Page 178 - Wastewater Solids Incineration Systems

Emission Control and Monitoring 145

Considering the global carbon cycle, CO is in a continual state of flux with bil-
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lions of tons of CO being absorbed by oceans and plant life and billions of tons being
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emitted from natural processes and from the combustion of fossil fuels by human
beings. The prodigious combustion of fossil fuels in the last century has upset this
balance. According to NOAA, the CO concentration in the atmosphere has increased
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from 280 ppm in preindustrial times to 379 ppm in 2005 and the current rate of
increase is 1.8 ppm by volume per year (NOAA, 2005).
Control technologies for GHGs are being developed. Technologies are available
to minimize CO emissions and to separate and capture CO in compressed or liquid
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form. The CO can then either be stored in geological deposits (saline formations),
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used in oil or gas recovery operations, or sequestered (absorbed) by plants as part of
the normal photosynthesis process. Regulations to control CO most likely will be
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directed at power and other industries that consume large quantities of fossil fuels.
In the future, incinerators may have to quantify and control their CO emissions just
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like any other regulated pollutant.

2.0 CONTROL DEVICES
A variety of control devices can be used to reduce emissions. Each has its own specific
characteristics, efficiency, and effectiveness in controlling one or more types of pollutants.

2.1 Afterburners
Afterburners are typically used on MHFs to control VOCs, CO, or odorous emissions
from an MHF. Afterburners can have a number of shapes and arrangements, but their
common purpose is to raise the flue gas temperature sufficiently high, with excess
oxygen, to combust any unburned organic matter in the flue gas. The most com-
monly used afterburner is a refractory lined steel chamber equipped with one or
more fuel oil or natural gas burners. In Figure 7.1, an afterburner consisting of a ver-
tical cylindrical chamber located at the breech of a furnace is shown. Alternatively, as
shown in Figure 7.2, the top hearth of an MHF can be used as an afterburner
chamber, a so called “zero hearth afterburner.” With this arrangement, feed cake is
introduced to the second or third hearth with the top one or two hearths acting as the
afterburner chamber. Typically, oil or gas burners will be added to the top hearth to
sufficiently increase the flue gas temperature. Providing sufficient residence time and
preventing short circuiting of the flue gas is critically important in the design of a