Crude Oil Processing

Chapter 3-Processing Operations

in a Refinery

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in a Refinery

Refinery Section� Crude oil transferred from Drilling site to Refinery

section, where Crude oil is completely analyzed.

� Crude Oil stored in a Floating roof tank to avoid loss of

vapors of dissolved gases.

� After the quantity and valuation of oil are established,

water in the tank must be drained.

Desalting/dehydration

• Crude oil often contains water, inorganic salts,

suspended solids, and water-soluble trace metals.

• Step 1 in the refining process is to remove these

contaminants so as to reduce corrosion, plugging, and

fouling of equipment and to prevent poisoning

catalysts in processing units.

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catalysts in processing units.

• The two most typical methods of crude-oil desalting

are chemical and electrostatic separation, and both

use hot water as the extraction agent.


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Free Water Solid Suspended Water Emulsion Water


• In chemical desalting, water and chemical surfactant (demulsifierslike Soda ash, NaOH) are added to the crude, which is heated so that salts and other impurities dissolve or attach to the water, then held in a tank to settle out.

Time : 48-50 hrs ,General Tank capacity : 3000 k Lit

Temperature : 75-80 C , High P : 6-8 Kg/cm2

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� Electrical desalting is the application of high-voltage electrostatic charges (20-33 kV AC) to concentrate suspended water globules in the bottom of the settling tank. Surfactants are added only when the crude has a large amount of suspended solids.

� Temp : 120-130 C

� DM water is added to dissolve the salt

� pH monitored nearly 7 (to monitor acid formation due to

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� pH monitored nearly 7 (to monitor acid formation due to chloride salts)

� Drum Pressure is monitored to avoid cavitation in discharge pump. Pressure maintained at 8-10 kg/cm2

� Interface level transmitter

• Automatically switch off if water level is high

• Low level carryover of crude oil with brine to drain


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Desalting/dehydration-unit

CHEE 2404: Industrial Chemistry 8

Atmospheric Distillation Unit (ADU)

190-200 C

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140-270 C

270-340 C

340-365 C

280-300 C

300-330 C

365 C

4-5% of Feed


The main column typically 50 m H and with 45-50

valve trays or Bubble cap(old refinery)

The vapour goes up in tremendous amount and at

high flow rate, large Diamter column above the flash

zone.

The bottom stripping steam(Superheated) is used

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The bottom stripping steam(Superheated) is used

to recover the light components from bottom liquid.

Stripping section contains 4-6 plates at bottom.

Overflash

Helps in removal of heavier components carried

over the lighter stream (bottom side stream.

Atmospheric Distillation Unit (ADU)-Preflash

If crude contains very high% of light ends, a flash

drum or prefractionator with condensing system is

added ahead of ADU.

The P required to suppress the vaporisation is too

high

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Gap : Difference between 5% Boiling

point of heavy fraction and 95% boiling

point preceding cut

When difference is positive , good

fractionation.

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fractionation.

Overlap

The negative called Overlap indicating

some light product is still in the heavier

product and vice versa.


Side Stripper

By using superheated steam , side stripper column

(4-6 plates) low boiling Hydrocarbon are stripped

out to improve the flash point of the product to the

requirement.

Improve the Gap

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Improve the Gap


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1. Buildup of vapor –

need large diameter

2. Quality of fraction

3. Economic utilization of

Top reflux (Type U)

Arrangements of Towers

3. Economic utilization of

heat is not possible

4. Simple design and

operation

1. Reflux from lower plate , cooled and feed into the column at higher section by 2 to 3 plates

2. This creates local problem of

Pump around reflux (Type A)


2. This creates local problem of uneven composition mixing of reflux and liquids present on the tray

3. More h and no of plates4. Loss of theoretical stage

Pump back reflux (Type A)


1. Reflux at regular interval, good amount of liquid in column

2. The tower is uniformly 2. The tower is uniformly loaded.

3. Design and operating cost is high.

4. Excellent service and product quality.

Pre-heating Trains

VDU

VDU

VDU

Documents

Crude Oil Processing