Also known as: VBU
In refining, the visbreaker is a mild bottoms conversion unit. It upgrades vacuum resid by cracking it so that viscosity is reduced and the amount of high-value cutter stock required to blend it into residual fuel oil is reduced.
The conversion of vacuum resid into light products is very low in a visbreaker -- typically less than 15% by volume. However, the cost of a visbreaker is much lower than for other, more severe bottoms upgrading units. This makes it an attractive investment in markets where the demand for residual fuel oil is high.