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Research Papers: Internal Combustion Engines

Modeling Species Inhibition of NO Oxidation in Urea-SCR Catalysts for Diesel Engine NOx Control

[+] Author and Article Information
Maruthi Devarakonda1

Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, Richland, WA 99352maruthi.devarakonda@pnl.gov

Russell Tonkyn, Diana Tran, Jong Lee, Darrell Herling

Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, Richland, WA 99352

See www.cleers.org.

1

Corresponding author.

J. Eng. Gas Turbines Power 133(9), 092805 (Apr 20, 2011) (6 pages) doi:10.1115/1.4002894 History: Received September 25, 2010; Revised September 27, 2010; Published April 20, 2011; Online April 20, 2011

Urea-selective catalytic reduction (SCR) catalysts are regarded as the leading NOx aftertreatment technology to meet the 2010 NOx emission standards for on-highway vehicles running on heavy duty diesel engines. However, issues such as low NOx conversion at low temperature conditions still exist due to various factors, including incomplete urea thermolysis, inhibition of SCR reactions by hydrocarbons, and H2O. We have observed a noticeable reduction in the standard SCR reaction efficiency at low temperature with increasing water content. We observed a similar effect when hydrocarbons are present in the stream. This effect is absent under fast SCR conditions where NONO2 in the feed gas. As a first step in understanding the effects of such inhibition on SCR reaction steps, kinetic models that predict the inhibition behavior of H2O and hydrocarbons on NO oxidation are presented in the paper. A one-dimensional SCR model was developed based on the conservation of species equations and was coded as a C-language S-function and implemented in MATLAB /SIMULINK environment. NO oxidation and NO2 dissociation kinetics were defined as a function of the respective adsorbate’s storage in the Fe–zeolite SCR catalyst. The corresponding kinetic models were then validated on temperature ramp tests that showed good match with the test data. Such inhibition models will improve the accuracy of the model based control design for integrated diesel particulate filter-SCR aftertreatment systems.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Effect of H2O on NOx conversion during standard and fast SCR reactions. Feed gas includes 350 ppm NOx, 350 ppm NH3, 2% H2O, and 14% O2 at a space velocity of 30,000/h.

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Figure 2

NOx conversion and NO oxidation percent as a function of temperature under dry and wet conditions. NOx conversion was obtained from the standard SCR test and NO oxidation percent from NO oxidation test.

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Figure 3

Effect of toluene on NOx conversion during standard and fast SCR reactions

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Figure 4

H2O storage model validation at a temperature of 100°C and at a H2O concentration of 2320 ppm

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Figure 5

H2O storage model validation at a temperature of 150°C and at a H2O concentration of 1080 ppm

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Figure 6

Comparison of NO, NO2 concentrations from H2O inhibition model, and the test data for a temperature ramp test. Feed gas includes 350 ppm NO, 14% O2, and 1.2% H2O at a space velocity of 30,000/h.

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Figure 7

Single site toluene storage model validation—150 ppm toluene, 100°C

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Figure 8

Arrhenius plot for Ktol

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Figure 9

Comparison of NO, NO2 concentrations from toluene inhibition model, and the test data for a temperature ramp test. Feed gas includes 350 ppm NO, 14% O2, and 25 ppm toluene (350 C1) at a space velocity of 30,000/h.

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