2. Removal of salts from crude is called
Desalting
3. The equipment used for the removal of salts,
suspended solids and water soluble trace
metals/slits, iron oxides, sand etc.
4. To reduce fouling and plugging of crude oil
fractionators and exchangers due to salt
deposition.
To reduce rate of corrosion of crude oil
fractionators.
To avoid lengthy and expensive plant shut downs.
To reduce consumption of Neutralizers.
5. 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. These salts are mainly chlorides and sulfates of
Calcium and Magnesium like NaCl, MgCl2, CaCl2
and MgCl2.
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. 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).
9. 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. Desalter in which chemical is added to the crude
in order to remove salts, sediments, water and
sludge.
Chemicals reduce the surface tension for making
removal of salts and water easy.
Both Natural and Chemical Desalter are useful for
crude having low salts or for Batch Process.
11. 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. 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.
13.
14. Provide electric filed.
A.C Current provided to Transformer.
Helps in emulsion breaking.
Cylindrical in shape having caps on both ends with
out holes in it.
Holes are random and flow is laminar.
15. To keep the required water level in the Vessel.
LCV on the effluent drain is connected to float
arrangement.
Rectangular in shape having circular holes in it.
16. The line is equipped with nozzles which enhance
the velocity head of water when operated.
Operated in order to remove sludge.
Having circular holes to drain effluent continually.
Containing LCV to maintain required water level.
17. Sample points used to check water level, interface
and Crude condition.
Electrodes are connected to Transformer.
Electrodes are in form of bed hanging in the vessel.
Bed vibrates when field created through them.
18. Mechanical Safety of Vessel because the
Desalter operate at high Pressure.
Used to form emulsion of water salts and crude at
the inlet of Desalter.
Exist above the effluent header.
To drain emulsion with out disturbing water level.
19. Components of wash water are Fresh water and
<50% of recirculation water.
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
21. 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.
22. 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.
23. Water settling follows Stroke’s Law
V = 2r2
g(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.
24. 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 90o
C to 150o
C varying
from crude to crude.
25. 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
26. 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.
27. 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.
28. 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.
29. 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.
30. 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.
31. 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.
32. High pressure keeps system from boiling.
Agitation results from boiling carry over lot of
BS&W.
33. 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.
34. 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.
35. 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 %
