Location: Cascade Canada, Guelph, Ontario.

Equipment: two Torit model DFT 3-18, tandem cartridge dust collector, self-cleaning pulse jet style.

Application: welding and cutting shop

Description: Client wanted to maximize the capacity of the dust collectors to meet the needs of their shop. These collectors were purchased second hand. A complete survey of the shop revealed that, in one case the collector was slightly undersized, and the other barely made it. It was noted to the client not to go by the catalogue CFM performance for these units. These ratings are always overstated and upon questioning Torit, they will advise the real performance of the collector. In this case, it was 5500-6000 CFM. The fan was sized to provide up to 10” WG of pressure. We judged that we had enough fan to do a level 1 retrofit of the collector to get them to the 7000 CFM they needed and reduce filter maintenance by 67%.

For more information on these retrofits, go to website; Quality Air Management /Retrofits

Problem: Shortly after starting up the dust collector, the pressure drop rose quickly to over 10” WG. The start-up pressure drop was 0.5” WG (better than expected). The filter cartridges were heavily loaded and full of dirt.

Investigation and Resolution: We checked that the retrofit was done properly, and it was. However, these dust collectors were purchased second-hand and the cleaning systems were defective. The client had to completely refurbish it. We removed the polyester spun bond pleated cartridge filters for inspection. They were heavily bridged with dust and welding fume. When using a compressed air hose with a good nozzle to manually clean the filters, very little air would blow through to remove the dust. We blew the cartridge from the dirty side and the dust blew off easily and completely. However, there appeared to be a staining on the filter media.

We sent a cartridge out to be tested. What we found in the test of the current filters;

•    The permeability test (ability for air to travel through the filter media) revealed that the filter media (spun bond polyester) was totally blinded.

•    Water cleaning only restored the permeability by 35%. Therefore the blinding dust is not easily water soluble.

•    Solvent cleaning restored it to 60-70 %, indicating it is solvent soluble but not totally. However, if the lab didn’t allow enough time (48 hours) for the media to dry, that could explain that the media would be swelled some when they checked it. This tells us that we are possibly dealing with something hydrocarbon based.

•    Dry vacuuming restored it to 90-95%. This could mean a very fine dry dust that squeezes into the larger pores of the polyester media but may not fit in the tighter pores of paper media and would sit on the surface. If that is the case, it would blow out when we try it.

•    Therefore it was decided to test two 80/20 paper cartridges in the dust collector for a week.

•    If the paper filters are no better, then we have a problem with the fume and the solution will be to use a “pre-coat” on clean filters to prevent this difficult material from getting onto the media.

At the end of the week,  as a result of the investigation mentioned above, I make the following comments:

•    We pulled the paper filters out and tried the blow test with a good nozzle on the air line. By simulating a pulse (quick short burses), the air seemed to go through adequately to clean the filters.

•    There was nonetheless a residue on the filter. In my opinion, this is attributed to the very fine hydrocarbon like nature of a component of the collected fume. However, there was very much less residue than with the polyester media. We took out one of the polyester filters, for comparison, and ran the same test. That one was completely blinded and no air got through.

•    After evaluating the test done by the lab and the ones we did on-site, our conclusion is that there is an unusually fine fume, although dry, exhibiting hydrocarbon-like properties, which is blinding the larger pores of the polyester filters but not as much the smaller pores of the 80/20 paper filters. This fume seems to imbed itself in the polyester media, making it impossible to dislodge, but for the most part rides on the surface of the paper media. This is a factor that we could not predict at the beginning of this project.

•    To confirm the unusual nature of this fume; when I washed my hands, the dirt on the surface washed out with a normal wash but there was something imbedded in my finger prints. After a second intense scrubbing that material did come out.

Our recommendation is to replace the polyester filters by 80/20 filters. However, it is not sufficient to leave it at that. I expect the filters will still clog in time and they are not washable (no matter what anyone may tell you). Paper expands when wet and does not restore itself, so you see similar characteristics after a wash, as we see with the polyester filters. Therefore, we also recommend using a “pre-coat” inert material. I must re-calculate the filter specifications since paper filters have a lower permeability than the polyester. I still want to keep the wide pleat spacing but can not have them as wide with paper as we had with the polyester filters. I am also investigating the use of “nano-fibre” coated media (somewhat like Torit Ultra-Web). I’m not particularly enamoroured with this stuff, but if they can convince me of its value in this particular case, it may be an alternative to pre-coating.

These dusts are highly combustible and present a very significant explosion hazard. There are some stringent fire codes dealing with these dusts which draw their regulations, for the most part, from NFPA 484, Standard for Combustible Metals.

Unfortunately, most end-users are not aware of these standards or safe methods of dust collection for these dusts. Worse, the dust collection industry is very negligent in guiding these people with proper and safe applications engineering. This document is an attempt to provide some of this valuable information.

First of all, we strongly encourage readers to obtain a copy of NFPA 484 and comply with it. There are far too many stipulations which go beyond the scope of this document. A copy of excerpts pertaining to each type of dust can be requested from Quality Air Management.

We will analyze the use of different dust collection methods to these dusts:

1. Dry Dust Collectors; include baghouse (both mechanical cleaning and pulse-jet self-cleaning), cartridge or pleated filter collectors, disposable media filters, electrostatic precipitators, cyclones.
2. Wet Dust Collectors; there are many styles of wet collectors available. The pro’s and con’s of each type is beyond the scope of this document.

In all cases the blower for drawing the dust-laden air into the collector shall be located on the clean air side of the collector. The dust producing equipment and dust collector must be

Mixing of Metals is not permitted, unless the entire system is disassembled and thoroughly cleaned prior to and after its use. A placard must indicate, for example, “Aluminum Metal Only – fire or explosion can result with other metals”.

Wet collectors are designed specifically to be used for all these dusts. These collectors are designed for collection of metal dust only, not for powder, smoke or fumes. The use of additional dry filter medium either downstream or combined with a wet collector is not permitted. Contact QAM technical support for a safe method to handle these contaminants which the wet collector can not handle. The cleaned air can be recycled to the work area if the collector is efficient enough to ensure safety of personnel. A provision for an unimpeded vent, when the machine is shut down, must be provided. Magnesium dust requires a powered positive venting of the sludge tank at all times during shutdown of the collector.

Dry collectors are allowable for aluminum, niobium  dusts, but are prohibited for all the other dusts. They must be located outside buildings. Filter media must dissipate static electric charge (be aware that grounded conductive media gives a false sense of security). You must avoid accumulation or condensation of water at all costs which could cause a hydrogen gas explosion. Explosion vents must be provided. Recycling of air into the building is prohibited.

Mechanical shaker style collectors; are highly susceptible to static electricity charges, and explosions.

Baghouse collectors; there are conventional designs, sold by 95% of dust collector suppliers, and new advanced technology designs.

1. Conventional; Due to the inefficient clean systems, only 10-20% of the filter media ever gets clean. This allows dust to accumulate in the collector beyond what is permissible by NFPA 484.
2. Advanced technology (i.e. Ultra-Flow); These are designed to clean 100% of the media on a regular basis. The cleaning frequency can be set to maintain a cleanliness that meets NFPA standards.

Electrostatic Precipitators are prohibited because they filter the air by applying an electrostatic charge across the air stream. That is a source of ignition and the dust will accumulate in the unit and coat the collection plates. This is a prescription of a very large and very load BOOM (explosion).

Cyclones; high efficiency models can be used for these dusts but must be located outside the building. Explosion vents are permitted. Recycling of air into the building is prohibited.

use this link to; wet dust collectors

The service engineer connected tubing to the correct ports from the solenoid valve enclosures.

After that was complete, the compressed air supply was again turned on. Again the pressure in the manifold would not increase enough to pressurize the manifold. From the sound of it, at least one diaphragm valve was open. To determine which one(s) was the culprit, He checked the ports that were open to atmosphere and found the solenoid valve that was open. He squeezed the flexible tubing leading to that valve and the valve de-energized and pressure built up in the manifold to 85 psig. He replaced the tubing and the collector started pulsing.

He next listened to the pulse. It had a hissing sound when the diaphragm valve was opened. The gauge on the manifold dropped to below 15 psig. Both of these symptoms indicate that a valve is open too long. (On the control panels it is usually a pot adjustment and labeled “on time”). This “on time” should be adjusted to the minimum time that shifts the diaphragm valve. All cleaning of the bags takes place in 5 milliseconds after the valve completely opens. It takes a valve 10 to 70 milliseconds to fully open depending on the valve used. The sound should be more like a thumping noise. The pressure in the manifold after each pulse should be no less than 50 psig. This proper adjustment of the “on time” often reduces air consumption by 50 to 90%.

Other General Considerations

Another cause of these symptoms may be debris in the compressed air line. In connecting the compressed air supply to a pulse-jet collector often new piping is installed. In the process of threading the pipes and installing fitting shavings may accumulate in the piping. Sometimes the air line filter is installed far away from the dust collector. If these shavings get into the collector valves they may clog up the internal vent port in the diaphragm valve and get into the actuator on the solenoid valves causing them to stay open. Before the piping is hooked up to the manifold on the collector, the pipes should be blown clean. The pulsing may cause the shavings to gradually move down the pipes and not show up until a few days after start up.

Another possibility occurs when it is noticed that diaphragm valves require frequent replacements of the diaphragms and the spools in the pilot solenoid valves also require unusually high replacement. It is possible the air line lubricant has the incorrect fluid and will attack the sealing materials. These valves are good for at least 100,000 cycles which is 4-5 years for a single shift operation, 5 days per week.

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The problem:
1.    The operator may have to reset the heat setting of the plasma head. It could be generating too much atomic static particles. This causes a “painting” effect on the cartridge media, eventually clogging it.
2.    Large heavy particles of molten metal can be generated in the process.
3.    You should use spun bond wide pleat cartridges, to ensure proper clean out of the cartridges. That way the dust will spread over a large surface of media, instead of on the outer surface only.
4.    Current cartridges that are clogging over time (can vary from hours to weeks, depending on loading). When clogging occurs, the air flow drops and sparks can slip through any spark arrestor (not just the Quencher). This sets fire to the combustible dust accumulated on the surface of the cartridges.

Normally, plasma cutters have different characteristics depending on the settings of the cutter torch. The quantity of dust produced is relatively small. At some torch settings the dust is reactive by initiating an atomic bond between the dust and the surface of the cartridge, forming a hard durable impervious coating which totally or partially plugs the filter media. This mechanism is an inherent part of the plasma coating process to put wear resistant coatings on shafts, turbine blades etc. that allow the parts to receive very long lives. In the plasma coating machinery, the key to collecting the overspray in cartridge or fabric collectors is to allow the atomic bond to dissipate. This is accomplished by extending the time that particles travel from the torch to the filter media elements. In plasma coating systems at this time, depending on torch settings will vary from 0.5 to 0.8 seconds depending on the metals being sprayed.

In plasma cutting applications often the dust being emitted from the torch does not require any special considerations. In fact, collectors can operate for many months quite well with moderate pressure drops. Then the torch settings are changed because of various factors such as the composition or thickness of the pieces that are cut. As the settings of the gun or the speed of the cut is changed, the dust can act as a plasma coating torch and the cartridges start plugging. Sparks are often produced. If the dust is combustible the sparks may ignite the coating on the cartridges. Normally the fuel on the cartridge surface is not very heavy so the fires do not damage the housing of the collector. The cartridges are then usually replaced. The QUENCHER spark arresters are sometimes applied to limit the risk of fires and extend cartridge life. In the tandem horizontal type collectors, the cartridges are usually tight spaced, so, as the pressure drop rises, the pleats are pinched in the valleys so the pressure drop goes up. Combustible dusts can put pounds of dust to be stored in the cartridges to fuel a fire in the collectors. However, the squeezing of the pleats also causes pressure drop to increase and slow the flow through the dust collector. This often allows dust to be released into the work area.

Although spark arrestors will protect the system from sparks, pieces of molten metal go through the spark arrestor unaffected. These heavy, hot particles lodge on the surface of the cartridge and ignite the combustible dust coating. The heavy molten particles need to be dropped out of the system prior to the spark arrestor and collected safely, so as not to cause a fire in that collection device. Cyclones and drop out boxes are sometimes used for this. However, be aware that these devices have little effect on sparks / embers which are light buoyant particles and slip through to the dust collector.

An excellent example of these effects was the experience of the Day division of Donaldson who supplies this design. In cutting the filter mounting plates for their design they plasma cut holes in a 1/4 inch thick plate. They found that the filters plugged quickly in the after filters. They added distance in the filters venting the operations. This experience occurred 20 years ago and we do not know how this operation is now performing.

Our recommendation is to replace the current cartridges with a wide spaced stiffened spun bond media carried and pre-coat the cartridges with a 1/64 inch thick coating of inert pre-coat material.

We suggest you send each job application data (layouts & pictures) to QAM technical support at garyb@qamanage.com and/or call 800-267-5585. We’ve dealt with plasma cutting applications for decades and feel that yours would be a common problem. If you contact us, we’ll be happy to work with you on this.

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It was a nice trip for our service engineer in Mexico City with a stay at the Camino Real, freely translated as the royal road. It was one of many sites visited that week all with the same complaint. The pressure drops of the systems were much lower than expected. The result was that power was wasted and in the case of an arc furnace the electrodes burned up at an alarming rate.

The problem boiled down to the fact that using the Industrial Ventilation manual produced higher pressure drops than those calculated in their procedures. The pressure drop across the collectors was lower than for historical numbers. After a couple of days in the office we came to a startling conclusion. The pressure drop was related to the Reynolds number.

We came up with a procedure that was quite simple. To figure pressure drops all you had to do was convert air flows to SCFM instead of ACFM. It worked like a charm. We were then able to modify fan speeds to suit each application. The fan speeds were selected based on actual density at the proper temperature and altitude. This procedure can be used to figure pressure drop at any density due to altitude or gas temperature.

Venturi Scrubber Modifications for fan exhausters.

The normal procedure is to use two factors one for the pressure at 30-49 inches of water for a typical venturi scrubber system and the other for the temperature. If the temperature is calculated to be 160oF a common value exhausting a melt furnace the density will be too high and the required pressure will not be developed. The pressure developed by the fan would be more than 40% less than using the multipliers found in the fan catalogs. The fan belt drive must be modified to compensate for these radical differences in density.

Vacuum Conveying System for GM Brake Shoe Plant in Ohio

The collector was designed to run eight inches of vacuum. Inspection revealed that the pressure drop across the bags was 5.5 inches water gauge of pressure drop. It was a 40 bag collector cylindrical in shape with a high inlet. The load was 30 grains per standard cubic foot and the compressed air pressure was 85 psig. The flow was 200 ACFM. It had seven valves 3/4 inch diaphragm size. The complaint was the collector required pulsing every 4 seconds to maintain the pressure drop. Since the gas density was approximately 50% of atmospheric the pressure drop was equivalent of running at 11 inches w.g. at atmospheric with a filtering velocity of 1:1  when based on SCFM instead of ACFM. The collector on this basis should have run at about 0.2 to 0.3 inches of water pressure drop across the filter mounting plate. After an investigation it was discovered that six of the blow pipes failed because of a manufacturing error. When they were replaced the pressure drop dropped below 0.4 inches and maintained that pressure when the collector was cleaned every four to five minutes. It was an excellent demonstration of the pressure drop across a pulse jet collector when the density drops.

General

In designing several pneumatic conveying systems based on actual CFM on positive displacement systems pressure drop and capacities, the pressure drop is higher than predicted. The collector should be designed on the basis of SCFM as outlined above.

use this link for; System design assistance

Explosive dusts have lower and upper explosive concentrations. An explosion can only occur if the following is true. Assuming we have outside air with 20% oxygen being used to ventilate the mill, it is probable that the outlet from the hammer-mill will be between the upper and lower explosive limit concentrations. Between these limits if there is enough energy in the spark that ignites the dust, an explosive flame front will be triggered and move along the duct toward the ventilation outlet and presumably toward a dust collector, and, we are assuming this is to be a fabric (baghouse) collector. Determining the upper concentration limit is very difficult. The lower explosion limit is around 30 grains per SCFM for combustible dusts like coal. Once an explosive flame front is ignited the normal procedure is to put explosion vents in the ducts and collectors.

The action of Quencher spark arrestor.

Our Quencher spark suppresser works by changing the flow in the duct to turbulent flow. During laminar flow the spark can be carried for extremely long distance as the spark travels with a layer of air which insulates it. When turbulent flow is induced, the spark is immediately cooled so it lacks sufficient energy to start a fire or trigger an explosive front. Most insurance underwriters require explosion venting of the duct systems and dust collectors. The way of achieving this conversion from laminar to turbulent flow is by slowing the air down to lower the power consumption of the conversion device. The conversion device thoroughly mixes the dust laden gas stream with propeller type fixed vanes to extinguish the spark(s). To rid the potential low velocity build up of coal dust in the spark arrestor, it is periodically boosted in air stream speed to sweep the dust into the collector. This uses a compressed air propelled stream identical in design to that of a reverse pulse jet collector with time durations similar to that in those dust collectors. This the “Booster – Duct Cleaner” option is offered with the Quencher spark arrester.

Please send further details of sizes, volumes, system layout so a suitable system can be selected.

use this link; for details on Spark Arrestors

FOREWORD

Many gas steam processes, especially in powder collection systems, are candidates for the application of low cost gas mixing products as the Quencher supplied by Quality Air Management.

Note that embers & sparks get extinguished in the Quencher cell itself.  Combusting  material, such as paper or wood shavings, must be completely consumed within 4 duct diameters past the Quencher (where there is still enough turbulence) and taken the form of embers to be extinguished.

1) SPARK COOLING

Prevention of Sparks entering Solids separator (dust collector) equipment and starting fires

Definition: First we must define a spark. A spark is a piece of solid particulate which is completely oxidized and is at a temperature of 600 degrees F or over and which is above the ignition temperature of the powder being collected or above the ignition temperature of the filter elements.

Effects of sparks: Sparks can be carried along in the exhaust gas stream in laminar flow and will not cool off since cooling requires a difference in velocity between the gas and the spark being transported. Therefore, the spark will be carried into the solids separator and deposited on the filter element surface where it has a possibility of igniting the surface. If ignition occurs, the fire may spread and cause damage and produce harmful gases.

Response by the QUENCHER to sparks occurring in exhaust stream: The static blender converts the laminar flow to turbulent flow by thoroughly mixing the solid sparks with the gas stream, reducing the temperature of the sparks below the ignition temperatures of the filter media and the powder transported through the system.

2) HIGH TEMPERATURE COATING AND CUTTING PROCESSES

Originally a lot of these operations were performed by cutting with an acetylene torch to cut metal and with flame spray equipment which fed a wire into the flame of a gas torch to produce coating on various metallic and non-metallic surfaces.

The torch cuts were very coarse and had to be ground or put into other cold forming devices to make the parts usable. Often these cutting torches were applied to cutting up and reclaiming scrap. Most venting systems for torch cutting were vented into general ventilation and HVAC systems.

The flame spray equipment was limited to certain thicknesses and uniformity was such that on many parts subsequent grinding and smoothing operations were necessary. The coating produced was relatively coarse and the overspray was easily collected by low pressure drop wet powder collection devices. This avoided any requirements for mixing equipment.

The Advent of high temperature technologies was developed in the 1980-90’s decade; Lasers, plasma, and arc tools have been applied to the processes long dominated by gas torches and sprays. These new technology systems are much more intense, quicker, more accurate and more efficient than the old gas flame units. The temperatures developed in the devices are sufficient to vaporize metals and actually increase the temperature above this value. These systems can take sharp cuts and make intricate cuts, cut fine round holes replacing shears, drill with little or no need for grinding or finishing. They can process thick plate or light gauge sheet metal with the same machinery. They are guided by CNC controls for maximum flexibility. Applying these processes to spray systems is also very effective. The spray process must be explained prior to treating the ventilation of the high temperature cutting devices. These are the fastest growing fabrication processes in the world.

Spray systems; These systems were vented into relatively large gas and powder over spray collection hoods. They produced particles with a very strong attraction to the parts being coated. Some have theorized that the bonding is at the molecular level. When it strikes the surface to be coated it bonds to the surface as if the coating was integral with the object that is in the path of the spraying device. The coating is either fed into the device as a powder or a wire.  The particulate overspray is relatively light in dust loading and the hood is vented to a dust powder collector. The wet collectors are not sufficiently effective to collect this much finer overspray. To develop sufficient collection efficiency, the overspray is vented to fabric or cartridge collecting device. The overspray is still attracted to any solid it gets near and will form a hard impermeable coating which can seal the surfaces of filter collection elements. These overspray particles though much finer than the sparks described above are carried along in ducts which have laminar flow. They must lose their attractive ability before they reach the dust collector / powder separator. If the powder spray is given sufficient time in flowing through the duct work, it will lose its coating ability. Typically the residence time of the dust flowing in the duct, is designed for about one second and sometimes up to 1.5 seconds. For a system running at 2400 feet per minute at least forty feet of duct work would be required between the hood and the collector. Most plants do not have the room for these long ducts. We theorize that a QUENCHER element could allow the reduction of this residence time by as much as 90% and be more predictable than the residence time especially as newer spray compounds are being developed.

Venting High Temperature Cutting Systems; Although the dust venting from the cutting processes do not have as high an attraction as the coating guns, the dust has the same problem. Residence times are often in the 0.5 to 0.7 seconds. Because the dust loadings are so low and the customer often removes the coated filter elements and vents outside, the emissions will be lower than most air pollution codes. However, if the dust could be collected and neutralized, the savings in heating and cooling costs could pay for a QUENCHER device in a month or so.

3) GAS MIXING IN POWDER SEPARATORS

QUENCHER gas mixing cooling of gas  streams; Usually all gas streams are designed for the lowest pressure drop to save on power consumption in moving the gas from one point to another. This is accomplished by moving the gas in a flow pattern called “laminar flow”. In effect the gas stream is divided into cylinders that flow parallel in the duct work so that little or no mixing occurs between these cylinders within the walls of the ductwork. The other flow in a duct occurs when “turbulent flow” occurs. This is a violent mixing that occurs and will quadruple the pressure drop if it occurs in a length of duct. The gas follows the path of least resistance and naturally wants to revert to “laminar flow” when the disturbance or duct element, which produces the turbulent flow is removed. Both laminar and turbulent flow pressure drops are a function of the average velocity through the ducts. If we mix two gas streams flowing through well designed transitions that maintain laminar flow in the total stream, the resultant is that the gas streams will continue in the duct with little or no mixing of the combined gas streams. For instance if a gas stream at 300 degrees F is mixed with one at 100 degrees F, the resultant gas stream will be stratified and continue through the system with part of the flow at 100 degrees and part at 300 degrees. There might be a very narrow layer of the flow that mixes.

The proprietary QUENCHER design is such that the whole cross section of the duct produces an effective mixing with a minimum penalty of pressure drop by producing turbulent flow through the mixing element.

Temperature Lowering Processes for Solids Separation; Some powder collection gas streams use various means to cool the powder laden gas streams by mixing ambient outside air to reduce the gas temperature (and associated powder temperatures) to a level where a fabric media powder collector can separate the powder and gas for subsequent collection of the solids. A typical operation of this type is on a clinker cooler system in a cement plant. The gas temperature may vary from 200 to 900 degrees F. For operation of the powder separator collector, the temperature entering the collector must be lowered to less than 500 degrees, usually 475 degrees. This can be accomplished by blending the ambient gas stream with process gas. When this mixture is designed, the resultant gas streams often remain stratified with low and high temperature streams entering the powder separator collector. In the past there were various schemes to mix these streams such as special duct fittings. However with these schemes, the air was mixed at high velocities which produced wear on the high velocity mixing components. Placing a QUENCHER in the gas streams achieves the cooling and mixing at minimal wear because of their low velocity designs. This application combines the most difficult circumstances that are likely to be faced in this type of circumstance.

4) FIRES IN POWDER SEPARATING SYSTEMS, CAUSES OTHER THAN SPARKS

There can be solids and liquids in exhaust systems that can cause fires in powder separation equipment.

Solids that are still burning when they enter the exhaust system; These can possibly develop into an explosion front entering the exhaust system. However more likely they will have the appearance of a spark in the exhaust system. A good example of this phenomenon is the collection of burning particles of paper usually strips. The paper provides both the oxygen and fuel to continue the burning process. The mixing process in the QUENCHER element may not cool the burning debris to lower it below the ignition temperature of the powder or filter media. The solution is to completely oxidize the solids before it enters the collection device (dust collector) and associated spark cooler. In that case multiple QUENCHERs may speed up the oxidation and may be a field for future consideration in expanding the QUENCHER market. Another approach might be to install sprays of water prior to the blender and to modify the blender to separate droplets from the cooled gas stream. We can modify the blender designs to make them water droplet separators. (This was the approach taken at Mueller Brass. That service report confirms the efficacy of this approach.)

Spontaneous Combustion; Some metallic and other compounds will oxidize when mixed at room temperatures. This process is well documented when we hear of fires that are smoldering after a fire that suddenly break out into a full scale fire. Catalytic combustion where oxidation takes place between 120 and 300 degrees F is another example of this phenomenon. These fires can be prevented with a combination of QUENCHER and control changes to the powder dust collector operating and will be covered in a separate report in the future.

Explosions; Explosions in the exhaust system can and do trigger fires in collectors. The combustion produces a sustainable conflagration which travels through the ducts at very high speeds. While a QUENCHER mixer can reduce the effect of this flame front by lowering the intensity, the QUENCHER cannot be an approach to prevent explosions.

5) QUENCHER AS PART OF EVAPORATIVE COOLING SYSTEM FOR WET AND DRY POWDER SEPARATORS (DUST COLLECTORS)

In venting furnaces for metallurgical processes; Typically, these furnaces will exhaust at temperatures between 900 and 1800 degrees F. They are vented to either wet collection equipment or through fabric filter element powder collection equipment. As the gas stream enters

Wet Collectors; Wet collection equipment are called air washers or gas scrubbers. These collectors are most effective if the exhaust stream entering the collection device is close to 100% relative humidity, typically 120 to 160 degrees. The temperature is usually reduced by coarse water sprays. The humidification efficiency is usually 80 to 85 percent. The efficiency of the humidifier has a drastic effect on the collection efficiency of the wet collector. The addition of a QUENCHER will increase this humidification efficiency to over 95 per cent. This simple addition might improve collection efficiency to meeting the existing air pollution codes.

Dry Collectors; Many Industrial Processes such as insulation processes or making Mineral, fiberglass insulation, perlite processes develop the process in a furnace. Then the exhaust stream from the furnaces, containing the insulating batts or powder, must be separated from the exhaust stream. The separation device is a dry powder/dust collector. Collecting in a wet form will not produce a usable type of product. Normally the method of cooling is with an evaporate cooling tower that forms a wet cyclonic action from top to bottom. The purpose is to cool the dust laden gas stream to a temperature below 400 degrees F and with dew point temperatures that avoid condensing on the cooling tower walls, as the process temperature rises and falls. The humidifying is controlled to maintain the  proper relationship of wet and dry bulb as determined by system operating parameters.. Fogging nozzles and the control of the water spray rates is used to control the outlet temperature and humidification. The controls are complex because of the relatively low velocity of gases in the tower.

QUENCHER adaptation; The cooling tower would be replaced by a spray mounted in the high temperature ductwork. The QUENCHER would cause the water to evaporate completely and the spray would be increased by the temperature measured at the entrance to the powder collector. This would be more effective and reliable than the big bulky cooling towers which try to control the residence time of the droplets as they evaporate.

CONCLUSION

Every metal working, foundry, Metal processing, Cement and woodworking plant is a candidate for QUENCHER Technology.

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 100×10-4 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%.

More info on Retrofitting to New Technology

Information on New Technology Dust Collectors

1. Collection efficiency increases which enables the users to decrease penetration of dust to the levels well documented on pleated cartridge units. The potential is outlets less than 8 x 10-5 grains per cubic foot with grain loadings below 15 grains per cubic feet. At 50 grains in pneumatic conveying applications, the outlet could still be under l0 x 10-5 grains per cubic foot. To achieve these numbers pressure drop must be kept below 6 inches water column. 
2. Bag lives can double or triple compared to cylindrical bags. 

Next we discuss the “bad news”, on the effects of these changes as they were observed: 

 Conclusions: 

i. The filter life is improved over the old cylindrical filter elements which were replaced.

ii. On many applications such as “bin vents” on silos venting pneumatic conveying these pressure drops will open the silo relief vents.

Please submit the particulars on your dust collector pleated filter element or cylindrical bags, to our technical support team for recommendations.

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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.