Crude oil consists of many different types of chemical constituents and separation and conversion of these constituents to usable form require many different types of operations to be carried out on crude oil.
Types of Operations Carried out in Petroleum Refining
All these operations can be classified into four major types of operations:
- Separation Processes
- Conversion Processes
- Finishing Processes
- Supporting Processes
Separation Processes
Separation processes are carried out to separate different constituents from crude oil. As we have discussed above crude oil is a mixture of different types of chemical constituents, Many different types of separation processes are carried out to separate these constituents into their usable form.
Separation Processes involve desalting, atmospheric distillation, vacuum distillation, deasphalting, dewaxing, light ends separation.
- Desalting is carried out to remove all types of salts and other water-soluble impurities from crude oil.
- Atmospheric distillation unit separates crude oil into major different constituents.
- Vacuum distillation is carried out for a higher molecular weight product of the atmospheric distillation unit to separate higher boiling point constituents with the use of vacuum.
- Deasphalting is carried out to separate bottoms of atmospheric distillation unit and vacuum distillation unit to separate its different parts like aromatic, paraffinic, etc.
- Dewaxing is carried out after deasphalting to remove waxy materials from deasphalted oil to use these oil in producing lubricating oil.
- Light end separation is carried out to separate refinery top products into different individual gases such as ethane, propane, and butane.
Conversion Processes
Conversion processes are carried out to convert products of the separation unit into more usable products which are further treated into finishing processes to make it usable. In conversion processes, Chemical constituents are reacted at higher temperatures or with the use of catalysts to convert them into more important constituents.
Conversion processes involve thermal cracking, visbreaking, coking, catalytic cracking, hydrocracking, reforming, alkylation, polymerization, and isomerization.
These processes are one of the most important processes in petroleum refining.
- Cracking is carried out in two ways, Thermally if higher temperatures and catalytically to convert long straight-chain hydrocarbons to shorter chain hydrocarbons.
- Visbreaking is carried out on vacuum distillation residue to increase flowability.
- Coking is carried out to convert residues to coke which is an important material for industries like metallurgical, chemical, etc.
- Hydrocracking is also a cracking which makes use of hydrogen for cracking purpose.
- Reforming is the conversion operation of naphtha coming out from the atmospheric distillation unit to high-octane reformate.
- Alkylation is carried out to combine light iso-paraffins and convert them to medium size iso-paraffins which are higher in octane number.
- Polymerization is its name suggests a combination of different olefins to convert higher molecular weight olefins.
- Isomerization is an operation in which isomers are generated from paraffinic constituents.
Finishing Processes
Finishing processes are final treatments carried out to products of separation and conversion processes to make them finally sellable.
Finishing Processes include hydrogenation, hydrotreating, and product blending.
- Hydrogenation is carried to convert unsaturated hydrocarbons to saturated hydrocarbon by reacting with it hydrogen.
- Hydrotreating is carried out to remove constituents of different heteroatomic compounds and metallic impurities.
- Product blending is an operation in which different product streams are added in a tank in calculated amounts to make final products.
Supportive Processes
Supportive processes play a supportive role in refining which supports other mainstream processes by producing raw materials for them or converting by-products of them into a usable form.
Supportive processes are acid gas removal, sulfur recovery, hydrogen production, and purification, and wastewater treatment.
- Acid gas removal is an operation in which amines are utilized to separate out acidic gases from gaseous streams like hydrogen sulfide to reduce corrosion possibility in pipelines.
- Sulpher recovery is used to recover sulfur from hydrogen sulfide which is the raw material for sulphuric acid.
- Hydrogen production and purification produce hydrogen by steam reforming which is utilized in many conversion processes.
- Finally, the wastewater treatment process is used to treat effluent water generated in the refinery.
Conclusion
All the operations carried out in petroleum refining are classified into three major types.
- Separation Processes: Desalting, Atmospheric Distillation, Vacuum Distillation, Deasphalting, Dewaxing, and Light Ends Separation.
- Conversion Processes: Cracking, Visbreaking, Coking, Hydrocracking, Reforming, Alkylation, Polymerization, and Isomerization.
- Finishing Processes: Hydrogenation, Hydrotreating, and Product Blending
- Supporting Processes: Acid Gas Removal, Sulfur Recovery, Hydrogen Production, and Purification, and Wastewater Treatment