Thermal conversion processes such as thermal cracking, visbreaking, coking, and coke calcination are used to convert heavy hydrocarbon fractions into more valuable products. Thermal cracking involves heating heavy hydrocarbons to high temperatures to crack long molecules into shorter ones. Visbreaking is a mild thermal cracking that reduces the viscosity of heavy residues. Coking uses heat to crack heavy residues into lighter fractions and petroleum coke in large drums. Coke calcination further processes petroleum coke by removing volatiles in a rotary kiln to increase the carbon ratio for uses such as anodes.

2. SECONDARY PROCESSING :
Thermal conversion process
•
•
•
•
T H E R M A L C O N V E R S I O N
P R O C E S S E S
Thermal Cracking
Visbreaking
Coking
Coke Calcination

3. GROUP MEMBERS
A.S.V.PARTHASARATHI 20011A0801
A.KEERTHI SAI 20011A0802
ASIYA ANJUM 20011A0803
A.SUSHMA 20011A0804
B.ANUSHA 20011A0805
B.ARTHIK 20011A0807

4. • THERMAL CRACKING
➢The processes is which hydrocarbons are decomposed
at elevated temperatures to from material of lower Mol. wt.
are called thermal conversion process. Any fraction of the
crude from Naphtha to Vac. Residue – can be processed
thermally.
➢The most important types of thermal conversion process
are thermal cracking, visbreaking and coking.
➢Thermal cracking is used for conversion of residues and
higher Mol. wt. hydrocarbons into more useful products by
cracking the large hydrocarbon molecules into smaller ones
at a temp. level of 4500 – 5000C.
➢Cracking activity varies with the type of hydrocarbons
and decrease in the following order:
n–paraffin > Isoparaffins > cycloparaffins > aromatics >
aromatics / naphthenics > polynuclear aromatics.
➢ Olefins crack to smaller olefins and di-olefins

5. ➢ Important variables in thermal cracking are Temp.;
pressure and residence time.
➢Cracking reactions begin to occur at Temp. of 315 – 3700C.
Pressure determines the phase in which the cracking
reactions take place. Thermal cracking conversion increases
with temp. and residence time.
➢Under very severe thermal cracking conditions, there is
tendency for coke formation.
Cracking also generates double bonded hydrocarbons
(olefins). Side reactions like condensation and polymerization
reactions also occur leading to gum formation and tar-like
polymerization products. (To avoid this, gasoline or diesel
blend produced from thermal cracking process are
hydrotreated to make them stable usable product).
Since products of thermal cracking have very poor stability
and require further treatment ; Fluid catalytic cracking FCC
finds more favors with refiners.

6. • Simplified Thermal Cracking Process :
➢Simple Thermal cracking process produces gas,
naphtha, middle distillates and thermal tar from almost
all variety of charge stocks from distillates to the
heaviest crude and residual oils.
➢The feed is heated to cracking temp. 4500 – 5000C
and the cracked products containing gas and Full
Boiling Range distillates enters the fractionators after
passing through an intermediates separator vessel.

7. Long
Residue
Short
Residue
Furnace
Furnace
Furnace
Cracked
Residue
Cyclone
Gas+ gasoline
Gas oil
Heavy Distillate
+ Recycle
Cracked Residue
Gas+ Gasoline
Gas Oil
F
R
A
C
T
I
O
N
A
T
O
R
F
R
A
C
T
I
O
N
A
T
O
R
Cracked Residue
Thermal cracking process

8. ➢TYPICAL operating conditions and The Yield Patterns in The
SHELL process for Long Residue (Atmospheric Distillation column
bottoms) and Short Residue (Vacuum Distillation column bottoms)
are :
Cracking temperature, 0C 450 – 500
Furnace outlet pressure, kgf/cm2
4
20
(a) For residue
(b) For heavy residue
Typical Yield Pattern
Products
The yield of fractions in the Shell process for long residue and short
residue
Yield, wt. % on feed
Long residue
(Two furnace operation)
Short residue
(One furnace operation)
2
4
12
C1 – C4
C5 – 1650C
165 – 3500C
4
8.5
23.5

9. • VISBREAKING
➢Visbreaking – an abbreviation for viscosity breaking or
viscosity lowering – is a liquid phase thermal conversion
process to reduce the viscosity of Atmospheric (long
residue) and Vacuum (short residue) to produce
specification fuel oil.
Small quantities of LPG and a fair amount of naphtha are
also produced.
➢Visbreaking is a mild thermal cracking process and
help in reducing the viscosities and pour point of long
and short residues. Refinery production of heavy oils can
be reduced by 30% using visbreaking. Visbreaking also
produces gas, gas oil stock and gasoline which go for
further processing.

10. ➢The principal reaction which occur during The Visbreaking are :
Cracking of the side chains attached to cycloparaffins and
aromatic rings.
Cracking of resins to light hydrocarbons (primarily olefins)
Some cracking of naphthene rings under higher temp.
of operations (5000C)
➢ 2. types of Visbreaking operations :
Conventional Visbreaking (Furnace or coil cracking)
Soaker Visbreaking
➢ Conventional Visbreaking :
Also known as coil cracking, the process uses Furnace
outlet temp. of 475-5000C and reaction time from one to three
minutes. This process produces minimum of Naphtha and a
maximum of fuel oil from long and short residues and other
heavier feed stocks.
Gas, Naphtha and light gas oils are recovered from the top
section of the fractionators. Gas and Naphtha can be further
processed in a gas concentration unit for the recovery of LPG.

11. Coil Visbreaker
Reduced
Crude
Charge
Tar
Gas Oil
Gasoline
Steam
Gas
Heater

12. ➢ Typical operating condition
Operating parameter
Equipment
Furnace
3400C
470 – 4900C
22
15
10
260
Furnace inlet temp. 0C
Furnace outlet temp. 0C
Furnace inlet pres; kg/cm 2
Furnace outlet pres; kg/cm 2
Residence time ; minutes
Quench temp; 0C
Columns
Fractionate
138
360
5.5
-
Stabilizer
50
160
8.5
100
Top temp. 0C
Bottom temp 0C
Pressure kg/cm 2
Feed temp. 0C
Flash zone temp. 0C 395 -

13. ➢Typical yield pattern
Gas plus loss 3
Naphtha
Fuel oil (Visbroken
residue)
4
93*
*If diesel production is to be maximized, a second
cracking furnace is added to the stream and the heavy
fraction boiling between 350 – 5000C, obtained by distilling
the visboken residue under vacuum is recycled to second
furnace for further cracking.
➢Run lengths of 3 – 6 minutes are common for coil
visbreakers.

14. ➢ Visbreaking is an effective and cost – effective
way to produce more valuable products from heavy
residues. Earlier, it used to reduce the viscosity and/
or pour point of a fuel oil but now it is employed to
obtain Cat. Cracker feed and to reduce fuel oil
production.

15. • Soaker Visbreaking :
➢In this process a soaker drum is added between the
furnace and the fractionator. This drum provide large
residence time for the feedstock. The cracking reactions
take place in soaking drum. Since higher residence time
allows improved conversion at lower temps. ; Soaker
Visbreaking Technology is more energy efficient and
provides higher run lengths as coking reactions in the
furnace coil are significantly reduced. Run lengths to 6-18
months for Soaker Visbreaker.
➢Other advantages of Soaker Visbreaking are :
Lower capital cost (10/15% lower)
Smaller furnace ; less waste Heat Recovery equipment
Less pressure drop through furnace
▪
▪
▪
▪
▪
Lower fuel consumption (15% less fuel : 0.2% on feed)
Better and more selective yields.

16. Soaker Visbreaker
Tar
Gas Oil
Naphtha
Steam
Gas
Heater
Residual
Stock
Steam
Soaker
Drum

17. ➢ Typical operating condition
Operating parameter
Equipment
Soaker Drum
5 – 15 bar (g)
4400C
Pre.
Temp.
Vapour Cracking
Liquid Cracking
Run length
minimum
Yes
300 days
Yield Pattern
Product
Gas
Naphtha (80-2000C)
Light gas oil (200-3500C)
Heavy gas oil (350-5200C)
Residue (5200C+)
Yield; % of feed
1.7
3.1
13.2
27.0
55.0

18. • COKING
➢Coking is the most widely practiced means of reducing
the C – H ratio of residual oils, Of the 2 main process –
delayed coking and fluid coking – more than 90% capacity is
in delayed coking units.
➢Delayed coking is a thermal cracking process in which a
hydrocarbon feedstock, mainly residue is converted to lighter
and more valuable products and coke.
➢Main advantage of the process is that it can take residual
stocks from a wide variety of process unit in a Refinery
Coking Furnace and the coke drums are the key elements in
the process. Cracking is initiated in the furnace tubes where
short residence time is allowed. Coking of the feed material
is delayed until it reaches large coking drums with larger
retention time; downstream of the coking heater.
➢Three types of coke structures can be produced shot,
sponge or needle coke.

19. Accumulator
Fractionator
Naphtha
Gas
P/A
Steam Stripper
Steam
Light gas oil
Steam
Heavy
gas oil
Steam Gen.
Feed
Condensate
Drum
Coke
Heater
Decoking
Waterjet
Delayed Coking
Coke Drum

20. ➢ Process Description
•Delayed coking is a semi continuous process in which
the heated charge is transferred to large coking drums
which allow the long residence time needed to allow the
cracking reactions to proceed to completion feed to
these units is normally heavy atmospheric residues,
although heavy catalytic cycle oils and cracked tars may
also be used.
•Feedstock gets pre heated by exchange of heat from
outgoing products and is partially vaporized in a specially
designed coking furnace. Mild cracking takes place in
the furnace where thermal cracking temps; of 4850 to
5050C are reached.

21. • From the furnace, the liquid-vapor mixture goes to the
coking drum (operating in batch-1 coking, the other
decoking). The vapors under-go cracking as they pass
through the coke drum.
•The cracked products go to fractionate where cracked
gas, Naphtha, Kerosene and gas oils are separated. The
petroleum coke is formed in the drum due to high
residence time of cracking in the drum.
• The feed stream is regularly switched between the
operating drum and drum under decoking. Decoking is
done using high pressure water jets. This generally fallows
a 12-16 hr. cycle.

22. ➢ decoking operation
Following procedure is used to remove the coke :
(i) The coke deposit is cooled with water.
(ii)One of the heads of the coking drums is removed
to permit the drilling of a hole through centre of the
deposit.
(iii)A hydraulic cutting device, which uses multiple
high pressure water jets, is inserted into the hole and
the wet coke is removed from the drum.
(iv)After the removal of coke from the coke drum, it is
flushed with water and is readied for reuse.

23. • Typical operating conditions
Furnace outlet temp.
Coke Drum Pressure
Fractionator top temp.
Fractionator Bottom temp.
Fractionator Pres.
4800 – 5150C
1.7 Kg/cm2g
1500C
3500C
1.4 – 3.4 Bar
Typical yield from delayed coker
Feed
0 API 7.4 12.0 12.5
Sulfur wt% 2.76 1.6 0.6
CCR wt % 19.6 9.6 14.8
Yields
Gases 13.2 12.0 6.4
Naphtha 11.1 15.7 21.6
Light gas oil 31.4 35.2 46.0
Heavy gas oil - 15.5 -
Coke 44.3 21.6 26.0
Sulfur in coke wt% 0.57 1.2 2.2

24. • Fluid Coking
➢Fluid coking is a continuous process that uses the
fluidized solids technique to convert residue including
vacuum pitches to more valuable products.
➢Fluid coking uses 2 vessels – a Reactor and a
Burner. Both the reactor vessel and the burner vessel
contain fluidized beds with coke particles circulating
between the two vessel by fluidized solids technique.
Coke particles are circulated to transfer heat to the
reactor. The residuum is cooled by distributing it as a
thin film of liquid on the outside of the hot-coke
particles.
➢The vapor products pass through cyclones that
remove most of the entrained coke.

26. • COKE CALCINATION PROCESS
➢ Petroleum coke is produced as delayed sponge
coke, delayed needle coke, fluid coke.
➢Calcination of raw petroleum coke (green coke) is
needed to transform it into useable material.
➢Calcined coke is mostly used by the Aluminum
Industry in the manufacture of anodes for Alumina
Reduction, Calcined needle coke is used to
manufacture. Graphite products and prebaked graphite
electrodes for use in electro – metallurgical furnaces.
• Process Description
Calcination of green coke is essentially a high
treatment involving drying,devolatilization
temp.
and
dehydrogenation by which the C/H ratio of the feed is
increased from about 20 to 1000. It may be carried out in a
rotary kiln.

27. To Stock
Steam
Green Coke
Fuel Gas
Rotary Cooler
Calcined
coke
Rotary Kiln
Coke Fines
Incinerator
&
Boiler
Coke calcination process

28. Ref:
http://www.setlaboratories.com/therm/tabid/107/default.aspx
http://en.wikipedia.org/wiki/Cracking_(chemistry)
Book:
Title:
Elements of Fuel, Furnaces and Refractories
Author:
O.P. Gupta

29. THANK YOU