Valve Problems - Pulse-Jet Dust Collectors

The collector was shipped with the pilot solenoid boxes being shipped separately. The service engineer came to start up the collector. When the compressed air was piped up and the main valve opened, the pressure would not build up in the manifold. Examination of the piping revealed that the wrong ports in the solenoid valves at the solenoid enclosures were connected to the valves. This kept all the solenoid pilot valves open to atmosphere causing all eight diaphragm valves to open at the same time. The compressed air supply was not sufficient to allow even one diaphragm valve to be opened continuously. The connection is sized to provide air to supply a single valve to run no more than a 10% duty cycle.

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 pulsejet 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.

Read more about ...Most Advanced Technology in Dust Collectors
See our ...  troubleshooting service for dust collectors

Pleated Bags, cause problems

Several suppliers are promoting pleated bags to replace existing cylindrical bags in baghouse dust collectors. The effects of these changes are often startling.

First, we discuss the “good news”, about the effects of these changes : 

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:

A) The pleats on the bags were often bridged to 80-90 % of the pleat depth.

B) Users changed the pressure drop reading gauges from the 0 to 6 inch WC. range to 0 to 15 inch WC range. The reason was that the 0-6 inch gauges were pegging and pressure drops were running consistently over 12 inches.

C) The compressed air consumption which is a function of the pressure drop across the filter elements was two to four times higher than with the old cylindrical filter elements.

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.

iii. These “bad news” effects are due to one important fact relating to application of pleated filter elements. They will capture very fine dust particles, which were formerly leaking through the filters, because of the jet velocity of the reverse air jet. With pleated filter elements these particles are collected. The collection of the finer particles is the reason for the lowered dust penetration through these elements. These finer fractions agglomerate poorly and require very low upward “can velocities” to fall into the hopper after each jet cleaning cycle. If the upward “can velocity” is too high the fine dust remains as a very low permeability filter cake. This increases the pressure drop and cleaning frequency dramatically. Once a certain pressure drop is reached, which is related to the physical properties of the dust, the dust is driven into the filter media until even “off line” cleaning will no longer restore the permeability of the media to a normal expected pressure drop. This drastically reduces filter element life.

iv. In general, the cleaning system of dust collector is not designed to work with pleated bags.

v. We have developed techniques to improve the operation of most collectors using these new filter elements. These involve lowering the “can velocities” in collectors using pleated bags. We will cover these techniques in a subsequent “service report” and “engineering bulletin”.

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

For more ...  Dust Collection Information

For help ...  Consulting Services

For more ...  Retrofitting Existing Baghouses or Retrofit Cartridge Dust Collectors

Condensation in Dust Collectors

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.

Read more about ... troubleshooting dust collection systems

Desiccant Salts

The problem was that humidity and water was plugging the bags and accumulating in the collector & ducts. We depended on information that we got from the customer. We looked at the furnaces and they looked pretty standard. We asked them about the operation. What kind of salts they were using in the molten salt vats. We were told Barium Chloride. Most of the rest of the discussion then was about the existing dust collector. We suggested that the chief problem of corrosion was that moisture was condensing on the wall since the collector was located outdoors. They agreed that was probably correct. We discussed the possibility of locating the collector inside. We said we could do this because of the high ratio advanced technology style of dust collector used.


At no time was the subject of continuous seeding with limestone discussed. They did discuss that the collector had been operating for several years and were running at six inches pressure drop. That is normal for MAC collector designs. From our view, this was consistent with other furnaces that we knew had fabric collectors venting quench furnaces with molten salts of Barium Chloride or Sodium Chloride (standard salt like you have in a salt shaker).

They told us that they had been working with a representative from a well known cartridge dust collector supplier. They showed us sketches of some wooden hoods that they built to determine volume including temperatures in the hoods. These hoods were close coupled to the molten surfaces and they wanted us to bid that type of hood, which was unlike the ones that were already in place. They said they wanted us to bid cartridge collectors but we had never heard of a single installation on these quench operations. The temperatures that they measured were close to 200 degrees F and that was problematic, however the cloth bags of a baghouse could withstand 275 degrees. We would not bid a cartridge collector at those temperatures. There was no doubt that they were impressed with Donaldson and all the work they had done together on this project.

We did not specifically ask about Calcium chloride. There are various salts applied in these heat treating furnaces. Normally, when Calcium chloride is used they install water wash scrubbers. At American Air Filter, our colleague ran the scrubber department and they sold more than a hundred scrubbers that were venting either sodium chloride or calcium chloride heat treating operations. From the discussion, no “red flags" were raised and we judged this as a low risk application.

We assumed someone else went to the site to make measurements and lay out the ducts and fan since we never made any measurements. Next thing we heard that the cartridge dust collector was a lower price than our dust collector. We told the client that a cartridge collector could not work. We asked them to go back to the supplier and find a place where cartridge collectors had been applied on this type application. As it turned out they could not find a single place where they had applied a cartridge collector on salt bath quench operations. As a result they gave us the order.

After we installed the equipment there were complaints of water in the system. We were absolutely surprised since we were sure the wall temperatures were much higher than the dew point of the process air. We were sure that our design kept any condensation from the process gas stream. The operation could not produce moisture from feeding parts into the bath since wet parts would cause an explosion in the molten baths and might injure workers in the area.

We got samples of the salts. Six of the bottles were Barium Chloride and two bottles were labeled Heat Treat Mixture XX. It looked like the Calcium chloride salts that we used to melt ice since the salt was in the form of spheres 1/8 inch in diameter. The heat quench salt supplier told us that it was Calcium Chloride. They were reluctant to send more information so we ran the tests in our oven. We determined that the barium chloride was stable from 50 degrees up to 180 degrees F.

The calcium chloride would absorb water vapor and was a desiccant. How much and how fast the vapor was turned to liquid depended on the relative humidity and temperature. For instance, at 80 degrees and 80% humidity the liquid would not appear for more than twenty minutes. At 100 degrees and 50% humidity, it took several hours. Air flowing across the calcium chloride speeded the reaction but we had no equipment to measure the values. We found out the reaction would stop at 130 degrees F and higher. If the liquid formed it would take temperatures of over 160OF to dry out the calcium chloride.

We installed heaters in the ducts. Unfortunately, when the new bags were installed, the volume through the system went up and the heaters only increased the temperature to 110 from the previous reading of 105, We fed some baking soda into the collector to neutralize the calcium chloride but It was not enough to stop the formation of the water. It is obvious that the reactant must be fed continuously since it looks like the soda gets pulsed off before the end of the day and when the collector is shut down water is formed and plugs the bags.

This is an example of getting into trouble when we are not given all the information especially after the system was installed. We are competent but not magicians. The cartridge collector would not have lasted two weeks even with lime feed. We continuously shot ourselves in the leg on this project:

1) When we were installing the hoods, they insisted we move the hoods back at least six inches because they wanted access to a thermocouple opening. This meant that we would have more cold air blowing in and the exhaust temperature would be lower. Looking at it from hindsight this was the beginning of a lot of trouble. From the expected 200 degrees we were now at 110. At the time it seemed OK, since we were unaware of the calcium chloride. We should have insisted they move the location of the thermocouple probe instead, but we never suspected temperature was a problem. At the time we figured cooler is better.

2) Because the hood was moved back, this indicated we had to use the narrow high hoods to capture the fume instead of the squat ones close to the vats. The further away from the furnace, the higher the hood must be. These higher hoods drew in even more cooler air and the temperature dropped to near 100.

3) We put in heaters but they were sized wrong. Our sales rep had the same view that we originally had that the problem was with the water condensing on the walls and ducts. All he needed was to raise the temperature by 20 degrees and we would be home free. He figured that the higher volume after the bags were changed would further raise the temperature to the collector. The temperature coming from the duct venting the calcium chloride bath was 180 degrees, but most the reaction always had taken place on the bags. Between that and the insulated ducts he judged that the problem was solved. If engineering had selected the heaters, we would have designed them for 165 degree entrance temperature to the collector. When we visited after the heaters were installed. I was a bit surprised. Besides the client was complaining about the $2,400 they had to pay to wire the heaters. We measured the current in the heaters. It was about 25% of what I was expecting. The wrong heater was installed

Here we must not lose sight that the problem is related to the desiccant properties. We now needed to try to extricate ourselves from this mess that would allow us to look reasonably competent.
A) The most obvious approach is to put in a feed system to feed sodium carbonate to the system especially at the end of the shift. It looks like the pressure climbs overnight. It was not known if the collector runs all night. They probably do it more than one way. We believe they shut the fan off over the weekend and continue pulsing. That is probably the worst thing that they can do.
B) We might put a damper on the fan and cut the flow back when they are not operating so duct heaters heat the air to the collector to 160 degrees. This would dry out the calcium chloride and allow it to be removed from the collector.
C) We might put a big heater on the duct from the third hood that does not have a heater.

For help with ... Fixing existing jobs or designing new dust collection applications
Read more about ... Most advanced technology dust collectors

Plasma Cutting & Cartridges

This is the result from using our cartridge and fabric filter element inspection service.

1) It was not the cartridge that was normally supplied to clients.
2) It had an inverted cone reinforcement in the bottom closed end cap. We always recommend a flat closed end cap for maximum life. The pleat spacing was optimum for this kind of application.
3) The seals (gasket) were resilient which insures effective sealing between the clean air and dirty air compartments. The cartridge exhibited no evidence of improper installation or handling.
4) You could expect indefinite life on this filter element on all suitable applications with an advanced technology pulse jet cleaning system like ULTRA-FLOW.

This plasma cutting operation is quite common and we see many cartridges with problems from these operations. The dust generated is extremely fine and problems with seals and installation account for a big majority of problems. The other problem, that we see is that the settings on the cutting head are such that the dust can be prone to plasma coat the filter elements. The solution of the coating problem is to give the dust time to lose its reactivity before it reaches the filter media. None of these usual problems were evident on this filter element.

A) My first observation was the color of the coating on the filter. In cutting ferrous metal with a plasma arc cutter, the dust is black and coated with fine easily removed powder. In handling of these filter elements, we usually wear a mask because of the fine dust generated in the inspection process. In this case there was no dust generated in the procedure. The color of the coating was brown.

B) My second observation was that there was hard inflexible crust covering the dirty side of the pleats as if the element had been painted. It had the same strength as baked on auto finish.

C) The only time I previously observed this kind of coating on a cutting operation was when the plates were covered with some kind of coolant, cutting oil or pickled. On some cutters they use compressed air at the head. I would suggest checking the air line lubricant as a possible source of the binder that is creating this paint like coating.

Finally, a continuous coating of filter aid could be maintained on the surface of the filter media. The dust load is usually quite light and the coating might be about a 64th thick. The surface coating would be painted instead of the media. When the collector pulses the inert filter aid, coated with the paint, would be ejected into the collection hopper. How often to clean would be a judgment call. I would expect the cleaning and re coating every 2- 4 hours would be appropriate.

Read more ... Retrofit Service for Cartridge Dust Collectors
Find out about ... Most Advanced Technology Dust Collectors

Compare Spark Arrestors

Spark Arrestors; and Spark Coolers

(A comparison of different methods)

There are several approaches to the issue of extinguishing sparks in a gas stream.

Important Factors in Spark Arrestor Selection

1. There is no such thing as an efficiency rating for spark arrestors. They either work or they don’t. Remember, it takes only one spark/ember getting through the device to cause a fire or explosion.
2. Maximum turbulence is the key to effective spark arresting and in the selection of a spark arresting device. Some devices do not impart enough turbulence (and/or pressure drop) to be 100% effective. The recommended pressure drop for an in-line device (one that is installed in a section of the ductwork) is between 0.75 and 1.5 inches WC. Anything less is highly risky. This is a basic law of physics.
3. Pressure drop across a QUENCHER style of spark arrestor is a function of the Reynolds number which is proportional to the density for air. This means that a unit can be sized smaller if operating at a higher temperature. For instance a spark arrestor operating at 440 degrees F is 2/3 the size of the typical unit applied at 70 degrees F and the pressure drop will be designed the same. This lowers the cost of the spark arrestor and ensures its effectiveness. The density is also affected by the water vapor in the gas stream. It has little effect at temperatures below 125oF but can be a major factor when operating at higher temperatures.
4. If the gas stream has dust that might drop out in the duct at the velocities in the blender style or QUENCHER spark arrestor, a booster must be provided to periodically remove this accumulation. If this unit is not kept clean, it might pose a threat by putting an extra load on the ductwork. Without an automatic duct cleaner-booster system, the spark arrestor would require periodic manual cleaning.
5. The duct cleaner - booster design is also temperature sensitive and must be altered to accommodate changing gas stream conditions.
6. Most suppliers do not have the capability to modify the designs as referred to in item (3), (4), (5) above.

Blender Type Air Mixers

A number of these air blender/mixers have been applied with varied success as in-line spark coolers, arrestors and suppressors. Over the last several years standard air mixers have been adapted and applied between the spark generating process and dust collector. They were applied in processes where fires in the dust collectors had previously occurred. One supplier hired a consultant to develop a market for these air blender/mixers as a spark arrestor/cooler. This air blending or mixer style design was an outgrowth of mixing two gas streams of different temperatures to insure a uniform temperature after the static mixer. It was deduced that the gas stream produced turbulent flow as it passed through the blades and this was the reason it could be adapted to spark cooling. However, these are air mixers first and spark arrestors second. They are marketed as having low pressure drop (maximum 0.5 inch WC) through them. There are performance limitations because not enough turbulence (and related pressure drop) is imparted to the spark/ember. To achieve spark suppression, we need to go from laminar to highly turbulent flow in the duct which strips away the hot air envelope around the spark/ember thereby cooling it and starving it of fuel (oxygen). For air blending this is not a requirement. Also, these devices have large gaps between the mixing blades, when looking through the inlet and downstream of the device. These gaps can allow a percentage of sparks/embers to slip through and cause a fire or even an explosion in the dust collector.

Improved In-Line Spark Arrestors

QAM developed the QUENCHER, which is a variation of the blender/mixer design. It is also an in-line spark arrestor. Employing a 60 year old spin vane mist eliminator technology developed by Sly Manufacturing in the early 1960’s, led QAM to vary the blade designs to have the most effective performance, inducing maximum turbulence to the gas stream, and lowering the cost. Maximum turbulence (and the pressure drop that results from it) is the key to spark arresting. After several tests it was found that the air blending/mixer design did not impart enough turbulence and some sparks got through, especially at low gas stream velocities. Eventually, there was a specific design which imparted the most effective swirling and turbulence thereby extinguishing the sparks quickly and most effectively. In fact, during testing of the QUENCHER, the arrestor cell would light up as a ball of fire, however, one inch past the cell nothing was left in the gas stream. These designs were incorporated into the QUENCHER. QAM has developed special application data in which the blade angles are adjusted to produce minimum effective pressure drop for different temperatures and gas densities. To our knowledge, no one else accounts for the gas density effects on spark arrestors. In truth, due to the advanced design, even applying the incorrect parameters to a QUENCHER may not result in a failure to put out sparks. Since the pressure drop across the device are a function of the velocity through it, the development of a pneumatically operated booster was introduced to prevent dust dropout accumulating in the static arresting cell. It also blows out accumulations on the blades.

Find out more ... Quencher spark arrestor

Liquid Spray Systems
For many years these systems were the only method to prevent fires caused by sparks. The system consists of electronic detectors that detect sparks and react to their presence. When a spark is detected liquid sprays are actuated and water sprayed into the duct. The sprays actually cool the gas stream below the dew point. However, in dust collection systems, the water then wets the filter bags or cartridges. This prevents fires but the gas flow is interrupted and the bags must be either replaced or dried out before the process can resume. It takes a whole day or two to dry out the bags or even to prevent blinding and replacement. The detector sensitivity can be lowered to prevent excessive actuations, but, this reduces the reliability of the systems. The detector missing a spark is an ever present danger and a fire may occur. Bag or cartridge replacement is definitely required.

Cyclone Dust Collectors
Contrary to common belief cyclones are not effective spark arrestors. For a spark arrestor / cooler to work, there must be high turbulence in the air stream. If you have turbulence in a cyclone the pressure drop is very high. Cyclones are designed to avoid turbulence. Many bag house fires occur in systems with cyclone pre-cleaners. Amazingly the inlet baffles on the baghouse are more effective as spark arrestors, however they are not foolproof.

Static Blade Spark Suppressor (Tri Pass)
These were developed in Japan to replace multiple cyclones in coal fired boilers. They found that the multiple cyclones did not stop sparks from entering the dust collectors. The first ones were installed in the early 1970’s. They ran at 1.5 inches of pressure drop and were fabricated from structural angles to resist the wear of the abrasive ashes in the coal that they fired. There are several of these applications installed in the USA and Canada designed by one of our colleagues.

Static Baffle-Box Spark Arrestor
Many dust collector suppliers offer this type of device as a spark arrestor. It consists of air entering at one end of a baffle box running over a baffle plate which drops out the sparks and much of the dust collected. The air exits at the other end, and then travels to the dust collector. The big drawback is that a hopper and flexible or solid hose connection to a collection barrel is required. Also, these devices do not eliminate all of the sparks. There is not enough turbulence generated to ensure 100% spark arresting. Sparks may also ignite the contents of the collection bin under it.

Mesh Filters
This is a common stop-gap measure where the filter is placed at the exhaust duct of hoods or installed in the ductwork. When clean, the mesh filter will stop at best 80% of sparks. These filters do not produce enough pressure drop to be fully effective. It only takes one spark to ignite dust in the duct or set a dust collector on fire. The only thing these filters do is clog up and add to your maintenance.

We trust that the above information will enable you to evaluate and select the most suitable method and supplier for your application. Buying our QUENCHER/BOOSTER spark arrestor combination will give you a risk free unit, fine tuned for each application.

See our engineering bulletin ... "Compare Spark Arresting Methods" (PDF)

Wet Collector Underperformance

Equipment:
C5-2500, orifice scrubber style wet dust collector, rated for 2500 CFM, purchased to handle explosive aluminum dust particles.

Problem:
The dust was going right through the collector and packing into the fan / outlet compartment. Very little dust was collected in the dust collector sump.

Investigation and observations:
We requested pictures and system layout drawings (sketches were actually provided). From these we observed that the client did not describe the application accurately at the time of purchase.
1. The dust was produced from a spray coating operation. Therefore, it was fine powder type aluminum dust. Wet collectors are designed for metal dust 5 microns and larger, as generated from grinding and cutting operations.
2. The inlet was connected to a properly sized 8” duct but was over 20 feet long with three elbows. These units are designed for maximum 10 feet of duct directly to the collection point.
3. The client also decided to exhaust the discharge of the collector to the outdoors with another 20-25 feet of duct, and three more elbows. These collectors are designed for an open, unrestricted discharge on the top of the unit.
The result of this was a questionable capability of collecting the powder type dust. The biggest problem was that the collector performance was choked by far too much resistance to airflow in the installation. By doing this the air entered the collector with far too little volume to cause the necessary turbulent energy in the “omega” style baffles. The necessary wetting action of the dust particles was not taking place and filtering action was non-existent.

Solution:
1. We asked the client to place some of the collected dust in a closed jar with water. Then shake it and let it sit for a few minutes. If the dust settles, it can be collected. If it doesn’t, a different dust collection solution must be found.
2. A wet dust collector is very particular about the airflow through it. You need to be in a range of +/_ 10% of the rated CFM for that model dust collector. In this case, the minimum flow that could be tolerated is 2250 CFM. Conversely, with more than flow than the 10%, water gets drawn up too much and discharges out the unit. We recommended bringing the collector closer to the application and remove the duct on the outlet. Alternatively, add a booster fan to overcome the restriction.

Other Considerations:
A. If the excess resitriction is minor (within the 10% range) but dust is discharging at the top, You would add more water to the collector, in small increments, until the dust/water stops coming out the top. The added water compensates for the higher restriction. Then reset the float control to maintain this new water level.
B. In some cases the discharge is required to be exhausted by code. An example is beryllium. In such a case, do not attach a duct on the outlet. Instead build a capture hood over the top of the wet collector outlet, approximately 4-6 above the top, and duct that to the outside. Install a fan to give you 5-10% more air flow than what is running through the collector, to ensure no contaminents escape back into the room.
C. If you oversized the wet collector, Do not restrict the flow with a damper more than the 10% tolerance. Install a bleed-in on the inlet duct with an adjustable shut-off damper. Open the damper to the point where the collector performs properly. This is often a scenario when you size the collector for multiple collection points but don’t have them all installed until later.

Need help? ... System trouble-shooting