Lecture Slides - Thermal cracking, visbreaking and delayed coking, flexi coking

petroleum refining technology

1. BITSPilani
K K Birla Goa Campus
Thermal cracking, visbreakingand delayed
coking

2. BITS Pilani, K K Birla Goa Campus
•Thermalcracking(orpyrolysis):Dissociationofhigh
molecularweightHCsintosmallerfragmentswiththe
applicationofonlyheat
•Cracking has become reality to meet market demands
•Requirement in all developed and developing countries
•Development of thermal cracking process
•1861 Thermal cracking
•1910 Batch thermal cracking
•1912 –13 Burton cracking
•1914 –22 Continuous cracking process
Thermal cracking -Introduction
02/09/2024
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AMOL DESHPANDE

3. BITS Pilani, K K Birla Goa Campus
•Fragmentation of high molecular weight paraffin components
(starting at 400 C)
•Saturated and unsaturated HCs are produced
•At higher temperatures
•Further cracking occurs
•Ultimate stable and end products are methane, hydrogen and carbon
•Light paraffinstendency for dehydrogenation
•Aromatics, saturated rings
•Chain detachment followed by dehydrogenation
•Extreme conditions ring opens producing hydrogen and carbon
•Thermal cracking operations (Table 5.1)
Reactions
02/09/2024
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AMOL DESHPANDE

4. BITS Pilani, K K Birla Goa Campus
•Free radical mechanism
•Free radicals?
•Reactions
•Initiation (radical production)
•Propagation
•Termination
•Stability of free radicals
•Bond energies (pg345)
Reactions -Theory
02/09/2024
4
AMOL DESHPANDE

5. BITS Pilani, K K Birla Goa Campus
Chemistry of thermal cracking
02/09/2024
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AMOL DESHPANDE

6. BITS Pilani, K K Birla Goa Campus
•Dependsoftheconditionofcracking
•Recyclestocks(productsneedsevereconditionsfor
furthercracking)
•Propertiesaffectedduetocracking
•Kfactordecreases
•B.P.,Pourpointandviscositydecreases
•Unsaturationandaromatizationincreases
•Octanenoincreases
•Sulfurcontentincreases
•Oxidationstabilitydecreases
Properties of cracked products
02/09/2024
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AMOL DESHPANDE

7. BITS Pilani, K K Birla Goa Campus
•Endothermic reaction External heat is required
•Desired products by cracking intermediates
•Important parameters (Pressure, temperature and time)
•Time
−Yield of light fractions is a function of time
−Time of cracking is a function of API gravity of the feed
•Pressure
−With decrease in pressure, gas yield/production increases
−Pressure retards cracking (but minimum 10 –15 kg/cm
2
recommended to
minimize coke formation
•Heat of decomposition and yield of gasoline (relation)
Properties of cracked products
02/09/2024
7
AMOL DESHPANDE

8. BITS Pilani, K K Birla Goa Campus
•Depth or severity of cracking and soaking factor
•Rate of reaction
•First order reaction (cracking per pass < 25%)
•Arrhenius equation to relate rate constant and temperature
•Heat of decomposition
•Based on molecular weight
•Using simple energy balance
•Problems
Properties of cracked products
04-06/09/2024
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AMOL DESHPANDE

9. BITS Pilani, K K Birla Goa Campus
•First stage of thermal cracking
•Leads to reduction in viscosity
•Important and relatively inexpensive bottom of the barrel
upgrading process
•Feed: Heavy crude
•Main products: Fuel oil / furnace oil (90 –95%), naphtha
(2 –3%), gas (1-2%); can be used as feed to catalytic
crackers
•Visbreaking vs Catalytic cracking
Visbreaking
06/09/2024
9
AMOL DESHPANDE

10. BITS Pilani, K K Birla Goa Campus
•Advantages:
•Cheaper device
•Can handle different types of feeds
•Quality of feed is not deterrent for operation
•Operating conditions are flexible
•Relatively easy to install and operate
•Basic parameters
•Cracking temperature
•Residence time
•Feed
•Asphalt, residuum, medium oil, blend of heavies
Visbreaking
06/09/2024
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AMOL DESHPANDE

11. BITS Pilani, K K Birla Goa Campus
•Types
•Coil type visbreaker
•Coil maintained at cracking temperature
•Reaction occurs in the coil in shortest possible time
•High cracking temp., Low residence time (typically 1 –2 min)
•Soaker type visbreaker
•Reaction initiated in the furnace coil and progresses only in a soaker drum
•Low temperature, high residence time (typically 10 -20 min)
•Advantages:
–Lower capital investment (smaller furnace with low ∆P, less waste heat recovery equipment)
–Low fuel consumption
Visbreaking
06/09/2024
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AMOL DESHPANDE

12. BITS Pilani, K K Birla Goa Campus
•Preheater (HE) increases the temperature of the feed to 250 –325 C
•Furnace: Temperature (475 –500 C) reaction occurs
•Quenching (with the
help of heating oils)
reaction stops
•Separation of products
(Separator : Fractionation
n column)
Coil VB -Operation
09/09/2024
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AMOL DESHPANDE

13. BITS Pilani, K K Birla Goa Campus
•Preheater (HE) increases the temperature of the feed to 250 –325 C
•Furnace: Temperature (427 –438 C) reaction initiates
•Soaker drum (residence time of 10 –20 min) reaction progresses
•Quenching (heating oils)
reaction stops
•Separation of products
(Separator : Fractionation
column)
Soaker VB
09/09/2024
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AMOL DESHPANDE

14. BITS Pilani, K K Birla Goa Campus
•Foster wheeler / UOP Coil type visbreakingprocess
•Tervahlprocess (IFP)
•Shell soaker visbreakingprocess
•UOP aqua conversion process
•Hydrovisbreakingtechnology
Visbreaking technologies
09/09/2024
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AMOL DESHPANDE

15. BITS Pilani, K K Birla Goa Campus
•Advantages:
•Capacity to handle less valuable feedstock, considerable reduction of coke
formation
•Operation:
•Coil -I and Coil -II handles heavy and light oil respectively; Coil –II temperature is
higher than Coil –I;
•(3) Reaction chamber (5) Evaporator
•High severity and low recycle ratio results in high octane gasoline (70)
Dubb’sTwo coil cracking process
09/09/2024
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AMOL DESHPANDE

16. BITS Pilani, K K Birla Goa Campus
•Petroleum coke
•Applications
•Raw material for electrodes (Electrochemical / electrometallurgical industries)
•Furnace linings
•Aluminiumindustry
•Coking
•Thermal cracking at high temperatures (> 500 C)
•Feedstock: Heavies not suitable for thermal or catalytic cracking; Aromatics
•Function of gravity , molecular structure, CCR of feed; CDE
•Delayed coking, fluid coking and flexi coking
•Coke yield (wt%) and Gas yield (wt%)
•Effect of sulfur: Sulfur is difficult to remove after coke formation and
especially after calcination.
Coking
09/09/2024
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AMOL DESHPANDE

17. BITS Pilani, K K Birla Goa Campus
•Aromatics and asphaltenesare desirable feedstock
•Coke: Product classification
•Raw Petroleum Coke (RPC)
•Calcination grade
•Fuel grade
•Calcined Petroleum Coke (CPC)
•Pure form of carbon
•Used for making anodes in aluminiumsmelting
•Source of carbon in the steel industries/other chemicals
•Petroleum coke (PetCoke): Can be used as an alternative solid
fuel for coal/lignite. Ash content is much lower in petcokeas
compared to coal/lignite
Coking
09/09/2024
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AMOL DESHPANDE

18. BITS Pilani, K K Birla Goa Campus
•General methods
•Hot oven method (1000 –1200 C operation in oven) –not used
•Thermal cracking (two coil Dubb’smethod) –Evaporators and flash chambers
•Delayed coking
•Fluid coking / Flexi coking
•Contact coking
•Delayed coking
•Mostly used (India –all coking units are delayed coking)
•Capability of cracking all types of feed
•Simplicity of operation
Coking
09/09/2024
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AMOL DESHPANDE

19. BITS Pilani, K K Birla Goa Campus
•Principle
•Heating in furnace (initiate cracking)
•Cracking reactions completed in huge and tall coke drums
•Series of coke drum are used and considered desirable
•Mostly two drums
−1 –Coking (Receiving feed)
−2 –Decoking
•Operating conditions
•Coke yield
−30 % (reduced coke)
−80 % (for tars and pitches)
•Coke content and properties
Delayed coking
09/09/2024
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AMOL DESHPANDE

20. BITS Pilani, K K Birla Goa Campus
•Fractionator (400C)
(Dephlegmator)
•Furnace (upto500 C)
•Coke drums
–Diaupto10 m
–Height upto40 m
•Coking time: 10–18 hrs
•Introduction of steam
at furnace –to avoid
coke formation
Delayed coking -process
09/09/2024
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AMOL DESHPANDE

21. BITS Pilani, K K Birla Goa Campus
•Decoking
–Hydraulic jets (150 –200 atm)
–Mechanical (hammer)
–Chain pulling technique
•Effect of feedstock properties on coke yields
–API gravity (5.10a)
–Recycle Ratio (5.10 c)
–Comparison of Delayed coking / Fluid Coking /Contact Coking
(5.10 b)
Delayed coking -process
09/09/2024
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AMOL DESHPANDE

22. BITS Pilani, K K Birla Goa Campus
•Continuous coking with fluidization
•Cracking and coking –catalyzed by hot coke particles
•Operating conditions
•20% coke formed-
consumed to maintained
coking reaction
•Process
–Reactor/Coker (480 –560 C)
–Burner/Combustor
(590 –650 C)
Fluid coking
11/09/2024
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AMOL DESHPANDE

23. BITS Pilani, K K Birla Goa Campus
•Combination of coking and gasification
•Vacuum residuum
and heavy stocks
treated to produce
sulfur free liquids
and gases (fuel)
•Process
–Reactor
–Fired heater (burner)
–Gasifier
–Fractionator
Flexi coking
11/09/2024
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AMOL DESHPANDE

24. BITS Pilani, K K Birla Goa Campus
•Oil wetted circulating coke particles are allowed to flow
downward in reactor where cracking, coking and drying
take place.
•Coke particles are circulated between reactor and heater
•Pelleted coke, gas, gasoline and gas oil are products
•Advantages
•Handling heavier residuums
•Great flexibility in operation and control
•Coke drum –cleaning is eliminated
Contact coking
11/09/2024
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AMOL DESHPANDE

25. BITS Pilani, K K Birla Goa Campus
•Foster Wheeler (SYNDEC) -Delayed coking
•Kellogg Brown -Delayed coking
•Exxon –Flexi coking
•Exxon –Fluid coking
•ABB Lummus–Delayed coking
•ConocoPhillips –Delayed coking
•Foster Wheeler/UOP–Delayed coking
Commercial coking processes
11/09/2024
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AMOL DESHPANDE

26. BITS Pilani, K K Birla Goa Campus
•Developmentofautomatedcokedrumunheading
devices(allowingtheoperatortocarryoutdecoking
operationsafely)
•Understandingprocessparametersaffectingyields,coker
productqualitiesandcokequalities
•Designandoperationofmajorequipmentitems
(especiallycokedrumsallowingshortercokingcycle)
Technological development in
delayed coking
11/09/2024
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AMOL DESHPANDE