Page 169 - Wastewater Solids Incineration Systems

136 Wastewater Solids Incineration Systems

some degree, lead will volatilize at incineration temperatures. These metals will con-
dense onto the fine particulate matter during wet scrubbing of the flue gas and will
be collected with the particulate matter in the wet scrubber. Because of its extremely
high vapor pressure, mercury is typically assumed to be 100% vaporized during the
incineration process and 100% emitted in the flue gas from a conventional incinerator
with only a wet scrubbing system. Nonvolatile metals (beryllium, chromium, copper,
and nickel) are mostly emitted from the incinerator as fly ash and, as a result, effec-
tively are controlled with a medium- to high-pressure drop wet scrubbing system
(Gerstle and Albrinck, 1982).
In general, with the exception of mercury, the same control devices used to con-
trol particulate matter are used to control metal emissions. Methods to control mer-
cury are discussed later in this chapter. Typical metal control efficiencies are pre-
sented in Table 7.1. Note that the metal control efficiency relates the amount of metal
in the feed cake to the incinerator to the amount of metal emitted from the stack.
Thus, if the metal feed rate to an incinerator is 100 mg/h and a metal emission rate
from the incinerator stack is 1 mg/h, the metal control efficiency is 99%. U.S. EPA
metal control efficiencies were compiled from a broad database of both MHF and
fluid bed sludge incinerators with different types of wet scrubbing systems,
including Venturi scrubber and impingement tray scrubber, Venturi and packed

TABLE 7.1 Metal control efficiencies.
U.S. EPA metal control efficiencies (%)* Typical metal
Metal Classification Range Average control guarantee (%)

Arsenic Volatile 93.90–100 98.62 98
Beryllium Nonvolatile 99.9–100 99.99 98.5
Cadmium Volatile 40.25–99.98 88.54 97.5
Chromium Nonvolatile 88.92–100 99.16 99
Copper Nonvolatile 92.28–100 99.39 99
Lead Intermediate volatility 34.22–99.97 92.24 99
Mercury Highly Volatile Negative control 0 0
Nickel Nonvolatile 89.15–100 98.68 99
Selenium Volatile 99.4–100 99.81 98
Zinc Volatile 87.58–100 98.45 97.5
*U.S. EPA (1989).