Page 97 - Wastewater Solids Incineration Systems

66 Wastewater Solids Incineration Systems

typically used to burn heat-treated solids, solids that have been dried, primary
sludge, scum and grease, or other materials such as wood chips or sawdust that can
be burned autogenously without heat recovery or with moderate heat recovery.

6.1 Hot Wind Box Fluid Bed
The hot wind box fluid bed is designed for maximum temperature exposure of
approximately 650 to 980°C (1200 to 1800°F) for most applications. It is used when
the wind box air temperature is greater than approximately 400°C (750°F). A cross-
section of a typical hot wind box fluid bed is shown in Figure 5.10. The unit is a ver-
tical steel shell made of carbon steel. The inside lining is made of refractory and insu-
lating brick. The refractory lining is necessary because of the inside temperature of
approximately 980°C (1800°F). The fluid bed is composed of four sections:
• The wind box section—the lower section is the wind box, which is a distribu-
tion chamber for fluidizing air and a combustion chamber for the preheat
burner. The hot wind box is a refractory-lined plenum in which the hot com-
bustion air is received. The wall of the wind box has openings for fluidizing
air supply, a preheat burner, observation port, and instrument ports.

• The bed support and air distributor section—the roof of the wind box sepa-
rates it from the next compartment. The roof can be constructed of refractory
or metal alloys, depending on the service and design temperature require-
ments. The refractory arch construction is self-supporting because of the spe-
cial shape of the refractory elements used, and is typically referred to as the
dome. It supports the weight of the bed material, when the bed is not flu-
idized, and is a distributor plate for the fluidizing air. To allow the passage of
air without the back drainage of sand, the dome has a number of air nozzles,
commonly referred to as tuyeres. These are of special shape and material to
prevent sand drainage, to provide uniform air distribution, and to withstand
operating temperatures. The refractory arch distributor and the refractory-
lined wind box are designed for a wind box temperature of approximately
980°C (1800°F). In a hot wind box with refractory arch distributor, the combus-
tion air is typically preheated to approximately 675°C (1250°F).

• The bed section—the section immediately above the distributor that contains
the fluidized mass of sand is called the bed section or combustion zone. The
air from the distributor causes the bed of sand to fluidize. There is no physical