Syngas Compressors Seal Oil Leaking on Discharge end

[SealOilz]

Good morning,

I have a turbine driven compressor train that seems to be leaking on the inboard side of the machines through the seals. We did measure flow rate to each seal by use of ultrasonic meter to be about 1.5 gpm on our LP casing and about 2 gpm to our HP casings. The system is a lube oil to seal-oil booster combined system that is level controlled for dP by use of an OH seal oil tank. The seals are a bushing style (with process side having a windback) for each seal.

We've done some troubleshooting trying to determine this phenomenon but still haven't identified the source of the root cause.
The initial catch was that we were not leaking into the contaminated seal oil traps for the discharge ends of the casing and has led us to finding that we have some LELs in our IB housings/reservoir which has elevated this investigation. There is a nitrogen blanket on the reservoir.

Our LP casing is a 2 stage machine, inlet is on the OB end- goes through an intercooler and returns on the IB end and works towards center to discharge. It is cooled again and loops over to the HP with is a single stack rotor with a recycle line on the IB. Inlet is on the OB.

We did notice that our OB bearing housings do gain a level in the contaminated seal oil traps over time but our Inboard SO traps do not. In the OB bearing housings, we also noticed that we pull a very small vacuum into the housing of air, versus the IBs seemingly puffing air out of the vent.

We verified liquid level in OH tanks is roughly 15.5 ft (equivalent to 5.6 psig) above CL to machine. Doesn't look like we have a deadleg in our reference gas lines to hold oil during accidental overfills during trips/shutdowns. (And no, there isn't an Overfill line to the oil traps.) Verified the demister was replaced with original, checked the 1/16" orifice to the vents are cleared. The LP case vents to flare, and the HP vents back to compressor suction. Traps measure 500 on LP traps and 1200 on HP traps on top of vessels.


Are there leads someone would have for troubleshooting? How could we prove it's either the seal leaking or an issue in the system and the symptoms are a non-leaking set of oil traps?
I had a couple of theories, but the seal manufacturer seems to have debunked them.

Thanks in advance!

 

[georgeverghese]

So both 2 stage LP casing and single stage HP casing machines are leaking syngas at the IB ends ?

My experience has been with dry gas seals so I may not be able to help with these oil seals. What do you mean by

"Traps measure 500 on LP traps and 1200 on HP traps on top of vessels"

Try posting on this forum also to see if you get better responses - mechanical seal engg

https://www.eng-tips.com/threadminder.cfm?pid=819

 

[SealOilz]

Thank you georgeverghese for the reply.

These are bushing style, wet oil, inner seals for our compressors. The intent is that with the Overhead seal oil tank giving a 5-7 psig differential to the oil supply to the seals that the small differential pressure will force the oil to leak a very small amount into the contaminated oil drain over time (maybe 2-5 gpd) which leads to the sour oil traps. Each end of the compressor has it's own sour oil trap with a demister on the vent side. The oil drops out and builds a level in the traps.

With that being said, the LP sour oil traps have a pressure gage that reads close to 500 psig (with no differential pressure gage between them), and the 1200 psig on the HP sour oil traps.

I thought about posting in that forum as well, but didn't want to duplicate threads and since it's a bushing style- felt more inclined to post in here. But maybe you're right..

Hoping JJPellin will also throw his wisdom my way as well. =)

 

[georgeverghese]

As no one has responded so far, think you have justification to duplicate or move this entire thread on to the seal forum.
Good luck