Sealing Condensate / Condensate Barrier

[Milkboy]

Hey Group

As I understand it hot water / condensate has a low lubricity and therefore we usually see Carbon v SiC faces in a Mechanical seal.

Now then, if you were to use cooled 'recliamed' condensate and a barrier fluid and was sealing against a product which required SiC v SiC, would a condensate barrier at about 40 - 50 °C cause concern where lubrication is concerned


Thanks

M

-
Milkboy

 

[msouza]

Some seal manufacturers use to recommend using water only with less than 65°C for sealing lubricating. It is far correct that above of it, water has poor lubricity, but how can it explain the use of Carbon x Silicon Carbide for LPG services, with its common low viscosity... It makes me consider that the major issue is, being sure the water is in the liquid phase during its way between the seal faces, checking vapor pressure curve, operating temperature and operating pressure (seal chamber pressure or seal faces pressure).

Having Sic x Sic, you can see a heat generating increase, comparing with Carbon x Sic, even though, it can run smoothly, if the water is in the liquid phase.

Hope it helps you.

Regards.

Mario Souza
Application & Product Engineering
WMF Solutions Brazil

http://www.wmfsolutions.com

 

[bk19702]

I usually stick with 60°C as a target temperature for water.

You could potentially use Sic vs. Sic at those temperatures. You most likely know the cost adder for a Sic rotating face will be much more than a carbon rotating face. A more thorough analysis should be done if you want to go this route. A reputable seal manufacturer should be able to help you in this area with regards to analysis and predicted performance under your process conditions. If your's can't go elsewhere.

Be careful with the direction in which you will be pressurizing the hard faces (if you use them). Hard faced combinations which see ID pressurization, such as in the inboard seal of a dual pressurized seal, tandem mounting, will tend to diverge with respect to the barrier pressure. This means the face profile will be concave with respect to the process fluid and you will not be getting barrier fluid across the inboard faces - it will be pinched off, so to speak. OD pressurization on dual seals with hard faced inboards are preferred in my opinion. Just some food for thought.

You may also want to consider a graphite impregnated Sic vs. Sic for your face combination. This material offers the best of both worlds as it will withstand abrasion but also be tolerant of sporadic lubricity. The upper PV limit for this particular face combination is very good and rivals carbon vs. Sic. Unfortunately, cost will most likely still be a factor with that material as well.

An upstream pumping design with hard face materials may also be an option, provided excessive water consumption into the process is tolerable.