Transport mechanisms and modeling of riser reactor
Department of Mechanical and Industrial Engineering
Doctor of Philosophy
Geskin, E. S.
Ho, Teh C.
Rosato, Anthony D.
Riser reactors are extensively employed in various industrial applications. In a riser reactor, the hydrodynamics is closely interacted with kinetic reactions. Common models for the performance prediction of riser reactors overlook this vital coupling effect, which not only miss the important reaction characteristics in the dense-phase transport regime of riser reactors but also misinterpret the kinetic properties via ad hoc adjustments. It is noted that the modeling of hydrodynamics in riser flows has major flaws in its predictability of phase transport in both dense-phase and accelerating regimes where most reactions occur. In addition, with the spray feeding of reactants at the bottom of a riser reactor, the catalytic reaction that coherently coupled with vapor-catalyst mixing in the spray vaporization process has never been investigated. Understanding of this reaction in the spray region is important because it provides the inlet conditions of phase transport to the follow-up reactions in the riser reactor. This dissertation hence is aimed at the development of mechanism-based parametric model that yields reliable prediction in transport and reaction characteristics in general catalytic riser reactors.
The dissertation consists of three integrated parts: 1) governing mechanisms and modeling of gas-solids transport in a riser, with special focuses on the solids transport in dense-phase and acceleration regimes; 2) interacting mechanisms between hydrodynamics and catalytic reactions in riser reactors, with special focuses on the modeling of the coupling of hydrodynamics with catalytic reactions and the determination of reaction properties that are independent of hydrodynamics; 3) modeling of reaction in the spray mixing and vaporization process, with special focuses on the coupling among spray evaporation, vapor-catalyst mixing and catalytic reaction.
On the hydrodynamic model, we have discovered the new control mechanisms that govern the solids acceleration. Most importantly, an additional resistant force, due to inter-solids collision in the acceleration regime, must be added to the momentum equation of solids. The new developed model has successfully predicted the axial profiles of transport properties throughout the entire transport domain, including dense phase, acceleration, and dilute phase regimes. To further explore the flow heterogeneity in both radial and axial directions, an integral-differential hydrodynamics model with a general third-order polynomial across any riser cross-sections has been developed. The model not only predicts the radial and axial phase transport but also yields the much-needed information of the wall boundary layer and backflow mixing for the popular core-annulus models.
On the coupling of hydrodynamics and catalytic reaction, a new correlation has been proposed to link the local reaction rate to the local transport properties (such as concentrations of catalysts and reactants, reaction temperature, and transport velocities). The resulted model not only predicts the correct reaction characteristics against the plant data but also demonstrates the feasibility of adopting the same reaction properties of the same type of catalytic reactions in different riser reactors.
The coupling of hydrodynamics and catalytic reaction has also been extended to investigate the catalytic reaction in the spray region. The resulted changes in transport properties provide the inlet conditions for the follow-up reactions in the riser reactor.
njit-etd2010-099 (147 pages ~ 6,671 KB pdf)
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Created October 21, 2011