Analysis of ammonia decomposition reactor to generate hydrogen for fuel cell applications

In this paper, reaction engineering principles are utilized to analyze process conditions for producing sufficient hydrogen in an ammonia decomposition reactor for generating net power of 100 W in a fuel cell. It is shown that operating the reactor adiabatically results in a sharp decrease in temperature due to endothermic reaction, which results in low conversion of ammonia. For this reason, the reactor is heated electrically to provide heat for the endothermic reactions. It is observed that when the reactor is operated non-adiabatically, it is possible to get over 99.5% conversion of ammonia. The weight of absorbent to reduce ammonia to ppb levels is calculated. An energy balance on the reactor exit gas indicates that there is sufficient heat available to vaporize enough water to achieve 100% relative humidity in the fuel cell. A suitable fuel cell stack is designed and it is shown that this stack is able to provide the necessary power to electrically heat the reactor and produce net power of 100 W.     

Demonstration of a scaled-down autothermal membrane methane reformer for hydrogen generation

A novel concept for hydrogen generation by methane steam reforming in a thermally coupled catalytic fixed bed membrane reformer is experimentally demonstrated. The reactor, built from three concentric compartments, indirectly couples the endothermic methane steam reforming with the exothermic methane oxidation, while hydrogen is separated by a permselective Pd membrane. The study focuses on the determination of the key operation parameters and understanding their influence on the reactor performance. It has been shown that the reactor performance is mainly defined by the dimensionless ratio of the methane steam reforming feed flow rate to the hydrogen maximal membrane flow rate and by the ratio of the oxidation and steam reforming methane feed flow rates.     

Properties of thermodynamic equilibrium-based methane autothermal reforming to generate hydrogen

The characteristics of methane autothermal reforming to generate hydrogen were studied with thermodynamic equilibrium constant method. Results show that the methane steam reforming reaction is prone to backward at low temperature, and there is an inflection point temperature that the reaction turns forward. When steam–methane molar ratio is 2, the inflection point temperature increases with raising air–methane molar ratio. When air–methane molar ratio is 1, the inflection point temperature maintains between 700 and 800 K. Hydrogen yield increases firstly and then decreases with elevated temperature. The increase of air–methane molar ratio leads to a lower hydrogen production when temperature exceeds 1000 K. Increasing steam–methane molar ratio promotes the hydrogen production. Methane autothermal reforming occurs much more easily when temperature keeps at 1000 K and the molar ratio of air–methane and steam–methane is 1 and 2 respectively. Changing the steam–methane molar ratio can regulate H₂/CO molar ratio.     

Design of compact methanol reformer for hydrogen with low CO for the fuel cell power generation

The effect of the heat transfer area and the thermal conductivity of the reactor materials are evaluated with three identical structured reactors having multiple columned-catalyst bed and using three different reactor materials, aluminum alloy, brass and stainless steel. A series of compact methanol reformers are then designed and fabricated with the use of large reactor surface area in catalyst beds and high heat transfer constant to produce hydrogen fuel with 2–4 ppm of CO for the fuel cell (FC) power generation. The same design principle is successfully used for easy scale up of the reactor capacity from 250 L/h to 10,000 L/h. This low CO hydrogen (68–70%) used as the fuel for the fuel cell power generation provides a very competitive cost of hydrogen and electric power, $0.20–0.23/m³ of H₂ and $0.196/KWh, respectively.     

Thermodynamic study of hydrogen production from crude glycerol autothermal reforming for fuel cell applications

This study presents a thermodynamic analysis of hydrogen production from an autothermal reforming of crude glycerol derived from a biodiesel production process. As a composition of crude glycerol depends on feedstock and processes used in biodiesel production, a mixture of glycerol and methanol, major components in crude glycerol, at different ratios was used to investigate its effect on the autothermal reforming process. Equilibrium compositions of reforming gas obtained were determined as a function of temperature, steam to crude glycerol ratio, and oxygen to crude glycerol ratio. The results showed that at isothermal condition, raising operating temperature increases hydrogen yield, whereas increasing steam to crude glycerol and oxygen to crude glycerol ratios causes a reduction of hydrogen concentration. However, high temperature operation also promotes CO formation which would hinder the performance of low-temperature fuel cells. The steam to crude glycerol ratio is a key factor to reduce the extent of CO but a dilution effect of steam should be considered if reforming gas is fed to fuel cells. An increase in the ratio of glycerol to methanol in crude glycerol can increase the amount of hydrogen produced. In addition, an optimal operating condition of glycerol autothermal reforming at a thermoneutral condition that no external heat to sustain the reformer operation is required, was investigated.     

Design of linear controllers applied to an ethanol steam reformer for PEM fuel cell applications

This paper focuses on the design of a controller for a low temperature ethanol steam reformer for the production of hydrogen to feed a protonic exchange membrane (PEM) fuel cell. It describes different control structures for the reformer and treats the control structure selection of this multiple input multiple output (MIMO) system. For each considered control structure, decentralised 2 × 2 controllers with proportional integral (PI) control actions in each control loop are implemented. The tuning of the PI parameters and the performance evaluation of the different controllers are based on a non-linear simulation model. For the validation and comparison of the considered controllers, the dynamic response for different setpoint changes and initial conditions is analysed, as well as the behaviour of the controlled system against disturbances.     

Modeling and dynamics of an autothermal JP5 fuel reformer for marine fuel cell applications

In this work, a dynamic model of an integrated autothermal reformer (ATR) and proton exchange membrane fuel cell (PEM FC) system and model-based evaluation of its dynamic characteristics are presented. The ATR reforms JP5 fuel into a hydrogen rich flow. The hydrogen is extracted from the reformate flow by a separator membrane (SEP), then supplied to the PEM FC for power generation. A catalytic burner (CB) and a turbine are also incorporated to recuperate energy from the remaining SEP flow that would otherwise be wasted. A dynamic model of this system, based on the ideal gas law and energy balance principles, is developed and used to explore the effects of the operating setpoint selection of the SEP on the overall system efficiency. The analysis reveals that a trade-off exists between the SEP efficiency and the overall system efficiency. Finally the open loop system simulation results are presented and conclusions are drawn on the SEP operation.     

Biogas steam reformer for hydrogen production: Evaluation of the reformer prototype and catalysts

This work aims to investigate a biogas steam reforming prototype performance for hydrogen production by mass spectrometry and gas chromatography analyses of catalysts and products of the reform. It was found that 7.4% Ni/NiAl₂O₄/γ-Al₂O₃ with aluminate layer and 3.1% Ru/γ-Al₂O₃ were effective as catalysts, given that they showed high CH₄ conversion, CO and H₂ selectivity, resistance to carbon deposition, and low activity loss. The effect of CH₄:CO₂ ratio revealed that both catalysts have the same behavior. An increase in CO₂ concentration resulted in a decrease in H₂/CO ratio from 2.9 to 2.4 for the Ni catalyst at 850 °C, and from 3 to 2.4 for the Ru catalyst at 700 °C. In conclusion, optimal performance has been achieved in a CH₄:CO₂ ratio of 1.5:1. H₂ yield was 60% for both catalysts at their respective operating temperature. Prototype dimensions and catalysts preparation and characterization are also presented.     

Concept design of a novel reformer producing hydrogen for internal combustion engines using fuel decomposition method: Performance evaluation of coated monolith suitable for on-board applications

Hydrogen addition effectively reduces the fuel consumption of spark ignition engines. We propose a new on-board reformer that produces hydrogen at high concentrations and enables multi-mode operations. For the proposed reformer, we employ a catalytic fuel decomposition reaction via a commercial NiO–CaAl₂O₄ catalyst. We explore the physical and chemical aspects of the reforming process using a fixed bed micro-reactor operating at temperatures of 550–700 °C. During reduction, methane is decomposed to form hydrogen and carbon. Carbon formation is critical to hydrogen production, and free space for carbon growth is essential at low temperatures (≤600 °C). We define a new accumulated conversion ratio that quantitatively measures highly transient catalytic decomposition. The free space of the coated monolith clearly aided low-temperature decomposition with negligible pressure drop. The coated substrate is therefore suitable for on-board applications considering that our reformer concept also utilizes the catalytic fuel decomposition reaction.     

Hydrogen production by autothermal reforming of LPG for PEM fuel cell applications

Indirect partial oxidation, or oxidative steam reforming, tests of a bimetallic Pt–Ni catalyst supported on δ$\delta$-alumina were conducted in propane–n  -butane mixtures (LPG) used as feed. _H2${\mathrm{H}}_2$ production activity and _H2/CO${\mathrm{H}}_2/\mathrm{CO}$ selectivity were investigated in response to different S/C, C/_O2$\mathrm{C}/{\mathrm{O}}_2$ and W/F ratios. It was confirmed that higher steam content in the reactant stream increases both the activity and the _H2/CO${\mathrm{H}}_2/\mathrm{CO}$ selectivity of the process. Low residence times created a positive impact on catalyst activity not only for hydrogen but also for carbon monoxide production due to the increased amount of fresh hydrocarbon in the feed stream. Hence, the highest selectivity level was obtained at intermediate residence times. The response of the system to C/_O2$\mathrm{C}/{\mathrm{O}}_2$ ratio was found to depend on the available steam content due to the complex nature of IPOX. The Pt–Ni catalyst was very prone to catalyst deactivation at low S/C ratios accompanied by high C/_O2$\mathrm{C}/{\mathrm{O}}_2$ ratios, but this problem was not encountered at high S/C ratios. A comparison of catalyst performance for different propane-to-n-butane ratios in the LPG feed indicated that the Pt–Ni catalyst has slightly better activity and selectivity at higher n-butane contents at the expense of becoming more sensitive to coke deposition.     

Diesel fuel reformer for automotive fuel cell applications

Fuel economy and emission abatement are issues, which are highly prioritized areas in the automotive industry of today. The debate about climate change has in recent years even more emphasized the importance of these issues and has increased the search for finding sustainable technical solutions. This paper describes an effort to develop an innovative and environmentally-benign hydrogen generation system operating on commercial diesel fuel to avoid running the engine to supply electricity at stand-still. The use of a fuel cell-based auxiliary power unit (APU) has the potential of delivering electricity at high efficiencies independent of the heavy-duty truck engine. During the reformer development phase, spray formation and mixing of reactants proved to be crucial to obtain high reforming efficiencies and low diesel slip. The diesel is being injected through a nozzle creating a spray of fine droplets of a size which can establish rapid evaporation. Air and steam are being pre-heated and injected into the mixture chamber and subsequently mixed with the evaporated diesel fuel. Depending on the operating parameters, a part of the fuel is being oxidized and produces heat. Autothermal reforming was chosen to circumvent the heat transfer problem in catalytic steam reforming. By supplying heat directly to the catalyst surface by an oxidation reaction the heat demand of the strongly endothermic steam reforming reaction can be fulfilled. We employed CFD calculations, which revealed the importance of avoiding large recirculation zones leading to a prolonged residence time of the hydrocarbon molecules and causing auto-ignition and excessive temperatures in the catalyst. Five different reformer generations are being described and discussed in detail in this publication. The first one was based on a fixed bed reactor, while the other four all relied on catalytic monoliths enabling low pressure drops. The early reactor designs all suffered from auto-ignition and instability problems. The latter generations exhibited a considerably more stable temperature profile in the reformer. The conversion of diesel and the reformer efficiencies are significantly higher than the early generation diesel reformers.     

Rapid start-up strategy of 1 kWe diesel reformer by solid oxide fuel cell integration

A rapid start-up strategy of a diesel reformer for on-board fuel cell applications was developed by fuel cell integration. With the integration with metal-supported solid oxide fuel cell which has high thermal shock resistance, a simpler and faster start-up protocol of the diesel reformer was obtained compared to that of the independent reformer setup without considering fuel cell integration. A reformer without fuel cell integration showed unstable reactor temperatures during the start-up process, which affects the reforming catalyst durability. By utilizing waste heat from the fuel cell stack, steam required at the diesel autothermal reforming could be stably provided during the start-up process. The developed diesel reformer was thermally sustainable after the initial heat-up process. As a result, the overall start-up time of the reformer after the diesel supply was reduced to 9 min from the diesel supply compared to 22 min without fuel cell integration.     

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

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

The evaluation of methane mixed reforming reaction in an industrial membrane reformer for hydrogen production

In this work, the performance of an industrial dense PdAg membrane reformer for hydrogen production with methane mixed reforming reaction was evaluated. The rate parameters of mixed reforming reaction on a Ni based catalyst optimized by using the experimental results. One-dimensional models have been considered to model the steam reforming industrial membrane reformer (SRIMR) and mixed reforming industrial membrane reformer (MRIMR). The models are validated by experimental data.The proficiency of MRIMR and SRIMR at similar conditions used as a basis of comparison in terms of temperature, methane conversion, hydrogen yield, syngas production rate and CO₂ flow rate. Results revealed that the methane conversion, hydrogen yield and syngas production rate in MRIMR is considerably higher than SRIMR. Furthermore, the operation temperature of MRIMR could be 195 °C lower than that for SRIMR. This would contribute to a major decrease in process costs as well as a reduction in catalyst sintering. On the other hand, although MRIMR consumes CO₂, the exited CO₂ flow rate at the SRIMR is three times more than that of at the MRIMR, which is a main advantage of MRIMR from the environmental issues point of view.     

Biogas as hydrogen source for fuel cell applications

In the last decade, production of biogas from biomass degradation has attracted the attention of several research groups. The interest on this hydrogen source is focused on the potential use of this gas as raw material to supply high temperature fuel cells (HTFC). This paper reports a wide research investigation carried out at CNR-ITAE on biogas reforming processes (steam reforming, autothermal reforming and partial oxidation). A mathematical model was developed, in Aspen Plus, and an experimental validation was made in order to confirm model results. Simulations were performed to determine the reformed gas composition and the system energy balance as a function of process temperature and pressure. The value of Gas Hour Space Velocity (GHSV) was selected for calculating compositions at full equilibrium, as it is expected in operative large scale plant. To obtain a realistic evaluation of the reforming processes efficiency, the energy balance for each examined process was developed as available energy of outlet syngas on inlet required energy ratio. The comparison between values of efficiency process gives useful indication about their reliability to be integrate with fuel cell systems.     

CFD simulation of Pd-based membrane reformer when thermally coupled within a fuel cell micro-CHP system

In this work, a bi-dimensional CFD simulation investigates a fuel processor for hydrogen production from natural gas or biogas composed by a steam methane reformer coupled with a palladium-based hydrogen permeable membrane, the so-called “membrane reformer” (MREF). The heat required for the endothermic reforming reaction taking place on the MREF is supplied by a stream of hot gas coming from an external source, typically represented by a combustor burning the unconverted fuel and the unpermeated hydrogen. The resulting fuel processor arrangement, which has already been simulated by the point of view of energy and mass balances, may achieve a very high efficiency and is particularly suited for integration with fuel cells. The interest on this configuration relies on the possibility to implement this technology within a PEMFC-based micro-cogenerator (also micro-Combined Heat and Power, or m-CHP) with a net electrical power output in a range of 1–2 kW. In particular, the work focuses on the temperature profiles along the membrane, which should be kept as close as possible to 600 °C to favourite permeation and avoid any damages, and examines the advantages of hot gas on co-current direction vs. counter-current with respect to the reformer flux direction.     

Temperature and hydrogen flow rate controls of diesel autothermal reformer for 3.6 kW PEM fuel cell system with autoignition delay time analysis

In this paper catalyst temperature and hydrogen flow rate controls are an area of interest for autothermal reforming (ATR) of diesel fuel to provide continuous and necessary hydrogen flow to the on-board fuel cell vehicle system. ATR control system design is important to ensure proper and stable performance of fuel processor and fuel cell stack. Fast system response is required for varying load changes in the on-board fuel cell system. To cope with control objectives, a combination of PI and PID controllers are proposed to keep the controlled variables on their setpoints. ATR catalyst temperature is controlled with feedback PID controller through variable OCR (oxygen to carbon ratio) manipulation and kept to the setpoint value of 900 °C. Additionally diesel auto-ignition delay time is implemented through fuel flow rate delay to avoid complete oxidation of fuel. Hydrogen flow rate to the fuel cell stack is kept to setpoint of required hydrogen flow rate according to fuel cell load current using PI controller. An integrated dynamic model of fuel processor and fuel cell stack is also developed to check the fuel cell voltage. Product gas composition of 35, 18 and 4% is achieved for hydrogen, nitrogen, and carbon dioxide, respectively. The results show fast response capabilities of fuel processor following the fuel cell load change and successfully fulfills the control objectives.     

Performance improvement of diesel autothermal reformer by applying ultrasonic injector for effective fuel delivery

Technology for the reforming of heavy hydrocarbons, such as diesel, to supply hydrogen for fuel cell applications is very attractive and challenging due to its delicate control requirements. The slow reforming kinetics of aromatics contained in diesel, sulfur poisoning, and severe carbon deposition make it difficult to obtain long-term performance with high reforming efficiency. In addition, diesel has a critical mixing problem due to its high boiling point, which results in a fluctuation of reforming efficiency. An ultrasonic injector (UI) have been devised for effective diesel delivery. The UI can atomize diesel into droplets (∼40 μm) by using a piezoelectric transducer and consumes much less power than a heating-type vapourizer. In addition, reforming efficiencies increase by as much as 20% compared with a non-UI reformer under the same operation conditions. Therefore, it appears that effective fuel delivery is linked to the reforming kinetics on the catalyst surface. A 100-W_e, self-sustaining, diesel autothermal reformer using the UI is designed. In addition, the deactivation process of the catalyst, by carbon deposition, is investigated in detail.     

Development of a hydrogen dual sensor for fuel cell applications

The development and application of a hydrogen dual sensor (HDS) for the application in the fuel cell (FC) field, is reported. The dual sensing device is based on a ceramic platform head with a semiconducting metal oxide layer (MOx) printed on Pt interdigitated contacts on one side and a Pt serpentine resistance on the back side. MOx layer acts as a conductometric (resistive) gas sensor, allowing to detect low H₂ concentrations in air with high sensitivity and fast response, making it suitable as a leak hydrogen sensor. The proposed Co-doped SnO₂ layer shows high sensitivity to hydrogen (R₀/R = 90, for 2000 ppm of H₂) at 250 °C in air, and with fast response (<3 s). Pt resistance serves as a thermal conductivity sensor, and can used to monitor the whole range of hydrogen concentration (0–100%) in the fuel cell feed line with short response-recovery times, lower than 13 s and 14 s, respectively. The effect of the main functional parameters on the sensor response have been evaluated by bench tests. The results demonstrate that the dual sensor, in spite of its simplicity and cheapness, is promising for application in safety and efficiency control systems for FC power source.