Coupling of hydrodynamics and catalytic reaction in FCC riser reactors

Fluid catalytic cracking (FCC) riser reactors convert heavy petroleum oils into light hydrocarbon products. The conversion rates, in principle, are dependent upon the coupling of hydrodynamics and reaction kinetics in the gas-solids transport process. The catalysts in a riser, on the other hand, undergo an accelerating transport process or a continuously diluting process, which is heavily influenced by the non-uniform cracking characteristics along the riser reactor. Most research on FCC riser reactor so far used hydrodynamic model of plug flow and reaction model based on overall catalyst-to-oil ratio (CTO), which not only neglects the non-uniform characteristics of hydrodynamics and reactions along the riser but also oversimplifies the intrinsic coupling of multiphase flow hydrodynamics and the cracking kinetics. This work is focused on the axial distributions and mechanistic coupling of local transport and reaction characteristics of catalysts and oils along the FCC risers. A simple four-lump reaction scheme is adopted to simulate the cracking reactions and all variable in both hydrodynamics and reaction models locally averaged over riser cross-sections. Modeling predictions are satisfactorily compared with the yield pattern and exit temperature of industrial scale plant data. The axial distributions of the hydrodynamic properties of the gas-oil and catalyst are plotted to study the effects of reaction kinetics on the axial distributions of the flow properties. Comparison against plug-flow-based modeling approach indicates that, the traditional methods tend to underestimate the vacuum gas oil (VGO) conversion percentage and gasoline yield in the lower part of the riser.