The accurate estimate of the head pressure on the distributor is essential for the project of a fluidized bed column. When a fluidizing gas goes through a bed of particles retained on an orifice plate or any distributor there is a fall of gas head pressure and an increase in speed. If the distributors head pressure is very small, this result is a poor fluidization, in other words, some part of the bed will receive less gas than the other, and may be temporarily or permanently non-fluidized, while in other parts, the gas forms channels or jets semi-permanent. The experiment shows that the distributor should have a head pressure sufficient (Dpd) suficiente to reach drainage over the entire cross section of the bed. It is adopted the following recommendation:
where Dpb is the pressure through the bed calculated by
It is important to know the minimum Dpd which would ensure uniformity of fluidization in change required in operations. For hole theory of equations and fixed bed, it can be shown that:
for flat plates;
for perforated plates and tuyere;
For bubbling beds of fine particles (Geldart category A), where U>Umb, supported by distributors of porous and perforated plates, Mori and Moriyama (1978) considered the consequences of interruption of the flow in the bed. The result of this analysis suggests that for a complete fluidization it should be followed:
where n = 1 for porous plate, n = 2 to perforated plate. This expression shows that Dpd must be high when it operates near to Umf, but it may be low, when the bed operates over U.
For U/Umf>10 for porous plate and U/Umf>3 for perforated plates, the equation 4 it reduced to:
and if L/Lmf=1,2-1,4, typical of bubbling beds, the equation 5 is reduced to equation 1.