For this short distance of 20 meters, using a standard dilute phase conveying system with a blower and rotary valve will be quite expensive. If you have compressed air available, a venturi will do the job and it will have a much lower capital cost.

A. T. Agarwal

Pneumatic Conveying Services LLC

polypcc@aol.com ■

For this low throughput and short distance, check into a vacuum loader system. An eductor venturi will work fine, but will be less efficient to operate than a simple vacuum loader. You can check with suppliers like Ktron, Premier, or Vac-U-Max. You will probably end up with a 1-1/2" or 2" pipe.

If you have an abundance of compressed air available in your plant, the eductor will have the lowest capital cost. If not, you will need a blower to drive it and the cost savings vs. the vacuum loader are lost. ■

Try contacting Paul Solt , he has a simple calculation program to dimension pneumatic conveying systems.

But by any means try it , there is no risk, use a 50 mm pipe , rent a compressor if need be.

design your bin ventury feeder with additional fluidizing entrances and bin head pressurization.

design a a crude air filter , do not use cyclons. consider the possivility of filter fires.

find your pressure drop., and then buy your blower if need be.

By the way what are your needs , do you need this to have a constant troughput, like on a burner . can this be a batch system . sometimes conveying sometimes not.

marco

where is it comming from , a bin , a truck.

where is it going to , is there back pressure ? is this a process vessel or a holding bin ?

I would guess you will have more problems getting the PET in than conveying it, that is the nature of flakes.

Marco ■

If you want to run calculations yourself, I have a simple Excel program that you can use and it is free. It will be published in a magazine very soon.

Regards,

A. T. Agarwal

Consultant

Pneumatic Conveying Services

polypcc@aol.com ■

Hello

Assuming an horizontal distance of 10 m and 3 bends , I reccomend to use a possitive pressure conveying system having

the following performance:

1.4" pipe diameter and a mean velocity of 22 m/sec

2.A centrifugal blower rated 800 c.m./hr and 1200 mm WG.The

working point should be on the declined / "vertical" part of

performance curve.

3.Material to air ratio 1.5

4.If you have a constant feeding to a well designed venturi you

do not need a rotary feeder.

Sincerly

S.Bar ■

good site , tried it myself and looks right at the ball park.

Marco

add filter pressure drop . ■

I'm sorry for the misunderstanding. It is quite common in the U.S. to refer to pellets as flakes.

The way you describe the bulk material, it has very irregular particle sizes and shapes. If it is post-consumer shredded beverage bottles, I have some experience with it. This material will not flow freeling out of conical hoppers and must be agitated. Also, rotary valves can be problematic, since the thickness of the shredded particles is sometimes thin enough to wedge in between the rotor and housing of typical rotary valves. I have some experience using rotary valves to feed this material into a pressure conveying pipe, but it must be pre-dosed. That means we need a metering device upstream of the rotary valve, like a screw feeder or a vibratory feeder. The rotary valve, then only functions as an airlock, to prevent back flow of conveying air up into the feeder.

An eductor system will not work either, since the feed opening to the eductor is very small. The irregular shape particles will bridge over this opening and not flow freely.

For your case, I believe the best solution will be to use a vibratory feeder and a suction conveying system. We have used tray type vibratory feeders and tubular type. They will both work. Screw feeders may also work, but you should consult with an expert company like Acrison or K-tron for specific screw geometry/configuration details. You will not need a rotary valve to feed a suction system, just a vertical chute from the feeder into a horizontal conveying pipe. Your big bag discharge station will need some type of agitator to keep the material from bridging.

I also agree with you, that a 2" pipe may be too small for such particles. I would use a 2-1/2" or 3" pipe, low solids loading (< 5:1), and a conveying velocity of minimum 20 m/s. The low loading ratio is good advice for this type of material, since the feed rate into the system will be inconsistent and cause surging in the system. Don't overload a system like this.

I hope this post is more useful to you than my last one. Good Luck.

bob ■

Dear dhruv,

From the dates of the various replies it can be concluded that your project has been put to a hold for about 4 years.

The various replies mention the existing possibilities, solutions and problems that can be encountered.

If you evaluate all these ideas, the pneumatic conveying solution might not be the most economical one.

If you still want to go pneumatic, I think that a vacuum system will be the best option.

Dump the PET flakes in a pit

Suck the flakes up, using a rotating nozzle (rotating nozzle to prevent flow problems)

Through a pipeline the PET flakes are transported to a cyclone (preventing the need for an airlock)

The air from the cyclone is cleaned finally in a self cleaning filter, to remove the finer particles

The finer particles are stored until the filter hopper is full and than dumped into the silo when the pneumatic conveying is intermitted.

The 4% water will not really affect this system.

As air pump a centrifugal fan is used.

This requires a low pressure drop

Therefore a large air volume and a low pressure drop is designed.

This results in low SLR.

For a proper design, consult an expert in the pneumatic conveying of your product as he knows the pneumatic conveying parameters of the PET flakes.

A 6”pipeline with 900 m3/hr fan gives an INDICATION (NOT a calculation) if the size of the installation.

A mechanical solution like a bucket elevator might be much simpler.

success

teus

Attachments

petflakeinstallation-model (JPG)

■

Dear Sir Teus ,

How to control the flow rate entering from the rotating nozzle and similarily the material.

Regards ■

dear sachin,

The nozzle takes care of its own feeding rate.

As the feeding increases, the vacuum increases and thereby the air mass flow decreases (property of a positive displacement pump)

When the air mass flow decreases, the pick up velocity decreases and the feeding also decreases.

The pump characrestic controls the feeding in a vacuum system

all for now

teus ■

The only real advantage of pneumatic conveying in this case is that it isolates the material from the atmosphere (no dust emissions). This open pit idea defeats that purpose. If there is no concern for the environment, then a mechanical system is a better bet. It will cost less to install and operate.

The idea of suction nozzle is a risky one. It will cost less than a feeder and probably work good enough. My only concern is how consistent the feed rate will be using this type of device with a non-free flowing bulk material. In any case, a closed chamber below the bag dump station will allow this feeding concept to function and still provide environmental isolation.

Also, a 6" pipe is much larger than necessary for this throughput. A system that large will only increase the cost. A simple vacuum loader reciever made by any number of manufacturer is all that is needed to disengage the material from the conveying air.

I would advise you to send a sample of your material to a manufacturer for testing. They can try these concepts and prove which will work best for your application. ■

Dear dhruv and Bob,

The nozzle is a rotating nozzle with scooping function.

If necessary the rpm can be controlled based on the vacuum.

Dust problem in pit is solved by a closed chamber with air inlet for vacuum system.

When emptying big bags, this problem has to be solved anyway and the vacuum flow will even be beneficial.

Using the pit as a surge bin, the vacuum conveying can be continuously consistent.

As the system has to be calculated, a definitive conclusion on pipe size and airflow cannot be given yet (unless field data of pneumatic conveying installations are available)

The 6” pipe is rather big for the intended rate, but is guessed because of the application of a centrifugal fan (not a blower). A low SLR is then necessary in order to keep the pressure drop as low as possible for the fan.

The cyclone should empty the bigger particles by itself at the bottom opening (principle of the cyclone).

The finer particles (less in weight and volume) are collected in a hopper underneath a filter and after a period of time emptied into the silo with the vacuum system stopped.

Gravity unloading will be rather fast.

I also suggested going mechanical.

F.i. A vibrating chute and a bucket elevator.

Quote Bob,

I would advise you to send a sample of your material to a manufacturer for testing. They can try these concepts and prove which will work best for your application

Unquote Bob

I can understand that the answers in this forum are not always giving a discrete solution, but merely some general information on technoligy and suggestions which way to proceed.

Designs and decisions have to be made by the responsible engineers and managers.

best regards

teus ■

Dear dhruv,

You made your point and you are right.

To avoid the problems of a rotary lock, you can use an airlock with an upper- and a lower slide valve.

That should work.

Yet another reason for a simple mechanical system?

take care,

teus ■

Dhruv,

You don't need a rotary valve for the cyclone if the material is passed through a materials handling fan and blown up to the top of the silo under positive pressure.

Allow the material to gravity feed a simple injector fitted to the top of a duct at the fan inlet.

Regulate the airflow with a damper in the duct ahead of the injector.

Regulate the material flow with a slide damper in the feed chute.

There will be some dust carryover because cyclones are not 100% efficient.

Michael Reid. ■

Dear Bob,

I have an application which is almost similar to this thread but is having some doubts. Anyway my question is, with your experience will conveying such high velocity generates fines and streamers - for PET flakes material? ■

Hello Mr. Lee,

Any pneumatic conveying system will create fines, regardless of velocity. The collision of particles with the hard surfaces of the pipe and with other particles will cause small appendiges to break off from the body of the particles. The more irregular the shape of the particles, the more fines it will produce. There are ways to minimize it:

1. convey at minimum velocities

2. minimize pipe distance and quantity of bends

3. design the system for the highest practical solids-to-gas ratio.

Streamer formation is more difficult to predict. There are many variables that can determine the occurence:

1. conveying velocity

2. temperature of the PET

3. roughness of interior pipe surface

4. bend geometry

The most significant variables are the velocity and temperature. If the surface of the particles reaches the melting temperature of the PET as they slide against the pipe surface, the skin of the particles will melt and deposit a film on the surface of the pipe. This can occur in bends and in extreme cases, in straight sections of pipe. Once the film cools and solidifies on the pipe surface, it will start to peel off in the form of threads and ribbons.

The degree to which these forms of degradation will occur can only be determined through testing.

It's kind of a long and nebulus answer, but I hope if gives you some idea of the complexity of this issue. There are many discussions and claims that you will find in these forums regarding this issue. It's one of the most challenging issues facing our industry.

Bob ■

Dear Bob,

Thanks for your informative reply.

Unlike Mr. Dhruv's particle sizes. I have with me crushed-sieved PET flakes with a top-end size of 10mm. I've observed that there are interstices in between particles after putting it ia a bottle.

My next question is, is it possible to convey in dense phase plug-flow for such irregular shape even though with this size? What if I were to crushed it further to size <5mm?

Please kindly advice. ■

Hello Mr. Lee,

It may be possible to convey in dense phase, but I would need to have a better description, or a photo demonstrating the particle form. If the particles are relatively uniform in size and shape and have a simple symetrical geometric form, It will be ideal for dense phase. If the particles are irregular in form, then it may be troublesome to convey in dense phase.

I think you also have to evaluate what you will gain by conveying in dense phase. There are complications to the technology that may be more trouble than it's worth.

If it is fines that you are mainly interested in reducing, an elutriator or deduster may be a better choice.

Bob ■

Hi Bob,

No, it is not fines that I'm interested in. Just exploring ways to convey the flakes more efficiently.

I've attached some photos and hope you can provide some expert advice.

If dense phase is not possible, what are the conveying velocities for dilute phase are we looking at? I intend to use suction conveying for this application with a minimum conveying velocity of 20m/s; horizontal distance of 46m, vertical 9m and 2bends, and with flowrate of 1ton/hr.

Please advice.

Attachments

pet flakes (ZIP)

■

Dhruv Shah,

It always gives a good feeling when one gets a feedback.

In case of a positive feedback, as in this case, it even feels better.

Going through all the posts, I conclude that you mastered this problem mainly on your own, because all the replies did not really converge to your solution.

Let us say that we were your sparring partners.

Nevertheless, you are in title to enjoy your personal achievement.

have a nice day

Teus ■

Hi falks!

Does anybody know if the software at: http://pneucalc.coperion.com/ is still available?

If not, if someone has it, could you share with me?

Thanks!

Walter ■

Walter,

Why don`t you contact Dr. Hoppe at Coperion direct?

https://edir.bulk-online.com/profile/2408-coperion.htm

Regards,

Reinhard ■

Thanks Reinhard, will try it!

KR,

Walter ■

Dear Mr. Amrit Agarwal,

I could receive your very useful article regarding the "theory and design of diluite phase pneumatic conveying systems".

Tank you! ■