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Gray/nongray gas radiation modeling in steam cracker CFD calculations

Authors

  • G. D. Stefanidis,

    1. Laboratorium voor Petrochemische Techniek (LPT), Ghent University, Krijgslaan 281 Block S5, Ghent B9000, Belgium
    Current affiliation:
    1. Dept. of Chemical Engineering and Center for Catalytic Science and Technology (CCST), University of Delaware, Newark, DE 19716
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  • B. Merci,

    1. Vakgroep Mechanica van Stroming, Warmte en Verbranding, Ghent University, St. Pietersnieuwstraat 41, Ghent B9000, Belgium
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  • G. J. Heynderickx,

    Corresponding author
    1. Laboratorium voor Petrochemische Techniek (LPT), Ghent University, Krijgslaan 281 Block S5, Ghent B9000, Belgium
    • Laboratorium voor Petrochemische Techniek (LPT), Ghent University, Krijgslaan 281 Block S5, Ghent B9000, Belgium
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  • G. B. Marin

    1. Laboratorium voor Petrochemische Techniek (LPT), Ghent University, Krijgslaan 281 Block S5, Ghent B9000, Belgium
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Abstract

A constant composition gray gas and a constant composition nongray gas radiation model are developed and applied in computational fluid dynamic simulations of an industrial scale steam cracking furnace. Both models are based on the exponential wide band model. The gray gas model simplification, commonly used for simulations of industrial applications, is found to have an effect on predicted variable fields like flue gas flow, temperature, and heat flux to the reactor tubes. When the nongray gas model is used, higher energy absorption by the flue gas in the furnace and lower energy transfer to the process gas in the reactor tubes is calculated because of the high absorption coefficients in the strongly absorbing bands of 2.7 and 4.3 μm. Thus, the calculated thermal efficiency increases from 37.5% when using the nongray gas model to 42.6% when using the gray gas model. A 5% difference in the thermal efficiency is large considering the scale and the importance of the process and should be taken into account by the furnace designer. It is also shown that although both models reproduce the basic characteristics of the flow pattern in the furnace, quantitative differences in the flue gas speed are predicted in some regions of the furnace domain. © 2007 American Institute of Chemical Engineers AIChE J, 2007

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