SEAL OIL TANK LEVEL INCREASING AND LUBE OIL TANK LEVEL DECREASING IN CENTRIFUGAL COMPRESSOR

[P.K.P]

IN OUR KEROSENE HYDRO-TREATING UNIT WE HAVE A RECYCLE GAS COMPRESSOR WITH SEAL OIL SYSTEM (FLOATING SEAL ) . IT'S HAVING A DEGASSING UNIT. THE COMPRESSOR IS EQUIPPED WITH SEPARATE LUBE OIL SYSTEM. IN IT THE LUBE OIL TANK LEVEL IS DECREASING (15 DAYS) AND THE OIL LEVEL IS INCREASING IN SEAL OIL TANK. WHAT MAY BE THE POSSIBLE REASONS? THERE IS OIL PURIFIERS IN BOTH UNIT ..

 

[JJPellin]

Let's see how well I can guess with so little information provided.

The seal is an Iso-sleeve design with an overhead tank to control differential pressure. When they shut down, the extra volume of the overhead seal oil tank would overflow the reservoir. In order to manage this, there is a line connecting the seal oil reservoir to the lube oil reservoir. This is used by the operators to transfer oil from one system to the other to manage this problem. The valve in this line is leaking by.

Johnny Pellin

 

[georgeverghese]

Sounds like you have old fashioned oil seals on the compressor shafts - this oil will pick up heavy hydrocarbons from the process gas and these heavies will accumulate in the seal oil tank, which could explain the increasing level here.

Level drop in the compressor lube oil tank is normally expected, but if this drop is unusual, it could be due to high mist losses in the lube oil tank vent line.

For process safety reasons, it is unlikely that the compressor lube oil and the shaft seal oil systems would be interconnected.

 

[JJPellin]

Actually, for systems older than 25 years, it is quite common for the lube oil and seal oil systems to share a common oil reservoir. We have perhaps five or six where the systems are common or interconnected. In any case, the system should prevent any significant accumulation of process liquids in the oil.

The OP describes what I would interpret as a degassing system to recover contaminated seal oil and return it to the tank. If that is so, I would recommend removing this system immediately. Any savings from recovered oil will be paid out in reduced reliability and increased process risk.

I have another guess. The degassing system uses a steam coil as the source of heat. The coil is leaking and the increase in level is a result of water building up in the bottom of the tank.

Based on previous interaction with this OP, I am not expecting to ever hear back if my guesses are correct. I only post them in case someone else might find them interesting or beneficial.

Johnny Pellin