Dual Polarity® Electrostatic Treater
Dual Polarity® Electrostatic Treater improves crude
oil dehydration
The Dual Polarity® Electrostatic Treater is
the single most effective method of crude
oil dehydration. Since its introduction in
the 1970s, it has out performed
mechanical and conventional AC
electrostatic treaters in hundreds of
applications. This treater provides lower
operating temperatures, higher
throughput rates, and lower BS&W
content, while handling larger volumes in
a smaller vessel.
Innovative AC/DC design
accelerates coalescence,
improves efficiency
The Dual Polarity® Electrostatic Treater
consists of a pressure vessel with a
heating/degassing section and firetubes,
an oil spillover box, and a coalescing
section with metered orifice distributors
(figure 1). In place of the conventional
alternating current (AC) electrical system,
the Dual Polarity® Treater uses a system
with both AC and DC fields.
The crude oil emulsion enters the Dual
Polarity® Treater and flows downward
over a hood baffle. Free water separates
immediately and is not heated, which
boosts heating efficiency and saves fuel.
The hood baffle also helps eliminate
firetube scaling by keeping the free water
from coming directly into contact with
the firetube.
Typical Dual Polarity® Electrostatic Treater
Dual Polarity® outperforms the
single field systems
Using the same dependable AC power
supply as a conventional electrostatic
treater, the Dual Polarity® Treater splits
the high voltage, with rectifiers, into
positive/negative components. Pairs of
electrode plates are charged in
opposition. Water droplets entering the
field are elongated and attracted to one
or the other plate, accepting the charge
of the electrode plate they are
approaching.
Oil and emulsion is heated as it flows up
past the firetube. Larger water droplets
coalesce and separate, while smaller water
droplets continue with the oil as it flows
into the coalescing section. Then, these
remaining water droplets are subjected to
the AC/DC electrostatic fields, causing
them to coalesce and settle to the bottom
of the vessel.
The benefits of this unique
design are:
• The Dual Polarity® field delivers twice
the voltage of an AC field, while
using the same power supply/
transformer requirements as an AC
field.
• Because of the unchanging polarity
of the DC field, water droplets have
time to respond by migrating
between electrodes. Movement is
virtually non-existent in a pure AC
fluid due to the very short cycle
duration.
• Once water droplets approach one of
the electrode plates, they become
charged with the same high voltage
static charge that is on that plate. In
a pure AC field no net charge is
imparted to water droplets; only the
attraction of polarization is available
to cause coalescence.
Figure 1 NATCO Dual Polarity® Electrostatic Treater
Issue 7
09.02
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Dual Polarity® Electrostatic Treater
DC field forces water droplets into
collision course for faster
coalescence
In an emulsion containing thousands of
water droplets, roughly half will accept
positive charges and the other half,
negative. Particles are electro-kinetically
driven toward the plate of opposite static
charge head-on and coalesce. When they
are large enough, gravity will overcome
the DC field which suspends them
between the plates, and they fall to the
water phase (Figure 4).
conventional treaters. The Dual Polarity®
process creates larger droplets than
conventional AC units. These droplets fall
through the opposing emulsion flow
more easily so more oil can be processed
in a given size vessel. For example, with
32.5º API gravity crude, the throughput
increase with a DP treater is 29%, up
from 70 to 90 as shown in Figure 7. That
means the Dual Polarity® Treater is ideal
for offshore production platforms, housed
arctic operations and for terminals where
large volumes are handled.
Figure 5 Decreased operating temperature
Benefits
Advantages
Lower operating temperatures
mean lower fuel costs
The Dual Polarity® Electrostatic Treater is
designed to operate at temperatures 15ºF
lower than a conventional electrostatic
treater, and up to 60ºF cooler than
ordinary heater treaters. The dual polarity
electrostatics provide for more complete
dehydration. Consequently, it can process
at higher viscosities, which means less
heat is required to lower the viscosity of
the oil at processing conditions. It
provides sizeable savings in fuel costs for
any gravity of crude oil. For example,
with 32.5ºF API gravity crude at 10,000
bopd and 1,000 bwpd, the Dual Polarity®
Treater achieves a 15ºF reduction in
temperature. This produces a savings of
1,156,250 btu/hr. At 60% heat transfer,
this results in a fuel savings of 46,250
scf/day (Figure 5).
Figure 6 Percent loss by volume vs. temperature
Figure 2 Electrode configuration
Figure 7 Increased rates
Figure 3 Electrostatic fields
The Dual Polarity® Electrostatic Treater
may operate at the minimum crude oil
inlet temperature, resulting in additional
fuel savings and eliminating the need for
a heating system in the vessel.
Also reduces volume loss,
produces more oil to sales
The lower operating temperature of the
Dual Polarity® Electrostatic Treater also
results in less vaporization and loss of
light ends from the oil. Using the same
example of 10,000 bopd, the 0.25%
decrease in vapor loss, achieved by the
DP treater, means an increase of 25 bopd
produced (Figure 6).
Increased throughout rates
The Dual Polarity® Electrostatic Treater
requires less space because the vessel can
handle much higher flow rates than
Issue 7
09.02
For more information on NATCO Dual Polarity®
Electrostatic Treater or other NATCO Group
products contact:
NATCO Group Head Office
Houston, USA
Tel:
+(1) 713 683 9292
Email: sales@natco-us.com
Figure 4 Electro-kinetic droplet movement between
DC Electrodes
Benefits
• More crude to sales
• Higher gravity crude to sales
• Lower fuel usage
• Reduced chemical consumption
• Less crude inventoried in the treater
• Products sold, not stored
• Lower BS&W cuts
• Better control of gas Btu content
• Rapid recovery from upsets
• Advanced, yet most reliable
technology available
NATCO Canada
Calgary, Canada
Tel:
+(1) 403 236 1850
Email: sales@natco.ab.ca
Scomi NATCO JV
Kuala Lumpur, Malaysia
Tel:
+(60) 32080 5080
Email: sales@natcosea.com
Axsia Group
Gloucester, England
Tel:
+(44) 1452 833800
Email: asbl@axsia.com
Axsia Howmar
Camberley, England
Tel:
+(44) 1276 681101
Email: ahl@axsia.com
www.natcogroup.com
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