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Research Papers: Multiphase Flows

Effects of Mixing Using Side Port Air Injection on a Biomass Fluidized Bed

[+] Author and Article Information
M. Deza

Department of Mechanical Engineering, Virginia Tech, Blacksburg, VA 24061

T. J. Heindel

Department of Mechanical Engineering, Iowa State University, Ames, IA 50011

F. Battaglia1

Department of Mechanical Engineering, Virginia Tech, Blacksburg, VA 24061 e-mail:fbattaglia@vt.edu

1

Corresponding author address: Department of Mechanical Engineering, Virginia Polytechnic Institute and State University, 107 Randolph Hall, Blacksburg, VA.

J. Fluids Eng 133(11), 111302 (Oct 27, 2011) (9 pages) doi:10.1115/1.4005136 History: Received April 17, 2011; Revised August 18, 2011; Published October 27, 2011; Online October 27, 2011

Fluidized beds are being used in practice to gasify biomass to create producer gas, a flammable gas that can be used for process heating. However, recent literature has identified the need to better understand and characterize biomass fluidization hydrodynamics, and has motivated the combined experimental-numerical effort in this work. A cylindrical reactor is considered and a side port is introduced to inject air and promote mixing within the bed. Comparisons between the computational fluid dynamics (CFD) simulations with experiments indicate that three-dimensional simulations are necessary to capture the fluidization behavior of the more complex geometry. This paper considers the effects of increasing side port air flow on the homogeneity of the bed material in a 10.2 cm diameter fluidized bed filled with 500-600 μm ground walnut shell particles. The use of two air injection ports diametrically opposed to each other is also modeled using CFD to determine their effects on fluidization hydrodynamics. Whenever possible, the simulations are compared to experimental data of time-average local gas holdup obtained using X-ray computed tomography. This study will show that increasing the fluidization and side port air flows contribute to a more homogeneous bed. Furthermore, the introduction of two side ports results in a more symmetric gas-solid distribution.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the (a) fluidized bed used in the experiment and (b) bed chamber used in the simulation including the side port injector

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Figure 2

Pressure drop versus superficial gas velocity comparing experiments and simulations for the fluidized bed with no side port (Qside =0)

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Figure 3

Time-average void fraction of the fluidized bed at Ug = 1.5Umf and Qs =10%Qmf for the (a) 2D simulation, (b) experiment, (c) 3D simulation, and (d) horizontal averages across the reactor diameter versus axial direction

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Figure 4

Time-average void fraction of the fluidized bed at Ug = 3.0Umf and Qs =10%Qmf for the (a) 2D simulation, (b) experiment, (c) 3D simulation, and (d) horizontal averages across the reactor diameter versus axial direction

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Figure 5

Time-average void fraction profiles of the fluidized bed at Ug = 3.0Umf and Qs =10%Qmf at (a) z = 3.2 cm and (b) z = 9.0 cm. Experimental data shown as symbols and simulations are shown as lines.

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Figure 6

Time-average void fraction for the 3.0Umf fluidized bed and side port injection flowrates of Qside = 5, 10 and 20%Qmf horizontally-averaged across the reactor diameter. Experimental data shown as symbols and simulations are shown as lines.

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Figure 7

Time-average void fraction for the 3.0Umf fluidized bed using side injection flowrates of (a) 5% Qmf, (b) 10%Qmf, and (c) 20%Qmf. Upper row: circular cross-sections at z= 9.0 cm (x-y plane), middle row: centerplanes through the port (x-z plane), and lower row: circular cross-sections at z= 3.2 cm (x-y plane).

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Figure 10

Time-average void fraction profiles of the 3.0Umf fluidized bed with side port injection flowrates of Qside = 0% and 10%Qmf and 2 ports with 5%Qmf through each port at (a) z = 3.2 cm and (b) z = 9.0 cm. Experimental data shown as symbols and simulations are shown as lines.

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Figure 9

Time-average void fraction predictions for the 3.0Umf fluidized bed using side injection flowrates of (a) 0%Qmf, (b) 10%Qmf, and (c) 2 ports with 5%Qmf each. Upper row: circular cross-sections at z= 9.0 cm (x-y plane), middle row: centerplanes through the port (x-z plane), and lower row: circular cross-sections at z= 3.2 cm (x-y plane).

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Figure 8

Time-average void fraction for the 3.0Umf fluidized bed and side port injection flowrates of Qside = 0, 10%Qmf and 2 ports with 5%Qmf through each port horizontally-averaged across the reactor diameter. Experimental data shown as symbols and simulations are shown as lines.

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