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New clues on what an incinerator spews.

Researchers at Argonne (Ill.) National Laboratory report developing the first instrument to continuously sample emissions from municipal and hazardous-waste incinerators.

A number of factors can affect how completely wastes burn, including temperature, oxygen levels, the composition of the wastes and the rate at which they are fed into the incinerator. And the less complete the combustion, the more pollution an incinerator emits. Argonne's new stack-gas monitoring system still needs a year or so of further development to withstand rugged field conditions, such as vibrations and dirt. But with those refinements, the system should offer incinerator operators their first opportunity for real-time stack-gas monitoring -- and, perhaps more important, a chance to develop complementary, pollution-minimizing feedback systems that can fine-tune combustion, the Argonne researchers say.

Their sampler relies on a spectroscopic process in which mirrors bounce a beam of infrared light back and forth through the incinerator's emissions. Because each compound in the flue gas absorbs a different pattern of infrared radiation, computer analysis of the exiting light identifies not only the chemical fingerprints of air pollutants going up the stack, but also the pollutants' concentrations.

Incinerator operators currently have no way to conduct realtime assays of pollutant emissions; a single test can take up to one month and cost $50,000, notes chemical engineer Michael J. McIntosh, principal investigator on the Argonne project. The new system should "provide continuous monitoring for an installed cost of about $50,000," he says.

In tests with a small incinerator burning chlorobenzene, the Argonne device "works beautifully," McIntosh reports. Every few seconds it provides analyses of more than 10 selected pollutants. It should be able to identify any molecules that occur in at least parts-per-billion concentrations, he says.

The system will not detect pure elements, such as metals. Moreover, since incinerator releases of toxic dioxins and furans typically remain below the system's detection limit, it will miss the more dilute levels of polychlorodibenzothiophenes (PCDTs) recently detected in emissions from two municipal incinerators. European researchers describe these newly recognized compounds -- the sulfur analog of furans (PCDFs), and chemical cousins of dioxins (PCDDs) -- in the September ENVIRONMENTAL SCIENCE & TECHNOLOGY.

Scientists have not determined the toxicity of PCDTs or how these compounds form. They might be generated "where large amounts of sulfur and [chlorinated] compounds are incinerated or accidentally burned. Such a case could be the burning of used automobile tires," suggests the European team, led by Hans-Rudolf Buser of the Swiss Federal Research Station in Wadenswil.
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Title Annotation:an instrument to sample emissions continuously
Publication:Science News
Date:Sep 21, 1991
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