A hybrid fuel cell system integrated with methanol steam reformer and methanation reactor

In this paper, a hybrid fuel cell system integrated with methanol steam reformer and methanation reactor is demonstrated. Methanol steam reformer employed in this system is to produce hydrogen-rich reformate in connection with a methanation reactor to reduce the carbon monoxide content effectively, and the reformate gas is sent into a low-temperature polymer electrolyte fuel cell for direct electric power generation. The optimum conditions (temperature, water to methanol ratio, and space velocity) for methanol steam reforming (MSR) reaction and methanation (MET) reaction are verified by experiments. A comparison between pure hydrogen, reformate surrogate, and actual reformate is performed. The results show that the power density of this hybrid system achieves 245.2 mW/cm² while it achieves 268.8 mW/cm² when employing pure hydrogen as the fuel. An alternative novel method to solve the problem of hydrogen storage and transportation is provided and the in-situ hydrogen production and utilizing through low-temperature fuel cell system is realized, which is helpful to accelerate the commercialization process of the fuel cell.     

Microfibrous structured catalytic packings for miniature methanol fuel processor: Methanol steam reforming and CO preferential oxidation

The microfibrous structured catalytic packings for miniature fuel processor consisting of a methanol steam reformer and a subsequent CO cleanup train has been investigated experimentally. A highly void and tailorable sinter-locked microfibrous carrier consisting of 3.5 vol% 8 μm diameter Ni-fibers is used to entrap 35 vol% 150-250 μm catalyst particulates for both methanol steam reforming (MSR) and CO preferential oxidation (PROX). We demonstrate a microfibrous entrapped Pd-ZnO/Al₂O₃ catalyst packings for high efficiency hydrogen production by the MSR reaction. The use of microfibrous entrapment technology significantly enhances the catalyst utilization efficiency by a 4-fold improvement of the weight hourly space velocity (WHSV), compared to the single Pd-ZnO/Al₂O₃ particulates as keeping the methanol conversion at >98%. The microfibrous entrapped Pt-Co/Al₂O₃ catalyst packings can drive the CO from 2% down to <50 ppm at 150 °C with O₂/CO ratio of 1 using a gas hourly space velocity (GHSV) of 32,000 h⁻¹. Finally, a prototype fuel processor system integrating MSR reformer and CO PROX train is demonstrated as three reactors in series. Such test rig is capable of producing roughly 1700 standard cubic centimeter per minute (sccm) PEMFC-grade H₂ (equivalent to ∼163 W of electric power) in a longer-term test, in which the MSR reactor is operated at 300 °C using a methanol/water (1/1.1, mole) mixture WHSV of 9 h⁻¹ and CO PROX reactors at 150 °C using an O₂/CO molar ratio of 1.3, respectively. In the test of this prototype system, MSR reactor delivers >97% methanol conversion throughout the entire 1200-h test; the CO cleanup train placed in line after 800-h MSR illustrates the capability to decrease the CO concentration from ∼3.5% to ∼1% at PROX-1 and then to less than 20 ppm at PROX-2 until to the end of test.     

Experimental investigation on hydrogen production by methanol steam reforming in a novel multichannel micro packed bed reformer

A novel multichannel micro packed bed reactor with bifurcation inlet manifold and rectangular outlet manifold was developed to improve the methanol steam reforming performance in this study. The commercial CuO/ZnO/Al₂O₃ catalyst particles were directly packed in the reactor. The flow distribution uniformity in the reactor was optimized numerically. Experiments were conducted to study the influences of steam to carbon molar ratio (S/C), weight hourly space velocity (WHSV), reactor operating temperature (T) and catalyst particle size on the methanol conversion rate, H₂ production rate, CO concentration in the reformate, and CO₂ selectivity. The results show that increase of the S/C and T, as well as decrease of the WHSV and catalyst particle size, both enhance the methanol conversion. The CO concentration decreases as the S/C and WHSV increase as well as the T and catalyst particle size decrease. Moreover, T plays a more important role on the methanol steam reforming performance than WHSV and S/C. The impacts on CO concentration become insignificant when the S/C is higher than 1.3, WHSV is larger than 1.34 h⁻¹ and T is lower than 275 °C. A long term stability test of this reactor was also performed for 36 h and achieved high methanol conversion rate above 94.04% and low CO concentration less than 1.05% under specific operating conditions.     

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.     

A complete miniaturized microstructured methanol fuel processor/fuel cell system for low power applications

A complete miniaturized methanol fuel processor/fuel cell system was developed and put into operation as compact hydrogen supplier for low power application. The whole system consisting of a micro-structured evaporator, a micro-structured reformer and two stages of preferential oxidation of CO (PROX) reactor, micro-structured catalytic burner, and fuel cell was operated to evaluate the performance of the whole production line from methanol to electricity. The performance of micro methanol steam reformer and PROX reactor was systematically investigated. The effect of reaction temperature, steam to carbon ratio, and contact time on the methanol steam reformer performance is presented in terms of catalytic activity, selectivity, and reformate yield. The performance of PROX reactor fed with the reformate produced by the reformer reactor was evaluated by the variation of reaction temperature and oxygen to CO ratio. The results demonstrate that micro-structured device may be an attractive power source candidate for low power application.     

Performance analysis of fuel cell thermoelectric cogeneration system with methanol steam reformer

A MATLAB/Simulink model is constructed of a fuel cell thermoelectric cogeneration system fed by a methanol steam reformer. The major components within the simulation model include the fuel cell stack, the hydrogen and oxygen supply systems, the heat recovery system, and the methanol steam reformer. It is shown that the simulation results for the dynamic response of the fuel cell given a step change in the load are in good qualitative agreement with the experimental results. Moreover, the simulation results show that the proposed thermoelectric cogeneration system has a thermal efficiency of 35%, an electrical efficiency of 45.6%, and a combined heat and power efficiency of 80.6%. The numerical results for the system efficiency deviate by no more than 4.4% from the experimental results. Finally, it is shown both numerically and experimentally that the methanol conversion rate is greater than 99%.     

Study on a compact methanol reformer for a miniature fuel cell

A compact methanol reformer for hydrogen production has been successfully fabricated, which integrated one reforming chamber, one water gas shift reaction chamber, two preheating chambers and two combustion chambers. It can be started-up at room temperature by the combustion of liquid methanol in the combustion chamber within 7 min without any external heating. The cold start response of the methanol reformer has been investigated using different parameters including methanol and air supply rate, and the experiments revealed that the optimum methanol and air flow rate were 0.55 mL/min and 3 L/min respectively. The results indicated that this methanol reformer can provide a high concentration of hydrogen (more than 73%) and the system efficiency is always maintained above 74%. It is further demonstrated in more than 1600 h continuous performance that the reformer could be operated autothermally and exhibited good test stability.     

Modeling and analysis of miniaturized methanol reformer for fuel cell powered mobile applications

In this paper a miniaturized packed bed reactor is analyzed, in which autothermal reforming of methanol occurs to produce sufficient hydrogen for generating 100 W of power. Mass balance equations are developed for each species in the reactor and an energy balance is developed for modeling non-isothermal operation. The pressure drop is modeled via the Ergun equation. Simulations are conducted in MATLAB to determine the effect of process parameters (e.g. steam to methanol ratio, inlet pressure, inlet temperature) on the production of hydrogen. It is shown that the pressure drop is negligible. Simulation results are compared with experimental results from the literature and it shown that there is excellent agreement between the simulation results and experimental results. Process conditions that lead to the generation of sufficient hydrogen for generating 100 W of power are developed.     

A combined methanol autothermal steam reforming and PEM fuel cell pilot plant unit: Experimental and simulation studies

An integrated system for hydrogen production via autothermal steam reforming of methanol and consequent power generation in a polymer electrolyte membrane (PEM) fuel cell has been developed and operated at C.P.E.R.I. The pilot plant comprises an autothermal reforming reactor to produce hydrogen, a preferential oxidation reactor (PROX) to reduce CO concentration below 50 ppm and a PEM fuel cell for power generation.The present paper deals with the study of this system, both from an experimental and a theoretical point of view. The experimental work aims to: (a) examine the effect of the reforming temperature on methanol conversion and on the effluent stream concentration, (b) investigate the effect of reaction temperature and O₂/CO ratio on the performance of the PROX reactor, and (c) evaluate the operation of a 10-cell PEM fuel cell, using pure hydrogen and air at three temperature levels. The experimental data are subsequently utilized for the validation of one-dimensional pseudo-homogeneous models that have been developed for the two reactors and also for the identification of the voltage–current characteristic curve of the PEM fuel cell. The validated models are then used to investigate the behavior and explore the interactions, both static and dynamic, among the various process subsystems.     

Fractal channel design in a micro methanol steam reformer

The aim of the present article is to study the fractal channel pattern design and the gradient catalyst layer in relation to their effects on the performance of a micro methanol steam reformer. A three-dimensional simulation model is established for the purpose of predicting the effects of bio-channel design on the performance of a micro-reformer. The CO concentration in the production gases, which is necessary to avoid the poisoned catalyst layers of low temperature fuel cells, is also investigated. In addition, the distributions of velocity and gas concentrations are predicted, and the methanol conversion ratios are also evaluated. Due to further decreases of the CO in product gases, a gradient catalyst layer arrangement is proposed to delay the timing of hydrogen generation and thus avoid the presence of hydrogen in the catalyst layer too long. This catalyst arrangement can effectively decrease the possibility of a reverse water gas shift reaction to reduce CO generation. Results showed that the fractal channel design increases the conversion ratio, decrease CO as well as decrease the pressure drop in the channels. Relative to a parallel channel design, the CO and methanol conversion ratio of this fractal channel design pattern with uniform catalyst layer can be decreased and increased by 17% and 8%, respectively, based on a 0.3 cc/min flow rate, respectively. Meanwhile, the pressure drops in the parallel channel design and in the fractal channel design were found to be 254 Pa and 51 Pa, respectively. From an energy consumption point of view, a low pressure drop also implies low input pumping power. Furthermore, compared to the fractal design with a uniform catalyst layer, the gradient catalyst layer was demonstrated to effectively increase the conversion ratio by 8.5% and decrease CO by 11% when the inlet liquid flow rate was fixed at 1.0 cc/min.     

A performance study of methanol steam reforming in an A-type microchannel reactor

The methanol steam reforming (MSR) performance in a microchannel reactor is directly related to the flow pattern design of the microchannel reactor. Hydrogen production improvements can be achieved by optimal design of the flow pattern. In this study, an A-type microchannel reactor with a flow pattern design of one inlet and two outlets was applied to conduct the MSR for hydrogen production. The MSR performance of the A-type microchannel reactor was investigated through numerical analysis by establishing a three-dimensional simulation model and compared with that of the conventional Z-type microchannel reactor. Experiments were also conducted to test the MSR performance and validate the accuracy of the simulation model. The results showed that compared with the conventional Z-type microchannel reactor, the species distributions in the A-type microchannel reactor were more homogeneous. In addition, compared with the Z-type microchannel reactor, the A-type microchannel reactor was shown to effectively increase the methanol conversion rate by up to 8% and decrease the pressure drop by about 20%, regardless of a slightly higher CO mole fraction. It was also noted that with various quantities of microchannels and microchannel cross sections, the A-type microchannel reactor was still more competitive in terms of a higher methanol conversion rate and a lower pressure drop.     

Performance assessment and evaluation of catalytic membrane reactor for pure hydrogen production via steam reforming of methanol

The steam reforming of methanol was investigated in a catalytic Pd–Ag membrane reactor at different operating conditions on a commercial Cu/ZnO/Al₂O₃ catalyst. A comprehensive two-dimensional non-isothermal stationary mathematical model has been developed. The present model takes into account the main chemical reactions, heat and mass transfer phenomena in the membrane reactor with hydrogen permeation across the PdAg membrane in radial direction. Model validation revealed that the predicted results satisfy the experimental data reasonably well under the different operating conditions. Also the impact of different operating parameters including temperature, pressure, sweep ratio and steam ratio on the performance of reactor has been examined in terms of methanol conversion and hydrogen recovery. The modeling results have indicated the high performance of the membrane reactor which is related to continuous removal of hydrogen from retentate side through the membrane to shift the reaction equilibrium towards formation of hydrogen. The obtained results have confirmed that increasing the temperature improves the kinetic properties of the catalyst and increase in the membrane's H₂ permeance, which results in higher methanol conversion and hydrogen production. Also it is inferred that the hydrogen recovery is favored at higher temperature, pressure, sweep ratio and steam ratio. The model prediction revealed that at 573 K, 2 bar and sweep ratio of 1, the maximum hydrogen recovery improves from 64% to 100% with increasing the steam ratio from 1 to 4.     

Integrated methanol reforming and oxidation in wash-coated microreactors: A three-dimensional simulation

A microreactor consisting of two parallel channels is numerically simulated where methanol steam reforming takes place in one channel, and the required heat is supplied by methanol oxidation in the other channel. Effects of different parameters on methanol conversion, hydrogen yield and CO concentration are examined. Results from the parametric study are then used to propose conditions for high methanol conversion and hydrogen yield. A microreactor with enhanced output conditions is thus designed which is capable of producing a gas stream consisting of 74% hydrogen (dry). CO concentration in the generated synthesis gas stream is low enough to require only a PROX reactor for CO clean-up, eliminating the need for a bulky water–gas shift reactor. The produced hydrogen from an assembly of such microreactors can feed a low-power PEM fuel cell. A cluster of these microreactors would take a volume of about 91 cm³ to feed a typical 30-watt PEM fuel cell.     

Experiments on hydrogen production from methanol steam reforming in fluidized bed reactor

A novel approach for the hydrogen production which integrated methanol steam reforming and fluidized bed reactor (FBR) was proposed. The reaction was carried out over Cu/ZnO/Al₂O₃ catalysts. The critical fluidized velocities under different catalyst particle sizes and masses were obtained. The influences of the operating parameters, including that of H₂O-to-CH₃OH molar ratio, feed flow rate, reaction temperature, and catalyst mass on the performance of methanol steam reforming were investigated in FBR to obtain the optimum experimental conditions. More uniform temperature distribution, larger surface volume ratio and longer contacting time can be achieved in FBR than that in fixed bed reactor. The results indicate that the methanol conversion rate in FBR can be as high as 91.95% while the reaction temperatures is 330 °C, steam-to-carbon molar ratio is 1.3, and feed flow rate is 540 ml/h under the present experiments, which is much higher than that in the fixed bed.     

Comparison between 1D and 2D numerical models of a multi-tubular packed-bed reactor for methanol steam reforming

The hydrogen-rich gas produced in-situ by methanol steam reforming (MSR) reactions significantly affects the performance and endurance of the high-temperature polymer electrolyte membrane (HT-PEM) fuel cell stack. A numerical study of MSR reactions over a commercial CuO/ZnO/Al₂O₃ catalyst coupling with the heat and mass transfer phenomena in a co-current packed-bed reactor is conducted. The simulation results of a 1D and a 2D pseudo-homogeneous reactor model are compared, which indicates the importance of radial gradients in the catalyst bed. The effects of geometry and operating parameters on the steady-state performance of the reactor are investigated. The simulation results show that the increases in the inlet temperature of burner gas and the tube diameter significantly increase the non-uniformity of radial temperature distributions in reformer tubes. Hot spots are formed near the tube wall in the entrance region. The hot-spot temperature in the catalyst bed rises with the increase in the inlet temperature of burner gas. Moreover, the difference in simulation results between the 1D and 2D models is shown to be primarily influenced by the tube diameter. With a methanol conversion approaching 100% or a relatively small tube diameter, the simplified 1D model can be used instead of the 2D model to estimate the reactor performance.     

Experiments on hydrogen production from methanol steam reforming in the microchannel reactor

The entire experiments were conducted for microchannel methanol steam reforming, by which, the selection of catalyst, the operating parameters and the configuration of microchannels were discussed thoroughly. It was found that the higher the Cu concentration is, the more the corresponding active surface area of Cu will be, thereby improving the catalytic activity. The Cu-to-Zn ratio in Cu/ZnO/Al₂O₃ catalyst should be set at 1:1. The impacts of reaction temperature, feed flow rate, mixture temperature, and H₂O-to-CH₃OH molar ratio on the methanol conversion rate were also revealed and discussed. Characteristics of micro-reactors with various microchannels, including that 20 mm and 50 mm in length, as well as non-parallel microchannels, were investigated. It was found that the increase of microchannel length can improve the methanol conversion rate significantly. Besides, non-parallel microchannels help to maintain flow and temperature distribution uniformity, which can improve the performance of micro-reactor. In the present experiments, the presence of CO was under the condition that the methanol conversion rate was above 70%.     

RuRh based catalysts for hydrogen production via methanol steam reforming in conventional and membrane reactors

Results of hydrogen production study in methanol steam reforming (MSR) process with the use of Ru_0.5–Rh_0.5 catalysts supported on different carbon materials: synthetic graphite-like material Sibunit, carbon black Ketjenblack EC600DJ, detonation nanodiamonds (DND) and ZrO₂-based material with fluorite structure, doped with ceria, have been described. The samples have been tested in conventional flow reactor and membrane (MR) reactor, containing Pd-based membranes with different composition, thickness and surface architecture. It has been shown that the catalytic activity of the composites depends on the support nature. The RuRh/DND catalyst exhibits the highest activity, whereas RuRh/Ce_0.1Zr_0.9O_2–δ is the most selective. The use of PdAg (23%) foil with the surface modified by palladium black showed great advantages comparing to the smooth dense membrane. The use of the MR with the PdAg membrane improves the MSR reaction and provides almost 50% increase in the hydrogen yield. The hydrogen produced with the use of the MR is ultra pure.     

Methanol steam reforming in a microchannel reactor by Zn-, Ce- and Zr- modified mesoporous Cu/SBA-15 nanocatalyst

Hydrogen production by steam reforming of methanol was studied over several Cu/SAB-15-based nanocatalysts in a parallel-type microchannel reactor. The catalysts were prepared through impregnation method and XRD, BET, FT-IR, FE-SEM, TEM, H₂-TPR and TGA techniques were used to characterize surface and structural properties of the synthesized catalysts. The effects of reaction temperature, WHSV and S/C molar ratio on the methanol conversion and selectivities of the gaseous products were studied. Then, effects of the metallic promoters were investigated to improve performance of the catalysts. It was revealed that ZnO and CeO₂ promoters have positive effects on decreasing CO selectivity and ZrO₂ promotes methanol conversion. Furthermore, ZrO₂ and CeO₂ were declared to improve stability of the catalyst. Among the evaluated catalysts, Cu/ZnO/CeO₂/ZrO₂/SBA-15 can provide optimal methanol conversion with low CO concentration in the gaseous products. For this catalyst, the methanol conversion and hydrogen selectivity reached 95.2% and 94.6%, respectively.     

Development of highly efficient methanol steam reforming system for hydrogen production and supply for a low temperature proton exchange membrane fuel cell

Methanol steam reforming (MSR) has been regarded as a promising hydrogen supply method for proton exchange membrane fuel cell (PEMFC), while the efficiency for hydrogen production and integration method of MSR with PEMFC are two major challenges for commercial applications. Here, we present a highly efficient MSR system for hydrogen production and supply for low temperature PEMFC (LT-PEMFC). The MSR system has a highly compact microreactor, wherein MSR, methanol combustion, and CO selective methanation reactions occur. The CO selective methanation is used to reduce the content of CO concentration to remit the CO poison, then the reformate of MSR system is mixed with air and supply for the LT-PEMFC. Then, experimental tests are conducted to investigate the effects of operating parameters on hydrogen production. A staged supply strategy is proposed, it enables to startup the system within 11.2 min and with methanol consumption of 34.72 g. Results show that the methanol conversion can reach up to 93.0% and system's energy efficiency of 76.2%. After integration with a LT-PEMFC, a maximum 160 W electricity can be generated. The results obtained in this study demonstrated that the developed MSR system can be used to supply hydrogen for LT-PEMFC and able to power mobile device requiring hundreds of watts power consumption.