Local percolation of non-spherical particles in moving bed waste heat recovery unit for hydrogen production by methanol steam reforming

To study the local percolation of non-spherical particles in a moving bed waste heat recovery unit (MBWHRU) for hydrogen production, the discrete element method (DEM) was applied to simulate the discharge. A local method was applied to determine the location and local intensity of percolation. The percolation maps were presented. Moreover, the effects of structural parameters of MBWHRU, fine particle parameters, and friction parameters on local percolation were also considered. Percolation mainly occurs at the bottom, flow mechanism transition region, and near the vertical segment wall. Among them, percolation above the orifice is the most intense. The velocity gradient (or shear) is not the only condition under which percolation occurs. Percolation is closely related to changes in multiple parameters. The effects of fine particle parameters and friction parameters relative to structural parameters on percolation are significant. Percolation can be effectively avoided by increasing the mass percentage and particle size of fine particles, which is beneficial to hydrogen production. Especially, for the particle size ratio of fine particles to coarse particles greater than 0.5, percolation is no longer evident. The percolation near the vertical segment wall is particularly sensitive to particle-wall friction (>0.45). Reducing particle-particle friction and wall roughness is also beneficial to hydrogen production.     

Effect of the vacancy close to heat exchange wall on the heat transfer performance of the solid particles steam generator using waste heat in a methanol steam reforming hydrogen production system

With the massive consumption of fossil fuels and it resulted in significant carbon emissions, it is urgent to find an alternative clean energy source. Hydrogen has been regarded as one of the most promising energy candidates for the next generation. It is a great approach that methane steam reforming for hydrogen production by rational utilization of industrial waste heat, which significantly minimizes carbon emissions and develops methanol steam reforming technology. A solid particle steam generator based on the primary heat exchange method has been proposed, which can provide the heat and steam in the methanol steam reforming hydrogen production system. The quasi-two-dimensional packing heat transfer model of solid particles steam generator was set up.The effect of distance change between the vacancy and the cold wall and distance change between vacancies on heat transfer performance of the steam generator and hydrogen production capacity were studied. As the distance between the vacancy and the wall increases, the heat transfer performance of the steam generator gradually deteriorates, so the steam production of the steam generator decreases, and the system's hydrogen production capacity is reduced, the maximum of the heat flux and the minimum of the apparent thermal resistance are 34.67 kW/m² and 12.02 K/W, respectively. As the distance between vacancies increases, the heat transfer performance of the steam generator is gradually optimized slightly. To maintain the hydrogen production capacity, vacancies should be avoided to appear 2 layers of particles away from the heat exchange wall in the particles steam generator. From the results of the study, the farther the distance between vacancies, the better the steam production and hydrogen production capacity.     

Effects of particle sizes on methanol steam reforming for hydrogen production in a reactor heated by waste heat

This paper reports the effects of particle sizes on methanol steam reforming for hydrogen production in a reactor heated by waste heat. The unsteady model was set up, which has been applied to investigate the effects of particle sizes (1.77 mm–14.60 mm) on particle temperature, heat transfer quantity, overall coefficient of heat-transfer, etc. The heat transfer performance of waste heat recovery heat exchanger is improved when the particle size increases, which is conducive to increase hydrogen production. The particle temperature change rate, the specific enthalpy change rate, the moving velocity of the maximum heat release rate particle, the contribution rate of solid phases, the heat release rate and the overall coefficient of heat-transfer increase, but the effective time of heat transfer decreases. When the particle size increases from 1.77 mm to 14.60 mm, the solid phase average contribution rate increases from 89.43% to 94.03%, the overall coefficient of heat-transfer increases from 1.39 W m⁻² K⁻¹ to 13.41 W m⁻² K⁻¹, the heat release rate increases from 48.9% to 99.9% and the effective time of heat transfer reduces from 48 h to 6.7 h.     

Performance improvement of methanol steam reforming system with auxiliary heat recovery units

The thermal energy of a methanol steam reforming system is balanced with heat-up by a methanol burner, heat absorption by an evaporator, and an endothermic reforming reactor. As the thermal energy of a methanol steam reformer is delicately controlled, its thermal efficiency is significantly improved. In this study, three different system configurations are compared, namely, (1) a reference methanol steam reformer with an external evaporator, (2) a methanol steam reformer with an internal evaporator and type-1 auxiliary heat recovery unit (AHRU) with a heat source gas, and (3) a methanol steam reformer with an internal evaporator and type-2 AHRU with a heat source gas and reformed gas. These three configurations are analyzed, and the two heat recovery units are investigated. Results show that the internally evaporated methanol steam reformer efficiently converts the methanol to a hydrogen-rich mixture as exit gases are utilized to heat up the inlet methanol/water mixture.     

Effects of particle sizes on performances of the horizontally buried-pipe steam generator using waste heat in a bioethanol steam reforming hydrogen production system

The discrete element geometric model of the horizontally buried-pipe steam generator was set up. The effects of particle size (20 mm–80 mm) on performances of the horizontally buried-pipe steam generator using waste heat in a bioethanol steam reforming hydrogen production system was studied. When the particle size increases, the particle layer flatness decreases, the particle layer flow ununiformity increases. The volatility of the particle residence time distribution increases with the particle size increases, and the standard deviation of the particle residence time increases. When the particle size increases, the voidage of the particle system increases. So the particle thermal resistance in the steam generator increases with the particle size increases, the steam production of the generator decreases, and the system hydrogen production of decreases.     

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%.     

Progress on methanol reforming technologies for highly efficient hydrogen production and applications

With the continuous development of human society, the shortages of fossil resource and environmental pollution are increasingly prominent. Hydrogen is a clean and efficient alternative energy, among various hydrogen production technologies, methanol reforming has been regarded as a promising candidate to produce hydrogen for daily energy supply due to its low cost and safe transportation. In this review, we discuss the sources of methanol and the methods of methanol reforming for hydrogen production. Then, we focus on the catalysts for methanol reforming and their preparation methods. Particular attention is paid to the structural design and manufacturing process to make methanol reforming microreactors. We also summarize recent studies on the practical applications of methanol reforming technologies, as well as the capture and utilization of the generated carbon to reduce its emission. Finally, the prospect challenges of methanol reforming for highly efficient hydrogen production technologies and contribution to the “double carbon” goals and the challenges are discussed. In summary, this review will be conducive to the development of hydrogen-methanol economy for practical and industry applications.     

Trapezoidal cavity for high reforming temperature performance of auto-thermal methanol steam reforming micro-reactor for hydrogen production

To realize high reforming temperature performance of auto-thermal methanol steam reforming micro-reactor (ATMSRM) for hydrogen production (HP) and enhance its long-term HP performance, a trapezoidal cavity on methanol steam reforming (MSR) chamber plate is proposed. A numerical simulation model of the ATMSRM for HP is built. The influence of different geometric sizes of the trapezoidal cavity on reforming temperature performance of ATMSRM is investigated by the numerical simulation model. The reforming temperature performance and HP performance of ATMSRMs using the optimal trapezoidal cavity, the combustion reaction support (CRS) with optimal multiple micro-channels and the non-optimization are compared. The reforming temperature performance and HP performance of the size-enlarged ATMSRM with the optimal trapezoidal cavity are also studied. The results show that compared to other trapezoidal cavities, reforming temperature difference per 1 °C (△TA) of the ATMSRM using the F-type trapezoidal cavity with 50 mm length, 76 mm width, 0.4 mm front end depth and 0.2 mm back end depth is smaller, which is 0.01709 °C °C^?1 under 0.9 mL/min combustion methanol injection rate and 4 mL/h reforming methanol-water mixture injection rate. Compared with ATMSRMs using the CRS with optimal multiple micro-channels and the non-optimization, ATMSRM using F-type trapezoidal cavity has a better comprehensive HP performance. Compared with non-enlarged ATMSRM using F-type trapezoidal cavity, size-enlarged ATMSRM using F-type trapezoidal cavity has bigger △TA, larger reforming methanol conversion rate, higher hydrogen yield and more carbon monoxide selectivity. This research work offers a new method for enhancing reforming temperature performance of ATMSRM for HP.     

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.     

A methanol autothermal reforming system for the enhanced hydrogen production: Process simulation and thermodynamic optimization

Methanol autothermal reforming is a potential way to produce hydrogen that can be used for vehicle power batteries like PEMFC. Combining a reformer with a combustor to produce substantial hydrogen is promising, but the challenge of heat transfer efficiency between the reformer and combustor must be considered. Furthermore, the complexity of the system structure is not conducive to its large-scale operation level. In this paper, a novel methanol autothermal reforming hydrogen production system without catalytic combustion was built and developed, aiming to produce hydrogen-rich gas with low CO concentration. Process simulation and thermodynamic optimization on the target system were detailedly performed using Aspen Plus software and parameter sensitivity analysis methods. In addition, a methanol autothermal reforming hydrogen production system using catalytic combustion was taken as the reference system. The results indicated that the novel system could achieve a self-sustaining operation by the coupled methanol partial oxidation and steam reforming. And the product gas contained very low CO concentration (<10 ppm) due to the combined effects of water-gas shifting and CO preferential oxidation reactions. It was verified that under the maximal exergy efficiency condition, the exergy efficiency of the novel system is not significantly improved compared with the reference system, but the hydrogen yield is increased by about 27.65%, the thermal efficiency is increased by about 17.51%, and the exergy loss when generating unit molar H₂ is reduced by 20.53 kJ/mol; Under the condition of maximum hydrogen yield, the indicators of the novel system also perform better. Notably, the reformer is the main exergy loss source in the novel system, which provides a theoretical basis for further optimization of parameter configuration. This work will be beneficial to researchers who study the miniaturization design of the integrated system of methanol hydrogen production coupled vehicle power battery.     

Oxidative pyrolysis reforming of methanol in warm plasma for an on-board hydrogen production

To achieve on-board hydrogen production with high energy efficiency and low energy cost, the oxidative pyrolysis reforming (OPR) of methanol using air as an oxidant in a heat-insulated gliding arc plasma reactor is explored. Effects of dioxygen/methanol (O₂/C) ratio, steam/methanol (S/C) ratio and specific energy input (SEI) on the OPR are investigated. The reaction rate ratio (α) of pyrolysis reforming to oxidative reforming in the OPR is deduced. The OPR of methanol strongly depends on the O₂/C ratio, with which methanol conversion increases rapidly. In the OPR, methanol conversions occur mainly by the oxidative reforming (partial oxidation) at the O₂/C ratios below 0.20, but by the oxidative reforming and the promoted pyrolysis reforming at the O₂/C ratios above 0.20, which is confirmed by the enthalpy change for the overall reaction of OPR. Higher O₂/C ratio results in higher energy efficiency and lower energy cost, however, higher S/C ratio or larger SEI leads to lower energy efficiency and higher energy cost. Under conditions of O₂/C = 0.30, S/C = 0.5, SEI = 24 kJ/mol, energy efficiency of 74% and energy cost of 0.45 kWh/Nm³ with methanol conversion of 88% are achieved.     

Recent trends in the development of reactor systems for hydrogen production via methanol steam reforming

Hydrogen is currently receiving significant attention as an alternative energy resource, and among the various methods for producing hydrogen, methanol steam reforming (MSR) has attracted great attention because of its economy and practicality. Because the MSR reaction is inherently activated over catalytic materials, studies have focused on the development of noble metal-based catalysts and the improvement of existing catalysts with respect to performance and stability. However, less attention has been paid to the modification and development of innovative MSR reactors to improve their performance and efficiency. Therefore, in this review paper, we summarize the trends in the development of MSR reactor systems, including microreactors and membrane reactors, as well as the various structured catalyst materials appropriate for application in complex reactors. In addition, other engineering approaches to achieve highly efficient MSR reactors for the production of hydrogen are discussed.     

Production of dimethyl ether and hydrogen by methanol reforming for an HCCI engine system with waste heat recovery – Continuous control of fuel ignitability and utilization of exhaust gas heat

Homogeneous charge compression ignition (HCCI) is a promising technique to achieve high thermal efficiency and clean exhaust with internal combustion engines. However, the difficulty in ensuring optimal ignition timing control prevents its practical application. Previous research has shown that adjusting the proportion of dimethyl ether (DME) and hydrogen-containing methanol-reformed gas (MRG) can control the ignition timing in an HCCI combustion engine fueled with the two fuels. As both DME and MRG can be produced in endothermic methanol reforming reactions, onboard reforming utilizing the exhaust gas heat can recover the waste heat from the engine. A very high overall thermal efficiency can be achieved by combining the high engine efficiency with HCCI and the waste heat recovery. This research investigates the basic characteristics of methanol reforming in a reactor tube with different catalysts with the aim to produce fuels for the HCCI combustion system.     

Effects of particle sizes on performances of the multi-zone steam generator using waste heat in a bio-oil steam reforming hydrogen production system

Hydrogen production by bio-oil steam reforming is an advanced production technology. It is a good method of coupling waste heat utilization with bio-oil steam reforming to produce hydrogen, which increases the cleaning ability of the bio-oil steam reforming system. A multi-zone steam generator using waste heat has been proposed, which can produce the heat source and steam source of the hydrogen system. The DEM model of the multi-zone steam generator was set up. The model has been used to investigate the effects of particle sizes (40 mm–80 mm). With increasing particle size, the flow index and the flow uniformity gradually decrease, the vertical velocity gradient increases in the area on both side with the zone steam generator, and the vertical velocity fluctuation amplitude gradually increases. So, the hydrogen production decreases from the particle size increasing.     

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.     

Research on the hydrogen production performance of methanol reforming microchannels with multi-scale structures

Methanol microreactors are of much application value in mobile hydrogen production (HP) thanks to their tiny volume, flexibility and safety and all that. Microchannels, the core of a reactor, provide a site and heat supply for the reaction. In this paper, a microchannel with multi-scale structures, i.e. submicro structure, corrugated structure, fin structure and matrix structure, is designed. Then the influence mechanism of these structures on the hydrogen production of methanol reforming is studied. Specifically, the influences of microstructures like submicro and corrugated structures on the performance of the catalyst in the microchannel as well as the influence of fin structure and matrix structure on the heat and mass transfer performance of the channel are studied. From the experimental research on the methanol conversion rate and H₂ flow rate of the microchannel with multi-scale structures, the influence rule of different structures on the HP performance of the channel is summarized. The experimental results show that these multi-scale structures not only improve the loading of the catalyst of the microchannel, but also its heat and mass transfer, which increases the methanol conversion rate of the microchannel with multi-scale structures by 33% and its H₂ flow rate by 0.266 mol/h.     

Effects of solid particle aspect ratio on the performance of hydrogen production by electrolyzed water

Hydrogen energy has become one of the important directions of future energy development. The hydrogen produced by electrolyzed water is regarded as "green hydrogen", is clean and pollution-free, and is considered the ultimate direction of hydrogen production. If the waste heat of solid particles can be used as the energy required for the water electrolysis process, the cost of "green hydrogen" will be much lower than that of fossil fuel hydrogen production. In order to study the effect of particle structure size on hydrogen production capacity, the heat transfer model of the ellipsoidal particles packed bed with single-vacancy was constructed. Further, the temperature, the apparent thermal resistance, the average heat flux, and the vacancy affects area were studied. With the increase of the particle aspect ratio, the apparent thermal resistance decreases, the average heat flux increase, and hydrogen production increases. When the particle aspect ratio increases from 0.5 to 2.0, the average heat flux of the packed bed with single-vacancy increases from 23.13 kW/m² to 28.87 kW/m², and the apparent thermal resistance decreases from 23.33 K/W to 9.27 K/W. As the particle aspect ratio increases, the area affected by single-vacancy increases, the hindering effect of the vacancy on the heat flow increases.     

Effects of fin structure size on methane-steam reforming for hydrogen production in a reactor heated by waste heat

This paper mainly describes the influence of changes in fin structure on the hydrogen production capacity of the methane-steam reforming system. The model of the triangular-fin-tube steam generator was set up. The effects of the fin height (34 mm–46 mm), fin root width (3 mm–6 mm) and the fin-type were studied. As the height of the fin increases (34 mm–46 mm), the CPC temperature at the outlet of the steam generator decreases (the maximum temperature decreases 23.6 K and the average temperature decreases 18.9 K). At the same time, the heat recovery efficiency increased from 96.3% to 98.4%, and so the system hydrogen production increases. As the fin root width increases (3 mm–6 mm), the CPC temperature at the outlet of the steam generator decreases (the maximum temperature decreases 3.7 K and the average temperature decreases 1.2 K). Meanwhile, the heat recovery efficiency increases from 97.5% to 98.1%, and so the system hydrogen production increases. When the fin type is changed from a straight fin to a triangular-fin, the average temperature of the solid particle decreases 30.5 K, the heat recovery efficiency increases by 7.9%, and the system hydrogen production increases.     

Evaluation of silica membrane reactor performance for hydrogen production via methanol steam reforming: Modeling study

The aim of this work is to analyze the potential application of microporous silica membrane reactor carrying out methanol steam reforming reaction for hydrogen production. As a further study, a comparison with dense Pd–Ag membrane reactor and a traditional reactor, working at the same operating conditions of silica membrane reactor, is realized.