A new two-stage design of feedback controllers for a hydrogen gas reformer

In this paper we have first reviewed operations of a hydrogen gas reformer and provided its linearized mathematical model. Then, we have simplified an existing algorithm for a two-stage design of feedback controllers for linear continuous-time time-invariant systems. The proposed design significantly reduces the computational requirements and provides flexibility of designing different type of controllers for different dynamic parts of the system. Since the hydrogen gas reformer (also known as a fuel processing system) possesses slow and fast modes (state variables), the newly proposed design is further simplified and specialized for this class of systems. The obtained algorithm is efficiently applied with very high accuracy to the hydrogen gas reformer. As a matter of fact, the eigenvalue placement problem is solved for the reformer dynamics for both slow and fast modes. The design is so flexible that combined hybrid controllers (optimal, robust, set-point, eigenvalue assignment controllers or any other linear controller) can be designed independently for particular subsystems of the hydrogen gas reformer. The hybrid linear feedback controller design for the hydrogen gas reformer that optimizes its slow subsystem and assigns the desired eigenvalues to its fast subsystem is also presented in the paper.     

Fuel processing for PEM fuel cells: transport and kinetic issues of system design

In light of the distribution and storage issues associated with hydrogen, efficient on-board fuel processing will be a significant factor in the implementation of PEM fuel cells for automotive applications. Here, we apply basic chemical engineering principles to gain insight into the factors that limit performance in each component of a fuel processor. A system consisting of a plate reactor steam reformer, water–gas shift unit, and preferential oxidation reactor is used as a case study. It is found that for a steam reformer based on catalyst-coated foils, mass transfer from the bulk gas to the catalyst surface is the limiting process. The water–gas shift reactor is expected to be the largest component of the fuel processor and is limited by intrinsic catalyst activity, while a successful preferential oxidation unit depends on strict temperature control in order to minimize parasitic hydrogen oxidation. This stepwise approach of sequentially eliminating rate-limiting processes can be used to identify possible means of performance enhancement in a broad range of applications.     

Hydrogen from coal-derived methanol via autothermal reforming processes

This paper reports on an investigation of hydrogen production via reformation of coal-based methanol. Through chemical analysis, coal-based methanol has shown to have higher amounts of trace hydrocarbons than chemical grade methanol derived from natural gas. While these trace hydrocarbons are typically insignificant for some energy conversion devices, fuel cell applications require ultra pure hydrogen. An autothermal reformer was investigated to find the optimal hydrogen production method with the existence of such trace impurities. Based on previous experimental results, steam reforming of coal-based methanol has shown significant catalyst degradation caused by the trace impurities. Autothermal reformation processes using coal-derived methanol avoids degradation with the trace impurities due to a higher operating temperature generated by the oxidation step. Autothermal reformation can also avoid some of the energy penalties of steam reformation but generally has a lower output concentration of hydrogen due to the diluent nature of using air as the oxidizer. This investigation shows that hydrogen production from coal-derived methanol via autothermal reformation is feasible when considering fuel cell applications.     

Micro methanol reformer combined with a catalytic combustor for a PEM fuel cell

This paper presents the development of a micro methanol reformer for portable fuel cell applications. The micro reformer consists of a methanol steam reforming reactor, catalytic combustor, and heat exchanger in-between. Cu/ZnO was selected as a catalyst for a methanol steam reforming and Pt for a catalytic combustion of hydrogen with air. Porous ceramic material was used as a catalyst support due to the large surface area and thermal stability. Photosensitive glass wafer was selected as a structural material because of its thermal and chemical stabilities. Performance of the reformer was measured at various test conditions and the results showed a good agreement with the three-dimensional analysis of the reacting flow. Considering the energy balance of the reformer/combustor model, the off-gas of fuel cell can be recycled as a feed of the combustor. The catalytic combustor generated the sufficient amount of heat to sustain the steam reforming of methanol. The conversion of methanol was 95.7% and the hydrogen flow of 53.7 ml/min was produced including 1.24% carbon monoxide. The generated hydrogen was the sufficient amount to operate 4.5 W polymer electrolyte membrane fuel cells.     

A safe and clean way to produce H2O2 from H2 and O2 within the explosion limit range

The direct synthesis of hydrogen peroxide (DSH) from hydrogen and oxygen is an attractive production route due to its green nature. However, it faces multiple technical challenges, the biggest being the explosion risk of the flammable gas mixture. Herein we have used microreactors to perform the reaction in an inherently safer way which allows the hydrogen concentration to fall within the explosion limit range. For the first time, we have studied the flame propagation phenomena inside a microreactor to determine the optimum channel dimension for DSH. A mechanism of “fast synthesis and slow destruction” has been proposed via investigation on the influence of channel length and liquid flow rate. Besides, a variety of reaction parameters including gas flow rate, oxygen: hydrogen ratio, catalyst composition and gas pressure have been studied carefully. The successful employment of a microreactor in this case has indicated the potential of using microreactors to inhibit the explosion risks of hazardous processes.     

A multi-membrane reformer for the direct production of hydrogen via a steam-reforming reaction of methane

We designed and prepared a multi-membrane reformer (MMR) for the direct production of hydrogen via a steam-reforming (SR) reaction of methane. The MMR consisted of two single modules containing coin-shaped nickel metal catalysts and Pd-based membrane. The SR reaction was performed in the MMR for relatively high-pressure operation ranges (P₂ = ∼21 bar) without sweep gas and the methane conversion and hydrogen production rate were observed under various experimental conditions. It was found that the high-performance of the Pd-based membrane and the porous metal catalyst and their configuration in the MMR guaranteed a high rate of hydrogen production. For instance, the methane conversion, the rate of hydrogen separation and the hydrogen purity were 75%, 30.6 L/h and 99.95%, respectively, under the experimental conditions of 540 °C, S/C = 3.0 and del-P = 20 bar. The design and performance of MMR show potential advantages, such as the simple preparation of a compact membrane reformer able to operate in relatively high-pressure ranges and easy enlargement of the hydrogen production capacity by stacking the modules, which is possible due to the disk-type shape of the metal catalyst and the membrane.     

Exergoenvironmental analysis of a steam methane reforming process for hydrogen production

Steam methane reforming (SMR) is one of the most promising processes for hydrogen production. Several studies have demonstrated its advantages from the economic viewpoint. Nowadays process development is based on technical and economical aspects; however, in the near future, the environmental impact will play a significant role in the design of such processes. In this paper, an SMR process is studied from the viewpoint of overall environmental impact, using an exergoenvironmental analysis. This analysis presents the combination of exergy analysis and life cycle assessment. Components where chemical reactions occur are the most important plant components from the exergoenvironmental point of view, because, in general, there is a high environmental impact associated with these components. This is mainly caused by the exergy destruction within the components, and this in turn is mainly due to the chemical reactions. The obtained results show that the largest potential for reducing the overall environmental impact is associated with the combustion reactor, the steam reformer, the hydrogen separation unit and the major heat exchangers. The environmental impact in these components can mainly be reduced by improving their exergetic efficiency. A sensitivity analysis for some important exergoenvironmental variables is also presented in the paper.     

Solar ground reformer

The possibility to couple a large-scale solar tubular reformer (a chemical reactor where a low hydrocarbon, e.g., methane, is reacting with steam and/or CO₂ to produce synthesis gas, a mixture of carbon monoxide and hydrogen), with a solar tower beam-down optics, is explored and analyzed. The reformer is installed on the ground and the concentrated solar energy enters through an aperture in the ceiling of the reformer enclosure and heats the reactor tubes, arranged within the enclosure along its walls. This arrangement enables, potentially, to adapt a large solar plant to a modified conventionally designed reformer. Through an example where about 50 MW of solar energy is introduced into an array of ground reformers, the optical path and the radiative heat exchange within the reformer cavity, coupled with the reactor tube side, are calculated and illustrated. Detailed calculation results describing the radiation flux profile inside the cavity, the surface temperatures of the reactor tubes and the composition of the process gas along the tubes, as well as the annual performance of the reformer, are shown. The results demonstrate that the solar reformer illustrated in this study can be connected to a combined cycle-power generation unit having a nominal capacity of 100-MW electricity. A power generation unit of this kind, if operating annually during roughly 2000 sunny hours, will produce about 25% of its power, supplied by the solar energy source.     

Numerical study on micro-reformer performance and local transport phenomena of the plate methanol steam micro-reformer

The objective of this work is to investigate the transport phenomena and performance of a plate steam methanol micro-reformer. Micro channels of various height and width ratios are numerically analyzed to understand their effects on the reactant gas transport characteristics and micro-reformer performance. In addition, influences of Reynolds number and geometric size of micro channel on methanol conversion of micro-reformer and gas transport phenomena are also explored. The predicted results demonstrated that better performance is noted for a micro channel reformer with lower aspect-ratio micro channel. This is due to the larger the chemical reaction surface area for a lower aspect-ratio channel reformer. It is also found that the methanol conversion decreases with increasing Reynolds number Re. The results also indicate that the smaller micro channel size experiences a better methanol conversion. This is due to the fact that a smaller micro channel has a much more uniform temperature distribution, which in turn, fuel utilization efficiency is improved for a smaller micro channel reformer.     

Methanol reformer integrated phosphoric acid fuel cell (PAFC) based compact plant for field deployment

Naval Material Research Laboratory (NMRL), based on the firm confidence of her core competence on material development, started an ambitious program on development of fuel cells for various Defense and non-Defense application in early nineties. The primary emphasis of this program is to develop phosphoric acid fuel cell (PAFC) based power plants integrated with hydrogen generators along with other accessories. In the process of development, it is understood that online generation of hydrogen from a liquid fuel is the key to success. Methanol, a liquid fuel, can be reformed easily with few side products and the resultant hydrogen rich reformer gas can be directly fed to a PAFC. Such configuration keeps the basic system simple and free of complicated filters and instrumentation.NMRL has developed a series of catalytic burners with high efficiency as the primary heat transfer source from the hot catalytic surface is based on conduction rather than convection as is done normally. Vaporizer is a coiled arrangement and reformer is hollow sections filled with Cu/Al₂O₃/ZnO catalyst, and the same is integrated with catalytic burners. Such arrangement is modular in nature and each reformer has hydrogen generation capacity of 90 lpm and start-up time is around half an hour. Modular design of reformer reactor allow them to used in different capacity plants such as a 2 kW plant configured with a reformer reactor with two vaporizer and 15 kW plant configured with seven nos. of reformer reactors and seven no. of vaporizer. The waste heat of the fuel cell and the same from the reformer burner flue is used to meet most of the reformer heat load. The catalytic burner of the reformer burns both waste hydrogen and methanol with very little excess air. PAFC being tolerant to CO (up to 1%) can be directly operated with the hydrogen rich reformer gas and the lean gas from the fuel cell is burnt into the reformer system.The raw DC output power is converted into either 100 VDC or 220 V single phase, 50 Hz sinusoidal AC power through appropriate power electronics. These configurations give overall efficiency of the plant to around 35-40 % based on LHV of Hydrogen. A battery bank is also incorporated to cater for the plant start-up and other temporary auxiliary power which get charged from the fuel cell output. Such configuration lead to the development of methanol reformer integrated PAFC based power plants of capacity ranging from 2 kW to 15 kW. The system is designed for continuous power production in the field. These plants are suitable for remote area, distributed power generation and application such as battery charging, domestic load etc.     

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.     

The performance evaluation of an industrial membrane reformer with catalyst-deactivation for a domestic methanol production plant

Methane reforming is the most important and economical process for hydrogen and syngas generation. In this work, the dynamic simulation of methane steam reforming in an industrial membrane reformer for synthesis gas production is developed. A novel deactivation model for commercial Ni-based catalysts is proposed and the monthly collected data from an existing reformer in a domestic methanol plant is used to optimize the model parameters. The plant data is also employed to check the model accuracy. It was observed that the membrane reformer could compensate for the catalyst deactivating effect.In order to assure the long membrane lifetime and decrease the unit price, the membrane reformer with 5 μm thick Pd on stainless steel supports is modeled at the temperature below the maximum operating temperature of Pd based membranes (around 600 °C). The dynamic modeling showed that the methane conversion of 76% could be achieved at a moderate temperature of 600 °C for an industrial membrane reformer. The cost-effective generation of syngas with an appropriate H₂/CO ratio of 2.6 could be obtained by membrane reformer. This is while the conventional reformer exhibits a maximum conversation of 64 at 1200 °C challenging due to its high syngas ratio (3.7). On the other hand, the pure hydrogen from membrane reformer can supply part of the ammonia reactor feed in an adjacent ammonia plant.     

Effect of hydrogen on stability of amorphous silicon thin films

This paper presents results of the investigation of hydrogen influence on the stability of low pressure chemical vapour deposition a-Si films. We measured boron- or phosphorus-doped films post-hydrogenated by ion implantation with different hydrogen doses. The dark conductivity after fast quenching and slow cooling and the isothermal relaxation were measured at different annealing temperatures. It was found that higher hydrogen concentration causes greater metastable changes but shorter relaxation time of defects.     

Dealing with fuel contaminants in biogas-fed solid oxide fuel cell (SOFC) and molten carbonate fuel cell (MCFC) plants: Degradation of catalytic and electro-catalytic active surfaces and related gas purification methods

Fuel cell and hydrogen technologies are re-gaining momentum in a number of sectors including industrial, tertiary and residential ones. Integrated biogas fuel cell plants in wastewater treatment plants and other bioenergy recovery plants are nowadays on the verge of becoming a clear opportunity for the market entry of high-temperature fuel cells in distributed generation (power production from a few kW to the MW scale).High-temperature fuel cell technologies like molten carbonate fuel cells (MCFCs) and solid oxide fuel cells (SOFCs) are especially fit to operate with carbon fuels due to their (direct or indirect) internal reforming capability. Especially, systems based on SOFC technology show the highest conversion efficiency of gaseous carbon fuels (e.g., natural gas, digester gas, and biomass-derived syngas) into electricity when compared to engines or gas turbines. Also, lower CO₂ emissions and ultra-low emissions of atmospheric contaminants (SO_X, CO, VOC, especially NO_X) are generated per unit of electricity output. Nonetheless, stringent requirements apply regarding fuel purity. The presence of contaminants within the anode fuel stream, even at trace levels (sometimes ppb levels) can reduce the lifetime of key components like the fuel cell stack and reformer. In this work, we review the complex matrix (typology and amount) of different contaminants that is found in different biogas types (anaerobic digestion gas and landfill gas). We analyze the impact of contaminants on the fuel reformer and the SOFC stack to identify the threshold limits of the fuel cell system towards specific contaminants. Finally, technological solutions and related adsorbent materials to remove contaminants in a dedicated clean-up unit upstream of the fuel cell plant are also reviewed.     

System optimization and cost analysis of plasma catalytic reforming of natural gas

Plasma reforming could provide advantages in hydrocarbon reforming especially in small-to-medium-scale plants and in plants with fast transients. The combination of a thermal plasma reformer operating in partial oxidation mode with a catalyst bed will be described. Reduced concentrations of CO (1–3% vol) can be achieved, with high hydrogen yields and minimal plasmatron electrical power requirements. A model for the cost of hydrogen production from natural gas has been developed. The model includes hydrogen cleanup utilizing a conventional pressure swing adsorption unit. The model uses experimentally determined conversion yields and operational parameters. The conditions that result in system optimization and cost minimization have been determined.     

Hydrogen production by reforming of liquid hydrocarbons in a membrane reactor for portable power generation—Model simulations

One of the most promising technologies for lightweight, compact, portable power generation is proton exchange membrane (PEM) fuel cells. PEM fuel cells, however, require a source of pure hydrogen. Steam reforming of hydrocarbons in an integrated membrane reactor has potential to provide pure hydrogen in a compact system. In a membrane reactor process, the thermal energy needed for the endothermic hydrocarbon reforming may be provided by combustion of the membrane reject gas. The energy efficiency of the overall hydrogen generation is maximized by controlling the hydrogen product yield such that the heat value of the membrane reject gas is sufficient to provide all of the heat necessary for the integrated process. Optimization of the system temperature, pressure and operating parameters such as net hydrogen recovery is necessary to realize an efficient integrated membrane reformer suitable for compact portable hydrogen generation. This paper presents results of theoretical model simulations of the integrated membrane reformer concept elucidating the effect of operating parameters on the extent of fuel conversion to hydrogen and hydrogen product yield. Model simulations indicate that the net possible hydrogen product yield is strongly influenced by the efficiency of heat recovery from the combustion of membrane reject gas and from the hot exhaust gases. When butane is used as a fuel, a net hydrogen recovery of 68% of that stoichiometrically possible may be achieved with membrane reformer operation at 600 °C (873 K) temperature and 100 psig (0.791 MPa) pressure provided 90% of available combustion and exhaust gas heat is recovered. Operation at a greater pressure or temperature provides a marginal improvement in the performance whereas operation at a significantly lower temperature or pressure will not be able to achieve the optimal hydrogen yield. Slightly higher, up to 76%, net hydrogen recovery is possible when methanol is used as a fuel due to the lower heat requirement for methanol reforming reaction, with membrane reformer operation at 600 °C (873 K) temperature and 150 psig (1.136 MPa) pressure provided 90% of available combustion and exhaust gas heat is recovered.     

Fuel flexibility study of an integrated 25 kW SOFC reformer system

The operation of solid oxide fuel cells on various fuels, such as natural gas, biogas and gases derived from biomass or coal gasification and distillate fuel reforming has been an active area of SOFC research in recent years. In this study, we develop a theoretical understanding and thermodynamic simulation capability for investigation of an integrated SOFC reformer system operating on various fuels. The theoretical understanding and simulation results suggest that significant thermal management challenges may result from the use of different types of fuels in the same integrated fuel cell reformer system. Syngas derived from coal is simulated according to specifications from high-temperature entrained bed coal gasifiers. Diesel syngas is approximated from data obtained in a previous NFCRC study of JP-8 and diesel operation of the integrated 25 kW SOFC reformer system. The syngas streams consist of mixtures of hydrogen, carbon monoxide, carbon dioxide, methane and nitrogen. Although the SOFC can tolerate a wide variety in fuel composition, the current analyses suggest that performance of integrated SOFC reformer systems may require significant operating condition changes and/or system design changes in order to operate well on this variety of fuels.     

Analysis of chemical-reaction-coupled mass and heat transport phenomena in a methane reformer duct for PEMFCs

Mass, heat and momentum transport processes are coupled with catalytic chemical reactions in a methane steam reforming duct. It is often found that endothermic and exothermic reactions in the ducts are strongly integrated by heat transfer from adjacent catalytic combustion ducts. In this paper, a three-dimensional calculation method is developed to simulate and analyze reforming reactions of methane, and the effects on various transport processes in a steam reforming duct. The reformer conditions such as mass balances associated with the reforming reactions and gas permeation to/from the porous catalyst reforming layer are applied in the analysis. The predicted results are presented and discussed for a composite duct consisting of a porous catalyst reaction layer, the fuel gas flow duct and solid layers. Parametric studies are conducted to reveal the importance of reformer designs and operating conditions. The results show that the variables, such as porous layer configuration, temperature and catalyst loading, have significant effects on the transport processes and reformer performance.     

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.     

Comprehensive study of the underground hydrogen storage potential in the depleted offshore Tapti-gas field

Hydrogen is becoming an alternative for conventional energy sources due to absence of any Greenhouse Gases (GHG) emissions during its usage. Geological storage of hydrogen will be potential solution for dealing with large volume requirement to manage uninterrupted Hydrogen supply-chain. Geological Storages such as depleted reservoirs, aquifers and salt caverns offer great potential option for underground hydrogen storage (UHS). There are several depleted gas fields in India. One of such field is located in Tapti-Daman formation. A comprehensive study is conducted to assess the possibility of hydrogen storage in this Indian field which is first of its kind. The geological characteristic of this site is assessed for its viability for storage. Additionally, several aspects including storage capacity, sealability, chemical and micro-biological stability, reservoir simulation, and production viability are assessed using various analytical and numerical models.The qualitative analysis of the Tapti-gas field suggests that the integrity of the storage site will be intact due to existing anticlinal four-way closed structure. The chemical and micro-biological losses are minimal and will not lead to major loss of hydrogen over time. The reservoir modeling results show that optimum gas production-injection scheme needs to be engineered to maintain the required reservoir pressure level in the Tapti-gas field. Also, the deliverability of the various seasonal storage time show that 80 days production scheme will be suitable for efficient operation in this field. Finally, a synergistic scheme to enable green energy production, storage, and transportation is proposed via implementation of UHS in the offshore Tapti-gas field.