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.
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.