Modelling of catalytic hydrocracking and fractionation of refinery vacuum residue

Abstract

AbstractThe main objective of this work was to create a kinetic model of refinery vacuum residue hydrocracking and to monitor the impact of the operating conditions on the product yields. Data and yield measurements were gathered from a residual hydrocracking unit (RHC). Reaction temperature ranged from 401°C to 412°C at the pressure of 18–20 MPa. A simplified kinetic yield model was applied; where the feed and each product fraction are represented by one lump (reactant or product of cracking) represented by the number of pseudo-components. The product fractions were determined by fractional distillation of the output mixture from the reactor. The kinetic model includes eight reaction steps and the following six fractions: vacuum residue, vacuum distillate, gas oil, kerosene, naphtha, and gas. In addition, a model for hydrodesulphurisation has been proposed. The average relative deviation between model and experimental yields was 5.36 %, and that for the sulphur conversion model was 1.04 %. An Excel file with the kinetic model was implemented in the Aspen Plus program using a user-defined model of the reactor. This model allows to input/output data between the Aspen Plus and Excel programs. The Excel subroutine calculates the reaction kinetics of cracking from the set temperature and residence time, and distributes the products into 30 pseudo-components created in the Aspen Plus program. The remaining part of the RHC unit was simulated in the Aspen Plus environment. The effects of the reaction conditions such as temperature and residence time on the conversion of the feed and on the distillation curves of the output mixture from the reactor were investigated. The model was verified by comparison of the distillation curves of simulated and real products.