Fluidized beds cross flow ratio

Example 7.5.2 Zinc concentrates are fluidized with air at 1500°F. If the bed diameter is 5 m and the bed height is 15 m, estimate the cross flow ratio, assuming that the bubbles in the system correspond to the largest stable size. 

A very simple, but also coarse, method of detertniriitig the minimally required gas volume flow rate is to define it as the flow rate creating conditions of minimal fluidization at the upper surface of a stagnant bed of solids placed in the equipment under consideratiort This derivation will be illustrated for the ProCell unit depicted schematically in Fig. 4.9. The superficial gas flow velocity at the free surface of the respective stagnant bed is the ratio of the gas volume flow rate Vg to the respective cross-sectional area, which is twofold the product of the width Wo and the length L of the apparatus, perpendicular to the plane of Fig. 4.9. By setting the superficial gas flow velocity equal to the minimal fluidization velocity u f and the gas volume... 

The procedure for the scale-up of an expanded-bed-adsorption process is relatively straightforward and the principles are similar to those used for a packed-bed process. It is important that the length of the laboratory column be equal to the pilot-plant column. If the pilot-plant equipment is not specifically designed for expanded-bed-adsorption procedures, it should be modified as described in the previous section on laboratory equipment. To verify that the expanded-bed flow patterns are similar for the lab and pilot-plant columns, pulse tests using NaCl solution should be carried out. The adsorbent used, whole-broth-solvent ratio, bed height, and linear velocity, should not be changed on scale-up. The volumetric flow should be increased m proportion to the mcrease in the cross-sectional area of the two columns. Thus, the superficial velocity will be maintained and the adsorption and the fluidization properties will be constant. 

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