A desalter is a key component in the distillation process that removes salts and impurities from crude oil. It mixes the oil with a wash water solution, separates water-soluble impurities, and uses an electrostatic field to separate water and impurities from the oil. It improves distillation efficiency and prevents corrosion and fouling.

1. Desalter & Desalting
Prepared By
ECOM Official

2. Desalting
 Removal of salts from crude is called
Desalting

3. Desalter
 The equipment used for the removal of
salts, suspended solids and water
soluble trace metals/slits, iron oxides,
sand, sulfur etc.

4. Purpose
 To reduce salt fouling and plugging of crude oil
fractionators and exchangers.
 To reduce rate of corrosion of crude oil
fractionators.
 To avoid lengthy and expensive plant shut downs.
 To reduce consumption of Neutralizers.

5. Purpose Cont’d
 To remove Metals which may poison
Reformer Catalyst.
 To achieve more then average Plant Life.
 To obtain high degree of operating flexibility
due to slug or high tank bottom
abnormalities.

6. Crude Salt’s Chemistry
 These salts are mainly chlorides and
sulfates of Calcium and Magnesium like
NaCl, MgCl2, CaCl2 and CaCl2.
 Chlorides hydrolyzed to hydrochloric acid
cause severe corrosion.
CaCl2 + H2O → Ca(OH)2 +HCl
 Salts act as catalyst to Plugging of
Exchangers and formation of coke (hot
spots) in heater tubes.
 Salts in residue contain high ash content
causing degradation of product.

7. Crude Salt’s Chemistry Cont’d
 Slats are generally measured in PTB
(parts per thousands barrels).
 Salts concentration in crude depends
upon the Source of Crude.
 Salts are inorganic in nature and are
soluble in water (inorganic) and
insoluble in crude (organic).

8. Types of Desalter
 Natural Desalter
 Chemical Desalter
 Electro Chemical Desalter

9. Natural Desalter
 Desalter in which Settling time is
given to salts, sediments, water and
sludge which under gravity settled
down in the bottom of Vessel and then
drained.
 Example is drainage of sludge and
water from tanks and Settling Vessel
F-2 at Lummus.

10. Chemical Deslater
 Desalter in which chemical is added to the
crude in order to remove salts, sediments,
water and sludge.
 Chemicals reduce the surface tension of
making removal of salts and water easy.
 Both Natural and Chemical Desalter are
useful for crude having low salts or for
Batch Process.

11. Electrochemical Desalter
 Desalting process by use of chemical
along with electric field.
 Demulsifier used as chemical while
electrodes connected to step up
transformer used for electric field
generation.

12. Type of Desalter in ARL
 Settler/Natural Desalter at lummus.
 Electrostatic/electrical Desalter use at
HBU’s
 Electrochemical Desalter use at HCU

13. Process Flow
 Preheated crude, fresh water along
with small amount of chemical
injected to Desalter through mixing
valve to form Emulsion.
 Small water droplets containing salts
converted to form big and heavy drops
through Electric Field (Emulsion
Breaking) and settle in the bottom.

14. Desalter's Hardware

15. Desalter's Hardware
Cont’d

16. Basic Component of Desalter
 Transformer
 Crude Inlet /Outlet Collection Header
 Float Arrangement
 Mud Wash Line
 Effluent Header
 Tri cocks
 Electrodes

17. Transformer
 Provide electric filed.
 A.C Current provided to Transformer.
 Helps in emulsion breaking.
 Setup transfer
Inlet Crude Header
 Cylindrical in shape having caps on
both ends with out holes in it.
 Holes are random and flow is laminar.

18. Float Arrangement
 To keep the required water level in the
Vessel.
 LCV on the effluent drain is connected to
float arrangement.
Outlet Collection Header
 Rectangular in shape having circular holes
in it.

19. Mud Wash Line
 The line is equipped with nozzles
which enhance the velocity head of
water when operated.
 Operated in order to remove sludge.
Effluent Header
 Having circular holes to drain effluent
continually.
 Containing LCV to maintain required
water level.

20. Tri cocks
 Sample points used to check water
level, interface and Crude condition.
Electrodes
 Electrodes are connected to
Transformer.
 Electrodes are in form of bed hanging
in the vessel.
 Bed vibrates when field created
through them.

21. Pressure Safety Valve
 Mechanical Safety of Vessel because
the Desalter operate at high Pressure.
Mixing Valve
 Used to form emulsion of water salts
and crude at the inlet of Desalter.
Cuff Header
 Exist above the effluent header.
 To drain emulsion with out
disturbing water level.

22. Process Variables
 Components of wash water are Fresh water
and <50% of recirculation water (Desalter
effluent).
 Injected to increase the contact b/w water
and Salts because salts are soluble in
water.
 Wash water should not contain any oxygen,
under spec carbonates, bicarbonates and
sulfates.
 pH should be maintained b/w 6 to 8.
Wash Water/Dilution Water

23. Quality of Wash Water
pH 5.5 – 7.5
Total Hardness <50ppm
Total CO3
-1/ HCO3-2 <50ppm
Ammonia <100ppm
Chlorides <2000ppm
Sulfates <200ppm
Oxygen <1ppm

24. Water Injection Points
Before charge pump
 Results maximum contact
 Reduce scale formation of calcium and magnesium
in the pre heat train.
Draw Backs
 Pumps capacity reduces.
 Strong emulsion form due to intense shearing
agitation of impeller in pump body.
 pH of water should be highly controlled.

25. Water Injection Point
Diagram

26. Down Stream of Charge Pump
 Before FCV.
 No Intense shearing due to impeller.
Braw Backs
 Emulsion formation
 Scales formation in the Pre heat train
Upstream of Mixing Valve
 Controlled mixing and emulsion
formation.
 No Scaling in the pre heat train.

27. Settling Time
 Water settling follows Stroke’s Law
V = 2r2g(d-do)/9η
 Settling Time
T α (1/ size of droplet)
 Droplet size should be >50 micron.
 Droplet Size increased through mixing
valve.
 Min. settling time is 20 to 30 minutes.

28. Temperature
 Decrease in temperature increase the
viscosity making settling of salts and water
difficult and vice versa.
T α (1/ Viscosity)
 High Desalter Temperature cause increase in
solubility of water, formation of tight
emulsion and carry over of Salts and Water.
 Temperate limit is from 90oC to 150oC
varying from crude to crude.

29. Demulsifying Agents
 These are Chemicals
used for breakage of
emulsion.
Types of Emulsion
Water/Oil Emulsion
(Refinery)
Micro size droplets of
water are surrounded
by oil.
Oil/Water Emulsion
 Micro size droplets of
Oil is surrounded by
Water.
Wate
r
Crude Oil
Crude
Oil
Water

30. Demulsifying Agents Cont’d
 Demulsifier weaken the oil layer
around water to coalesce with other
droplets.
 In some cases changes the polarity
and so the droplets attract each other
to coalesced.
 Excess demulsifying agent effects
adversely.

32. Demulsifing agent working

33. Types of Desalting chemicals
 Soap : migrates to interface and weaken
interfacial films.
 Polar : Migrates to interface and alter
polarity, so particles will coalesce.
 H2O Soluble : Acts as Soap or Polar but
remain in water phase
 Ionic : Increase Electric conductivity, which
increase tendency to demulsify.

34. Electric Field
 High voltage Electric
field is provided to
break Emulsion.
 Alternating electric
field is provided.
 Step up Transformer is
used to provide high
voltage of 10 to 18KV
depending upon the
salts in crude.

35. Electric Field cont’d
 Electric field break the
emulsion layer formed
across water and so
water coalesce to form
large droplets which
settled under gravity.
 Vibration of water
droplets occur due to
A.C
 High voltage electric
field will be provided
when salts in crude are
low and vice versa.

36. ∆P across Mixing Valve
 Used for max mixing of wash water,
Demulsifier and crude.
 Pressure difference across mixing valve is
important varying from few to60 psi
depending upon:
Nature of Crude
 ∆P should be increase with increase in salts
in crude and vice versa.
Operating Temperature
 At high operating Temperature ∆P should
be reduced and vice versa.

37. Flow Velocity:
 ∆P should be reduced when flow velocity is high
and vice versa.
Emulsifying agents presence in crude:
 ∆P should be reduced and vice versa.
Rules of Thumb:
 If Emulsion is reported from tri-cock, decrease in
∆P will help to normalize the process
 Reduce ∆P when salts are carry over with crude.
 Increase/Decrease ∆P by <5psiwhile maintaining
the cuff 6-12 inches thick. If cuff increased more
then 12 inches the ∆P must be lowered. If Cuff
decreased less then 6 inches, ∆P must be
increased.
∆P across Mixing Valve cont’d

38. Pressure
 High pressure keeps system from
boiling.
 Agitation results from boiling carry
over lot of BS&W.
 Recommended pressure 50-250psi.

39. Level
 Operating level of water must be
maintained below lover electrode.
 Conductivity of water cause electric current
flow and could shut down the electric
system.
 If level is allowed to raise it will carry over
the interface with crude to the tower
causing tower upset and exchangers fouling
as well.
 Low level cause carry over of crude with
effluent water.

40. Desalting problems
 Under design Desalter for current crude oil
and through put.
 Insufficient attention by operating person
 Improper operating conditions.
 Improper chemical dosage.
 Inadequate water wash supply , rate and
quality.

41. Desalting Efficiency
 Desalter efficiency can be calculated
as:
SE = (Si – So ) * 100 / Si
Where:
SE salt removal efficiency (%)
Si salt content of raw crude oil (ptb)
So salt content of desalted oil (ptb).
Ptb stands for Pounds per Thousand Barrels
Desalter efficiency should be 90-95 %

42. Trouble shooting
A high salt content in the
desalted crude oil
• Feed salt content high
• Increase the wash
• water rate
Wash water injection low
• Reduce the crude oil
• From
• Crude oil flow rate
exceeds the design
flow rate
• Increase the mix
value pressure drop
• Insufficient mixing of
the crude oil and wash
water

43. Trouble shooting
Oil in the desalter effluent
water
• "Interface" level too low
• Increase the interface
• Level
• Wide emulsion band at
the "interface"
• Inject a chemical or
dump the emulsion
• Excessive crude oil
wash water mixing
• Reduce the mix valve
pressure drop
Poor wash water quality • Check for any waste
in the wash water
source

44. Trouble shooting
High water carry over in
desalted crude oil
Crude temperature too low
Wash water flow rate too
high
• Reduce the wash
water flow rate and
commence
or increase chemical
Injection
• Excessive formation
water in the crude oil
• Reduce the interface
level and check the
effluent water valve

45. Thanks