Dry Gas Seal pressure controlled

[HamzaNossair]

Hello folks,

On a Dry Gas Seal, which has a diff presure control method, do we need to

Alarm and trip on supply, primary?
Alarm only on supply, primary?
How about secondary seal protection?

 

[Airsporter1st]

There are many ifs and buts, however generally, you would only have a trip on High High primary leakage and alarm on Low seal gas supply.

Assuming you have a tandem seal with an interstage laby and secondary seal gas supply (usually nitrogen)secondary seal condition may be indicated by primary seal leakage; i.e. if secondary seal fails or is leaking excessively, the secondary seal gas which would have been exiting through the primary vent, will now exit through the secondary seal and thus you see a low pressure/flow in the primary vent. This depends very much on relative pressures and settings etc. and has to be considered on a case by case basis.

High Secondary leakage is usually alarm only.

 

[jbattershell]

alarm on primary seal flow supply. whether to also have a trip on low low supply is up to the user and the process criticality.

secondary seal also has to have protection. supply flow meter on N2 supply to secondary seal. flow meter on primary vent. compare the two values in the controls. they should be nearly equal to each other. if the vent flow goes up, but the N2 supply flow did not, then that is a back up alarm to primary seal issues. primary alarm is increasing pressure in the vent line.

if the N2 supply goes up but the primary vent flow didn't change much, then that is a problem with the secondary seal as now a good portion of the N2 flow is going out through the secondary seal instead of flowing past the inter laby and out the primary vent.