An updated functional-group-based approach to modeling the vacuum residue oil gasification kinetics

Abstract

Gasification of heavy petroleum residues can convert low-value feedstock to hydrogen-rich syngas, which can further be used for power generation and/or chemical production. The present work proposed an updated functional-group-based approach (FGMech) to modeling the gasification of a vacuum residue oil (VRO), which is helpful for better understanding the detailed kinetics of the gasification and improving gasifier performance. Elemental, average molecular weight (AMW) and nuclear magnetic resonance (NMR) analyses were conducted experimentally to characterize VRO, including elemental composition, average molecular formula and the functional group distribution, which were further used for model construction. A lumped mechanism for VRO devolatilization was constructed based on the updated FGMech approach: stoichiometric parameters of stable gases, tars and char were obtained from experiments, while those of radicals were based on the multiple linear regression (MLR) correlations; thermodynamic and kinetic parameters were derived from Benson group additivity method and rate rules, respectively. A merged detailed model was adopted for describing the conversion of gases and tars, and a global model was used for char. To test the reliability of the present model approach, Orimulsion gasification experiments from literature were simulated using an integrated perfectly stirred reactor (PSR) and plug flow reactor (PFR) model. It shows that the present model can reasonably predict measured results under various equivalence ratios, and has better performance on the prediction of CH4 compared with most literature models. Based on model analyses, syngas comes from the conversion of C2H4, H2S, CH4 and char in different gasification stages. Benzene, toluene, naphthalene and 1-methylnaphthalene are initial tar species considered in the devolatilization of the VRO. They can undergo hydrogen abstraction acetylene addition (HACA) and C3H3/C5H5 addition reaction pathways to produce large PAHs.