A Comparison of Flow Dynamics and Flow Structure in a Riser and a Downer

Wu, Bangyou; Zhu, Jesse; Briens, Lauren

doi:10.1002/ceat.200600281

Cited by 14 publications

(25 citation statements)

References 14 publications

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“…Low values of entropy were found at this radial position (r/R = 1.0). As observed by Wu et al, [1] in the wall region of the riser, solids tended to form large clusters, especially in the bottom section of the riser, where solids holdup was very high. For the developed zone, the difference between core and wall regions can be easily be seen, especially in the case of lower G s .…”

Section: Kolmogorov Entropysupporting

confidence: 56%

“…[1] CFB risers have many advantages over conventional bubbling and turbulent fluidised bed reactors, such as high gas-solids contact efficiency and reduced axial dispersion. [2] On the other hand, it is been well-recognised that gas-solids two-phase flow in CFBs is extremely non-uniform, owing to the influence of a variety of phenomena, such as particle clustering, turbulence and interactions between particles and between gas and solids.…”

Section: Introductionmentioning

confidence: 99%

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Study of gas–solids flow in a short CFB riser by statistical and chaotic deterministic analysis of optical fibre probe signals

Castilho

Cremasco

2012

Can J Chem Eng

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In this work, a short CFB riser with a height of 2.42 m and an ID of 82 mm was operated under different dilute operating conditions to study the fluid dynamics of FCC catalyst particles (d p = 80 m, p = 902 kg/m 3 ) in air. The electrical signals from the optical fibre probe were sampled at a frequency of 1000 Hz for a period of 30 s and were obtained at different positions along the radius and height of the riser. Data were analysed using both statistical methods (time average, standard deviation and frequency distribution) and chaos methods (construction of attractors; correlation dimension, D ML ; and Kolmogorov entropy, K ML ). Some results on solids holdup deduced from the electrical signal are also presented for the developed zone of the riser. It was verified that for very dilute conditions, increasing gas velocity produces more complex and less predictable fluctuations in solids concentration, while increasing solids flux generally reduces complexity and increases predictability. However, results for the most dilute condition used shows that for the radial position where solids holdup is higher (near the wall), the increase in solids concentration does not affect the mean free path of the particles, resulting in higher values of D ML than in the dilute region (core).

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Section: Kolmogorov Entropysupporting

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Study of gas–solids flow in a short CFB riser by statistical and chaotic deterministic analysis of optical fibre probe signals

Castilho

Cremasco

2012

Can J Chem Eng

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“…Since then, the flow characteristics in the riser have been delineated and understood in both the industrial and the academic fields. Due to the counter‐gravity flow, CFB risers tend not to have uniform gas and solids flow structure; with more particles accumulate at the riser bottom and near the wall inside the reactors . The nonuniform axial and radial flow structure has many disadvantages, for example, there is serious gas by‐passing through the core dilute region and extensive backmixing of solids in the wall region.…”

Section: Introductionmentioning

confidence: 99%

A comparison of flow development in high density gas‐solids circulating fluidized bed downer and riser reactors

Wang

Zhu

et al. 2015

AIChE Journal

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Comparison of flow development in high density downer and riser reactors is experimentally investigated using fluid catalytic cracking particles with very high solids circulation rate up to 700 kg/m2s for the first time. Results show that both axial and radial flow structures are more uniform in downers compared to riser reactors even at very high density conditions, although the solids distribution becomes less uniform in the high density downer. Solids acceleration is much faster in the downer compared to the riser reactor indicating a shorter length of flow development and residence time, which is beneficial to the chemical reactions requiring short contact time and high product selectivity. Slip velocity in risers and downers is also first compared at high density conditions. The slip velocity in the downer is much smaller than in the riser for the same solids holdup indicating less particle aggregation and better gas‐solids contacting in the downer reactors. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1172–1183, 2015

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“…In order to use RFMBRs more effectively and understand the gas-solid flow behavior, an understanding hydrodynamics of RFMBRs via numerical modeling is necessary [9,10]. The CFD approach as an emerging technique holds great potential in providing detailed information of the complex fluid dynamics [11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

A Two-Phase CFD Modeling Approach to Investigate the Flow Characteristics in Radial Flow Moving-Bed Reactors

Xiao

Luo²

2014

International Journal of Chemical Reactor Engineering

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Based on a complete CFD Eulerian-Eulerian two-fluid approach, a comprehensive three-dimensional (3D) two-phase reactor model was suggested to describe the flow behavior in radial flow moving-bed reactors (RFMBRs). A porous media model was incorporated into the reactor model in order to describe the flow resistance provided by the porous walls of the center and annular pipes. Compared with these previous reactor models, the reactor model considers the solid-phase movement instead of immobilization, which benefits for predicting the formation of cavity practically. The simulation results are agreement with the published experimental data. By employing the verified model, the flow field parameters in the reactors such as pressure drop and flow velocity were obtained. Besides, the simulations were then carried out to investigate the effect of the bed voidage on the flow behavior and to understand the phenomenon of cavity in the RFMBRs. The simulation results showed that both the centripetal and the centrifugal flow configurations have the inhomogeneous flow distribution and the phenomenon of cavity. Furthermore, the inhomogeneous distribution increases with the increase of the bed voidage, whereas the phenomenon of cavity is more obvious with the increase of gas inlet velocity. As a whole, this work provided a realistic modeling and a useful approach for the understanding of RFMBRs.

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A Comparison of Flow Dynamics and Flow Structure in a Riser and a Downer

Cited by 14 publications

References 14 publications

Study of gas–solids flow in a short CFB riser by statistical and chaotic deterministic analysis of optical fibre probe signals

Study of gas–solids flow in a short CFB riser by statistical and chaotic deterministic analysis of optical fibre probe signals

A comparison of flow development in high density gas‐solids circulating fluidized bed downer and riser reactors

A Two-Phase CFD Modeling Approach to Investigate the Flow Characteristics in Radial Flow Moving-Bed Reactors

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