Hi Barbara
the baby poo pumping project was stillborn owing to the high cost of the
high compression thickener required to produce the solids density.
10% solids is not a big ask; I routinely pump 30% (by weight, solids
true SG about 2.7, D50 around 60 micron). The hardest bit is regulating
the density.
A couple of years back we reprocessed the tails stored in a dam. For
reclaim, we used a proprietary dredging pump unit mounted on a 20T
excavator, mounted on a pontoon. The pumping unit consisted of a
hydraulically driven centrifugal pump with two hydraulically driven
agitators alondsige to stir up the solids. The pumping unit was
dunked/rammed into the pond bottom, the agis stirred up the bottom and
the pump sucked up the slurry and sent it to the processing plant about
1200m away, with the help of an in-line booster pump. It worked, but the
pumping unit (with the exception of the agis which were magic) was
unreliable, and was modified almost beyond recognition by the time we
were finished with it. However the duty was very severe, so problems had
to be expected.
It you can remove the solids using eductors, then either you have only a partially settling slurry or you are using something else to resuspend the solids. I would be looking at a vertical axis sump type centrifugal slurry pump as made by Weir/Warman, GIW etc etc, with the pump bowl in the drink. If density control is an issue, you will need to arrange something. You could look at either raising the pump, or having liquid feed/recycle to the inlet. We use a few peristaltic pumps, and they are quite good on fine slurries. However coarse particles tend to cut out the tube, and ours (I forget the make) are pigs to retube.
The "Bingham" bit should cause no real problems at 10% provided you can quantify the shear stress.
Cheers
steve
-----Original Message-----
From: James, Barbara [mailto:bjames@mitsuibabcock.com]
Sent: Friday, December 24, 2004 12:22 AM
To: 'PipingDesign@yahoogroups.com'
Subject: [PipingDesign] Pumping Bingham Plastics
Steve (+ Gents + the other 1)
I was wondering how you got on with the baby poo pumping problem that you posted to the list in August? What sort of pump did you end up going along with? Is it working well?
I have a similar sort of problem; pumping contaminated sludge (10% solids in water) over 250m. The sludge has formed at the bottom of a large pond which is to be completely emptied. I don't have details of density, viscosity etc.
Most important consideration here is total reliability of the pump as it won't be possible to change out parts that have been in contact with the process fluid.
The sludge could contain solids up to 6mm diamter, so the pump will have to be something very robust. I was thinking of a positive displacement progressive cavity pump or possibly an eductor.
The client already has eductors in use, the lack of moving parts is a very attractive feature and the client does like to stick with familiar technology. But, I am not sure that there will be sufficient steam available and the client is not keen to use large quantities of demin water due to the issue of decontaminating it after it has been in contact with the sludge.
The positive displacement progressive cavity pump is widely used in the sewage industry and the manufacturer's claim that they are tolerant of entrained solids. They certainly look simple enough and don't require an additional motive fluid.
The project is in very early stage and I have been asked to come up with a high level document to outline the options. Detail design of pumps will be done by a real pumping expert.
Can anyone suggest alternative pumps types that are known to work well for this sort of duty?
I know to keep the pipe route as straight as possible, avoid low points and use large radius bends but does anyone have other useful tips for pumpimg sludges and slurries?
Barbara
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