Thermal Cracking

Thermal cracking encompasses a range of non-catalytic processes used to enhance the heavy fraction of crude oil by conversion and separation.

In order for a refinery to produce more valuable products, the heavy "residue" fractions can be processed into lighter fractions. Thermal cracking produces gas, naphtha and distillate (kerosene and diesel).

Examples of this separation method are:

• Vis-breaking, which improves fuel oil quality
• Delayed coking, which also produces coke
• Flexi-coking, which includes coke gasification

Vis-breaking entails the use of mild cracking, whereby the residue is converted into lighter products so that the viscosity is reduced. Typical yields from this process are 25% diesel and 75% fuel oil. Operating conditions vary, but are typically; temperature 450° C and pressure 5 - 10 barg.

Delayed coking completely converts residue into gas, naphtha, diesel and coke. It is normally a semi-continuous process. Operating parameters are typically; temperature 450° - 500° C in the coke drum and 2 - 3 barg pressure.

Flexi-coking produces a range of lighter products and coke. Typical yields are 67% light products (high energy LPG, naphtha and diesel) and 33% low energy fuel gas. Flexi-coking does not produce fuel oil residue.