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.
Desalting/dehydration
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Free Water Solid Suspended Water Emulsion Water
Desalting/dehydration
• 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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Desalting/dehydration
� 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
Desalting/dehydration
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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
Atmospheric Distillation Unit (ADU)
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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Atmospheric Distillation Unit (ADU)
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.
Atmospheric Distillation Unit (ADU)
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
Atmospheric Distillation Unit (ADU)
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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)
Arrangements of Towers
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)
Arrangements of Towers
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