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Centrifugal Compressoer Sealing System


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#1 woo

woo

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Posted 17 November 2015 - 12:23 AM

Dear All!

 

Next year, we are going to install compressor package(gas turbine+compressor) for the first time.

 

I will be in charge of controling a compressor package.

 

I have spent most of time on reading and checking document about compressor..

 

In fact, the most difficult point of it is sealing system for me.

 

here are my questions about that..please help me to understand compressor a bit

 

1. I need more detailed information about sealing system.

  - function, mechanism, location, component, etc

  - definition of buffer gas and dry seal gas

 

2. what is the pressure of buffer gas and dry seal gas in startup and normal operation conditions?

 

3. how to control and monitor seal gas system

 

4. where do dry seal gas come from?

 

thank you..

 

best regards.



#2 Bobby Strain

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Posted 17 November 2015 - 10:19 AM

A bit of research will get answers to all your questions.

 

Bobby



#3 Abhimanyu Dagla

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Posted 17 November 2015 - 12:21 PM

I have worked on dry gas seals. Here is some information I have.

 

Dry gas seals are a breakthrough in compressor sealing technology, which eliminates the hassles of pumps, exchangers, and coolers etc, and handling of seal oil.  The consumed power is very small; almost zero due to the fact there is no contact. Almost all the gas compressors (90%) used in upstream oil industry are supplied with dry gas seals today.

 

Dry gas seals are end faced mechanical seals which are non contacting (during operation), and gas lubricated. The heat produced by conventional seals is dissipated by the seal oil, here as such there is no contact, but the gap is of order of 3-4 microns, that is too small ( human hair is 50-100 microns thick !), heat produced is due to a phenomenon called viscous shear and is taken by the seal gas flow.

2ltsu4l.jpg

 

io15ra.jpg

Seen above is the dry gas seal tandem seal assembly. Two seals are in series. At bearing side, the lube oil is prevented by separation air to enter the dry gas seal assembly. It is very important to start this air before starting lube system, otherwise the seals might get damaged by the lube oil.

The seal gas supply enters the space between process side labyrinth and the seal. Majority of the gas supplied enters into the compressor through the inner labyrinth seal. Thus a positive differential pressure of around 4-5 psi is maintained. The primary vent contains the gas which leaks between the seal faces. The secondary vent which is normally routed to vent to a safe location, contains small gas which leaks past secondary seal and around 50% of separation air injected into the separation seal. Separation seal may be labyrinth seal or it may be segmented carbon seal. At MSP the separation seals are labyrinth seals.

The primary seal absorbs the total sealing pressure to primary vent pressure and in case of failure; secondary seal can take care while compressor is safely shut down.

 

In a hurry,Please contact for any other information

 

Abhimanyu Dagla

Deputy Superintending Engineer ( Production)

ONGC India


Edited by Abhimanyu Dagla, 17 November 2015 - 12:32 PM.


#4 ankur2061

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Posted 17 November 2015 - 01:11 PM

woo,

 

Refer the link below and the attachment with the blog entry:

 

http://www.cheresour...r-seal-systems/

 

Regards,

Ankur.






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