A more efficient system for removing environmentally harmful chemicals from industrial smoke -- thereby reducing acid rain and global warming due to the greenhouse effect -- is being developed by a Yale physicist with funding from a three-year, $895,835 grant from the U.S. Department of Energy DOE.
The researcher will use a special type of particle accelerator to generate electron beams suitable for "scrubbing" industrial flue gases to remove sulfur dioxide and nitrogen oxides, which can cause acid rain that damages forests and streams. The scrubber also would remove carbon dioxide, a primary contributor to global warming, according to Jay L. Hirshfield, professor adjunct of physics.
The DOE grant will enable Yale to upgrade its cyclotron, an accelerator in which electrons travel a spiral path in a tapered magnetic field synchronized with a microwave power source. The rotating electric field produced in Yale's cyclotron autoresonance accelerator CARA will generate electron beams much more powerful than those generated by a conventional cyclotron.
"The burning of fossil fuels poses a grave risk to the environment, and we hope to develop an economically feasible way of helping industry reduce harmful emissions," says Professor Hirshfield, who adds that the prototype developed at Yale also might be useful for treating waste sludges, sterilizing medical supplies and foodstuffs, as a source of high-power microwaves, and for basic research in physics.
Electron beam scrubbing with the CARA system could prove to be more efficient and less costly than conventional methods for scrubbing industrial smoke, such as limestone slurry scrubbing and selective catalytic reduction, notes the Yale physicist. Electron beam scrubbing was introduced in Japan in 1970 and has since been demonstrated in Indianapolis; Karlsruhe and Baden, Germany; Warsaw, Poland; and Fujisawa, Japan, he said.
"The method would be used more widely if we could develop a compact, low-cost method of producing high-power electron beams," Professor Hirshfield says. "Recent experiments in the Yale Beam Physics Laboratory have shown that beams of up to 10 megawatts of peak power can be generated with 96 percent efficiency, which means only a 4 percent loss of energy in the accelerator. We expect to produce beams with a peak power of at least 30 megawatts and average power of about 100 kilowatts."
Based on early test results, Yale physicists believe that an upgraded CARA system would be far more efficient than linear accelerators used today in industry, which have an efficiency ranging between 50 and 85 percent. In fact, seven CARA modules would be expected to remove up to 95 percent of sulfur dioxide and 90 percent of nitrogen oxides from the flue gases of a typical coal- burning power plant, according to Yale calculations. One or two CARA modules would be enough for smaller polluters, such as ships, refuse incinerators and locomotives, notes Professor Hirshfield, adding that the estimated cost for one module is less than $300,000.
Other research in the Yale Beam Physics Laboratory includes the study of other novel accelerators such as inverse free electron laser accelerators, inverse Cherenkov accelerators and dielectric Wakefield accelerators. Yale physicists working on the DOE grant will include research affiliate Michael LaPointe, associate research scientist Changbiao Wang and graduate student Rodney Yoder.