Pumping Underflow ffrom an FL Smidth Milk of Lime Clarifier 1

[flyerfan56]

Hello all:

We are in the process of constructing a milk of lime treatment plant to process pregnant gold leaching solution prior to its entrance into a CIC plant. We are located in Eastern Nevada.

I am having difficulty in getting a sufficient underflow pump designed and quoted.

Pertinent Information Is As Follows:

Clarifier Diameter - 115 ft
Clarifier Rated Throughput - 15,000 GPM
Expected Solids Concentration by weight in Underflow - circa 28%
Expected Solids Concentration by volume in Underflow - circa 17%
Desired Underflow Pump Rated Flowrate: 50GPM

Assumptions by Pump Engineering Vendor for Underflow Pump:
d85 value: 44 micron
d50 value: unknown at this time - this is what our design/contruct engineering firm is questioning, and viscosity
NOTE: Initial design by our engineering firm looked at viscosities of minimum 50cP
HP: 15
Specific Gravity of Slurry: 1.2
Specific Gravity of Solids: 2.3-2.7
Design Flowrate: 50 GPM
Speed at Design Flowrate: 2766 RPM
TDH: 115 ft
NPSH: 8.5 ft
Max/Min Ambient Temps: 104F, -32F

We are going to pump our underflow approximately 1800 ft to a disposal facility. Total rise from the clarifier to the disposal point is about 80 ft. The rest of TDH is attributed to friction losses. There has been much debate about viscosity of the slurry.


The quoted pump is:

Weir/Warman: 1.5/1 BAH Series A "AH" Metal
Casing Pressure Rating: 300 psi (20 bar)
Impeller: 6 in
Discharge Diamete: 1 in Suction Diameter: 1.5 in
Discharge Piping to Disposal Site will be 2.5 in, HDPE (do we need to account for the HDPE welds for headloss, if
this piping will be in sections)

I am unable so far to confirm a d50 value for expected slurry in the underflow of our new clarifier. I am trying to find a suitable like system already in service at our facility to sample and compare slurry data.

We will, of course, have to flush this system after each use; our expectation is that we will operate this pump every other day or so.

So, bottom line, I need to know the following:

(1) For a milk of lime clarifier, what would be a good number for recommended flow velocity to prevent settling? I have heard numbers ranging anywhere from 2-4 FPS to 5-7 FPS. Is a 3 in line adequate?
(2) Can anyone give me some idea of what range of d50 values we might expect to see; I have no data to go on at this point
(3) Does the quoted pump appear to be sufficient for the application?

I have done the calcs for velocity, etc., but am stumped on a d50 value.

Thanks,

Bob

 

[Artisi]

All I can offer at this stage is to ensure that the selection has been undertaken by Warman themselves and not a sales guy from an intermediate supplier.
Warman have many years of experience and a wealth of data to use in pump selection for slurry pumping, this has been collected and analysed from pump applications world-wide and they can be relied on to make accurate assumptions and selections of equipment. However, you must give accurate slurry data and you are wise to seek out like applications to confirm the likely slurry make-up.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[flyerfan56]

Thanks very much for your input. Your suggestion was my next step. If anyone else can offer some experience, I'd appreciate it.

Thanks much,

Bob

 

[Artisi]

Just re-reading your post, a couple of comments - not having access to the Warman pumps curves I can not advise in detail but, I would query the pump speed of 2766rpm and would also query the metal selection in lieu of elastomer - unless the metal selection is very one of the extremely hard irons now available which maybe Ok.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[moltenmetal]

I right away thought "Discflo pump"- and a quick Google search of "lime slurry pumping" turned up this "case study":

http://www.discflo.com/images/stories/pdf/casestudies/DelrayBeach.pdf

My experience with clarifier/thickener underflows is at sizes and flowrates much lower than this, where centrifugals are not an option and AODDs or peristaltic pumps are used. Warman may have a magical centrifugal for you which will survive 28% solids long term, but I suspect you'll have some maintenance to do well beyond flushing it out. I'm with Artsi- get the quote direct from Warman to ensure it has been competently selected.

The Discflo pump has some native advantages for slurry service which may benefit you. Worth a look, at least.

 

[cvg]

I wouldn't be too concerned with welded joint minor losses but do add check valve losses
I would think that velocity should be higher than 2 - 4 fps, are you trying to save energy, wear and tear or trying to avoid plugging the pipe? 7 fps would be more normal.

http://www.pumpfundamentals.com/slurry/Warman_slurry_pumping.pdf

FIGURE A3-1 TYPICAL Hf CURVE FOR CATEGORY ‘A’ SLURRIES
this curve indicates velocity of about 7 fps or higher to avoid settling

 

[DubMac]

The rule of thumb number used for vertical pumps to keep solids (usually sand) from dropping out or settling while being pumped up the discharge column is minimum 5' per second; I was told to always try to keep it above 7fps to be safe. I don't know how your solids compare to sand, but probably not worse. Of course the faster you move the fluid, the greater the wear, so it is a balance. Going over 10fps you really have friction concerns also.

Not having looked at pump curve and hydraulics, I wouldn't want to say about applicability for your particular service, but I have always had a great deal of respect for Warman. They usually have fairly knowledgeable reps/distributors and most likely have run your application through the Weir Minerals Group so I would trust it (never hurts to make sure it was run through the factory's Application Engineering Group though).

 

[flyerfan56]

Thanks to all for your responses. It is most appreciated. I have had some time since I first posted to do the following:
(1) Contact our Weir/Warman distributor to let him know about our concerns with the quoted unit. He is a very experienced and was most accomodating. I asked for a contact at the Warman main offices (Madison, WI which he was more than glad to do. I spoke to a mechanical design engineer there who has been working with our distributor on this issue. He had already been talking to our distributor at length.
(2) I am awaiting a new proposal which I should have by Monday or Tuesday of next week. (Jan 28-29)- after our discussions with Weir/Warman and our plant process group, we have asked for the higher velocity, say 5-6 ft/s, increased HP (perhaps 25) and a VFD.

I have seen discflow pumps when I was in pulp and paper maintenance. They worked well for us in several applications. Centrifugal units, Warman, are the norm here.

I should have clarified that the impeller will be of a high chrome B1127AO5.

I will let everyone know what Weir/Warman comes back with on a new recommendation. I am confident that they can give us a sufficient unit.

I should mention too that the original plan for disposal of underflow was to pump it to the top of our maximum leach pad height, some 315 ft or so of vertcal lift - this would have required a skid unit with three pumps in series, at 50 HP each. This idea was quickly dropped by our people.

Artisi, your Sherlock Holmes quote is right on by the way. Data is defintely important.

Thanks to all again for your responses.

 

[flyerfan56]

One other note. I did consider peristaltic pumps but could not get anyone to buy in on them.

Thanks,

Bob

 

[micalbrch]

You are in Nevada? Then check this site:

http://www.tech-flow.com/linecard.html

I visited several mines in the early 2000s and I saw centrifugal pumps (mainly), peristaltic and diaphragm pumps on thickener underflow applications. On a trip to Utah I met one of the guys from TechFlow in a mine. We were both waiting for our site contacts and had a conversation. From that I know that they are specialized in mining, focus on Utah and Nevada and that they represent various pump manufacturers.

 

[flyerfan56]

Thanks for the further info and link. I will be cotinuing

 

[flyerfan56]

Oops, hit submit by mistake, a little too soon. Thanks for the further info and link. We are working closely with our Weir/Warman distributor, Daidson Engineering and Sales, in Salt Lake and the Madison, WI office. I hope to have a revised proposal from them on Monday. Davidson has been working with my firm for many years and Weir/Warman has been very helpful.

I will continue to post what we learn.

Thanks again.

 

[DubMac]

I worked with the boys at Davidson years ago and you are right, they are as good as it gets.

 

[flyerfan56]

Thanks much DubMac. That makes me feel a lot better about this. I've researched this every way but Sunday and done calcs that I could. Davidson has been very helpful for sure.

Thanks much.

 

[QualityTime]

I beleive there will be a lot of plating of the piping and the pump interior. I assume this has been given some thought?

 

[QualityTime]

The high pH of your slurry will cause calcium carbonate precipitation of the slurry water. Eventually the interior of your pump and piping will be clogged solid with calcium carbonate. It will be a maintenance nightmare

 

[Verder]

Verderflex peristaltic pumps work great for this application.

 

[Verder]

Peristaltic pumps work very well on underflow drain up to 70 -80 percent solids.