Re: (Not) Coping With Fines And Angel Hairs
John
There are several forms of devices known as elutriators, fines separators, alleviators, scalperators, etc., which are used at the terminal end of a dilute phase conveying system to remove the angel hairs and fines from the product.
Some of the equipment specializes in fines and others are better at angel hairs. You can expect to lose some good product as carry over as the fines and angel hairs are removed.
A good company to contact for product information is Zeppelin, a German company with a sales office in Houston, Texas - Contact Harald Wilms.
Aother potential is Pelletron in Lancaster, PA. - contact Jerry Paulson.
If you would like a complete engineered package to fit into your system, contact ENGlobal Engineering in Houston, Texas - 281-821-7100 - ask for Mike Cannon.
If you need some assistance in reviewing your situation, analyzing the different options available and recommending a soultion, we can help - drop me an e-mail to the address below. ■
Fines, Angel Hair, And Streamers
Dear John,
Fines, angel hair, and streamers are a common problem when high velocity dilute phase pneumatic conveying many of the plastics. Fines are small size particles similar to dust, angel hair are up to a few inches long, stringy and hair-like materials, and streamers are long ribbon-like materials that may be up to 10 or 20 feet in length and up to 2 inches wide.
Generation of streamers in pneumatic conveying lines must be prevented because they will jam rotary valves and bin openings besides there is no practical way to remove them from the process. Commonly used prevention method is roughening of the internal surface of the conveying lines by shot blasting. This method prevents streamer generation but it does create fines and angel hair due to impact with the rough surfaces.
Fines and angel hair can be removed from the process by various methods depending upon the process and finished product requirements. For example, if the finished product specifications limit the fines and angel hair content to about 100 ppm, the only method is a high efficiency elutriator/ fines removal system installed at the final product loading station. But if the requirement is only to prevent blockages of bin openings because of bird nests formed by angel hair, a simple solution is to install a high efficiency cyclone above the receiving bin or silo, especially when the polymer being conveyed is not very soft. Pelletron's Deduster or elutriators can also be used in this service but they will cost much more.
Your technique of using crushed ice or dry ice has been used sometimes but it is not a common method. It is not used on a routine, long term basis because of its cost.
In my opinion, you should consider roughening the pipeline. Once you have done that use a cyclone if the polymer is relatively not very soft, and if it is, to use a Deduster or an elutriator. Elutriators are made by several vendors or can be designed in-house using published data.
Regards,
Amrit T. Agarwal
Consulting Engineer
Pneumatic Conveying Consulting Services
polypcc@aol.com
Ph and Fax: 304 346 5125 ■
Streamer Issue
The more cost-effective approach to solving your problem is streamer prevention rather than streamer removal after-the-fact.
Shot peening of the conveying pipe is a proven method of reducing streamer formation, although the total fines content may increase somewhat. It requires that the entire pipe net be taken down, shot peened, and replaced, or if downtime must be minimized, that the existing pipe be replaced with new shot peened pipe. For a long pipeline the cost may be prohibitive.
Also understand that the shot peened surface will wear away in 3 to 5 years and the pipe will require retreatment.
A better way. Streamers are the result of pellet-to-wall contact. This pellet-to-wall contact is infinitely greater in the area of the pipe bends or sweeps. There are several companies that make "special bends" that have also proven effective in reducing streamer formation, two that come to mind are the Pellbow by Pelletron and the Gamma Bend by Coperion-Waeschle.
The "special bend" approach may be best when the budget is limited.
Dennis Hauch ■
Fines And Angel Hair
Thankyou all for your advice, it has definately expanded my available options. I have seen Pelletron's Deduster and Pellbow on their website and they certainly look like what we need.
I have not seen any streamers in our system, only thin angel hairs up to around 6 inches long. We also suffer from fines, generated in our pelletising system as well as transfer system and so I am cautious about shot peening lines if it is known to generate even more fines.
In our transfer line the pellets are introduced through a rotary valve into a 6m horizontal section which then goes into a 25m vertical section with 90° bends top and bottom. There are then three more shallow 30° bends, 2 shortly after the vertical section to raise the pipe 3m, and a final bend just before the silo's 50m away.
Would I need to fit a 'special bend' to all of our bends, or just the 90° bends?
Thanks,
John. ■
Re: Streamer Issue
I think you should look at the conveying velocities in your system. Simple rule of thumb is "Higher the velocity higher the fines generated". If the exit velocities are above 20 m/s use a stepped pipe to reduce the exit velocities. This will reduce the generation of fines in the first place. Bend geometery also helps in reducing fines use long radius bends. ■
Fines And Angel Hair
Dear John,
Since you do not have streamers, you do not need internally roughened conveying lines.
If you are receiving this material from a supplier, please check the quality of the incoming material to make sure that it does not contain fines and angel hair.
If you produce this material yourself, using a high-effiiciency cyclone, or an elutriator, or a "deduster" will remove the fines and the angel hair, therefore replacing the present bends is not necessary.
Low conveying velocities are helpful but you will still need one of these removal devices to really solve your problem.
Regards,
A. T. Agarwal
Consulting Engineer
Pneumatic Conveying Consulting Services
Email: polypcc@aol.com
Ph and Fax: 304 346 5125 ■
Re: (Not) Coping With Fines And Angel Hairs
John
It seems the view has come back to my original recommendation to your initial thread to consider some form of fines removal at the terminal end of the system. The recommended suppliers I listed are good ones to consider. The Pelletron DeDuster is very efficient on removal of fines.
However, to reply to your post about bends, the shallower the angle, the less likely they will generate fines. While the Pellbow and the Gamma bends have shown success, the use of ordinary pocket tees has also been successful in many installations.
The dead pocket fills with product while conveying and forms an impact zone of product on product. The pocket then sweeps clean when the convey cycle is over. Short radius elbows have also been successful in reducing product degradation.
Some will say that tees and short radius elbows will have higher pressure drops. Each system and pipeline configuration has to be reviewed on it's own merit before that statement can be substantiated. From what you describe, your system has a minimal number of bends and extra pressure loss, if any should not be a problem. ■
Fines And Angel Hair
John,
In addition to Pelletron, several other vendors manufacture pellet dedusting equipment. We can give you a list of vendors if you need one. Suggest you do an engineering and cost study before selecting a vendor.
Regards,
A. T. Agarwal
Consulting Engineer
Pneumatic Conveying Consulting Services
email: polypcc@aol.com
Ph and Fax: 304 346 5125 ■
Angel Hairs & Fines
Thankyou all for your advice on this subject.
I will put together a project plan with improvements ranging from fitting 2 'special bends' up to fitting dedusting devices to each of our 6 silos. Including all of the other suggestions from this thread in between.
I would appreciate your vendor recommendations for dedusters, special bends etc so that I can put a cost plan forward ranging from the quickest and cheapest to the most expensive.
I do not fully understand the stepped pipe theory. Could someone answer a few questions for me please - Stepped pipe means increasing the pipe bore, right? Where would I need to place the stepped section? Does this reduce overall transfer rate?
Thanks,
John. ■
Re: (Not) Coping With Fines And Angel Hairs
John
Stepping a conveying line involves increasing the pipe diameter at the point in the system where the conveying air has expanded to the sufficient volume to continue to carry the material in the larger cross sectional area. It serves to reduce conveying velocities and lower over-all pressure drop. It does not reduce capacity and in many cases, can be a way to actually increase capacity in an existing system.
If you need help in developing your action plan and cost studies, please do not hesitate to contact me at the e-mail address below.
We offer these services and can assit you in the necessary analysis. ■
Only One Real Answer
Hello,
There is already an answer to your problem - true Dune Phase technology. This system can be retrofitted to existing lean phase systems at very low cost and will do the following :
1) Reduce the transfer velocity to 2-3 m/sec
2) Eliminate angel hairs and dust
3) Eliminate the need for terminal filters
4) Eliminate static build-up in the pellets
5) Eliminate the noise associated with conventional lean phase
6) Increase the transfer rate (if required)
7) you will not even have to change your blower set
It's true - and there are many systems operating with this technology today! My company (based in the south UK) has a demonstration CD, Video (emailable) and a full demonstration rig where we can prove the above on your product.
Just leave me a message with contact details and i will phone you. ■
List Of Vendors For Special Bends And Dedusters
John,
I will be glad to send you a recommended list of vendors who sell these special bends and dedusters. You may contact me on the email address given below. I will also be glad to help you in your study.
In general, conveying line diameter is increased in 2 steps, located about 1/3 distance apart. In addition, other factors are also considered for locating the steps such as location of vertical pipelines and location of bends. The main objective of the stepped pipeline is to reduce the system pressure drop, and thus increase the conveying rates if system pressure drop is limiting its capacity. This method is not used to solve fines and dust problem because the effect of reduced conveying velocity due to the steps is marginal at best.
Regards,
A. T. Agarwal
Consulting Engineer
Pneumatic Conveying Consulting Services
polypcc@aol.com ■
Re: (Not) Coping With Fines And Angel Hairs
The positioning of the change in pipe bore (and the size change)will be critical in getting the system running correctly. Change the bore too soon and the conveying velocity will drop and the material will saltate possibly giving a blockage - change the size too late and the velocity will not fall enough to give a significant improvement. You need to know what the safe minimum conveying velocity is and then calculate what the actual velocity will be at the position that you intend to change the bore size.
If you e-mail me your address I can post some published papers of ours on this topic to you.
Regards
Richard Farnish
The Wolfson Centre for Bulk Solids Handling Technology
University of Greenwich, London
mailto: r.j.farnish@gre.ac.uk
URL: www.bulksolids.com
Tel: 0208 331 8646 ■
Re: (Not) Coping With Fines And Angel Hairs
John --
Depending on the polymer, completely eliminating fines and angel hair formation in a 100m pressure conveying system will be difficult, although many of the suggestions offered above will significantly alleviate the problem. You did not mention what the polymer is, but some are more prone to fines and angel hair generation than others.
Unless you have a significant capital budget to apply to this project, if I were in your shoes I would do the following:
First -- Review the design of your conveying system to make sure you are not conveying the product at an excessive velocity. If you care to provide me with type of polymer(s) handled, diameter of existing conveying line, site elevation, and the desired conveying rate, I will be happy to run a quick calculation giving you my recommendation for blower ICFM. It would also be helpful to know the details of your existing pressure blower (manufacturer, model number, HP, etc.), along with the maximum gauge pressure at the blower when conveying at the maximum rate to the farthest point. You may be able to simply slow your blower down and solve much of your problem. It is doubtful that stepping the pipe size will be warranted in a 100m system. For a detailed analysis, you should probably contact a paid consultant, or you may be able to get some free help from the company that designed or furnished your system.
Second -- Once you are satisfied that you are conveying at an optimum velocity for the product you are handling, you may wish to experiment with some of the "special bends" mentioned above. The ones with the roughened interior surface are considerably less expensive than those that employ some form of the "blind tee" principle, although they are somewhat less effective.
Third -- Depending on the polymer, you may want to consider cooling the blower discharge air before it contacts the material. Soft polymers with a relatively low melt point (LDPE for instance) almost always require some form of cooling of the conveying air in a pressure system. The temperature rise across a PD pressure blower can be as much as 90 degrees C, depending on the pressure. Added to the ambient temperature, this elevated temperature can accelerate the "smearing" of the polymer in the bends.
Fourth -- After your attempts to reduce the angel hair formation have been exhausted, if acceptable results are not achieved, you will need to resort to some form of removal. If you were only conveying to one point, this might be a "first choice" since it is a positive means of dealing with the problem. However, six removal systems (one on each of your silos), will not be inexpensive. If your problem is not excessive, and you have access to the top of your silos, I have furnished a "simple" alternative to sophisticated removal systems on a few occasions. This amounts to a 20 inch diameter cylinder X approximately 36" tall, flanged on the bottom to bolt to the standard center dome on a typical silo sold here in the US. Near the base of the tube is a 1" mesh screen which will trap the majority of the angel hair, but allow the chips to pass. The conveying line is introduced tangentially about the way up the tube. A level sensor is positioned between the screen and the material inlet. Close to the top of the cylinder is an "overflow" tube that bypasses the screen. The lid is made of 3/4" clear polycarbonate and is fastened with quick release latches. As the pellets enter the cylinder they filter through the screen into the silo while the angel hair remains trapped above the screen. Should the screen become plugged with angel hair, chip will fill the tube activating the level sensor (wired to an alarm panel). The chip will then flow out the overflow on top and back into the cylinder below the screen. Obviously, the plan is to inspect the screen frequently by visually looking through the lid, and remove the collection of angel hair before the screen is fully plugged. Again this is a relatively inexpensive option for dealing with the problem if purchasing six removal systems is out of the question. You might wish to try this approach on one silo to gage the frequency required for cleaning the screen. Hopefully, by employing the relatively inexpensive preventive measures above, the screen maintenance interval can be reduced to something manageable. ■
Fines And Angel Hair
Reducing the air velocity, reducing the incoming air temperature, using high solids to air ratios, using special bends/elbows are all good ideas to reduce fines and angel hair but these ideas will not be able to eliminate them or to reduce them substantially. Some means for their removal will still be necessary. This being so, it should be more economical to use a viable method for fines and angel hair removal.
Selection of this method depends upon various factors such as batch or continuous operation, product quality requirements, operating and capital cost, and plant shut-down and restart-up costs. Types of methods generally used have already been discussed above.
Regards,
A. T. Agarwal
Consulting Engineer
Pneumatic Conveying Consulting Services
polypcc@aol.com ■
Removal Of Fines And Streamers
Hi John
I have just seen your posting.
My company Jenco are UK system integrators for Pelletron de-dusting systems which will remove streamers and fines down to 1 micron and 5 ppm.
I you e-mail me pjensen@jenco.co.uk, I will send you details
regards
Paul Jensen ■
Pelletron Deduster Model P120 Galvenized Frame
I realize that this is an old thread but not sure if you accomplished what you need to fix your problem:
Here is some infor that I ahve on the Pelletron:
http://mail.ezead.com:7080/users/too...erEnglish.pdf
And if you need a substantial one I do have one listed under used equipment at at very reasonalbe price that is all ready to go. ■
Shot Peening Of Stainless Steel Pipes & Bends
We are glad to inform you that we undertake the process of internally roughening of the Pipe & Bends through process of Shot Peening, which reduces the Angel Hair or Streamers formed while transporting plastic pellets through Pneumatic Conveying System.
Our plant is equipped with automatically controlled shot peening machines for wide range of components of job diameter upto 1 metre with consistent and unerring results. We can deliver Stainless Steel Pipe & Elbows as per the required Grades & Drawing having roughness value as per your Specifications required at affordable prices and short delivery periods.
Please do read the attachment for further details.
Thus, we request you to give us an opportunity to serve you and we assure you our best service.
Warm Regards,
V.C. Chandan
VIKAS METALS
4-4-168, Mahakali Street,
Ranigunj,
Secunderabad-500003.A.P.(India)
E-Mail: vikasmetals@yahoo.co.in
Ph: +91-40-27712995/66385055/9885977337
Attachments
shot peening-solution for angel hair formation (PDF)
■
(Not) coping with fines and angel hairs
We transfer thermoplastic elastomer pellets in lean phase over 100m to 20MT capacity silo's. We get fines and angel hairs mixed in with the pellets in the silo which we want to avoid. We do not have the capital or political will to switch to dense phase, so I was wondering if there are any methods out there for filtering fines/angel hairs before they drop into the silo. We have run 50kg of ice cubes through the transfer lines in the past which seems to collect fines, is this a common practice or are there better methods that we could use?
Would very much appreciate some advice on this subject.
Thanks,
John. ■