Research Papers: Fuel Combustion

A Computational Investigation of Industrial Selective Catalytic Reduction Systems for NOx Control

[+] Author and Article Information
Oghare Victor Ogidiama

Department of Mechanical and
Materials Engineering,
Masdar Institute of Science and Technology,
P.O. Box 54224,
Abu Dhabi, United Arab Emirates

Tariq Shamim

Department of Mechanical and
Materials Engineering,
Masdar Institute of Science and Technology,
P.O. Box 54224,
Abu Dhabi, United Arab Emirates;
Mechanical Engineering Program,
University of Michigan-Flint,
Flint, MI 48502
e-mail: shamim@umich.edu

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received February 16, 2017; final manuscript received March 4, 2018; published online April 9, 2018. Editor: Hameed Metghalchi.

J. Energy Resour. Technol 140(8), 082202 (Apr 09, 2018) (11 pages) Paper No: JERT-17-1081; doi: 10.1115/1.4039606 History: Received February 16, 2017; Revised March 04, 2018

The selective catalytic reduction (SCR) is a promising NOx (a mixture of NO and NO2) reduction technology for various applications. The SCR process entails the conversion of NOx by the use of a reducing agent such as ammonia and a suitable catalyst. Due to increasingly stricter NOx emission regulations, the SCR technology for NOx control needs continuous improvement. The improvement requires better understanding of complex processes occurring in the SCR system. The current study employs a mathematical model to elucidate the effect of key operating and geometric parameters on the performance of SCR systems. The model considers both standard and fast SCR reaction processes. The model was used to investigate the effects of NH3/NOx and NO2/NOx ratios in the exhaust on the SCR performance and the effect of using a dual layer SCR system. Furthermore, the effect of different operating parameters and the interdependence of parameters is analyzed by using a factorial approach. The results show that the SCR performance is very sensitive to NH3/NOx ratio. The SCR performance is also affected by the NO2/NOx ratio particularly at low temperatures. The optimal NOx conversion performance requires a combination of NH3/NOx ratio of 1.0, NO2/NOx ratio of 0.5, low space velocities, and high inlet temperature. The results depict that adding a second catalyzed layer results in increased reaction activity especially when the concentration is still high after the first layer.

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Fig. 1

Schematic of the SCR system

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Fig. 2

Model validation: (a) pressure drop and (b) NOx reduction

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Fig. 3

(a) NO mass fraction, (b) NO2 mass fraction, and (c) temperature profiles along the center line of the SCR channel

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Fig. 4

NO mass fraction profile across the SCR channel at (a) low space velocity (8300 h−1), (b) medium space velocity (25,000 h−1), and (c) high space velocity (58,300 h−1)

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Fig. 5

NO2 mass fraction profile across the SCR channel at (a) low space velocity (8300 h−1), (b) medium space velocity (25,000 h−1), and (c) high space velocity (58,300 h−1)

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Fig. 6

Effect of channel shape on pressure drop and NOx conversion

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Fig. 7

Velocity magnitude across the cross section of (a) circular, (b) square, and (c) triangular SCR channels at NH3/NOx = 0.6 and 650 K

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Fig. 8

Reaction kinetic across the cross section of (a) circular, (b) square, and (c) triangular SCR channels at NH3/NOx = 0.6 and 650 K

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Fig. 9

Effect of inlet exhaust gas temperature

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Fig. 10

Effect of NO2/NOx ratio at NH3/NOx of 1

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Fig. 11

Effect of channel length at base case conditions

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Fig. 12

Effect of different parameters on the NOx conversion performance using factorial approach: (a) main factors response, (b) Pareto chart of the standardized effects, and (c) normal plot for different operational parameters' effects

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Fig. 13

Surface reaction kinetics for the dual-layer SCR system: (a) NO conversion, (b) NO2 conversion, and (c) NO conversion at 450 K and 0.6 NH3/NOx ratio

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Fig. 14

Comparison between NOx conversion for single long catalyzed layer and a dual-layer SCR system




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