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Third stage separator
The final separator here is a two phase separator, also
called a flash-drum. The pressure is now reduced to about
atmospheric pressure (100 kPa) so that the last heavy gas
components will boil out. In some processes where the initial
temperature is low, it might be necessary to heat the liquid (in a
heat exchanger) again before the flash drum to achieve good
separation of the heavy components. There are level and pressure
control loops.
As an alternative, when the production is mainly gas, and
remaining liquid droplets have to be separated out, the two phase
separator can be a Knock-Out Drum (K.O. Drum).

Coalescer
After the third stage separator, the oil can go to a coalescer
for final removal of water. In this unit the water content can be
reduced to below 0.1%. The coalescer is completely filled with
liquid: water at the bottom and oil on top. Inside electrodes form
an electric field to break surface bonds between conductive water
and isolating oil in an oil water emulsion. The coalescer field
plates are generally steel, sometimes covered with dielectric
material to prevent short circuits. The critical field strength in oil is
in the range 0.2 to 2 kV/cm. Field intensity and frequency as well
as the coalescer grid layout is different for different manufacturers
and oil types.

Electrostatic Desalter
If the separated oil contains unacceptable amounts of salts,
it can be removed in an electrostatic desalter (Not used in the
Njord example) The salts, which may be Sodium, Calcium or
Magnesium chlorides comes from the reservoir water and is also
dissolved in the oil. The desalters will be placed after the first or
second stage separator depending on Gas Oil Ratio (GOR) and
Water cut.

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