Blower
As per your description, I would look into the blowe assembly first.
One of the internal seals might be leaking, or might not be sealing at all.
Regards,
Marco Flores ■
Blower
Dear Sir,
Densephase Conveying System is most suitable for the application.
Dilute Phase system always gives problem for the system, as envisaged by you.
With regards
Raman Lamba
Macawber Beekay Pvt. Ltd.
https://edir.bulk-online.com/profile...ber-beekay.htm
raman@macawberbeekay.com ■
Dense Phase Conveying
A retrofit to provide dense phase conveying, while a good idea, is likely to prove very costly. The current conveying line inlet air velocity (pick-up velocity) is about 18 m/s, which is ideal for dilute phase conveying. Once this air velocity drops below about 14 m/s, for the transition to dense phase conveying, the material flow rate will decrease rapidly with further reduction in air flow rate. To achieve 30 tonne/h will then require a compressor rather than a blower and if the conveying velocity is very low a larger bore pipeline will also be required.
Power requirements, and hence operating costs, also increase with decrease in pick-up velocity below about 14 m/s. If you are concerned about the generation of angel hairs in the product then this is a price that is generally worth paying. If angel hairs is not a problem then dilute phase conveying is generally best. ■
Pellet Conveying Problem
Air flow appears to be critical (e.g. Froude number at the pipe step could be only around 14, and also at the pick-up point).
Even a slight reduction in blower performance could be enough to cause such problems (product deposition, build-up and blockage) - especially in large-diameter pipes like 8 inch. Combo of pipe step, bend/pipe layout, etc will exacerbate problem (and deposition can occur downstream for this reason - that is, instead at pick-up point). In our Labs we demonstrate this quite clearly and easily with our glass pipeline. Seeing is believing!!
I would suggest a blower with min. 50 to 54 m3/min (approx) at 1.2 kg/m3...but I would need to know actual pipe internal diameters and pipeline layouts before confirming optimal air flow.
I think air velocities still will be low enough to avoid angel hair formation, but of course this also would need to be checked.
Good luck (and stick to dilute-phase, unless of course you have plenty of money for a dense-phase system)
peterwypch@uow.edu.au ■
Blower
I concur with Prof. Wypich. Stick to dilute phase, you already have a sizable investment to start again.
Again, look into your compressor. As you have no flow instrumentation, anything we say is mere guess work, so if if was working well, don't move it, check your compressor, something is wrong with your re-vamp compressor.
As Prof. Wypich mentioned, because you hav a step pipeline, you have settling down stream. This is very common with step pipelines.
About going up, normally you need less flow to go up that to avoid settling in a horizontal line.
As a lateral line of thought, your lines are not sloped, nor have you made any change in your pipelines after the compressor was replaced, right?
Again, look into your compressor, something is wrong with it. Look into your air filters, or your discharge system, soething might be plugged.
Good luck! And again, look at your compressor.
Marco ■
Pp Pellet Conveying Problem
I agree with Mr. Peter Wypch that your air flow appears to be critical and a slight reduction in blower performance can cause problems.
Product build up can take place in the pipeline even at intermediate points, and especially after the step up to the higher line size, if not properly evaluated. Is your step up point from 7" to 8" in the vertical section or at the silo top. If so be the case then the product is falling out of suspension and settling after the succeeding elbow.
A more detail evaluation can be made on receipt of the complete line details and drawings.
A lasting solution to the problem can be either moving the step point further down or by increasing the air flow.
Thanks and Regards,
Vikas Gaikwad ■
Thanks For Your Advice
Thanks to all of you for enlightening me on this problem. We are now expediting the replacement of blower. As additional countermeasure we are now studying to increase the blower speed by changing blower pulley (upto given margin of the existing motor ~ 20% flow increase)
However I am still not sure why the pellet should settle out in the horizontal pipe after rising the height of the silo (approx 15m). The pipe step up from 7" to 8" is located in the midway of vertical rise. I am surprised that pellet settle out do not take place in the vertical rise if the velocity is quite close to saltation veliocity for the present solid to air ratio.
Another issue on which I am trying to solve is " How to find out the Saltation velocity if no test data or facility is available". Our plant design is basically scale up of our technology supplier experience at its plant. Thus it had very big factor of safety in design. Using this FOS we gradually increased the conveying capacity from 21 to 30t/hr without any problem till recently. This problem indicates that we have reached limits of the system. The Rizk co-relation as available in the literature gives a saltation velocity which is almost 20% higher than our existing condition. So how can I find out the Solid to Air ratio limits for this system and saltation velocity to some degree of accuracy?
I have also been asked to study to scale up this conveying system from 30 to 32t/hr while using the same blower and motor (Blower has a margin of about 40% against its design capability while the motor has a margin of about 25%) My calculation shows that increasing the 8" pipelength along with with increasing the blower flow by about 16% I can achieve this capacity. However as the saltation velocity cannot be calculated accurately I cannot confirm whethet any pellet settling in the line after step up will take place.
Looking forward for your valuable advice and suggestions
Regards
Tima ■
Pellet Conveyg Problems
The pellets will slow down slightly in 8" section of vertical lift. Then they will slow down further due to vertical to horizontal bend - also roping will occur with most of the pellets hitting the bottom of horizontal section of pipe (small distance downstream after bend). If air flow is close to critical, then the above combo of step and bend may be enough for saltation and build-up. Also, the pipe layout before the vertical lift may be slowing down the product (to exacerbate the above problem/s). Of course, we can avoid all this with higher air flow/velocity.
The min. conveyng velocity in vertical lift < min. conveying velocity in horizontal pipe. Hence, you will see problems in horizontal before the vertical.
Do not trust saltation and min/ conveying velocity model predictions - see my paper:
Yi, J, Wypych, PW and Pan, R, Minimum conveying velocity in dilute-phase pneumatic conveying, Powder Handling & Processing, Vol 10, No 3, 1998, pp 255-261 (which should be readly available).
This paper demos how things can go crazy for relatively large pipe sizes and tonnages.
Personally, I would work with a min. Fr = 16 for poly pellets (as a starting point) and then adjust this number for different conditions/situations.
The "best" test rig is the plant...by varying air flows and monitoring pressure fluctuations, etc, you can fine-tune the system to achieve min. air flows reliably (and also for different pipe layouts) - but many plants do not like fiddling.
peterwypych@uow.edu.au ■
Pp Dilute-Phase Limit
At the stated conveying conditions (30 t/h, 47.0 m3/m, 0.78 K) the solids loading is 8.86, which is high for a dilute-phase system of this length (162 m).
Applying the Rizk correlation for saltation velocity (at the pickup point) we find that the blower flow should be 56.2 m3/m, so already we are some 16% below the minimum required conveying flow. That fact, coupled with a suspect replacement blower, would explain the blocking of the pipeline that you experienced.
32 t/h will require a blower flow of 63.1 m3/m at an estimated conveying pressure of 0.98 K. The teminal velocity (at the end of the 8" section) will be 32.4 m/s. It is a certainty that streamers will be generated.
It is clear that you are operating at the very limit of your system, moving the stepping point will likely not get you to 32 t/h. At this point I would suggest that you include a new system in the capital plan for 2006.
Kind regards,
Dennis Hauch ■
Pellet Conveying Problem
Dear Mr. Tima,
If the pressure safety flap opens while conveying that shows that more air quantity has to go directly into the conveying line instead to the pellet feeding and this will drop down the pressure due to its dilutation.
We recommend you a pressure regulating system which opens a bypass if pressure rises up and closes when pressure drops down.
Hope we have given you an idea.
best regards
Peter Kohler
www.intec-kohler.ch ■
Pp Pellet Conveying Problems
Tima,
From the description the problem occurs when conveying to the last 2 silos, 5 and 6, but the other 4 silos are O K.
From the description, blockage at the silos or the end of the line, it sounds like the silos 5 and 6 could be full of pellets.
Alternatively the lines to silos 5 and 6 are damaged or partially blocked, or the diverter which divides silos 5 and 6 is blocked or leaking, or stuck in the half way position. Also check exhaust from silos 5 and 6 are clear.
Changing the blower will not help.
Kind regards
Harold Coles ■
Pp Pellet Conveying Problem
Dear Tima,
In my opinion you should check the clearances of the new re-conditioned blower, if not already done, before buying a new blower. If these clearances are much more than those of of your old blower, the air capacity of this blower will be reduced. My calculations show that the old blower was supplying barely enough air to maintain the necessary solids velocity throughout the conveying line, especially after the last bend above the silos where this velocity is the lowest. If the blower clearances are higher than those of the old blower, solids velocity after that bend will be less than the saltation velocity in a 8 inch line.
To account for the higher slip due to these clearances, you could increase the speed of the new blower because you don't seem to be horse power limited.
Do you have an air cooler at the blower outlet? What is the air temperature after the cooler?
Best regards,
Amrit Agarwal
Pneumatic Conveying Consulting Services ■
Re: Pp Pellet Conveying Problem
Dear Sir
In response to Your question from 17 March 2005 we kindly inform that basing on our experience and parameters of pneumatic conveying we are able to elaborate the system for transportation of PP Pellets together with the optimalisation of the unit’s operation. For the in depth analysis of the problem it would be necessary to made measurements on the chosen installation, which would enable a detailed examination of multiphase flows, with a use of oar databases.
For further information don’t hesitate to contact us.
Best regards
Damian Homa ■
Re: Pp Pellet Conveying Problem
Dear All
I am continuing on to my previous info. During the recent plant turn around the PP conveying system was upgraded with the following changes:
1) Blower was overhauled and speed increased to give flow rate of about 49.5 Nm3/min (a increase of about 5% over original)
2) The step (7" to 8") was brought towards the pickup point by about 33.5m ( 7" reduced by 33.5 m and 1 LR elbow and replaced by 8" line) and now is in the horizontal segment of the system.
3) Pellet feed RV rpm got increased to 35.9RPM from original 30RPM(this change was not intended- suspected due to some misinterpretation of our request)
After plant startup we observed the follwing:
- The RV capacity is reduced from earlier 29 t/hr to 28t/hr
-The line pressure for first 3 silos is lower than before by about 0.03K
- The line pressure for 4th silo is almost same as before (0.78K) but slowly keeps on increasing at the rate of 0.01K/1hr and slowly reaches to 0.83K and then shoots up to 0.85K (safety limit at pickup point)
My checking of the system gives me the following results:
a) Vel at pickup point- 23.7m/s
b) Vel at stepping point- 23.5m/s
c) Fr no at pickup point- 18
d) Fr no at stepping point- 16.7
Solid to air- 7.11 (at pickup)
Another observation worth mentioning is that when vent is unrestricted (the vent valve is open to atmophere- againt normal return to feed hopper) the line pressure rise is much faster while transfering to 4th silo.
I would like to seek advise from experts in this field can the RV RPM increase contribute to reduction of cap. and signs of pellet settling in the line?
Looking forward for any insight or similar experienc from esteemed members of this forum.
Thanking you all for your advise and cooperation ■
Re: Pp Pellet Conveying Problem
Dear Tima,
The results of your modifications do not seem to bring the expected improvements.
As you changed 3 main variables (blower, rotary lock and pipe diameter transition), it is not so easy to separate the influence of each of these parameters.
An evaluation needs the following extra data.
-particle size distribution
-material density
-bulk density
-rotary lock volume per revolution
-rotary lock diameter
-rotary lock length
-rotary lock clearance (standard value)
-pipe routing (if available on dwg)
From there it is possible to calculate the original installation.
A second calculation for the modified installation will show the influence of the modifications.
It seems (but I am not sure of it yet), that your rotary valve is the key factor.
You experienced problems at higher pressures.
At higher pressures, the rotary lock leaks more air out of the pneumatic conveying system.
The remaining, lower, air volume through the pipeline might cause the sedimentation,
causing rising pressures.
By increasing the rotary lock rpm you increased this effect, but compensated that (partly ?) by a higher blower rpm.
Let us know the necessary info and we can advise you better.
best regards
teus ■
Teus
PP Pellet Conveying Problem
We are using Dilute phase pneumatic conveying system for conveying PP Pellet from the production unit to storage silo area. There are 6 storage silos each located about 5m apart. The conveying length with about 140m (horizontal) and 22m(vertical). The conveying pipe dia at start is 7inch and increased to 8inch midway. The blower cap. is about 47m3/min at 0.85 Kg/cm2g (K). The capacity of the conveying system is about 30t/hr during peak conveying condition. The line pr. under such condition at the pellet pickup point is about 0.78 K.
Recently due to conveying root blower trouble it was replaced with a identical spare blower. The replaced set was a reconditioned unit.
After changing the blower we faced the following problem:
While conveying to initial 3 silos the line pr. is about 0.73 to 0.78K. (which is quite close to condition while using original blower). However while transfering to last two silo the blower discharge pressure shoots up and blower discharge SV lifts up at 0.91K. During this phenomenon we observed that conveying line between 3rd and 4th silo on silo top was getting packed with pellet.
To troubleshoot this problem we carried out the following:
1) Line packing was suspected due to air leaking from initial silos inlet divertor valve. These lines (4 lines) were blinded to eliminate air leakage. No improvement was observed.
2) All other divertor valves were checked for internal passing: no passing was observed.
3) Since the conveying line does not have flow measurement the new blower efficiency could not be acertained. However conveying air before pellet pickup point was observed to be 5 to 6oC higher than before. There was no change in the motor current drawn.
4) No pellet settling was observed in the vertical segment which is very close to the end point of the conveying system
5) No external leaks were observed from the piping system
6) The pellet settling is taking place about 15 m after the last elbow in the conveying route on the silo top.
By pneumatic conveying principles the settling of particle due to lower flow rate should take place at the pellet pickup point as the air velocity is lowest at that point. No such phenomenon was observed.
We are at deadend of our investigation except of replacing the old blower back which we are not sure will help.
Could the experts in this field guide us for further trouble shooting and possible cause of the problem?
Thanking You All in Advance
Tima ■