1 October 1997
waste with other unburned hydrocarbons to form any number of chlorinated hydrocarbons,
including small amounts of dioxin and furan.
i. Secondary Chamber Turbulence.
(1) High turbulence in the secondary combustion zone is necessary in order to assure
proper mixing of the organic vapors and gases with the secondary combustion air. Complete
mixing assures that the oxidation reaction proceeds to completion, since all of the carbon and
hydrogen in the gases and vapors can come in contact and react with an adequate supply of air
(oxygen) to convert these hydrocarbons into carbon dioxide and water vapor.
(2) Improper design and/or operation of the devices intended to provide proper turbulence in
the solids and the gases will retard and impede the drying, volatilization, and oxidation processes
critical to high-efficiency destruction of municipal solid waste. This results in low throughput, a high
percent of unburned material in the ash, and serious emissions problems. Improper operation of a
well-designed furnace by excessive loading or improper balance of the draft system can produce
the same effect.
3-6. COMBUSTION PROCESS CONTROL.
a. Process Controlled by Design.
(1) The most recent combustion research indicates that the best correlation to complete
destruction of individual compounds is the unique combination of the "3 Ts" required for that
specific compound. Thus, a design for a municipal waste furnace that does not provide for either
the careful control and monitoring of the envelope of three "Ts" required for the constituents in
MSW nor the proper apportionment of air can only expect poor performance, excessive
maintenance problems, and the release of unacceptable levels of pollutants to the environment.
(2) Fortunately, the reactions involved in the combustion process can be modified
significantly by restricting/balancing the flow of air during the different stages/phases of the
b. Effect of Air Control on the Primary Combustion Process.
(1) The four phases in the thermal destruction of waste by oxidation release chemical
compounds generated from these reactions that can be altered by the conditions under which
these compounds are formed. The amount of air available to the process will determine how far
each different stage or phase can go through to completion, assuming all other conditions are met.
Excess amounts of air has drawbacks as well.
(2) Drying Phase. Since this phase involves the driving off of absorbed and bound moisture
in the waste, this phase of the combustion process does not produce energy, but it does produce
products (water vapor and excess air) that can have a negative effect on subsequent phases of the
total oxidation process. It is, therefore, advantageous to provide only the necessary heat and air
required to remove as much moisture from the bed/fuel as is practical. The air-control system must
inject only that amount of air needed to dry the waste, since this same air will be used downstream
to provide oxygen to the other phases of the combustion process. Excessive amounts of air (i.e.,