Visbreaker operation

Visbreaking is a mild thermal cracking process that reduces the viscosity of heavy fuel oils and reduces the amount of low-viscosity blending stocks that must be added to the heavy residuals to meet viscosity specifications of the specific heavy fuel oil. The amount of heavy fuel oil production by a refinery is reduced by 20—30 percent if a visbreaker is used. The refinery profitability is improved with visbreaker operation, because heavy fuel oils are low value products. 

Visbreaking severity is monitored to help minimize cracking and alteration of the nature of asphaltenes within the visbreaker feed. Paraffinic side chain cracking or destruction of the asphaltene-resin complex may occur during visbreaking operations and may result in precipitation of asphaltenes from solution. Asphaltene precipitation has been seen especially when visbroken material is blended with lighter-viscosity paraffinic fuels. 

Straight-run fuel oil fractions from the same crude oil normally are stable and mutually compatible. However, fuel oil produced from the thermal cracking and visbreaking operations may be stable by themselves but can be unstable or incompatible if blended with straight-run fuels and vice versa. Furthermore, asphaltic deposition may result from the mixing of (distillate and residual) fuel oils of different origin and treatment, each of which... 

Used in Germany during World War II. A version developed by Veba Oel EntwicklungsgeseUschaft mbH was operated in Bottrop, Germany, from 1988 to 1994, using vacuum residues from crude oil distillation and visbreaking operations, with plastics from municipal wastes, and with chlorinated organic compounds. 

Visbreaking being a thermal process, the yields of the various hydrocarbon products and residue conversion are commanded by the reaction temperature. That is, the temperature at which the feed is heated and fed to the furnace is a direct measure of reaction severity of the visbreaking operation. 

The severity (reaction temperature and residence time) of visbreaker operation is normally limited by the need to produce a visbroken residue that can be blended to produce a stable fuel oil, which is a product with low sediment formation tendency when stored. Sediments are undesirable as they can quickly foul the filters of pumps used to move the oil needing time-consuming maintenance. 

Stratiev, D., Kirilov, K., Belchev, Z., Petkov, P. 2008. How do feedstocks affect visbreaker operations Hydrocarbon Process. 6(June) 105-112. 

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