1. Treatment of Produced Fluids:
Crude Oil and Water:
Desalting of Crude Oil
By Pn Khairunissa Syairah
Credit to Pn Azduwin

2. INTRODUCTION • The removal of salt from crude oil for refinery
feed stocks has been and still is a mandatory
step.
• This is particularly true if the salt content exceeds
20 PTB (pounds of salt, expressed as equivalent
sodium chloride, per thousand barrels of oil).
• The remnant brine is that part of the salty water
that cannot be further reduced by any of the
dehydration methods.
• It is commonly reported as basic sediments and
water (B.S.&W.).

3. REMNANT BRINE • This remnant water exists in the crude oil as a
dispersion of very fine droplets highly
emulsified in the bulk of oil.
• The mineral salts of this brine consist mainly
of chlorides of sodium, calcium and
magnesium.

4. • The amount of salt in the crude oil is a
function of the amount of the brine that
remains in the oil, WR (% B.S.&W.) and of its
salinity, SR in parts per million (ppm);
γBrine = the density of the saline water
SG=Spesific gravity

6. RELATIONSHIP AMONG VOLUME OF REMNANT
WATER, ITS SALINITY AND SALT CONTENT
• Taking one-tenth of 1% by volume of water to
remain in the crude as a basis for our
calculation, the relationship between the salt
content of the remnant water expressed in
pounds of salt per thousand barrels of oil (PTB)
and its concentration or salinity expressed in
ppm is presented graphically in Figure 1.
• For other volumes, simple multiples of the
numbers given by this graph are used.

7. FIGURE 1 oil (PTB) as a function of salinity of its remnantwater 0.1%
Salt content of crude
oil (PTB) as a function
of salinity of its
remnantwater 0.1%
(1/1000) by volume
remnant water.

8. Solutions [Sodium Chloride (NaCl)]
Densities of Aqueous Inorganic
Solutions [Sodium Chloride (NaCl)]
Unit = g/cm3

9. EXAMPLE 1 • Find the PTB of a crude oil having 10% by
volume remnant water if its concentration is
estimated to be 40,000 ppm at 25°C.

10. EXAMPLE 2 Assuming that the water salinity is 40,000 ppm
instead of 20,000 ppm and dehydration is done
to two-tenths of 1%. Calculate the PTB of the oil.

11. DESALTING PROCESS • Single-stage desalting system
• A two-stage desalting system

12. Single-stage desalting system
Wash water, also
called dilution water,
is mixed with the
crude oil
The mixing results in
the formation of water–
oil emulsion. The oil
(and emulsion) is then
dehydrated.
The separated water is
disposed of through the
field-produced water
treatment and disposal
system.

13. Two-stage desalting system
In the two-stage
desalting system,
dilution water is added
in the second stage
The disposed water in the
second stage is recycled and
used as the
dilution water for the first
stage.
Two-stage desalting
systems are normally
used to minimize the
wash water
requirements.

14. Mixing device • The usual mixing device is simply a throttling valve.
• A useful device for such a
purpose is the application of
multiple-orifice-plate mixers
(MOMs)
• Accomplished by pumping
the crude oil (which is the
continuous phase) and wash
water (which is the dispersed
phase) separately through a
mixing device.

15.  The chemical desalting process involves adding chemical agents
and wash water to the preheated oil followed by settling.
 The settling time varies from a few minutes to 2 h.
 Some of the commonly used chemical agents are sulfonates,
long-chain alcohols, and fatty acids.

16. ELECTROSTATIC DESALTING
• An external electric field is applied to coalesce the
small water droplets and thus promote settling of the
water droplets out of the oil.

17. Chemelectric Desalting System
The chemielectric concept utilizing both chemical
agents and electrical field

18. DETERMINING DILUTION WATER REQUIREMENT
• The amount of water of dilution WD added in the desalting
of crude oils is in the range of 5–10% by volume, based on
the amount of remnant water and its salinity.
WR, SR, SD :(salinity of the dilution water)
E: The efficiency of mixing between the two phases.
SD and SR are in parts per million
To set the acceptable limits on the salt content in crude oil;
SB refers to some average salinity in the
bulk of the homogeneous phase as a
result of mixing the remnant water with
the fresh water

19. EFFECT OF OPERATING PARAMETERS
The efficiency of desalting is dependent on the following
parameters ;
1. Water–crude interface level. This level should be kept constant; any
changes will change electrical field and perturbs electrical
coalescence.
2. Desalting temperature. Temperature affects water droplet settling through
its effect on oil viscosity; therefore, heavier crude oils require higher desalting
temperatures.
3. Wash water ratio. Heavy crudes require a high wash water ratio to increase
electrical coalescence. A high wash ratio acts similarly to raise temperatures,
as illustrated in Table 4.

20. EFFECT OF OPERATING PARAMETERS
4. Pressure drop in the mixing valve. A high-pressure-
drop operation results in the formation of a fine stable
emulsion and better washing. However, if the pressure
drop is excessive, the emulsion might be difficult to
break. The optimum pressure drop is 1.5 bar for light
crudes and 0.5 bar for heavy crudes.
5. Type of demulsifiers. Demulsifiers are added to aid in
complete electrostatic coalescence and desalting. They
are quite important when heavy crudes are handled.
Levels ranging between 3 and 10 ppm of the crude are
used.

21. Problems, Causes, and Solutions

22. Problems, Causes, and Solutions

23. DESIGN CONSIDERATION
The following major parameters are considered when
designing the desalting system:
1. Flow scheme arrangements (conventional one-stage or
countercurrent
contact desalters)
2. Number of desalting stages
3. Dehydration levels achieved
4. Salinity of the brine in the crude
5. Efficiency of valve mixing
6. Salinity of dilution water
7. Target PTB specification

24. Calculation Methods
Single-stage Desalting System

25. • Basic equations for calculating required dilution
water are as follows

27. Calculation Methods
Two-stage Desalting System

30. CLASS EXERCISE
An oil field produces 200,000 bbl/day of net oil with a salt
content of 10 PTB. The oil out of the emulsion treater contains
0.3% water (salinity=250,000 ppm and specific gravity=1.07). In
the desalting– dehydration process, the oil is mixed with dilution
water (3000 ppm salinity and 1.02 specific gravity) and
dehydrated down to 0.1% BS&W. Assuming that the mixing
efficiency is 80%, determine the following:
(a) The salt content in PTB of the oil out of the emulsion treater
(b) The amount of dilution water required (in bbl/day)

31. THE END