The presence of dead zones in the distributor should be avoided, especially if the solids are cohesive. The movement of particles induced by the gas which exits from the orifice depends on the flow properties of the solid, partially characterized by the minimum fluidization velocity and flow of the gas hole.
However, small bubbles produced on porous plate do not have enough energy to cause a vigorous movement necessary for the mixing of large particles that may be segregated or non-fluidized.
On the other hand, if perforated plates with large orifices are used, a great distance between the orifices allows the solids to settle down. Figure 4 illustrates the penetration of gas into the bed of particles and the identification of dead zones.
As zonas mortas são facilmente eliminadas, usando tuyeres com orifícios horizontais múltiplos, ou bubble caps de topo cônico. A orientação dos orifícios influencia na formação de zonas mortas, sendo estas quadrangular ou triangular (Figura 5).