Mechanical Seal Barrier Fluid

[me3]

We used to use Propanol as a barrier fluid for our Ethylene Transfer Pump which uses a double, back to back mechanical seal arrangement, and which pumps Ethylene at
-104Deg C (-155F).

But we can not use this Propanol any more as it will contaminate the process in case of seal failure.

Is there any other liquid which is having a freezing point lower than -104Deg C and which we can use as a barrier fluid for our pump.

Thanks,

 

[assco]

If this contaminates your process whats to say another fluid wouldn't do the same? Is there a compatable product? If your product can stand nitrogen have you considered a gas seal?

 

[Wilkie]

You don't mention the conditions under which your system operates (aside from temperature), but you might want to consider using a mag-drive (seal-less) pump.

 

[eljauzy]

Depending on your suction pressure, you may wish to consider using Non Pressurize Tandem Seal. Since ethylene S.G is around 0.5 you may opt to use gas seal as a secondary seal and keep the liquid seal as a primary one. With this arrangement you can make do without the barrier vessel and only N2 supply is needed for the upper ( secondary ) seal. There will be no leakage into the process because the uppper seal cavity is atmospheric.

Consult you pump vendor for the conversion.

Are you using Sundyne for this transfer pump?

 

[PVRV]

Wonder what the pump nss is ?

 

[eljauzy]

TO PVRV,

NSS = SUCTION SPECIFIC SPEED

ITS DIMENSIONLESS

NSS = ( N * Q^0.5 ) / NPSHR ^0.75

N = RPM
Q = M3/MIN
NPSHR = m

 

[PVRV]

eljauzy,


Appreciate your feedback; I was wondering what me3 pump nss was

 

[me3]

Actually it is a vertical, multistage pump. And I was mainly looking for a fluid which is having a freezing point below -104 deg.C (as this will be the easiest way to solve this problem).

But, if I do not find one, I will go for modifying the seal system which will be a bit more complicated and costly.

In addition, I am already in contact with the vendor (which ic an Italian company), but t is taking a long time.

Thanks,

 

[longeron]

Have you considered using a gas seal? Perhaps a dual gas seal using Nitrogen as a barrier fluid would do the trick. The leakage rates across the face into the seal can be manageable, depending on your service. Barrier gas seals usually experience longer life because the seal faces do not contact. Sparking concerns can be alleviated with brass bushings.

Using Nitrogen as a buffer fluid at a lower than process pressure with a contacting seal on the inboard side is also an option.

 

[javaatayde]

In case of considering using a non-pressurized secondary seal, Is it really necessary N2 buffer? I think a N2 buffer is imperative If you need zero emission. Gas seal is too expensive. I recommend a secondary containment dry running seal and keep the liquid seal as a primary one, configuration 2CW-CS API-682 2nd Edition Plan 11/71/76.

 

[mlm2]

for a barrier fluid check out royal purple barrier fluid. reccommend keeping clear of gas seals unless it is last option. check out circo-flex, manufactured in georgia i believe.

 

[longeron]

Just wondering, which elastomer are you using in this service? Darn Cold.

 

[me3]

The O-rings which are used in this seal are TEFLON/GLASS. The Wedge of the mechanical seal is made of special PTFE material.

 

[upm]

ME3
looks u r in olefins plant, we do have similar arrangment as the one you have. we are using plan 53B using exxon barrier fluid. i am off my office now but tomorow i will get u the spec..in addition, i have some alternativ chart which might help. do u have low level (pressure )alarm in acse of primary failure?
will come back 2 u
upm

 

[me3]

upm
Thanks for your help. We do have both low level and low pressure alarms in the system.
The problem is that the temp. is so low to have a suitable barrier flid with the right freezing point!

 

[Bensley]

Naturally the behaviour of the fluid to be sealed at low temperatures must be considered. They are mostly a question of liquified gases. Due to the existance of large temperature gradients when operating at low temperatures, thermal distortions must be kept as low as possible by the use of suitable materials, Furthermore the entry of atmospheric vapour into the seal should be prevented so that the seal is not endangered by the formation of ice.

Buffer fluids for cryogenic seals that can beare single or multiple alcohols such as ethyl alcohol, ethylene glycol, glycerine or propyl alcohol, this last one may be used down to - 120 deg C.