Modeling fixed-bed residue hydrotreating processes

Residue hydrotreating was studied in a fixed-bed reactor over a wide range of operating conditions and using various feeds. Based on the experimental data, a model was developed to predict the performance of fixed-bed residue hydrotreating units. The reactor model is a heterogeneous one-dimensional plug flow model, which accounts for diffusion inside the catalyst pellets. To describe the various transformations, a kinetic model was developed based on eight chemical lumps (gas, saturates, aromatics-aromatics-, aromatics+aromatics+, resins-resins-, resins+resins+, asphaltenes, and metal deposits) that were further subdivided into sub-species to track their atomic composition (C, H, S, N, O, Ni, V). Between these various sub-species, 84 reactions were taken into account. After deriving the rate equations and subsequent parameter estimation, a comparison was carried out between the simulation results and experimental data. The model accurately predicts the evolution along the reactor of the concentration profiles of the various lumps, the impurities in the total liquid effluent, and the evolution of the atomic composition of each lump. A comparison between an experimentally measured profile of vanadium deposited inside the catalyst pellet and the simulated intraparticle profiles for asphaltenes and resins+resins+ illustrates the representativity of the modeling approach and the importance of accounting for intraparticle diffusion when modeling residue hydrotreating processes.