Refining oil
Photo of distillation tower
A distillation tower.

An oil refinery changes crude oil into many useful products. The refinery products can be taken away by sea, by pipeline or go to the chemical plant to be made into synthetic materials.

The first step is always primary distillation. Crude oil is a complicated mixture of compounds - most of them hydrocarbons. This mixture is split up into different fractions in the distillation tower. The fractions come out of the column at different levels.

A distillation tower is often called a still. The atmospheric still is the tall steel tower in the middle.

The crude oil is heated in the furnace to the right. The different fractions come out at different levels. You can see the pipes that take them away. The residue from the atmospheric still passes to the vacuum still on the left. Here it is split into more fractions.

Some of the fractions are nearly ready to use. However, other fractions need more treatment.

Some treatments, like cracking, split the hydrocarbons into smaller groups. Others, like reforming and polymerisation, change the structure of the molecules.

Some of the lighter molecules are used as feedstock for the isomeriser and reformer.

Heavier molecules are often fed to the catalytic cracker (to be broken into smaller hydrocarbons). Or are cleaned up in the residfiner before being used as fuel oil.

Refining process
An overview of some of the refinery processes.