Environmental Engineering Reference
In-Depth Information
temperature air, then the combustion efficiency is very high with minimum pollution.
Stable flame can be obtained with HiTAC using very low heating value fuels. High
temperature air can be effectively used for clean conversion of coal to gaseous fuels
and its subsequent conversion to thermal energy. The HiTAC technology can also
be developed to increase the calorific value of the gases evolved.
6.4
VOLATILE ORGANIC COMPOUNDS
High temperature air combustion technology can be effectively used for the destruc-
tion of volatile organic compounds (VOCs) and use the subsequent thermal energy
evolved. Combustion systems have been used for the thermal destruction of odors
associated with smelly vapors for a long time and are highly efficient and reliable
for the removal of odors. However, in most cases auxiliary fuel is required in the
combustion system since the concentration of hydrocarbon vapors in the odors (fuel)
is not high enough to sustain combustion. The direct combustion process developed
in the United States during the 1950s was widely used for the destruction of VOCs
in the domestic market. The catalytic combustion process featuring a low combustion
temperature of 300 to 350˚C (as opposed to combustion temperature in excess of
750˚C ) was developed around 1970 for direct combustion process. Regenerative
heat combustion process was developed in the United States in 1975 as a version
of a direct combustion system with high heat recovery rate for greater energy savings.
The market for low to medium waste gas treatment was expanded due to the stringent
regulations on VOC emissions (implemented around 1990). Thus, the regenerative
heat combustion process was employed in the market, which expanded rapidly in
Europe and the United States. Recently, Japan has also made much progress for the
destruction of VOCs using high temperature air combustion principles. Practical
applications involve introduction or technical development and various types of
equipment based on the three-tower system. Development efforts to reduce dioxin,
based on the high temperature air combustion technology principles in exhaust, are
in progress.
6.5
ASH MELTING
High temperature air combustion technology also has the potential for use in the
ash melting and treatment process. The ash melting of bottom and fly ash lies in the
range of 1300 to 1400˚C . It will be quite natural to apply the high temperature air
combustion technology to this process. The reburning process in a stoker furnace
resembles, in principle, the high temperature air combustion process. Therefore, its
application to ash melting and handling is conceivable. It should be noted that all
of the above factors might not be applicable to some furnaces, depending on the
type of regenerative media or available regenerative process. Therefore, one must
design and develop a suitable type of the regenerative media as well as the process
(for example, installation of preduster, automatic replacement system) from the
beginning to develop this application and technology.
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