- Visbreaking is a non-catalytic thermal process that converts atmospheric or vacuum residues via thermal cracking to gas, naphtha, distillates, and visbroken residue.
- Atmospheric and vacuum residues or solvent deasphalter pitch are typically charged to a visbreaker to reduce fuel oil viscosity and increase distillate yield in the refinery
- The main purpose of a Visbreaker is to reduce the need for Cutter Stock in the production of fuel oil
How It Works
- There are two types of visbreaking technology that are commercially available: the ‘coil’ or ‘furnace’ type and the ‘soaker’ process.
- In the coil process, conversion is achieved by high temperature cracking for a predetermined, relatively short period of time in the heater.
- In the soaker process, which is a low temperature/high residence time process, the majority of conversion occurs in a reaction vessel or soaker drum, where the two-phase heater effluent is held at a lower temperature for a longer period of time.
- In a ‘coil’ type operation, charge is fed to the visbreaker heater where it is heated to a high temperature, causing partial vaporization and mild cracking.
- The heater outlet stream is quenched with gas oil or fractionator bottoms to stop the cracking reaction.
- The vapor-liquid mixture enters the fractionator to be separated into gas, naphtha, gas oil and visbroken resid (tar).
- The visbroken bottoms are then blended with lighter materials (cutter stock) to meet fuel oil specifications. The fractionated visbreaker gas oil is often used as the cutter stock.
- A visbreaker heater is used to heat the raw materials
- A soaker drum is the reactor where the cracking takes place
- A fractionator separates the components