5 replies to this topic

[aliceglen21]

Hi Everyone,

Before I delve into the problem associated with this separator, I first want to give some background information. The oil/gas separator operates at approximatley 1,100 psig with a high gas oil ratio inlet stream. The poduct gas stream, combined with another gas stream from the compressor, is then fed to a glycol scrubber. Recently, we have noticed higher than nomal hydrocarbon level in the glcyol scrubber.

Liquid carry-over from the gas stream leaving the compressor has been ruled out because if this were the case, the compressors would have suffered significant damage and there is no evidence of this. Therefore, it was established that the most likely source of oil contamination is the oil/gas separator.

I have analysed data from the separator and found that the current gas flow rates are midway between the early and late case for which the separator was sized. Also, from analysis of data trends there was no conclusive evidence to show that liquid carry-over was due to high liquid levels in the oil/gas separator. The trend shows that even though the liquid levels in the separator was fairly constant at the set-point, high liquid levels in the glycol scrubber was still observed. And high liquid levels were observed in the glycol scrubber at both high and low gas flow rates (still between design flows).

The separator consists of a cyclonic inlet device, a distributed baffle close to the inlet and a vane mist extractor at the outlet.

Any other advise as to what other possible causes of this liquid carry-over and how it could be verified would be appreciated. Also, all the internal in the separator vessel are intact.

Thanks,
aliceglen21

[ashetty]

[quote name='aliceglen21' date='Oct 23 2008, 10:00 AM' post='23033']


Liquid carry-over from the gas stream leaving the compressor has been ruled out because if this were the case, the compressors would have suffered significant damage and there is no evidence of this. Therefore, it was established that the most likely source of oil contamination is the oil/gas separator.
Is there any change in temperature/pressure when the two streams combile?
I have analysed data from the separator and found that the current gas flow rates are midway between the early and late case for which the separator was sized. Also, from analysis of data trends there was no conclusive evidence to show that liquid carry-over was due to high liquid levels in the oil/gas separator. The trend shows that even though the liquid levels in the separator was fairly constant at the set-point, high liquid levels in the glycol scrubber was still observed. And high liquid levels were observed in the glycol scrubber at both high and low gas flow rates (still between design flows).
Check the gas velocity @ current seperator pressure.Verify that it does not exceed the allowable maximum velocity for current gas flows. If it is possible try and increase the operating pressure of the seperator as much as you can to study the effect.

The separator consists of a cyclonic inlet device, a distributed baffle close to the inlet and a vane mist extractor at the outlet.
Any other advise as to what other possible causes of this liquid carry-over and how it could be verified would be appreciated. Also, all the internal in the separator vessel are intact.
Contact the seperator supplier and inform him of the problem and take his inputs.

Thanks,

A.Shetty

[Zauberberg]

Alice, I have a few questions:

1. Is there a cooler/condenser downstream of compressor dicharge? Is there any possibility of partial condensation across the cooler?
2. How do you recognize liquid carry-over to the glycol contactor? By level indication only, or by measuring the amount of skimmed hydrocarbons?
3. What makes you think that level controller in high-pressure separator is functioning OK or not? Do you have a redundant device for level measurement/checking?
4. Has the mixing of vapor streams from compressor discharge and high-pressure separator been the standard/normal practice in plant operation, from the day No.1?

[ashetty]

One more question to the list, has there been a change in the gas/oil compostion of the feed to the seperator lately.The vessel manufacturer would have been supplied with data initially, if you could get the datasheet, pls check if the fluid properties are similar to the inlet fluid in the current situation.

[Qalander (Chem)]

One more question to the list, has there been a change in the gas/oil compostion of the feed to the seperator lately.The vessel manufacturer would have been supplied with data initially, if you could get the datasheet, pls check if the fluid properties are similar to the inlet fluid in the current situation.

Dear aliceglen21 Hello/Good evening, although much is alredy adviced.
However I will suggest my little bit
1) Please have Gas Liquid sampling carried out at different Day-Night intervals and compresssor downstream and separator in-out and
2)if manageable get these analyzed through GC (Gas Chromatography) and compare Verses design values at these points.
3) after Re Calibration Check the temperatures downstream of compressor discharge and scrubber top bottom and middle;again do this for different Day-Night timing.
The above will take you to Identifying the possible variances areas and needful remedial actions.
The contents of two layers of Glycol scrubber should also be analyzed. Again I prefer GC for Day-Night different timing.
This may Take a shape of test run for a specified period and intervals to uniformly generate this analytical/diagnostic data.
Hope this helps
Qalander

[aliceglen21]

Hi Everyone,

Thanks so much for the reply and the help. I am currently gathering data to the questions asked to have a better understanding of the problem.

I will reply shortly.

Thanks again,
aliceglen21