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Modeling Competitive Adsorption in Urea-SCR Catalysts for Effective Low Temperature NOx Control

[+] Author Affiliations
Maruthi Devarakonda, Russell Tonkyn, Diana Tran, Jong H. Lee, Darrell Herling

Pacific Northwest National Laboratory, Richland, WA

Paper No. IMECE2010-39977, pp. 589-595; 7 pages
doi:10.1115/IMECE2010-39977
From:
  • ASME 2010 International Mechanical Engineering Congress and Exposition
  • Volume 11: New Developments in Simulation Methods and Software for Engineering Applications; Safety Engineering, Risk Analysis and Reliability Methods; Transportation Systems
  • Vancouver, British Columbia, Canada, November 12–18, 2010
  • Conference Sponsors: ASME
  • ISBN: 978-0-7918-4448-9
  • Copyright © 2010 by ASME

abstract

Although the SCR technology exhibits higher NOx reduction efficiency over a wider range of temperatures among the lean NOx reduction technologies, further improvement in low-temperature performance is required to meet the future emission standards and to lower the system cost. In order to improve the catalyst technologies and optimize the system performance, it is critical to understand the reaction mechanisms and catalyst behaviors with respect to operating conditions. For example, it is well known that the ammonia coverage on catalyst surface is critical for NOx reduction efficiency. However, the level of ammonia storage is influenced by competitive adsorption by other species, such as H2 O and NO2 . Moreover, hydrocarbon species that slip through the upstream DOC during the cold-start period can also inhibit the SCR performance, especially at low temperatures. Therefore, a one-dimensional kinetic model that can account for the effects of such competitive adsorption has been developed based on steady state surface isotherm tests on a commercial Fe-zeolite catalyst. The model is developed as a C language S-function and implemented in Matlab/Simulink environment. Rate kinetics of adsorption and desorption of each of the adsorbents are determined from individual adsorption tests and validated for a set of test conditions that had all the adsorbents in the feed gas. Using the competitive adsorption model, a kinetic model for standard-SCR reaction involving NH3 and H2 O is developed and validated.

Copyright © 2010 by ASME

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