Crude Distillation Unit (CDU)

Explore this topic

In petroleum refining, the Crude Distillation Unit (CDU), also known as as the Atmospheric Distillation Unit, is usually the first processing equipment through which crude oil is fed. Crude oil is composed of a mixture of hydrocarbons, and the distillation process separates this crude oil into broad categories of its component hydrocarbons, or "fractions," which serve as feedstocks for all other processing units at the refinery. 

As oil is being fed into the crude distillation unit, the first thing that happens is the crude is heated to a temperature between 215°F and 280°F (100°C - 137°C).  This allows salts, which can be harmful and corrosive to some equipment, to be removed at the desalter.  The now desalted crude is further heated to temperatures up to 750°F (400°C) as it is fed into the atmospheric distillation tower where the vapors and liquids separate based on the different temperatures at which they boil/condense. At temperatures above 750°F (400°C), the oil would thermally crack, or break apart, which would hinder the distillation process.

The lighter hydrocarbons condense at higher points in the distillation tower, while heavier hydrocarbons condense lower in the tower. These hydrocarbons (e.g., naphtha, kerosene, diesel and gas oil) are then moved out of the tower through different streams at various heights and sent to other units at the refinery for further processing or blending. The heaviest hydrocarbons that do not vaporize are drawn from the bottom of the atmospheric tower and sent to the vacuum distillation unit to be further refined.



Related Topics

Relevant Links

Topic Tools

Share this Topic

Contribute to Definition

We welcome updates to this Integripedia definition from the Inspectioneering community. Click the link below to submit any recommended changes for Inspectioneering's team of editors to review.

Contribute to Definition
Articles about Crude Distillation Unit (CDU)
Online Article

Vacuum distillation plays a critical role in improving yields for petroleum refiners by producing high-value petroleum products out of the heavier oils left over from atmospheric distillation. When short-term disturbances cause temporary cooling...

Authors: Massimo Capra
Partner Content

Ethos has assembled a team of experts who apply what they learned through years of process safety experience in the industry and dealing with OSHA and EPA. Click here to learn more about our services.

    News related to Crude Distillation Unit (CDU)

      Inspectioneering Journal

      Explore over 20 years of articles written by our team of subject matter experts.

      Company Directory

      Find relevant products, services, and technologies.

      Training Solutions

      Improve your skills in key mechanical integrity subjects.

      Case Studies

      Learn from the experience of others in the industry.


      Inspectioneering's index of mechanical integrity topics – built by you.

      Industry News

      Stay up-to-date with the latest inspection and asset integrity management news.


      Read short articles and insights authored by industry experts.

      Expert Interviews

      Inspectioneering's archive of interviews with industry subject matter experts.

      Event Calendar

      Find upcoming conferences, training sessions, online events, and more.


      Downloadable eBooks, Asset Intelligence Reports, checklists, white papers, and more.

      Videos & Webinars

      Watch educational and informative videos directly related to your profession.


      Commonly used asset integrity management and inspection acronyms.