Petroleum Fraction

1. Syed Nawaz
Petroleum Engineering 3rd Year,
Al Habeeb College of Engineering and Technology

2. Unit# 3
 Fractionation of Petroleum
 Dehydration and desalting of crudes
 Heating of crude- Pipe still heaters
 Distillation of Petroleum
 Blending of Gasolines

3. Dehydration and desalting of crudes
 All crudes contain moisture and salts to varying
degrees
 No harm to the distillation because of moisture as
there is always steam inside.
 Dehydration is due to remove salts in Crude oil
 Water being good solvent for these salts, removal is
must effective in the form of brine.
 These salts hydrolyze in presence of steam at 150-200
degC and forms HCl vapors, which cause corrosion to
the equipment.

4. Why dehydration of crude?
 Any crude that contains more than 5Kgs of total salts
expressed in terms of NaCl per 1000 barrels regarded
as Salty Crude.
 Dehydration removes all the salts.
 Dehydration is practiced in two stages
 At the site of the mine
 Later in the refinery

5. Methods for dehydration of
crude oil
 1. Chemical Treatment
 2. Gravity Settling
 3. Centrifugal Separation
 4. Electric desalter

6. Process Conditions in
treatment of crudes

7. Chemical Treatment
 Salts are removed by settling or by adding chemicals or
by combination of these two.
 Soda ash, sodium hydroxide, salts of fatty acids,
petroleum sulfonates are the chemicals which hasten
the agglomeration of water droplets
 After adding the chemicals, the crude mixture allowed
to stand at 75-80 degC and at a pressure of 15 Kgf/cm2
 When it is allowed to stand for 48 hrs, good separation
into hydrocarbon and aqueous phase.

8. Gravity Settling
 Free water in the system,
will settle to the bottom.
 The time it takes to the
water to separate will
depend on temp, oil
type.
 Any oils holding water in
suspension rather than
to allow it separate out,
then gravity effect
inefficient and time
consuming

9. Centrifugal Separation
 Not economical due to
huge energy
requirement.
 Only less quantity can be
handled
 So all these have given
way to electric desalting.

10. Desalting techniques

11. Electric Desalting
 Simultaneous desalting and dehydration is achieved
with removal of more than 90% of salt in less than half
an hour.
 A potential of 20,000 to 30,000 volts is applied
between electrodes thru which crude is passed.
 Water agglomerates into a stream entrapping all the
salts.
 Brine collects at the bottom of the desalter, while
crude floats above and form a separate stream.
 Advantages: Compact, efficient and easy to operate

12. Electric Desalting contd…
 Temp is maintained at 90 Deg C and a pressure of 5 to
6 Kgf/cm2 and power consumption is very small, in
the order of 0.01 KWHr per barrel.
 Catalyst poisoning salts can also be removed

13. Pumping of waxy crudes
 An imp factor that stands in the way of pumping crude
is its pour point. Pour point is directly related to the
wax content of oil.
 Indian crudes are waxy and hence high pour point.
 East crudes have low pour point.
 It is seen that viscosity near the pour point abruptly
shoots up, adding to the difficulties of pumping.
 Such crudes can be transported only after
conditioning.

14. Diluent Addition
 Chemical additives which can depress the pour points.
These additives can change the structure of wax and
retard the crystal growth.
 Modification of structure reduces the viscosity
 Small amounts can depress the pour point by 10 to 16
degC.
 After adding the additives, crude needs to be stabilized
for 40 to 60 hrs and the crude will be ready for
transportation to refinery.

15. Atmospheric distillation Unit
(ADU)

16. ADU Contd….

17. Chemical Reaction in Cracking

18. ADU --2

19. Vacuum Distillation Unit

20. Flow pattern

21. Trays