Sniffing Something.
You are extending the horizontal pipe 37m. Tub (trailer) pressure of 1.8 bar is well above the usual. It requires a test pressure of 2.7 bar at least: is your system compliant or has the compressor been turned up at some stage? One hour is not so far off the mark at present but 3 hours really is too much.
You are correct that air injection will do more harm than good: back-flow is also possible as the tub empties.
For what it is going to cost, why not fit 4" NB pipe? Put a flanged reducer at the silo end and see how you go. If you eventually need a new, longer, 4" nozzle you will only have to throw the reducer away.
PS. If your 3 hour unloading time overlaps dusk you also risk pulling some vacuum as the ullage shrinks. That might affect your silo specification and rectifying that would be very expensive unless a snifting valve is already fitted.
More learned colleagues may suggest different diameters. I never understand, or accept, what is meant by severe wear in pipelines. Why not just use the highest schedule you can afford and reduce the replacement costs and process downtime accordingly? It must be the cheaper option. ■
John Gateley johngateley@hotmail.com www.the-credible-bulk.com
Re: Silica Powder Pneumatic Conveying Rerouting
Dear Pedro,
Extending a pneumatic conveying pipeline from approx. 13m to approx. 40m, which is approx. 3 times. it is obvious that the conveying rate reduces significantly.
The amount of conveying air does not need to be changed, as the pipe size (3”) stays the same as well as the compressor pressure.
Actually, you designed a new pneumatic conveying installation with a new conveying rate.
To maintain the previous conveying rate, the pipeline size needs to be increased and thereby the compressor size. (Do not forget the silo filter size)
Also a good opportunity to design as efficient as possible.
Ask Mr. Agarwal for his calculation Excel sheet.
Success ■
Teus
Re: Silica Powder Pneumatic Conveying Rerouting
Dear all,
Thankyou very much for your replies. As suggested, we will go for a larger bore pipeline, although the compressor power (tub) is something we can not change. I will ask Mr. Agarwal for his excel, I want to do some numbers to keep velocity above 15 m/s all the way.
Silo filter size is something I have to check on, thanks Mr. Tuinenburg.
Mr. Gateley, by severe wear (I am new at this) I meant there was a feeling among the staff that performed the test that it could be dangerous for the pipes to have a second tub truck filling the silo.
As said before, thanks for your help. We are installing the larger bore pipe soon, will let you how it goes. ■
Re: Silica Powder Pneumatic Conveying Rerouting
Dear Pedro,
Just installing a larger bore pipeline, seems engineering by the hit and miss method.
To modify your pneumatic conveying installation, you have to evaluate the existing installation first.
Compressor size
pipe line geometry (length horizontal/vertical number of bends)
filter size
Altitude
Particle size (distribution)
Conveying rate
conveying pressure.
This enables you to determine the existing operational parameters, one of which the air velocity is important to know.
Then you define the new (modified) pipe line geometry (length horizontal/vertical number of bends)
and calculate the new operational parameters.
This approach can save you considerable cost, disappointments and comments from the management.
Success
Teus ■
Teus
No Magic Wands Here.
The compressor and PTO are fixed items, albeit trailer mounted, and so are the available pipeline sizes between 3"NB & 6"NB & beyond.
Suppose you start with 3", go to 4" and then to 5" (if you can get it) it will have to be within the lengthened horizontal section. This will result in a new larger nozzle at the silo inlet.
Regarding the filter sizing: you should examine this in detail. It is quite unlikely that you will achieve the original 24th-1 throughput whatever you do.
You will have to live with the 3 hours unloading time, or something similar. If you park 2 tubs and duplicate the pipelines you will need a non-return flap which may not be reliable, but worth a try if you have the parking space. However the silo filling loads will again need to be investigated further.
This is a classic example of expensive tubs falling short because of their inflexibility. I have a thread lurking somewhere within these here forums which outlines the benefits of using tipper trucks, fluidising lances and external compressors of any affordable size. There is an easy solution. ■
John Gateley johngateley@hotmail.com www.the-credible-bulk.com
Re: Silica Powder Pneumatic Conveying Rerouting
Hello Again, I have done some calculations using Mr. Agarwal's article. With a stepped pipe 3"-4"-5" I get 38% more cpacity than 3" all the way. Silo inlet is 6" actually, so the nozzle will not be stretched at the end. As for the filter, filtrating area is 25 m2, I think it is enough.
Next step is calculating a straight 4" pipeline, since I have noticed the mojority of dP occurs in the first 3" section (10m vertical pipe + antiwear 90º elbow). Of course I will try to keep velocity above saltation.
Regards, ■
Re: Silica Powder Pneumatic Conveying Rerouting
Dear Pedro,
Thank you for the feedback.
A few questions.
-Have you calculated the existing installation and did this calculation match the existing performance and pressures?
-Did you have to change the K-factor in order to match the existing performance and pressures?
-If you conclude that the Filter size of 25 m2 is sufficient, then you must also know the compressor volume. As long as the compressor volume does not increase, the filter area should be OK
-If the velocities in the larger bore pipeline with the same bulk truck compressor are sufficient, the velocities in the 3”pipeline were probably too high, explaining your wear problems.
Interesting to know your further calculation results.
Have a nice day ■
Teus
Re: Silica Powder Pneumatic Conveying Rerouting
Dear Teus, I answer to your questions below:
Originally Posted by Teus Tuinenburg
I did for the 3" pipeline we have and it matches the performance. Unfortunatelly there is no way to know the pressures along the pipeline in this case, so that remains "unchecked"
Originally Posted by Teus TuinenburgThe performance was matched without changing K. However I changed rugosity from 0,0005 to 0,00015 for it suits better my pipe.
Originally Posted by Teus TuinenburgThe compressor volume is the same, so no changes will take place on this.
Originally Posted by Teus TuinenburgThere is still one thing that I have to check, and this is velocity in the first part of the pipe. I am assuming that the existing pipe was calculated for a pickup-plus-safe margin velocity, and this is an input data I am using, but I still have to check if this is correct.
We are installing the stepped pipe, with several pressure gauges spread troughout the pipeline. When the prerformance test is done, I will be able to check the theory with pressure data. I will get back here when I am done.
Regards, ■
Re: Silica Powder Pneumatic Conveying Rerouting
Dear Pedro,
I am assuming that the existing pipe was calculated for a pickup-plus-safe margin velocity
I understand that this assumption is for the existing 3” pipeline.
That means, if you assume the same “pickup-plus-safe margin velocity” for the larger bore pipe, the compressor volume must increase.
Take care ■
Teus
Re: Silica Powder Pneumatic Conveying Rerouting
Dear Teus,
You are right. However, there is a possibility that pick up velocity is too high, so I could afford a 4" pipe without changing the compressor volume. That would be the best case scenario for me, but I still have to do more research on the pick up velocity I have.
As for the K factor, I have noticed it has a dramatic impact on the dP. Is there any way that K factor can be estimated? I am working now with silica sand, and everything seems to fit in place, but I plan to do the same calculations for silica powder. ■
Re: Silica Powder Pneumatic Conveying Rerouting
Dear Pedro,
However, there is a possibility that pick up velocity is too high, so I could afford a 4" pipe without changing the compressor volume.
Hmmm, this not engineering but guessing.
The pickup velocity is related to the suspension velocity of the silica particles.
The suspension velocity is a function of the particle size distribution, the particle density, particle shape and the gas density
The pickup velocity along the pipe wall must be higher than the local suspension velocity, in order to keep the particles in suspension.
This is the reason, why you need to know the compressor volume displacement as input to calculate the gas velocities (mean gas velocity and wall gas velocity).
The gas velocity at any place in the pipe is depending on the local absolute pressure.
Therefore, you need to calculate the pressure (drop) at a certain conveying rate.
One condition is that the compressor pressure minus the pressure drop over the pipeline equals the system end pressure. (normally the atmospheric pressure).
As the gas velocity (and thereby the material velocity) is now dependent of the pressure and the pressure is dependent of the velocities, the complexity of pneumatic conveying calculations becomes eminent.
As you noticed, the K-factor has a significant influence on the pressure drop.
The K-factor is supposed to account for the influence of the presence of material in the gas flow.
The K-factor is, amongst others, accounting for the energy losses due to inter particle collisions and wall collisions.
Therefore, the K factor is depending on the Solid Loading Ratio (Number of collisions) and the turbulence (Reynold Number).
Pneumatic conveying: The principle is simple, the calculations are not simple.
Have a nice day ■
Teus
Silica powder pneumatic conveying rerouting
Hi all, this is my firs post in this very helpful forum, so I will introduce myself first. My name is Pedro, and I am a chemical engineer, with piping and hydraulics experience among others, and recently have been put in charge of several (not too complicated I think) solids conveying projects.
I work in a factory where part of the process involves pneumatic conveying, mostly in dilute phase. The project I am currently working on is rerouting an existing series of pipelines in order to have the inlet point of the pipeline outside of the building (now it is inside).
The current system consists on a series of pipelines, all identical, that are used to fill the silos from a vessel truck. If we take one of them, it is 3" carbon steel SCH 40, 10m vertical up, 3m horizontal and 1m vertical down, with two "antiwear" 90º elbows. Every day a 24 ton truck comes and fills the silo using this pipeline, and takes about an hour to empty the truck vessel. We have wear problems in elbows and lets say 1m of the pipe following the elbows exit. Compressed air is supplied by the truck, at 1,8 bar, and the silo operates at atmospheric pressure. This is all we know.
The system projected consists on the same only the horizontal pipe will be longer, about 40m. We have undertaken a test with SCH 40 3" all the way and severe wear happened. Also the truck took 3 hours to deliver the powder.
A solids provider that works with us has suggested to inject air every 12m as a posible solution, but to my understanding this will only get things worse.
I would like to do some calculations for a stepped pipe, which I think will work recover system capacity and get back to less wear, but the problem is I lack of experience in ths field. I have a copy of Perry's Cme Eng Handbook and other powder manuals I am working with, but I would like someone with more experience to give me some advice or a hand on where to start, or what to expect.
Thanks in advance. ■