Stationary transversal hot zones in adiabatic packed‐bed reactors

Viswanathan, Ganesh A.; Luss, Dan; Bindal, Aditya; Khinast, Johannes G.

doi:10.1002/aic.10542

Cited by 24 publications

(46 citation statements)

References 33 publications

(35 reference statements)

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“…7) couple bed and particle equations, so that they cannot be solved independently. When considering catalytic packed-bed reactors some authors neglect the transient terms in particle level with the assumption that transport phenomena occur much faster in the solid phase compared with that in the bed [60,61], e.g. the partial pressures in the particle are in dynamic equilibrium.…”

Section: Particle Equationsmentioning

confidence: 99%

A heterogeneous dynamic model for the simulation and optimisation of the steam methane reforming reactor

Pantoleontos

Kikkinides

Georgiadis

2012

International Journal of Hydrogen Energy

106

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Section: Particle Equationsmentioning

confidence: 99%

A heterogeneous dynamic model for the simulation and optimisation of the steam methane reforming reactor

Pantoleontos

Kikkinides

Georgiadis

2012

International Journal of Hydrogen Energy

106

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“…As for realistic conditions Pe C\ [ Pe T\ and assuming that the ratio of the mass to heat dispersivities in the axial and transversal directions are equal (Pe C\ /Pe T\ ¼ Pe C /Pe T ), condition (6) can be satisfied only in an upstream propagating front (y m \ B), and in the case of stationary fronts (y m ¼ B) is reduced to Pe C \ Pe T , which coincides with the bifurcation condition derived for a simplified shallow reactor (RD) model. 32 Several reported studies focused on numerical analysis of transversal instabilities of planar fronts [25][26][27] : In one of the first studies of the subject, Balakotaiah et al 25 using a threevariable (two species and temperature) model with Langmuir-Hinshelwood kinetics, simulated stationary (nonrotating) transversal patterns with…”

Section: Introductionmentioning

confidence: 99%

Transversal thermal patterns in packed‐bed reactors with simple kinetics: Bifurcation criterion and simulations

Nekhamkina

Sheintuch

2011

AIChE Journal

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We derive a new criterion for transversal instability of planar fronts based on the bifurcation condition dV f /dK| K¼0 ¼ 0, where V f and K are the front velocity and its curvature, respectively. This refines our previously obtained condition, which was formulated as a ¼ (DT ad Pe T )/(DT m Pe C ) [ 1 to a [ 1 þ |d|, where DT ad and DT m are the adiabatic and maximal temperature rise, respectively, Pe C and Pe T are the axial mass and the heat Pe numbers, respectively, and d is a small parameter. The criterion is based on approximate relations for DT m and V f , which account for the local curvature of a propagating front in a packed bed reactor with a first-order activated kinetics. The obtained relations are verified by linear stability analysis of planar fronts. Simulations of a simplified 2D model in the form of a thin cylindrical shell are in good agreement with the critical parameters predicted by dispersion relations. Three types of patterns were detected in simulations: ''frozen'' multiwave patterns, spinning waves, and complex rotating-oscillating patterns. We map bifurcation diagrams showing domains of different modes using the shell radius as the bifurcation parameter. The possible translation of the 2D cylindrical shell model results to the 3D case is discussed. V V C 2010 American Institute of Chemical Engineers AIChE J, 57: 735-748, 2011 Keywords: reactor analysis, simulation, process, fronts, bifurcations, transversal patterns IntroductionHeterogeneous catalysts are extensively used in the chemical and petrochemical industry and for pollution abatement purposes. It is usually assumed that the temperature and concentrations of the reactants at any transversal cross section of an adiabatic packed-bed reactor are uniform. However, various industrial and laboratory experimental observations revealed formation of nonuniform temperature in the reactor cross section. Such patterns may pose severe safety hazards by altering the wall strength and inducing cracks. Ignoring such patterns in design and simulations may lead to erroneous results. Understanding which kinetics may lead to spatiotemporal pattern formation is essential for the development of design and control strategies that circumvent them.Symmetry-breaking leading to either spatial and/or spatiotemporal pattern formation has been observed in many biological, physiological, chemical, and electro-chemical systems [1][2][3][4][5][6][7][8] governed by the interaction of diffusion and reaction processes. Majority of the studies of pattern formation in chemically reacting systems are of homogeneous systems. Pattern formation in heterogeneous catalytic and electrochemical systems, like wires, pellets, and packed bed reactors has been known for 20 years. Recent reviews of the and Krischer. 12 The current knowledge and understanding about the formation of transversal temperature patterns has been reviewed by Viswanathan et al. 13The obtained results are kinetics-dependent 14 and in the present study we focus on kinetics that admits multiple steady sta...

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“…As explained in the Introduction, using the classical mechanism, one can reason that (for a uniformly active bed with identical particles or uniform porosity, and constant physical properties) SPs cannot emanate from a homogeneous state. This is due to the fact that the temperature is the autocatalytic species (for the case of linear kinetics) and thermal diffusivity is always higher than mass or species diffusivity under realistic conditions (Balakotaiah et al, 1999a, b;Yakhnin and Menzinger, 2001;Viswanathan et al, 2005). While this reasoning is correct, it does not preclude the possibility of the unstable patterned states emerging from the (unstable) homogeneous branches gaining stability through secondary bifurcations (which happens as illustrated in this work).…”

Section: Estimation Of the Range Of Parameter Values For Pattern Formmentioning

confidence: 55%

“…first-order reaction) with pseudohomogeneous models or two-phase models with very small inter-phase gradients. Other authors (Viswanathan et al, 2005;Viswanathan and Luss, 2006) have reached a different conclusion and state that there is no qualitative difference between pseudohomogeneous models and two-phase models with respect to pattern formation.…”

Section: Estimation Of the Range Of Parameter Values For Pattern Formmentioning

confidence: 93%

“…Marwaha et al (2004) and Sundarram et al (2005) have shown that global coupling can lead to formation of hot zones on the top of a packed-bed reactor. Recently, Viswanathan et al (2005) and Viswanathan and Luss (2006) showed that a stable stationary hot zone can form in the cross-section of a packed-bed reactor only under the unrealistic assumption that the transversal species dispersion exceeded that of the temperature.…”

Section: Introductionmentioning

confidence: 99%

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