Page 174 - Petroleum and Gas Field Processing

in the settling section to speed up the buildup and the formation of water
drops, (2) applying centrifugal force to the emulsion that can promote
separation, and (3) applying an electrical field in the settling section of the
treater.
The principle of breaking oil–water emulsions using electrical current
is known as electrostatic separation. Ionization of these emulsions with the
aid of electric field was introduced in 1930 for crude oil desalting in
oil refineries. High-voltage field (10,000 to 15,000 v) is used to help
dehydration according to the following steps:
1. The water droplet is made up of polar molecules, because the
oxygen atom has a negative end, and the hydrogen atoms have
positive charges. These polar forces are magnetized and respond
to an external electrical force field. Therefore, a dipole
attraction between the water droplets in the emulsion is
established, leading to coalescence, hence settling and separation
(see Fig. 17).
2. As a result of the high-voltage field, the water droplets vibrate
rapidly, causing the stabilizing film to weaken and break.
3. The surface of the water droplets expand (their shapes change
into ellipsoids); thus attracted to each other, they collide and
then coalesce, as depicted in Figure 18.
4. As the water droplets combine, they grow in size until they
become heavy enough to separate by settling to the bottom of
the treater.

5.7 CHEMIELECTRIC DEHYDRATROS
(EMULSION TREATERS)

It is normal practice to call emulsion treaters ‘‘heater treaters.’’ However,
when other or additional treating aids are used, the name of the treater
would be made to reflect such aids of treatment. Consequently, a name
such as chemielectric dehydrator is used to indicate that both chemical and
electrical aids are used (in addition to heating) in the treatment.
Figure 19 is a sketch illustrating a typical chemielectrical treater. The
vessel is basically the same as the horizontal heater treater described
earlier. Once the oil is heated, it flows to the settling section. Free water,
which separates from the emulsion (under the effect of both heat and
chemicals), settles to the bottom. The oil on the other hand moves slowly
upward, passing across the electric grid in the settling section, where

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