Interactive heat transfer characteristics of 5 kW class shell-and-tube methane steam reformer with intermediate temperature heat source

A 5 kW class shell and tube methane steam reformer (MSR) with intermediate temperature heat source was evaluated to find a correlation between the methane conversion and heat transfer performance. First, performance evaluation of MSR1 was conducted by varying experimental conditions such as reformer reactant flow rate, steam to carbon ratio (SCR), inlet temperature of reforming zone, and inlet temperature of heat source. Sensitivity study of overall heat transfer coefficient was also carried out to find the major parameter affecting the heat transfer. Next, the heat transfer performance and methane conversion rate of MSR1 and 2 were compared. Both reformers have the same gas hourly space velocity (GHSV) in the form of shell and tube heat exchangers, but are designed to compare the heat transfer characteristics of the reformer by designing with the different heat transfer areas. The results show that the main factors affecting the performance of the reformer are load, heat source inlet temperature, and heat transfer area.     

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).     

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.     

Hydrogen production using integrated methanol‐steam reforming reactor with various reformer designs for PEM fuel cells

A 95 mm × 40 mm × 15 mm compact reactor for hydrogen production from methanol‐steam reforming (MSR) is constructed by integrating a vaporizer, reformer, and combustor into a single unit. CuO/ZnO/Al₂O₃ is used as the catalyst for the MSR while the required heat is provided using Platinum (Pt) ‐catalytic methanol combustion. The reactor performance is measured using three reformer designs: patterned micro‐channel; inserted catalyst layer placed in a single plain channel; and catalyst coated directly on the bottom wall of single plain channel. Because of longer reactant residence time and more effective heat transfer, slightly higher methanol conversion can be obtained from the reformer with patterned microchannels. The experimental results show that there is no significant reactor performance difference in methanol conversion, hydrogen (H₂) production rate, and carbon monoxide (CO) composition among these three reformer designs. These results indicated that the flow and heat transfer may not play important roles in compact size reactors. The reformer design with inserted catalyst layer provides convenience in replacing the aged catalyst, which may be attractive in practical applications compared with the conventional packed bed and wall‐coated reformers. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis of phase change heat transfer with annulus 1 kW class methanol steam reforming reaction under high-pressure operation

A fuel cell air independent propulsion (AIP) system of underwater vehicle requires a hydrogen storage system. The methanol steam reforming system is a candidate of hydrogen storage which can produce hydrogen from chemical reaction. Different from reforming system for station fuel cell system, the methanol steam reformer (MSR) for underwater vehicle requires high-pressure operation.Since the longitudinal temperature uniformity is a core parameter of conversion efficiency of steam reforming system, this study is focused on computational analysis of phase change heat transfer through the annulus for methanol steam reforming reaction. The annulus MSR using phase change material was developed to improve the temperature uniformity. The simulation model is verified with safety and performance analysis code (SPACE). The performance parameters of MSR were flow arrangement, steam to carbon ratio (SCR), and gas hourly space velocity (GHSV). The results were analyzed in terms of the hydrogen yield, heat flux, liquid mass flow rate, and methanol conversion rate. The flow arrangement varied the methanol conversion rate to a minor extent of approximately 0.1% because wall temperature was maintained uniformly. In the case of SCR, the hydrogen yield at SCR 2.5 was 0.637 (dry basis), which was the highest yield rate. Also, if GHSV was increased, hydrogen yield decreased from 0.690 (dry basis) to 0.527 (dry basis). The heat transfer pattern was also analyzed and it was found that steam is interactively condensed along with the progress of the reforming reaction.     

Experimental evaluation of methanol steam reforming reactor heated by catalyst combustion for kW-class SOFC

The distributed power generation of methanol steam reforming reactor combined with solid oxide fuel cell (SOFC) has the characteristics of outstanding economic advantages. In this paper, a methanol steam reforming reactor was designed which integrates catalyst combustion, vaporization and reforming. By catalyst combustion, it can achieve stable operation to supply fuel for kW-class SOFC in real time without additional heating equipment. The optimal operating condition of the reforming reactor is 523–553 K, and the steam to carbon ratio (S/C) is 1.2. To study the reforming performance, methanol steam reforming (MSR), methanol decomposition (MD), water-gas shift (WGS) were considered. Operating temperature is the greatest factor affecting reforming performance. The higher the reaction temperature, the lower the H₂ and CO₂, the higher the CO and the methanol conversion rate. The methanol conversion rate is up to 95.03%. The higher the liquid space velocity (LHSV), the lower the methanol conversion rate, the lowest is 90.7%. The temperature changes of the reforming reactor caused by the load change of stack takes about 30 min to reach new balance. Local hotspots within the reforming reactor lead to an excessive local temperature to test a small amount of CH₄ in the reforming gas. The methanation reaction cannot be ignored at the operating temperature. The reforming gas contains 70–75% H₂, 3–8% CO, 18–22% CO₂ and 0.0004–0.3% CH₄. Trace amounts of C₂H₆ and C₂H₄ are also found in some experiments. The reforming reactor can stably supply the fuel for up to 1125 W SOFC.     

Conceptual design of an integrated thermally self-sustained methanol steam reformer – High-temperature PEM fuel cell stack manportable power generator

We have investigated the concept of an integrated system for small, manportable power units. The focus of this study is the direct thermal coupling of a methanol steam reformer (MSR) and a high-temperature proton exchange membrane fuel cell (HT PEMFC) stack. A recently developed low-temperature (LT) MSR catalyst (CuZnGaO_x) was synthesized and tested in a designed reforming reactor. The experimental data show that at 200 °C the complete conversion of methanol is achievable with a hydrogen yield of 45 cm³ min^?1 g_CAT^?1. An experimental setup for measuring the characteristics of the integrated system was designed and used to measure the characteristics of the two-cell HT PEMFC stack. The obtained kinetic parameters and the HT PEMFC stack characteristics were used in the modeling of the integrated system. The simulations confirmed that the integrated LT MSR/HT PEMFC stack system, which also includes a vaporizer, can achieve a thermally self-sustained working point. The base-case scenario, established on experimental data, predicts a power output of 8.5 W, a methanol conversion of 98.5%, and a gross electrical efficiency (based on the HHV) of the system equal to 21.7%. However, by implementing certain measures, the power output and the electrical efficiency can readily be raised to 11.1 W and 35.5%, respectively.     

Microwave-activated methanol steam reforming for hydrogen production

Methanol steam reforming (MSR) was carried out in a catalytic packed bed reactor under electrical and microwave heating using the two most common catalysts for this process-CuZnO/Al₂O₃ and PdZnO/Al₂O₃. Significant two-dimensional temperature gradients were found, especially in the latter case. Our results show that for the same average bed temperature, methanol conversion is higher under microwave heating (>10%). On the other hand, the product distribution is not affected by the heating mode. We demonstrate that even in cases where the maximum temperature along the entire height of the bed is significantly higher under electrical heating, conversion is either higher in the microwave case or approximately the same between the two heating modes. Finally, our experimental data indicate that a given methanol conversion can be achieved with lower net heat input to the reactor under microwave heating. This does not mean lower total energy consumption in the microwave process due to the limitations in the magnetron efficiency and the reflected power. However, it may be an implicit indication of higher temperature at metal sites than in bulk phase (microscale hot spot formation) due to the selective heating principle.     

Four different configurations of a 5 kW class shell-and-tube methane steam reformer with a low-temperature heat source

The methane steam reforming reaction is an extremely high endothermic reaction that needs a high temperature heat source. Various fuel cell hybrid systems have been developed to improve the thermal efficiency of the entire system. This paper presents a low temperature steam reformer for those hybrid systems to maximize the utilization of energy from a low temperature waste heat source. In this study, the steam reformer has a shell and tube configuration that is divided into the following zones: the inlet heat exchanging zone, the reforming zone and the exit heat exchanging zone. Four different configurations for methane steam reformers are developed to examine the effect of heat transfer on the methane conversion performance of the low temperature steam reformer. The experimental results show that the overall heat transfer area is a critical parameter in achieving a high methane conversion rate. When the heat transfer area increases about 30%, the results showed elevated dry mole fractions of hydrogen about 3% with about 30 °C rise of reformer outlet temperature.     

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.     

Thermodynamic performance analysis of the influence of multi-factor coupling on the methanol steam reforming reaction

This work presents the H₂ production from methanol steam reforming (MSR) process by thermodynamic equilibrium analysis using the Gibbs free energy minimization method and multi-factor coupling method. To determine desirable procedure parameters with maximum methanol conversion and H₂ content and minimum CO content, the impacts of the temperature: 100–400 °C, steam-to-methanol (S/C) molar ratio: 1.0–3.0, and pressure: 0.5–3.0 atm were investigated. The dominant factor under the action of multiple factors and the specific influence of each factor on the MSR process were verified, simultaneously. For proton exchange membrane fuel cell (PEMFC), to keep the CO content of the reformate within a desired range, and under the premise of complete methanol conversion, the MSR process can be operated at lower temperature, higher S/C ratio and atmospheric pressure. Combined with practice process, the optimum values of the temperature, S/C ratio and pressure to produce reformate were identified to be 200–300 °C,1.6–2.0 and 1.0 atm, respectively.     

A compact and high-efficiency electrified reactor for hydrogen production by methane steam reforming

An electrified reactor driven by renewable electricity, substituting conventionally fired reactors, will reduce CO₂ and provide a compact manner for hydrogen generation. Herein, we proposed a high-efficiency electrified reactor based on a high-temperature heat pipe (HTPR). The start-up of the HTPR powered by electricity was firstly evaluated, showing a start-up duration of 250 s and maintaining significant temperature uniformity of 96.7%. Then, the feasibility and performance of the HTPR were validated by experiments. The methane conversion and hydrogen mole fraction were 80.0% and 70.5% at a steam to carbon ratio of three, respectively. Finally, the reaction performance under different operating conditions was simulated. The methane conversion and the hydrogen mole fraction were attenuated with the increase in flow rate, and improving catalyst porosity is beneficial for the heat transfer between catalysts and gases. This study serves as a framework for designing an electrified reactor for endothermic reactions.     

H2 production in silica membrane reactor via methanol steam reforming: Modeling and HAZOP analysis

The main aim of this work is the presentation of both qualitative safety and quantitative operating analyses of silica membrane reactor (MR) for carrying out methanol steam reforming (MSR) reaction to produce hydrogen. To perform the safety analysis, HAZOP method is used. Before the HAZOP analysis, a comprehensive investigation of most important operating parameters effects on silica MR performance is required. Therefore, for a quantitative analysis, a 1-dimensional and isothermal model is developed for evaluating the reaction temperature, reaction pressure, feed molar ratio (steam/methanol) and feed flow rate effects on silica MR performance in terms of methanol conversion and hydrogen recovery. The model validation results show good agreement with experimental data from literature. As a consequence, simulation results indicate that the reaction pressure and feed molar ratio have dual effect on silica MR performance. In particular, it is found that methanol conversion is decreased by increasing the reaction pressure from 1.5 to 4.0 bar, whereas over 4.0 bar, it is improved. Moreover, the hydrogen recovery is decreased by increasing the feed molar ratio from 1 to 5, while over 5, it was approximately constant. After the evaluation of modeling results, the HAZOP analysis for silica MR is carried out during MSR reaction. The analysed operating parameters in the modeling study have been considered as key parameters in the HAZOP analysis. The safety assessment results are presented in tables as check list. By considering the HAZOP results, safety pretreatment works are recommended before or during the experimental tests of MSR reaction in silica MR. According to different parameters consequences, reaction temperature is the most critical parameter in MSR reaction for the silica MR studied in this work. In particular, to avoid the consequences of temperature deviation, it is recommended to use a PID temperature controller in the silica MR for MSR reaction.     

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.     

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.     

Ultracompact methane steam reforming reactor based on microwaves susceptible structured catalysts for distributed hydrogen production

Hydrogen is a potential green energy vector. Since the heating of the reforming processes commonly used for its production is obtained by burning hydrocarbons, it has a substantial CO₂ footprint. One of the most critical aspects in the methane steam reforming (MSR) reaction is the heat transfer to the catalytic volume, due to the high heat fluxes required to obtain high methane conversions. Consequently, the reactor has complex geometries, along with the heating medium being characterized by temperatures higher than 1000 °C; expensive construction materials and high reaction volumes are therefore needed, resulting in slow thermal transients. These aspects increase the costs (both operative and fixed) as well as cause a decrease in the whole process efficiency. The heat transfer limitations due to the endothermicity of methane steam reforming reaction could be effectively overcome by microwave (MW) heating. This heating technique, that depends only on the dielectric properties of the materials, can result in an efficient and faster method for transferring heat directly to the catalyst, thus generating the heat directly inside the catalytic volume. In this work, Ni-based catalysts, differing from each other by the Ni loading (7 and 15 wt% with respect to the washcoat) were prepared. The catalysts were characterized by means of several techniques and tested in the MW-assisted methane steam reforming reaction. Furthermore, the energy balance of the entire process was performed to calculate the energy efficiency, making a preliminary evaluation of its feasibility in distributed hydrogen production also possible. The results of the preliminary tests showed that the prepared structured catalysts are very susceptible to the MW radiation, and that in the presence of the MSR reaction, it is possible to make the system reach a temperature of 900 °C. In the same tests, the CH₄ conversion showed a good approach to the thermodynamic equilibrium values starting at temperatures of about 800 °C at a value of gas hourly space velocity (GHSV) of about 5000 h^?1. The energy efficiency of the lab-scale system, calculated as the ratio among the energy absorbed by the system and the energy supplied by the microwaves, was about 50%. Future studies will deal with the microwave reactor optimization, aiming at the increase of the energy efficiency of the system, as well as to obtain a higher CH₄ conversion at lower temperatures and increase the H₂ yield and selectivity.     

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.     

Modelling and experimental investigation of compact packed bed design of methanol steam reformer

A comprehensive mathematical model was developed to analyse methanol steam reforming in catalytic packed-bed tubular reactor. All the important aspects of reaction kinetics of main reactions and thermodynamic terms of heat and mass transfer were studied for commercially available CuO/ZnO/Al₂O₃ catalysts from Süd-Chemie. This numerical model was simulated using Engineering Equation Solver (EES). Through the set of organized simulation studies, the basic operational boundary conditions of operating temperature (573 K) with respect to complete conversion of methanol and optimum hydrogen generation, optimum S/C ratio (1.4) of methanol water mixture feed and operating capacity of one tubular reactor array were discovered. At temperatures near 573 K it was found that the reformate gas does not require any purification/filtration to be supplied to a HT-PEMFC as the CO concentration in reformate gas was low (below 30000 ppm). The simulation work for understanding the effect of different operating condition(s) on the reformer performance generated design of experiment for investigation of the efforts carried out to evaluate, build and demonstrate a 0.25 kWe equivalent methanol reformer for HT-PEM fuel cell system.The paper discusses few of the important aspects on the experimental investigation of effect of operating conditions on methanol steam reformer design with packed bed configuration for hydrogen production. The basic investigation included the analysis of effect of design and operating parameters on the methanol conversion and quality of reformate gas generation (amount of CO). The investigation also covers the analysis of heat and mass transfer along with chemical reaction and generation of species to achieve optimum process parameters and system efficiency. These investigations led to finalise, the operating parameters and basic design philosophy of the packed bed tubular methanol steam reformer for 5 kWe HT-PEMFC system application.     

A transient study of double-jacketed membrane reactor via methanol steam reforming

A non-isothermal unsteady-state model was established to simulate methanol steam reforming using a double-jacketed Pd membrane reactor. At steady state, a self-sustained membrane reactor was achieved by the oxidation of residual methanol and hydrogen from reformer for endothermic steam reforming. The molar fractions of species and reformer temperature were analyzed under co-current operation between oxidation and reformer sides. The start-up of reformer was simulated under two conditions: (1) The catalyst temperature was lower than the influent temperature and (2) The catalyst temperature was higher than influent temperature. Condition 1 yielded higher methanol conversion and reformer temperature than condition 2 at steady state. Moreover, the instability of species can be minimized on condition 1 during start-up. The fluctuation of membrane reactor at steady state was also studied. Two strategies were compared to analyze the reformer response when temporary extra hydrogen was required. The results showed that increasing inlet methanol outperformed increasing reformer temperature.     

A novel thermally autonomous methanol steam reforming microreactor using SiC honeycomb ceramic as catalyst support for hydrogen production

Methanol steam reforming (MSR) is an attractive option for in-situ hydrogen production and to supply for transportation and industrial applications. This paper presents a novel thermally autonomous MSR microreactor that uses silicon carbide (SiC) honeycomb ceramic as a catalyst support to enhance energy conversion efficiency and hydrogen production. The structural design and working principle of the MSR microreactor are described along with the development of a 3D numerical model to study the heat transfer and fluid flow characteristics. The simulation results indicate that the proposed microreactor has a significantly low drop in pressure and more uniform temperature distribution in the SiC ceramic support. Further, the microreactor was developed and an experimental setup was conducted to test its hydrogen production performance. The experimental results show that the developed microreactor can be operated as thermally autonomous to reach its target working temperature within 9 min. The maximum energy efficiency of the microreactor is 67.85% and a hydrogen production of 316.37 ml/min can be achieved at an inlet methanol flow rate of 360 μl/min. The obtained results demonstrate that SiC honeycomb ceramic with high thermal conductivity can serve as an effective catalyst support for the development of MSR microreactors for high volume and efficient hydrogen production.