Partial oxidation of o-xylene to phthalic anhydride in a fixed bed reactor with axial thermowells

The present study analyses the thermowell system for monitoring temperatures in a fixed bed catalytic reactor for the highly exothermic partial oxidation of o-xylene to phthalic anhydride. Particle-resolved computational fluid dynamics (CFD) simulations are presented for the cases of randomly-packed spheres inside cylindrical tubes with tube-to-particle diameter ratios (N) of 3.96, 5.96 and 7.99. Results are obtained for each N value for cases with inner thermowell radius to outer tube radius ratios of 0.0 (no thermowell), 0.05, 0.1 and 0.2. Comparisons of radial void fraction and axial velocity profiles, axial pressure drop and axial temperature profiles under reaction conditions are presented. The presence of the thermowell did change the mass and heat transfer and reaction inside and around the particles, especially at the bed center. The configurations of catalyst particles were rearranged, leading to changes in voidage, flow and temperature profile. The axial temperature profiles from the thermowells differed from the profiles in the undisturbed beds. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.