Incline Pipe
If the pipe is incline then you get bed material rolling back. this will really reduce transfer rates and increase pressure from accelerating . the mechanics at our plant strung a sandbasting hose from a dust collector dense phase pot to the top of a silo at ~60 deg at 60psi. We changed to vertical pipe and dropped the pressure to ~15psi and reduce cycles. ■
Re: Inclined Lines In Pneumatic Conveying
Dear serdman,
This issue is an ongoing debate in pneumatic conveying.
Your explanation is the most usual one.
Some have experimental prove, however, mostly without the full information, regarding air velocities, particle suspension velocity, flow pattern etc.
I have witnessed cement conveying installations slope lengths of pipe, which worked fine. although with air wall velocities well above the local suspension velocity.
If the pipe is incline then you get bed material rolling back
If the material is forming a bed in a slope pipe, then this must also occur in a horizontal section.
It must then be concluded that the air velocity is not sufficient to keep the material fully in suspension.
Keeping this in mind, then the situation in a vertical pipe section must be worse than in a slope section (at the same air velocities).
Another issue is that, in order to keep particles in suspension in a horizontal pipe, the required air velocity is higher than in a vertical pipe, because the gravity is in a horizontal pipe perpendicular to the driving air force.
We changed to vertical pipe and dropped the pressure to ~15psi and reduce cycles
What you would expect is, an increasing capacity after the modification rather than a pressure reduction and considering the reduced number of cycles, you lowered the capacity (number of cycles * pressure pot material content)
Have a nice day
Teus ■
Teus
Re: Inclined Lines In Pneumatic Conveying
Teus,
Thanks for your response to my post, I have read many of yours and I am aware you have a deep understanding of handling bulk materials.
My goal when modifing the system was to reduce the pressure becuase the pot was not a certified pressure vessel, increasing capacity of the system was not required as it ran only to empty the dust collector hopper.
Having the line incline I think was a problem but I would guess that replaceing the hose with the pipe made the biggest difference for the hose was hung with a few minor deflections where holes would form.
The pot does not have a level sensor in it but is on a timer and I don't believe pot ever fully emptied before I changed the system.
This system was the kind of thing you get when a mechanic tries to copy a system without knowing the critical point of design.
As for your comments about the sliding material bed I have the same mindset as you regarding the flow at different angles. I think the part that makes the difference is direction of gravity and the effect that a bed has on the boundary layer. In my mind it seems that the material in the bed that is not getting stirred up and reintroduced into the motive zone, be it air or material stream, is only affected by gravity and moves backwards untill accelerated forward again. Of course we don't use clear pipe so these are just presumptions.
Another neat point about that system was that when the conveying air was shut off while there was material in the line the material would fall back so fast that it would run back through the air balence piping and wear through the elbows!
But I do know that you can have a "sluggy" bed in a horizontal line an still go vertical as the saltation velocity and terminal velocity are different. If you get a chance it can be fun to play with a pneumatic tanker unloading coarse sand! ■
Re: Inclined Lines In Pneumatic Conveying
Dear serdman,
But I do know that you can have a "sluggy" bed in a horizontal line and still go vertical as the saltation velocity and terminal velocity are different.
You are right, however as you already say, these phenomena are velocity related and influence the existence of the “inclined pipe problem”.
A pneumatic conveying calculation, based on the data of the installation (compressor, material particle size, pipe geometry(original-new), etc.) can show the conveying regime.
Have a nice day
Teus ■
Teus
Inclined Lines in Pneumatic Conveying
On some papers, they tell us avoid "inclind lines" in pneumatic conveying. But WHY? ■