then stays attached to the pieces and to adjoining particles to prevent dust generation. The spreading of presumably water based solution increases the rate of evaporation. In colder climates the dust and product does not allow the material to freeze so that loading and unloading are facilitated.

Venting of Dust Producing Operations
The most common contaminant in industrial manufacturing operations is solid particulate. First the contaminant is contained by putting enclosures or hoods around the dust generating machines that will allow access for the workers. The hood is then ventilated and the contaminated gas stream is cleaned by a dust collector. The dust is separated from the gas stream and the gas stream is vented to the work environment or outdoors. The process of collecting this dust, disposing of it, maintaining and servicing the dust collector equipment can expose the workers to serious hazards
a) The first hazard often present is accumulation of dust in the bottom portion of the horizontal duct runs. Most well designed vent ducts have cleanout doors every several feet. These ducts are near the ceiling usually 12 or more feet above the floor. The cleanout doors are located on the lowest underside of the duct and when the doors is opened dust will pour out towards the floor exposing the worker and environment to dust that might be inhaled. Special man hoists are recommended and breathing masks are indicated. A better approach is to install pneumatically actuated Duct Cleaner-Boosters in the system. These will momentarily increase the velocity in the ducts pushing the dust accumulation toward the dust collector. It makes the duct cleaning operation automatic and safe, with minimum exposure to the dust.
b) The next hazard is when flammable dusts are produced in the machine being vented to the dust collector. If dry dust is collected, sparks can be entrained from the hood(s), and carried into the collector. There is a coating of flammable dust on the filter elements. The velocities through the filters are much lower than in the duct and if a spark reaches the filter elements, the dust may reach the ignition temperature and start a fire. In well designed ductwork the flow is designed to be laminar. Sparks may be transported for more than a hundred feet. To guard against this occurrence, an in-line spark suppressor with a duct cleaner – booster should be installed. The suppressor device will induce extreme turbulent flow which cools the spark below the ignition temperature and protects against fires.
c) Explosions are another operating hazard. To have an explosion the concentration of dust in the housing or duct must be between the lower and upper explosive concentrations and a spark must be present. In mechanical cleaning (shaker) collectors, the flow is stopped in the filter compartment and the filter elements are agitated all at the same time. A potential for an explosion occurs since the concentration will likely pass through the explosive limits during this action. Protection consists of grounding the filter elements to prevent sparks generated during cleaning. Additional explosion rupture panels are installed and vented outdoors. In continuous cleaning pulse jet collectors, only small sections of the collector are reverse flushed. Around each bag in the cleaned section is a very small volume of air which can pass through the explosive limits. Even if a spark is present, an explosion would be dissipated without danger. If the collector filters are to be replaced the first procedure is to remove as much flammable or explosive dusts from the filters as possible. The exhaust fan’s direction is reversed to maintain a low flow and prevent dust from returning to the hood. The collector is cleaned one section at a time allowing time for the dust to settle into the collection hopper. After several complete cleaning cycles a large portion of the dust will be ejected. This lowers the exposure of the worker in handling the filter elements.
There are two general types of filter elements; those with smooth surfaces usually cylindrical or oval with smooth surfaces, and, pleated filter elements. There is a potential for pleated filter elements to bridge and have dust collected in the valleys of the pleats. Even if a reverse pulse collector is cleaned slowly with the fan reversed, considerable dust may be present in the valleys. Recent new technology provides for wider pleat spacing and stiffer filter media which allows off line cleaning as described above to be effective.
d) There are some contaminants either liquid or solids which are not suited to fabric media collectors. They will not form a filter cake or the dust is very unstable. Gunpowder and the propellant for inflating air bags in an automobile are two common examples. The most common approaches are gas washers that scrub the contaminant from the vent stream. Another approach is to mix inert dust into the vent system so the dry powder mixture is no longer flammable or explosive. Some operations will produce dust that is so wet that it will quickly turn the filter cake into a mud which will blind the filter elements.
e) Wet Dust Collectors have a variety of designs and must deal with the problem of surface tension of the water which is used to clean the gas. To get adequate collection efficiency, historically designers have resorted to higher pressure drop designs so that the solid and liquid contaminants might penetrate through the scrubbing surfaces. The same types of compounds, as in dust suppression systems, allow operating at very high efficiencies with minimal power consumption. It was necessary to design special multi-pass mist eliminators to collect the overspray from the scrubbing surfaces. Therefore gas leaving the collector is often below saturation from the heat regain as it passes through the exhaust fan.

Other Hazards and Considerations
Rotary Feeders located in the bottom of a collection hopper can pose a danger to maintenance personnel. There are instances where the feeder fails and dust builds up in the hopper. This dust can ignite and burn. The main approach is to shutdown the section of the collector and let it burn depriving it from getting oxygen. Normally, it will self extinguish. Spraying in water can create an explosion as the water displaces the dust with steam and will go through the explosive limits. On a power plant boiler, a maintenance man decided to pour water into the hopper. The dust was agitated and an explosion occurred.
A) It is preferable to install collectors where the filter elements can be changed from outside the collector housing. Collectors with removable roof doors are widely available. When a filter element extends 8 feet above the doors, even a moderate wind is a problem and workers must plan to protect themselves from these forces.
B) Another type of design is walk-in-plenums. There is a housing tall enough to change the filters, out of the weather elements. The entrance is usually a hinged access door. Rarely do these chambers have lighting. A particular hazard is when in the housing the door slams shut. It is hard to find the door in the dark and a wind can keep it closed. It is advisable to clamp the door with a cable and lock it. Remember the bags and cages must be lowered to the ground and hauled up again and fed to the collector through the access door. The pulse pipes must be removed and temporary storage space provided. These pulse pipes can fall through the holes in the filter mounting plates, forcing a man to enter the collector. Toxic gases can seep into the clean air plenum, so, the breathing zone should be monitored. When a collector is initially started, dust will seep into the plenum until a filter cake is formed. Personnel should not enter the plenum until this conditioning of the filters is completed.

For more information:
Gary Berwick, P.Eng.
Phone: (519) 746-2424
e-mail: gary@qamanage.com
www.qamanage.com

Moisture and Freezing in Pulse Jet Dust Collectors

The root of the problem comes from the fact that as you compress air the moisture holding capacity decreases. Compressors have after coolers in which most of the condensed water is removed before the compressed air enters the distribution system. The compressed air is usually a bit higher temperature than the ambient temperature. As it flows from the compressor to the machines some additional water will condense. Usually any large droplets will be collected in the air line filters before they reach the machines. There is still some moisture but it does not affect the operation of most machines. On other machines where this remaining moisture is undesirable or harmful, dryers are installed between the machinery and the compressor. On compressed air powered pulse jet collectors, the presence of liquid moisture in the pneumatic lines can have serious effects:

1. The water can collect in the compressed air manifold. When sufficient water is collected, it may “squirt” into the filter elements during a cleaning cycle. The drenching of the filter elements is intermittent, but the long term effect is higher pressure drop, more frequent cleaning and premature filter element replacement. Often the filter will dry itself from the exhaust flow through the collector. But residual effects from this wet dry cycling are cumulative. Cellulose cartridge filter elements are especially vulnerable as each wet cycle causes the permeability to increase and harmful effects are much faster.
2. If a collector is installed outdoors in below freezing conditions, even very small amounts of moisture droplets can condense on the diaphragms of air valves. The diaphragms will then stick to the seats of the valves and will not close. This will discharge all the air from the system, since typically 150 to 400 SCFM can be discharged through the valve. Since these valves operate with internal pilot ports, the valve will not close until the supply pressure reaches 25 psig. There needs to be an external shutoff to get the collector (and sometimes associated compressed air supply) back to an operating mode.

Quality Air Management has a two different products to address these problems:

• Manifold Tank Automatic Drain Valve System
• Thermostatically control compressed air manifold heater. This system will allow the collector to operate even when the compressed air dryer is malfunctioning by turning any liquid moisture to water vapor.

QAM also provides dust collector retrofit and consulting services to help resolve common problems that no one else seems to have found solutions.

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

Shot Peener and Blasting Operations

The abrasive generated dusts have some unique properties that need to be addressed to accomplish the following by application of advanced technology dust collector designs:

1)    Lowering the dust penetration through the filter cake filtering mechanism will protect the environment and employees.

2)    Re-circulation of the vented air can reduce energy consumption.

3)    Further economic savings, by lowering energy consumption, for operating the vent system at lower pressure drops and reducing pulsing air consumption.

4)    Filter life can be increased by 3 to 4 times.

 

For many years, abrasive blast operations were vented from the blast cabinets through mechanical shaker dust collectors. In these units the initial collection efficiency was relatively low. As the cake became thicker, the pressure drop increased. It would eventually increase so high that the flow through the system would be choked. 

Several mechanical arrangements to remove excess dust were development. During the process of removing the dust, a portion of the dust remained on the media. This residual dust had formed a filter cake and even after cleaning the collection efficiency was high enough to allow re-circulation. In the early 1960’s continuous cleaning pulse jet collectors were introduced. These collectors were much smaller than the mechanical cleaning collectors and reduced the complexity of the venting duct-work. The typical collector was 15-25% of the size of the compartment-ed mechanical cleaning collector. However, the average particulate load penetrating through the collector was about 2.5 milligrams per cubic meter, which could not be re-circulated into the working environment.

In 1973, pleated filter elements were introduced into the dust collection market. It was believed that pulse jet collectors would be more efficient if they were pleated because of low velocities through the filter element. Most dust collector manufacturers and designers packed too many pleats in the cartridge filter element. Also, the cleaning system was undersized for the amount of media at that must be cleaned.  The result is dust bridging on the inner pleat.  In many cases, we can lose up to 80% of the effective workable area of filter media.  This led to short filter life and high maintenance cost.

Advanced technology modifications have improved the operations of each of these types of collectors, reducing the foot print, lowering pressure drop (with lower power consumption) and reducing penetration of dust through the collectors. The next breakthrough in the advanced technology reverse pulse jet designs came in the realization that the capacity of a filter element depended on the reverse air volume of the cleaning jet. More volume could be applied per filter element and the footprint reduced drastically.

 

Cleaning System Designs must be sufficiently sized to develop the required volume to vent the process. The most volume that can be filtered depends on the number and size (or equivalent size) and number of valves. The advanced technology uses a proprietary supersonic nozzle design which increases the reverse jet flow by 70 per cent over a conventional orifice by getting a more efficient pressure to velocity conversion.

There are several considerations for safety and reliability that must be taken into account.

View and print ... Shot Peeners (PDF)
Read more about ... Advanced Technology pulse jet dust collector

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,

Furnace and Dust Collector Fire Hazards

Fires in brass furnaces have always been a danger.

First let us review the process; as the material is fed into the furnace it has many metals including zinc, tin etc. Some of these actually go to vapor and then condense and turn into solids.

The key is that these metals are very fine with very large area to weight ratios. The exhaust is generally cooled by mixing with ambient air so the metals are not appreciably oxidized. The dusts collect, with the other dusts, in the dust filter cake.

When the collector is shut down the metals start to oxidize and the effect is like catalytic combustion. The oxidation produces heat. The dust is usually a good heat insulator and "hot spots" occur. Sometimes the temperature is high enough to start a fire when the flow was stopped. More often, when the collector is turned on, the initial flow fans the sparks and when conditions are optimum for combustion, a fire will start. Most of the time small holes or scorching can be noticed on the bags before a fire.

Sparks may occur as scrap is added to the molten metal. This is common when the scrap is oily.  The usual time to add scrap into the furnace is at the end of the shift when the collector is especially vulnerable to fires.

The approach to prevent fires is to extinguish sparks if they are present and to cool the hot spots when air is not flowing through the system.

To extinguish sparks the flow before the collector must be changed from laminar to turbulent flow. This is accomplished by installing a QUENCHER spark arrestor in the air conduit to the dust collector.

To keep the "hot spots" cool, my suggestion is to pulse the collector off line every thirty minutes or so for one complete cycle to cool the "hot spots". If the off-line cleaning is too frequent, the cake will be destroyed or damaged, so, the cleaning must be controlled.

When selecting a fabric pulse jet collector, high-ratio technology designs can operate at filter ratios of 16:1.  Cartridge collectors are not a good selection as the pleats may promote formation of the hotspots described above.

We first used this technique at St Joe Mineral, which was near Pittsburgh, 30 years ago, on their zinc oxide furnaces. We were informed that they were venting through an AAF pulse jet collectors. AAF has managed to put out some of the worst pulse jet collector designs in the Industry. From the description it sounds like a AAF FabriPulse. That collector if it is top access design has these venturies that wedge in the top of the bag. Using the American vernacular, it sucks. The purpose of the venturi is to seal the top of the bag with the cleaning jet. There are openings around the top of the bag below the wide part of the venturi. This, in effect, allows the jet to grow until the growth is stopped by the walls of the bag. That is an over simplification of the process, but it is a fact that it sucks. The net result is that the collector cleans poorly and there is a lot of dust that is forced into the surface and subsurface filter cake.

On any kind of brass furnace it is best to keep the dust cake porous and thin. As I explained previously, in a brass and other process, the zinc goes from vapor to liquid to solid and forms zinc fume. This zinc fume because of its large surface area to weight ratio can burn or explode quite easily.

We were involved in a legal action where the customer hired a man to change bags on a MikroPul collector venting a zinc dipping operation where they were coating pipes. The young man, after he was half finished (inside removal) sat on the temporary grate and decided to light up a cigarette. The collector exploded and then burned down. He was blown out the access door with the explosion and the sprinkler heads went on after the fire started and water poured over him as he was lying on the ground.

Since we were told that the fires started when the process flow continued we need to look at the source of ignition. If the ignition is caused by sparks, the best way to suppress sparks is by going from laminar to turbulent flow in the dust before reaching the collector, with a good in-line spark arrestor. The next source of ignition might be through the cleaning jet. The cleaning jet can supply oxygen from the compressed air and when it reaches the cake maybe sufficient to cause some sparks similar to small explosions to occur in the cake. This may ignite the rest of the fine fume fuel to start a fire. This would be very pronounced, if the collector was running at a high pressure drop with a dense thick cake and frequent pulsing.

We can attack the symptoms or the causes. One way to attack the symptoms is to limit the thickness of the cake. This can be accomplished by installing PTFE membrane laminated bags. Another way to attack the symptoms is to clean the collector with compressed nitrogen instead of compressed air.

One cause may be because of the atrocious design of the cleaning system. The way to remedy the poor design is to modify the cleaning system design. To implement the change we need to throw away the venturies and modify the pulse pipes so they can run without venturies. We can get the pulse pipes modified so they will induce more cleaning air per unit of compressed air, possibly lowering the formation of sparks on the bag surface. It would allow the collector to run at a lower pressure drop with less frequent pulsing.

I always like to look at how the operation of the collector interacts in the process of venting the furnace. 

Read More...  About assistance with dust collection applications.

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