Let’s look at three service reports which illustrate the problems of condensation and outline the possible solutions.

London, Ontario Installation;
Cartridge Dust collector retrofit on Plasma cutting stations
The client complained of having to service the cartridges every 1-2 days because they would plug up. The pressure drop across the collector would rise to 8-10 inches water column. The cleaning system was totally redesigned, and six 36” high ratio style cartridge filters replaced twenty-four 26” tandem cartridges. 80/20 paper blend cartridges were installed temporarily until special anti-pinch style polyester filters could be supplied. Within two days the paper cartridges blew apart, mostly at the closed end-cap. They did run the pulsed cleaning system at 100psi instead of 85psi, with no regulator on the line. However, that was not enough to rip the media apart, so, something else was the cause. Upon inspection of the cartridges, we observed that the media was dry but had the look of being wetted. Also there were watermark stains on the clean side of the media. There was an accumulator tank on the compressed air line leading to the collector. The maintenance people told us the accumulator was installed because the valve manifold wasn’t large enough to hold enough residual pressure during a pulse. The manifold was just fine. What was happening is that the air line was very long (over 200 feet) from the compressor to the collector. Moisture would condense in the line then drop out at two elbows, which was the low point just before going up to the manifold. This choked the line which made the manifold appear like it was too small, and then suddenly a slug of water would blow through to the valves and into the cartridges. We recommended taking out the accumulator tank and, just before the connection to the valve manifold, installing an air line coalescing filter, top quality dryer, and a regulator set for 85psi. We also recommended an automatic drain valve system on the manifold tank. The collector now runs continuously at 3-3.5inch pressure drop. The client says they’ve never been able to control the contaminants at the plasma stations so well since they installed the system 1.5 years prior to the retrofit.

Maine Installation; Energy Recovery from Trash and garbage.
This collector installation was venting a large room where garbage was dumped. Front-end loaders took this garbage and carried it to the hoppers that fed an incinerator. Steam was produced that fed a boiler. The pulse jet collector vented 65,000 ACFM at ambient conditions. It was running at a 15:1 filter ratio and at 2 “ water column from January to June. In June the pressure drop started to creep upwards about 1/8 of inch per week. This collector was well instrumented with continuous recording of wet bulb and dry bulb temperatures as well as pressure drop. We compared the pressure drop increases with the weather reports in the local newspapers. The increases occurred early in the morning on days when the wet bulb and dry bulb temperature were closer than 5 degrees F. There were several kinds of trash being handled in the facility. We recommended that they not load the wet trash into the incinerator until after 10:00 a.m. This stopped the rising pressure drop problem. Since they shut the system down on weekends we recommended that they clean the collector for two hours on Saturday afternoon with the outlet fan damper 90% closed. This was almost as effective as off line cleaning and the dust was not blown back into the loading room during the procedure. The dust collector ran for at least two years, at less than three inches water gauge pressure drop after implementing these recommendations.

General Comments:  The cleaning system was running at 85 psig. Under typical conditions the compressed air expands to critical pressure which is 37psig. beyond this pressure, the pressure to velocity conversion stops and from 37 psig to atmospheric pressure, 0 psig, the energy is turned to heat from turbulence. This nullifies the refrigeration cycle as the compressed air expands to critical pressure. This collector used converging diverging nozzles which had a complete conversion of pressure to energy so that the refrigeration cycle was reducing the temperature in the jet by approximately 5-8 degrees F. Actually the turbulence below 37 psig causes some heat regain but the jet is still 5-8 degrees cooler despite this. Without the regain it would be about 9-12 degrees cooler. With a converging diverging nozzles the amount of cooling from expanded compressed air in the jet is a bit colder but the amount of induced air from the plenum is almost twice as much as with an ordinary orifice so the jet temperature is about 6-8 degrees cooler but not enough to make a difference. In Maine, the problem was mainly in the summer when the trash was wet from people dumping beer and other associated liquids. They did not have the problem in the winter when the trash was dry.

There were two other approaches that could have been used to counter the rising pressure drop:
1) Larger pulse valves and eliminating the nozzles. However, this would increase air consumption by over 35%.
2) Manifold heaters could be installed that would raise the temperature of the cleaning jet above ambient even to the point where wet garbage could be processed in high humidity conditions.
In either case, the collector could not handle vent volume where the gas entering the collector has condensed water droplets.

Low pressure compressed air, in the range of 7 to 22 psig is often employed for pulse jet cleaning systems. These have the same effect as the cleaning system with converging diverging nozzles since no turbulence occurs as complete expansion occurs in the orifice or nozzle. The best remedies are as follows:
1. Locate the low pressure compressor near the pulse valves and insulate the manifold leading to the pulse valves.
2. Use a manifold heater in the compressed air header, same as described above.

Other Comments and observations. There are many other installations in energy recovery plants that use high ratio reverse air fan collectors, The temperature regain on the reverse air fan is higher than ambient and eliminates condensation considerations described above.

East Tennessee Installation; Powder coating
This plant in the upper elevations in the mountains used a pulse jet collector to vent a powder coating operation that coated the internals of residential wash machines. This pulse jet collector started in July and ran until the middle of the winter when it developed a creeping rise in pressure drop characteristics. The wet and dry bulb spread was usually over 15 degrees F except early in the morning when it was about ten degrees. Investigation of the operation was conducted and we measured wet and dry bulb temperatures with a sling psychrometer mounted through a hole in the main vent duct. What we discovered is the booths were manually washed with a hot water hose every morning. At times the gas would go through the dew point for several minutes and then immediately go back to operation at a wide dew point spread. We recommended mounting a heater with a damper on a branch line to the vent system. The heater was triggered by pressure switches on the hot water hoses in each booth. This eliminated the creeping pressure drop problem permanently.

Use these links to obtain more information:
Dust Collector retrofits
Dust collection
Baghouse, cartridge dust collector

Below is a sketch of the Star Bag.

They came out about 10 -15 years ago as a pre-cursor to the pleated bags. It was a way to get the results of a cartridge filter style dust collector at high temperatures. Cartridges are limited to a maximum of 170degF. Also, the objective was to reduce dust penetration to adjoining bags during a cleaning cycle. It offered more surface area per bag to increase dust collection capacity per filter element. The dust collector could run at lower air-to-cloth ratios, thereby reducing the pressure drop. Our dust collector correspondence course teaches that this is a fallacy.

We believe someone in Canada makes these but we couldn’t tell you who. Some filter suppliers may know someone. These are very much more expensive than standard bags and cages. You can accomplish the same and have better results with a new advanced technology baghouse or retrofitting an existing dust collector to the new technology.

Ask for our free correspondence dust collector course and read numerous articles on dust collection technology at our internet website www.qamange.com.

Transport of sparks through ducts; Referring to the sketch below, there is a glowing ember (red particle) surrounded by some hot air (yellow envelop) which gives the spark buoyancy. This spark and the hot gas associated with it can travel hundreds of feet in a duct. The ductwork is designed to give laminar (smooth ) flow. This is illustrated on the left. Spark suppressors are placed in the duct to change the flow to turbulent (coarse) flow, as shown on the right. This agitation or turbulence strips the air from around the ember thereby removing the fuel (oxygen), therefore extinguishing and cooling the spark below ignition temperature (pink particle).

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

Quencher Spark Arrester, click here.

New Advanced Technology eliminates design flaws; allows for High Ratio Operation.

The History of Reverse Jet and Pulse Jet Design and Development must be reviewed to determine proper selection of collectors.

The first pulse jet collector was developed by Pulverizing Machinery of Summit New Jersey in the early 60’s, to collect dust from their Pulverizers. They had tried to use the Blow-ring design but they could not handle the dust (powder ) loads as their grinder Pulverizers became bigger. The typical load to the collectors from the Pulverizers were between 150 and 300 grains per cubic foot. The collector design was based on the same blow-ring filtering velocities at these loads. The cages were based on available designs from shipping pulverizer shafts. The pulse valves selected were diaphragm valves that were the fastest and the lowest cost valve available. This valve happened to be a ¾ inch diaphragm pilot operated valve. They decided to use several valves in a collector and pulse them with an electronic timer. It was found the hole sizes and venturi formed  an air ejector design that had the same jet velocity that the blow-ring collector was using. But the big breakthrough came with the realization that the dust was ejected from the bag during the first 4 or 5 milliseconds of the valve opening. The valves were operated as fast as the mechanical design allowed. The operation was completed in less than 0.10 seconds. It became apparent that the frequency of cleaning was a function of the load to the collector. For instance for loadings of 300 grains the collectors would operate at a filtering velocity of between 7 and 9 ft per minute. At material handling facilities such as quarries, the collector would run at  velocities of 14 to16 feet per minute. The typical pressure drop in these collector designs were about 3.5 inches water gauge pressure for the high loads and  2.0 for the lower dust loads. The typical compressed air usage on the high loads were 1 to 2 SCFM  per 1000 CFM of filtered air. For loads under 10 grains per cubic foot, the air usage was 0.2 to 0.8 SCFM per 1000 CFM of filtered air.

Determining the filter velocity (then referred to as filter ratio) became a rather complicated procedure. The ratio presumably was determined by dust load, fineness of the dust, temperature of process gas stream, and other factors.

The hopper inlet was a carry over design from both the blow-ring collector and the previous mechanical shaker collectors.

By 1969, there were over 10,000 collectors in operation. Almost all of them were installed on process exhaust from Pulverizers or in foundries. Pulverzing Machinery changed their name to Mikropul and licensed FlexKleen to also build and Market collectors. The collectors for MikroPul had 4 ½ inch diameter bags 72 inch long and the FlexKleen units had 5 inch bags 102 inches long. Bag life was 3-5 years on Pulverizer applications and over eight years on low loading applications.

Engineering Disaster 1971

In 1971, the patent was challenged and the Pulverizing Machinery patent was declared invalid. The market changed radically because Air Pollution Control Regulations also became effective at the same time. Many new suppliers entered the market. In order to compete, Mikropul changed their design. They went from 6 foot to 10 foot bags. They increased their pulse pipe holes by the same ratio. The whole industry followed and copied the new design for hole size and venturi throat diameter. At the time, Mikropul had 40,000 venturies in stock and kept the same venturi sizes. This increased the jet velocity of the cleaning jet by 66 per cent.

This was when the dust collector market was growing at a 20% annual rate. With the new designs:
(1)    pressure drop increased to 4 ½ to 6 ½ inches w.c..
(2)    Compressed  air consumption increased by over 50% for similar applications.
(3)    Bag life was reduced by over 50%.
(4)    In reaction to these problems the filter ratios were reduced to between 4 & 6 on almost all applications.

Reasons for Disaster

What happened was no one at that time realized what might have been a rather obvious truth, that the velocity with which the dust is ejected from the bag during cleaning is proportional to the velocity of the cleaning jet. At the new velocities, dust is driven toward adjacent rows of bags in the filter mode. Depending on the dust density, the dust will be driven through the adjoining cake into the clean side of the bags. The cake becomes more dense and the pressure drop increases until the process stabilizes which takes 16-100 hours. Even after the equilibrium, the dust still penetrates and bag wear is high. With low filter ratios it takes longer for the bag to wear out and require longer times between replacements.

Today’s Conditions

This disastrous design continues to be employed by most of the pulse jet collector suppliers in the world.

New Technology eliminates design flaws

Twenty-four years ago a new technology was developed, a new pulse jet collector that basically changed the cleaning system design. The key to this design was to change the jet velocity to a fraction of the existing designs. New Technology eliminated the penetration of dusts from the row of cleaning bags to the adjoining row in a filtering mode.

This allowed pulse jet collectors to operate at:
(1)    lower pressure drops (1- 3 inches w.c.),
(2)    lower air consumption (50-75% less)
(3)    3 to 4 times longer bag life
(4)    filter ratios of over 14 : 1 on any application
(5)    decrease dust penetration by up to 90%.

There have been several suppliers building and selling these New Technology collectors since 1982. In fact the patents have now expired. There are over 4000 installations worldwide.

WHY IS THIS NEW TECHNOLOGY NOT ACCEPTED BY ALL THE MAJOR SUPPLIERS?

1)    If you produced 40,000 collectors after the development of the new technology was published over 20 years ago, you might be subject to legal action for poor judgment and causing the public to be overcharged for their dust collection.
2)    They do not have the engineering expertise to build these new technology collectors.
3)    People using the old obsolete technology control over 90% of the market world-wide.
4)    The suppliers of valves and filter elements would have their markets cut in half.
5)    Air compressor sales and service for pulse jet collectors would be cut by 60%

MODIFYING EXISTING COLLECTORS WITH ALMOST NO RISK TO THE PURCHASER.

We can supply new bags, pulse pipes and bag plugs to alter performance to high technology low pressure drop, reduced air consumption, lower penetration (immediately noticeable) and long bag life (it takes some time to verify that but it should be obvious from the other indications). The modifications take only a few hours and if a customer is not satisfied, he can return pipes and cages for credit and re-install the old components.

If this was not an absolute certainty customers would not pay for the equipment.

For more information go to website: http://www.qamanage.com/

General Considerations
The effects of static electricity on the collection of dry particulate in fabric collectors is rather simple but misunderstood. For the most part, cartridge dust collectors experience the same issues.
First we must consider the cause of static charge build up in a collector. It occurs because the dust being collected is akin to a capacitor in an electronic circuit. In this day of computer chips the designer may not be familiar with this phenomenon. The capacity has two conductive plates separated by a layer of insulating material that has high enough insulation values that the static charge remains for relatively long periods. The charge can be removed by grounding one side of the capacitor. The charges then drain.
In dust collectors where the dust forms in the filter cake, the static charges may enter the collector on the surface of dry particulate dust. If the dust has high dielectric resistance properties, it can accumulate and build up in the filter cake. It can be viewed as many particles each carrying a static charge and acting like a miniature capacitor. The static charge will then build up on the surfaces and may reach a high enough level where a spark can be produced. This spark can trigger the explosion of explosive dusts.

Mechanical Cleaning (Shaker) Dust Collectors
In a fabric collector with a mechanical shaking mechanism to remove the dust, the collector is most vulnerable during the cleaning process. The dust is shaken from the filter bags in the process of shaking the cake, sparks sometimes are produced. Invariably, the dust/ gas mixture passes between the upper and lower explosive limits. A serious explosion may occur.
Usually these collectors will have explosion vents which relieve the high pressures that are generated in an explosion, presumably keeping the housing from being damaged and protecting the operating personnel near the dust collector.
In an attempt to keep this static charge from building to threatening levels, measures are included in an attempt to bleed this charge to ground. These include one or more of the following:
1)  Sewing in grounding wires into the filter media.
2)  Impregnating carbon or other conductive coating into the filter cloth.
These often give the designer a false sense of security in applying these to dust collectors. As explained above the dust, itself, insulates the charge and it remains in the cake until it reaches a point where a spark is generated. If the dust concentration is above the lower explosive limit and below the upper explosive limit, an explosion can occur. Fortunately, generation of the spark may not occur if the timing of the spark and dust concentration level do not coincide. An explosion does not occur in these cases.

Continuous Cleaning Reverse Jet Pulsed Dust Collectors
When dust, with the same properties described above, is vented in the same operations, using a reverse pulse jet cleaning system, the danger is considerably diminished unless the pulsing is applied in “off line” cleaning mode where the fan is stopped.
These collectors clean the bags by injecting air from the clean air plenum backwards through individual bags as the flow continues through the collector.   This cleaning agitates the filter cake so the static charges are dissipated.
The danger of explosion occurs when the dust concentration coming into the collector reaches a level between the lower and upper explosive limit concentrations. This is highly unlikely but we recommend that properly sized explosion vents are installed which normally coincides with the requirements of insurance underwriting firms.
The explosions can occur when there is dust build up in ducts especially when long horizontal runs are encountered. The spark can be generated in ducts and the explosion front can travel down the duct into the dust collector, igniting a secondary explosion as the concentration in the collector housing is driven above the lower explosive limit for that dust. Even with no build up in the ductwork, an upset can occur in the process which generates sufficient dust concentrations.
One method of nullifying the possibilities of danger due to duct build up is to install an automatic booster / duct cleaner device (www.qamanage.com/products/Booster.htm) . This booster can serve to automatically clean out any drop out in long horizontal duct runs.
Another phenomenon can affect of dust collector systems, is where the dust has high dielectric properties and the dust, because of static charges, will build up on the outside bend of an elbow. This dust can trigger an explosion if this dust is also flammable and explosive. Some examples of dust where this problem is often a factor are toners for copy machines and electrolyte powder used in alkaline batteries. The solution is to insert a pulsed air jet that agitates the built up dust that dissipates the charge. Some dry powder coating compounds are also subject to static charge build up in powder coating systems.

For more information see these web-pages:

Booster / Duct Cleaner; www.qamanage.com/products/Booster.htm

Quencher spark arrestor; www.qamanage.com/products/quencher_spark_arrestor.htm

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 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 collector, 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 cause 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:
A) Manifold Tank Automatic Drain Valve System
B) 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.

For dealing with moisture problems, click here.

The original Design of most contemporary reverse pulse jet collectors was developed in the early 70”s. This design was a breakthrough in dust collector technology. In 1978, several technologies were developed to remedy operating problems of Fabric Pulse jet collectors. The cause of these operating problems was a flaw in the design.

Cause of Operating Problems

The main flaw in the contemporary design of fabric pulse jet collectors was that during the cleaning cycle dust was driven from the cleaning bags at very high velocities, then driven through the adjoining bags through the filter cake and filter media. The bags became partially blinded. These velocities were typically 20,000 to 36,000 feet per minute. The permeability of the filter cake and dust imbedded in the media increased. The bag developed a coating to resist further penetration until the system stabilized.

These high cleaning jet velocities resulted in short filter element life, high pressure drops and high compressed air usage.

It is and was common for fabric pulse jet collectors to run at pressures between 4 and 6.5 inches, and air consumption of over 1.4 SCFM of compressed air per 1000 CFM of filtered air at 80 psig. As might be expected the heavier density dust an powders ran at the highest pressure drops.

NEW TECHNOLOGIES

Four new technologies were developed to combat these operating problems:

The cartridge collector with pleated filter elements.

The high ratio fabric collectors.

PTFE Laminated Fabric Filter Bags

Bag Diffusers

Cartridge Collector

The cartridge collector was immediately widely accepted because it solved a problem with venting electrostatic powder paint systems. Previously, fabric pulse jet collectors on this application gave unsatisfactory service. Within months of the introduction hundreds of collectors were sold and installed with spectacular results. The cartridge collector remedied some operating problems in the contemporary fabric pulse jet collectors. An example of this was the experience of Nordson Corporation of Ohio, who supplied powder pigment spray systems that sprayed powder on metal surfaces that were then cured to a hard coating. They vented the spray booths into Fabric Pulse jet collectors. On some pigments, they had bag lives of less than eight weeks and pressure drops of 6 to 8 inches w. g. Even at filter ratios as low as three to one. They were desperate for a new technology and were the first to embrace it.

Laminated Filters

In 1975 the Gore Corporation introduced PTFE membrane laminated bags. This prevented the dust driven from the bag in the cleaning mode from penetrating below the surface of the media through the filter cake. Hundreds of thousands of bags were successfully installed that eliminated many operating problems with contemporary designs. The laminated bags lowered the bag permeability, which sometimes limited filter ratio. Typically the bags cost 5-6 times more than conventional bags. Since then patents for this construction have expired.

Low Velocity Cleaning Jets and High Ratio Pulse Jet Fabric Collectors

In 1978, Scientific Dust Collectors introduced another breakthrough in Pulse Jet Dust Collector Technology. The venturies were removed from the bags and jet was changed so that velocity of the jet decreased by 60 to 80%. The velocity of the dust leaving the bag was also decreased by 60 to 80%. At the same time the volume of the air jet was increased by more than 3 times. As an adjunct of these changes, these collectors were operated filter ratios between 12 and 20:1 with pressure drops under 2 inches. In 1983 Carter Day Corp. introduced the same design with oval bags. Since then over 4,000 of these collectors operating at high filter ratios have been installed and are operating with those parameters.

These collectors must have special inlets which eliminate any upward velocity of dust laden air entering the filtration section of the collector. The lowering of jet velocities increases the collection efficiency on fine particulates. These may have difficulty falling into the hopper if the collector has a hopper inlet.

Bag Diffusers

These diffusers consist of light gage are perforated cylinders inserted into the bags below the venturies of existing collectors. They operate to improve dust collector operation by slowing the velocity of the jet as the cleaning air exits the filter bag toward adjoining bags. Because they too increase collection efficiency on finer dust, collectors with bottom inlets can may encounter limited effectiveness with this modification.

American Foundry Society Tests 1978

A test run by AFS on foundry dust showed that the penetration of the dust compared to a standard pulse jet was astounding:

STD Fabric Pulse jet at 4:1 filter ratio 800 x 10^-5 grains per cubic foot with 10 grain inlet

Cartridge Collector at 2:1 filter ratio 3 x 10^-5 grains per cu. ft with 10 grain inlet

Gortex laminated bags 10 x 10^-5 grains per cu.ft. with 10 grain inlet

Low Velocity Cleaning Jet Fabric Collectors* 10 x 10^-5 grains per cu. ft.

*These are New Technology collectors as described below.

This test was run in 1978 prior to the introduction of the new technology low velocity jet high ratio dust collectors but other independent tests showed the performance shown above.

Later tests of New Technology cartridge dust collectors, such as ULTRA-FLOW, revealed that they operate at 2 x 10^-5 grains per cu.ft. but at 6-8:1 filter ratio.

Determination of Flow ratings of New Technology versus Contemporary Designs

The flow capacity of a bag or cartridge in a reverse jet self cleaning collector is limited by the volume of the reverse cleaning jet. It is obvious that if I have 50 CFM flow in the filter element and the reverse jet volume is 40 cfm, the flow in the bag will not be reversed and no cleaning will take place on line. If the bag has ten sq. ft. of media or 100 sq.ft. of media it will not clean on line. However if I take this reverse jet and increase the flow to 200 CFM (50 CFM x 4) it will clean on line easily. If we temporarily accept the premise that you need four times the cleaning flow to maintain equilibrium, adding more square feet to the filter element will not increase filtering flow capacity unless you also increase the reverse flow volume. Another limitation is the operating permeability of the filter media and dust cake as covered in the first part of this memo.

Another limiting factor in filtering volume through collectors is the well- known “can velocity” parameter. This effect is most pronounced on very light density dusts such as paper dust, feathers, grain, dried organic fertilizers, dust from recycling etc. Dried manure is similar to grain and is susceptible to “can velocities” New technology collectors have special inlets where there is no vertical component to the dust laden gas as it enters the filter compartment of the dust collector.

If we consider the conventional designs where they have basically a reverse air volume of 250-350 cfm, and 20,000 to 30,000 FPM cleaning jet velocities, specifying a low filter ratio is excellent engineering.

However, specifying the new advanced technology results in better filtration, lower operating costs and longer filter life.

The better engineering approach is to specify dust collectors by considering the capacity and design of the cleaning system. This can be accomplished by taking the compressed air flow capacity of various sizes of diaphragm valves and multiplying by the number of valves, if orifices are installed in the pulse pipes: (This assumes that the total area orifice opening are maximum at 85% of throat area) If the pulse pipes have converging diverging nozzles installed the cleaning jet volume is increased by 50% with same increase is filtering flow in the collector.

¾ “ valve orifices 688 CFM nozzles 1032 CFM

1 “ valve orifices 1224 CFM nozzles 1836 CFM

1 ½ “ valve orifices 2754 CFM nozzles 4406 CFM

Example of comparing two collectors

Standard Design Collector with 81 bags 9 -¾ inch valves 10 sq. ft. per bag

9 x 688 CFM = 6,192 CFM 6192/1000 sq. ft. = 6.192 (nominal filter ratio) based on cleaning volume with no regard to can velocity. For low density dusts ratio must be lowered for lower density dust.

Advanced Technology Collector with 81 bags with 9- 1 inch valves with nozzles, and special inlet to eliminate can velocity considerations.

9x 1836 CFM = 16,524 CFM 16524/1000 sq. ft = 16.524 (nominal filter ratio)

The net cleaning jet velocity should be specified as no more less than 9,000 fpm and gross cleaning velocity no more than 15,000 fpm for dense dusts.

Upward component flow air entering compartment should be limited to 150 fpm for lower density dusts and 350 FPM for higher density dusts.

Specifying collectors based on filter ratio alone penalizes the supplier who provides more cleaning capacity with the larger more expensive cleaning components, and better engineered cleaning systems, depriving the client of superior performance at lower cost.

When to specify Fabric or Pleated filter elements

The other decision is between pleated filters and unpleated filters. The selection for pleated filters is confined to dust that has a thin filter cake. If the cake is deep bridging will take place in the valleys of the pleats rendering the media below the bridges uncleanable.

This blog is a guide to dust collection and solving common and difficult to resolve issues.

It is also meant as an introduction to NEW Technology that is more efficient, lower cost to operate and more reliable than conventional designs.

Unique accessories that improve performance will be introduced and explained.

90% of all dust collectors in operation today can be retrofitted to new technology which makes them at least 4 times more efficient, 30% lower power consumption, and up 70% lower operating cost.