LIGHT HYDROCARBON (VOC) SEALING CENTRIFUGAL PUMP 3

[javaatayde]

What's the best solution for light hydrocarbon(LPG, propane, etc.)centrifugal pump sealing? I use dual seals API Plan 11/52, but I think It is very expensive,not so reliable and the operation is not so simple. I have read some papers about dry contacting secondary containment seal. I would like to know whether someone is using that. Is that really good? What about failure rate?
Regards, Javã

 

[JJPellin]

We have been using a contacting containment seal in similar services for the past 12 years with good results. The first seal that we installed was in a sour propane service (single stage overhung pump). This seal lasted for over 8 years (continuous operation)and was finally replaced when the pump was pulled out for a bearing problem. The manufaucturer suggests a purge in the barrier area of this seal design. We vent our seals to a flare system with slight positive pressure and cannot tolerate a continuous purge flow. We probably have about 150 pumps running with this technology and have had very good results. I would not suggest using this design piped this way in streams that would not vaporize at flare pressure. A buildup of liquid product in the barier area will reduce life on the containment seal.

 

[milr]

I recommend to use a dual arragment, other point that you have to consider is the SG and steam vapor, if the product is flashing, you have to avoid a leaking.

 

[scalleke]

A quick check on the internet shows me that this woul;d be something like a John Crane type 28 seal.

These seals do a really good job, if you are sure that you never get liquid on the secondary dry seal. Something I believe you cannot guarantee in a liquid propane application. You will at least sometimes during start up see some liquid propane in the buffer cavity.

why not look at some other dry seconrdary seal options. There are more rudimentry dry gas seals that have lift off pads machined in the carbon face and not in the hard face as is the case for the JC type 28 seal. My personal experience is that they do a very good job and they withstand liquid contamination by wet HC's at start up.

Don't get me wrong the JC 28 is a great seal. and will have less leakage than the more rudimentary seals I describe. It's just a bummer to have to pay so high a price for the repair parts if they have been started up with liquid contamination.

What type of pump are we talking about?

Best Regards.

Scalleke

 

[javaatayde]

John Crane type 28 is a compressor seal (non-contacting seal). We are talking about JC type 48C/S48SC. It's a full contact dry running secondary containment seal.

 

[milr]

I was investigating about LPG application, and the best option for this kind of product is gas dry seal, in special, if the pressure bore is close to steam pressure product.
John Crane has a 28VL seal, that is special for it. It is not necessary to use a Plan 52, maybe the inicial cost is high comparative than the wet seal, but then the seal will pay itself quickly because its maintenance cost will be lower.