CEMP-ET
EI 11C302
1 October 1997
more than is required for drying) will only upset the balance needed to control the subsequent
phases.
(3) Volatilization Phase. Depending upon the availability of air, the chemical compounds
released as the rising temperature reaches and exceeds the respective volatilization temperatures
may or may not burn. Careful apportionment of air will determine how these reactions proceed.
Typically, a primary combustion zone/chamber operating with a S.R. of 0.5 to 0.9 will provide less
air through the bed and thus produces less agitation of the bed; as a result, fewer particulates are
released from the bed. Also, the less the released gases and vapors are oxidized, the greater the
amount of gases and vapors that will survive unburned through the primary combustion zone; as a
result, a greater amount will be available as fuel in the secondary combustion zone. At lower gas
temperatures, less NOx is likely to form, and it will take longer to achieve the completion of this
volatilization phase. The lower temperature and larger volume of unburned gases will require
additional heat be supplied to the secondary combustion chamber in order to ensure that the
requisite temperature for final destruction is attained and maintained. On the other hand, primary
combustion zones/chambers operating with a S.R. of 0.95 to 1.1 will produce more particulate
matter, because almost twice as much air is passing through and around the bed. In addition, the
chamber will operate at higher temperatures since more of the gases and vapors will burn in and
above the bed, resulting in higher levels of NOx. It will also discharge smaller amounts of unburned
gases and vapors to the secondary zone chamber, although they will be at a very high temperature
and will therefore probably not require significant additional heat beyond that provided by the
unburned gases and vapors as they are burned in the secondary combustion process. Even when
operating with a primary combustion chamber S.R. of 1.0 to 1.1, the primary combustion gases will
still contain significant amounts of CO and other partially burned combustible gases, vapors, and
particulates. This fuel, when burned, will contribute enough heat to the secondary combustion
process that usually there is no problem maintaining the gas temperature well above the minimum
temperature of 1,600oF for autogenous combustion of the gases and vapors. This is true even
when additional air for secondary combustion is added to raise the S.R. to the desired 1.4 to 1.5.
(4) In-place Oxidation of Burnable Solids. This third phase of the primary combustion
process produces the hottest zone of the bed. It is controlled by introducing only enough air to
complete the burndown of the nonvolatile organic materials. Insufficient air in this stage will mean
that these materials will go unburned, only be partially burned, and/or will require a longer time for
burndown. If the burndown is not completed in this phase, it will occur concurrent with and compete
for the air in the burndown of the char in the last stage. Any material not burned will mean that heat
will not be generated and effectively lost to this stage of the process. Excess air during this stage
will produce hotter combustion products because of the higher rate of combustion, which will also
gases.
(5) Char Burndown. This phase normally requires only enough air to achieve final
destruction of the carbonaceous material remaining after the burning of the hydrocarbon during the
third stage. Insufficient combustion air at this stage will mean that the ash residues will contain
excessive amounts of carbon. Thus, the primary combustion process will not have achieved
maximum volume and weight reduction in the waste destruction process, and the ash residues will
be biologically active since it contains organic material. Excessive air to this stage will achieve the
desired destruction of the carbon, but it will also introduce more air into the primary chamber, which
will counter the effect of trying to maintain the control of air introduced to the system in the other
stages. Since this final stage requires the lowest percentage of the primary combustion air, the
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