A comprehensive program for visbreaking simulation: product amounts and their properties prediction

The visbreaking process is adopted in many refineries, particularly in Europe and the Far East. It consists of a liquid phase pyrolysis of atmospheric or vacuum residues, with the aim to reduce the viscosity of the visbroken residues and, in doing that, to significantly increase the distillate yields. In spite of the importance of the process, mainly empirical models have been proposed. However rising interest appears to be towards a deeper understanding of the phenomena influencing process performance. The largest difficulties, in principle, are connected with the infinite number of components, reactions involved and, in the mean time, to the relatively poor level of the available data for the feedstock characterisation. Also, the prediction of the product amounts and their properties presents considerable problems. A mechanistic approach to this process is proposed, including aspects such as fouling of the coils, effluent amounts and properties (residue stabilities, sulphur and asphaltene content, viscosity, specific gravity and so on). A set of results is compared with data from literature, research lab tests and commercial units. (C) 1997 Elsevier Science Ltd.