The document discusses desalting, which is the removal of salts from crude oil. It describes the purpose and types of desalters, which are equipment used to remove salts, sediments, and metals from crude. The main types are natural desalters, chemical desalters, and electrochemical desalters. Electrochemical desalters use chemicals and an electric field to break emulsions and cause salt droplets to coalesce and settle. Key parameters that affect desalting include temperature, electric field strength, pressure across the mixing valve, water level, and flow velocity. Maintaining proper operating conditions is important for effective desalting.

1. DESALTER AND DESALTING
ELECTROCHEMICAL DESALTER

2. PAGE 1
Desalting
Removal of salts from crude is called desalting
Desalter
The equipment used for the removal of salts, suspended solids and water soluble trace
metals, iron oxides, sand etc.
Purpose
 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.
 To remove Metals which may poison
Reformer Catalyst
 To achieve more than average Plant Life.
 To obtain high degree of operating flexibility due to slug or high tank bottom
abnormalities.
Crude Salts Chemistry
These salts are mainly chlorides and sulfates of Calcium and Magnesium like NaCl, MgCl2
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.
Types of Desalter
1) Natural Desalter
2) Chemical Desalter
3) Electro Chemical Desalter
Natural Desalter
In natural desalter, 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.
Chemical Desalter
In chemical desalter 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 desalters are useful for crude having low salts or
for Batch Process.
Electro Chemical Desalter
 Desalting process occur by use of chemical along with electric field.
 Demulsifier used as chemical while electrodes connected to step up transformer
used for electric field generation.
 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.

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Components of Electrochemical Desalter
Transformer
 Provide electric filed.
 A.C Current provided to Transformer.
 Helps in emulsion breaking.
Inlet Crude Header
 Cylindrical in shape having caps on both ends without holes in it.
 Holes are random and flow is laminar.
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.
Mud Wash Line
 The line is equipped with nozzles which enhance the velocity head of water
when operated.
 Operated in order to remove sludge.

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Effluent Header
 Having circular holes to drain effluent continually.
 Containing LCV to maintain required water level.
Tricocks
 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.
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 without disturbing water level.
Wash Water
 Components of wash water are fresh water and <50% of recirculation water
which comes from other desalters.
 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.
Quality of Wash Water
 pH 5.5 – 7.5
 Total Hardness <50ppm
 Total CO3
-2
/ HCO3
-1
<50ppm
 Ammonia <100ppm
 Chlorides <2000ppm
 Sulfates <200ppm
 Oxygen <1ppm
Water Injection Points
Before charge pump
 Results maximum contact
 Reduce scale formation of calcium and magnesium in the pre heat train.
Drawbacks
 Pumps capacity reduces.
 Strong emulsion form due to intense shearing agitation of impeller in pump
body.
 pH of water should be highly controlled.

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Down Stream of Charge Pump
 Before FCV.
 No Intense shearing due to impeller.
Drawbacks
 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.
Settling Time
 Water settling follows Stroke’s Law
V = 2r2
g(d-do)/9ɳ
 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.
Control Parameters
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 carryover of salts and water.
 Temperature limit is from 90o
C to 150o
C varying from crude to crude.
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.
 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.
ΔP Across Mixing Valve
Used for max mixing of wash water, demulsifier and crude.
Pressure difference across mixing valve is important varying from few to 60 psi
depending upon:
Nature of Crude
ΔP should be increase with increase in salts
in crude and vice versa.
Operating Temperature
At high operating Temperature ΔP should

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be reduced and vice versa.
Flow Velocity:
ΔP should be reduced when flow velocity is high
and vice versa.
Emulsifying agents presence in crude:
ΔP should be reduced and vice versa.
Rules of Thumb:
 If Emulsion is reported from tri-cock, decrease in
 ΔP will help to normalize the process
 Reduce ΔP when salts are carry over with crude.
 Increase/Decrease ΔP by <5psiwhile maintaining the cuff 6-12 inches thick. If
cuff increased more than 12 inches the ΔP must be lowered. If Cuff decreased
less than 6 inches, ΔP must be increased.
Pressure
 High pressure keeps system from boiling.
 Agitation results from boiling carry over lot of salts.
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 carryover of crude with effluent water.
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.
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 %