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Dirty water

Dirty water

Dirty water

(OP)
First time I've ever asked for help here- imagine a 'cave' that holds 60,000 gals of dirty water. Cave is divided in two - a 50,000 gal side and 10,000gal side- by a 'weir' extending almost to the ceiling.The fine particles in the water are supposed to settle on the large side and the 11 stage centrifugal pump draws from the smaller side. However, the retention time is not suffiecient for settling, so I end up pumping 'dirty water'. Cleaning the accumulated 'sludge' is almost impossible & its impractical to construct another cave. The pumps operate automatically (ie no attendant)for approx 12 hrs/day. A strainer is impractical because no-one there to clean it constantly.My question- is there anything else I can install on suction line to remove very fine particles? hydroclone etc?  Suction size is 4", length approx 20', pump is 11 stage, 325gpm, 1125' head

RE: Dirty water

How large are the particles and what is the material if you have any idea?  You have over a 2 hour residence time on the 'dirty' side assuming no short cuts in liquid flow through it (which may be a bad assumption, how do you introduce the water and remove it?) but in any event, if the some of the particles are close to the water density, gravity separation might be of little use.  

I realize some material is settling out but depending on the distribution curve, even without bypassing you might have enough material remaining to result in 'dirty' water compared to what you need.

I wouldn't put the hydrocyclone on the suction, they need pressure drop to work and that's going to affect your NPSHA.  You can install automated filters with backwash provisions but again, they are going to need to go on the discharge to avoid suction problems.

RE: Dirty water

(OP)
The water is introduced to the'cave' by drainholes from above it - The main reason for having something on the suction side is preventing premature wear of the pump- when the pump is not running , a check valve closes on the dischrage side  & a couple times the 'standing' water has partially blocked the intake side -I thought hydroclones  (or hydrocyclones) would negatively affect NPSH-I haven't done any partice sizing (yet)   

RE: Dirty water

Some additional questions:  

a)  is the pluggage occuring in the suction pipe? inlet to the suction pipe? or in the pump itself?  (I assume that entrained material pumps OK, it's the idle time that creates the problem?)

b)  what is you pump suction piping arrangement, layout?

RE: Dirty water

ruble3:

My guess is your de-watering a mine.  Would it be better to just buy a slurry pump and deal with the solids on the surface?  Surface retention ponds are low cost to build and maintain, at least by comparison.  I have that type operation here and each slurry pump is 2000 GPM.  Pump life is not a problem.

The big problem for underground separation is what do you do with the fines even if you buy something like a Kenny strainer?  

Good Luck!

RE: Dirty water

(OP)
pablo02- I'll try and describe it best I can- pump sits on a concrete base- pump centre line is 21" above that- there is a 90 degree elbow & concentric reducer on pump inlet- that elbow is connected to a vertical pipe 23" in height- on the vertical is another 90 degree elbow connected to the inlet pipe from the 50,000 gal'reservoir' - the inlet pipe is approx 71' long- there is a screen on the inlet pipe(according to the drawing) & approx 8'10" of water above the pipe ( ie 8'10" of head)- I'm not sure when the reservoir was excavated in the rock , but it was many years ago) I should have mentioned it's in an underground mine   (was going to post it on the mining forum, but thought this forum might draw from wider sources)- I believe the problem occurs after pump sits idle for some time & the fine particles settle in the pump itself& the bottom elbow & inlet- hope you could understand that

RE: Dirty water

(OP)
d23- you're excatly right- its an u/g mine- I hadn't heard of Kenny strainers - we do have retention ponds on surface-the fines do settle there but we have 5 of these 'pump staions u/g and pump changes are not only costly in terms of pump repairs but manpower etc to change them-
I guess its a matter of changing pumps when required & absorbing the cost- every time we send one for repair however, the rebuild shop says we should do something about the 'fines' and thats whats causing the premature wear- I thought there may be a 'simple ' fix out there

RE: Dirty water

ruble3:

To get the TDH you require from slurry pumps you will need several pumps in series.  This is common in your industry.  I have seen GIW, Gorman-Rupp and Gould slurry pumps used.  The big problem with the mines I work with is quartz fines (roadways.)  Slurry pumps will last four to five years pumping slurry.  The only problem is seal water for the pumps.  If you have seal water you can get a long life from the pump.  

One possible thing you may want to consider is two lower volume slurry systems in parallel.  You need to keep fluid moving 24 hours/day to keep fines moving in the pipe line.  If it would help send me your email address and I'll give you a contact name or two that can explain this better than I can.  

I sell multi stage pumps.  In one application like yours they have a two sump system set-up.  On the second sump I have my pumps running pumping only clean water, if there is such a thing in a mine.   On the first sump they have a GIW slurry pump.  Both pumps have one common discharge header/pipe-line out of the mine.  My pumps move most of the liquid and the slurry's pump the trash.

There is option "B".  If you have a low spot behind a seal area, gob pile etc...  you can drill a bore hole into the mine and install a sub-pump system.  350 GPM at your depth is a piece of cake for a sub-pump.  By doing this you will pump water behind a seal, let it run over a couple thousand feet of mined out area to a low spot to be pumped to the surface.  The low velocity flow through a gob or mined out area is a great natural filter putting the fines underground out of your way.  This pump is powered from the surface.  If you have to kill the power underground due to a fan etc.  the water is still being pumped out.  This also prevents the miners from working on the pumping system, that is done by contract people from the surface.

You use the terms "GPM" and "FEET" so I assume you are in the USA.  MSHA has some new rules for sub-pump installed in mines.  I have a copy of their rules.  I can find it and give you the number or a copy.  I have designed a system to meet their specs.    

When using pumps underground the big question is still what will you do with the fines that you separate underground?  At some point you will commit a large amount of time and resources working with them.  If you use some means of pumping them out like a slurry pump they will be in an area (surface) that you can manage them.  

If I can offer info let me know.

davidlsus@yahoo.com

RE: Dirty water

I have experienced a similar problem with a filter press in a mining appliaction. The press was run 12 hours a day continuously. The problems arose on the next shift startup. The pumps were posotive displacement (Wilden). Our suggestion was to try to get the fine settled particles back into suspension before sarting the pump(s). You could try using either a compressed air blast through nozzles in the problem areas or alternativley use a water blast through nozzles the same way. This could easily be automated into the start up sequence of the pumps. Tell me what you think.

RE: Dirty water

(OP)
Thanks for your input guys- we had a look at slurry pumps , but the cost of replacing the 5 multi-stage ones with slurry pumps kind of scared us off- we are looking at ways to control the fines at the source, but again this is labour intensive ( you can tell by my spelling I'm not in the US)- I looked at the drawings of the sumps again and see one problem- the 'clean' side is the larger area & the dirty side is the smaller- this should be the other way around so the fines have a larger retention time ( ie more time to settle)- I was thinking of using a small pump/centrifuge arrangement with the small pump providing the flow to the multistage- still have to handle the sludge tho!- thanks for your input- will be in touch if I need more
help

RE: Dirty water

ruble3

The problem with fines is “labour intensive” as you point out.  If you use sumps in time they fill in causing you to build new sumps or cleanout the existing ones.  Both ways cost manpower.

Pumping fines will cause a high initial cost with slurry pumps or high repair cost on your existing “close-tolerance” pumps.

Some of the other options I’ve seen so far:
1) Use a mined out area as a low velocity natural flow filter.
2) You can drill bore holes ahead of your longwall or miners and pump water some water out before you mine an area.  You could operate a pump in an open bore hole using something like fiberglass pipe and a jet/hydraulic pump in order to pump part of the water before you get to it.  Using fiberglass pipe as a flow string you can leave it in the bore hole and mine through it without damaging you mining equipment.  If you are in a coal mine and real lucky you can produce enough methane to pay for the drilling cost with gas sales, co-gen etc…

I don’t know of any “black-magic fix” for what you are working with.  If you do find a better way please post it.  The rest of us can use the help too!

D23

RE: Dirty water

(OP)
Thanks for the thoughts d23- actually its a hard rock mine- we as far down as 5700' & the mine has been in opertaion for some 50+ years - the water dowsn't have much of a chance to be -pre-filtered before entering the sumps- it basically runs in ditches, then though 'down'boreholes to get to the main pump levels-if I could get it 'up' to the old workings it might do some good, but then I need another whole system- its hard for some people to imagaine what the 'workings ' look like in a 50 yr old mine
- as far as the methane, we do get some but in very small amounts usually, and it being so dangerous its a scary thing to address
I'll work on a few ideas & if I come up with something beneficial to all will certainly post it

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