Radial Flow Reactor Research Articles

Hydrodynamic problems of industrial radial-flow ammonia synthesis reactors

The cheapest way to upgrade existing production lines is to rebuild catalytic reactors with axial reagent flows as radial-flow reactors. The aim of this work is to attract the attention of engineering companies and developers of ammonia synthesis reactors to the hydrodynamic problems encountered in their reconstruction. Alternative approaches to the design of distributing devices that ensure the radial introduction of reagents into a catalyst bed and their uniform distribution are considered. The obtained results allow us to estimate the proposed technical solutions and to choose reliable and technically feasible variants of reconstruction.

A dynamic membrane reactor concept for naphtha reforming, considering radial-flow patterns for both sweeping gas and reacting materials

Hydrogen will become an essential energy source in the near future. In this regard, refineries can be considered as alternative sources of hydrogen production. In the present study, a tubular membrane reactor with radial-flow patterns of the sweeping gas and the naphtha feed named RF-TMR is proposed as a novel configuration for radial-flow naphtha reformers. Radial-flow reactors are used in refineries as a remedy for high pressure drop through the catalytic packed-bed reactors which disturbs the reactor operation. The cross section area of the tubular membrane reactor is divided into some subsections. The walls of the gaps are coated by a Pd–Ag membrane layer to separate hydrogen from reaction side and enhance the hydrogen and aromatic production rates by 0.33 ton/day and 5.5 ton/day, respectively (compared with the AF-TR). The performance of this novel configuration is investigated and compared with the axial-flow conventional tubular reactor (AF-TR) and axial-flow tubular membrane reactor (AF-TMR). Set of coupled partial differential–algebraic equations are solved by the orthogonal collocation method. Owing to a slight pressure drop in the tube side of RF-TMR, smaller catalysts’ particles with a negligible internal mass transfer resistance can be used to increase aromatics and hydrogen yields. This novel approach has the feasibility to be applied in the radial-flow moving bed reformers which are widely installed in refineries by licensors.

Investigations on hydrodynamics of multilayer Π‐type radial flow reactors

ABSTRACTConsisting of two or three different layers of catalyst or adsorbent, the multilayer radial flow reactor is a novel radial reactor with compact structure and high performance. In this article, pressure profiles in the flow channels and layers of a three‐layer radial flow reactor were measured and the properties of the fluids in the flow channels and layers were investigated. Results show that the uniformity of the pressure profiles in the distributing and collecting channels in the axial direction has a significant effect on the flow distribution of each layer. The uniformity of the flow distribution in multilayer Π‐type radial flow reactors varies in the radial direction. It is better in the outer layer than in the inner layer when the pressure variation in the center channel is more significant than that in the annular channel. The main contributions of this work are helpful to the proper design and optimum operation of the multilayer radial reactor. Copyright © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.

Study of Pulsed Plasma in a Crossed Flow Dielectric Barrier Discharge Reactor for Improvement of NOx Removal in Raw Diesel Engine Exhaust

Improved performance of plasma in raw engine exhaust treatment is reported. A new type of reactor referred to as of cross-flow dielectric barrier discharge (DBD) was used, in which the gas flow is perpendicular to the corona electrode. In raw exhaust environment, the cross-flow (radial-flow) reactor exhibits a superior performance with regard to NOX removal when compared to that with axial flow of gas. Experiments were conducted at different flow rates ranging from 2 L/min to 25 L/min. The plasma assisted barrier discharge reactor has shown encouraging results in NOX removal at high flow rates.

Modeling of adiabatic moving-bed reactor for dehydrogenation of isobutane to isobutene

The dehydrogenation of isobutane to isobutene in adiabatic radial-flow moving-bed reactors was studied. First order rate expressions were considered for the primary reaction and deactivation kinetics incorporating the reversibility of dehydrogenation reaction. Kinetic data from a fixed-bed lab-scale reactor were used for modeling of the commercial size moving-bed reactor. The model was solved numerically by dividing the reactor into differential isothermal moving-bed reactors. The conversion of isobutane to isobutene was found to be equilibrium limited in commercial-sized reactors. The model predicted the trends of conversion, temperature, and catalyst activity with conversion levels somewhat lower than observed values which was attributed to the side-reactions.

Evaluation of Optimum Design Parameters and Operating Conditions of Axial- and Radial-Flow Tubular Naphtha Reforming Reactors, Using the Differential Evolution Method, Considering Catalyst Deactivation

In this study, a new flow pattern (radial-flow) in a tubular reactor is proposed for the naphtha reforming process. The operating conditions of axial-flow and radial-flow tubular packed-bed reactors have been optimized by the differential evolution (DE) method. The DE optimization method has been applied to maximize hydrogen and aromatic yields in the steady-state and dynamic conditions. Some parameters, such as total pressure, the hydrogen mole fraction in the recycled stream, the length per diameter of the reactor, and the mass distributions of the catalysts, have been optimized for the steady-state conditions. Moreover, the inlet temperature of the gas at the entrance of each reactor is optimized for the unsteady-state condition to compensate for the effect of catalyst deactivation. A set of coupled partial differential equations are solved by the orthogonal collocation method. The results demonstrate that, by utilizing the optimization technique and alternating the flow pattern in conventional catalyt...

A comparative study on a novel combination of spherical and membrane tubular reactors of the catalytic naphtha reforming process

Refineries have been looking for ways of improving the performance of the reformer by enhancing the octane number of the product via increasing the aromatics content. To reach this goal, more improved configurations should be investigated. The aromatics production rate could be enhanced by shifting the reactions to the production side by using hydrogen perm–selective membranes. In the present study, we have investigated theoretically the best combination of membrane tubular reactors and spherical radial-flow reactors for the conventional naphtha reforming unit consist of three fixed-bed reactors. Hydrogen permeation through the membrane shifts the reaction to the product side (aromatics and hydrogen) according to the thermodynamic equilibrium. Spherical reactors reduce the pressure drop in the catalytic naphtha reforming units and consequently increase the efficiency. The results show higher aromatics production in the new configurations compared with the membrane tubular and conventional reactors despite using lower membrane surface area.

Dynamic optimization of a multi-stage spherical, radial flow reactor for the naphtha reforming process in the presence of catalyst deactivation using differential evolution (DE) method

In the present research, differential evolution (DE) method has been used to optimize the operating conditions of a radial flow spherical reactor containing the naphtha reforming reactions. In this reactor configuration, the space between the two concentric spheres is filled by catalyst. The dynamic behavior of the reactor has been taken into account in the optimization process. The achieved mass and energy balance equations in the model are solved by orthogonal collocation method. The goal of this optimization is to maximize the hydrogen and aromatic production which leads to the maximum consumption of the paraffins and naphthenes. In order to reach this end, the inlet temperature of the gas at the entrance of each reactor, the total pressure of the process, as well as the catalyst distribution in each reactor have been optimized using the differential evolution (DE) method. The results of the optimization of the spherical reactor have been compared with the non-optimized spherical reactor. The comparison shows acceptable enhancement in the performance of the reactor.

Dynamic optimization of a novel radial-flow, spherical-bed methanol synthesis reactor in the presence of catalyst deactivation using Differential Evolution (DE) algorithm

In this work, a novel radial-flow spherical-bed methanol synthesis reactor has been optimized using Differential Evolution (DE) algorithm. This reactor's configuration visualizes the concentration and temperature distribution inside a radial-flow packed bed with a novel design for improving reactor performance with lower pressure drop. The dynamic simulation of spherical multi-stage reactors has been studied in the presence of long-term catalyst deactivation. A theoretical investigation has been performed in order to evaluate the optimal operating conditions and enhancement of methanol production in radial-flow spherical-bed methanol synthesis reactor. The simulation results have been shown that there are optimum values of the reactor inlet temperatures, profiles of temperatures along the reactors and reactor radius ratio to maximize the overall methanol production. The optimization methods have enhanced additional yield throughout 4 years of catalyst lifetime, respectively.

Disk-shaped packed bed micro-reactor for butane-to-syngas processing

A novel disk-shaped packed bed micro-reactor containing Rh/ceria/zirconia nanoparticles is investigated with respect to catalytic butane-to-syngas processing at moderate temperatures of 550 °C. The main goal of this study is the development of an efficient butane processor which can be integrated into a micro solid oxide fuel cell system due to its small size, easily packaged geometry in layered microdevices, high compactness, low pressure drop, and low reaction temperature. It is shown that Rh/ceria/zirconia has an excellent long-term stability and achieves very high C 4H 10 conversion and syngas selectivity, considering the relatively low operating temperature. The yields of H 2 and CO can be increased up to 71% and 57%, respectively, by optimizing operational parameters such as the C/O ratio and the total inlet flow rate. The introduced disk-shaped packed bed reactor shows significant advantages in catalytic behavior, at a 6.5 times lower pressure drop compared to an equivalent tubular packed bed reactor. This increased catalytic performance is pursued extensively by investigating possible reaction pathways in three regions of the radial-flow reactor, leading to the significant discovery of a threefold pathway of syngas production on a single catalyst. To this end, it is shown that the excellent selectivities to H 2 and CO for high flow rates are due to the combination of partial oxidation, steam reforming, and dry reforming of C 4H 10, indicating one direct and two indirect reaction paths.

Modeling of a radial-flow moving-bed reactor for dehydrogenation of isobutane

A mathematical model for the performance of a radial-flow moving-bed reactor for dehydrogenation of light paraffins was developed. Assuming relevant kinetic expressions for the main reaction and catalyst deactivation, the kinetic parameters were obtained through lab-scale fixed-bed reactor testing using the integral method of analysis. The conversion was found to be a function of a dimensionless decay time, i.e., the ratio of a “catalyst deactivation time constant” to the residence time of the catalyst within the reactor. For a large dimensionless decay time (negligible catalyst decay), the performance equation approached that of a simple packed-bed reactor. The predictions of the model were compared with those of a commercial unit, and fair agreements were observed.

Modeling the Pyrochemical Reduction of Spent UO2 Fuel in a Pilot-Scale Reactor

A kinetic model has been derived for the reduction of oxide spent nuclear fuel in a radial flow reactor. In this reaction, lithium dissolved in molten LiCl reacts with UO2 and fission product oxides to form a porous, metallic product. As the reaction proceeds, the depth of the porous layer around the exterior of each fuel particle increases. The observed rate of reaction has been found to be dependent only upon the rate of diffusion of lithium across this layer, consistent with a classic shrinking core kinetic model. This shrinking core model has been extended to predict the behavior of a hypothetical, pilot-scale reactor for oxide reduction. The design of the pilot-scale reactor includes forced flow through baskets that contain the fuel particles. The results of the modeling indicate that this is an essential feature in order to minimize the time needed to achieve full conversion of the fuel.

Optimization of Radial Flow Reactors of Styrene Production

A mathematical model is developed to optimize the performance of the radial flow reactors of styrene production through an oxidative reheat process. The model integrates the hydrodynamic configuration of the reactors with the underlying chemical reactions where the kinetic expressions were found in the literature. The predictions of the model were compared with the actual plant data and satisfactory results were obtained. In order to optimize the performance of the plant, a combination of yield and selectivity styrene was adopted as the objective function. The global criterion multi-objective method using Levenberg-Marquardt algorithm was used in order to search for the optimal solution of the process. Three main process variables, i.e., the flow rate of steam injected to the second and third reactor and the fraction of oxygen injected to the secondary injection port of the second reactor, were determined in the optimization. The results show that the optimal operating conditions may lead to 2.6 % increase in the styrene yield and 1.5% increase in styrene selectivity, which significantly improves the profitability of the whole styrene production process.

Implementation of a geometrically based criterion for film uniformity control in a planetary SiC CVD reactor system

The development and application of a geometrically based uniformity criterion is presented for film uniformity control in a radial-flow epitaxy reactor system. In this multi-wafer reactor system, individual wafers rotate on a rotating susceptor in a planetary motion to reduce the effects of reactant depletion on deposition uniformity. The uniformity criterion developed for this system gives an unambiguous criterion for minimizing non-uniformity of any film property and gives physical insight into the reactor operating conditions that most influence uniformity. The uniformity criterion is used to demonstrate run-to-run uniformity control capabilities on a commercial system for SiC CVD.

Simulation of Flow Distribution in Radial Flow Reactors

Flow distribution in four possible configurations, CP-z, CP-π, CF-z, and CF-π, of a radial flow reactor is investigated using computational fluid dynamics (CFD). The CFD models are validated using published experimental data. It is found that one of the π-flow configurations always has the most uniform flow distribution. Results show that the ratio of the center pipe cross-sectional area to that of the annular channel has a significant effect on the flow distribution. For a ratio less than one, the CF-π configuration gives the most uniform flow, while the CP-π is preferred for a ratio larger than one. It was also shown that the uniformity of the flow distribution is enhanced by lowering the porosity of the center pipe and that of the bed. To ensure good distribution, partial blockage of the center pipe must be avoided.

Radial-Flow Reactor Packed with a Catalytic Cloth: Nitrate Reduction in Hydrogen-Saturated Water

A novel flow reactor packed with a fibrous catalytic cloth is proposed to carry out a gas−liquid reaction. Radial flow and separation of the transport of the gaseous reactant and the reaction are the main features of the new design. An activated carbon cloth supported 2 wt % Pd−0.6 wt % Cu bimetallic catalyst installed in the reactor was applied for the water-phase nitrate hydrogenation, showing selectivity up to 84% toward nitrogen at a nitrate conversion of up to 93%. The reactor performance has been evaluated using the diagnostic criteria associated with varying the hydrogen pressure, liquid flow rate, and catalyst loading in the reactor; it was described by a simplistic model, assuming one-dimensional, plug-flow, and steady-state operation. The significance of mass-transfer effects on the reactor performance has been analyzed. The results obtained indicate that the reactor investigated has a high potential for further development and scale-up.

A study on naphtha catalytic reforming reactor simulation and analysis

A naphtha catalytic reforming unit with four reactors in series is analyzed. A physical model is proposed to describe the catalytic reforming radial flow reactor. Kinetics and thermodynamics equations are selected to describe the naphtha catalytic reforming reactions characteristics based on idealizing the complex naphtha mixture by representing the paraffin, naphthene, and aromatic groups by single compounds. The simulation results based above models agree very well with actual operation unit data.

Activated carbon cloth-supported Pd–Cu catalyst: Application for continuous water denitrification

Pd–Cu catalysts supported on woven fibrous cloths have been tested for continuous nitrate hydrogenation in water. The results demonstrate that activated carbon cloth (ACC) is an adequate support for the Pd–Cu bimetallic catalysts giving better activity and selectivity than that of supports like glass fibers cloth (GFC) and GFCs coated with Al 2O 3 or SnO 2, which were also studied. A series of 2% Pd–Cu/ACC catalysts were prepared by selective deposition of Cu on Pd/ACC and examined at steady state in a continuous three-phase radial flow reactor. The activity and selectivity of the bimetallic catalysts depend on the Cu:Pd ratio and the metal loading. The beneficial effect of copper on nitrate hydrogenation activity with a Pd–Cu/ACC catalyst is probably related to the formation of an active Pd–Cu ensembles working as active sites for nitrate-to-nitrite reduction. The maximal nitrate conversion was achieved with 0.6 wt.% Cu–2 wt.% Pd/ACC catalyst showing a 92% selectivity towards gaseous products.

Modeling of Radial Flow Reactors of Oxidative Reheat Process for Production of Styrene Monomer

AbstractStyrene plays an important role in industrial production plants due to its increasing use in the production of various products. Thus, availability of a simulating program for styrene monomer reactors is of major importance in reducing the problems of a styrene unit. In oxidative reheat technology, styrene monomer is produced from ethylbenzene dehydrogenation in radial flow reactors in the presence of the generated heat from hydrogen oxidation reaction. In this article mass, energy and momentum equations on radial direction are developed for styrene monomer reactors. Required kinetic rates and parameters have been adopted from the literature [1,2]. Then, by means of experimental data from industrial reactors and sequential quadratic programming (SQP) methods, suitable kinetic parameters are obtained. Comparison of simulator prediction data with industrial ones show that the simulation has been achieved adequately.

Formulation of Reduced-Order Models for the Dynamic and Stability Analyses of Autothermal Radial Flow Reactors

Autothermal radial flow reactors typically consist of a reactor setup of multiple catalyst-beds with internal heat exchange. These reactors are widely used because of their high efficiency due to the internal heat exchange, and radial flow arrangements are preferred due to their low pressure drops. Although an efficient multi-functional reactor arrangement, this setup has shown to provide for an additional destabilizing mechanism via the heat feedback. Thus, additional stability considerations are necessary when operating autothermal or non-adiabatic reactors at high conversions. This work proposes the formulation of a simplified model to investigate the effect of the heat transfer feedback on the stability of autothermal radial flow reactors. The present work focuses on a lumping approach to reduce the order of a complex distributed parameter system. The model is complex enough so as to preserve the intricacies of this reactor arrangement, but still yield a tractable dynamic formulation. The industrial ammonia synthesis process has been chosen as a case study to illustrate the proposed methodology. The lumped model predictions are qualitatively compared against numerical simulations of a detailed mathematical model.