Nitrogen oxides (NOx) are gas byproducts of manufacturing processes regulated by the Environmental Protection Agency due to their negative effects on human health and ability to create smog in combination with volatile organic compounds and heat. Industrial NOx scrubbers commonly use a combination of catalytic solvents and mechanical filtering to separate NOx into nitrogen and oxygen gases for safe release into the atmosphere. The specific NOx scrubber investigated experienced three issues: frothing, clogging, and loss of pressure gradient. These problems result in the early termination of production runs and lengthy cleaning procedures. Multiple theories were developed to diagnose and recommend solutions for these issues. Because the chemical components of the scrubber are similar to those in a soapmaking process, Hypothesis 1 is that a saponification reaction is causing the formation of micelles and frothing. Froth replication and mitigation experiments confirmed this hypothesis and that the froth may be reduced by a variety of surfactants. For the chemical components of this individual scrubber, the surfactant that worked the best of the seven tested was simethicone. Hypothesis 2 theorized that the clogging issue was caused by NaOH and Al(OH)4contained in the scrubber solution precipitating out as hot NOx gas at the top of the scrubber column meets the cooled recirculated scrubber solution. Flow simulations and ICP-OES analysis confirmed this theory, resulting in .94 ppm aluminum and 17.5 ppm sodium. We further believe that the loss of pressure gradient is caused by the clogging and frothing issues, which will be evaluated during future operation runs. This research contributes to the body of knowledge for diagnosing and mitigating issues common to industrial scrubbers. Additional recommendations for scrubber solution ratios, mechanical modifications, and cleaning procedures have the potential for general application for packed-bed NOx scrubbers.

Investigation and improvement of an industrial NOx scrubber

ACS Fall 2021

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