How does refinery work

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Refining breaks crude oil down into its various components, which are then selectively reconfigured into new products.

Petroleum refineries are complex and expensive industrial facilities. All refineries have three basic steps:. Modern separation involves piping crude oil through hot furnaces. The resulting liquids and vapors are discharged into distillation units. All refineries have atmospheric distillation units, while more complex refineries may have vacuum distillation units.

Inside the distillation units, the liquids and vapors separate into petroleum components called fractions according to their boiling points. Heavy fractions are on the bottom and light fractions are on the top. The lightest fractions, including gasoline and liquefied refinery gases , vaporize and rise to the top of the distillation tower, where they condense back to liquids.

Medium weight liquids, including kerosene and distillates , stay in the middle of the distillation tower. Heavier liquids, called gas oils, separate lower down in the distillation tower, while the heaviest fractions with the highest boiling points settle at the bottom of the tower.

After distillation, heavy, lower-value distillation fractions can be processed further into lighter, higher-value products such as gasoline. This is where fractions from the distillation units are transformed into streams intermediate components that eventually become finished products. The most widely used conversion method is called cracking because it uses heat, pressure, catalysts, and sometimes hydrogen to crack heavy hydrocarbon molecules into lighter ones. A cracking unit consists of one or more tall, thick-walled, rocket-shaped reactors and a network of furnaces, heat exchangers, and other vessels.

Cracking is not the only form of crude oil conversion. Petroleum refining separates crude oil into components used for a variety of purposes. The crude petroleum is heated and the hot gases are passed into the bottom of a distillation column.

As the gases move up the height of the column, the gases cool below their boiling point and condense into a liquid. The liquids are then drawn off the distilling column at specific heights to obtain fuels like gasoline, jet fuel and diesel fuel. The liquids are processed further to make more gasoline or other finished products. Some of the liquids undergo additional processing after the distillation process to create other products.

These processes include: cracking, which is breaking down large molecules of heavy oils; reforming, which is changing molecular structures of low-quality gasoline molecules; and isomerization, which is rearranging the atoms in a molecule so that the product has the same chemical formula but has a different structure.

Much like a simple still, in a distilling column, liquid is heated to a vapor and lifted upward to be distilled again into separate substances. This is the beginning of the refining process.

Distilling exploits the characteristic of the chemicals in crude oil to boil at different temperatures, a phenomenon that engineers chart along distillation curves. Unlike a still, a distilling column contains a set of trays that allow heated vapors to rise and collect at different levels, separating out the various liquids derived from crude oil.

The top of the column is cooler than the bottom, so as liquids vaporize and rise, they condense again, collecting onto their respective trays.

Butane and other light products rise to the top of the column, while straight-run gasoline, naphtha, kerosene, diesel, and heavy gas oil gather on the trays, leaving straight run residue at the base of the column.

Because there is more demand for some distilled products like gasoline, refiners have an incentive to convert heavy liquids into lighter liquids. The term cracking comes from the process of breaking up long hydrocarbon molecules into smaller, more useful molecules. The cracking process converts heavy straight run liquids into gasoline.