Thermal Cracking – continued.

Notice in the diagram, the feed is introduced to a furnace to heat it up to the desired temperature. After that, it is routed to a vertical column, referred to as the “soaker”. The soaker provides the necessary residence time to allow heat to crack the feed. To prevent over-cracking, the effluent from the soaker is quenched by gas-oil at the top and then introduced into a fractionator.

Visbreaking is used to reduce the pour point of waxy residues and reduce the viscosity of of other residues used for blending with lighter fuel oils. The term "pour point" refers to the minimum temperature at which a fluid begins to flow under specific laboratory conditions.

Middle distillates may also be produced, depending on product demand. The thermally cracked residue tar, which accumulates in the bottom of the fractionation tower, is recycled or processed further in other systems.