Criteria for Fabric Selection

The basic criteria for fabric selection are temperature, inlet loading, particle size distribution, gas composition, abrasion, static charge, release and efficiency requirements.   1.         Temperature:   Match inlet gas temperature with the fabric capable of continuous operation at or above the maximum temperature the system might experience. 2.         Inlet loading:   Inlet grain loading (normally expressed in grains/dry standard cubic feet) is especially important when the loading is very light.  Light loadings can make it difficult for the media to operate with sufficient dust cake. 3.         Particle size distribution:    Finer the distributions often require using higher efficiency media. 4.         Gas composition:   The designer must make sure that if corrosive compounds or hydrocarbons are present in the gas stream, that the media selected will hold up in that environment. 5.         Abrasion:   When the dust is abrasive, the designer might look at using heavier felt or adding wear cuffs to the bottom of the filter bags on hopper entry inlets. 6.         Static charge:  Explosive dusts and gases or dust that can develop a static charge in the duct system require some time of static grounding.  This can come in the form of a braided grounding wire sewn into the filter bag and attached to the tubesheet.  Grounding can also be done through the bag material such as epitropic (using carbon or graphite fibers throughout the bag, or by using 3-4% stainless steel fibers throughout the bag.  In these cases it is important to make sure the bag collar (top loaded bags) are fabricated out of the same material so that there is conductivity to ground. 7.         Release:   A properly designed dust collector has two (2) functions.  The first is to collect the dust, the second is to release the dust off of the filter bag after it is collected.  In the case where the dust is oily or sticky, the fabric may require a treatment to the filtering surface in order to aid in the release.  This can take the form of modifying the surface with treatments such as singing or glazing.  It can also mean a coating such as a PTFE bath or even a membrane.  There are also specialty fabrics that treat the fiber before the felting process providing a longer lasting surface than typical coatings. 8.         Efficiency:   Last but certainly not the least important is collection efficiency.       Expressed as a mass loading (gr/dscf), the required efficiency is determined by the environmental engineer based on EPA, State or regional regulations that coincide with the particular plants allowable discharges to the atmosphere. We have tried to give you an overall view of fabrics and the criteria used for the correct selection used in various types of air pollution control equipment.  This information should be used as a guideline.  There can be multiple choices for any particular application.  The ultimate choice depends on the experience of the designer.

Case Study – Mayville Limestone (Scrubber)

Mayville Limestone located in Wisconsin contacted Sly (Bill Harding) regarding the replacement of their existing wet scrubber on their rotary limestone dryer.  In discussions with the customer it was determined that they did not know the emission level of the existing unit, particle sizing or whether it was currently meeting the existing regulations. The system includes multi-clone precleaners, hydroclones (for water recirculation) which were wearing out and a large settling pond. Since no inlet data existed we convinced the customer that the only way to safely approach this project with any guarantees on outlet emissions was to do a simultaneous inlet and outlet test for loading and particle size distribution.  Since the existing scrubber was only operating at a 3” pressure drop we felt the efficiency was very low.  Test results indicated a very high inlet loading (22 gr./cf) and a mean particle size of 11.5 microns. During the interim the customer was cited by the DNR and required to file a plan of action.  At this point the discussions involved a new venturi running at a 40” wg pressure drop to meet an outlet emission requirement of 0.03 gr/dscf or a baghouse.  Also at issue was the replacement of the multi-clones that were experiencing high maintenance.  The customer perception was that wet scrubbers were always used on this application and had not considered a baghouse.  Since the dew point was relatively low (110 deg. F) we felt a baghouse was a viable option.CConsiderationsNew venturi wet scrubber:Pros:    Less expensive than baghouse            Eliminate hydroclones since pond was large enough            Less maintenance than baghouse                         (bag replacement)Cons:   Higher energy costs (40” wg pressure drop)            Higher energy costs due to                         pump for water supply.            Must have pre-cleaner.            Pond maintenance.  New baghouse: Pros:    Eliminate pre-cleaner by using                         high side inlet.            Lower energy costs (lower pressure                         drop/ no pump).               Lower emission rate.Cons:   More maintenance due to bag changing.            Higher capital costs. The competition on this project for the baghouse option was DCE and MAC.  DCE offered a collector at a 7:1 A/C based on not using a cyclone and no high inlet or classifier on the collector.  They stated to the customer that the high inlet loading would make the collector more efficient.  MAC offered a high inlet at a 5:1 A/C.  MAC’s high inlet eliminated a few bags and installation of a target plate forcing the air down to the hopper.  This type of inlet does not allow for settling that reduces the load on the filter bags. Sly offered a 4:1 A/C and a high inlet that provides a large section of the collector to bring the air into with full partitions on either side to eliminate bag wear.  This inlet section runs the full width of the collector reducing the downward velocity to less than 800 fpm assisting gravity and low velocity to help settle out the majority of the inlet dust loading. As with many projects there were some budget constraints.  Since the dryer only ran 10-12 hours per week we were asked to increase our A/C.  Our final quote was at a 5:1 A/C which we felt was still conservative considering the low drying hours. Sly received the order for a STJ-1415-10 with high side inlet to handle 16,860 ACFM at 187 deg.F.   The unit was configured with (1) hopper that would discharge into a screw conveyor to return the dust back into the building and the process.  We also insulated the entire collector (factory installed by Sly in Mississippi) to help prevent condensation.  The initial start-up did not go well.  One of the operators started the dryer by throwing in a lit newspaper and turned on the gas.  They had to replace the initial set of bags.  All the operators were given specific instructions on the proper start-up and shut down sequence to further avoid any condensation and fires.  Proper start-up requires pulling warm air into the collector before any material is feed into the dryer.  By pre-heating the collector condensation caused by hot moist air entering a cold baghouse is avoided.  Likewise on shut down it is proper to run warm air through the collector after the product feed has been stopped to pull any humidity out of the collector.  We also supplied a temperature controller and thermocouple to alarm high temperature since the collector was supplied with polyester felt bags.  The collector was started up in December of 1999 and has only had one (1) bag change.  The DNR was so pleased with the initial stack test that yearly testing was deleted from their permit requirements.

The Sly Tubejet Line

The Sly TubeJet collector was introduced to the market in 1990.  Over the years it has developed into our largest product line.  With (4) four distinct products, the TubeJet can handle almost any baghouse application.

 

Out of the four products, the STJ is by far the most popular.  It is simple in design and can be modified to fit a large number of applications.  The STJ has many features not found on other collectors.

 

-                  Hinged top access doors that are double gasketed to maximize sealing against the weather.

-                  Pulse pipes that are held in place by a stainless steel Morris coupling and requires no tools for removal.

-                  The fixed end of the pulse pipe is designed to be installed only one way which guarantees the pulse pipe is installed properly.  The end of the pipe is flattened with a pin welded on the top.  The back wall of the collector has a slotted bracket that guarantees the pulse pipe can only be installed so that the blow holes are always centered directly over the venturi opening.

 

The following features are part of any TubeJet collector:

 

-                  The complete cleaning system which includes the compressed air header, pulse valves, solenoid valves, timer, tubing and wiring are all factory installed.  Furthermore, the cleaning system is hooked up and tested before the collector leaves the plant.

-                  All interior surfaces are primed.

-                  All exterior surfaces receive a full prime and finish enamel.

-                  All steel for supports and filter access is blasted prior to shipping to Sly’s plant.

-                  Supports and walkways are pre-assembled and match marked.  All pieces have a tag that is attached to the piece with a wire tie.  The tag has the part number clearly marked and then the tag is sealed in plastic.

 

While selling standard units might be our preference, we all know that customizing based on application or customer preference is something that happens on a regular basis.  For this reason, you might want to be aware of some of the modifications we have made over the years.  Some of these are standard options while some have a high degree of customization.

 

-                  Walk-in clean air plenums.

-                  Special filter bag diameters such as 4-1/2” and 5-1/4”.  Smaller bag diameters may be used due to the need for wider bag to bag spacing.  Wider spacing is required if the material is fibrous with a tendency to bridge between the filter bags.  Normal bag to bag spacing with 5-3/4” diameter filter bags is 2-1/8”.  If we keep the row spacing standard (8”) and change to 4-1/2” dia. bags then the bag to bag spacing opens up to 3-1/2”.  This wider spacing can also be used to decrease interstitial velocities in low bulk density materials.

 

-                  Alloy construction for either product contact parts (tubesheet, filter housing and hopper) or gas contact, which includes the clean air plenum and pulse pipes.

 

-                  Many times with stainless steel construction  the application requires a special finish on the interior surfaces in contact with the product.  There are a couple of options that our shop is capable of doing.  Grinding all interior welds either smooth or flush.  Polishing these welds to either an 80 grit or 120 grit finish.

 

-                  Explosion protection.  This can include a copper or stainless steel grounding wire sewn into each filter bag.  Special NEMA 7/9 explosion proof electrical enclosures for the solenoid valves and timer.  Explosion relief vents designed to follow the most current NFPA 68 guidelines.  Internal sprinkler fittings.  In some cases we have worked with the customer to install fittings for a suppressant system.  Special filter bag material may also be required.  This would include fabric that is constructed either with some content of carbon or stainless steel fibers to dissipate static charges.

 

-                  In most high temperature applications or in the event of installation on a dryer or other process where moisture is present, the collector should be insulated.  This is typically done by installing a fiberglass mat or board on all exterior surfaces of the collector and then covering the insulation material with a metal cover.  We would normally use a 18 ga. galvanized sheet that is sheet metal screwed to lagging.  On occasion we have used aluminum and stainless steel sheeting.  All seams are overlapped and gasketed to weather proof the collector and protect the insulation.  Special attention is paid to the hinged top access doors and any hopper access.  All access doors are insulated by building a cavity on the inside of the door and then filling the cavity with insulation material.

 

-                  High side inlets of various configurations are available for applications requiring low interstitial velocities, material drop out to reduce the load on the filter bags.  Another reason we might use a high inlet would be to facilitate the inlet ductwork.  Some situations make it difficult to use a hopper inlet.

 

These are only some of the special adaptations we can use based on the application and/or the customers requirements.

Training Seminars

 

Over the past few years Sly has developed presentations that cover baghouses, cartridge collectors and wet scrubbers.  These presentations have been given as seminars to customers and trade organizations as a method of instructing their personnel and members. Topics that we have presented include theory of filtration, establishing baseline system performance, selection of baghouse fabrics, guidelines for establishing air-to-cloth ratio and interstitial velocity, basic scrubber technologies, troubleshooting, and tips for creating effective maintenance schedules and logs.

 

The seminars are specifically designed to provide technical information and maintenance training in order to educate the end user so that they can make better decisions at the point of purchase and reduce long term operating costs and maintenance problems.  It is not a sales pitch.   While it is clear that Sly is providing the training, we focus on technical information and do not talk specifically about Sly products unless we are explicitly requested to do so.  We have received very positive feedback in this regard which has allowed us to be invited back where other vendors have not.

 

The presentations are done in PowerPoint.  We also show some props such as bag and cage samples, pleated bags, timers, etc.  The seminars can be fine-tuned for a specific industry or equipment type and generally take 1 to 4 hours depending on the specific material presented.

 

Over the past few years we have put on seminars for Unimin Corp., Philip Morris and the Industrial Minerals Association.  They have been very effective in keeping our name in front of existing customers and in establishing relationships with new prospects.

 

If you have similar opportunities in your territory, we invite you to talk with either Wendy or myself to see how this might fit into your marketing strategy for the coming year.  Typically it takes about 4-6 weeks to plan and customize the presentation.  We like to do this for at least 6-8 people and generally at their place of business.

 

If this makes sense for a customer or prospect with large potential, please call to discuss.

Consider various type units to solve the issue.

 

One of the unique aspects of Sly is that we design and manufacture so many different types of air pollution control equipment.  This is important to our prospects and customers because we can look at a particular application and make a recommendation based on what technology will work best and not try to make a certain technology fit the application.

 

Most of the time there is a clear choice on what is best, but there are times when the choice is not so obvious.  A good example of this is in the minerals industry and specifically, silica sand.  We know that silica sand is abrasive and that the particle size distribution is not extremely fine (not a large percentage below 10 microns).  From a technology viewpoint you can look at baghouses, cartridge filters and wet scrubbers.  We have seen outlet loading requirements in the 0.02gr/cf area, which is not particularly difficult to achieve with any of the above technologies.

 

Let’s examine each technology at an air volume of 10,000 cfm at ambient temperature handle nuisance dusts from various mechanical conveying and screening pick up points.

 

A STJ baghouse sized at a 5.5:1 A/C ratio with support, Option A access, rotary discharge valve and a 30 HP exhaust fan would cost $31,000.  Bag life is going to be in the 3-4 year range and a bag change out including labor will run about $2000.  On top of that there will be periodical maintenance on the pulse valves, solenoid valves and timer.  Wear will also be a factor on the rotary valve.

 

A HCF cartridge filter at a 2:1 A/C ratio with support, walkway, rotary discharge valve and a 25 HP exhaust fan would cost $24,000.  Cartridge life is going to be in the 1-2 year range and a complete change out including labor will run about $1600.  You also have the same periodical maintenance issues as the baghouse.

 

An Impinjet wet scrubber with support legs, basic instrumentation and a 25 HP exhaust fan will cost $26,000.  However, there are no ongoing maintenance issues with bags or cartridges or the cleaning system.  You might trade off some pump maintenance for the rotary valve maintenance.

 

Although the Impinjet is not the most economical selection on the capital equipment purchase side, savings in maintenance over the life of the equipment make it the logical choice.

 

There are however, there is a prerequisite for using a wet scrubber economically.  The site must have a settling pond available for receiving the scrubber discharge and then supplying the scrubber with ample water for scrubbing.  In our experience, many customers mining minerals have such a water supply and this is especially true of the silica sand producers.

 

Next time you’r in a similar situation, step back a minute and look at all the options.  It might provide you with a opportunity to provide the customer a more economical solution for him and set up a less competitive environment for you.

SBR

SBR

 

Last year the entire TubeJet product line represented about 70% of Sly’s yearly sales.  Of that 70%, STJ =79%; CBR= 13.5%; CBR = 6%; and CTR = 1.5%.  These values will fluctuate from year to year but generally stay near these values.

 

While STJ’s dominate there is still a place for SBR and CBR style collectors.  Commonly referred to as bottom or side bag collectors, they are well suited for smaller air volumes such as bin vents and filter receivers.

 

SBR style collectors can be used in low headroom applications that require the use of a baghouse in lieu of a cartridge filter.  They can usually be placed very near the dust source or in an out of the way place that may not take up valuable floor space.  SBR’s can use standard filter bags or spun bonded polyester pleated filter bags.  Using pleated bags can help dramatically in low headroom situations.

 

In many circumstances the bottom bag removal style can be more cost effective mainly due to the access for changing bags.  If the customer does want the collector vendor to furnish access platforms and ladders, this package is much less expensive than the access packages for top removal collectors.  Some customers even prefer to use their own mobile platforms to gain access to the collector for maintenance which further reduces the initial cost.

 

The PV bin vent line offers an economical price for this style collector and can include fan packages.  Although the PV limits the number of options available, most bin vents don’t require much customizing.

 

CBR’s can have interesting applications.  Because they are round, uses include high pressure and cleanability.  We have sold many on pneumatic conveying systems at pressures up to 14.7 psi.  Cleanability issues can lead to special weld treatment and eliminating any corners.  Our shop is capable of cleaning and polishing to a 120 grit finish.

 

There are occasions where a SBR must be used for larger air volumes.  The challenge here is to design a unit that will make it easier to change filter bags.  Part of the bag changing problem is conveniently getting into the collector and laying planking down so the bag changing people can access the top of the bag and remove the clamp.  Large collector bag change over can be  very time consuming and expensive.  As a general rule, we try not to use filter bags over 8 ft..  Even this length can make bag changing a dreaded event.  We furnish many units with pipes running across the unit below the door.  This provides some support for wood planking that can act as a work platform.  On large collectors we have designed internal walkways either running from front to back or through the middle of the collector length wise.  The platform can be positioned so the men can easily reach the bag clamp.  It can also be designed so that there is no more than a 3 or 4 bag reach from the platform.  This would be either 24” or 32”.  Obviously this is more expensive because the collector must get larger to accommodate the walkway, but it may be the only alternative.

Case Study – Cellulose Insulation (SBR)

SBR TUBEJET

An Ohio company approached Sly about designing a dust collector for venting equipment used in manufacturing cellulose insulation.  They had experience with standard collector designs that eventually plugged up. In those cases a cyclone was added as a precleaner prior to the collector to reduce the inlet loading.  While this helped, plugging eventually occurred.

 This company has designed a system to take recycled paper and process it into insulation by grinding and adding chemicals.  It uses a hammermill and various conveyors.  This particular plant is owned by the company but they license the technology to other people. The paper dust generated is very light and bulky.  Bridging of material between the bags would definitely occur if standard bags and spacing were used.  Discussions were about the correct design centered on upward velocities and bag-to-bag spacing.  Sly felt a safe design would be one that addressed both issues.  The collector chosen was a SBr-2511-10 (4.5) with high inlet.  Using  4-1/2″ dia bags on 8″ centers would allow almost 3-1/2″ bag-to-bag spacing and virtually eliminate bridging between bags.  Since we utilized the standard 8″ spacing between bags in both directions, using a smaller 4-1/2″ dia bag made sure the wider bag-to-bag spacing was in both axis. A conservation 4.85:1 air-to-cloth ratio was used reducing the upward (interstitial) velocity to 163 FPM.  We felt this velocity was slightly high and also wanted to help reduce the load to the bags.  A high side inlet was added for this reason. The collector was to be installed  inside so a SBR was furnished.  Since access for bag changing can be difficult, 1-1/2″ diameter Sch 40 pipes were welded across the top of the hopper to provide an internal support for a removal work platform.  In most cases customers use wood planking which is light and maneuverable. A glazed finish was chosen for the polyester felt bags to eliminate the chance of paper fibers clinging to the bag fibers.  The glazing process on the bag fibers is done by first singing the fibers by passing the felt over a flame and then through a hot colander roll.   The result is a very smooth surface devoid of any fibers for material to attach to. This collector has been successfully running since the fall of 2001.  The customer has since ordered an additional collector.

Pactecon – PC

PC-Pactecon 

Sly Developed the PC Pactecon in 1968 to answer the market demands for small, compact, quick-ship dust collectors.  Both the S-model shaker and the PC model pulse-clean where developed at the same time.  These units were designed using our envelope style filter bags and bolted modular construction.  Today we will discuss the PC-200 model.

 At the time pulsejets were being developed (1960’s), there was much debate on their collection efficiencies and bag life.  Most designs were at very high air-to-cloth ratios.  Ratios of 10-20:1 was common and as we know today, did not work very well.  The Pactecon was developed in answer to these common pulse jet problems. Using envelope bags and off-line cleaning, the Pactecon has unique dust collector features that no one else in the industry offers.  Reference Sly Drawing P-1121. -                  Down flow inlet – Air enters the inlet plenum on top of the unit and flows down into the filter section.  Down flow and gravity help settle out the heavier dust and to move the dust cleaned off of the filter bag into the hopper.-                  Off-line filter bag cleaning – Each collector is divided into cells with 8 or 12 bags per cell.  A partition sheet separates each section from the bottom of the inlet plenum to the hopper and from front to back.  A damper located just above the clean air section of each cell closes prior to pulsing and stays closed, sealing off any air flow through the cell, until the cell gone through its entire cleaning cycle.-                  No interstitial problems – Off-line cleaning and down flow eliminate this problem that is typically associated with light dusts.-                  Lower compressed air consumption – Air consumption is generally less than a comparably sized pulse jet because the cleaning air does not have to overcome the air to be filtered.-                  Longer bag life – Bag life is exceptional because of the way the bags are cleaned.  Off-line cleaning provides a quiet air space for the pulse to affectivity clean the bags.  The cleaning is much gentler than a conventional pulsejet.  As we know, it is the violent cleaning that determines bag life more than any other factor.-                  Outside bag removal – Because the bags are removed from the side of the collector while standing outside of the housing, these units van be installed indoors with very low headroom.  This would be for superior to using a SBR (bottom bag removal) and having to inter the housing to change bags. Obviously over the years we have had many customers successfully use the Pactecon for many nuisance dust applications.  Even with as many attributes as the Pactecon has, industry pressures forced Sly to enter the round bag pulsejet market.  While the vast majority of baghouses we sell are TubeJets, there remain a few loyal Pactecon users.Philip Morris has been installing Pactecons in their plants to handle the dust from the maker machines since 1988Many of these collectors are installed in areas around the plants that have 22 f. of head room or less.  Since all collectors discharge into a standard cardboard container that must have 60″ clearance below the rotary valve discharge, it makes the over all height requirement even more challenging.  All of these collectors are running somewhere between 5.5 and 6:1 air-to-cloth ratios.  Even though tobacco can be abrasive, average bag life has been over 5 years.  In some of the forms of tobacco that the collector sees can be very light in bulk density, some below 20 pcf.  For design reasons stated above, the Pactecon handles these dusts with no modifications and no problems. Another loyal Pactecon user is Sara Lee in their instant coffee and tea plant.  Their issues where similar to Philip Morris in that there was limited headroom and low bulk density material.  These installations have been very successful.  Plant personnel have told us that the only collectors in the plant that work are the Pactecons.  While the Pactecon is more expensive than a TubeJet, some applications and situations might warrant taking a look at its operating advantages.

Case Study – Reichold Chemical (CBR)

In 1997 we were approached by Reichhold Chemical whose headquarters are in North Carolina, concerning a new toner plant they planned on building in Wisconsin.  We were excited about this project because multiple collectors were involved and toner was something we had not collected before.  They more we learned about handling toner the more complex the project became.

 

Toner dust is extremely fine and will leak even through even a small pin hole.  Toner is also explosive.  It also has trouble flowing. 

 

This was a grass roots plant and subject to some building code restrictions that proved to be challenging in the placement of equipment.  All of the dust collectors were required to be indoors and the height of the building fixed which presented some headroom limitations.

 

All of the processes the collectors would ventilate where high pressure.  Designing the collector for 140”wg meant that we would have to use cylindrical units.  A round design would work well for another reason.  Since these were product collectors, round housings and cones eliminate corners for toner to accumulate in from a material discharge.  This might also reduce the chances for an explosion by reducing the amount of toner that is allowed to accumulate in the collector.

 

As mentioned before, head room was at a premium.  Although bag changing would be more difficult using a bottom bag load collector, there was no choice.  In order to reduce the height and keep the diameter of the units reasonable, we chose to use spun bonded polyester pleated filter bags.  The other major advantage to using the spun bonded was the high collection efficiency required because the dust is so fine.

 

Since toner is explosive, precautions were required  for explosion venting, bag grounding and electrical protection.  All of the collectors were installed within a few feet of an outside wall.  The spun bonded media was given an aluminized surface treatment and a ground wire to dissipate any potential static build up.  All of the electrical timer boxes were equipped with a purge system to prevent any dust from entering the enclosure.

 

When all was said and done, Sly received an order for (8) CBR-60-59-3.5SB, (3) CBR-20-4-1.5SB, (2) CBR-15-

Case Study- Limestone Mining Company

MINI CASE HISTORY  A limestone mining company contacted Sly regarding the replacement of their existing wet scrubber on their rotary limestone dryer.  In discussions with the customer it was determined that they did not know the emission level of the existing unit, particle sizing or whether it was currently meeting the existing regulations. The system includes multi-clone precleaners, hydroclones (for water recirculation) which were wearing out and a large settling pond. Since no inlet data existed Sly discussed with the customer that the only way to safely approach this project with any guarantees on outlet emissions was to do a simultaneous inlet and outlet test for loading and particle size distribution.  Since the existing scrubber was only operating at a 3” pressure drop we felt the efficiency was very low.  Test results indicated a very high inlet loading (22 gr./cf) and a mean particle size of 11.5 microns. During the interim the customer was cited for emissions by the DNR and required to file a plan of action.  At this point the discussions involved a new venturi running at a 40” wg pressure drop to meet an outlet emission requirement of 0.03 gr/dscf or a baghouse.  Also at issue was the replacement of the multi-clones that were experiencing high maintenance.  The customer perception was that wet scrubbers were always used on this application and had not considered a baghouse.  Since the dew point was relatively low (110 deg. F) we felt a baghouse was a viable option. ConsiderationsNew venturi wet scrubber:Pros:    Less expensive than baghouse            Eliminate hydroclones since pond was large enough            Less maintenance than baghouse                         (bag replacement)Cons:   Higher energy costs (40” wg pressure drop)            Higher energy costs due to                         pump for water supply.            Must have pre-cleaner.            Pond maintenance.  New baghouse: Pros:    Eliminate pre-cleaner by using                         high side inlet.            Lower energy costs (lower pressure                         drop/ no pump).               Lower emission rate.Cons:   More maintenance due to bag changing.            Higher capital costs.     Sly designed a baghouse at a 5:1 air-to-cloth ratio and a high inlet that provides a large section of the collector to bring the air into with full partitions on either side to eliminate bag wear.  This inlet section runs the full width of the collector reducing the downward velocity to less than 800 fpm assisting gravity and low velocity to help settle out the majority of the inlet dust loading. A slightly higher than normal air-to-cloth ratio was selected by the customer since the dryer only runs 10-12 hours per week.   Sly furnished an STJ-1415-10 with high side inlet to handle 16,860 ACFM at 187 deg.F.   The unit was configured with (1) hopper that would discharge into a screw conveyor to return the dust back into the building and the process.  We also insulated the entire collector (factory installed by Sly in Mississippi) to help prevent condensation.  All the operators were given specific instructions on the proper start-up and shut down sequence to further avoid any condensation and fires.  Proper start-up requires pulling warm air into the collector before any material is feed into the dryer.  By pre-heating the collector condensation caused by hot moist air entering a cold baghouse is avoided.  Likewise on shut down it is proper to run warm air through the collector after the product feed has been stopped to pull any humidity out of the collector.  Sly supplied a temperature controller and thermocouple to alarm high temperature since the collector was supplied with polyester felt bags.  The collector was started up in December of 1999 and has only had one (1) bag change.  The DNR was so pleased with the initial stack test that yearly testing was deleted from their permit requirements.