A Thermal Photolytic Destructor (TPD) for Post-Combustion Dioxin Control (123)

Incineration of hazardous and municipal wastes continues to be one of the most controversial environmental issues facing our nation. Public and regulatory concern over emissions of toxic combustion by-products such as polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) and other chlorinated hydrocarbons have resulted difficulty in citing of facilities and a general shortage of waste treatment capacity. Emissions of PCDDs and PCDFs which are often referred to simply as dioxins have been of particular concern due to their extreme toxicity.

Control of these emissions is essential to the success of thermal disposal technologies. Although it is not well known, much of the emissions from incinerators is a result of pollutant formation after the combustion zone. Thus efforts to control emissions by improving combustion efficiency will only be moderately effective. Air pollution control devices (APCD) that simply remove the pollutant are not the answer as they are only transferring the pollutant from one medium to another. What is needed is a true “destructor” that can operate as a downstream APCD in a safe and economical manner.

Researchers within our Environmental Science and Engineering Group have developed an innovative, yet simple technology to control combustion emissions. It is based on the concept of high-temperature photochemistry. Results from our on-going fundamental research program have shown that the rates of photochemical reactions of chlorinated hydrocarbons and other pollutants can be increased from 10 to 10,000 times by moderate heating. Dioxins prove to be particularly susceptible to this acceleration. The research program has demonstrated effectiveness on several dozen pollutants of concern. The effects of reaction temperature, time, and photolysis wavelength and intensity have been determined for representative pollutants from different classes and performance models have been developed. The success of the research has led to the development of solar-based technologies for decontamination of polluted air and water streams using solar concentrator technology.

Using this information, a design for a Thermal Photolytic Destructor (TPD) has been developed. The system uses high energy, medium pressure mercury arc lamps, and operates at temperatures ranging from 300 to 600°C. The operating temperature range is important because depending upon the type of facility and its design, these temperatures can be achieved by moderate energy recovery at relatively small additional cost. The cost of energy for operation is modest and the main cost of operation is maintenance of the lamps, which is also reasonable.

The TPD is appropriate for many industrial process operations and particularly those with effluent streams containing halogenated hydrocarbons at mildly elevated temperatures. However, the most immediate application is the control of dioxins from combustion sources. This is a problem of international prominence for which billions of dollars are being spent annually. The TPD represents a technology of proven technical basis, sound principles of design, and simplicity of installation, operation, and maintenance.

U.S. Patent 5,650,549 issued July 22, 1997.

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