Page 93 - Wastewater Solids Incineration Systems

62 Wastewater Solids Incineration Systems

chlorides, deposition of iron oxides can occur. Scaling of these materials can obstruct
the exhaust gas duct, which can result in excessive backpressure and lead to oper-
ating difficulties and shutdown of the plant. These problems can be eliminated by
chemical addition (Jeffers et. al., 1999). With new trends in liquid stream biological
nutrient removal (BNR), phosphorus concentration in sludge could be higher than
before. Caution should be taken when designing sludge incinerators for disposal of
waste activated sludge. Increased concentrations of phosphorus in the ash could
change the eutectic characteristics and result in lower ash fusion temperatures.
To neutralize sodium and potassium, kaolin clay (a mixture of hydrous alu-
minum silicates) is used. It is typically available in a very fine powder and is a conve-
nient source of both SiO and Al O . It will react with sodium and potassium chlo-
2 2 3
rides to form high melting point crystalline sodium and potassium aluminum
silicates. These silicates have a melting point of approximately 1100°C (2000°F).
Lime is used to convert iron phosphate to iron oxides in the sand bed at bed tem-
perature. This conversion prevents iron from forming gaseous iron chlorides, which
can precipitate and form scales in the freeboard and in the exhaust gas duct.
To calculate the dose of chemical additives, a complete analysis of both soluble
and total concentrations of the components in the ash is required. Details of the cal-
culations can be found elsewhere (Jeffers et. al., 1999).

5.0 DESCRIPTION OF MAJOR COMPONENTS
The incineration system typically is composed of three major components: the fluid
bed incinerator with subsystems such as for feeding of the wastewater solids and
sand and other auxiliary equipment; the heat recovery system; and the air pollution
control system. The heat recovery system and the air pollution control system are
detailed in Chapters 6 and 7; this chapter is limited to the incineration system and its
subsystems.
The fluid bed incineration plant could be located indoors or outdoors. Puerto
Nuevo, Puerto Rico is an outdoor plant. It is composed of a hot wind box fluid bed, a
heat exchanger to preheat combustion air to approximately 675°C (1250°F), a quench
section followed by a cooling tray and multiple Venturi scrubber, a wet electrostatic
precipitator, and a stack. An overview of the plant is shown in Figure 5.7.
The storage and feed system remains the same most of the time and is composed
of a live-bottom bin and piston pumps for the feed. Incineration, heat recovery, and
air pollution control systems, however, could be different from project to project. The
fluid bed could be of either the hot or cold wind box types. The heat recovery system