HAZARDOUS WASTE TREATMENT - Environmentally Conscious Materials Handling - page 188

incineration is the flare. Flares are used to burn landfill and digester gases, as
well as waste refining gases.
Thermal incineration is applied to gas streams with low energy value that
require supplemental fuel to carry on combustion. These gases may have heating
values and operate at lower temperatures. If the incinerator is missing in any
of the three Ts, carbon monoxide and intermediate combustion byproducts may
be formed. However, under proper operating conditions, significant destruction
efficiencies can be achieved.
Catalytic incinerators use catalysts to enhance the oxidation at desired tem-
peratures. Due to the presence of a catalyst, the oxidation rate of wastes can
be achieved at lower temperatures and shorter residence times. The catalyst is
subject to deterioration at sudden increases in temperatures; therefore, the VOC
content of the waste being fed to the incinerator should be kept homogenous.

4.2 Incineration of Liquid Wastes

For the incineration of liquid waste, proper mixing is necessary in order to
feed uniform mixture of waste into the incinerator. If liquids do not vaporize at
ambient temperatures, they must be injected into the furnace with an atomizer
in the form of fine spray. This would help proper mixing of combustion air with
the liquid droplets and will allow combustion to proceed. There are primary and
secondary combustion units. The wastes with high heating values are burned in
the primary combustion chambers, and remaining organics are oxidized in the
secondary combustion chamber for complete oxidation.

4.3 Incineration of Solid Wastes

Solid waste is more difficult to incinerate and requires processing for size reduc-
tion prior to burning. Since most solid waste contains materials that are not com-
pletely combustible, there will also be residual ash. Incinerator types employed
for solid wastes include the following:
Controlled air incinerators are incenerators with a two-chamber fixed heart
system where wastes are vaporized under low air conditions in the first chamber
and then ignited with auxiliary fuel in the second chamber. It is constructed in a
modular form and has low capital cost.
Rotary kiln incinerators use a rotating horizontal cylinder that partially mixes
the waste to improve combustion. They can be continuous or batch fed. Rotary
kiln incineration works well with emission control equipment. It is used for
wastes with higher solids content or larger solids size and has high ash residual.
Fluidized bed incinerators consist of a bed of sand or alumina in which the
waste is fed continuously for upward flow through a fluidized bed. Air flow
provides good mixing and keeps the particles in bed in suspension. This system
has low oxygen requirements, lower air emissions, and is suitable for burning