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Most of the vapors and gases constituting odors are hydrocarbon or organic compounds that are capable of being oxidized completely in air at elevated temperature to odorless carbon dioxide and water vapor. Even when the odors are sulfur-or nitrogen-containing compounds, the resulting oxides have lower odor thresholds than their parent cpmpounds. In addition to vapors and gases, odorous effluents frequently contain mists or particulate matter which may also carry adsorbed odorants. The presence of water vapor and mist represent an extra heat load op the combustion system. The need for virtually complete combustion (i.e., approaching 100 per cent) must be emphasized because the incomplete combustion or partial oxidation of many organic compounds produces intermediate oxidation products, such as aldehydes and organic acids, which are worse odor offenders than the original materials.Of the several methods now acceptable for odor abatement, the combustion methods are unique in that they combine in one step the function of capture, destruction, and final dmisposa! of the materials responsible for the odor. Combustion methods are particularly suited to situations in which: ( 1 ) the odorant has small recoverable value, ( 2 ) the concentration of odorant is sufficient to contribute appreciable heat of combustion, (3) the effluent is already well above ambient temperature, and (4) the waste heat can be used for process heating or returned regeneratively to lower system fuel costs. When handling gas streams in which the concentration of combustible odorant is in or near the limits of flammability, safety precautions, including dilution with air and the use of flash-back arrestors, must be incorporated in the system.There are two kinds of combustion methods in use for odor control: (1) hightemperature oxidation in a combustion chamber fired directly with flame (incinerating or atterburning) and ( 2 ) oxidation at lower temperatures on catalytic surfaces. In special cases, when the effluent is rich enough to support combustion, an open flare can be burned at the top of a tall stack. However, flares are usually considered safety devices and are not discussed in this paper. This paper describes direct-flame and catalytic combustion as applied to odor control and discusses operating costs and recent developments.

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