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3.8 T Fluid–Solid Fluidized Bed Reactors w o-Phase, 213
For Group B powders (Type B fluidization)
0.54 0.4 0.5 0.8
d u ( u z ) ( N 4 ) (3.507)
bub 0.2 s fm
g
and
u bub bub gd( ) 0.5 (3.508)
bub
where:
d bub the equiolume diameter of the b alent v v ubble
z the height aboe the fluid distributor (bed bottom) v
N the number of holes per unit area in the distrib 1/m utor , 2
bub a constant dependent on the bed diameter D :
0.64 for 0.1 m D
bub 1.6 D 0.4 for 0.1 1 m
D
1.6 for 1 m D
To calculate an aerage value of the bubble v an aerage bubble diameter should v
,
v
elocity
also be used, which can be taken to be equal to the bubble diameter at Z H f /2. An iter-
ation method should be used (Figure 3.60). As an initial Z f value, the fed-bed height ix Z
multiplied by 1.4 could be used.
For Group A powders (Type A bubbling fluidization)
For this kind of particles, bubbles reach a maximum stable size, which may be estimated
wing equations: from the follo
u 2 ter,2.7
d 2 (3.509)
bub
g
u gd( ) 0.5 (3.510)
bub bub bub
where:
1 for D 0.1 m
bub 2.5 D 0.4 for 0.1 1 m
D
2.5 for 1 m D
and u ter ,2.7 is the terminal free-fall velocity for particles of diameter 2.7 times the actual
mean particle diameter. In all equations, SI units should be used.