Status of Compressor lube oil and seal gas system Under shutdown

[Sawsan311]

Dear All,

For compressor with dual tandem seal with intermediate labyrinth using : process gas with booster for primary seal during normal operation and external fuel gas for start-up, secondary seal as nitrogen, separation tertiary seal as instrument air. I would like to ask whether in most of the cases compressor vendor tends to trip the seal gas system and lube oil system during compressor shutdown. On the other hand, In case we have a global plant shutdown, all utilities including Nitrogen,Instrument air and fuel gas + compressor itself trips... is there any concern of keeping the compressor pressurized under settle out in absence of a running seal (even with no secondary nitrogen seal) or there shall still be an external source for primary seal/secondary seal.

I am aware that in case of the failure of the seal gas system, compressor vendors tend to shutdown and automatically depressurize the machine. However,the same is not applicable if the compressor shutdown as it will only be depressurized after specific time duration in order to prevent seal gas condensation, seal failure as well as casing gas condensation,during this settle out time, is there any requirement of backup seal?
Regards,

 

[georgeverghese]

It is not a good idea to use high dewpoint temp process gas as primary seal gas. Low dewpoint non corrosive fuel gas or similar is preferred to avoid condensation, dirt and corrosion in the dry gas seal components. From a process safety perspective, shutting down utility gas feeds to dry gas seals while the compressor is pressurised is in any case not advised