Porous plate or compressed distributors:
These plates provide a more uniform fluidization. However, there are few practices at the industrial level. Furthermore, it is frequently the closing of the pores by fine particles over time and they resist badly to thermal cycles.
Perforated plate distributor:
The perforated plate distributors are widely used in industry because they are cheap and easy to manufacture. Figure 1 illustrates several variations of a simple perforated distributor plate (Kunii and Levenspiel, 1991).
(a) perforated plate (b) perforated alternate plate (c) perforated curved plate (d) grid bar
Figure 1- Types of distributors
In Figure 1a there is a distributor, which consists of two perforated sandwich plates with a metal screen that prevents solids from passing through the orifices, when the gas flow is interrupted. A variation on this distributor (Figure 1b) has two perforated alternate plates, and has not screen. However, these distributors have problems with rigidity, with deflection, when the bed is composed of heavy particles. So, it is necessary to strengthen them, or curved plates are used, as shown in Figure 1c. The curved plates are best suited to a bed of heavy particles and thermal stresses, and help contain the tendency of channels and bubbling that occur preferably near the center of the fluidized bed.
Curved plates distributors to the top reach a good contact, only when there is more orifices next to the perimeter than to the center, being a disadvantage for its manufacture. Alternatively, parallel grids bars (Figure 1d) can be used. These bars may be considered as two-dimensional versions of perforated plates, with limited usage.
The diameters of the orifices in the perforated plate distributors have an average of 1 to 2mm in small beds and approximately 50mm for large units.
The perforated plate's distributors have a disadvantage; they cannot be used under operating conditions such as high temperatures or in a highly reactive environment.
OThe most common metals in the manufacture of perforated plate distributors are ceramics and porous sintered metals.
Tuyeres and Caps distributors (caps):
The tuyeres are distributors used to severe operating conditions. The multiple porous plate type, in Figure 2a, provides a good distribution of gas over each filter, but with a deposition of particles between the adjacent tuyeres. In Figure 2b, c and d are due to tuyeres used to prevent the deposition of solids (dripping) to the windbox, which is the bottom region of the distributor.
(a) porous plate (b) socket (c) cap bubble (d) open nozzle
Figure 2: Distributors type Tuyere (Kunni e Levenspiel, 1991)