1.
 Bubble Characteristics in Three-Phase Circulating Fluidized Beds
 

  

^†  *

 

*  

(2000 5 12 , 2000 8 31 )

Bubble Characteristics in Three-Phase Circulating Fluidized Beds

Seok-Hee Nam, Yong-Jun Cho, Yong Kang^† and Sang-Done Kim*

Department of Chemical Engineering, Chungnam National University, Teajon 305-764, Korea

*Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, Teajon 305-701, Korea (Received 12 May 2000; accepted 31 August 2000)



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Abstract−Bubble characteristics have been investigated in a three-phase circulating fluidized bed of 0.102 m I.D. and 3.5 m height. Effects of gas(0.01-0.07 m/s) and liquid velocities(0-0.31 m/s) and solid circulating rates(2-8 kg/m²s) on the bubble characteristics such as rising velocity, chord length and frequency have been determined. Probability density of bubble chord length has been examined with the variations of experimental conditions to analyze the bubble characteristics in the solid cir- culating regime. As a result of this study, The bubble rising velocity and frequency have increased with increasing gas and liq- uid velocities, but the former has decreased while the latter has increased slightly, with increasing solid circulating rates. The bubble chord length has increased with increasing gas velocity but it has decreased with liquid velocity and solid circulating rate in the riser of three-phase circulating fluidized beds. The probability density of bubble chord length becomes more narrow representing more uniform bubble size distribution with increasing liquid velocity as well as solid circulating rate in the beds.

The rising velocity, chord length and frequency of bubbles have been well correlated in terms of operating variables.

Key words: Three-Phase Circulating Fluidized Bed, Bubble Characteristics, Bubble Size Distribution

†E-mail: kangyong@hanbat.chungnam.ac.kr

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Operating condition

Bed height [m] 3.5

Column diameter [m] 0.102

Solid Glass bead

d_p [mm] 2.l

ρ_p [kg/m³] 2500

Liquid Tap water(room temperature)

Gas Compressed air(room temperature)

Gas velocity(U_G) [cm/s] 0.01-0.07 Liquid velocity(U_L) [cm/s] 0.00-0.31 Solid circulating rate(G_S) [kg/m²s] 2-8

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Fig. 3. Effects of U_G on the bubble rising velocity(U_B), chord length(L_V) and frequency(F_B) in three-phase circulating fluidized beds.

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F_B= 963.151U_G^0.517U_L^2.614G_S^0.016 (9)

Fig. 4. Effects of U_L on the bubble rising velocity(U_B), chord length(L_V) and frequency(F_B) in three-phase circulating fluidized beds.

Fig. 5. Effects of G_S on the bubble rising velocity(U_B), chord length(L_V) and frequency(F_B) in three-phase circulating fluidized beds.

Fig. 6. Probability density of bubble chord length in circulating fluid- ized beds.

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d_p : particle diameter [mm]

F_B : bubble generating frequency [s−¹] G_S : solid circulating rate [kgm−²s−¹] L_V : bubble chord length [m]

L_Vi : individual bubble chord length [m]

t : time [s]

U_b : bubble rising velocity [ms−¹]

U_bi : individual bubble rising velocity [ms−¹] U_G : superficial gas velocity [ms−¹] U_L : superficial liquid velocity [ms−¹]

 

ρ_p : particle density [kg/m³]



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Fig. 7. Probability density of bubble chord length in circulating fluid- ized beds.