New additive scrubs away NOx-ious gases.
Flue-gas scrubbers to remove sulfur dioxide ([SO.sub.2]) -- a leading source of acid rain -- are required today on most new utility and industrial boilers in the United States. But the scrubbers that remove [SO.sub.2] don't trap nitrogen oxides ([NO.sub.x]) -- a poorly controlled contributor to both acid rain and smog ozone. Commercially available stack-gas technologies are available to tackle [NO.sub.x], but these are costly and subject to efficiency-robbing engineering problems (SN: 4/29/89, p. 271). Now, chemists at Lawrence Berkeley (Calif.) Laboratory have "lucked" onto what they say could prove a major engineering advance -- the discovery of a simple additive that allows existing [SO.sub.2] scrubbers to efficiently remove [NO.sub.x] as well.
The most widely used [SO.sub.2] scrubbers are towering structures that bathe exiting stack gases in a mist of limestone and water. The water-soluble [SO.sub.2] dissolves into the mist, becomes neutralized, and rains down the scrubber tower, eventually flowing out the bottom. Because nitric oxide (NO), which makes up about 95 percent of most [NO.sub.x] emissions, is not water soluble, it passes through this limestone/water slurry and out into the atmosphere -- unless, that is, yellow phosphorus is added to the scrubbing mist.
Phosphorus reacts with oxygen in the flue gas to form ozone. This in turn reacts with NO to form water-soluble nitrogen dioxide ([NO.sub.2]), Shih-Ger Chang and D.K. Liu explain in the Jan. 11 NATURE. The [NO.sub.2] can then dissolve into the slurry mist for removal in the same manner as the [SO.sub.2]. In one experiment, the researchers managed to remove all of the [SO.sub.2] and NO.
If the patented technology performs as well in field tests as it did in the preliminary bench-scale experiments, it should offer a "tremendous, commercially economic improvement" over existing industrial options for removing [NO.sub.x], Chang says.
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|Date:||Jan 27, 1990|
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