Minimum Fluidization Porosity

The minimum fluidization porosity (emf) can be estimated from the  experimental data of the fixed bed. Table 2 shows some experimental facts of porosity.

Table 1 – Minimum fluidization porosity for different materials and diameters (Kunii and Levenspiel, 1991)

dp (mm)

Particles
0,02
0,05
0,07
0,10
0,20
0,30
0,40
Rounded Sand, f = 0,86
-
0,56
0,52
0,48
0,44
0,42
-
Coal and Glass beads
0,72
0,67
0,64
0,62
0,57
0,56
-
Carbon for Absorption
0,74
0,72
0,71
0,69
-
-
-
Catalyst (Fischer-Tropsch), f = 0,58
-
-
-
0,58
0,56
0,55
-

 

Few studies have been developed in order to develop equations for minimum fluidization. Wen and Yu (1966) proposed a correlation that relates the drag force exerted on an isolated particle and when it is placed on multi-particles system.

Broadhurst and Becker (1975) performed a series of tests by varying the physical properties of solids (700<dp<1100mm; 1300<rp<7600 kg/m3), and gas (0,17<rg<5,2kg/m3), the height of the fixed bed (1 to 60 times the column diameter) and the column diameter (0.025 to 0.21 m). Based on a dimensional analysis, the authors proposed the following correlation:

valid for the following conditions:

Considering two diameters of the fluidization column (0.10 and 0.15 m) and different types of particles, Fatah et al. (1990) proposed the following correlation:

for following variation of the Archimedes and Reynolds numbers:

Tannous et al. (1994) propose a function for the minimum fluidization porosity based on the relationship proposed by Richardson and Zaki (1954) for large particles in laboratory scale and pilot, as follows: