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DANGEROUS SCR ? * USA - Engines May Emit Toxins
CARB Staffer’s Letter Warns
CAL,USA -Transport Topics, by Eric Miller -10 Aug 2009: -- The selective catalytic reduction process that most engine manufacturers will use to comply with 2010 federal diesel emission standards could emit toxic byproducts, the California Air Resources Board’s top researcher wrote in a recent letter filed in federal court by Navistar Inc.... Navistar, which is suing the U.S. Environmental Protection Agency in federal appeals court, filed the letter July 30 and said it bolsters the truck maker’s claim that EPA could be endangering public health by skipping the federal rule-making process in its approval of SCR... Written to “alert” a Boston nonprofit organization planning tests on 2010 engines, the letter said that SCR technology represents a “large departure from conventional emission controls by introducing a liquid additive containing an organic form of nitrogen”... The June 12 letter, written by Bart Croes, chief of CARB research, to the Health Effects Institute, said that a comprehensive literature search showed that the “primary concern is the release of organonitrogen compounds, many of which are carcinogenic or toxic in other ways”... “Some toxic air contaminants that have been identified with SCR technology include hydrogen cyanide, cyanic acid, nitromethane, hydrazine, acrylonitrile, acrylamide, acetonitrile, and acetamide,” Croes wrote in his letter. “It is hoped that any exotic substances emitted from SCR technology will be at levels insignificant to exposure health effects”... “Although we are encouraged by findings to date, which suggest that the technology can deliver significant reductions of many species of toxicological relevance, this work has also documented the increase in some emissions such as some metals, nitrous oxide and nanoparticles,” CARB’s letter said... SCR systems reduce NOx in the aftertreatment by mixing the exhaust output with diesel exhaust fluid, a blend of pure urea and demineralized water, through a catalyst that converts NOx into harmless nitrogen and water vapor... Navistar, Warrenville, Ill., manufacturer of International trucks, is the only engine maker planning to use exhaust gas recirculation to meet EPA’s 2010 emission standard... The manufacturers using SCR include independent truck engine manufacturer Cummins Inc.; Daimler Trucks North America and its engine subsidiary, Detroit Diesel Corp.; Volvo Group America and Volvo subsidiary Mack Trucks... (Image from wikipedia: An aqueous ammonia SCR Process Overview; note that a vaporizer would not be necessary when using anhydrous ammonia)
Labels: EGR vs SCR
posted by Unknown @ 10:06 AM
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