Slurry pumping in a vertical pipe
Slurry pumping in a vertical pipe
(OP)
I am pumping an iron ore slurry approximately 60' through a vertical pipe. After calculating the limiting settling velocity I have found the actual velocity to be roughly 1 ft/sec slower than the settling velocity, I am trying to avoid dropping pipe size due to a drastic rise in velocity.
My question is, since the particles have a very limited possiblity of settling out due to the upward movement of the water, is the limiting settling velocity a major concern in vertical pipes? I have looked thrugh Warman Slurry Pumping Handbook as well as the Slurry Systems Handbook, however neither cover the issue, they are strictly horizontal piping. Would it be better to simply reduce the pipe size, to speed the actual velocity up above the settling velocity, until the last couple feet at which point I could enlarge it again to slow down the fluid flow.
Any advice is appreciated.
My question is, since the particles have a very limited possiblity of settling out due to the upward movement of the water, is the limiting settling velocity a major concern in vertical pipes? I have looked thrugh Warman Slurry Pumping Handbook as well as the Slurry Systems Handbook, however neither cover the issue, they are strictly horizontal piping. Would it be better to simply reduce the pipe size, to speed the actual velocity up above the settling velocity, until the last couple feet at which point I could enlarge it again to slow down the fluid flow.
Any advice is appreciated.





RE: Slurry pumping in a vertical pipe
In an effort to get better advice from regular slurry pumpers, why not specifically state the exact pipe size (ID), the settling velocity, and the fluid velocity you have now.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Slurry pumping in a vertical pipe
I came up with the following - might be worth a try.
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RE: Slurry pumping in a vertical pipe
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Slurry pumping in a vertical pipe
The specs for the system I have are as follows:
-pipe length (actual) is 60' all of which is vertical discharging into a bottom fed distributor
-Actual slurry velocity is 4.25ft/sec
-Settling velocity is 5.86 ft/sec
-Concentration by volume is 5.94%
-Maximum d50 size is 210 micron
-Flow rate is 93.57 GPM
-Pipe size is 3"
My thinking is that, although the slurry velocity is less than the settling velocity, the vertical flow and low quantity of solids, will keep the particles in suspension, allowing me to use velocities slightly lower than the settling velocity. I don't have a ton of experience in this area so am hoping others might be able to offer a suggestion. If I downsize to a 2" pipe, my velocities jump to 9.56 ft/sec actual and 4.79ft/sec settling.
RE: Slurry pumping in a vertical pipe
RE: Slurry pumping in a vertical pipe
RE: Slurry pumping in a vertical pipe
I'm sorry, I have difficulty wrapping my head around what physically happens to a "rocks in water"-type, fast-settling slurry in a vertical pipe, flowing at a velocity less than the settling velocity for the largest diameter particles. Does it function as a particle size classifier, ultimately leading to plugging? Or do the larger particles merely get entrained in slugs out the pipe? Or does something else happen? If you find out from credible sources, I'd appreciate a description!
RE: Slurry pumping in a vertical pipe
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Slurry pumping in a vertical pipe
RE: Slurry pumping in a vertical pipe
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Slurry pumping in a vertical pipe
Settling Velocity = FL * square root of (2gD((SGs-SGL)/SGL))
where FL is obtained from Durand's Modified Limiting Settling Velocity Parameter, g is gravitational constant of 32.2, D is pipe diameter in feet, SGs is specific gravity of the solids, and SGL is Specific grvaity of the carrying liquid.
In our case SGs = 3.27 and SGL is water and therefore = 1
From what I see in the book and experience with the iron ore and waste material, I suspect the settling velocity is pretty close to accurate (of course in saying that, it wouldn't be the first time I was completely wrong either). I have since increased the rubber lining thickness slightly in the piping and have made the velocities better balance out so that I am above limiting settling velocities in all aspects of the pipng. I am still curious about the vertical flow though if anyone has any information, advice, or comments. Thank-you for all the advice and comments so far though, it has definately been a help.
RE: Slurry pumping in a vertical pipe
Take a few of your ore particles to the lab and watch them settle in a tall measuring cylinder. There is nothing to beat seeing it with your own eyes. This will give you an appreciation of just how fast 5.86 ft/s really is.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Slurry pumping in a vertical pipe
Out of curiosity, how are you calculating the sphere size? I am thinking that you are actually calculating bouyancy effect rather than slurry settling velocity, two differant effects. In the case of terminal velocity of spherical particles (where you calculate the rate of fall in a vertical chanber with no liquid velocity) the determination of a 2" diameter sphere would be accurate for a velocity of 5+ft/sec. However for limiting settling velocity, the speed of the slurry is being calculted to keep the spheres in suspension, essentially how fast the carrying liquid is moving over the suspended particles in order to create a bouyancy effect. As the particles are moving, as well as the carrying liquid, the speeds are relatively high in order to get a velocity differential between the two that is high enough to prevent the particles from settling (similar to an aircraft wing travelling through wind that is blowing in the same direction as the aircraft is flying)
RE: Slurry pumping in a vertical pipe
Thank-you for all your help, this has been greatly appreciated.
RE: Slurry pumping in a vertical pipe
Yes, I am calculating the terminal velocity. In my opinion it is the same thing because all you are interested in is the relative velocity between the particle and the fluid. How the fluid is moving is irrelevant IMO. The only difference between terminal velocity calculations and settling velocity in a pipe is that the terminal velocity calc looks at a single particle, while in a pipe system you are interested in hindered settling. In hindered settling there are so many particles that as they settle they cause a significant upflow of fluid which hinders the particles. Hindered settling rates are therefore lower than calculated terminal velocities and I would expect my TV calculations to be conservative.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Slurry pumping in a vertical pipe
It seems you have your answers, I have just noticed your post. One comment in an earlier post in relation to the low solids content to keep the slurry in suspension. This seems to be correct however ther are some exceptions. A noteable exception was with a kaolin clay that remained in suspension above 25% solids. Below 20% solids we had trouble with the clay settling out. This limit was established with settling tests at different percent solids. The application was to solve an erosion problem, we had been dosing small amounts of clay from a recirculation pipe at high velocity to keep the clay in suspension. By keeping the solids high we were able to reduce the velocity and the erosion problem. Relevence here, check the behaviour of the slurry across a range of solids content, it may behave counter to your assumptions.
Mark Hutton
RE: Slurry pumping in a vertical pipe
The main pumping system pumps the slurry at 40% solids by weight, then we seperate out the iron (approx 48%) and recirculate 25% of the waste material through a separate line, so the recirculation is a relatively low concentration of solids. It'll be interesting to see how the two differant concentrations react.
RE: Slurry pumping in a vertical pipe
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Slurry pumping in a vertical pipe
RE: Slurry pumping in a vertical pipe
These engineers all work for Geogia Iron Works Pump Company, now part of KSB. They also run courses on Slurry transport. The book covers vertical pipelining.
Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng
www.waterhammer.bigblog.com.au
RE: Slurry pumping in a vertical pipe