Dry Gas Seals 1

[centeng11]

I'm slowly learning more about dry gas seals and I'm hoping someone out there can help me with a question that keeps bugging me. Focusing on double dry gas seals for the moment, the N2 sealing gas pressure must be higher than the buffer (process) gas being injected into the inner chamber (separated by a laby from the suction process). My question is, what is the point of having this buffer (process) gas injected into the inner chamber? It seems pointless. The inner laby will result in a reduction in process gas pressure, and as long as the N2 pressure is higher then this pressure then it accomplishes its task. It just seems to me that injection of process gas into the inner chamber is unnecessary. Any who can enlighten me would prove a big help.

 

[JJPellin]

I assume that the configuration you refer to is a double seal. The amount of nitrogen leaking across the inner set of seal faces is tiny. It is not enough to keep the dirty process gas swept out of the seal chamber. In a traditional double configuration, the process gas would be at the inside diameter of the inner set of seal faces. Contamination from the dirty process gas could build up at the ID of the inner seal faces, potentially causing the seal to fail.

The buffer gas is usually not just the same process gas that would be there anyway. It is either a cleaner version of the gas or it has been conditioned and filtered. In many of our gas seals, the process gas is recycle Hydrogen. The seal gas is nitrogen. The buffer gas is pure Hydrogen. The separation gas is air. The recycle Hydrogen contains compounds that can form salts. Formation of salts at the ID of the inner seal could cause the faces to hang up. The pure Hydrogen buffer gas prevents this.


Johnny Pellin

 

[centeng11]

Thanks for clarifying Johnny.

So, my understanding, correct me if I'm wrong, is that despite the low flow across the primary seal faces, the sealing pressure is higher than the buffer gas, which in turn must be higher than the gas on the process side of the compressor; resulting in the net gas flow direction across the inner labyrinth and into the process side of the compressor.

 

[JJPellin]

Correct.

Johnny Pellin