Steam reforming of propane in a fluidized bed membrane reactor for hydrogen production

Steam reforming of propane was carried out in a fluidized bed membrane reactor to investigate a feedstock other than natural gas for production of pure hydrogen. Close to equilibrium conditions were achieved inside the reactor with fluidized catalyst due to the very fast steam reforming reactions. Use of hydrogen permselective Pd₇₇Ag₂₃ membrane panels to extract pure hydrogen shifted the reaction towards complete conversion of the hydrocarbons, including methane, the key intermediate product. Irreversible propane steam reforming is limited by the reversibility of the steam reforming of this methane. To assess the performance improvement due to pure hydrogen withdrawal, experiments were conducted with one and six membrane panels installed along the height of the reactor. The results indicate that a compact reformer can be achieved for pure hydrogen production for a light hydrocarbon feedstock like propane, at moderate operating temperatures of 475–550 °C, with increased hydrogen yield.     

Demonstration of a scaled-down autothermal membrane methane reformer for hydrogen generation

A novel concept for hydrogen generation by methane steam reforming in a thermally coupled catalytic fixed bed membrane reformer is experimentally demonstrated. The reactor, built from three concentric compartments, indirectly couples the endothermic methane steam reforming with the exothermic methane oxidation, while hydrogen is separated by a permselective Pd membrane. The study focuses on the determination of the key operation parameters and understanding their influence on the reactor performance. It has been shown that the reactor performance is mainly defined by the dimensionless ratio of the methane steam reforming feed flow rate to the hydrogen maximal membrane flow rate and by the ratio of the oxidation and steam reforming methane feed flow rates.     

Enhancement of pure hydrogen production through the use of a membrane reactor

Pure hydrogen production is of great interest as it is an energy carrier which can be used in PEM fuel cells for power production. Methane Steam Reforming (MSR) is commonly used for hydrogen production although the produced hydrogen is not free of other components. Membrane Reactors (MR) enable a pure hydrogen product stream and allows the reaction to take place at significantly lower temperatures (lower than 550 °C) than in conventional reactors (greater than 800 °C) with comparable methane conversion. This is achieved by hydrogen removal through a permselective Pd–Ag based membrane that cause a favorable shift in chemical equilibrium towards hydrogen production. In the present study, a two-dimensional, nonlinear, and pseudo-homogeneous mathematical model of a catalytic fixed-bed membrane reactor for methane steam reforming over a nickel-based foam supported catalyst is presented. Simulated results referring to the distribution of species, methane conversion, temperature and hydrogen flowrate along the reactor for different radial positions are obtained and analyzed. The performance of structured catalyst and catalyst supported on foam configurations under the same operating conditions is also studied. Experimental results for the membrane facilitate the identification of suitable operating conditions.     

Modeling and simulation of circulating fast fluidized bed reactors and circulating fast fluidized bed membrane reactors for production of hydrogen by oxidative reforming of methane

Modeling and simulation of circulating fast fluidized bed reactors (CFFBR) and circulating fast fluidized bed membrane reactors (CFFBMR) for hydrogen production by oxidative reforming of methane are presented in this paper. The results show that the CFFBR suffers from serious problems of hot spot temperatures. The combined effect of the oxygen distribution and the hydrogen membrane in the CFFBMR eliminates the hot spot temperatures and the danger of the reactor thermal runaway and mitigates nicely the temperature along the length of the CFFBMR. The investigation shows that the oxidative reforming of methane in the CFFBMR with oxygen distribution is cost-effective and inexpensive alternative route to the conventional steam reforming of methane processes due to the in situ heat integration of exothermic and endothermic reactions. The key role of the design parameters on the performance of the reactors are recognized through sensitivity analysis. The simulation results indicate that almost complete conversion of methane (99.99%), high exit hydrogen yield of 3.00 and low exit temperature of 569.8 °C are obtained by proper selection of design parameters of the CFFBMR with oxygen distribution. This achievement occurs at low feed temperature of 350.0 °C, which does not have destructive effects on the catalyst, reactor and membrane.     

H2 production by low pressure methane steam reforming in a Pd–Ag membrane reactor over a Ni-based catalyst: Experimental and modeling

Nowadays, there is a growing interest towards pure hydrogen production for proton exchange membrane fuel cell applications. Methane steam reforming reaction is one of the most important industrial chemical processes for hydrogen production. This reaction is usually carried out in fixed bed reactors at 30–40 bar and at temperatures above 850 °C. In this work, a dense Pd–Ag membrane reactor packed with a Ni-based catalyst was used to carry out the methane steam reforming reaction between 400 and 500 °C and at relatively low pressure (1.0–3.0 bar) with the aim of obtaining higher methane conversion and hydrogen yield than a fixed bed reactor, operated at the same conditions. Furthermore, the Pd–Ag membrane reactor is able to produce a pure, or at least, a CO and CO₂ free hydrogen stream. A 50% methane conversion was experimentally achieved in the membrane reactor at 450 °C and 3.0 bar whereas, at the same conditions, the fixed bed reactor reached a 6% methane conversion. Moreover, 70% of high-purity hydrogen on total hydrogen produced was collected with the sweep-gas in the permeate stream of the membrane reactor. From a modeling point of view, the mathematical model realized for the simulation of both the membrane and fixed bed reactors was satisfactorily validated with the experimental results obtained in this work.     

Steam reforming of simulated pre-reformed naphtha in a PdAu membrane reactor

Process intensification in a membrane reactor is an efficient and compact way to produce hydrogen. A methane-rich gas mixture that simulated the composition of pre-reformed naphtha (PRN; with a steam-to-carbon ratio of 2.7) was reformed at temperatures of 550 °C–625 °C and pressures up to 40 barg. The reactor contained commercial steam reforming catalyst and a 14.8 cm long, 2.6 μm thick Pd-1.8Au (wt. %) membrane on a porous alumina support. Methane conversions approaching 90% were obtained in the membrane reactor at a gas-hourly space velocity of 676 h^?1, compared to ≤30% conversion at the same conditions in conventional reactor mode (CM) without withdrawing hydrogen through the membrane. The results were compared to steam methane reforming (SMR) in the membrane reactor at similar conditions. The nitrogen leak through the membrane increased slowly during the testing, because of both pinhole formation and some leakage through the end seals.     

Solar enriched methane production by steam reforming process: Reactor design

A novel hybrid plant for a mixture of methane and hydrogen (enriched methane) production from a steam reforming reactor whose heat duty is supplied by a molten salt stream heated up by a concentrating solar power (CSP) plant developed by ENEA is here presented. By this way, a hydrogen stream, mixed with natural gas, is produced from solar energy by a consolidated production method as the steam reforming process and by a pre-commercial technology as molten salts parabolic mirrors solar plant. After the hydrogen production plant, the residual heat stored in molten salt stream is used to produce electricity and the plant is co-generative (hydrogen + electricity).The heat-exchanger-shaped reactor is dimensioned by a design tool developed in MatLab environment. A reactor 3.5 m long and with a diameter of 2″ is the most efficient in terms of methane conversion (14.8%) and catalyst efficiency (4.7 Nm³/h of hydrogen produced per kg_cat).     

Thermodynamic analysis of hydrogen production via sorption-enhanced steam methane reforming in a new class of variable volume batch-membrane reactor

Combined reaction–separation processes are a widely explored method to produce hydrogen from endothermic steam reforming of hydrocarbon feedstock at a reduced reaction temperature and with fewer unit operation steps, both of which are key requirements for energy efficient, distributed hydrogen production. This work introduces a new class of variable volume batch reactors for production of hydrogen from catalytic steam reforming of methane that operates in a cycle similar to that of an internal combustion engine. It incorporates a CO₂ adsorbent and a selectively permeable hydrogen membrane for in situ removal of the two major products of the reversible steam methane reforming reaction. Thermodynamic analysis is employed to define an envelope of ideal reactor performance and to explore the tradeoff between thermal efficiency and hydrogen yield density with respect to critical operating parameters, including sorbent mass, steam to methane ratio and fraction of product gas recycled. Particular attention is paid to contrasting the variable volume batch-membrane reactor approach to a conventional fixed bed reaction–separation approach. The results indicates that the proposed reactor is a viable option for low temperature distributed production of hydrogen from methane, the primary component of natural gas feedstock, motivating a detailed study of reaction/adsorption kinetics and heat/mass transfer effects.     

Methane membrane steam reforming: Heat duty assessment

Membrane reactors are an innovative technology with huge application potentialities for equilibrium limited endothermic reactions. Assembling a membrane selective to a reaction product avoids the equilibrium conditions to be achieved, supporting the reactions at lower operating temperatures. Taking as an example the natural gas steam reforming, a methane conversion around 98% can be reached imposing an operating temperature of 823 K, much lower than that of the traditional process. In the present paper, a stringent analysis of heat power requirement needed to carry out the natural gas steam reforming process by applying a membrane reactor is made. The simulations allows to understand how the main operating parameters (inlet temperature, inlet methane flow-rate, steam to carbon ratio, ratio between sweeping steam and inlet methane, operating reaction pressure) influence the total heat power required by the process, divided among power contributions for the reaction heat duty, reactant steam and permeation steam generation and preheating. Moreover, the specific thermal energy per mole of pure H₂ is computed and assessed. Optimizing the operating conditions set, a specific thermal energy per mole of pure hydrogen of 92.3 kWh kmol⁻¹ is obtained corresponding to a total thermal power of 687.4 kW required to convert, in a single membrane reactor, a methane flow-rate of 2 kmol h⁻¹ (GHSV = 9.590 h⁻¹) with a conversion around 98%.     

ANOVA analysis of an integrated membrane reactor for hydrogen production by methane steam reforming

Steam methane reforming is an endothermic reaction and it used to produce hydrogen and syngas. In this research, a factorial design is developed for an integrated Pd-based membrane reactor, producing hydrogen by methane steam reaction. In literature, no analogous works are present, because a simple sensitivity analysis is carried out without finding significant factors for the process. The reactor is modelled in MATLAB software using the Numaguchi kinetic. The reactor does not use conventional catalysts, but a Ni(10)/CeLaZr catalyst supported on SSiC ceramic foam. In ANOVA analysis, inlet temperature (550 K-815 K), methane flow rate in the feed (0.1 kmol/h-1 kmol/h), hydrogen permeability (1000 m³μmm⁻²hrbar^0.5–3600 m³μmm⁻²hrbar^0.5), the thickness of membrane (0.003 m-0.02 m) are the chosen factors. The analyzed responses are: hydrogen yield, carbon dioxide conversion and methane conversion. Results show that only inlet temperature, methane flow rate, their interaction and the thickens of membrane are significant. Also, the optimal operating conditions are obtained with inlet temperature, methane flow rate, hydrogen permeability and thickness of membrane equal to 550 K, 0.1 kmol/h, 3600 m³μmm⁻²hrbar^0.5 and 0.003 m.     

Dry reforming of methane has no future for hydrogen production: Comparison with steam reforming at high pressure in standard and membrane reactors

The methane dry-reforming and steam reforming reactions were studied as a function of pressure (1–20 atm) at 973 K in conventional packed-bed reactors and a membrane reactors. For the dry-reforming reaction in a conventional reactor the production yield of hydrogen rose and then decreased with increasing pressure as a result of the reverse water-gas shift reaction in which the hydrogen reacted with the reactant CO₂ to produce water. For the steam reforming reaction the production yield of hydrogen kept increasing with pressure because the forward water-gas shift reaction produced additional hydrogen by the reaction of CO with water. In the membrane reactors the methane conversion and the hydrogen production yields were higher for both the dry-reforming and steam reforming reactions, but for the dry reforming at high pressure half of the hydrogen was transformed into water. Thus, the dry-reforming reaction is not practical for producing hydrogen.     

Millisecond methane steam reforming for hydrogen production: A computational fluid dynamics study

The potential of methane steam reforming to produce hydrogen in thermally integrated micro-chemical systems at short contact times was theoretically explored. Methane steam reforming coupled with methane catalytic combustion in microchannel reactors for hydrogen production was studied numerically. A two-dimensional computational fluid dynamics model with detailed chemistry and transport was developed. To provide guidelines for optimal design, reactor behavior was studied, and the effect of design parameters such as catalyst loading, channel height, and flow arrangement was evaluated. To understand how steam reforming can happen at millisecond contact times, the relevant process time scales were analyzed, and a heat and mass transfer analysis was performed. The importance of energy management was also discussed in order to obtain a better understanding of the mechanism responsible for efficient heat exchange between highly exothermic and endothermic reactions. The results demonstrated the feasibility of the design of millisecond reforming systems, but only under certain conditions. To achieve this goal, process intensification through miniaturization and the improvement in catalyst performance is very important, but not sufficient; very careful design and implementation of the system is also necessary to enable high thermal integration. The channel height plays an important role in determining the efficiency of heat exchange. A proper balance of the flow rates of the combustible and reforming streams is an important design criterion. Reactor performance is significantly affected by flow arrangement, and co-current operation is recommended to achieve a good energy balance within the system. The catalyst loading must be carefully designed to avoid insufficient reactant conversion or hot spots. Finally, operating windows were identified, and engineering maps for designing devices with desired power were constructed.     

Thermal analysis of a micro tubular reactor for methanol steam reforming by optimizing the multilayer arrangement of catalyst bed for the catalytic combustion of methanolr

Packed bed tube reactors are commonly used for hydrogen production in proton exchange membrane fuel cells. However, the hydrogen production capacity of methanol steam reforming (MSR) is greatly limited by the poor heat transfer of packed catalyst bed. The hydrogen production capacity of catalyst bed can be effectively improved by optimizing the temperature distribution of reactor. In this study, four types of reactors including concentric circle methanol steam reforming reactor (MSRC), continuous catalytic combustion methanol steam reforming reactor (MSRR), hierarchical catalytic combustion methanol steam reforming reactor (MSRP) and segmented catalytic combustion reactor with fins (MSRF) are designed, modeled, compared and validated by experimental data. It was found that the maximum temperature difference of MSRC, MSRR, MSRP and MSRF reached 72.4 K, 58.6 K, 19.8 K and 11.3 K, respectively. In addition, the surface temperature inhomogeneity U_f and CO concentration of the MSRF decreased by 69.8% and 30.7%, compared with MSRC. At the same reactor volume, MSRF can achieve higher methanol conversion rate, and its effective energy absorption rate is 4.6%, 3.9% and 2.6% higher than that of MSRC, MSRR and MSRP, respectively. The MSRF could effectively avoid the influence of uneven temperature distribution on MSR compared with the other designs. In order to further improve the performance of MSRF, the influences of methanol vapor molar ratio, inlet temperature, flow rate, catalyst particle size and catalyst bed porosity on MSR were also discussed in the optimal reactor structure (MSRF).     

Modeling of fluidized bed membrane reactors for hydrogen production from steam methane reforming with Aspen Plus

Hydrogen production via steam methane reforming with in situ hydrogen separation in fluidized bed membrane reactors was simulated with Aspen Plus. The fluidized bed membrane reactor was divided into several successive steam methane sub-reformers and membrane sub-separators. The Gibbs minimum free energy sub-model in Aspen Plus was employed to simulate the steam methane reforming process in the sub-reformers. A FORTRAN sub-routine was integrated into Aspen Plus to simulate hydrogen permeation through membranes in the sub-separator based on Sieverts' law. Model predictions show satisfactory agreement with experimental data in the literature. The influences of reactor pressure, temperature, steam-to-carbon ratio, and permeate side hydrogen partial pressure on reactor performances were investigated with the model. Extracting hydrogen in situ is shown to shift the equilibrium of steam methane reactions forward, removing the thermodynamic bottleneck, and improving hydrogen yield while neutralizing, or even reversing, the adverse effect of pressure.     

Autothermal reforming of methane for producing high-purity hydrogen in a Pd/Ag membrane reactor

Autothermal reforming of methane includes steam reforming and partial oxidizing methane. Theoretically, the required endothermic heat of steam reforming of methane could be provided by adding oxygen to partially oxidize the methane. Therefore, combining the steam reforming of methane with partial oxidation may help in achieving a heat balance that can obtain better heat efficacy. Membrane reactors offer the possibility of overcoming the equilibrium conversion through selectively removing one of the products from the reaction zone. For instance, only can hydrogen products permeate through a palladium membrane, which shifts the equilibrium toward conversions that are higher than the thermodynamic equilibrium. In this study, autothermal reforming of methane was carried out in a traditional reactor and a Pd/Ag membrane reactor, which were packed with an appropriate amount of commercial Ni/MgO/Al₂O₃ catalyst. A power analyzer was employed to measure the power consumption and to check the autothermicity. The average dense Pd/Ag membrane thickness is 24.3 μm, which was coated on a porous stainless steel tube via the electroless palladium/silver plating procedure. The experimental operating conditions had temperatures that were between 350 °C and 470 °C, pressures that were between 3 atm and 7 atm, and O₂/CH₄ = 0–0.5. The effects of the operating conditions on methane conversion, permeance of hydrogen, H₂/CO, selectivities of CO_x, amount of power supply, and the carbon deposition of the catalyst after the reaction is thoroughly discussed in this paper. The experimental results indicate that an optimum methane conversion of 95%, with a hydrogen production rate of 0.093 mol/m². S, can be obtained from the autothermal reforming of methane at H₂O/CH₄ = 1.3 and O₂/CH₄ near 0.4, at which the reaction does not consume power, and the catalysts are not subject to any carbon deposition.     

Fast start-up of microchannel fuel processor integrated with an igniter for hydrogen combustion

A Pt–Zr catalyst coated FeCrAlY mesh is introduced into the combustion outlet conduit of a newly designed microchannel reactor (MCR) as an igniter of hydrogen combustion to decrease the start-up time. The catalyst is coated using a wash-coating method. After installing the Pt–Zr/FeCrAlY mesh, the reactor is heated to its running temperature within 1 min with hydrogen combustion. Two plate-type heat-exchangers are introduced at the combustion outlet and reforming outlet conduits of the microchannel reactor in order to recover the heat of the combustion gas and reformed gas, respectively. Using these heat-exchangers, methane steam reforming is carried out with hydrogen combustion and the reforming capacity and energy efficiency are enhanced by up to 3.4 and 1.7 times, respectively. A compact fuel processor and fuel-cell system using this reactor concept is expected to show considerable advancement.     

Transient numerical modeling and model predictive control of an industrial-scale steam methane reforming reactor

A steam methane reforming reactor is a key equipment in hydrogen production, and numerical analysis and process control can provide a critical insight into its reforming mechanisms and flexible operation in real engineering applications. The present paper firstly studies the transport phenomena in an industrial-scale steam methane reforming reactor by transient numerical simulations. Wall effect and local non thermal equilibrium is considered in the simulations. A temperature profile of the tube outer wall is given by user defined functions integrated into the ANSYS FLUENT software. Dynamic simulations show that the species distribution is closely related to the temperature distribution which makes the temperature of the reactor tube wall an important factor for the hydrogen production of the reformer and the thermal conductivity of the catalyst network is crucial in the heat transfer in the reactor. Besides, there exists a delay of the reformer's hydrogen production when the temperature profile of the tube wall changes. Among inlet temperature, inlet mass flow rate and inlet steam-to-carbon (S/C) ratio, the mass flow rate is the most influencing factor for the hydrogen production. The dynamic matrix control (DMC) scheme is subsequently designed to manipulate the mole fraction of hydrogen of the outlet to the target value by setting the temperature profile trajectory of the reforming tube with time. The proportional-integral control strategy is also studied for comparison. The closed-loop simulation results show that the proposed DMC control strategy can reduce the overshoot and have a small change of the input variable. In addition, the disturbances of feed disturbance can also be well rejected to assure the tracking performance, indicating the superiority of the DMC controller. All the results give insight to the theoretical analysis and controller design of a steam methane reformer and demonstrate the potential of the CFD modeling in study the transport mechanism and the idea of combining CFD modeling with controller design for the real application.     

Design of an annular microchannel reactor (AMR) for hydrogen and/or syngas production via methane steam reforming

A bench-scale annular microchannel reactor (AMR) prototype with microchannel width of 0.3 mm and total catalyst length of 9.53 × 10⁻² m active for the endothermic steam reforming of methane is presented. Experimental results at a steam to methane feed molar ratio of 3.3:1, reactor temperature of 1023 K, and pressure of 11 bar confirm catalyst power densities upwards of 1380 W per cm³ of catalyst at hydrogen yields >98% of thermodynamic equilibrium. A two-dimensional steady-state computational fluid dynamic model of the AMR prototype was validated using experimental data and subsequently employed to identify suitable operating conditions for an envisioned mass-production AMR design with 0.3 mm annular channel width and a single catalyst length of 254 mm. Thermal efficiencies, defined based upon methane and product hydrogen higher heating values (HHVs), of 72.7–57.7% were obtained from simulations for methane capacities of 0.5–2S LPM (space velocities of 195,000–782,000 h⁻¹) at hydrogen yields corresponding to 99%–75% of equilibrium values. Under these conditions, analysis of local composition, temperature and pressure indicated that catalyst deactivation via coke formation or Nickel oxidation is not thermodynamically favorable. Lastly, initial analysis of an envisioned 10 kW autothermal reformer combining 19 parallel AMRs within a single methane-air combustion chamber, based upon existing manufacturing capabilities within Power & Energy, Inc., is presented.     

CFD simulation of methane steam reforming in a membrane reactor: Performance characteristics over range of operating window

Methane steam reforming is the most widely used pathway for hydrogen production. In this context, the use of a fixed bed catalytic reactor with a hydrogen-selective membrane is one of the most promising technologies to produce high purity hydrogen gas. In this work, the membrane reactor three-dimensional computational fluid dynamic (CFD) model was developed to investigate the performance. In this model, methane steam reforming global kinetic model has been coupled with the CFD model using User-Defined Function (UDF). Whereas, hydrogen permeation across the membrane is implemented by introducing source and sink formulation. The CFD simulation results were compared to the experimental data, where the developed model successfully captured the experimentally observed trends. We studied the influence of the various operating parameters, as temperature, steam to carbon ratio, sweep gas flow configuration and space velocity on the overall performance. The main observation and attained optimal operation windows from the study was discussed to provide insight into the factors affecting the overall performance.     

Experimental validation of a pilot membrane reactor for hydrogen production by solar steam reforming of methane at maximum 550 °C using molten salts as heat transfer fluid

An innovative steam reformer for hydrogen production at temperatures lower than 550 °C has been developed in the EU project CoMETHy (Compact Multifuel-Energy To Hydrogen converter). The steam reforming process has been specifically tailored and re-designed to be combined with Concentrating Solar plants using “solar salts”: a low-temperature steam reforming reactor was developed, operating at temperatures up to 550 °C, much lower than the traditional process (usually > 850 °C). This result was obtained after extensive research, going from the development of basic components (catalysts and membranes) to their integration in an innovative membrane reformer heated with molten salts, where both hydrogen production and purification occur in a single stage. The reduction of process temperatures is achieved by applying advanced catalyst systems and hydrogen selective Pd-based membranes. Process heat is supplied by using a low-cost and environmentally friendly binary NaNO₃/KNO₃ liquid mixture (60/40 w/w) as heat transfer fluid; such mixture is commonly used for the same purpose in the concentrating solar industry, so that the process can easily be coupled with concentrating solar power (CSP) plants for the supply of renewable process heat. This paper deals with the successful operation and validation of a pilot scale reactor with a nominal capacity of 2 Nm³/h of pure hydrogen from methane. The plant was operated with molten salt circulation for about 700 h, while continuous operation of the reactor was achieved for about 150 h with several switches of operating conditions such as molten salts inlet temperature, sweep steam flow rate and steam-to-carbon feed ratio. The results obtained show that the membrane reformer allows to achieve twice as high a conversion compared to a conventional reformer operating at thermodynamic equilibrium under the same conditions considered in this paper. A highly pure hydrogen permeate stream was obtained (>99.8%), while the outlet retentate stream had low CO concentration (<2%). No macroscopic signs of reactor performance loss were observed over the experimental operation period.