Refining fuels is a complicated process. Check out this Into the Outdoors video, which features the Pine Bend refinery and describes the process of refining oil in a way that is understandable for all ages.
Crude oil is delivered to Pine Bend by a series of pipelines that stretch across the United States and Canada. Crude oil contains a mixture of molecules which are pumped or mined from underground reservoirs. In its natural state, it has very little value, so Pine Bend separates the molecules from each other by distilling the mixture into gasoline, propane and asphalt. Each molecule in crude oil boils at a different temperature, which is the basis of distillation.
After the distillation process, Pine Bend refines the separated mixtures to remove impurities that would cause emissions during the combustion of the fuel products.
The process of hydrotreating uses hydrogen and a catalyst to remove sulfur from oil by converting it to hydrogen sulfide. Sulfur removal is required to protect refinery processes and to minimize emissions from vehicles. Each day approximately 1,000 tons of sulfur are removed from our oil and processed in our sulfur plants. Sulfur is sold for use in the manufacturing of fertilizers, sulfuric acid, and a variety of pharmaceutical products, such as antibiotics.
The next step in the refining process – cracking – breaks large molecules into many small ones. This helps transform the materials in the distilled product into highly desirable ones. There are two types of cracking mechanisms:
- Thermal: Heating the distilled product to 900°F to break molecules, making mostly gasoline and diesel. Thermal cracking is non-selective and cannot be adjusted.
- Catalytic: Using a catalyst to promote the cracking of large molecules of carbon atoms into smaller molecules at temperatures of 960°F-1,000°F. Catalytic cracking is selective and can be adjusted if necessary.
After the cracking process, catalysts are captured through the electrostatic precipitator – the largest single piece of equipment at Pine Bend – to reduce emissions. A high-voltage current is applied to metal plates which attract the catalyst particles. A hammer pings the plates, and the catalyst falls down into a bin for disposal. At Pine Bend, 100% of the catalyst fines are reused in the production of portland cement.
Once the molecules have been split, they are combined into larger molecules. For example, propane and butane are made into eight-carbon molecules to be blended into gasoline.
Each individual refinery gasoline product is sent to a large storage tank. At this point, none of the individual gasoline products meet specifications for consumer use. The gasoline products are combined in a way that satisfies the specifications to be certified for sale. Pine Bend makes more than 100 grades of gasoline.
Water, which is supplied to the Pine Bend refinery via a system of seven wells, is an integral part of the refining process. It is used to make steam, cool the process, and reduce corrosion.
Cooling water is circulated to heat exchanges throughout the refinery where it cools process streams. The heated cooling water is returned to the tower where it is re-cooled with large fans through the process of evaporation. Approximately 2,000 gallons of water per minute evaporate at Pine Bend’s five cooling towers. All of the water that does not leave the refinery by evaporation is treated by the wastewater treatment plant. After approximately two to three days of treatment, clean water is discharged to the Mississippi River.
Lab analysis is a crucial way to control our processes and ensure that we meet regulatory requirements. Pine Bend’s onsite lab operates around the clock and processes approximately 35,000 tests each month.
Pipelines deliver the vast majority of gasoline and diesel fuel to terminals, where the product is then loaded on trucks and delivered to retail gas stations. Other products distributed include sulfur, asphalt, petroleum coke, propane, butane, and aviation gasoline.
For more information, read our Oil and Natural Gas Processing Overview.