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How Oil Refineries Work

Exploring the process of refining crude oil into useful products.


The world of oil refineries is a complex and fascinating one, integral to modern life yet often shrouded in mystery. In this article, we'll demystify this crucial industry by answering some key questions and providing a clear overview of how oil refineries operate.


What is Crude Oil?


Crude oil is a naturally occurring, unrefined petroleum product composed of hydrocarbon deposits and other organic materials. Crude oil is extracted from the earth, and it's constituent components are used to produce various forms of energy and materials civilization relies on.


Crude oil originates from ancient organic materials, primarily microscopic marine organisms such as plankton and algae. The process begins when these organisms die and settle on the ocean floor, mixing with sediments. Over time, layers of sediment and organic matter accumulate, subjecting the lower layers to intense heat and pressure. This environment initiates a transformation process, turning this organic mixture into a waxy substance known as kerogen.


As geological shifts occur, such as the movement of tectonic plates, these kerogen-rich layers may be buried deeper, exposing them to even higher temperatures and pressures. It's in these deep, hot, and high-pressure conditions that kerogen gradually breaks down into hydrocarbons, forming crude oil.


The formation of crude oil is not a quick process; it spans millions of years. The exact time frame can vary significantly depending on numerous factors such as the type of original organic material, the depth of burial, the temperature, and the geological changes the region undergoes. Generally, it's thought that the oil we use today began forming 10 to 600 million years ago.



How Do Oil Refineries Work?


Crude oil by itself is not very useful.  It needs to be refined, or separated into its constituent parts.  Each of those parts has a specific use.


An oil refinery is a carefully orchestrated industrial process where crude oil is transformed into several usable products. The core of this process is the separation of crude oil into different components, achieved through a method called fractional distillation.



In fractional distillation, crude oil is heated in a giant column. Different hydrocarbon chains have different boiling points.  The longer the carbon chain, the higher the temperature at which the compound will boil.  Crude oil is heated so that the compounds in it are vaporized into gasses. As these gasses rise through the distillation column, their temperatures drop. Once the temperature of the gasses drops below their boiling point, they condense back into liquids. The condensed liquids are drawn off the distillation column at different heights. The height at which the compounds are drawn off corresponds to the boiling point of those compounds and, therefore, the length of the carbon chains. The length of the carbon chain determines what the compound is.  Through this fractional distillation process, crude oil can be separated into the following products:


  • Gasoline: Primarily used as fuel in automobiles. It's the most well-known and widely used product of crude oil.

  • Diesel: Used as fuel in vehicles, especially trucks, buses, and trains, and also in generators.

  • Home Heating Oil: Similar to diesel in composition but is specifically formulated for use in home heating systems.

  • Jet Fuel: Specialized fuel used in aircraft. It’s similar to kerosene but is refined to meet aviation standards.

  • Kerosene: Used in heating, lighting, and as a jet engine fuel. It's also the base for jet fuel production.

  • Liquefied Petroleum Gas (LPG): Includes propane and butane, used in heating, cooking, and as fuel for certain vehicles.

  • Heavy Fuel Oil: Used in large ship engines and as a fuel for power generation in power plants.

  • Asphalt and Road Oil: Used in the paving of roads and roofing materials.

  • Lubricants: Such as motor oil and grease, which reduce friction in engines and other machinery.

  • Paraffin Wax: Used in candles, packaging, and as an anti-caking agent in food.

  • Petrochemicals: These are used as raw materials in the manufacturing of plastics, synthetic rubber, synthetic fibers (like polyester and nylon), detergents, and other chemicals.

  • Sulfur: By-product used in the production of sulfuric acid, fertilizers, and other chemicals.

  • Coke: A solid carbonaceous material derived from oil refinery coker units, used in metallurgical processes.


This wide range of products demonstrates the versatility of crude oil and underscores its role as a cornerstone of global industrial and economic activities. Each product has a specific application, reflecting the diverse utility of crude oil in our daily lives.


Two distillation columns operating at different pressures are usually used in refineries.  The atmospheric distillation unit (ADU) operates at normal atmospheric pressure.  However, some of the longer hydrocarbons can't be separated this way, so they flow into a vacuum distillation unit (VDU) for further separation.  Operating under vacuum pressures lowers the boiling point of the hydrocarbons, allowing for lower temperatures for distillation than are possible in the ADU.




A Note on Gasoline


Although all fractions of crude oil have uses, the greatest demand is for gasoline.  Transportation demands require that over 50% of crude oil be converted into gasoline, but crude oil only contains 30-40% gasoline.  In order to meet gasoline demand, other crude oil compounds can be converted into gasoline in three ways:


  1. Cracking - breaking down large molecules of heavy heating oil

  2. Reforming - changing the molecular structures of low-quality gasoline molecules

  3. Polymerization - forming longer molecules from smaller ones


Light vs. Heavy, Sweet vs. Sour


Crude oil is categorized into "light" and "heavy" based on its density and viscosity. Light crude oil is less dense and flows more freely at room temperature, making it easier and cheaper to refine. Heavy crude oil, thicker and more viscous, requires more complex refining processes and thus is more expensive to process.


"Sweet" crude oil refers to oil with low sulfur content. It's termed "sweet" because of its relatively less sour taste compared to high-sulfur oils. Refining sweet crude is simpler and cheaper, as sulfur is a corrosive element and complicates the refining process.


U.S. Crude Oil Refinery Dilemma


The United States is one of the world's largest oil producers, with a significant portion of its production comprising light and sweet crude oil. This type of oil is typically found in shale formations and is abundant in areas like the Permian Basin in Texas and New Mexico.


Interestingly, despite the U.S. producing large amounts of light crude, many of its refineries are equipped to handle heavy crude oil. This disparity arose from historical import patterns and investments in refinery upgrades designed to process heavier imports. As a result, the U.S. often exports its light crude oil and imports heavier varieties.


Understanding how oil refineries work and the types of crude oil they process offers a glimpse into a critical yet often overlooked industry. Oil refineries play a pivotal role in our lives, from powering our vehicles to providing raw materials for everyday products. As the energy landscape evolves, so will these industrial giants' operations and significance.


It will be interesting to see how crude oil is processed and used as the world transitions to other, more sustainable primary energy sources. Technologies such as electric vehicles and home heat pumps can change the balance of the hydrocarbons we need as a civilization, and oil refineries will have to make adjustments.


Questions for you:


  • With the global shift towards renewable energy, what do you envision as the future of oil refineries?

  • Was there anything in the article that particularly surprised or intrigued you about the process of oil refining?

  • Given that we rely on the products of crude oil for so many things, what alternative energy sources do you think could realistically replace oil in the near future, and why?

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