FCC Grid Design

Example 1 A 13-m-ID bed of FCC catalyst 3 m deep, is to operate at a superficial gas velocity of 0.6 m/s. The bed density is 480 kg/m3. The density of the gas entering the bed is 0.64 kg/m3. Design the following grid types (i) a flat perforated plate, and (ii) concentric-ring type downflow sparger. Assume a grid thickness to be 0.025 m. 

Various combinations of N and dh satisfy the pressure drop requirements for the two grid types as shown in the table below. 

To proceed with the design, it is necessary to select a hole size (judgement call). For the purpose of this example, a hole size of 0.025 m will be chosen to compare the different grid types. This hole diameter does not result in an excessive number of holes for either type of grid. 

There is a good agreement between the initial and calculated value for Cd. If not, one must repeat the calculations using the calculated Cd until both values agree. 

Concentric-Ring Sparger Consider for example, a configuration of four concentric rings of 0.4-m diameter supplied by a number of gas entry points. 

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