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.     

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.     

Numerical investigation of a multichannel reactor for syngas production by methanol steam reforming at various operating conditions

A novel multichannel reactor with a bifurcation inlet manifold, a rectangular outlet manifold, and sixteen parallel minichannels with commercial CuO/ZnO/Al₂O₃ catalyst for methanol steam reforming was numerically investigated in this paper. A three-dimensional numerical model was established to study the heat and mass transfer characteristics as well as the chemical reaction rates. The numerical model adopted the triple rate kinetic model of methanol steam reforming which can accurately calculate the consumption and generation of each species in the reactor. The effects of steam to carbon molar ratio, weight hourly space velocity, operating temperature and catalyst layer thickness on the methanol steam reforming performance were evaluated and discussed. The distributions of temperature, velocity, species concentration, and reaction rates in the reactor were obtained and analyzed to explain the mechanisms of different effects. It is suggested that the operating temperature of 548 K, steam to carbon ratio of 1.3, and weight hourly space velocity of 0.67 h⁻¹ are recommended operating conditions for methanol steam reforming by the novel multichannel reactor with catalyst fully packed in the parallel minichannels.     

Simultaneous production of two types of synthesis gas by steam and tri‐reforming of methane using an integrated thermally coupled reactor: mathematical modeling

In this work, tri‐reforming and steam reforming processes have been coupled thermally together in a reactor for production of two types of synthesis gases. A multitubular reactor with 184 two‐concentric‐tubes has been proposed for coupling reactions of tri‐reforming and steam reforming of methane. Tri‐reforming reactions occur in outer tube side of the two‐concentric‐tube reactor and generate the needed energy for inner tube side, where steam reforming process is taking place. The cocurrent mode is investigated, and the simulation results of steam reforming side of the reactor are compared with corresponding predictions for thermally coupled steam reformer and also conventional fixed‐bed steam reformer reactor operated at the same feed conditions. This reactor produces two types of syngas with different H₂/CO ratios. Results revealed that H₂/CO ratio at the output of steam and tri‐reforming sides reached to 1.1 and 9.2, respectively. In this configuration, steam reforming reaction is proceeded by excess generated heat from tri‐reforming reaction instead of huge fired‐furnace in conventional steam reformer. Elimination of a low performance fired‐furnace and replacing it with a high performance reactor causes a reduction in full consumption with production of a new type of synthesis gas. The reactor performance is analyzed on the basis of methane conversion and hydrogen yield in both sides and is investigated numerically for various inlet temperature and molar flow rate of tri‐reforming side. A mathematical heterogeneous model is used to simulate both sides of the reactor. The optimum operating parameters for tri‐reforming side in thermally coupled tri‐reformer and steam reformer reactor are methane feed rate and temperature equal to 9264.4 kmol h^?1 and 1100 K, respectively. By increasing the feed flow rate of tri‐reforming side from 28,120 to 140,600 kmol h^?1, methane conversion and H₂ yield at the output of steam reforming side enhanced about 63.4% and 55.2%, respectively. Also by increasing the inlet temperature of tri‐reforming side from 900 to 1300 K, CH₄ conversion and H₂ yield at the output of steam reforming side enhanced about 82.5% and 71.5%, respectively. The results showed that methane conversion at the output of steam and tri‐reforming sides reached to 26.5% and 94%, respectively with the feed temperature of 1100 K of tri‐reforming side. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Methanol steam reforming in a planar wash coated microreactor integrated with a micro-combustor

A numerical simulation of methanol steam reforming in a microreactor integrated with a methanol micro-combustor is presented. Typical Cu/ZnO/Al₂O₃ and Pt catalysts are considered for the steam reforming and combustor channels respectively. The channel widths are considered at 700 μm in the baseline case, and the reactor length is taken at 20 mm. Effects of Cu/ZnO catalyst thickness, gas hourly space velocities of both steam reforming and combustion channels, reactor geometry, separating substrate properties, as well as inlet composition of the steam reforming channel are investigated. Results indicate that increasing catalyst thickness will enhance hydrogen production by about 68% when the catalyst thickness is increased from 10 μm to 100 μm. Gas space velocity of the steam reforming channel shows an optimum value of 3000 h⁻¹ for hydrogen yield, and the optimum value for the space velocity of the combustor channel is calculated at 24,000 h⁻¹. Effects of inlet steam to carbon ratio on hydrogen yield, methanol conversion, and CO generation are also examined. In addition, effects of the separating substrate thickness and material are examined. Higher methanol conversion and hydrogen yield are obtained by choosing a thinner substrate, while no significant change is seen by changing the substrate material from steel to aluminum with considerably different thermal conductivities. The produced hydrogen from an assembly of such microreactor at optimal conditions will be sufficient to operate a low-power, portable fuel cell.     

Performance analysis of a membrane‐based reformer‐combustor reactor for hydrogen generation

Hydrogen is mostly produced in conventional steam methane reforming plants. In this work, we proposed a membrane‐based reformer‐combustor reactor (MRCR) for hydrogen generation in order to improve heat recovery and overall thermal efficiency. The proposed configuration will also reduce the complexity in existing steam methane reforming (SMR) plants. The proposed MRCR comprises combustion zone, hydrogen permeate zone, and SMR zone. A computational fluid dynamics model was developed using ANSYS‐Fluent software to simulate and analyze the performance of the proposed MRCR. Results show that high hydrogen yields were observed at high reformer pressures (RPs) and low gas hourly space velocities (GHSVs). Furthermore, by increasing the steam to methane ratio and addition of excess air in the combustion side, the hydrogen yield from the MRCR decreases. This is attributed to the reduction in the effective temperature of the hydrogen membrane. High RP, low GHSV, and low steam to methane ratio that increased the hydrogen yield also decreased carbon monoxide (CO) emissions. For an increased RP from 1 to 10 bar, the CO emission decreased by about 99%. The reduction in CO emission at high RP would be attributed to the effect of water gas shift reaction in the MRCR. Results of the extensive parametric study presented in this work can be used to determine the operating conditions based on tradeoffs between hydrogen yield (mole H₂/mole CH₄), hydrogen production rate (kg of H₂/h), allowable CO emissions, and exhaust gas temperature for other applications such as gas turbine.     

Operation of Rh/Ce0.75Zr0.25O2-δ-ƞ-Al2O3/FeCrAl wire mesh honeycomb catalytic modules in diesel steam and autothermal reforming

The Rh/Ce_0·75Zr_0·25O_2–δ-ƞ-Al₂O₃/FeCrAl structured catalytic blocks of length 10, 20, and 60 mm were prepared and tested in the reactions of steam and autothermal reforming of n-hexadecane. It was found in a series of experiments on hexadecane steam reforming with the catalyst heating solely through the reactor wall that the complete conversion of hexadecane at a furnace temperature below 750 °C was not achieved even at GHSV = 10,000 h⁻¹. Under these conditions, the formation of carbon on the catalyst surface was observed. At the reactor wall temperature of 800 °C, the complete conversion of hexadecane was achieved even in the 10 mm long catalytic block (GHSV = 60,000 h⁻¹), accompanied by the formation of various intermediate light hydrocarbons. To achieve complete conversion of these intermediate compounds (mainly 1-alkenes), it is necessary to carry out the steam reforming reaction at GHSV = 10,000 h⁻¹. At hexadecane autothermal reforming, heat is supplied to the reaction zone by exothermic oxidation reaction, which makes this process more efficient. In experiments with the use of additional external heat supply through the reactor wall, complete conversion of hexadecane occurred at GHSV = 120,000 h⁻¹. To convert all by-products (mainly 1-alkenes) and achieve a nearly thermodynamic equilibrium distribution of the main reaction products (H₂, CO, CO₂), the reaction should be carried out at GHSV = 20,000 h⁻¹. Without external heat supply, hexadecane conversion decreased, while the content of light hydrocarbons in the reaction products increased. An increase in the inlet amount of oxygen helps to compensate the heat losses in the reactor and to increase the efficiency of hexadecane autothermal reforming. The performed experiments allow better understanding of the processes which occur during the steam and autothermal reforming of diesel.     

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.     

CFD study of heat and mass transfer in ethanol steam reforming in a catalytic membrane reactor

This work shows the analysis of ethanol steam reforming process within a catalytic membrane reactor. A 2-D non-isothermal CFD model was developed using Comsol Multiphysics, based on previous experimentally validated isothermal model. A comprehensive heat and mass transfer study was carried out utilizing the model. Operating conditions such as liquid hourly space velocity (LHSV) (3.77–37.7 h^?1), temperature (673–823 K), reaction side pressure (4–10 bar) and permeate side sweep gas flow pattern were discussed. A temperature gradient along the reactor was observed from the model and a “cold spot” was seen at the reactor entrance area, which is unfavorable for the highly endothermic ethanol steam reforming process. By changing the sweep gas pattern to counter-current, the “cold spot” appears to be smaller with a reduced temperature drop. By studying the individual reaction rates, reverse methane steam reforming (methanation) was observed, caused by the low temperature in the “cold spot”. Optimal operating conditions were found to be under LHSV = 37.7 h^?1 and counter-current sweep gas conditions.     

Oxidative steam reforming of ethanol over a Pt/Al2O3 catalyst in a Pd-based membrane reactor

In this study, the ability of a Pd-Ag membrane reactor of producing ultrapure hydrogen via oxidative steam reforming of ethanol has been evaluated. A self supported Pd-Ag tube of wall thickness 60 μm has been filled with a commercial Pt-based catalyst and assembled into a membrane module in a finger-like configuration. In order to evaluate the hydrogen yield behavior under different operating conditions, experimental tests have been performed at temperatures of 400 and 450 °C and pressures of 150 and 200 kPa. The oxidative steam reforming of ethanol has been carried out by feeding the membrane reactor with a gas stream containing a dilute water-ethanol mixture and air. Different water/ethanol feed flow rates (5, 10, 15 g h⁻¹), several water/ethanol (4, 10, 13) and oxygen/ethanol (0.3, 0.5, 0.7) feed molar ratios have been tested. The results pointed out that the highest hydrogen yield (moles of permeated hydrogen per mole of ethanol fed) corresponding to almost 4.1 has been attained at 450 °C and 200 kPa of lumen pressure by using a water/ethanol/oxygen feed molar ratio of 10/1/0.5.The results of these tests have been compared with those reported for the ethanol steam reforming in a Pd-Ag membrane reactor filled with the same Pt-based catalyst. This comparison has shown a positive effect on the hydrogen yield of small oxygen addition in the feed stream.     

Hydrogen production for PEM fuel cell by gas phase reforming of glycerol as byproduct of bio-diesel. The use of a Pd-Ag membrane reactor at middle reaction temperature

Glycerol as a byproduct of biodiesel production represents a renewable energy source. In particular, glycerol can be used in the field of hydrogen production via gas phase reforming for proton exchange membrane fuel cell (PEMFC) applications. In this work, glycerol steam reforming (GSR) reaction was investigated using a dense palladium-silver membrane reactor (MR) in order to produce pure (or at least CO-free) hydrogen, using 0.5 wt% Ru/Al₂O₃ as reforming catalyst. The experiments are performed at 400 °C, water to glycerol molar feed ratio 6:1, reaction pressure ranging from 1 to 5 bar and weight hourly space velocity (WHSV) from 0.1 to 1.0 h⁻¹. Moreover, a comparative study is given between the Pd-Ag MR and a traditional reactor (TR) working at the same MR operating conditions. The effect of the WHSV and reaction pressure on the performances of both the reactors in terms of glycerol conversion and hydrogen yield is also analyzed. The MR exhibits higher conversion than the TR (∼60% as best value for the MR against ∼40% for the TR, at WHSV = 0.1 h⁻¹ and 5 bar), and high CO-free hydrogen recovery (around 60% at WHSV = 0.1 h⁻¹ and 5 bar). During reaction, carbon coke is formed limiting the performances of the reactors and inhibiting, in particular, the hydrogen permeation through the membrane with a consequent reduction of hydrogen recovery in the permeate side.     

Hydrogen production from ethanol over Co/ZnO catalyst in a multi-layered reformer

A Co/ZnO catalyst was prepared by coprecipitation method, and was applied for ethanol steam reforming. The effect of reaction conditions on the ethanol steam reforming performance was studied in the temperature ranges from 400 °C to 600 °C and the space velocity ranges from 10,000 h⁻¹ to 120,000 h⁻¹ in a fixed bed reactor. The Co/ZnO showed high activity with an ethanol conversion of 97% and a H₂ concentration of 73% at a gas hourly space velocity of 40,000 h⁻¹ and a moderately low temperature of 450 °C. EXAFS analysis for fresh and spent samples confirms that Co phase maintains during reaction. The catalyst was then loaded into a multi-layered reformer of which the design concept allows for integrating endothermic steam reforming, exothermic combustion and evaporation in a reactor. The performance of the compact reformer demonstrated that the hydrogen production rate satisfy a PEMFC stack power level of 540 W suitable for portable power supplies.     

Real-time sensing of methane steam reforming by YSZ oxygen sensor

In this study, a new and convenient technique for the in-situ analyisis of methane steam reforming in the chamber was proposed. The YSZ oxygen sensor was used as the sensing device, which provided the partial pressure of oxygen in the reactor. The oxygen sensors were set in the catalytic bed of 1 wt.% Ni/Al₂O₃ along the gas flow direction and the progress of catalytic reforming was monitored at each position. The methane conversion derived from the oxygen sensor agreed well with that from the gas chromatograph set at the outlet part of the catalyst layer. Along the gas flow direction in the reactor, the change in the gas composition was clearly observed; the methane conversion changed significantly depending on the reaction temperature and space velocity of reactant gas. Furthermore, the deterioration behavior of catalytic activity was successfully monitiored when a highly humidified methane with a steam to carbon ratio of 4.0 was supplied with a high space velocity of 6250 l kg⁻¹ h⁻¹.     

Hydrogen production from methane using vanadium-based catalytic membrane reactors

The application of vanadium-based membranes as the hydrogen separation membrane for a catalytic membrane reactor system was investigated for the direct production of hydrogen from methane. The methane conversion and hydrogen production rates of the catalytic membrane reactor system with Pd-coated 100 μm-thick vanadium-based membranes were comparable with the reactor using 50 μm-thick Pd–Ag alloy membrane at all temperatures examined. The methane conversion rates of the catalytic membrane reactor with the Pd-coated vanadium-based membranes were approximately 35% and 62% at 623 K and 773 K, respectively. The hydrogen production rates were around 660  μmol min⁻¹ at 623 K, and reached over 1710  μmol min⁻¹ at 773 K. The relationship between the methane conversion rates and hydrogen permeation fluxes of the catalytic membrane reactor confirmed that the removal of hydrogen from the reaction site enhances the methane decomposition reaction. Further, the vanadium based membrane exhibited good stability against Fe in a hydrogen containing atmosphere.     

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.     

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.     

Pure hydrogen production in a Pd-Ag multi-membranes module by methane steam reforming

An experimental test campaign has been carried out in order to investigate the performances in terms of pure hydrogen production of a multi-membrane module coupled with a methane reforming fixed bed reactor. The effect of operating parameters such as the temperature, the pressure, the water/methane feed flow rates and the feed molar ratio has been studied. The hydrogen produced into the traditional reformer has been recovered in the shell side of the membrane module by vacuum pumping. The membrane module consists of 19 Pd/Ag permeator tubes of wall thickness 150 μm, diameter 10 mm and length 250 mm: these dense permeators permitted to separate ultra-pure hydrogen.The experiments have been carried out with the reaction pressure of 100-490 kPa, the temperature of the reformer of 570-720 °C and the temperature of the Pd/Ag membranes module of 300-400 °C. A water/methane stream of molar ratio of 4/1 and 5/1 has been fed into the methane reformer at GSHV of 1547.6 and 1796.1 L_(STP) kg⁻¹ h⁻¹. Hydrogen yield value of about 3 has been measured at reaction pressure of 350 kPa, temperature reformer of 720 °C and methane feed flow rate of 6.445 × 10⁻⁴ mol s⁻¹.     

Modeling and analysis of a 5 kWe HT-PEMFC system for residential heat and power generation

We present a high-temperature proton exchange membrane fuel cell (HT-PEMFC) system model that accounts for fuel reforming, HT-PEMFC stack, and heat-recovery modules along with heat exchangers and balance of plant (BOP) components. In the model developed for analysis, the reaction kinetics for the fuel reforming processes are considered to accurately capture exhaust gas compositions and reactor temperatures under various operating conditions. The HT-PEMFC stack model is simplified from the three-dimensional HT-PEMFC CFD models developed in our previous studies. In addition, the parasitic power consumption and waste heat release from the various BOP components are calculated based on their heat-capacity curves. An experimental fuel reforming reactor for a 5.0 kW_e HT-PEMFC system was tested to experimentally validate the fuel reforming sub model. The model predictions were found to be in good agreement with the experimental data in terms of exhaust gas compositions and bed temperatures. Additionally, the simulation revealed the impacts of the burner air-fuel ratio (AFR) and the steam reforming reactor steam-carbon ratio on the system performance and efficiency. In particular, the combined heat and power efficiency of the system increased up to 78% when the burner AFR was properly adjusted. This study clearly illustrates that an HT-PEMFC system requires a high degree of thermal integration and optimization of the system configuration and operating conditions.     

A model of steam reforming of iso-octane: The effect of thermal boundary conditions on hydrogen production and reactor temperature

Steam reforming of iso-octane in a monolithic type reactor was simulated by a three-dimensional computational fluid dynamics model. The variations of hydrogen production and reactor temperature along the length of the reactor were calculated at isothermal, adiabatic and constant heat flux conditions. The reaction rate expressions based on steam reforming of methane in the Langmuir-Hinshelwood format were used to model steam reforming of iso-octane. The difference between the simulated results and experimental data on hydrogen produced was less than 18%. The results indicated that a large drop in temperature was in the first one-tenth of the reactor under adiabatic conditions with inlet temperatures of 600–900 °C. To achieve the same mole fraction of hydrogen (0.27, dry basis) at the exit of the reactor, the maximum temperature difference across the reactor was much smaller at certain heat flux conditions than that at adiabatic conditions. Further, rate of hydrogen production may be evenly distributed in the reactor under certain conditions of constant heat flux.