Dynamic behaviour of an adiabatic trickle bed reactor

“…When mass transfer through the liquid phase is rate limiting, direct access elevates the reaction rate and raises local temperatures substantially (Hanika et al, 1975). For exothermic reactions, increased reaction rate leads in turn to formation of narrow reaction zones with steep temperature gradients (Hanika et al, 1976(Hanika et al, , 1977 and a hot spot in the bed. Development of a hot spot takes time and can be cut off by periodically fl ooding the trickle bed with the liquid phase.…”

Section: Conceptsmentioning

confidence: 99%

“…Appearance of a hot spot often results from evaporation of the liquid phase. Motion of the hot spot is caused by axial heat transfer and resembles propagation of a fl ame during combustion (Hanika et al, 1976(Hanika et al, , 1977. An equilibrium trickle bed model describing hydrogenation, developed by , attributes hot spot formation to the interaction of heat and mass transfer when the reactant mixture has a volatile component present.…”

Section: Hot Spot Controlmentioning

confidence: 99%

Periodic Operation of Three — Phase Catalytic Reactors

Silveston

Hanika

2004

Can J Chem Eng

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Periodic operation of three phase reactors has been explored for more than two decades. This type of forcing changes selectivity and can increase either conversion or throughput. Experiments and simulation demonstrate periodic flow interruption or variation enhances reaction rates for concurrent trickle beds provided reactants are in the gas phase or can be volatilized under bed operating conditions. Temperature excursions in trickle beds can be controlled by either flow variation or switching the feed between an inert and a reactant. Several approaches to increasing rate through faster mass transfer using flow pulsing have been studied. Pulsing flow can be induced by low amplitude modulation. Periodic switching of flow direction in airlift reactors increases gas hold up and thereby the mass transfer rate. Periodic operation of three phase reactors, thus, appears to be a fertile area for engineering research.

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“…A plethora of transversal–perpendicular to flow patterns have been reported to form in lab-scale and industrial catalytic packed-bed reactors (PBRs) used to conduct exothermic reactions. − Rich and complex dynamics of (small- and medium-sized) hot zones are typical characteristics of spatiotemporal temperature patterns in PBRs. , The presence of hot zones may strongly affect performanceyield, selectivity, catalyst lifeand may also pose challenges for safe operation when present near a reactor wall . In fact, for the catalytic reforming process, development of operation procedures ensuring control of hot spots, particularly during reactor start-up, is recommended .…”

Section: Introductionmentioning

confidence: 99%

Wall Temperature Modulates Transversal Spatiotemporal Pattern Selection in Shallow, Nonadiabatic Packed-Bed Reactors

Narendiran

Viswanathan

2019

Ind. Eng. Chem. Res.

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Transversal temperature pattern formation has been observed in laboratory and industrial catalytic packed-bed reactors (PBRs) used for conducting exothermic reactions. These patterns or nonuniform states can strongly affect reactor performance and pose severe safety issues. Recent studies show that symmetry-breaking bifurcations may cause transversal pattern formation in a reactor operated under nonadiabatic conditions. In this study, we show that wall temperature, which dictates the instantaneous and overall heat exchange rate, strongly influences the selection and dynamics of various target and rotating patterns exhibited in a shallow nonadiabatic PBR. We demonstrate this by linear stability analysis-guided extensive numerical simulations of a shallow reactor model assuming periodic blocking-reactivation kinetics for the catalytic reaction. Transversal spatiotemporal patterns predicted in lab-scale (∼6 cm diameter) and/or bench-scale (∼60 cm) reactors, include rotating patterns, inward/outward/multi-ring targets, quasi-stationary moving patterns, and symmetric and asymmetric spirals. We show that wall temperature modulates the transition between these targets and rotating transversal nonuniform states at both scales. We argue that rich and intricate patterns observed much more in bench-scale reactors than those in lab-scale reactors are possibly due to reduction in the heat removal time upon increase in diameter by 10-fold. We further classify the simulated transversal patterns into three regimes, viz., (i) heating, (ii) heating and cooling, and (iii) cooling, based on the nature of wall heat exchange rate dynamics dictated by the (instantaneous) local temperature near the reactor wall. Wall heat exchange rate dynamics being an experimental observable makes it a signature of a nonuniform state present inside the reactor.

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Dynamic behaviour of an adiabatic trickle bed reactor

Cited by 19 publications

References 9 publications

Modeling of an industrial fixed bed reactor based on lumped kinetic models for hydrogenation of pyrolysis gasoline

Modeling of an industrial fixed bed reactor based on lumped kinetic models for hydrogenation of pyrolysis gasoline

Periodic Operation of Three — Phase Catalytic Reactors

Wall Temperature Modulates Transversal Spatiotemporal Pattern Selection in Shallow, Nonadiabatic Packed-Bed Reactors

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