Cartridge Collector Question
The pleated cartridge with its corrugated construction was initially developed for disposable intake air service. The more media that could be squeezed into a particular size filter, the more dust holding capacity bacame available to the purchaser. The more media that could be provided also would lower the pressure drop across the filter and make the cartridge even more desirable.
The tendency was to cram the pleats so close together that the pleats actually started to compress the corrugations.
However...............when applied to "dust collector service", the designers overlooked the fact that for most granular dusts there is a surface filter cake that is usually approximately 0.010" to 0.20" thick ( 0.0254 cm to 0.508cm) This "cake" will bridge the bottom of closely placed pleats rendering them "uncleanable". Once uncleanable, pressure drop rises.
Re: Acceptable or normal pressure drop.
Always difficult to "state", as it varies from application to application, however, if asked, I would indicate that a "desireable" pressure drop on a cartridge filter would be no greater than 6" w.g.
Troubleshooting the pressure drop problem. Here are some "typical" causes:
1.) High initial filtration velocity / air to cloth ratio when designed.
2.) Filter media is plugged. If possible, utilize off line cleaning to see if media can be cleaned.
3.) Was correct media type initially selected? Was a surface treatment applied?
4.) Have you checked the pulse cleaning system for correct operation? IE: timer board, diaphragms, solenoids.
5.) Is there sufficient clean, dry, oil free compressed air getting to the cleaning system?
6.) Have pulse pipes been inspected for correct orientation? I know it sounds silly but I've seen many, many pulse pipes reinstalled upside down!!!
7.) Are you confident in the accuracy of the pressure differential instruments being used? Magnehlic / Photohelic gauges. ■
Cartridge Dust Collector
Cartridge collectors are certainly not ideal for this application. My experience is:
1. In just about ANY application, design air-to-cloth (filter ratio) must be limited to 2:1 (2 fpm) for cartridges.
2. Clean, dry compressed air is essential, even instrument quality air.
3. Pressure must be not less than 85 psi to be effective.
4. 6" pressure differential is high. Cartridges are probably ruined if they are at 15".
As Richard suggests, they may be rejuvinated by off-line cleaning, AFTER you have made sure eveything else is fixed and normal.
There is no substitute for well planned regular maintenance!
Michael Reid. ■
Re: Cartridge Dust Collector
Gentlemen,
Thanks for the replies. I am not sure of the air to cloth ratio. The most recent modification was to add 3 more modules, and at that time, it was recognized that the system was marginal. Casting on our blast furnace is not continuous. We cast for about 2 hours with a gap between of 30 to 40 minutes. In that gap the system cleans off line. It seems to have somewhat lower differential most of the time after the off line cleaning, perhaps 12 inches, but it quickly builds back up. The system timing is such that it can only clean once through all 12 modules while the fans are off.
I have found cartridges with filter cake on them nearly 1 inch thick. I believe this is due to the wet air.
We have checked the transmitters, I have dp transmitters on each module, so I can trend them in real time.
As to the clean air, I agree with you completely. I have repeatedly suggested additional air drying capacity. The system is running off of 3 compressors with virtually NO accumulator space. I have suggested accumulators so that we can run the cleaning sequence faster while the system is "off line" and maybe get throught the modules twice. What I am finding is that the maintenance organization has little understanding of the requirments for this kind of system.
thanks again for the replies, and to anyone else, feel free to join the discussion.
hcrosmun ■
Wet Air?
That phrase certainly sets off the alarm bells! With a 1" dust cake it would appear that your problems are self evident.
Can you identify the cartridge media?
What is the inlet air temperature to the collectors? ■
Re: Cartridge Dust Collector
We don't always find that kind of dust cake, but it has been observed. Like I said, I think it is the cleaning air being wet.
The inlet air temp varies but never exceeds 170 or so.
I can get the exact cartridge if you are interested, but it has about 1" pleates. Our maintenance group once changed them to more pleats per cartridge, but the "stiffer" cartidges made it worse.
When the system was new, it ran 7-12 inches of water. It never ran as low as 6. We had an "event" last July, and the differential "pegged" AFter much shouting, I stopped them from re-ranging all of the transmitters to 0-25 inches and managed to convince that the problem was the cartridges/cleaning of. Some were re-ranged and those tend to run 17 inches plus.
I think it is safe to say that NO cartridge air filter unit is routinely operated over 15 inches?
Thanks again for the interest.
Hcrosmun ■
Cartridge Filters
Cartridge filters when properly selected and applied, should show less than 1" across the tube plate when new. The 'final' pressure loss would normally be about 4". This is the pressure differential measured across the tube plate, not the full dust collector assembly.
Michael Reid. ■
Status Of The Problem
To anyone who has interest in this post:
Cartridges are 27 inches long with 49 one inch pleats I believe.
We found that many of the inlet dampers were incorrectly marked as to position. We went back and positioned them to give the highest differential on each module, with intention of fixing correctly later. Cartidges have been replaced. (no name versions of originals) Some dP transmitter impulse lines were bad. Since we replaced them, some of the no name cartridges have "balooned" while cleaning. I suspect that they are NOT equivelent to the original equipment. (crooked salesman deserve a special place in you know where)
Current dp overall runs 9-12 inches.
Thanks for all of the advice. ■
Beltech Engineering
Dear Sir,
What is the orientation of the cartridge? inclined horizontal, or vertical?
What is the size of the pulse valves?
What is the size of the air header?
what is the material of the cartridges?
what is the make of the collector? Model?
what is the design A/C ratio?
Design CFM?
Is it a hopper inlet or side inlet?
What is the baffle plate/diffuser style?
What is the spacing of the cartridges?
How many on a lateral(assuming they are oriented vertical?
What is the orfice size of the blow tube?
What is the design CFM, and fan static pressure?
Email these answers to us and we can help! ■
Cartridge Cleaning System
Hcrosmon, Another option to help you out with your cartridges expenses is to have the filters cleaned by using the Sonic Dry Clean System. You would be able to safely reuse your cartridges and at least save your company money until you are actually able to sort out the problem with you dust collectors! If you want more information, just let me know. I will be able to save you at least 75% of you new cartridge filter costs!!! ■
Re: Cartridge Dust Collector
It's a common thing for casting fume emmissions control. You may find an explanation at http://www.ivteng.com/img/articlev2 . ■
Cartridge Dust Collector
I would like to invite you to take a look at our last article at http://www.ivteng.com/img/articlev2 . The article describes how one commonly overlooked design factor for pulse-jet cartridge dust collectors, called the filter-periphery airflow velocity, can lead to poor filter reconditioning and, eventually, a malfunctioning of the Dust Collection system.
I would appreciate any comments.
Thank you, ■
Differential Pressure And More
I've read your problem you have many different things going on . I can help you with some of your issues and you can get back to me and I will help you with whatever I forget this time. Just a bit of water in your cleaning lines can be one of the biggest problems. Your allowing moisture and dirt to have a greayer chance at eating the bladders out of your diaphrams. If you are in a colder climate you will have much more trouble than you can imagine. If you need to take and by pass your air drier try a holding tank with a bottom inlet and a top outlet before it reaches the diaphrams. This won't stop all the water but it will help some. Your compressors have to be running like crazy and working a lot harder than necessary due to diaphrams being gone. Becasue there is nothing to hold the air back and I am not sure what type of collection device your using. But if it's a bag it's going to be shot in no time because by trying to clean bags with water in your clean air side your bag life is going to be less than 1/3 it's normal life. If you start by installing a holding tank with a petcock or small ball valve on it to get rid of access water and then change the bad diaphrams out you will see a big difference in money spent on bags and a big decrease on wear and tear of your compressor. I hope this helps. Also by the clean air side diaphrams not closing the exhaust fan that is taking it away is running on screech and once you run through this stuff you will be suprised. It's a big money saver in the end trust me. I've worked in a plant with 20 - 30 units. If you have more questions contact me at Bdraggingazz@hotmail.com . ■
Cartridge Collector On Fume
Dear HCROSMUN,
Have been reading the info going back and forth. I have the following questions:
1) What is the temperature of each module when cleaned off line?
2) What is the temperature of the module when on line?
3) How many pounds of material is collected in each module when cleaned?
4) How many modules are on line when collecting the fume?
5) How many modules are cleaned at 1 time?
6) What diameter are the reverse pulse valves (diaphram) for each row of cartridges?
7) How many cartridges to pulse valve?
8) What is the clean air exit diameter of each cartridge?
If you can provide the answers to the above, I can begin to analyze some other potential problems with this system.
Sincerely,
Uncle Melvie ■
Cartridge Dust Collector
I have a cartridge style collector with 12 modules, 80 or so cartridges per module, moving about 200,000 cu ft of air per minute. Cartridges are pulse cleaned. It is on a blast furnace casthouse, for casting fume emmissions control. Dust is mostly fine oxides, some graphite.
Modules tend to run high on differential, well over 12-15 inches. Design criteria of modules said tube sheet and sidewalls should be limited to 25 inches differential.
What would be considered "normal" for a differential accross the cartridges? I cannot find a "normal" number in any of the documentation, but all of the dp transmitters were originally ranged to 15 inches max.
I think that is the maximum "normal range" but a superior doesn't seem to like that answer.
I believe that the problems we have with the dust collector are related to the cleaning air, in that there is a bypass around the air dryer which will allow high temperature, wet air out to the cleaning air lines. It is common to see dew point up to 10 or 15 degrees F, but some air may be bypassing the dryer altogether. The air pressure is frequently pulled down as low as 50 psi on the cleaning air, I think because of sticking pulse valves.
I have suggested eliminating the bypass and installing a backup air dryer, rebuilding pulse valves, as well as some accumulators on the tower itself to minimize pulse air pressure "pull down" when the modules are cleaning.
Would anyone who views the forum care to comment and or make suggestions?
Hcrosmun ■