A 1-D model for highly sensitive tubular reactors

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We consider the steady state operation of wall-cooled, fixed-bed tubular reactors. In these reactors the temperature rise ..delta..T must normally be limited to small fractions of the adiabatic temperature rise ..delta..T/sub ad/, both to avoid runaway and maintain product selectivity. Yet ..delta..T/..delta..T/sub ad/ << 1 can only occur if eta = t/sub dif//t/sub reac/ << 1, where t/sub dif/ is the timescale on which heat escapes the reactor by ''diffusing'' to the cooled walls, and t/sub reac/ is the timescale over which the reaction occurs. So here we use asymptotic methods based on eta << 1 to analyze the 2-d ... continued below

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Pages: 24

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Hagan, P.S.; Herskowitz, M. & Pirkle, J.C. January 1, 1987.

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Description

We consider the steady state operation of wall-cooled, fixed-bed tubular reactors. In these reactors the temperature rise ..delta..T must normally be limited to small fractions of the adiabatic temperature rise ..delta..T/sub ad/, both to avoid runaway and maintain product selectivity. Yet ..delta..T/..delta..T/sub ad/ << 1 can only occur if eta = t/sub dif//t/sub reac/ << 1, where t/sub dif/ is the timescale on which heat escapes the reactor by ''diffusing'' to the cooled walls, and t/sub reac/ is the timescale over which the reaction occurs. So here we use asymptotic methods based on eta << 1 to analyze the 2-d reactor equations, and find the radial concentration and temperature profiles to leading order in eta. We then obtain a 1-d model of the reactor by substituting these asymptotically correct profiles into the reactor equations and averaging over r. This model, the ..cap alpha..-model, is identical to the standard (Beek and Singer) 1-d model, except that the reactor's overall heat transfer coefficient U is a decreasing function of the temperature rise ..delta..T. This occurs because as ..delta..T increases, the reaction becomes increasingly concentrated near r = 0, causing a decreased heat transfer efficiency through the reactor's walls. By comparing it with numerical solutions of the original 2-d reactor equations, we find that the ..cap alpha..-model simulates the 2-d equations very accurately, even for highly sensitive reactors operated near runaway. We also find that a runaway criterion derived from the ..cap alpha..-model predicts the runaway transition of the original 2-d equations accurately, especially for highly sensitive reactors. 19 refs.

Physical Description

Pages: 24

Notes

NTIS, PC A02/MF A01; 1.

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  • American Institute of Chemical Engineers annual meeting, New York, NY, USA, 15 Nov 1987

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  • Other: DE87013174
  • Report No.: LA-UR-87-2561
  • Report No.: CONF-871113-1
  • Grant Number: W-7405-ENG-36
  • Office of Scientific & Technical Information Report Number: 6250310
  • Archival Resource Key: ark:/67531/metadc1114225

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  • January 1, 1987

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  • Feb. 22, 2018, 7:45 p.m.

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  • March 20, 2018, 5:14 p.m.

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Hagan, P.S.; Herskowitz, M. & Pirkle, J.C. A 1-D model for highly sensitive tubular reactors, article, January 1, 1987; United States. (digital.library.unt.edu/ark:/67531/metadc1114225/: accessed August 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.