Geldart’s classification of powders

Incorporation of Geldart s classification of powders in relation to fluidisation characteristics (Chapter 6). 

Figure 7.6 Simplified diagram showing Geldart s classification of powders according to their fluidization behaviour in air under ambient conditions (Geldart, 1973)...

The time required to remove a given amount of moisture increases as the square of the particle diameter for a Geldart s type B particle, all other conditions being equal. For type A particles the effect is much smaller. Geldart s classification of powders is discussed in Chapter 3, Bubbling Fluidized Beds. 

Figure 49 shows a set of bed collapsing curves for a Geldart Group A-A (for Geldart s classification of solid particles, see Geldart, 1972, 1973) binary solids mixture, two closely sized alumina powders, of average particle diameter 104 and 66 microns, respectively. The curve on the extreme left with 0% fines represents the pure coarse component, which is... 

The following test materials have often been used FCC catalysts, aluminium oxide, silica gel, glass beads, silica or quartz sand, sea sand, coal and coal ash, petroleum coke, metal powders, resin particles, boric acid, and magnesite powder. Mean particle size ranges from 11 /un to 1,041 /rm, and particle density, from 384 kg/m3 to 7,970 kg/m3. According to Geldart s classification (1973), most of these materials belongs to Class A, some to Class B, and a few to Class D or C, as listed in Table II. 

The properties of concern in this section are to do with behaviour of powders in an aerated state this is relevant in gas fluidization, powder transport and handling. Probably the most important tests in this category are those derived from fluidization and the results of such tests are not necessarily restricted to the area of gas fluidization. It should be emphasized that the following notes apply largely to fine powders (i.e. groups A and AC in Geldart s classification). 

Behavior of bubbles for a typical fluidized Group B powder (Geldart s classification). 

It has long been recognized that pressure exerts a strong influence on the bubbling behavior of gas-fluidized beds. The literature up to 1993 was reviewed by Yates (1996), and this is reproduced and extended to 1998 in Table 3. The three principal groups of powders in Geldart s classification will be considered in turn. 

Figure 1.7 Geldart s empirical classification of aeratable (A), bubble (B), cohesive (C) and dense (D) fiu-idisable powders.

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