3 replies to this topic

[Reid]

Hi there,

I am designing a 3-phase separator for a FPSO. The processed water from this unit is sent to a hydrocyclone. My problem is that HYSYS simulates an oil in water content equal to approximately 40 g/kg. I believe this is way to high.

Does anyone have some experience with how to handle this? Or is HYSYS not capable to solve these problems? Have anyone seen verification studies for such problems?

Reid.

[JoeWong]

Hi Reid,

I guess the oil-in-water of 40g/kg as your mentioned is dissolved oil and it is very high. However, this may be possible especially fluid contains high solubility HC compound i.e. benzene and present of high affinity fluid e.g. MEG. TEG, etc.

Normally 3000-5000 mg/l of dispersed oil-in-water may present in produced water even with a proper design separator.

We would have better appreciation of your problem if you can advise the 3phase separator feed composition and it's operating condition (PT) to furhter investigate.



regards,

JoeWong

[JoeWong]

Hi Reid,

Recent hacker invasions have partially deleted some responses on this topic.
I manage to recover the response.

********* By Reid ***************

Hi Joe, and thanks for answering.

Yes, I will expect a water content of about 5 g/kg oil, but not as much as 40 g/kg. The feed contains about 43 mole % methane, 19 mole % c2 - c6, and the rest are larger hydrocarbons, defined as different pseudo compounds. The pressure is set to 12 barg.

The heaviest compound (2 mole %) has a density of 985 kg/m3, i.e. quite close to water. It has a MW = 650,9 kg/kgmole, Tc = 738 C, Pc = 1424 kPa and accentricity factor = 1,3043. May such a compond cause the problems in the separator? I am not really familiar with how HYSYS is dealing with the water / oil split.


***************************

I suspect the heavy component has gone into your water stream looking at the density. You can check it out from the produced water stream composition

Secondly you may try to set this particular heavy component to zero and see if the HC-in-Water back to expected "normal" concentration.

If possible, please upload the native file.


The reported density (985 kg/m3) is very close to water. It will form a stable emulsion in the separator and it may not be easy to be separated from water by gravity separation i.e 3phase separator

Eventhough the HYSYS predicted this component may stay in condensate, you may needs to use engineering judgement where poor separation and results majority of this heavy component stay in PW. Further oil-water separation units e.g. hydrocyclone, flotation unit, CPI, etc may required



regards,

JoeWong

[Steve McGahey]

Hi there,

I am designing a 3-phase separator for a FPSO. The processed water from this unit is sent to a hydrocyclone. My problem is that HYSYS simulates an oil in water content equal to approximately 40 g/kg. I believe this is way to high.

Does anyone have some experience with how to handle this? Or is HYSYS not capable to solve these problems? Have anyone seen verification studies for such problems?

Reid.

HYSYS doesn't model the problem of "how much carryover do you get" from a three phase separator.

HYSYS would be assuming perfect equilibrium separation - so any carryover you are seeing at all, will be due to a fixed number in the three phase separator model - either a default value, or something someone else has punched into the model.

What you need is something that will predict the separation efficiency as a function of feed flowrate. I'd suggest looking at previous (eg from other projects done in-house) separators that were similar, and getting measured oil-in-water carryover values.