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%.     

A study of methanol steam reforming on distributed catalyst bed

Heterogeneous catalytic fixed bed usually suffers from severe limitations of mass and heat transfer. These disadvantages limit reformers to a low efficiency of catalyst utilization. Three catalyst activity distributions have been applied to force the reactor temperature profile to be near isothermal operation for maximization of methanol conversion. A plate-type reactor has been developed to investigate the influence of catalyst activity distribution on methanol steam reforming. Cold spot temperature gradients are observed in the temperature profile along the reactor axis. It has been experimentally verified that reducing cold spot temperature gradients contributes to the improvement of the catalytic hydrogen production. The lowest cold spot temperature gradient of 3 K is obtained on gradient catalyst distribution type A. This is attributed to good characteristics of local thermal effect. Low activity at the reactor inlet with gradual rise along with the reactor flow channel forms the optimal activity distribution. Hydrogen production rate of 161.3 L/h is obtained at the methanol conversion of 93.1% for the gradient distribution type A when the inlet temperature is 543 K.     

Qualitative investigation on effects of manifold shape on methanol steam reforming for hydrogen production

Fluid velocity distribution among microchannels plays important role on the reaction performances. In this work, the velocity distribution among microchannels with two different manifold structures is compared by a three-dimensional CFD model under two situations respectively, no reaction and methanol steam reforming occurs. Then the performances of methanol steam reforming in both plates are experimentally investigated, and the effect of manifold shape on the hydrogen production performances is qualitatively analyzed by the combination of simulation results of velocity distribution. It is found that the microchannel plate with right-angle manifold enables narrow velocity distributions under different entrance velocities and reaction temperatures, whether no reaction occurs or methanol steam reforming is progressing, which can be the critical element results in better conversion rate and selectivity of process than that of the microchannel plate with oblique-angle manifold. Optimizing the structural parameters to facilitate a relatively uniform velocity distribution to increase the hydrogen production performances may be a key factor to be considered.     

Synergetic integration of a methanol steam reforming cell with a high temperature polymer electrolyte fuel cell

In this work an integrated unit, combining a methanol steam-reforming cell (MSR-C) and a high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) was operated at the same temperature (453 K, 463 K and 473 K) allowing thermal integration and increasing the system efficiency of the combined system. A novel bipolar plate made of aluminium gold plated was built, featuring the fuel cell anode flow field in one side and the reformer flow field on the other. The combined unit (MSR-C/HT-PEMFC) was assembled using Celtec^® P2200N MEAs and commercial reforming catalyst CuO/ZnO/Al₂O₃ (BASF RP60). The water/methanol vaporisation originates oscillations in the vapour flowrate; reducing these oscillations increase the methanol conversion from 93% to 96%. The MSR-C/HT-PEMFC showed a remarkable high performance at 453 K. The integrated unit was operated during ca. 700 h at constant at 0.2 A cm^?2, fed alternately with hydrogen and reformate at 453 K and 463 K. Despite the high operating temperature, the HT-PEMFC showed a good stability, with an electric potential difference decreasing rate at 453 K of ca. 100 μV h^?1. Electrochemical impedance spectroscopy (EIS) analysis revealed an overall increase of the ohmic resistances and charge transfer resistances of the electrodes; this fact was assigned to phosphoric acid losses from the electrodes and membrane and catalyst particle size growth.     

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.     

Methanol steam reforming over highly efficient CuO–Al2O3 nanocatalysts synthesized by the solid-state mechanochemical method

CH₃OH steam reforming is an attractive way to produce hydrogen with high efficiency. In this study, CuO.xAl₂O₃ (x = 1, 2, 3, and 4) were fabricated based on the solid-state route, and the calcined samples were employed in methanol steam reforming at atmospheric pressure and in the temperature range of 200–450 °C. The results revealed that all samples have a high BET area (173–275 m² g⁻¹), and their crystallinity was reduced by increasing the alumina content in the catalyst formulation. The catalytic activity tests showed that the CH₃OH conversion and H₂ selectivity decreased by rising the Al₂O₃·CuO molar ratio. The methanol conversion enhanced from 13% to 85% by increasing the reaction temperature from 200 °C to 450 °C over the CuO·Al₂O₃ catalyst, due to the higher reducibility of this catalyst at lower temperatures compared to other prepared samples. The influence of calcination temperature (300–500 °C), GHSV (28,000–48000 ml h⁻¹. g⁻¹_cat), feed ratio (C:W = 1:1 to 1:9), and reduction temperature (250–450 °C) was also determined on the yield of the chosen sample. The results revealed that the maximum methanol conversion decreased from 90 to 79% by raising the calcination temperature from 300 to 500 °C due to the reduction of surface area and sintering of species at high calcination temperatures.     

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.     

Cu supported on ZnAl-LDHs precursor prepared by in-situ synthesis method on γ-Al2O3 as catalytic material with high catalytic activity for methanol steam reforming

A novel catalyst precursor ZnAl-LDHs/γ-Al₂O₃ was prepared by in-situ synthesis method, and the copper was supported on calcined hydrotalcite catalyst precursor by wet impregnation. The correlation between the structure and the catalytic activity for methanol steam reforming was studied by XRD, SEM, TPR, chemisorption N₂O, IR and N₂ adsorption techniques. The results showed that the ZnAl-LDHs was successfully synthesized by in-situ synthesis method on γ-Al₂O₃ and the copper mass fraction had a great effect on the interactions between support and copper species. Furthermore, the catalyst reducibility and copper surface area evidently influenced catalytic activity for methanol steam reforming. The 10% Cu/γ-Al@MMO exhibited the best catalytic activity, that was, the methanol conversion was 99.98% and the CO concentration was only 0.92% at 300 °C in hydrogen production by methanol steam reforming.     

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.     

Methanol steam reforming in microreactor with constructal tree-shaped network

The construcal tree-shaped network is introduced into the design of a methanol steam microreactor in the context of optimization of the flow configuration. A three-dimensional model for methanol steam reaction in this designed microreactor is developed and numerically analyzed. The methanol conversion, CO concentration in the product and the total pressure drop of the gases in the microreactor with constructal tree-shaped network are evaluated and compared with those in the serpentine reactor. It is found that the reaction of methanol steam reforming is enhanced in the constructal tree-shaped microreactor, since the tree-shaped reactor configuration, which acts an optimizer for the reactant distribution, provides a reaction space with larger surface-to-volume ratio and the reduction of reactant velocities in the branches. Compared with the serpentine microreactor, the constructal reactor possesses a higher methanol conversion rate accompanied with a higher CO concentration. The conversion rate of the constructal microreactor is more than 10% over that of serpentine reactor. More particularly, the reduction of flow distance makes the constructal microreactor still possess almost the same pressure drop as the corresponding serpentine reactor, despite that the bifurcations induce extra local pressure loss, and the reduction of channel size in branches also causes pressure losses.     

Simulation of an hydrogen production steam reforming industrial plant for energetic performance prediction

This paper presents the results of a theoretical investigation whose aim was the development of a simulation tool for performance prediction of a steam reforming hydrogen production plant, and particularly of its overall energetic efficiency. A 1500 Nm³/h hydrogen production plant was simulated. Field data coming from an industrial plant were used for model validation in both design and off design operating conditions. To evaluate the plant performances in terms of energetic efficiency, a particular attention was paid to the simulation of all plant auxiliaries consumptions. Nevertheless the large uncertainty in most of the field data values, the model was able to capture all the relevant phenomena taking place in all the plant components, from reformer reactor up to CO₂ sequestration unit, in the investigated plant capacity range (40–100%).