Nitrogen Purity for Secondary seal gas of Hydrocarbon Centrifugal compressors 2

[Sawsan311]

Dears,

Across many designs and existing installations of associated HC gas centrifugal compressors, nitrogen used as secondary labiranth seal is typically of 95%-98% purity and easily supplied by membrane technology.
Recently, there has been some views on the need to change the required purity to+99% to account for potential sulfur dusts formation in presence of high H2S and corrosive residues. Any similar expertise feedback on the need for such high purity knowing that there will be a cost increase in N2 generation technology selection.

thanks

 

[Heaviside1925]

OP,
It sounds like you are referring articles, could you share a link or the article themselves?

 

[georgeverghese]

First stage seal gas is always filtered gas (usually a slipstream from superheated and dewpoint conditioned HP fuel gas), so I dont see how sulfur dust can get into the 2nd stage where this N2 is injected.

 

[Sawsan311]

Thanks

There is no article being referred to, this is from the operational experience and compressor vendors recommendations. @georgeverghese, yes primary seal gas is filtered and superheated slipstream process gas, yet, still there has been issues such as compressor fouling in presence of high amount of asphaltene and Btex components. There has been some seal leakage observed also at the secondary seal vent so OEM recommended to increase purity of N2 which now I am questioning.

 

[georgeverghese]

First stage seal gas is injected on FIC or dPIC, and there should be a low low flow trip of the compressor on loss of seal gas flow, and compressor auto depressured. So there is no way process gas can get into the dynamic gas seal, unless the Operator has deliberately disarmed low low flow trip.
N2 injection is also on FIC or dPIC , and there are similar trips for this also.

 

[Heaviside1925]

OP,
Thank for the full description. I agree with georgeverghese that there should be instrumentation and controls to prevent this scenario.

change the required purity to +99% to account for potential sulfur dusts formation in presence of high H2S and corrosive residues

My assumption is, this was a vendor's suggestion. Consider that the vendor may have suggested this remedy for a past customer, and it worked. Now it's the vendors preferred suggestion in scenarios such as yours when it may have been a correlated effect as opposed to the actual cause. I would request more information from the vendor. Additionally, if this is a known issue, I would expect the compressor or seal company would have produced a white paper covering the theory and remedy of this issue, which may provide you with more information than just a vendor suggestion.

 

[horacio Torres]

A 100 % agree with georgeverghese

Horacio

linkedin.com/in/horacio-torres-molina-429a7b1b