Sand Etc.
Originally Posted by justinjs2004
We are using tanker to transfer sand to a silo of height 22-25m with horizontal length apprixomately 2m, the size of the sand is rather fine < 1mm.
The compressor used at the tanker is rated at 2 bar. Can this sand be conveyed at dense phase? Because based on estimation, the conveying air velocity (from 3-4 m3/min air supply) is below the saltation velocity. Therefore, i assuming it cannot be conveyed at lean phase.
Can you advise?
Thanks.
JS
A lot of missing items
The air flow and 2 bar pressure you have mentioned is of no use with out further information.
what are the compressor specs?
what type of air compressor or blower is it.?
What makes you think you cannot convey the sand at lean phase?
We need to know the pressure gradients involved.
What size is the discharge and silo piping?
Has the piping ever been cleaned with a a chimney brush or a pipeline pig using a rope to pull it from the roof of the silo or on the ground level with the pig fed from the roof. ■
Can Sand Be Conveyed At Dense Phase
Hi,
Thanks for your reply.
The compressor is centrifugal and running air supply is 3 m3/min while pipe diameter is 100mm.
Based on the above, i estimated that the air supply velocity is below the saltation velocity but above the terminal velocity.
Does this mean horizontally it is conveyed in dense/bed flow but in fluidized/lean phase vertically?
Can you advise?
The pipe wasn't cleaned before.
Thanks.
JS ■
Sand Conveying
Hello,
we have helped a customer build a conveying system for sand and gravel. It has always been in dilute phase though as sand normally has quite a bit of moisture (at ever changing values) in it. Is it possible yes. At what rate? As Izaharis mentioned you left quite a bit of info out.
Note: Sand has a nasty habit to cake and build up right around where it enters the conveying pipe. Good luck with it and let us know how you make out.
Ralf ■
Re: Can Sand Be Conveyed At Dense Phase
Yes sand can be conveyed is true dense phase a 3-4 m/s velocities. But will require 3-4 barg conveying pressure. Since you are in a tanker off loading situation and restricted to 2 barg you cannot have true dense phase conveying. You can off load with 2 barg compressor with 900 m3/hr air flow. It will be very aggressive so ceramic bends are required. No chance with 180 m3/hr compressor for tanker unloading. ■
Can-Sand-Be-Conveyed-At-Dense-Phase
Hi All,
In fact, during actual run, the sand was managed to be conveyed at much higher height (20-30m) and completed 12 ton in around 1 hr.
Can advise?
Thanks.
JS ■
Re: Can Sand Be Conveyed At Dense Phase
Hi Teus,
Can you advise me on this? I had completed a pressure drop calculation based on the actual loading rate and the air supply rate (3 m3/min) @ 2 bar or less, the pressure drop was estimated to be around 0.4-0.6 bar for dense phase and 0.4-0.5 bar for lean phase.
I did two calculations as i wasn't sure which phase it was operating at.
Can you advise me?
(i) The actual phase of the conveying?
(ii) The pressure drop at such condition?
(iii) The required air supply rate?
Thank you.
JS ■
Re: Can Sand Be Conveyed At Dense Phase
Dear JS,
Up till now. you have left out the necessary information to evaluate your questions.
Particle size distribution
Particle density
bulk density
The air supply is, according to your information, a centrifugal fan of 3 m3/min
The mentioned pressures of 0.4 – 0.6 bar seem far too high for a normal centrifugal fan, or is it a real turbo compressor.
The mentioned 3 m3/min creates an atmospheric air velocity of approx 6.3 m/sec, which seems to be very low. (lower than the suspension velocity of a 0.75 mm sand grain)
As you have run an actual operation at 12 tons/hr, did you not measure the pressure?
And when actually running the 12 tons/hr, what was the compressor performance?
Have a nice day
Teus ■
Teus
Re: Can Sand Be Conveyed At Dense Phase
Hi Teus,
Thanks alot for your reply.
For your information, the mean particle size is around 0.25mm.
We do not check the particle density and bulk density. Can i know how would these 2 properties affect the conveying process?
It should be a compressor system which its capacity is at 6m3/min and 2 bar when running at 1000rpm.
During actual running of pumping 12 ton/hr, the RPM is 500 RPM, pressure is around 2 bar. Slowly as conveying process progresses, the pressure drops ultimately to 0 bar gage pressure.
Can i ask, is this conveying in dense or lean phase?
I was estimating the saltation velocity > 15 m/s, much higher than the supply air velocity. For horizontal conveying of 2m.
While the terminal velocity is 1-2 m/s, which indicates that air supply velocity is sufficient?
Teus, can you give me a favor to do a simple calculation on that to verify?
I was using spreadsheet from Pneu for dense phase and some correlations for lean phase calculation.
Thanks alot.
JS ■
Re: Can Sand Be Conveyed At Dense Phase
Teus
Re: Can Sand Be Conveyed At Dense Phase
Hi All,
Is there any way i can better understand the calculation method because i am rather blur based on the calculation result given.
I wish to learn on manual calculation. Would this be feasible? Please advise how to interpret the data from your calculation sheets.
(i) Total horizontal pressure drop
(ii) Total Vertical pressure drop
(iii) Total pressure drop due to bends
(iv) Phase of conveying
(iv) Total volumetric flow required
Thank you a lot.
JS ■
Re: Can Sand Be Conveyed At Dense Phase
Dear JS,
All the information that you require is available on the screen “Calculation Table Pressure Conveying”.
Part number 6 is the vertical section.
In the column “”Pressure”, the pressure at the end of that section is given.
The required air displacement of the compressor is given at the Input screen under the section “Gas pump”.
Whether this is dense or dilute phase, I did not check.
The meaning of dense or dilute phase is discussed before in this forum and defined as left or right from the lowest point in the Zenz diagram. (do a search in this forum on Zenz)
To figure out whether this installation is dense or dilte, I have to calculate for various airflows and derive the Zenz diagram for this installation.
How the program works, look at:
Pneumatic conveying, Performance and Calculations:
https://news.bulk-online.com/?p=65
Dense phase- or dilute phase pneumatic conveying:
https://news.bulk-online.com/?p=238
Pneumatic conveying, turbo- or positive displacement air mover:
https://news.bulk-online.com/?p=309
Energy consumption per ton of a pneumatic conveying system:
https://news.bulk-online.com/?p=331
Pneumatic conveying, an unexpected relationship.
https://news.bulk-online.com/?p=445
Pneumatic unloaders: Problems to avoid
https://news.bulk-online.com/?p=74
Influence of electro static charge on pneumatic conveying.
https://news.bulk-online.com/?author=15
Bacterial heating of cereals and meals.
https://news.bulk-online.com/?p=216
Have a nice day
Teus ■
Teus
Re: Can Sand Be Conveyed At Dense Phase
Dear Teus,
Based on my understanding, the air pressure supplied by the compressor is 2 bar. The total mass flow loading rate is 12 ton/hr (instead of 9.1 ton/hr).
(i) From the "Calculation Table Pressure Conveying", is the total pressure drop = 0.6 bar?
(ii) As shown in your calculation, the supply pressure is 0.6 bar instead. Is it?
Sincerely wish to learn more on this calculation, can you advise? Like for Lenz Diagram. Thank you.
JS ■
Re: Can Sand Be Conveyed At Dense Phase
Dear JS,
The Zenz diagram is described in:
Dense phase- or dilute phase pneumatic conveying:
https://news.bulk-online.com/?p=238
A recalculation of your system for a compressor volume of 3 m3/min (0.05 m3/sec) failed, as the air velocities become too low and the pipeline chokes.
Operating at such low velocities, it is very important to know the suspension velocity of the particles.
Therefore, at least the particle density and the particle size must be known.
In addition, the description of the compressor is rather vague.
You mentioned a
The compressor is centrifugal and running air supply is 3 m3/min
.
Then you mentioned 2 bar and 6m3/min at 1000 rpm.
A 1000 rpm is very low for a screw compressor (normally 4000 – 6000 rpm)
Running such a screw compressor at such a low rpm results in low volumetric efficiencies and very high outlet temperatures.
For better calculations, we need better information, s.a. exact pipe routing, material properties and accurate data of the compressor.
In addition, the operational data(pressure and capacity) must be more precise in time.
Without this information, the calculations will only generate confusion.
Have a nice day
Teus ■
Teus
Re: Can Sand Be Conveyed At Dense Phase
Hi Teus,
Attached is the type of compressor used. This is the new model. The one we using now is older which not in the pdf (its specs are: 6m3/min at 1000 RPM).
During actual running, the compressor runs with only around 500 RPM and the inlet air pressure is 2 bar (max).
The exact routing is:
(i) From flexible hose of around 1m to horizontal pipe of 1m,
(ii) Follows by a 90 deg. bend from horizontal to vertical pipe
(iii) Vertical pipe height is around 25m-27m
(iv) Second 90 deg. bend to another short horizontal pipe
Diameter of pipe: 100mm
Particle density: Typical density of dried sand with particle distribution as follows
Particle Size % passing through
0.02 3.51
0.03 4.11
0.09 15.98
0.24 53.13
0.37 86.70
0.51 97.93
1.00 100.00
During actual trial, 12 ton of sand was completed pumped in 1 hr time.
Can you advise further? Please let me know if you require more information.
Thanks.
JS
Attachments
■
Re: Can Sand Be Conveyed At Dense Phase
Dear JS,
I processed your info as follows:
-modeling the installation
-set the airflow at 0.05 (3 m3/min at 500 rpm)
-defined the average particle size at 300 micron (suspension velocity = 3.85 m/sec)
-calculated the Solid Loss Factor for 12 tons/hr and 2 bar pressure.
The result was that the SLF must be negative (- 3.6E-13), which is a not existing condition.
It means that the required pressure drop for keeping the particles in suspension + acceleration + gas + elevation is more than the 2 bar available.
The program calculates then a negative SLF, which generates a negative pressure drop for collision losses.
This is caused by a too low velocity (3 m/sec – 7.5 m/sec), also causing sedimentation.
Experience learns that these velocities are even too low for cement .
Lowering the particle size to 30 micron, resulted in a positive SLF.
This indicates that the particle properties must be defined better.
-particle size distribution (already given)
-particle density (now used 2400 kg/m3)
-bulk density (now used 610 kg/m3)
-suspension velocity
Also check the airflow again, because at 1000 rpm (0.1 m3/sec), the figures become more realistic.
Have a nice day
Teus ■
Teus
Re: Can Sand Be Conveyed At Dense Phase
Hi Teus,
That is what actually confusing us. Because in actual run, we managed to pump the sand at the rate stated.
Is this a lean or dense phase conveying? Based on estimation using Pneu spreadsheet, the estimated pressure drop is only 0.4-0.7bar. This is well below 2bar.
This determination seems to be rather complicated for a begineer like me in pneumatic conveying. Hope you can guide me further.
Thanks.
JS ■
Re: Can Sand Be Conveyed At Dense Phase
Dear JS,
I now understand that you have a real installation and 2 calculations (Pneu spreadsheet and my calculation) that do not match.
When theory and reality do not match then the theory is wrong and the cause of the mismatch has to be investigated.
That means that all the influencing parameters have to be determined, step by step and compared with the input of the programs.
Run the installation at different pressures and airflows and measure the pneumatic conveying conditions and observe closely what happens.
In addition, measure the material conveying properties as required by the calculation algorithms.
Run the computer program for the different conditions and search for calculation adaptations and identify why there is no match between calculations and practice.
These kind of events are an opportunity to understand pneumatic conveying better than before.
When I calculate your installation for cement, (50 micron), then a capacity at 2.0 bar is calculated of 11 tons/hr, with considerable sedimentation in the pipeline.
It is hard to believe that this installation would perform better with coarser sand.
You have an interesting case.
Success
Teus ■
Teus
Re: Can Sand Be Conveyed At Dense Phase
Hi Teus,
I agree with you on that. But in Pneu spreadsheet, input of material properties is not required. Can I know why is it so?
Meantime, I will try to double verify the actual air flow capacity at that RPM mentioned. Thank you.
JS ■
Re: Can Sand Be Conveyed At Dense Phase
Hi Teus,
Can i have your personal email so that I can send you more detail information which maybe confidential for further discussion on this? Thank you.
JS ■
Re: Can Sand Be Conveyed At Dense Phase
Dear JS,
in Pneu spreadsheet, input of material properties is not required
This is best asked from the author of that program.
I assume that at least the pickup velocity and a product friction coefficient must be given.
These 2 figures are then related to the considered material.
It means that, f.i. when you change the particle size of the same material, you have to adapt these 2 parameters.
For getting in direct contact, you can use the private message option of the forum.
Have a nice day
Teus ■
Teus
Re: Can Sand Be Conveyed At Dense Phase
Teus,
I had verify with compressor supplier. They supply compressor affixed to trailer with typical air presure of 2-2.5 bar and air flow of 6-8 m3/min.
Based on configuration of the piping, it is more like a blow tank for dense phase application as air is continuously fed into the tank to pressurize the tank while having another air inlet pipe at the discharge point of the sand.
What is the best method to estimate the convey-ability of this case? Can you advise me further?
Thanks.
JS ■
Re: Can Sand Be Conveyed At Dense Phase
Dear JS,
(from 3-4 m3/min air supply)
centrifugal and running air supply is 3 m3/min
Appeared to be a wing compressor for 6-8 m3/min at 2 bar
air supply rate (3 m3/min) @ 2 bar or less
pressure drop was estimated to be around 0.4-0.6 bar for dense phase and 0.4-0.5 bar for lean phase
If calculations cannot be matched with the practice, the calculation must be reviewed.
compressor system which its capacity is at 6m3/min and 2 bar when running at 1000rpm.
During actual running of pumping 12 ton/hr, the RPM is 500 RPM, pressure is around 2 bar
Calculating the system with 3m3/min still results in a choked pipeline.
Can you confirm that the compressor was running at 500 rpm during the test?
While the terminal velocity is 1-2 m/s, which indicates that air supply velocity is sufficient?
This velocity in a 100 mm pipe would mean an airflow of 0.94 m3/min, which is far below 3 m3/min as claimed.
I calculated your system for a compressor of 6 m3/min (0.1 m3/sec) at 2 bar and derived the required Solid Loss Factor for 12 tons/hr at 2 bar.
Then I increased the airflow in the calculation and found lower pressures. (Zenz diagram)
This indicates that the conveying is dense phase.
However, I still doubt the 500 rpm observation.
Have a nice day
Teus
Attachments
■
Teus
Can Sand be Conveyed at Dense Phase
Hi All,
We are using tanker to transfer sand to a silo of height 22-25m with horizontal length apprixomately 2m, the size of the sand is rather fine < 1mm.
The compressor used at the tanker is rated at 2 bar. Can this sand be conveyed at dense phase? Because based on estimation, the conveying air velocity (from 3-4 m3/min air supply) is below the saltation velocity. Therefore, i assuming it cannot be conveyed at lean phase.
Can you advise?
Thanks.
JS ■