Enhancing the Thermal Performance of Slender Packed Beds through Internal Heat Fins

Nico Jurtz,Matthias Kraume,Steffen Flaischlen,Sören C Scherf,Gregor D Wehinger

doi:10.3390/pr8121528

Nico Jurtz, Matthias Kraume + Show 3 more

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https://doi.org/10.3390/pr8121528

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Abstract

Slender packed beds are widely used in the chemical and process industry for heterogeneous catalytic reactions in tube-bundle reactors. Under safety and reaction engineering aspects, good radial heat transfer is of outstanding importance. However, because of local wall effects, the radial heat transport in the vicinity of the reactor wall is hindered. Particle-resolved computational fluid dynamics (CFD) is used to investigate the impact of internal heat fins on the near wall radial heat transport in slender packed beds filled with spherical particles. The simulation results are validated against experimental measurements in terms of particle count and pressure drop. The simulation results show that internal heat fins increase the conductive portion of the radial heat transport close to the reactor wall, leading to an overall increased thermal performance of the system. In a wide flow range (100<Rep<1000), an increase of up to 35% in wall heat transfer coefficient and almost 90% in effective radial thermal conductivity is observed, respectively.

Highlights

Multitubular packed bed reactors are widely used in the chemical and process industry for highly endothermic or exothermic catalytic reactions
The pressure drop needs to be kept low, that is why relatively large particles are used, which leads to slender packed beds characterized by a low tube-to-particle diameter ratio N. For this reactor configuration the assumption of a homogeneously distributed void fraction does not hold true, as the confining walls exert an ordering effect on the particle structure. This leads to a radial void fraction distribution that is characterized by several distinct minima and maxima, as exemplary shown in Figure 1 for spheres
In the scope of this work, we investigate the fluid dynamics and heat transfer packed beds made of spherical particles with a diameter of dp = 7 mm that are filled in a cylindrical container with a nominal diameter of D = 25.4 mm

Summary

Introduction

Multitubular packed bed reactors are widely used in the chemical and process industry for highly endothermic or exothermic catalytic reactions They consist of up to thousands of tubes filled with catalyst particles, whereby a heat transfer media, e.g., a molten salt or gas heated by combustion, is circulated around the tubes to either provide or remove the heat of reaction. The pressure drop needs to be kept low, that is why relatively large particles are used, which leads to slender packed beds characterized by a low tube-to-particle diameter ratio N. For this reactor configuration the assumption of a homogeneously distributed void fraction does not hold true, as the confining walls exert an ordering effect on the particle structure. Because of the ordering wall effect, particles tend to build a Processes 2020, 8, 1528; doi:10.3390/pr8121528 www.mdpi.com/journal/processes ax

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