Department Of Chemical Engineering
Academic Session 2022-23
Sixth Semester
Subject – Petroleum Refining
(CHT-304)
Topic:-
Visbreaking
Submitted To :- Dr. Shiv Om Meena (Assistant Professor, MNIT Jaipur)
Submitted By :- Piyush Beniwal(2020UCH1355)
Harshwardhan Bhaskar Parade Patil (2020UCH1351)
❏ Content
❖ Introduction
❖ Process Description
❖ Classification
■ Coil Visbreaking
■ Soaker Visbreaking
❖ Advantages of visbreaking
❖ Disadvantages of visbreaking
❖ Conclusion
❏
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Introduction
A visbreaking is a processing unit in oil refinery.
It converts atmospheric or vacuum residues via thermal cracking to gas, naphtha, distillates and
visbroken residues.
❏ Process Description
● The process
name of visbreaker refers to the fact that the process reduces i.e. breaks
the viscosity of the residual oil.
●The process
is mild form of thermal cracking that significantly lowers the viscosity of
heavy crude oil without affecting the boiling point.
●The process
is non-catalytic.
Vacuum residue fed to a visbreaker can be considered to be composed of the
following :
❏
Coil Visbreaking
●Units in which cracking process
occurs in the
furnace tubes(or “coils”).
●Charge is fed to the visbreaker heater where
it is heated to a high temperature causing
partial vaporization and mild cracking.
●The heater outlet stream is quenched with
gas oil or fractionator bottoms to stop the
cracking reaction.
●The vapour liquid mixture enters the
fractionator to be separated into gas, naphtha, gas
oil and visbroken tar.
●The visbroken
bottoms are then blended with lighter materials (cutter stock} to meet
fuel oil specifications.
●The fractionated visbreaker gas oil is often used as the cutter stock.
❏
Soaker Visbreaking
●
In soaker visbreaking, the bulk of the cracking
reaction occurs not in the furnace but in a drum
located after the furnace called the soaker.
●
Here the oil is held at an elevated temperature
for a predetermined period of time to allow
cracking to occur before being quenched.
●
The oil then passes to a fractionator.
●
In soaker visbreaking, lower temperatures are
used than in coil visbreaking.
Applications and Advantages
●
●
●
●
●
To reduce the quantity of residual oil produced in the distillation of crude oil.
To increase the yield of more valuable middle distillates(heating oil and diesel)
To reduce the pour point and viscosity of waxy residues used for blending with
lighter fuel oil.
Viscosity is reduce by :
A. Vacuum distillation
B. Hydro skimming
Increase the proportion of middle distillates in the refinery output, Middle
distillate is used as diluent with residual oils to bring their viscosity down to their
marketable level.
❏ Disadvantages
●
Fouling: It is the accumulation of unwanted material on solid surfaces to the
detriment of function.
●
Formation of coke: The formation of coke normally starts at temperatures >300
Grand is therefore a major problem.
●
Asphaltenes precipitation: Asphaltenes makes precipitation with i-octane.
❏ References
https://www.sofraser.com/news/visbreaking-in-petroleumrefineries/#:~:text=Visbreaking%20is%20a%20mild%20form,heating%20parameters%20
and%20optimize%20distillation.
https://www.sciencedirect.com/science/article/pii/S1026309812000612
https://www.valv.com/industries/downstream-chemical-processing/visbreakingapplication-overview/