Page 199 - Adsorption, Ion Exchange & Catalysis- 2007, Elsevier - Copy

Else_AIEC-INGLE_cH003.qxd 7/13/2006 1:46 PM Page 195
3.8 T Fluid–Solid Fluidized Bed Reactors w o-Phase, 195

where:
d p the diameter for spherical particles or the nominal diameter for irre - gular
shaped particles
the density of the fluid
g the gravity acceleration constant (=9.81 m 2 /cm)
the dynamic viscosity of the fluid
the f oidage ed-bed v ix
u s the superficial fluid v elocity
the sphericity of the particle
S
G the superficial mass v . elocity

Note that while the fluid density may be a function of the pressure in the bed in a com-
w
pressible flo, the superficial mass velocity is constant. The Ergun equation in the form
given in eq. (3.450) is more conenient when analyzing the effects of pressure drop in the v
fluid density.

Minimum fluidization velocity

The minimum fluidization velocity can be calculated if the pressure drop in a fluidized
bed (eq. (3.448)) is set equal to the pressure drop in a fed bed (eqs. (3.449) and
ix
(3.450)):

150 1
u 1.75 u 2 1
fm fm fm g ( ) (3.451)
s 2 d p 2 3 fm sp d 3 fm h

or
 150 1
G 1.75 G 2 1  1
 fm fm fm  g ( ) (3.452)
h
  s 2 d p 2 3 fm sp d fm  
3
where:
h the hydraulic density of the particles
G fm the superf elocity elocity based on the minimum fluidization v icial mass v
fm the voidage at minimum fluidization.
This equation can be expressed as a function of the minimum Reynolds number for flu-
idization ( Re fm ) and the Archimedes number ( Ar ):

(1 ) 1
Ar 150 fm Re fm 1.75 Re fm 2 (3.453)
2 S 3 fm Sf m 3

where
3
d g )
(
Ar p h (3.454)

2