Elbows-But Not For Macaroni:^)
Greetings,
The one thing you did not spell out is whether it is a pnuematic
or gravity delivery system into a vessel such as is done at iron
ore and coal docks with elevated hoppers and drop chutes.
Any elbow or incline no matter the radii will consume huge
amounts of electrical and pnuematic energy.
Most pnuematic delivery systems are of a small diameter-6 inch or
less of piping for blowing cement, animal feed, salt, sand in dilute
phase only. As a rule. gravity and energy and gas law go hand in
hand with the design of any pnuematic system to determine
adequate delivery rates.
Gravity is your big problem period!!!!!!!!!!!!!!!!!!!!!!!!! and not
your friend!!!!!!!!! a diameter like that will allow the cement to
linger and fall, and not knowing everything for this algebra
problem such as length of delivery system, piping size for the
entire system from A to B the type and size of elelectrical power
are but a few of the pieces to this algebra problem.
Assuming anything on my part will make an ass out of me but a
radii bend like that with a dilute phase pnuematic delivery system
will require huge horsepower in low pressure pnuematic energy
and a new blower unless you are willing to tolerate a slower
delivery rate and plugging than what you had with alumina.
Anyone can sell you a elbow pipe casting with schedule 120
grade steel but with a 29 inch radius BUUUUUUUUUUUT
we need to know if it is to be welded in place or bolted in place
with gaskets etc.
Their are a lot of pipe foundries world wide but you need an
expert like my friend Teus to give you credible advice or you
could consult the manufacturer that installed you system
originally if they are still a going concern.
With regard to the (elephant in the refridgerator that leaves his
foot prints in the coconut creme pie)- being your recieving vessel
you may be money ahead by installing a new elbow with a
smaller diameter piping system and reducing the piping size as
the better option, BUT since we have no knowledge of your
receiving and delivery system I/we cannot help much :^(0
A smaller pipe and delivery piping will save you headaches in
the long run in my opinion simply beacuse you are dealing with
materials(cement) that weight 197 pounds per cubic foot versus
alumina which weighs 60 pounds per cubic foot so here in lies the
problem as your recieving/down stream system is ment to handle
alumina to begin with!!!!!!!!!! -hence the elephant with his toes
in the coconut creme pie and so forth.
I look forward to your reply
lzaharis ■
Re: Type Of Elbow For Conveying Cement
Yes, it is a pneumatic system with elbows being flanged and gaskets. The original design calls for Hammertek smart elbows, but the radius is too long to fit in the alotted space. ■
Re: Type Of Elbow For Conveying Cement
Originally posted by webivs
Yes, it is a pneumatic system with elbows being flanged and gaskets. The original design calls for Hammertek smart elbows, but the radius is too long to fit in the alotted space.
Finding a reputable pnuematics reseller is number 1 to graph the flow rates, estimate blower air demand, relef valve values, friction loss before you do anything like I said before. ■
Re: Type Of Elbow For Conveying Cement
With all the usual provisos, it depends on the actual system, the conveying velocity, lean phase / dense phase, etc. but:
As a rule of thumb, I would work on the pressure drop across short radius bends (3 times diameter) being approx 20% greater than a long radius bend and the pressure drop across a "Blind Tee" approx 100% greater than long radius. Your very short radius would be somewhere in between.
This assumes the system performs reasonably well with the long radius bend though, if you are getting pressure spikes / partial blockages or whatever then putting a very short radius bend in it may make any problems worse.
If your system has plenty of capacity in hand, if you are only changing one or two bends then you will probably be OK. If you are changing all the bends on a complex system you may have problems.
As was previously indicated though, changing materials (particularly if the differences are as great as suggested) is likely to have more of an effect on your system performance than changing an odd bend or two. ■
Re: Type Of Elbow For Conveying Cement
Dear Mr Webvis,
The use of a standard mild steel elbow R=1.5D is no problem at all for pneumatic cement conveying.
20 inches is a normal pipe size in pneumatic conveying cement, especially in vacuum systems.
I have an example of the same size of elbow, which today lasts already for at least 2.000.000 tons of cement in a vacuum system.
The bend is positioned at the lower end of a downstream pipe section to the horizontal.
(Eventually this elbow will wear out at the outer side, but then it will be repaired with an outer box, to cover the hole. For another 2.000.000 tons of cement)
The effect of an elbow is yhat the product velocity is reduced to a low(er) value, but certainly not to zero (that would be a blockage).
The difference of reducing the velocity to 20% or 30% of the original value is not so important anymore (energy wise)
Very important though is the entrance velocity.
To know this velocity requires a complete pneumatic conveying calculation.
Is your system vacuum or pressure ?
What is the capacity ?
How is the pipe line geometry ?
Is the bend located at the beginning of the pipe line or at the end ?
Have a nice day
teus ■
Teus
Good Advice
Thanks for your response. I will pass your comments along to the designers of the system. ■
Type of elbow for conveying cement
We are remodeling an alumina import terminal to receive cement. We have an application that requires transporting cement into a receiving vessel. The radius needs to be short to relieve the cost of refurbishing the vessel.
Is there an elbow that can withstand the wear and fit our needs.
The pipe dia. is 20" and the required radius we seek is 29" (on the centerline). ■