Monitoring heat and exhaust gas - new sensor measures temperature inside waste-treatment furnaces and monitors levels of toxic and heavy metals in exhaust - Brief Article

Science News, May 6, 1995 by Ivars Peterson

Operating high-temperature furnaces for treating a variety of wastes -- and for other purposes, such as manufacturing and power production -- requires reliable, accurate sensors for measuring temperature inside a furnace and for continuously monitoring toxic and heavy metals in the gaseous exhaust. Researchers at MIT's Plasma Fusion Center have now developed instrumentation to handle each of these tasks.

To measure the temperature of internal furnace surfaces, Paul P. Woskov and his coworkers rely on detecting emissions of millimeter-wave radiation, which has a wavelength between that of microwaves and infrared light. Unlike infrared light, millimeter- wave radiation readily penetrates the swirling dust and smoke in a hot furnace and even passes through surface deposits on viewing windows or mirrors. Yet its wavelength is short enough to provide good spatial resolution.

To monitor emissions of heavy metals, MIT's David Y. Rhee and his collaborators have developed and are now testing a microwave device to detect such metals as iron and manganese. A microwave- induced plasma vaporizes particles and ionizes vapors that pass through it. Spectroscopic measurements of light emitted by excited metal atoms enable researchers to determine the types of elements and their concentrations in the exhaust gas.