Coking :An Overview
The crude oil after being processed through physical separation processes especially
Vacuum Distillation Unit (VDU) is left with heavier residual fuel oils in the bottom of
a distillation unit which are undesirable for any refining unit.
Coking involves conversion of these heavier fractions into solid coke and lower boiling point hydrocarbons, generally liquid , using various thermal and chemical processes.
The liquid fractions so produced is highly olefinic and aromatic as well as contain high sulfur content. These liquid products can prove to be a feedstock for other refinery units by converting into a high value fuel using reforming , desalting ,hydrodesulfurization (HDS),etc.
Coking is a carbon rejection process of converting heavier residues ,rich in sulfur content, at the bottom of VDU into lower molecular fractions like gases, naptha , Light gas oil (LGO ) and heavy gas oil (HGO ) and solid product Petroleum Coke or Pet Coke (Carbon).
The sulfur content in the products from coking is relatively lower than the feed because much of the sulfur remains in the pet coke.
These conversions are processed in units known as Coking Drums or Coker.
Important :
Generally Coking is carried out at high pressure and high temperature as high pressure allows decomposition of heavier hydrocarbons into lighter ones like naptha, gases ,LGO etc. in contrast to VDUs where operation is carried out at very low pressure due to which Atmospheric Distillation Unit (ADU) residue does not decompose ,and therefore we get LGOs and HGOs along with vacuum residue as products from VDU.
There are various types of coking processes depending upon the product requirements and feed properties :
1. Flexi-Coking and Fluid Coking
2. Delayed Coking
3. Vis-breaking
In upcoming articles ,we are going to discuss fluid coking and flexi-coking processes.
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