Group A materials

Bubble growth will be hmited by the containing vessel and the bubble hydrodynamic stability. Bubbles in group-B systems can grow to several meters in diameter. Bubbles in group-A materials with high fines may reach a maximum stable bubble size of only several cm. 

Subzwari et al. (1978) also reported that bed voidage and bed expansion increased with pressure for FCC catalyst (a Group A material). However, Knowlton (1977) reported little change in either bed density or bed expansion at with increasing pressure over the range of 1 to 70 atmospheres for large, -2000/+74 micron material. 

Temperature and pressure also interact with particle size to affect bubble size and frequency in fluidized beds. Information on the effect of temperature on bubble size in the literature is somewhat inconsistent. However, the information that does exist suggests that bubble size decreases slightly with temperature for Group A materials (Geldart and... 

Typical Group A materials (e g., cement, baghouse fly ash, pulverized coal, carbon fines) are the best candidates for fluidized dense-phase (Wypych,... 

Lohrmann,P. C., andMarcus,R. D., The Performance of a Bottom-Discharge Blow Vessel Pneumatically Conveying Three Group A Materials, Bulk Solids Handling, 4(2) 409-412 (1984)... 

Peptone was used as a source of blood group A material by Goebel, who showed that the active substance it contained was principally carbohydrate and contained D-galactose and D-glucosamine. 

Group B powders are characterised by having nmb = umf. Bubbles rise faster than the interstitial gas velocity, coalescence is the dominant phenomenon and there is no evidence of a maximum bubble size, as defined for Group A materials. Bubble size increases with increasing fluidising gas velocity, see Figure 14. The interparticle forces are considered to be negligible for these powders. 

Up to a maximum concentration of 10 per cent. Group A materials below may be used with any grade of anaerobic to DTD s 5630-33 inclusive. Above this level the stronger grades of DTD s 5632 and 5633 must be evaluated. The final choice will depend largely upon component design and use. 

Although the automatic L-valve is geometrically simpler and less expensive to install than the loop seal, for the reason given above, the automatic L-valve can be more difficult to operate when using group B materials. Loop seal operation requires fewer adjustments, and is often preferred over the L-valve for automatic operation with group B materials. For group A materials, either automatic device can be used. 

---