Fluidized Bed Catalytic Reactor Research Articles

Analysis of volume change effects in a fluidized bed catalytic reactor

AbstractA mathematical model based on the concept of an improved bubble assemblage model is developed for calculating the conversion of a reaction system involving a volume change in fluidized beds. The influence of volume change on the hydrodynamic behavior of gas in the bed, such as bubble size variation, superficial gas velocity change, and volume fraction occupied by each phase, is also investigated. It is found that increasing stoichiometric coefficient values results in larger bubble size, higher superficial gas velocities, higher crossflow rate between emulsion phase and bubble phase, and greater volume fraction of bubble phase, but smaller volume fraction occupied by the emulsion phase as well as lower conversions.

Bifurcation, instability and chaos in fluidized bed catalytic reactors with consecutive exothermic chemical reactions

A two-phase model for the non-isothermal fluidized bed catalytic reactor with consecutive exothermic reactions has been used to investigate the bifurcation, instability and chaotic characteristics of this industrially important unit. The investigation, although in a restricted region of the parameter space, has uncovered a good part of the rich dynamic characteristics of this system, including; 2 n and 2 n k period doubling sequences leading to chaos, banded and fully developed chaos, interior crises, tangent bifurcation leading to intermittency, periodic windows interrupting chaotic regions and alternating periodic-chaotic sequences. Within the chaotic region a new type of periodic windows (termed periodic horns) which differ quantitatively and qualitatively from ordinary periodic windows have been discovered.

Three-phase multi-compartment model for fluidized-bed catalytic reactors: autothermicity and multiplicity of steady states

Abstract This paper concerns the mathematical modelling of a catalytic process carried out in a non-isothermal fluidized-bed reactor. A three-phase multi-compartment model of the fluidized bed is used for elucidating the hydrodynamics of the bed as well as for the simulation of a non-isothermal catalytic process. A basic version of the reactor model is proposed and two simplified models are developed. One assumes the stagnation of the gas in the emulsion phase within each compartment distinguished by the model; the other, for the case of back flow of the gas, assumes homogeneity of the concentration field in the emulsion phase. Both assumptions which have been introduced are discussed quantitatively and in detail. Some numerical computations have been performed for the purpose of comparing the degree of conversion and temperature distribution obtained according to different models. The Kunii—Levenspiel model and two multi-compartment models were considered. An analysis of the multiplicity of steady states has also been carried out. Hysteresis loops were obtained in the fluidization ratio—emulsion temperature system of coordinates. Over a certain range of feed temperature two separate areas of multiple steady states were shown to exist.

Fluidized bed catalytic reactor: a learning model for fast reaction

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFluidized bed catalytic reactor: a learning model for fast reactionRichard G. Pigeon and James J. CarberryCite this: Ind. Eng. Chem. Res. 1990, 29, 6, 1013–1019Publication Date (Print):June 1, 1990Publication History Published online1 May 2002Published inissue 1 June 1990https://doi.org/10.1021/ie00102a010RIGHTS & PERMISSIONSArticle Views329Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (792 KB) Get e-Alerts Get e-Alerts

The effect of particle size distribution on the performance of a catalytic fluidized bed reactor

The performance of a fluidized bed reactor has been investigated using the ozone decomposition reaction for fresh and spent fluid cracking catalysts, each having three particle size distributions - wide, narrow and bimodal - all with the same mean particle diameter. The superficial gas velocity was varied from 0.06 to 1.8 m/s and the rate constant from 1 to 9 s −1. The wide size distribution usually gave the highest reactor efficiency, while the narrow blend gave the lowest. The differences are not solely a function of the “fines content”. The reasons for the influence of particle size distribution were examined by testing the “bimodal” distribution with different fractions active. In the bubbling fluidization regime and for Group A particles, this influence can be predicted using the Two-Phase Bubbling Bed Reactor Model with modifications to allow for increased concentration of fine particles in the dilute phase.

Safe design and operation of fluidized-bed reactors: Choice between reactor models

For three different catalytic fluidized bed reactor models, two models presented by Werther and a model presented by van Deemter, the region of safe and unique operation for a chosen reaction system was investigated. Three reaction systems were used: the oxidation of benzene to maleic anhydride, the oxidation of naphthalene to phthalic anhydride, and the oxidation of ethylene to ethylene oxide. Predictions of the optimal yield, the operating temperature and the conversion were also subjects of our study. It appeared that for reactions carried out in a fluidized bed operating under conditions of good fluidization all models predicted the same region of safe and unique operation. For a well-designed fluidized bed only the constraint of uniqueness is affected by the reactor model chosen. Predictions of the yield, conversion and operating temperature appeared to fit slightly less well. But still a good indication can be obtained from any of the models since the deviation in the results was less then a few percent for all three reaction systems. The strongest deviations between the models occurs in the region of gas loads only slightly higher than the minimum fluidization velocity. As the heat transfer characteristics are bad at low gas loads this region is unsuitable for highly exothermic reactions where large amounts of heat have to be removed by the coolant. In the region of good heat transfer with gas loads at least several times higher than the minimum the three models predict the same results. For this reason we finally recommed the use of simple models.

Stable design and operation of catalytic fluidized-bed reactors for multiple reactions: uniqueness and multiplicity

A method is presented of designing a fluidized-bed reactor in which a system of either two simultaneous or two consecutive reactions is carried out. A simple version of the two-phase model is used to describe the temperature and concentrations in the reactor. The method enables one to determine the region of unique and stable operation. Dimensionless groups are introduced which are exclusively representative of either the properties of the reaction systems or the design and operating variables only. In a plot of the slope of the heat withdrawal rate line vs the dimensionless residence time the area is determined in which operation is feasible and safe when a certain desired yield or selectivity has to be achieved. The method also accounts for the various physical constraints. The method is illustrated with two examples: the air oxidation of napthalene to phthalic anhydride and the oxidation of ethylene to ethylene oxide.

A non-isothermal grid model for catalytic fluidized-bed reactors

Gas enters a fluidized bed through jets which at a given height are stopped and the gas flow divided between bubbles and the dense phase. To describe the non-uniform mixing of the catalyst, the grid region, with a height equal to the jet penetration depth, is divided into three zones one above the other: the dead region, the quasi-dead region and the intermittently mixed region. Each of them and the dense phase are considered with lumped parameters. The jet and bubbles are assumed to be in plug flow. The catalytic reaction occurs in the three grid zones and the dense phase. There is mass and heat transfer between each of the grid zones and the jet, and between the dense phase and the bubble phase. The bubbles cause the solid movement between the three grid zones and the dense phase. There is heat transfer from the grid zones and the dense phase to the surroundings, especially through the cooling tubes. This model accounts for the thermal gradients reported in some industrial fluidized-bed reactors. It seems to be well suited to fast exothermic catalytic reactions.

Optimum particle size in a gas-liquid-solid fluidized bed catalytic reactor

The effect of particle size on the reactant conversion for a pseudo-first-order reaction in a gas-liquid-solid fluidized bed catalytic reactor is rigorously examined based on a comprehensive model developed in this study. The model takes into consideration inherent transport properties of the reactor including gas-liquid and liquid-solid mass transfer, axial liquid dispersion, solids mixing, and phase holdups. The reactant conversion predicted by the model exhibits a maximum with respect to particle size, which is shown to vary with process variables such as gas and liquid velocities, reaction rate constant, and intraparticle diffusivity. The effect of solids mixing on conversion is shown to be insignificant for a wide range of process variables. Overall reaction rates in the fluidized-bed system are also compared to those predicted for a slurry bubble column utilizing a model based on sedimentation and dispersion of the solids.

Mathematical modeling of catalytic fluidized-bed reactors—I. The multistage three-phase model

The purpose of this paper is to develop a novel model for gas-solid fluidized-bed catalytic reactors. This model is called the “multistage three-phase model”. It considers the fluid bed to be composed of a number of equivalent stages in series. Within each stage exchange of gas takes place between the bubble, cloud-wake and emulsion phases. An exact analytical solution for the concentration profiles along the bed is obtained. All parameters in the model are correlated with known or experimentally obtainable quantities. Model predictions are shown to compare reasonably well with various published experimental data on conversions of gas-fluidized catalytic reactors. A worked numerical example is given to demonstrate the applicability of the proposed model.

Model reference adaptive control system of a catalytic fluidized bed reactor

This paper presents a study of the control of a fluidized bed catalytic reactor using the model reference adaptive control algorithm with independent tracking and regulation objectives as presented by Landau and Lozano (1981). The purpose of the control is to maintain the temperature of the reactor as near as possible to a desired set value (490°C). Some of the heat produced by the exothermal reaction taking place between propylene, ammonia and oxygen is carried away by a ventilator. The control action is based on a low order mathematical model with time varying parameters. This method of control results in a significantly improved control for both servo and regulatory control.

The effect of bubble size variation on the performance of fluidized bed reactors

The effect of bubble growth by coalescence on predictions of reactant conversion in a fluidized bed catalytic reactor has been investigated for reactions that are described by either Langmuir—Hinshelwood or a simple first order kinetics. The two-phase model of Orcutt et al. with continuous change of bubble size with height has been employed in all calculations. The results of these calculations have been compared with those of models using a constant bubble diameter. These effective bubble diameters have been determined in three ways: by calculating an integral average bubble diameter, by calculating the bubble diameter which gives the same bed expansion and by calculating the bubble diameter which gives the same total number of mass transfer units. It was found that, in the absence of significant interphase mass transfer resistance, predicted values of conversion, and/or multiplicity of steady states obtained from models using the effective bubble diameter determined from the bed expansion are in very good agreement with those obtained using models which incorporate bubble size variation with height. However, an accurate description of bubble size variation with height is required when the bubble growth is fast and the local mass transfer rate decreases rapidly with distance from a distributor. Under these conditions, the values of conversion obtained using the model with perfect mixing of the dense phase gas may be higher than the ones obtained from the model which assumes plug flow of the dense phase gas. This type of behaviour has not been observed when models with constant bubble size are used.

Steady states of an autothermal catalytic fluidized bed reactor

Steady states of an autothermal catalytic fluidized bed reactor

Model Reference Adaptive Control System of a Catalytic Fluidized Bed Reactor

This paper presents a study on the control of a fluidized bed catalytic reactor. In this study, the model reference adaptative control algorithm with independent tracking and regulation objectives as presented by Landau-Lozano (1981) has been investigated. The purpose of the control is to maintain the temperature of the reactor as near as possible to a desired set value (490°C). Some of the heat produced as a result of the exothermal reaction tacking place between propylene, ammonia and oxygen is carried away by a ventilator. The control action is based on a simple mathematical lower order with time varying unknown parameters. This method of control results in a significantly improved control for both servo and regulatory control.

Model of solid gas reaction phenomena in the fluidized bed freeboard

AbstractA comprehensive model incorporating elutriation, entrainment and reaction is presented to describe the chemical reaction and hydrodynamics occurring in the freeboard of a fluidized bed. A comparison of experimental data on the amount of particles elutriated and the concentration profiles of SO2 and NOx obtained from the freeboard of fluidized bed coal combustion (FBC) by the Babcock & Wilcox Company with the calculation based on the proposed model to include the effect of interaction among the entrained particles is desirable. More experimental data with chemical reactions in the freeboard are needed to validate the model for applications to fluidized bed catalytic reactors.

Reactant dynamics in catalytic fluidized bed reactors with flow reversal of gas in the emulsion phaset

In the present study both the steady-state and transient behavior of reactant gas in a bubbling fluidized bed reactor are analytically investigated with the occurrence of flow reversal of emulsion phase gas. The model developed contains no adjustable constants and no major two-phase theory assumptions. In addition, the concept of local flow reversal of emulsion phase gas and emulsion phase de-gassing coefficients are introduced. The transient behavior of reactant gas as a function of the extent of flow reversal of gas, rate constant and reaction order, and operating superficial gas velocity is discussed. Finally, model predictions are shown to compare favorably to various reported experimental results including the division of gas flow analysis, steady-state axial concentration profiles, overall conversions, and cumulative residence time distributions.

Simulation of catalytic fluidized bed reactors by a transient axial dispersion model with invariant physical properties and nonlinear chemical reactions

This paper presents a transient axial dispersion model for an isothermal, catalytic fluidized bed reactor, which is frequently employed in synthetic production processes including coal gasification and liquefaction. A non-linear chemical reaction is considered to occur in the reactor. This model of a fluidized bed reactor takes into account the axial dispersion in the three phases, bubble, cloud-wake and emulsion. The physical properties along the axial coordinate are invariant in the model. Transient characteristics of the gas reactant, and the length of the transient period have been examined based on the model. The model compares favorably with experimental data in the steady state condition.

Process Design for a Packed Fluidized Bed Catalytic Reactors

Process Design for a Packed Fluidized Bed Catalytic Reactors

Experimental investigation of models for fluidized bed catalytic reactors

AbstractThe countercurrent backmixing model of a fluidized bed reactor predicts axial concentration profiles quite different from those suggested by simple two‐phase models. The models can also be distinguished in terms of the dependence of conversion on operating variables.An experimental study of ozone decomposition in a reactor of 22.9 cm diameter has provided extensive data for comparison with backmixing and two‐phase models which incorporate bubble size variation. The measured profiles show a minimum concentration within the bed at gas velocities above a critical value, as predicted only by the backmixing model. The effect of operating variables on the shape of the profiles is also well accounted for by this model. The backmixing model is further supported by good agreement between predicted and measured reactant conversion. In particular, the variation of conversion with rate constant and gas velocity is fitted more accurately by the backmixing model than by two‐phase models.

Mathematical modelling of fluidized bed reactors—III: Axial dispersion model

An axial dispersion model has been developed for a continuous fluidized bed catalytic reactor with a cocurrent flow of the emulsion phase gas and the catalyst particles. The influence of some parameters on multiplicity of steady states has been reported. Several examples illustrating the transient behavior of the system are presented. In cases where three steady states are possible it appears that the intermediate steady state is unstable, while the lower and the upper steady states are locally stable. It was noted that the initial temperature of the emulsion phase is a predominant factor in determining which steady state will be approached.