Refining fundamentals

Learn about the main characteristics of the refining process and the refinery configurations.

The process of refining

Crude oil is composed of several types of hydrocarbons. Petroleum refining is a process that takes advantage of the different weights, volatilities and boiling temperatures of hydrocarbons to separate them, creating intermediate and final products.

Typically, there are four major stages of refining to separate crude oil into usable substances:

  • Physical separation of the various types of hydrocarbons through distillation.
  • Purification of intermediate products in pre-treatment units.
  • Chemical processing of lower value fractions into lighter products.
  • Treatment and mixing of intermediates by removal of undesirable elements and compounds for integration into final products.

The process begins with the heating of crude oil. The vapours that then form rise through a fractionation column, equipped with compartments at different heights. The most volatile and low boiling point components rise to the top of this column.Components with the highest boiling point remain in the lower layers. This technique of physical separation of fractions is also referred to as fractional distillation and is the starting point for the petroleum refining process.

Each step of the refining process is designed to maximise the added value to the materials processed in it. The simplest refineries only perform crude distillation. More complex refineries also perform the other three functions.

Configuration of the refineries

The range and quality of refined products produced in a refinery depends on the types of crude used as raw material and the structures installed in the refinery.

Light and sweet crudes - Generate higher amounts of higher value refined products, such as gasoline, jet fuel and diesel.

Heavier and sour crudes - Produce larger quantities of lower-value products, such as fuel oils.

The configuration of certain refineries, particularly in North America, is typically geared towards the production of light distillate products, such as gasoline, while the configuration of refineries in most other regions, such as Europe, is typically geared towards the production of medium distillate products such as diesel and jet fuel.
On the other hand, there are refineries configured to produce different specialised products, such as base oils, naphtha and bitumen.

Refineries can usually be divided into two main categories:

  • Simple hydroskimming refineries - Mainly execute the distillation process. 
  • Complex refineries - Perform two additional functions: conversion of the hydrocarbon fractions produced in the crude distillation process into other products, and the processing of intermediate products to obtain higher value products. 

The configuration of complex refineries is focused on maximising either gasoline production (catalytic cracking) or intermediate distillate products (hydrocracking). In addition, these refineries use a number of secondary processing capabilities for vacuum residue recovery.

Refineries configured for a high conversion and desulphurisation capacity can obtain higher yields on higher value refined products as they process heavier and sourer crudes than refineries with a lower conversion and desulphurisation capacity.

The complexity of a refinery is therefore related to its ability to process raw materials, such as heavier and higher sulphur crudes, into value-added products. Typically, the greater the complexity, the more flexible the range of crudes the refinery can process and the better positioned it is to take advantage of lower cost crudes, which results in increased refining margins.