Coker units recover valuable elements, including petroleum coke, from residual oil or pitch through thermal cracking. The coke is collected in a drum and ejected by water jets for further processing into fuel or anode grade products.
A coker unit is a thermal cracking process in the petroleum refinery industry used to recover valuable elements, the most important of which is petroleum coke from the residues of the main refinery process. The coking process involves feeding heated residual oil or pitch to the bottom of a large vertical vessel known as a coke drum, where thermal cracking occurs. The cracking process causes the oil to separate into gases and vapor which exit the top of the coke drum and solidified coke which collects inside the drum. Once the coke has built up to a predetermined level, the process is stopped and the mass of coke is ejected from the coke unit by high pressure water jets. The coke collected from the unit is then sent for further processing to produce anode grade fuels or end products.
Residual petroleum and coal tar pitch from atmospheric and vacuum distillation columns at 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 pet 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 types such as needle coke, for the manufacture of anodes used in steel, titanium and aluminum foundries . These products are extracted from the refinery residues in a section of the plant called the coker, typically one of the final stages of the refinery process.
The coker unit exploits a phenomenon pioneered by William Burton and Vladimir Shukhov known as thermal cracking in which long-chain hydrocarbons are broken down, or cracked, into short-chain variants. This cracking process takes place in a large vertical vessel known as a coke drum. The residual oil or pitch is first heated to approximately 930° Fahrenheit (500° Celsius) and fed to the bottom of the coke drum where the cracking process begins. During cracking, vaporized gases and oils escape from the top of the coker unit for collection, while solid, porous coke builds up to form a mass inside the bowl.
Once there is sufficient coke buildup in the drum, the feed is shut off and the process ceases. When the coke in the drum has cooled sufficiently, jets of high pressure water are lowered into the top of the drum from tall structures known above as derrick decokers. These jets cut the mass of coke into smaller pieces which protrude from the bottom of the drum for collection and treatment to produce fuel or anode grade products. Coke oven units are typically equipped with two coke drums allowing the process to continue in one drum while the other is decoked. Many larger refineries have several twin drum coker units to keep up with production demands.
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