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A cool way to recycle solvents from exhaust-air streams

By Chemical Engineering |

Messer Group GmbH (Krefeld, Germany; edlinks.chemengonline.com/6516-531) has commercialized a liquid-nitrogen- (LNâ‚‚) based process for purifying exhaust air that contains high (100–1,000 g/m3) loads of chlorofluorocarbons (CFCs) or solvents. Unlike incineration (which can have problems, such as dioxin formation, with chlorinated compounds) or absorption methods (which require subsequent handling or disposal of spent sorbants), Messer’s DuoCondex process recovers compounds from the exhaust in a single step, while bringing the air into compliance with EU clean-air or TA-Luft limits, says process engineer Friedhelm Herzog. Instead of simply condensing with a counterflow of liquid Nâ‚‚, the patent-pending DuoCondex process (flowsheet) uses cold (–160 to –100°C) Nâ‚‚ gas. LNâ‚‚ is first vaporized in a thermocontroller, and the cold N2 used to liquefy compounds in the exhaust. The warmed Nâ‚‚ is then returned to the thermocontroller, where it is used to vaporize more LNâ‚‚. Because the heat required to vaporize LNâ‚‚ is about the same as that released when cooling N2 gas from 0 to –160°C, the total LNâ‚‚ consumed by DuoCondex is half that required by alternative…
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