Pneumatic Conveying 2

[Graybeard]

Am currently designing a dilute phase pneumatic transfer system to convey a dense powder. Have a 6 foot lift and a 2 foot lift with about 30 feet horizontal between 2 lifts. Question - should "horizontal" pipe (between 2 lifts) be horizontal, sloped up or down from 1st to 2nd lift. Can find plenty info on velocities and such but no web info on which way if any to slope. Since I can't slope back at 30 deg. my feeling is back slop won't do any good - pipe won't drain clear if I loose air. And no good to slope down to 2nd lift, because that just causes me to lift sloped height differential twice. So am tending to run "horizontal" run horizontal. Suggestions?

 

[DSB123]

Graybeard,
I've seen plenty of pneumatic conveying lines which are horizontal. However when you loose air the powder will settle out in the pipe. On restarting the flow could become "slug" flow and the powder "slug" will be accelerated down the system. May not be a problem for you with such short lengths but for long lines it is a definite problem as the "slugs" hit any changes in direction.

 

[Graybeard]

Thanks for your response. I'm pretty certain I don't want to make slope down from 1st to base of 2nd lift as this would tend to aggravate problem you mentioned. But I could make 1st lift only about 5 ft. & run slope up to 2nd lift at about 1 ft in 30, as opposed to a 6 ft 1st lift and a 30 ft horizontal run. Piping engineer want to run horizontal as existing pipe supports can be used. 1st reason for horizontal was it makes fab easier, but that went away when we subd bent pipe for welded 90s. Fab can just as easily make a 2 80 deg bends. Just not sure which way is BEST

 

[Graybeard]

A little more thought/question this topic. Which is BEST - a vertical lift or a long steep slope say 30 to 70 deg that accomplishes the same effective vertical lift?

 

[quark]

I agree with DSB123 about horizontal piping. We have been using this for sugar transfer and never had problems. Slope seems to be better(rather than vertical lift)as far as energy consumption is concerned. Further, you can minimize separation due to turbulence at bends.

Better experts, on the web, are at

http://www.bulk-online.com/Forum/forumdisplay.php?forumid=11

Good luck,

 

[Graybeard]

Thanks Quark.
Apologies for getting knotted up in my own thread but...
I followed up with similar post on forum you recommended. Already got back a reply -
"Stick to truly vertical and horizontal lines of you can...inclines between 20 and 80 degrees to horizontal will require more air to avoid deposition and recirculation. Also, keep number of bends as low as possible. Inclining downwards should be OK for relatively short runs."

 

[quark]

Graybeard,

As I already said, they are better experts. However my idea was totally not baseless and I see nobody suggesting to strictly avoid the slope against the direction of air flow.

Basically when you have to work against a weight on a slant plane, you have to take care about the axial component of its weight only(which is always lesser than total weight). This may or may not hold good for fluidized particles as lot of other parameters come into picture, but I still feel sure that it is more difficult to lift a mass straight upwards.

Regards,

 

[Graybeard]

Again, thanks Quark. The thread created as a result of your suggestion the the bulk-online forum proved invaluable. For those of you interested.

http://www.bulk-online.com/Forum/showthread.php?threadid=4562&goto=newpost