The visbreaking process simulation: products amount and their properties prediction

Abstract

The visbreaking process is adopted by many refineries. It consists of a liquid phase pyrolysis of atmospheric or vacuum residues with the aim of increasing the production of light fractions and simultaneously reducing the viscosity of the visbroken residues. In spite of the economical importance of this operation, the literature is lacking of scientific informations; only empirical models have been presented. Major difficulties are constituted by the huge number of components and reactions that is characterising the system and by the relatively poor level of the available data for the feedstock characterisation. Due to the complexity of the feed to the reactor also the characterisation of the products properties, besides their amount, presents considerable problems. The results coming from a mechanistic approach are here presented. They are compared with experimental data from literature, research lab tests and commercial units. Moreover they are covering different aspects like fouling in the coils, effluents amounts and properties (residues stability, sulphur and asphaltenes content, viscosity, specific gravity, Conradson carbon residue and so on). The developed model constitutes a valid support for the understanding and prediction of the complex phenomena that are occurring during the HC liquid phase pyrolysis and can find a practical and important application both for improving the visbreaking furnaces design and for monitoring and control of the V.B. operations.