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Sealing NaOH 1

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CJD1984

CJD1984

Mechanical
Aug 23, 2008
6
I am looking to select a pump that will dose 4-6 GPM of 25% NaOH at 110ºF.

The big issue I have seen in the past is mechanical seal selection in any NaOH application due to its crystallization when it contacts atmosphere.

Obviously, a double seal would work if the sealing area is starved of oxygen, but the negatives are utility cost needed for a seal support system.

I am inclined to look at a sealless, mag-drive pump.

Any thoughts, experiences, etc.
 
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Two previous threads on this subject:

thread407-207269
thread407-115830

Patricia Lougheed

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I like these mag-drive gear pumps. I've used with great success. Product data page of their website is


Non-pulsing flow (like with peristaltic pumps) is eliminated, and no danger if hose/tube fails.

You are correct that the air/liquid interface is the biggest seal problem. Note mag-drives don't like running dry, but this one is as forgiving as any I've used.
 
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All, thanks much for the input. I am very familiar with each of these centrifugal, peristaltic and helical gear technolgies and each has their place.

Yet, my issue now is differential pressure abilities.

I need to provide 200 PSI differential at 6 GPM......the helical gear and peristaltic fall short and the centrifugal would have to have a 10" impeller or up and would be very inefficient at that low of flow/high head.


 
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At a flow as high as 6 gpm you might get away with a gear pump with something as low viscosity as NaOH solution, but I wouldn't put my money on it. Gear pumps misapplied can turn into maintenance nightmares rather easily, unless they're pumping lube oil in which case they last forever.

A multi-stage centrifugal with a double mechanical seal, such as one of side-channel pumps offered by Grundfos, might be something to look at. A thermosiphon-cooled buffer fluid system won't cost you much in utilities.

The other option is a diaphragm PD pump. Seal-less, reliable, but inefficient and produces pulsile flow. At 6 gpm you could buy a triplex unit and get rid of the pulsing. But it'll cost you...6 gpm's a lot of flow for one of these.
 
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I would consider a progressive cavity pump with packing.
 
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This is a typical application for regenerative turbine pump (low flow high head characteristics) made from Polypropylene for Caustic, and with Mag-drive to avoid ANY seal problems.

Packed gland was mentioned, but the problem with Caustic is the formation of crystal as the liquid comes into contact with atmosphere, seal life is always a factor to consider, mag-drive is an absolute first class choice for such liquid, and have served withour maintenance or service for many years - do watch the temperature of Caustic - if it drops below 20'C then it has a very steep viscous curve - a common cause of those beloved 'pump problems' that people like to shout at manufacturers about !!

Sorry if this is sales man talk here but have just the animal - usually very quick delivery, and used widely in these applications !!

Ash Fenn

 
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I have found that packing works very well with NaOH.
 
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Thanks for the inputs.

Ultimately, I am going with a regenerative turbine pump with a seal quench stariving the sealing area from oxygen. The quench will not require any additional utility costs over and above operating the pump.

The end user went with this option due to the low purchase price of the pump.

 
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Wow- you're getting 200 psid across a single stage regen turbine pump?! Definitely got to check those out- let us know how well they work!
 
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If you consider using a single mechanical seal, try piping plan 11/62, with Direct-Sintered Silicon Carbide x Carbon (not antimony carbon), 316 metal parts and Fluoroelastomers gaskets.

As a piping plan 62, it will have continuously quench, not accumulating crystals. Perhaps a rotating bellows seal can help to have a free displacement of the rotating element (bellows) even with a little build up of crystals, in case of a piping plan 62 failure, but bellows seals use to be more expensive than pusher seals tough.

Hope it helps.

Mario Souza
Application & Product Engineering
WMF Solutions Brazil
 
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Water quench as mentioned above will work pretty well.

Another option is an unpressurized dual seal with Plan 52. The buffer fluid will help keep oxidation from occuring within the seal.

A third option is something called active lift or upstream pumping. This is another version of an unpressurized seal but utilizes a simplified support system- water supply to a reservoir only. There was a paper on this presented at the 2005 Pump Symposium.
 
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Using a single seal with Plan 11 & 62 is fine however you will need to seal the water quench and my experience in usin lip seals as secondary seals in such applications become the weak link an you will experience excessive water leakage to atmosphere. to add to the problems you may experience water contamination into the bearing housing which will result in premature bearing failures.
Investigate the Upstream pumping seal Longeron mentions above. This is effetively a tandem seal with very simple utilities attached, it will solve your crystalization problem and provide a reliable secondary seal.

Good Luck
 
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