Dawei Wang - Academia.edu (original) (raw)
Papers by Dawei Wang
Riser reactors are extensively employed in various industrial applications. In a riser reactor, t... more 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 ACKNOWLEDGMENT I would like to express my deepest appreciation to Dr. Chao Zhu, who gave me guidance, supervision and research intuition, but also is a sincere friend providing experience, support, encouragement, and reassurance throughout my life during my study at New
The hydrodynamics of a liquid droplet in motion impinge with a particle are of direct relevance t... more The hydrodynamics of a liquid droplet in motion impinge with a particle are of direct relevance to many engineering problems. In recent years, the phase transfer mechanism of droplet-solid phase collisions has grown in importance in industrial operations. Many power and petrochemical industries need detailed knowledge of the fundamental physical phenomena employed droplet impact on solid surface with limited surface size. However, very limited studies are available on the droplets hitting on surfaces with finite dimensions, which are comparable to the sizes of the droplets. This work illustrates the phenomena of impact of a droplet on the solid ball or balls both experimentally and theoretically. Measurements were performed using a high precision pipette and electronic scale, yielding both qualitative and quantitative information about the droplet-solid phase collisions. These experimental results are compared with modeling. Effects of the droplet size, velocity and the off-centre c...
Recent measurement of solid concentration in gas-solid riser flows by Electric Capacitance Tomogr... more Recent measurement of solid concentration in gas-solid riser flows by Electric Capacitance Tomography (ECT) reveals a strong heterogeneous structure, typically represented by a core-annulus-wall zone pattern. In this paper we present a mechanistic model in which the formation of the heterogeneous structure is due to the radial migration of solid flow from the wall toward center as well as due to the non-uniform acceleration of solids across the cross-section near the bottom of the riser. Firstly we present the general governing equations and discuss problem closure; then a simplified model with one-way flow coupling between the wall region and the core-annulus region is proposed to simulate the formation and development process of heterogeneous flow structures in the riser. Typical results of the three-zone flow structure along the riser are illustrated, which include the axial distributions of solids concentration and phase velocities in each zone, in addition to the pressure distr...
Industrial & Engineering Chemistry Research, 2009
The gas-solid flow in a riser has strong inherent nonuniformities both in the flow structure and ... more The gas-solid flow in a riser has strong inherent nonuniformities both in the flow structure and in the dynamic phases. The flow structure in a riser can be altered with the implementation of different solids feeding devices, and hence may affect the reactor performance. This paper is aimed at investigating the effect of various riser entrances on the overall flow structure and its stability at different operation conditions. Three riser entrances are selected to simulate the common solids feeding devices of risers, namely, the J-bend feeder, the L-valve feeder with a distributor, and the L-valve feeder after a taper section. The study is first focused on the flow dynamics in the riser entrance region. This is to identify the characteristic height of the entrance region as well as to obtain the radial distributions of phase transport properties at the end of the entrance region. These radial profiles are then used as the flow inlet conditions in the mechanistic model for the study of overall flow structure and stability in the riser main region. The study shows that the flow structure in the entrance region can be strongly affected by the selection of solids feeding patterns but weakly dependent upon the operation conditions. The flow structure in the main riser region, however, is weakly dependent upon the selection of solids feeding patterns but strongly affected by the operation conditions. The riser characteristic length of the entrance region is nearly independent of the gas inlet velocity and solids mass flow rate; however, it is moderately influenced by the solid feeding pattern. As part of model validation, some simulation results are directly compared with available experimental measurements, with reasonably good agreement.
AIChE Journal, 2011
The Fluid catalytic cracking (FCC) process has been the most widely used technology for the conve... more The Fluid catalytic cracking (FCC) process has been the most widely used technology for the conversion of various refinery hydrocarbon streams into high-octane gasoline and high-value petrochemical feed-stocks. Great strides have been made to develop predictive process models for riser reactor performance; with development focused on molecule-based cracking kinetic network and little attention has been paid to fundamental coupling of multiphase hydrodynamics and reaction kinetics. Local coupling between hydrodynamics and reaction kinetics is critical to the development of riser reaction models, as most reactions occur inside catalysts pores. The reaction performance relies strongly on catalyst temperature, local CTO, spent-fresh catalyst composition (due to back flow near wall), and reaction time duration; which are all functions of local reactioncoupled hydrodynamics. Few of these coupling mechanisms have been investigated. As a first step, we develop modeling approach to capture dominant features of flow-reaction coupling in FCC riser reactor. The model predictions reasonably match with plant data and shows the cracking intensity at the riser bottom is much greater than that calculated from conventional riser models, which neglects oil-catalyst hydrodynamic coupling and catalyst dilution due to volume expansion.
Riser reactors are extensively employed in various industrial applications. In a riser reactor, t... more 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 ACKNOWLEDGMENT I would like to express my deepest appreciation to Dr. Chao Zhu, who gave me guidance, supervision and research intuition, but also is a sincere friend providing experience, support, encouragement, and reassurance throughout my life during my study at New
The hydrodynamics of a liquid droplet in motion impinge with a particle are of direct relevance t... more The hydrodynamics of a liquid droplet in motion impinge with a particle are of direct relevance to many engineering problems. In recent years, the phase transfer mechanism of droplet-solid phase collisions has grown in importance in industrial operations. Many power and petrochemical industries need detailed knowledge of the fundamental physical phenomena employed droplet impact on solid surface with limited surface size. However, very limited studies are available on the droplets hitting on surfaces with finite dimensions, which are comparable to the sizes of the droplets. This work illustrates the phenomena of impact of a droplet on the solid ball or balls both experimentally and theoretically. Measurements were performed using a high precision pipette and electronic scale, yielding both qualitative and quantitative information about the droplet-solid phase collisions. These experimental results are compared with modeling. Effects of the droplet size, velocity and the off-centre c...
Recent measurement of solid concentration in gas-solid riser flows by Electric Capacitance Tomogr... more Recent measurement of solid concentration in gas-solid riser flows by Electric Capacitance Tomography (ECT) reveals a strong heterogeneous structure, typically represented by a core-annulus-wall zone pattern. In this paper we present a mechanistic model in which the formation of the heterogeneous structure is due to the radial migration of solid flow from the wall toward center as well as due to the non-uniform acceleration of solids across the cross-section near the bottom of the riser. Firstly we present the general governing equations and discuss problem closure; then a simplified model with one-way flow coupling between the wall region and the core-annulus region is proposed to simulate the formation and development process of heterogeneous flow structures in the riser. Typical results of the three-zone flow structure along the riser are illustrated, which include the axial distributions of solids concentration and phase velocities in each zone, in addition to the pressure distr...
Industrial & Engineering Chemistry Research, 2009
The gas-solid flow in a riser has strong inherent nonuniformities both in the flow structure and ... more The gas-solid flow in a riser has strong inherent nonuniformities both in the flow structure and in the dynamic phases. The flow structure in a riser can be altered with the implementation of different solids feeding devices, and hence may affect the reactor performance. This paper is aimed at investigating the effect of various riser entrances on the overall flow structure and its stability at different operation conditions. Three riser entrances are selected to simulate the common solids feeding devices of risers, namely, the J-bend feeder, the L-valve feeder with a distributor, and the L-valve feeder after a taper section. The study is first focused on the flow dynamics in the riser entrance region. This is to identify the characteristic height of the entrance region as well as to obtain the radial distributions of phase transport properties at the end of the entrance region. These radial profiles are then used as the flow inlet conditions in the mechanistic model for the study of overall flow structure and stability in the riser main region. The study shows that the flow structure in the entrance region can be strongly affected by the selection of solids feeding patterns but weakly dependent upon the operation conditions. The flow structure in the main riser region, however, is weakly dependent upon the selection of solids feeding patterns but strongly affected by the operation conditions. The riser characteristic length of the entrance region is nearly independent of the gas inlet velocity and solids mass flow rate; however, it is moderately influenced by the solid feeding pattern. As part of model validation, some simulation results are directly compared with available experimental measurements, with reasonably good agreement.
AIChE Journal, 2011
The Fluid catalytic cracking (FCC) process has been the most widely used technology for the conve... more The Fluid catalytic cracking (FCC) process has been the most widely used technology for the conversion of various refinery hydrocarbon streams into high-octane gasoline and high-value petrochemical feed-stocks. Great strides have been made to develop predictive process models for riser reactor performance; with development focused on molecule-based cracking kinetic network and little attention has been paid to fundamental coupling of multiphase hydrodynamics and reaction kinetics. Local coupling between hydrodynamics and reaction kinetics is critical to the development of riser reaction models, as most reactions occur inside catalysts pores. The reaction performance relies strongly on catalyst temperature, local CTO, spent-fresh catalyst composition (due to back flow near wall), and reaction time duration; which are all functions of local reactioncoupled hydrodynamics. Few of these coupling mechanisms have been investigated. As a first step, we develop modeling approach to capture dominant features of flow-reaction coupling in FCC riser reactor. The model predictions reasonably match with plant data and shows the cracking intensity at the riser bottom is much greater than that calculated from conventional riser models, which neglects oil-catalyst hydrodynamic coupling and catalyst dilution due to volume expansion.