Coker Units

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Coker Units, or Cokers, are oil refinery processing units that convert residual oil and process residues leftover after the initial crude distillation into higher value products and petroleum coke, a coal-like material used as a fuel input or a manufacturing raw material in a variety of industries. During the coking process, residual oil from the vacuum distillation unit is transferred into large, vertical reactors known as coke drums. There, it is placed under high heat and pressure in a process called thermal cracking to separate the lighter vapors, including hydrocarbon gases, naphtha, and light and heavy gas oils (which exit at the top of the coke drum for further refining) from the solidified petroleum coke. This coke will build up in the drum, and once full, the drum must be taken offline and the coke removed using high pressure water cutters for either reclamation or storage.

Types of Coker Units

There are two primary types of coker units used in petroleum refining: delayed coker units (DCU) and fluid coker units. Of the two, the delayed coker unit (DCU) is by far the most common and involves two or more drums working in tandem. When one drum is taken offline, production is simply shifted to the next drum. This allows a facility to have one coker online continuously, avoiding unnecessary downtime. In a fluid coker, the feed goes through the same thermal cracking process, but the formed coke is transferred to a separate heater as a fluidized solid where some of it is burned to provide the heat necessary for the coker to continue to convert residual oil into gases, distillate liquids, and coke. Fluid coking can provide a higher distillate yield and a lower coke yield than delayed coking.


  1. Johnson, E., Kaley, L., and Tallin, A., 1996, "Reliability of Coke Drums," Inspectioneering Journal, The Woodlands, Texas, 2(6), pp. 4-6.
  2. U.S. Energy Information Administration, "Coking is a refinery process that produces 19% of finished petroleum product exports," January 28, 2013,

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Articles about Coker Units
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Leveraging and combining the correct inspection tools on complex problems can yield the best overall data and understanding of actual conditions.

Authors: Grant Jacobson
March/April 2018 Inspectioneering Journal

Hot spots – localized areas of overheating in pressure equipment – can lead to deformation or even loss of process containment. It is important to understand the effects of elevated temperature caused by hot spots on the mechanical integrity of...

January/February 2016 Inspectioneering Journal

The enormous decline in oil prices over the past 14 months has definitely slowed projects and changed the energy and production landscape. Despite this, refineries, petrochemical plants, and chemical facilities must continue to run safely,...

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January/February 1997 Inspectioneering Journal

This is Part II of a series of reliability of coke drums. Part I discussed some of the causes of bulging and cracking in coke drums. Here, the effect of operation on damage will be covered, along with possible solutions for increasing drum life...

November/December 1996 Inspectioneering Journal

Petroleum coke production is an important source of revenue for many refineries. While coking units were initially constructed to deal with a waste product, these units are now of significant economic value.

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