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3.9 P article Analysis 229

Table 3.13

Sphericity of selected materials (McCabe et al., 1983; Perry
and Green, 1984 and 1999; Broadhurst and Beck 1975) , er
Material Sphericity
Spheres 1
Iron shot 0.95
Clover seed 0.95
Cracking catalyst 0.95
Ottawa sand 0.95
Tungsten powder 0.89
Short cylinder (length = diameter) 0.87
Rounded sand 0.83
Cube 0.81
Sand (aerage for v arious types) v 0.75
Coal dust 0.73
Cork 0.69
Flint sand (jagged) 0.65
Coal dust (natural and up to 3/8 in) 0.65
Crushed glass 0.65
Most crushed materials 0.6–0.8
Wilcox sand (jagged) 0.6
Raschig rings 0.33–0.58
Berl saddles 0.3
es Mica flak 0.28

alent v For polydispersed beds consisting of particles having different diameters, the equi
diameter d v a vlo should be preferably used (P et al ., 1979):
eq
1
d
eq n w (3.555)
∑ i
1 d i
where:
n the number of fractions
d the aerage screen size of the v i -th fraction
i
w the mass content of the i -th fraction in the particle mixture.
i
The aerage screen size of a fraction is the mean arithmetical value of the a v v erage size
of the screen mesh through which a fraction passes and the mesh that retains the fraction.
xpressing the par- Finally, the United States standard screen series is used (mesh size) for e
ticle size. In Table 3.14, the conersion from mesh size to (cm) is gi v v en.

3.9.4 Pore structure

olume,
Beyond the surface area and the pore v the distribution of the pore radii of a cata-
wn,
lyst has to be kno since the pore radius allows or does not allow a molecule to mo e v