The oil industry is booming stronger than ever. Crude oil is the base product for a large majority of products on Earth; Fuels, plastics, roads, and much more rely on the extraction and refinement of crude oil. Although companies are devising new methods to eradicate the necessity of fossil fuels, most countries remain reliant on the massive oil industry. However, converting sludge into enough fuel to meet humanity’s demands requires an extensive network of oil refineries.
Most people understand crude oil as the dino-goop that is extracted from the ground. Although, a much lesser known fact is the remarkable process that permits the conversion of crude oil into jet fuel.
For once, the movies got it right – oil products begin their journey far into the reaches of the ground as a thick black liquid. Crude oil, the raw base of most fuels, contains a mixture of hydrocarbons ranging from kerosene to gasoline. The chemicals bear similar resemblance, although for them to be of any use, they need to be refined.
How Oil Refineries Work
The process of refining crude oil requires a few basic steps and a little knowledge of chemistry.
When oil arrives at the refineries, it contains a mixture of fuels that can be extracted through several industrial processes. Almost every refinery uses a series of similar steps to extract the various types of fuels contained within crude oil. The process calls for Distillation, Cracking, Treating, and Reforming.
The composition of crude oil contains a plethora of fuels that need to be separated before the products can be of any use.
Each hydrocarbon within the oil has a specific boiling point and molecular mass. Using this property, specific types of oil can be extracted with a high degree of precision by using what us known as a distillation column.
Oil refineries are renowned for their massive metallic towers. Although the towers appear rather basic from the outside, they serve as a critical component in the oil refining process.
The main function of the tower is to separate the oil based on molecular structure and composition. As previously mentioned, different types of products in oil have different boiling temperatures. With this feature in mind, engineers have devised a distillation tower that can extract different products within crude oil based on their chemical properties – specifically their boiling point.
How it works
The process begins by transporting oil into massive heaters that causes the substance to evaporate.
Since each product within the oil has a different mass and boiling temperature, the products can be made to precipitate from a gas into a liquid at varying levels inside a distillation column.
Separating and collecting products from crude oil
At the bottom of the distillation column, the oil is heated to a balmy temperature of 360-Degrees Celsius. At the top, the column remains at a much lower 100-Degrees Celsius.
The temperature gradient is imperative to the distillation process.
As vapor travels through the column, it begins to cool until it precipitates back into a liquid once it cools below its boiling temperature. Large perforated trays span the column at strategic points that line up with the precipitation points.
The small perforations in the tray allow the vapor to continue to rise up while collecting the liquids as they precipitate back into a liquid at a specific level. Since each product within crude oil has a different boiling point, different oil types will collect separately on specific trays.
The lighter products, like propane and butane, rise to the top of the column. Slightly heavier products like gasoline, jet fuel and diesel fuels, collect and condense in the middle. The heaviest of the molecules, known as gas oils, condense towards the lower portions of the distillation column.
At the very top of the column is a pipe that extracts the excess gasses and uses it as fuel to power the heaters that evaporate the oil entering the distillation column.
Distillation Column in use at oil refineries. [Image Source: Chevron Pascagoula Refinery]
Maximizing profits while minimizing waste
In this day and age, oil refineries are under more pressure than ever to ensure their environmental impact is as minimal as possible. However, reducing residual products from the distillation process increases profits for oil refineries, giving the incentive to maximize their profits by minimizing their waste.
A thick black residual oil remains at the bottom of the distillation column after the other fuels have been extracted through the distillation process. However, the residue can be re-processed through another series of distillation columns that exists under lower pressures to further enhance the evaporation and separation of the oil. The extra processes ensure the refineries produce minimal waste products.
Maximizing profits requires maximizing the yield of high-value products. The thick residue that is left over from the distilling process contains larger hydrocarbon chains. However, the longer hydrocarbons are significantly less valuable than the lighter distillates.
The biggest difference between products is not their atomic composition, but rather, the length of their molecular structure. Heavier crude oil products have longer (but similar) chains to the lighter (and more valuable) short-chain fuels.
Oil refineries try and maximize profits by splitting the larger chains into smaller ones of greater value.
“At the Pascagoula Refinery, we convert middle distillate, gas oil and residuum into primarily gasoline, jet and diesel fuels by using a series of processing plants that literally “crack” large, heavy molecules into smaller, lighter ones.” states the oil refinery company, Chevron.
Splitting the longer chains requires the addition of a catalyst – a material that reduces the amount of energy needed to break a bond – and of course, heat. There are three processes that can break down the molecular structure of oil: Fluid catalytic cracking (FCC), hydrocracking (Isomax), and coking (or thermal-cracking).
Catalytic cracking splits longer chains by introducing a catalyst and increasing temperatures. The catalysts prompts the long chains to change molecular structure by “cracking” the chains. The process is ideal for manufacturing gasoline.
[Image Source: Chevron Pascagoula Refinery]
The process of hydrocracking similarly involves the use of a catalyst to crack long chains into smaller ones. The system, however, remains under high pressure and temperatures to ensure smaller sections of chains are broken. As a result, the method can produce both jet fuel and gasoline.
[Image Source: Chevron Pascagoula Refinery]
The last conversion technique involves the user of a Delayed Coking Unit (Coker). The Coker processes low-value residuum and converts it into higher-value products. Large coke drums contain the residuum under high temperatures for prolonged periods of time. Eventually, the large molecules once again “crack” into smaller chains. The leftover product is known as petroleum coke and is predominantly used as a fuel source or cement agent.
While the main purpose of the cracking methods is to break molecules down into smaller segments, combining involves the opposite function.
The cracking process generates some molecules that are lighter than gasoline. Many refineries specialize in the production of transportation fuels, making the extremely small chains of no particular value as they stand.
However, there exists a process that reverses the effects of cracking, causing the small chains to expand. For combining to occur, sulfur and an acidic catalyst are added to convert the small chains into high octane* gasoline.
Through the various cracking and combining processes, oil refineries can maximize the useful product extraction and keep the toxic waste material to a minimum.
High-performance vehicles typically have a high compression ratio requiring a high octane fuel so the gasoline does not prematurely ignite.
*The octane rating of gasoline describes how much the fuel can be compressed before it spontaneously ignites. A high octane rating means the fuel will not easily ignite under high pressures. If the fuel prematurely ignites as a result of compression and not the spark plug, the engine will begin to knock and will quickly become damaged.
Treating and Removing Impurities
While the distillation process separates and recollects various fuel types, it cannot separate out impurities that naturally collect in crude oil.
Removing sulfur, nitrogen, and other impurities require a process known as hydrotreating – a milder version of hydrocracking. Hydrotreating removes impurities to reduce air pollution when the fuel combusts.
To extract the unwanted chemicals, extra catalysts are introduced to convert sulfur into hydrogen sulfide. A Sulfur Unit can then extract elemental sulfur from the compound.
The nitrogen that remains in the fuel is converted into ammonia using another catalyst.
After the nitrogen is transformed, it is removed by water-washing the ammonia out of the distilled product. Once it is removed, the ammonia is recovered from the water as a pure product. Later, it is sold or used to manufacture fertilizer.
For a car to run well, the fuel on which it runs must have a high octane level. High levels of octane are generally a good measure of the quality of the fuel.
Much of the oil that streams from the Cracking Units or low-pressure distillation columns maintain a low octane level that will not burn well in a car.
Using another catalyst system made from platinum and rhenium, the compounds can be reformed to boost the octane levels by rearranging the molecular structure by splitting bonds and removing hydrogen. The process strips some hydrogen from the molecules, allowing the fuel to compress more before the fuel spontaneously combusts.
[Image Source: Chevron Pascagoula Refinery]
Finally, after separating the field, removing impurities, and boosting octane levels, the fuel is ready to be shipped. A single oil refinery typically manufactures a wide variety of products intended for many applications.
The fuel is shipped off to be further processed into fuels, plastics, and many other products.
The incredible process of oil refining enables companies to convert thick dinosaur goop (or ancient plant matter) into a fuel that will power a car, train, or plane.
Featured Image Source: Wikimedia Commons