How Do Oil Refineries Work?
An oil refinery is a plant that processes crude oil. A typical plant processes thousands of barrels of oil a day,
continuously. Refineries are operated continuously in order to optimize the process and the refineries’ capacity.
Refineries process crude oil because in its raw form, crude oil is dangerous and produces explosive vapors. Before the oil can be used as fuel or other products such as, crayons, kerosene, plastic, and heating oil, it needs to be processed and refined.
The Distillation Process
The main way of processing crude oil is to separate it using fractional distillation. Oil is made up of many different hydrocarbons of different boiling points, so the oil is heated and different hydrocarbon chains vaporize at different times, allowing them to be collected and used as products. The first step in distillation is to boil the oil to a very high temperature, usually around 1112 Degrees Fahrenheit. When the solution boils, it forms vapors, which enter the fractional distillation column, which has many trays to collect the liquid. As the height in the column increases, the temperature gets cooler, so as the vapors rise, they cool. Since every hydrocarbon chain has a different boiling point, as a chain reaches a height where the temperature is lower than the boiling point, it will cool into a liquid and be collected by a tray. This method allows for all parts of the oil to be separated and collected so that they can be further processed and refined. A very good animation of the distillation process can be found HERE.
Units of a Refinery
Here is a step-by-step procedure of the process that crude oil goes through in a refinery in order to make products. The process does not always go this way, but this is a basic overview:
1. It starts in the Desalter Unit, where the crude oil is washed to remove the salt.
2. It then goes to the Atmoshperic Distillation Unit where the oil is separated into fractions by the process in the paragraph above.
3. The Vacuum Distillation Unit then further distills the smaller, lighter parts of the oil.
4. Then one of the fractions from the crude oil, Naptha, goes to the Naptha Hydrotreater Unit, where hydrogen is used to remove the sulfur from the Naptha and hydrotreat it.
5. The Naptha then goes to the Catalytic Reformer Unit, which converts Naptha molecules into octane reformate, a type of product. During this process, hydrogen is released, which is then used again in the Hydrotreating process.
6. The rest of the fractions go to the Distillate Hydrotreater Unit, which removes sulfur from distillates, like diesel.
7. They then go to the Fluid Catalytic Cracker Unit, which turns heavy fractions into lighter products that are more valuable and safe to be used.
8. The Hydrocracker Unit does the same thing as the Fluid Catalytic Cracker Unit, except it uses hydrogen to turn the heavy products into lighter ones.
9. The Visbreaking Unit does the same thing as the above two units using a process called thermal cracking, which uses heat to reduce the viscosity by getting rid of extra, residual oil.
10. The Merox Unit oxidizes a fraction called mercapatan into disulfides to create LPG, kerosene, and jet fuel.
11.The Coking Unit take the heavy extra, residual oils and process them to make gasoline and diesel fuel. The process creates petroleum coke as a byproduct.
12.The Alkylation Unit makes a high-octane component to blend gasoline and upgrade petroleum.
13. The Dimerization Unit converts a fraction called olefin into a higher-octane gasoline blending component to make gasoline.
14.The Isomerization Unit takes lighter, linear hydrocarbons and converts them to heavier, higher-octane, branched molecules.
15. The Steam Reforming Unit produces hydrogen used in the hydrotreater and hydrocrackers.
16.The Liquified Gas Storage Units are spherical vessel, which maintain a specific pressure in order to store propane and other fuels in a liquid form.
17. Storage Tanks are special tanks designed to store crude oil and other products, so that they contain spills and control harmful vapors.
18. There are also many important Utility Units, such as towers for cooling water, boilers to create steam, and electrical power units.
19. The Wastewater collector and API Separator treat the wastewater so that it can be reused in the refining process or safely disposed.
20. Solvent Refining and Dewaxing Units further refine the oil by removing unwanted materials and heavy, waxy components.
For more information on the specifics of the refining process, CLICK HERE.