Oil refineries use a coking unit to recover valuable elements.
A coking unit is a thermal cracking process in the oil refinery industry, used to recover valuable elements, the most important being petroleum coke from the main refinery process waste. The coke process involves feeding heated residual oil or pitch to the bottom of a large vertical vessel known as a coke drum, where thermal cracking takes place. The cracking process causes the oil to separate into gas and steam that exits from the top of the coke drum and solidified coke that accumulates inside the drum. Once the coke has accumulated to a predetermined level, the process is stopped and the coke mass is removed from the coke unit using high pressure water jets. Coke collected from the unit is then sent for further treatment to produce fuel or anode grade end products.
Gasoline, kerosene and petroleum are refined from crude oil in refineries.
Residual coal tar and oil pitch from atmospheric and vacuum distillation columns in an oil refinery still contain several valuable elements, including naphtha, gas oils and hydrocarbon gases. One of the most important of these elements is a porous carbonaceous solid known as petroleum coke or petroleum coke. Commercial grade coke has a very high carbon content and can be used as an efficient, low-emission combustion fuel or, in the case of grades such as needle coke, for the manufacture of anodes used in steel foundries. , titanium and aluminum . These products are extracted from refinery waste in a section of the plant known as the coking unit, typically one of the final steps in the refinery process.
The coking unit takes advantage of a phenomenon initiated by William Burton and Vladimir Shukhov, known as thermal cracking, during which long-chain hydrocarbons are decomposed, or cracked, into short-chain variants. This cracking process takes place in a large, vertical container known as a coke drum. The residual oil or pitch is first heated to about 930° Fahrenheit (500° Celsius) and fed to the bottom of the coke drum, where the cracking process begins. During cracking, vaporized gases and oils exit the top of the coke unit for collection, while solid, porous coke accumulates to form a mass within the drum.
Once a sufficient buildup of coke is present in the drum, the feed is cut off and the process ceases. When the coke in the drum has cooled sufficiently, high pressure jets of water are lowered to the top of the drum from tall structures known as de-icing towers. These jets cut the coke mass into smaller pieces that fall from the bottom of the drum for collection and treatment to produce fuel or anodic grade products. Coke units usually feature two coke drums that allow the process to continue in one drum while the other is being thawed. Many larger refineries feature multiple double drum coker units to meet production demands.