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3.4 Slurry Reactors 101

Then, the actual mass transfer coef which co are about f icients, v er a hundred-fold range,
1.5 –8 times that predicted from the correlations for fixed particles if the terminal velocity is
used to calculate the particle Reynolds number. McCabe gives the narrower range of 1.5 –5,
for a wide range of particle sizes and agitation conditions (McCabe et. al. , 1993). Using these
values and Table 3.7, we can calculate the ranges of the actual mass transfer coefficients.
The solid–liquid mass transfer coeficient without aeration is a function of power con- f
sumption per unit volume of the liquid. One typical case is the Levins and Glastonb ury
correlation for small particles (<2 mm), fully suspended and moderate density dif ferences
(Treybal, 1980):

kd f p  13 23  0.62 D   0.17
d (  43 P g ) L   a  S Sc 0.36 (3.118)
2 0.47
D  p s c
L  D  
f T
where P s is the power consumption per unit volume of liquid (W/m 3 ) and D f the diffusion
coefficient of the solute in the fluid phase. For the rest of the parameters, SI units should
be used. In practice, for baf the v fled tanks, alue of P s is 33–82 W/m 3 for blending, 82–247
W/m 3 for homogeneous reactions, around 824 W/m 3 for liquid–liquid mixtures, 824–1647
W/m 3 for gas–liquid mixtures, and around 1647 W/m 3 for slurries.
For large particles ( 2 mm), fully suspended,

kd f p  23  34
0.222 d (  p 43 P g ) s c 13 L Sc  13 (3.119)
D f 
L 

One more correlation is that of Calderbank–Moo–Young for the solid–liquid mass trans-
fer coefficient in stirred tanks without aeration (Kato et al ., 2001)

 P  0.25
23
k 0.13 sL Sc (3.120)
f   L  
where is the kinematic viscosity of the liquid.
L
The high shear stress around an agitation impeller is not acceptable for cell cultures or
other sensitie materials in stirred (bio) reactors (Kato v et. al. , 2003; Michell et al ., 1999).
In these cases in which the solid phase is sensitive to high shear stress, shaking vessels can
be used. The main types are the reciprocally and rotational shaking vessels. For these
cases, see Kato et al . (2003).

3.4 SLURRY REACTORS

3.4.1 General

Slurry reactors are similar to fluidized-bed reactors in that a gas is passed through a reac-
tor containing solid catalyst particles suspended in a fluid. In slurries, the catalyst is sus-
pended in a liquid, whereas in fluidized beds, the suspending fluid is the reacting gas itself.