THE VISBREAKING PROCESS SIMULATION - PRODUCTS AMOUNT AND THEIR PROPERTIES PREDICTION

The visbreaking process is adopted by many refineries. It consists of a liquid phase pyrolysis of atmospheric or vacuum residues with the ai m of increasing the production of light fractions and simultaneously r educing the viscosity of the visbroken residues. In spite of the econo mical importance of this operation, the literature is lacking of scien tific informations; only empirical models have been presented. Major d ifficulties are constituted by the huge number of components and react ions that is characterising the system and by the relatively. poor lev el of the available data for the feedstock characterisation. Due to th e complexity of the feed to the reactor also the characterisation of t he products properties, besides their amount, presents considerable pr oblems. The results coming from a mechanistic approach are here presen ted. They are compared with experimental data from literature, researc h 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, specif ic gravity, Conradson carbon residue and so on). The developed model c onstitutes a valid support for the understanding and prediction of the complex phenomena that are occurring during the HC liquid phase pyrol ysis and can find a practical and important application both for impro ving the visbreaking furnaces design and for monitoring and control of the V.B. operations.