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

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.

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

Processes ◽

10.3390/pr9081343 ◽

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.

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A method for measuring the residence time distribution of particles in a fluidized bed based on digital image analysis

International Journal of Chemical Reactor Engineering ◽

10.1515/ijcre-2020-0177 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Jiamin Li ◽

Xiaoping Chen ◽

Jiliang Ma ◽

Cai Liang

Keyword(s):

Image Analysis ◽

Fluidized Bed ◽

Residence Time ◽

Digital Image ◽

Time Distribution ◽

Residence Time Distribution ◽

Digital Image Analysis ◽

Color Space ◽

The Difference ◽

Accuracy And Repeatability

AbstractTraditional methods for measuring the residence time distribution (RTD) of particles in a fluidized bed are complex and time-consuming. To this regard, the present work proposes a new measurement method with remarkable efficiency based on digital image analysis. The dyed tracers are recognized in the images of the samples due to the difference of colors from bed materials. The HSV and the well-known RGB color space were employed to distinguish the tracers. By enhancing the Saturation and the Value in HSV and adjusting the gray range of images, the recognition error is effectively reduced. Then the pixels representing the tracers are distinguished, based on which the concentration of the tracers and RTD are measured. The efficiency, accuracy and repeatability of the method were validated by RTD measurements experiments. The method is also fit for distinguishing the target particles from multi-component systems consisting of particles of different colors.

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Numerical analysis of operating conditions for establishing high-density circulating fluidized bed by CPFD method

Powder Technology ◽

10.1016/j.powtec.2018.07.012 ◽

2018 ◽

Vol 338 ◽

pp. 446-457 ◽

Cited By ~ 7

Author(s):

Qiao Ma ◽

Fulin Lei ◽

Yunhan Xiao

Keyword(s):

Numerical Analysis ◽

Fluidized Bed ◽

Circulating Fluidized Bed ◽

High Density ◽

Operating Conditions

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Residence time distribution of particles in circulating fluidized bed risers

Chemical Engineering Science ◽

10.1016/j.ces.2018.04.027 ◽

2018 ◽

Vol 186 ◽

pp. 168-190 ◽

Cited By ~ 15

Author(s):

Leina Hua ◽

Junwu Wang

Keyword(s):

Fluidized Bed ◽

Residence Time ◽

Time Distribution ◽

Residence Time Distribution ◽

Circulating Fluidized Bed

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Dynamic simulation of the circulating fluidized bed loop performance under the various operating conditions

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1177/0957650919838111 ◽

2019 ◽

Vol 233 (7) ◽

pp. 901-913 ◽

Cited By ~ 2

Author(s):

Seongil Kim ◽

Sangmin Choi ◽

Jari Lappalainen ◽

Tae-Ho Song

Keyword(s):

Heat Transfer ◽

Fluidized Bed ◽

Heat Transfer Rate ◽

Dynamic Simulation ◽

Transfer Rate ◽

Gas Flow ◽

Circulating Fluidized Bed ◽

Operating Conditions ◽

Temperature Behavior ◽

Furnace Temperature

In a circulating fluidized bed boiler, the large thermal mass and flow characteristics of the solids strongly affect the transient response of the circulating fluidized bed loop temperature, which determines the heat transfer rate to steam flow. Therefore, it is essential to interpret the dynamic response of the solid behavior in the circulating fluidized bed loop for the stable and efficient operation of the circulating fluidized bed boiler. In this study, the dynamic simulation of the solid behavior along with the flue gas flow in a circulating fluidized bed loop was performed by applying the core-annulus approach for the solid-gas flow inside the furnace and selected models for other physical phenomena of the fluidized bed. The circulating fluidized bed loop of a commercial boiler was selected as the target system. Especially, the model simulates the characteristics of the solid behavior, such as the local solid mass distribution, and the solid flow inside the furnace and the circulating solid according to the various operating conditions. These aspects are difficult to measure and quantify in a real power plant. In this paper, the simulated furnace temperature behavior as the representative performance parameter of the circulating fluidized bed loop was discussed along with the qualitative operation experiences reported in the literature. The operating conditions include the feed rate of fuel and air, the particle size, the solid inventory and the solid circulation rate. Furnace temperature behavior was reproduced through the simulation for each operating case in the literature and was analyzed with the solid behavior along with the combustion rate and heat transfer rate of the circulating fluidized bed loop. The simulation enables quantitative evaluation of the effect of the solid behavior on the temperatures of the furnace and return part in the various operating conditions.

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