Fluidized Bed Membrane Reactor Research Articles

04/01507 Investigation of methane-steam reforming in fluidized bed membrane reactors: Abashar, M. E. E. et al. Chemical Engineering Research and Design, 2003, 81, (A2), 251–258

04/01507 Investigation of methane-steam reforming in fluidized bed membrane reactors: Abashar, M. E. E. et al. Chemical Engineering Research and Design, 2003, 81, (A2), 251–258

Novel Circulating Fluidized-Bed Membrane Reformer Using Carbon Dioxide Sequestration

A novel circulating fluidized-bed membrane reactor employing a reactor−regenerator type of configuration is proposed for hydrogen production by the steam reforming of natural gas. The reactor section of this configuration is investigated. CO2 sequestration using the CO2−lime reaction is utilized to assist/replace the hydrogen permselective membranes for “breaking” the thermodynamic equilibrium of the reversible reforming reactions. Cases with and without CaO and hydrogen permselective membranes are considered and compared. A slip velocity factor is incorporated to investigate the effect of CaO particle size/residence time on the conversion of lime and the overall performance of the reformer.

Coupling of steam and dry reforming of methane in catalytic fluidized bed membrane reactors

A rigorous mathematical model is used for the simulation of steam and CO 2 reforming in fluidized bed membrane reactors. A well-mixed catalyst pattern is implemented to couple the reactions. It has been shown that the combined effect of the membrane and reaction coupling provides exciting opportunities to overcome the equilibrium conversion limits and to achieve complete conversion of methane. The results indicate that the complete conversion of methane at low temperature is possible. Optimal conditions are observed to exist and an effective reactor length criterion is used to evaluate the reactor performance. The influence of some key parameters on the optimal conditions and the reactor such as temperature, pressure, steam to carbon ratio and membrane thickness have been investigated.

Coupled Steam and Oxidative Reforming for Hydrogen Production in a Novel Membrane Circulating Fluidized-Bed Reformer

A novel circulating fluidized-bed membrane reactor employing a reactor-regenerator type of configuration is proposed for hydrogen production by the steam reforming of natural gas. The removal of hydrogen through hydrogen-permeable membranes pushes the equilibrium toward higher production of hydrogen. In the present paper, modeling studies are carried out on the reactor section of this configuration. Cases with and without hydrogen-selective membranes (cocurrent and countercurrent) are considered and compared. The model results show the great advantages associated with the breaking of the thermodynamic limitations coupled to the hydrodynamic limitations associated with the previous generations of bubbling fluidized-bed reformers. It is shown that autothermal operation can be achieved through simultaneous oxidative reforming, giving high hydrogen yields and productivities with low net consumption of energy.

Application of the Generic Fluidized-Bed Reactor Model to the Fluidized-Bed Membrane Reactor Process for Steam Methane Reforming with Oxygen Input

A generic fluidized-bed reactor model (Abba et al. Chem. Eng. Sci. 2002, 57, 4797-4807; AIChE J. 2003, in press) is adapted to evaluate the performance of a fluidized-bed membrane reactor for steam reforming with oxygen input in a large-scale unit (16 m high and 2 m wide) described by Adris and Grace (Ind. Eng. Chem. Res. 1997, 36, 4549-4556). This allows flow regimes beyond bubbling to be modeled and facilitates the treatment of the impacts of changes in volumetric flow due to variations in molar flow, temperature, and hydrostatic pressure. Improvement in the reactor performance is shown when one considers these changes. Permselective membrane tubes are shown to substantially improve the performance of the reactor. The simulation results show that an ultrathin membrane coating could result in reversal in hydrogen diffusion with height, especially at elevated temperatures. The influences on the reactor performance of several other parameters such as the superficial gas velocity and steam-to-carbon ratio are also examined. Given the right combinations of key operating parameters such as the methane-to-oxygen ratio, feed temperature, and reactor temperature, the reactor can be operated autothermally.

Investigation of Methane–Steam Reforming in Fluidized Bed Membrane Reactors

The theme of this work is to investigate the performance of cocurrent and countercurrent fluidized bed membrane reactors for steam reforming of methane. A mathematical model is used to simulate the experimental data and to explore the potential application of high flux membranes to enhance the methane conversion in fluidized bed membrane reactors. It has been shown that complete conversion of methane is achieved by implementing high flux membranes. The influence of some key parameters on the reactors performance has been reported. It was found that in most cases of large bed lengths, the countercurrent configuration is superior to cocurrent configuration and more sensitive to the parameters changes. However, for short bed lengths at relatively low temperatures the cocurrent configuration is superior to countercurrent configuration.

Modeling of Autothermal Steam Methane Reforming in a Fluidized Bed Membrane Reactor

Fluidized bed reactors for steam methane reforming, with and without immersed membrane surfaces for withdrawal of hydrogen, are modeled with oxygen added in order to provide the endothermic heat required by the reforming reactions. Porous alumina, palladium and palladium-coated high-flux tubes are investigated as separation materials, the latter two being permselective. Hydrogen yield and permeate hydrogen molar flow are predicted to decrease with increasing oxygen flow, and to increase with temperature. When the steam-to-carbon ratio increases, permeate hydrogen yield decreases slightly, while the total hydrogen yield increases for all configurations. The flow of oxygen required to achieve autothermal conditions depends on such factors as the reactor temperature, steam-to-carbon ratio and preheating of the feed.

Butane partial oxidation in an externally fluidized bed-membrane reactor

An externally fluidized bed-membrane reactor (EFBMR) for partial oxidation reactions is described. This novel reactor concept combines the advantages of fixed bed and fluid bed reactors. Catalyst is loaded inside a porous membrane tube into which the hydrocarbon is fed. An oxygen rich gas fluidizes a powder on the shell side. Oxygen crosses the membrane wall and reacts. Butane partial oxidation to maleic anhydride was adopted as the model reaction and the kinetic parameters were derived based on a full scale commercial pilot plant. A detailed reaction engineering model of the EFBMR showed that hot spots are minimized and the reactor is inherently safer because the flammability potential is lower. Maleic yields are potentially 50% higher in an EFBMR compared to a conventional fixed bed reactor and the reactant concentration operating range is much wider.

Equilibrium modelling of catalytic steam reforming of methane in membrane reactors with oxygen addition

It has previously been demonstrated that permselective membranes can increase the yields of hydrogen, improve the product quality and minimize or even eliminate the adverse effect of system pressure in catalytic steam methane reforming. At the same time, oxygen addition can lead to autothermal operation by providing some or all of the required endothermic heat of the reforming reaction. Previous comparison of reactor model predictions with experimental results has demonstrated, at least for the fluidized bed membrane reactors (FBMRs) investigated so far, that the product distribution in the non-permeate stream approaches very closely to the shifted chemical equilibrium after allowance is made for the removal of hydrogen. In this paper, we adapt an equilibrium model devised for gasification to predict the influence of various process parameters. It is shown that it should be possible to operate autothermally and free of coke formation over a considerable range of temperature, pressure and steam-to-methane ratio.

Simulations of the effect of hydrodynamic conditions and properties of membranes on the catalytic performance of a fluidized‐bed membrane reactor for partial oxidation of methane

AbstractIn a fluidized‐bed membrane reactor the selectivity of separation can be controlled by influencing the hydrodynamics of the fluidized bed. In this reactor type, with the mass transport limitation between bubbles and the emulsion phase, even with the non‐selective membranes, high selectivity of separation can be achieved. This opens the possibility for applications of membrane reactors for reaction systems for which selective membranes do not exist, e.g. when Knudsen‐type membranes or form‐selective separation can not be applied. This paper is aimed at explaining the interaction between the selectivity of separation and the hydrodynamics of the fluidized bed by means of simulations that were performed for a fluidized‐bed membrane reactor for catalytic partial oxidation of methane.

Comparative study of the partial oxidation of methane to synthesis gas in fixed-bed and fluidized-bed membrane reactors.: Part II – Development of membranes and catalytic measurements

The catalytic partial oxidation of methane (CPOM) to synthesis gas was carried out in fixed-bed and fluidized-bed membrane reactors over a Ni/α–Al 2O 3 catalyst. For gas separation silicalite membranes inside an alumina and a porous stainless-steel matrix were synthesized and applied in the catalytic measurements. Moreover, a membrane obtained by deposition of palladium on the stainless-steel silicalite membrane was tested. The zeolite membranes were stable in the whole investigated temperature range (700< T<750°C). The Pd-membrane was not stable; palladium layer did not withstand temperatures above 650°C. In the catalytic measurements in the fixed-bed reactor and in the fluidized bed ( P CH 4 =66.6 kPa, P O 2 =33.3 kPa, m cat/ V=14 gs/ml) nearly thermodynamic equilibrium was achieved. However, neither in the fixed-bed reactor nor in the fluidized-bed membrane reactor an improvement in the syngas yield by means of the integrated product separation could be achieved. In the fixed-bed membrane the unselective separation of methane was detrimental for methane conversion. In the fluidized-bed membrane reactor the amount of permeated hydrogen was not sufficient to shift significantly the equilibrium towards higher syngas yield. However, in the fluidized-bed membrane reactor significant better selectivities of separation were achieved.

Comparative study of the catalytic partial oxidation of methane to synthesis gas in fixed-bed and fluidized-bed membrane reactors: Part I: A modeling approach

Catalytic partial oxidation of methane (CPOM) to synthesis gas over a Ni/ α-Al 2O 3 catalyst in fixed-bed and fluidized-bed reactors with and without membranes was investigated by means of mathematical modeling and simulations. The reactors were simulated by applying conditions which are of relevance for industrial applications ( p=5 and 30 bar, T=750–800°C). Since, at high pressures, the performance of a fixed-bed reactor for the CPOM reaction was strongly influenced by the intraparticle mass-transport limitation, the yield of syngas in fluidized-bed reactor was higher compared to the fixed-bed reactor. In both reactor types, the conversion of methane and yield of syngas could be significantly improved by means of integrated product separation on applying porous membranes. Due to the higher selectivity of separation the membrane fluidized bed was superior to the fixed bed. In turn, the higher selectivity of separation in fluidized-bed membrane reactors was attributed to the mass-transfer limitation between the bubble and emulsion phases that acted as a prefiltering membrane. However, the improvement of the selectivity of separation due to the interphase gas exchange decreased with increasing pressure.

Characteristics of Fluidized-Bed Membrane Reactors: Scale-up and Practical Issues

Fluidized-bed membrane reactors (FBMR) are examined from a scale-up and practical point of view. Mathematical modeling is utilized to explore potential configurations for commercial FBMR steam methane reforming (SMR) as well as to quantify the effects of key design parameters such as membrane capacity, distribution of membrane surface between the dense bed and dilute phase, permeate side pressure, and sweep gas flow. Key factors affecting the performance of a commercial FBMR are analyzed and qualitatively compared with corresponding factors in packed-bed membrane reactors. Issues which pose challenges to the commercial viability of this technology are identified. These include maintenance of bed mobility in the presence of gas withdrawal, providing sufficient membrane capacity, wear, and mechanical forces on vertical surfaces.

The fluidized-bed membrane reactor for steam methane reforming: model verification and parametric study

A new approach is presented for the modelling of a fluidized-bed membrane reactor (FBMR). The model considers the two-phase nature of the fluidized-bed reactor system and the parallel reactions taking place in stream methane reforming, as well as selective permeation through the walls of membrane tubes immersed in the bed. The model is based on the two-phase bubbling bed model with allowance for some gas flow in the dense phase. Plug flow is assumed for the combined sweep gas and permeating hydrogen flowing through the membrane tubes. Freeboard non-isothermal effects and reactions are also taken into account. The coupled differential equations for the fluidized bed and membrane tubes are solved numerically. The model is in very good agreement with experimental data, both with and without permeation, obtained in a pilot-scale reactor system. Parametric investigations demonstrate the effect of key operating variables and design parameters over a wide range. The model is also tested for its sensitivity to changes in hydrodynamic parameters. Increasing the permeation of hydrogen through the membrane tubes is of key importance in achieving high methane conversions and in minimizing adverse reactions in the freeboard region. Hydrodynamic and kinetic properties have limited influence for the conditions studied.

The fluidized bed membrane reactor system: a pilot scale experimental study

An experimental investigation has been performed to examine a novel reactor which combines advantages of fluidized beds as catalytic reactors, in particular catalyst bed uniformity, improved heat transfer and virtual elimination of diffusional limitations, with advantages offered by permselective membrane technology, in particular shifting the conventional thermodynamic equilibrium and the in situ separation and removal of a desirable reaction product. A pilot scale reforming plant was commissioned to study the new fluidized bed membrane reactor (FBMR) system for steam reforming of natural gas. The reactor has a hydrogen production capacity of 6 m 3/h (STP) and a main body diameter of 97 mm, designed to withstand temperatures up to 1023°C and pressures up to 1.5 MPa. Thin-walled palladium-based tubes are provided as hydrogen permselective membranes. The experiments validated the FBMR concept, showed the relative importance of different operating variables influencing the reactor performance and allowed the effectiveness of hydrogen permeation through palladium-based membranes in a fluidized bed environment to be evaluated.

A fluidized bed membrane reactor for the steam reforming of methane

AbstractIn the present investigation a realistic two‐phase model accounting for the change in the total number of moles accompanying the reaction is utilized to explore a novel reactor configuration suggested for the methane steam reforming process. The suggested design is basically a fluidized bed reactor equipped with a bundle of membrane tubes. These tubes remove the main product, hydrogen, from the reacting gas mixture and drive the reaction beyond its thermodynamic equilibrium. The proposed novel design is also equipped with sodium heat pipes which act as a thermal flux transformer to provide the large amount of heat needed by the endothermic reaction through a relatively small heat transfer surface, assuring better reactor compactness. Two options for fluid routing through the membrane tubes are proposed; each is suitable for a certain industrial application. The performance of this novel configuration is compared with that of an industrial fixed bed steam reformer and the comparison shows the potential advantages of the suggested configuration.