Visbreaker
processing unit
A visbreaker is a processing unit in an oil refinery whose purpose is to minimize the quantity of residual oil produced in the distillation of crude oil and to increase the yield of more valuable middle distillates (heating oil and diesel) by the refinery. A visbreaker thermally cracks large hydrocarbon molecules in the oil by heating in a furnace to lower its viscosity and to produce small quantities of light hydrocarbons. (LPG and gasoline). The process name of "visbreaker" refers to the fact that the process lowers (i.e., breaks) the viscosity of the residual oil. The process is non-catalytic.
Process objectives
The objectives of visbreaking are:
Lower the viscosity of the feed stream: Typically this is the residue from vacuum distillation of crude oil but can also be the residue from hydroskimming operations, natural bitumen from seeps in the ground or tar sands, and even certain high viscosity crude oils.
Lower the amount of residual fuel oil produced by a refinery: Residual fuel oil is generally regarded as a low value product. Demand for residual fuel continues to decrease as it is replaced in its traditional markets, such as fuel needed to generate steam in power stations, by cleaner burning alternative fuels such as natural gas.
Increase the proportion of middle distillates in the refinery output: Middle distillate is used as a diluent with residual oils to bring their viscosity down to a marketable level. By lowering the viscosity of the residual stream in a visbreaker, a fuel oil can be made using less diluent and the middle distillate saved can be diverted to higher value diesel or heating oil manufacture.
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