Three phase separation
Three phase separation
(OP)
We have a three separator (HC, HC-Water vapor, Water). We are facing difficulties in separation of water and hydrocarbon. There is carryover of HC with water. Is there is any effect of gas velocity on separation of water and hydrocarbon in liquid phase.





RE: Three phase separation
Liquid-liquid separation due to gravity is governed Stoke's Law
There are various factors that affect liquid-liquid separation. Some of them are listed below
1. Particle size or droplet size
2. Viscosity of HC and water
3. Is HC present as finely dispersed liquid.
4. Density difference between HC and water.
5. Internals provided for separation
Please check the calculations or provide more details.
Revert in case of any query.
Dinesh S SHELATKAR
Process Engineer
RE: Three phase separation
RE: Three phase separation
1) Malfunctioning level controls (this is quite common in separators handling two different liquid phases);
2) Undersized separator (compare the actual G/L/L rates versus design rates and calculate actual phase velocities);
3) Possibility of clogging somewhere in the oil phase circuit, including the downstream piping;
4) The actual ratio of water to oil is far away from the design value - or even inverted - making this type of separator unsuitable for current operating conditions/flows;
5) Any other issue we are not aware of.
Here is a DEP available online to assist you with calculations, but make sure you do proper data collection in the field before you start crunching figures. Bad data in = wrong conclusions out. Proven over and over again. http://razifar.com/cariboost_files/Liquid-Liquid_2...
Dejan IVANOVIC
Process Engineer, MSChE
RE: Three phase separation
RE: Three phase separation
RE: Three phase separation
dear george, the subject separator is not located in offshore as u mentioned in your post.
This is FCC main fractionator reflux drum (temp: 60-70 C), there is no internal as such for separation of three phases. we only have elevated liquid hydrocarbon outlet nozzle as water content is very high.
RE: Three phase separation
If you don't supply more information, there's not much more anyone can do.
We need some data such as:
Size of separator, liquid (H/C and water) and gas flows, operating pressure, residence time, liquid levels in the separator, measurement / control over water / HC level, how much carryover are you getting?, and the other data requested baove.
What is the difference between design flow rates and actual flow rates?
If the water cut has increased a lot, then you could just be vortexing the H/C flow into the water outlet which is flowing at a much higher flow than the design or simply not have enough residence time or margin between water/ H/C level and the wate routlet nozzle.
Who knows - we can't see your vessel.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Three phase separation
Other potential culprits stand as well - as mentioned in previous posts.
Dejan IVANOVIC
Process Engineer, MSChE
RE: Three phase separation
Interim options may be to
(a) change the interface level detector to a direct mount dp cell with impulse lines which are diaphragm sealed
(b)check with plant chemists / corrosion engineers if there are some emulsion stabilising chemicals being injected into FCC overheads (for corrosion management?). If this is the case, reduce the injection rate if possible, or find some other corrosion inhibitor.
Obviously, flux rates for water and hydrocarbon should be within limits in this sep; if flux rates are higher than permissible foe either phase, the plate pack may help.
RE: Three phase separation
with these informations you gave I think that it is a matter of operation at first! If there is HC in water, it means that your system works good! The inlet flow water content is very low! check from when this happened? From the first begining day of plant startup or from a specific date
1.Check level transmiters calibration.especially stand pipe if its cloged or not.
2.check Water outlet control valve operation and calibration.
3. Check mechanical drawings for water nozzle elevation and where inlet nozzle placed(if there is)
4. If every thing is ok, just close water outlet valve and let drum get some water level. Instruct operator that water is a good thing.
5. Also check if there ahould be some wire mesh inside drum and if its installed properly.