The separation gas system shall be a permissive to start lube oil pumps in order to avoid ingress of

[lahori]

Hi,
can somebody please help me here. What does it mean " A permissive to start lube oil pumps ".Actually I am working with seal gas system and this logic is on pressure differential transmitter (PDT) for both at the inlet and out of the compressor barrier gas.

Regards
YB

 

[JJPellin]

Your terminology is not clear. A diagram would be helpful. If you are referring to separation gas, it is not uncommon for the introduction of gas to be required before the lube oil pumps can be started. This gas is injected into a seal between the bearing and the dry gas seal and is intended to prevent the migration of lube oil to the dry gas seal faces. There is probably also a second permissive that requires that the primary seal gas is in service and maintaining a positive differential pressure above compressor reference pressure before the lube oil pumps can be started. In both cases, the intent to be absolutely certain that lube oil is not allowed to get between the faces of the dry gas seal which would likely cause it to fail on start-up.

Johnny Pellin

 

[lahori]

Hei JJpellin,
Please find the attached below.What will happen if you remove this "Permissive to start lube oil pump logic"?
Regards
Lahori

 

[JJPellin]

As I already noted, without the separation gas, there is a higher risk of lube oil reaching the faces of the dry gas seal, causing a seal failure on start-up. Personally, I consider this to be a low probability. Do you have some reason that you cannot introduce the separation gas before starting the lube oil pumps? One example comes to mind. In order to complete oil circulation and screening, you might need to override the permissive to be able to run the oil system and screen the oil. If the oil flow was bypassing the bearing housings using high velocity jump-over lines, this is a perfectly reasonable thing to do. During the final screening, with the oil flowing to the bearings, this would create a risk of seal failure.

Johnny Pellin

 

[georgeverghese]

Do not override this permissive; you may introduce lube oil into the dry gas seal, and / or contaminate the lube oil if it comes into contact with the process gas stream. Start the aux LO pump only after all DGS trip loops are normalised and re armed.
Else explain why you want to disable this trip loop for startup.