Hydrodynamics in downflow fluidized beds (1): solids concentration profiles and pressure gradient distributions

Zhang, H.; Zhu, Jianfeng; Bergougnou, M.A.

doi:10.1016/s0009-2509(99)00284-5

Cited by 82 publications

(32 citation statements)

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“…Figure 2a and 2b show the results of the CFD simulations using Matsen's 31 closure for drag, and its comparison with experimental data. 33,34 The simulations were able to predict the experimentally observed velocity profiles to acceptable accuracy. 30 …”

Section: Cfd Modeling Of Downer Reactormentioning

confidence: 92%

“…32 The open literature is scarce in experimental data on hydrodynamics in downers. To validate the CFD model, data published by Zhang et al 33,34 was used as a reference. The downer dimensions and other geometrical and process parameters were chosen as per that publication.…”

Section: Cfd Modeling Of Downer Reactormentioning

confidence: 99%

“…model'' for each phase then by matching the variance of the RTD curve of given phase with the dispersion number, one can determine the effective ''dispersion coefficient'' of that phase. Though the CFD simulation is done for 9.3 m downer column (same as that of experimental setup 33,34 ), for the reactor model simulation, a downer of length 22 m is chosen as base case and the flow parameters are subsequently scaled up for this column. This scaling was essential to allow sufficient residence time for solids phase in the reactor.…”

Section: Scalar Transport Simulationmentioning

confidence: 99%

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Modeling of partial oxidation in gas–solids downer reactors

2009

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Selective partial oxidations represent an important class of reactions in the process industry. Of particular interest is the partial oxidation of n-butane to maleic anhydride (MAN), which is arguably the largest commercialized alkane partial oxidation process. Partial oxidation of n-butane, which uses vanadium phosphorous oxide (VPO) as a heterogeneous catalyst, is believed to operate through a unique mechanism in which lattice oxygen oxidizes n-butane selectively to MAN. Past work has shown that performing partial oxidation reactions in gas-solids riser configuration is realizable and commercially viable, which has lead to commercialization of this technology in the last decade. Though the riser configuration allows optimal and independent control of the oxidation and reduction steps, the riser unit suffers from solid backmixing at walls, which in turn result into lower conversion, nonoptimal selectivity and diminished overall yield of desired product. In recent years, there has been growing interest in downers involving cocurrent downflow of both solids and gas phases, hence offering relatively uniform flow characteristics. In this contribution, we explore through modeling the implications of effecting partial oxidation reactions in a downer (gas-solids cocurrent downflow) compared to that in a conventional riser reactor (gas-solids cocurrent up flow) operated under equivalent operating conditions. Further, we explore the operational space of downers for these reactions, suggesting ways for improving the productivity of downer for partial oxidation applications. V

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Section: Cfd Modeling Of Downer Reactormentioning

confidence: 92%

Section: Cfd Modeling Of Downer Reactormentioning

confidence: 99%

Section: Scalar Transport Simulationmentioning

confidence: 99%

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Modeling of partial oxidation in gas–solids downer reactors

2009

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“…Solids from the fast separator are returned to the storage tank during normal operation. More details about this system can be found in Zhang et al [23].…”

Section: Methodsmentioning

confidence: 99%

Direct Measurements of Instantaneous Solid Flux in a CFB Riser using a Novel Multifunctional Optical Fiber Probe

Zhu

2009

Chem Eng & Technol

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With a novel optical fiber probe that can measure instantaneous local particle velocity and solid concentration simultaneously, extensive experiments were conducted to study transient flow structures in a 15.1-m long circulating fluidized bed (CFB) riser of 100 mm in diameter. This study analyzed the radial and axial distributions of solid concentration, particle velocity, and their variations with nine operating conditions and at six axial levels. Instantaneous local solid concentration and particle velocity were found to be well correlated at most of the radial positions. The detailed time evolution, axial and radial distribution of instantaneous solid flux, and the variation of solid flux with operating conditions were also investigated. The radial solid flux profile showed a flat shape with a maximum at near wall area under most operating conditions. The instantaneous solid flux was found to have a strong fluctuation at a radial position of r/R = 0.8~0.9.

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“…However, the number of particles that can be taken into account in this technique is limited. Therefore, it is not yet possible to simulate even a pilot scale unit (for instance, downer of length 9.1 and diameter 0.1 m will have at least 2.3 × 10 9 particles of 67 µm diameter, at merely 0.5% solids fraction) (Zhang et al, 1999) using modern day computational power. However such modeling even done at the small finite volume of an Eulerian simulation can play an important role in building closure relationships for particle-particle interactions, in large scale E-E model.…”

Section: Modelingmentioning

confidence: 99%

DEM Simulation of Gas-Solids Circulating Fluidized Beds

Suryawanshi

Roy

2009

J. Chem. Eng. Japan

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Gas-solids circulating fluidized beds involve multiscale interactions and hence it is a challenge to model flow in such a system with detail at a particle level. In present work, flow in co-current upflow mode (riser) as well as co-current downflow mode (downer) is simulated using distinct element method (DEM). Simulations were performed for number of operating conditions. Detailed post processing results of the fluctuational kinetic energy (granular temperature) are presented.

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Hydrodynamics in downflow fluidized beds (1): solids concentration profiles and pressure gradient distributions

Cited by 82 publications

References 0 publications

Modeling of partial oxidation in gas–solids downer reactors

Modeling of partial oxidation in gas–solids downer reactors

Direct Measurements of Instantaneous Solid Flux in a CFB Riser using a Novel Multifunctional Optical Fiber Probe

DEM Simulation of Gas-Solids Circulating Fluidized Beds

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