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Research Papers: Internal Combustion Engines

Effect of Mass Transfer on the Performance of Selective Catalytic Reduction (SCR) Systems

[+] Author and Article Information
Nimrod Kapas, Tariq Shamim

Department of Mechanical Engineering, University of Michigan-Dearborn, Dearborn, MI 48128-2406

Paul Laing

Department of Chemical Engineering, Research and Advanced Engineering, Ford Motor Company, Dearborn, MI 48121

J. Eng. Gas Turbines Power 133(3), 032801 (Nov 09, 2010) (9 pages) doi:10.1115/1.4001766 History: Received June 16, 2009; Revised March 13, 2010; Published November 09, 2010; Online November 09, 2010

This paper presents a computational investigation of the effect of mass transfer on the performance of selective catalytic reduction (SCR) catalysts, which are employed to reduce NOx emissions from diesel engines. The paper employs a single-channel based, one-dimensional, isothermal model. The heterogeneous surface chemistry is modeled by considering standard and fast SCR mechanisms, and the mass transfer rate is described by using a one-dimensional film model and dimensionless Sherwood (Sh) number. The paper investigates the effect of Sh numbers on the catalyst conversion performance at various temperatures and space velocities. The results show that the effect of the Sh number on the SCR catalyst performance is temperature dependent and is more pronounced at high space velocities. In general, higher Sh numbers lead to increased conversion efficiencies.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of an SCR catalyst

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Figure 2

Model results and measured TPD data (NH3inlet=260 ppm, space velocity=30,000 h−1)

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Figure 3

Model results and measured NH3 oxidation data (NH3inlet=350 ppm, space velocity=30,000 h−1)

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Figure 4

Model results and measured NO oxidation data (NO inlet=350 ppm, space velocity=30,000 h−1)

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Figure 5

Model results and measured NH3 conversion data (NO and NH3inlet=350 ppm, space velocity=30,000 h−1, 60,000 h−1)

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Figure 6

Model results and measured NOx conversion data (NO and NH3inlet=350 ppm)

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Figure 7

Model results and measured NOx conversion data for different ratios of NO–NO2 in the exhaust gases (NOx and NH3inlet=350 ppm, space velocity=80,000 h−1)

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Figure 8

Sherwood number as a function of catalyst length (space velocity=100,000 h−1, temp.=350°C)

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Figure 9

Comparison of NOx conversion performance with different Sh number models (space velocity=100,000 h−1)

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Figure 10

Effect of Sh number on NOx conversion (space velocity=100,000 h−1)

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Figure 11

Effect of Sh number on various reaction rates (space velocity=100,000 h−1): (a) NH3 adsorption rate; (b) NH3 desorption rate; (c) NH3 oxidation rate; (d) NO oxidation rate; (e) standard SCR rate; (f) fast SCR rate

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Figure 12

Effect of Sh number on NOx conversion for different space velocities (SVs): (a) SV=30,000 h−1; (b) SV=60,000 h−1; (c) SV=200,000 h−1

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Figure 13

Effect of Sh number on NOx conversion for different SVs: (a) temperature=300°C; (b) temperature=350°C; (c) temperature=400°C

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Figure 14

Effect of Sh number on NOx conversion for different ratios of NO–NO2 in the exhaust gases (space velocity=200,000 h−1): (a) NO–NO2ratio=100%−0%; (b) NO–NO2ratio=80%−20%; (c) NO–NO2ratio=50%−50%

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Figure 15

Effect of Sh number on fast SCR reaction rates for different ratios of NO–NO2 in the exhaust gases (space velocity=200,000 h−1): (a) NO–NO2ratio=100%−0%; (b) NO–NO2ratio=80%−20%; (c) NO–NO2ratio=50%−50%

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