Determination of the critical residence time for the stability of uniform down-flow in a packed-bed reactor

Christoforatou, Evangelia L.; Balakotaiah, Vemuri

doi:10.1016/s0009-2509(97)00160-7

Cited by 4 publications

(2 citation statements)

References 8 publications

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“…Viljoen et al pointed out that various temperature patterns may be generated by the natural convection when an exothermic reaction is conducted in a porous media. Stroh and Balakotaiah, , Nguyen and Balakotaiah, , Subramanian and Balakotaiah, and Christforatou and Balakotaiah presented extended analyses of when natural convection will generate spatiotemporal temperature patterns in a PBR. This is expected to happen mainly for flow rates lower than those used in most commercial PBRs.…”

Section: Impact Of Flow Mal-distribution and Of Physical Propertiesmentioning

confidence: 99%

Transversal Hot Zones Formation in Catalytic Packed-Bed Reactors

Viswanathan

Sheintuch

Luss

2008

Ind. Eng. Chem. Res.

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Spatiotemporal patterns reported to form in the cross sections of packed-bed reactors (PBRs) may pose severe safety hazard when present next to the reactor wall. Understanding what causes their formation and dynamic features is essential for the rational development of design and control strategies that circumvent their generation. We review the current knowledge and understanding about the formation of these transversal temperature patterns. Simulations and model analysis revealed that the formation of the hot spots and their dynamics are sensitive to the assumed kinetic and reactor models. Under practical conditions, stable symmetry-breaking bifurcation to nonuniform states, from stable, stationary, transversally uniform states cannot be predicted by common PBR models with a rate expression that depends only on the surface temperature and concentration of the limiting reactant. However, analysis and simulations reveal that transient nonuniform transversal temperatures may emerge in an upstream moving traveling front under practical conditions. Microkinetic oscillatory reactions predict the formation of a plethora of intricate spatiotemporal temperature patterns and temperature front motions that are sensitive to the reactor operating conditions and properties such as diameter and initial conditions. The predicted temperature patterns may be rather intricate as a result of conjugation of several modes. The nonlinear coupling between the states at different axial positions, that is, the interaction among the local temperature and concentrations at different cross-sections of the bed, may explain the intricate conjugation of several modes and modulation of the observed spatiotemporal patterns. While some simulations predicted spatiotemporal pattern evolution in PBRs, there is a need to understand which reaction mechanisms may lead to their formation. Most previous simulations and analysis utilized two-dimensional reactor models. However, hot zones are three-dimensional structures, often very small, and difficult to detect in large reactors. A 3-D simulation, although tedious, is necessary to provide full information about the size, shape and dynamic features of small hot zones. Moreover, common PBR models may have to be modified to account for the impact of local states such as flow distribution and nonuniform packing. Verification of the various model predictions requires in situ measurements of 3-D hot zones.

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Section: Impact Of Flow Mal-distribution and Of Physical Propertiesmentioning

confidence: 99%

Transversal Hot Zones Formation in Catalytic Packed-Bed Reactors

Viswanathan

Sheintuch

Luss

2008

Ind. Eng. Chem. Res.

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“…While the application of the perturbation theory to chemical systems is not new, for most works reported in literature [19][20][21] the reaction systems adopted are in general rather simple, including simple reaction networks, and the reactors are frequently assumed to be homogeneous or pseudo-homogeneous. More recent works deal with the modeling of local hot spots in packed bed reactors [22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Thermal Stability of Gas Oil Hydrotreating Processes: Numerical Issues of the Matrix-Eigenvalue Approach

Schweitzer

Elia

García

et al. 2010

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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Résumé -Stabilité thermique de procédés d'hydrotraitement des gazoles : aspects numériques de l'approche par valeurs propres matricielles -Les procédés qui mettent en oeuvre des réactions très exothermiques nécessitent une attention particulière afin d'éviter l'augmentation non contrôlée de la température connue comme emballement thermique. Une analyse de stabilité thermique est nécessaire afin d'établir les conditions d'opération sûre et productive des procédés exothermiques. L'hydrotraitement de gazoles met en oeuvre principalement des réactions d'hydrogénation ; l'hydrotraitement de charges très insaturées comme les gazoles light cycle oil peut être fortement exothermique. Pour cette raison, ce procédé fait l'objet d'une étude de stabilité thermique. La théorie des perturbations a déjà été appliquée pour effectuer une analyse de stabilité de ce procédé en conditions dynamiques. Cette méthode consiste à perturber le modèle et à résoudre le modèle perturbé sous forme d'un problème aux valeurs propres. La condition de stabilité impose que toutes les perturbations doivent s'amortir (tendre vers zéro) quand le temps tend vers l'infini. Quelques aspects sur l'application de cette théorie ainsi que des aspects numériques sont étudiés dans ce travail ainsi que leur effet sur les conclusions de stabilité. La formalisation de la solution du modèle perturbé comme un problème aux valeurs propres standards est comparée au problème aux valeurs propres généralisées. Aussi, le calcul du Jacobien par une approche numérique a-t-il été comparé au calcul par les expressions analytiques. Dans les deux cas, les résultats sont comparés et l'influence sur les résultats de stabilité/instabilité sont présentés. Oil & Gas Science and Technology -Rev. IFP Energies nouvelles, Vol. 65 (2010), No. 5, pp. 771-783 Copyright © 2010, IFP Energies nouvelles DOI: 10.2516 Design of Sustainable Processes Eco-conception des procédés D o s s i e rOil & Gas Science and Technology -Rev. IFP Energies nouvelles, Vol. 65 (2010)

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