145
16
Thermal Oxidizers
Dan Banks
Banks Engineering, Inc., Tulsa, Oklahoma
16.1 DEVICE TYPE
Thermal oxidizers (TOX) are used to destroy objectionable hydrocarbons contained
in waste streams from manufacturing plants. The wastes may be solids, liquids, or
vapors. They are usually generated continuously—otherwise landll may be eco-
nomically preferred for solids and liquids, while emergency ares might be preferred
for destruction of many waste gases. Thermal oxidizers are designed to use heat
energy to convert hydrocarbon contaminants to carbon dioxide and water vapor, and
contaminant metals to their oxide form, under controlled conditions.
16.2 TYPICAL APPLICATIONS
Thermal oxidizers are used to control combustible contaminant emissions from
dozens of sources. Major areas include printing operations; chemical and hydro-
carbon processing; painting, coating, and converting; distillation; sludge drying;
soil remediation; plasticizer emissions control; extruder emissions; and textile
manufacturing.
They are often used after wet scrubbers where the gas stream contains both water-
soluble and hydrocarbon emissions. They are often followed by wet scrubbers where
the volatile organic compound (VOC) is halogenated and, upon combustion, can
form inorganic acids such as hydrochloric acid (HCl).
In general, if the source emits a combustible VOC that is not economical to
recover, it is a candidate for control by a TOX.
16.3 OPERATING PRINCIPLES
A TOX simply heats the waste material in the presence of air to allow the hydrocar-
bon molecules present to burn (oxidize at elevated temperature). The simplest TOX
consists of a burner, a holding chamber (furnace), and a stack (to duct the combus-
tion products to atmosphere). Furnace temperature can range from 500 to 2500°F,
depending on TOX design and the degree of hydrocarbon destruction needed. If 99%
of the incoming hydrocarbons are destroyed, the TOX efciency is 99% (expressed
as 99% destruction and removal efciency, or 99% DRE). Usually natural gas or
other auxiliary fuel is ignited in the burner to heat up the TOX and often to supple-
ment the heating value of the waste stream(s) to ensure proper temperature control.
146 Air Pollution Control Equipmenet Selection Guide
If the waste is rich in hydrocarbons, extra air or sometimes water sprays are used
to prevent overheating. Various methods have been developed to reduce fuel usage,
keep generation of NO
x
and other pollutants low, recover available heat from the
combustion products, and remove any particulate or acid gas (HCl, SO
2
) formed
during waste destruction.
To make the best use of this application of heat energy, the thermal oxidizer is
usually lined with insulating refractory material.
Figure 16.1 shows a thermal oxidizer used for the control of noncondensable
gases from a paper pulp mill. The unit consists of a specially designed burner, burner
controls, insulated combustion chamber, and temperature controls.
16.4 PRIMARY MECHANISMS USED
Reacting hydrocarbons with oxygen results in release of energy. An example is the
oxidation of natural gas (methane):
FIGURE16.1 Noncondensable gas thermal oxidizer (Banks Engineering, Inc.).

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