Liquid Carry-over and Gas-blowby in oil gas separators

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Vertical Oil Gas Separator

when we talk about oil gas separators in the modern designs of GOPS, the designers took into consideration all operation problems, by adding high sensitivity control valves, and accurate pressure and level indicators which decreased these problems to the minimum, most operation problems now are occurring because of bad operation, human mistakes, or any malfunction of these control valves.

Carry Over in Oil-Gas Separator:


Oil Gas Separator control signals


In simple words Liquid Carry Over means: exit of crude oil droplets with the gas already separated from oil; this will lead to a very black smoke from the flare; and burning the small amounts of oil from time to time, it will further lead to the reach of oil droplets to the gas treatment facility, which may contain gas compressors; these amounts of oil will lead to gas compressor vibration.

Carry Over Causes:

– high inlet flowrate to the oil gas separator which is caused by bad manifold distribution , this will lead to high flowrate to some separators and low flowrate to others.

– closing oil outlet valve mistakenly , or a technical problem in it.

– oil level indicator false signal, which will lead to raise the oil level in the separator.

– a technical problem in pressure control valve, this will decrease the separator pressure causing oil level to increase and pass the mist extractor, then escape with gas.

How to solve this problem?

– if there is a bad manifold distribution, we have to re-organize the flowrate to each oil gas separator, this will guarantee not to overload any separator with excessive flow.

– If there is idle manual valve in any separator, then we have to shut down it, then fix or replace this valve.

– Calibrate the control valves. then check level and pressure indicators.

Gas-blowby in oil-gas separators:

This problem is simply the entrance of gas in oil outlet stream; this will lead to gas pockets in the oil export pipeline, especially if these pipelines are long, this problem happens also when the flow is much less than its design capacity.

So what?

This problem will lead to a backpressure on the oil gas separator, causing high oil level and high separator pressure in the same time.

Gas Blowby Causes:

– a decrease in oil level because of an out of order in the oil level control valve, or a false set point given to this control.

– a sudden increase in the separator pressure because of a disorder of pressure control valve, or changing its set point mistakenly .

How to solve this?

If there is any malfunction in the control valve; they need to be fixed then re-calibrated.

Then we have to have a look at pressure and level indicators, to be sure that they are accurate, but in all cases we have to vent the pipeline from any vent point.

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