Numerical Studies on Average Solids Holdup in a Liquid–Solid Circulating Fluidized Bed Riser

2012 ◽  
Vol 54 (2) ◽  
pp. 97-112 ◽  
Author(s):  
Tanmay Voore ◽  
Sangram Roy ◽  
P.S.T. Sai
Keyword(s):  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Numerical Studies ◽  
Solids Holdup

Solids Holdup of High Flux Circulating Fluidized Bed at Elevated Pressure

2012 ◽  
Vol 35 (5) ◽  
pp. 904-910 ◽  
Author(s):  
S. Yin ◽  
B. Jin ◽  
W. Zhong ◽  
Y. Lu ◽  
Y. Zhang ◽  
...  
Keyword(s):  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Elevated Pressure ◽  
High Flux ◽  
Solids Holdup

scholarly journals Effects of Riser Diameter on Solids Holdup and Particle Velocity Profiles in Circulating Fluidized Bed Riser Systems

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
Ronald W. Breault ◽  
Steven L. Rowan ◽  
Justin M. Weber ◽  
Jingsi Yang
Keyword(s):  
Fluidized Bed ◽  
Particle Velocity ◽  
Circulating Fluidized Bed ◽  
Velocity Profiles ◽  
Small Scale ◽  
Sauter Mean Diameter ◽  
Particle Size Range ◽  
Cold Flow ◽  
Solids Holdup ◽  
Radial Profiles

Abstract Tests were performed in a 0.1-m diameter small circulating fluidized bed (SCFB) and 0.3 m diameter cold flow circulating fluidized bed (CFCFB) riser systems located at the National Energy Technology Laboratory (NETL) to study the effects of riser diameter on the riser hydrodynamics. These tests were performed at solids circulation rates of Gs = 20 and 75 kg/m2 s and superficial gas velocities of Ug = 5.8 and 6.5 m/s using high-density polyethylene (HDPE) pellets with a density of 0.863 g/cm3, particle size range of 600–1400 µm (with a Sauter mean diameter of 871 µm, placing them in the Geldart B classification). Comparisons of riser axial pressure and solids fraction profiles, radial particle velocity profiles, and radial profiles of higher statistical moments and select chaos analysis parameters were considered. The results showed that for a given Ug and Gs, the smaller diameter riser exhibited characteristics associated with more dilute solids flow than that observed in the larger diameter riser. Additionally, the larger diameter riser exhibited a downward flow of solids near the wall under all test conditions, whereas the smaller diameter riser data exhibited little or no indications of solids downflow near the wall. These findings suggest that, from an industrial standpoint, a direct scaleup of small-scale tests cannot readily be accomplished as the solids holdup and the solids velocity profiles in small units (those normally tested in the laboratory) are not similar to those of large units and the performance of large units can therefore not be predicted from small-scale tests.

scholarly journals 3D CPFD Simulation of Circulating Fluidized Bed Downer and Riser: Comparisons of Flow Structure and Solids Back-Mixing Behavior

Processes ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 161
Author(s):  
Yancong Liu ◽  
Yingya Wu ◽  
Xiaogang Shi ◽  
Chengxiu Wang ◽  
Jinsen Gao ◽  
...  
Keyword(s):  
Fluidized Bed ◽  
Residence Time ◽  
Circulating Fluidized Bed ◽  
Operating Conditions ◽  
Solids Holdup ◽  
The Difference ◽  
Large Clusters ◽  
Small Clusters ◽  
Cluster Behavior ◽  
Back Mixing

The difference of gas-solids flow between a circulating fluidized bed (CFB) downer and riser was compared by computational particle fluid dynamics (CPFD) approach. The comparison was conducted under the same operating conditions. Simulation results demonstrated that the downer showed much more uniform solids holdup and solids velocity distribution compared with the riser. The radial non-uniformity index of the solids holdup in the riser was over 10 times than that in the downer. In addition, small clusters tended to be present in the whole downer, large clusters tended to be present near the wall in riser. It was found that the different cluster behavior is important in determining the different flow behaviors of solids in the downer and riser. While the particle residence time increased evenly along the downward direction in the downer, particles with both shorter and longer residence time were predicted in the whole riser. The nearly vertical cumulative residence time distribution (RTD) curve in the downer further demonstrated that the solids back-mixing in the downer is limited while that in the riser is severe. Solids turbulence in the downer was much weaker compared with the riser, while the large clusters formation near the wall in the riser would hinder solids transportation ability.

scholarly journals Comparison of Riser-Simplified, Riser-Only, and Full-Loop Simulations for a Circulating Fluidized Bed

Processes ◽  
2019 ◽  
Vol 7 (5) ◽  
pp. 306 ◽  
Author(s):  
Min Wang ◽  
Yingya Wu ◽  
Xiaogang Shi ◽  
Xingying Lan ◽  
Chengxiu Wang ◽  
...  
Keyword(s):  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Fluid Model ◽  
Pilot Scale ◽  
Pressure Balance ◽  
Solids Holdup ◽  
Mass Flow Rates ◽  
Scope Of Application ◽  
Two Fluid Model ◽  
Reasonable Prediction

With the development of computing power, the simulation of circulating fluidized bed (CFB) has developed from riser-simplified simulation to riser-only simulation, then to full-loop simulation. This paper compared these three methods based on pilot-scale CFB experiment data to find the scope of application of each method. All these simulations, using the Eulerian–Eulerian two-fluid model with the kinetic theory of granular theory, were conducted to simulate a pilot-scale CFB. The hydrodynamics, such as pressure balance, solids holdup distribution, solids velocity distribution, and instantaneous mass flow rates in the riser or CFB system, were investigated in different simulations. By comparing the results from different methods, it was found that riser-simplified simulation is not sufficient to obtain accurate hydrodynamics, especially in higher solids circulating rates. The riser-only simulation is able to make a reasonable prediction of time-averaged behaviors of gas–solids in most parts of riser but the entrance region. Further, the full-loop simulation can not only predict precise results, but also obtain comprehensive details and instantaneous information in the CFB system.

scholarly journals Correlation for solids holdup in riser of circulating fluidized bed with two-component particles.

1991 ◽  
Vol 17 (2) ◽  
pp. 426-429 ◽  
Author(s):  
Kazuya Ijichi ◽  
Yasushi Nishiyama ◽  
Yasuhiko Tanaka ◽  
Yoshimitsu Uemura ◽  
Yasuo Hatate ◽  
...  
Keyword(s):  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Solids Holdup ◽  
Two Component

scholarly journals Study on the Flow Characteristics of Desulfurization Ash Fine Particles in a Circulating Fluidized Bed

Processes ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 1343
Author(s):  
Xiao Yang ◽  
Chengxiu Wang ◽  
Xingying Lan ◽  
Jinsen Gao
Keyword(s):  
Fluidized Bed ◽  
Flue Gas ◽  
Circulating Fluidized Bed ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Current Status ◽  
Circulation Rate ◽  
Wall Region ◽  
Gas Treatment ◽  
Solids Holdup

In view of the current status of catalytic cracking flue gas treatment, it is necessary to study the flow environment of desulfurization ash particles, which are a type of Geldart C particle, in a circulating fluidized bed (CFB) for semi-dry flue gas desulphurization using CFB technology. This study investigated the flow characteristics of desulphurization ash particles in a riser with an inner diameter of 70 mm and a height of 12.6 m, at a gas velocity of 4–7 m/s and a solids circulation rate of 15–45 kg/m2·s. The solids holdup in the axial distribution is relatively high near the bottom of the riser, and gradually decreases as the riser height increases, with a stable value from the middle to the top of the riser. In the radial distribution, the solids holdup of desulfurization ash particles is low in the center and high in the wall region. Within the above operating conditions, the solids holdup ranges from 0.008 to 0.025. The particle-based Archimedes number has a linear relationship with the solids holdup at all operating conditions.

Effect of Various Parameters on the Solids Holdup in a Liquid-Solid Circulating Fluidized Bed

2008 ◽  
Vol 6 (1) ◽  
Author(s):  
Natarajan Palani ◽  
Velraj Ramalingam ◽  
Seeniraj R.V.
Keyword(s):  
Experimental Data ◽  
Fluidized Bed ◽  
Flow Rate ◽  
Liquid Flow ◽  
Circulating Fluidized Bed ◽  
Liquid Flow Rate ◽  
Tap Water ◽  
Solid Particles ◽  
Circulation Rate ◽  
Solids Holdup

A liquid-solid circulating fluidized bed (LSCFB) is operated at high liquid velocity, where particle entrainment is highly significant and between the conventional liquid fluidized bed and the dilute phase liquid transport regimes. In the present work, systematic experiments were carried out in a 0.094 m ID and 2.4 m height laboratory-scale liquid-solid circulating fluidized bed apparatus by using various solid particles and tap water as a fluidizing medium to study the hydrodynamics (axial solids holdup and solids circulation rate). The effects of operating parameters, i.e., primary liquid flow rate in the riser (jf), auxiliary liquid flow rate (ja), total liquid flow rate (jl), particle density (?s), particle diameter (dp) and solids feed pipe diameter (do) on the axial solids holdup distribution were analyzed from the experimental data. Finally, a correlation was developed from the experimental data to estimate average solid holdup in the riser, and it was compared with present experimental and available data in the literature. They agree well with a maximum root-mean-square deviation of 9.12 %.

Gas-Solids Flow Properties of a Square Circulating Fluidized Bed with Secondary Air Injection

2010 ◽  
Vol 8 (1) ◽  
Author(s):  
Shaozeng Sun ◽  
Zhengyang Wang ◽  
Hao Chen ◽  
Dong Li ◽  
Qigang Deng ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Pressure Drop ◽  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Injection Level ◽  
Flow Properties ◽  
Solids Concentration ◽  
Solids Holdup ◽  
Secondary Air ◽  
Air Staging

Effects of secondary air (SA) injection or air-staging on the gas-solids flow properties in the riser of a circulating fluidized bed (CFB) were investigated. The experiments were carried out in a CFB cold model with a square cross-section of 0.25m×0.25m and a height of 6.07m. The axial pressure drop profile along the riser was reported. And the local solids holdup profile at the centerline and the diagonal line of some cross sections which influenced by the SA injection was measured with an optical fiber probe. Two SA arrangement modes, i.e. four SA nozzles located on four walls (Wall SA) and four corners (Corner SA) were conducted. Air-staging results in a denser bottom bed for both two SA modes. The Wall SA case has a higher solids holdup than the Corner SA case in most regions of lower bed except the corner region but was leaner in the vicinity of SA injection level. W-shaped solids concentration profile was found in the region immediately above the SA injection level for Wall SA case but not obvious for Corner SA case. Fractal dimension was analyzed for pressure drop fluctuations and local solids concentration signal. Air-staging led to smaller fractal dimension value than the case without SA injection. The SA jets affected the local gas-solids distribution and fluctuation in the region close to the SA injection. Radial and axial solids transfer should be considered for the fractal analysis.

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