2 replies to this topic

[Behnam Bashokooh]

I need to define/size a gas/liquid separator for such a system:

1- works as inlet separator
2- two-phase gas and liquid phase separation
3- 100 bar pressure range
4- high gas/liquid ratio (low water-cut)
5- sour service
6- waxy service
7- high separation efficiency required

refering to Shell DEP, a vertical vane-type separator (SVS) gan be used for such a service, but not recommended for pressures above 70 bar.

can anyone give me any information about separators in almost same service (waxy fluid)? please also give any information about using a wax wash-off system used in separator internals. thank you.

[Zauberberg]

Behnam,

Wax formation should not be an issue in high-pressure systems characterized by low CGR (condensate-to-gas-ratio) due to the fact that significant amounts of light hydrocarbons (C1-C5) are dissolved in the liquid phase, acting as very efficient pour point depressant. You can confirm this effect of light ends simply by flashing the separator feed at several different pressure levels, ranging from 100 bar to atmospheric pressure, and watch for changes of the liquid phase pour point value; in spite of the fact that Aspen is not very accurate in prediciting cold flow properties of hydrocarbon fractions, the pattern of pour point vs. pressure change will give you a very good indication of system behavior. Wax washing system is definitely not required for this application, in my opinion.

As far as separator type is concerned, the important issue is that the gas is already above or very close to its critical value, making the separation between phases more complex - and that is why many standards call for special attention at extremely high pressures. In your case, if you are feeding the compressor or another process unit sensible to liquid carry-over from the plant inlet separator (e.g. sweetening or TEG unit), I would definitely include suction/inlet K.O. drum immediately upstream of those units, regardless of the efficiency of inlet separator. Inlet separator will be there to handle feed fluctuations, occasional slugs, possible pressure swings, and even if you find a way to design it with a 99.9% efficiency, you still have a good chances to encounter liquid carry-overs due to abovementioned reasons. Make a two-stage protection by providing another scrubber downstream of the inlet separator, and Operations people will be grateful to you once when the plant is commissioned.

Good luck,

[nguyen_trung_dung]

Behnam,

The WAT(Wax Appearance Temperature) is a function of pressure hence it's worth it to run the test at operating pressure, the test results may dominate the operating pressure. In my experience the "live WAT" can be 3-5C below the "dead WAT". The Laboratory who can run this test is KAT in UK.

Good luck

Dung