5. CFL components

5.1 Fluidizing grid

CFLs generally include a grid for introducing the carrier phase (i.e., the fluid), whose role is essentially to distribute the gas uniformly over the cross-section of the column. In some types of oil risers, the grid is replaced by an injection nozzle projecting fine droplets of oil which vaporize on contact with the hot catalyst coming from the outer bed. For other types of CFL, the distribution grid is similar to that of bubbling fluidized beds. Given the significantly higher fluidization rates for CFLs, it is necessary either to use nozzles with larger holes (several millimeters) to avoid multiplying the number of nozzles, or to accept operating with a greater pressure drop, i.e. above the value of 3,400 Pa which is considered the lower admissible limit (cf....