SEAL OIL TANK LEVEL DECREASING CONSIDERABLY

[P.K.P]

ONE OF RECYCLE GAS COMPRESSOR (PIGNONE-WITH SUCTION 660 AND DISCHARGE 760 PSI) ,DRIVEN BY STEAM TURBINE SHOWING A PROBLEM FROM LAST FEW DAYS.ITS SEAL OIL LEVEL IS CONSIDERABLY REDUCING SOME TIMES.THE SEAL OIL TANK CAPACITY IS 14 BARRELS AND OVERHEAD TANK 1.5 BARREL RESPECTIVELY AT MAXIMUM LEVEL AND 75% FOR OVERHEAD TANK.IT IS EQUIPPED WITH A DEGASSING FACILITY.THERE ARE TOTAL 4 VENTS FROM THE SYSTEM, 1,SEAL OIL TANK TO ATMOSPHERE.2,DEGASSING TANK TO ATMOSPHERE 3,MIST ELIMINATOR TO KNOCK OUT DRUM 4,JUST BEFORE THE MIST ELIMINATOR AND AFTER THE SEAL TRAPS TO HIGH VENT.THE KNOCK OUT DRUM IS NOT SHOWING ANY SIGN OF OIL IN ITS DRAIN . YESTERDAY WE ADDED ALMOST 25 BARRELS OF OIL.WHILE OUR OBSERVATION WE SAW SOME MALFUNCTION IN THE PDCV. THE ACTUAL PDCV SETTING IS 660+120=780 PSI , BUT WE FOUND THE SEAL OIL PUMP DISCHARGE PRESSURE 1000 PSI.WE REMOVED THE PDCV AND OPEN THE BYPASS FOR REGULATING THE PRESSURE.IN WHICH WAY THE OIL IS LOSING ?ITS AN OLD MODEL (BELOW 1980) COMPRESSOR.IS THERE IS CHANCE TO MIX WITH THE PROCESS GAS? {THERE IS A SIGN OF FLOATING SEAL LEAK}.

 

[JJPellin]

Is this the same machine that had increasing seal oil reservoir level in August? Without more information I cannot help you. I have grown tired of offering advice and never getting a response.

Johnny Pellin

 

[rotw]

Yes and let alone the fact that you have been offering advice of especially precious value.

 

[P.K.P]

yes the same , there is lube oil migration .and the lube oil tnk level was decreasing and seal oil tank level increasing.But in this case seal oil is not migrating to lube oil.

 

[P.K.P]

At present we changed the PDCV , the seal oil pump discharge pressure is come to 830 psi, and tank level is not decreasing ..As i told before the compressor is an old model , Still my question is through which way the oil loses??

 

[JJPellin]

How was the lube oil migrating into the seal oil during the August event? You may not think it is relevant to the current problem, but I want to know. Did I guess correctly?

I had made a number of assumptions based on your last post. It now seems that many of my assumptions may be incorrect. Is this an Iso-Carbon, Iso-Sleeve, cone or bushing seal? The differential pressure control valve that you are talking about seems strange to me. I would expect the pump discharge pressure to control to a fixed pressure by spilling the excess oil flow back to the reservoir. Downstream of that, I would expect a separate differential pressure control valve to make the final drop to hold the seal oil DP for a bushing seal, cone seal or iso-carbon seal. I would expect a level control valve to hold constant level in the overhead seal oil vessel if it is an Iso-Sleeve seal. If your PDCV was holding 1000 psi (340 psi above compressor inlet pressure) were the seals exposed to this full differential pressure? If so, you may have damaged the seals or blown out o-rings.

In any case, if you are losing oil but it is not migrating into the lube oil and it is not running out on the ground, then it must be going into the process. I cannot say with more certainty without a seal drawing and an oil system diagram.

Johnny Pellin

 

[P.K.P]

The seal is a busing seal.Your assumption about different pressure control valves are right.The problem was found in the first valve(PDCV) to control the pump discharge pressure.And we found during that period the PDCV was not functioning and observed oil flow back to the tank through the safety release valve.This is first case we observed.Before that we noticed this high oil discharge pressure , the problem occurred -seal oil tank level decreasing considerably.Still I would like to know in which way oil level decreased?
Regarding the oil migration problem I have noticed in one more compressor also.Lube oil tank level increasing and seal oil tank level decreasing.