Experimental and theoretical analysis of a monolith type auto-thermal reforming reactor

In this study, the effects of inlet conditions on the performance of a natural gas autothermal reforming reactor loaded with a commercial monolith catalyst are investigated. The reactor has a hydrogen production capacity of 1.5 kW and, is a part of a fuel processor, applicable in a residential-scale fuel cell system. Experimental, kinetic and equilibrium results are all presented. The experimental data were input into commercial software, Aspen HYSYS (ver.8.8). Equilibrium state calculations are based on the maximization of entropy. Monolith catalyst performance is consistent with thermodynamics, especially for lower oxygen feeding. The kinetic is also run into HYSYS and the results are in harmony with the experimental findings. The effects of the operating parameters, namely the oxygen-to-carbon ratio, the steam-to-carbon ratio and the reactor inlet temperature, on the hydrogen yield, fuel conversion, efficiency, and compositions are discussed experimentally and theoretically. The main impact among the parameters that affect the monolith performance is determined as the oxygen-to-carbon ratio. The favourable operating conditions are determined as inlet temperatures of 400 °C–550 °C, the steam-to-carbon ratio of 3.0, and the oxygen-to-carbon ratio of 0.5 with the hydrogen yield of 2.32–2.46, fuel conversion of 90%–96.5% and the efficiency of 67–72%.     

Start-up strategies of an experimental fuel processor

In this work, cold start-up of a methane fuel processor is explored. The experimental fuel processor is intended to provide hydrogen for a proton exchange membrane (PEM) fuel cell for the power generation (3 kWe). A dynamic model describing a series of reactors, the reformer, three water–gas shift reactors, and preferential reactor is constructed. Two important factors for rapid start-up are identified: speed of temperature front propagation and acceptable CO concentration. Steady-state analyses reveal that the fuel feed flow rate with fixed steam-to-carbon and air-to-carbon ratios is an ideal manipulated variable. Considering both large initial heat flux and gradual transition back to nominal operation, the shape of feed manipulation is determined. With the feed scenario available, the fuel processor start-up can be formulated as a constrained optimization problem and can be solved numerically. From optimization result, a heuristic is generated for rapid start-up of a fuel processor. This leads to a 25% improvement in the start-up time. Finally, issues of design modification are explored for further reduction in the start-up time.     

A natural-gas fuel processor for a residential fuel cell system

A system model was used to develop an autothermal reforming fuel processor to meet the targets of 80% efficiency (higher heating value) and start-up energy consumption of less than 500 kJ when operated as part of a 1-kWe natural-gas fueled fuel cell system for cogeneration of heat and power. The key catalytic reactors of the fuel processor – namely the autothermal reformer, a two-stage water gas shift reactor and a preferential oxidation reactor – were configured and tested in a breadboard apparatus. Experimental results demonstrated a reformate containing ∼48% hydrogen (on a dry basis and with pure methane as fuel) and less than 5 ppm CO. The effects of steam-to-carbon and part load operations were explored.     

Experimental investigation on the effect of natural gas composition on performance of autothermal reforming

This paper presents experimental study on catalytic autothermal reforming (ATR) of natural gas (NG) for hydrogen (_H2${\mathrm{H}}_2$) production over sulfide nickel catalyst supported on gamma alumina. The experiments are conducted on a cylindrical reactor of 30 mm in diameter and 200 mm in length with “simulated” NG of different composition under thermal-neutral conditions and fed with different molar air to fuel ratio (A/F$A/F$) and molar water to fuel ratio (W/F)$(W/F)$. The results showed that reforming performance is significantly dependent on A/F$A/F$, W/F$W/F$ and concentration of _C2+${\mathrm{C}}_{2+}$ hydrocarbons in inlet fuel. Fuels containing higher _C2+${\mathrm{C}}_{2+}$ hydrocarbons concentration have optimum performance in terms of more _H2${\mathrm{H}}_2$ at higher A/F$A/F$ and W/F$W/F$ but lower conversion efficiency. Good performance for ATR of fuel containing 15%–20% _C2H6${\mathrm{C}}_2{\mathrm{H}}_6$ can be achieved at A/F=5–7$A/F=5–7$ and W/F=4–6$W/F=4–6$, much higher than that for optimum performance of ATR of methane (A/F=3,W/F=2–2.5$A/F=3,W/F=2–2.5$). _CO2${\mathrm{CO}}_2$ in the inlet fuel does not have significant effect on the reversed water–gas shift reaction. Its effect on reforming performance is mainly due to the dilution of inlet fuel and products.     

Performance analysis of a 5 kW PEMFC with a natural gas reformer

Power systems based on fuel cells have been considered for residential and commercial applications in energy Distributed Generation (DG) markets. In this work we present an experimental analysis of a power generation system formed by a 5 kW proton exchange membrane fuel cell (PEMFC) unit and a natural gas reformer (fuel processor) for hydrogen production. The performance analysis developed simultaneously the energy and economic viewpoints and enabled the determination of the best technical and economic conditions of this energy generation power plant, and the best operating strategies, enabling the optimization of the overall performance of the stationary cogeneration fuel cell unit. It was determined the electrical performance of the cogeneration system in function of the design and operational power plant parameters. Additionally, it was verified the influence of the activation conditions of the fuel cell electrocatalytic system on the system performance. It also appeared that the use of hydrogen produced from the natural gas catalytic reforming provided the system operation in excellent electrothermal stability conditions resulting in increase of the energy conversion efficiency and of the economicity of the cogeneration power plant.     

Fast start-up of a diesel fuel processor for PEM fuel cells

Fuel cell systems based on liquid fuels are particularly suitable for auxiliary power generation due to the high energy density of the fuel and its easy storage. Together with industrial partners, Oel-Waerme-Institut is developing a 3 kW_el PEM fuel cell system based on diesel steam reforming to be applied as an APU for caravans and yachts. The start-up time of a fuel cell APU is of crucial importance since a buffer battery has to supply electric power until the system is ready to take over. Therefore, the start-up time directly affects the battery capacity and consequently the system size, weight, and cost.     

Hydrogen production by natural gas in a compact ATR-based kW-scale fuel processor

In the present work, the design and testing of a very compact reaction system thermally integrated for the distributed hydrogen production by natural gas reforming is reported. The system is based on hydrocarbon Auto-Thermal Reforming, followed by a Water-Gas Shift module. A compact heat exchanger was placed between the two catalytic stages, in order to assure an appropriate thermal integration, thus avoiding any other external heat duties. Experimental results demonstrated that the integrated configuration assured a good management of thermal fluxes in the system, in which an effective heat recovery from ATR exhaust gas to reactants was realized. Preliminary tests showed very impressive performances of the system, both by processing methane and natural gas. Despite a quite inefficient WGS stage, the processor was able to produce up to 10 Nm³/h of hydrogen, assuring a thermal efficiency higher than traditional systems.     

Impact of Australian natural gas and coal bed methane composition on PEM fuel cell performance

Several PEM fuel cell systems are currently being marketed or developed as natural gas fuelled stationary power generation or cogeneration systems. Whilst each of these may perform adequately when fuelled with methane, the composition of natural gas varies widely around the world, according to the source and even the season. This study investigated the variation in composition of fuel gas supplied in pipeline systems around Australia and how its chemical composition may affect the performance of PEM fuel cell systems than employ steam reforming, shift and selective preferential oxidation to convert the fuel gas to hydrogen. The study showed that the performance of the fuel cell system is affected by the chemical composition and that ammonia formed from gases with high nitrogen concentrations could limit the applicability of PEM fuel cells, and should be taken into account when manufacturers specify the allowable fuel gas compositions for their systems.     

Experimental investigation on a methane fuel processor for polymer electrolyte fuel cells

This study presents experimental study on a novel methane fuel processing system for hydrogen (H₂) production. The unit includes into a single package the autothermal reformer, the CO shift converter, the preferential oxidation reactor and the internal heat exchangers. Effects of operative conditions, related to the H₂ productivity, on the performances, were investigated experimentally, in order to evaluate the integration of the fuel processor with a Polymer Electrolyte Fuel Cell (PEFC) system for residential applications. The sensitivity analysis showed that the overall performance is strongly dependent upon the operative conditions considered.     

Analysis of the energy efficiency of innovative ATR-based PEM fuel cell system with hydrogen membrane separation

In this work we report a simulative energy efficiency analysis performed on innovative fuel processor – PEM fuel cell systems in which hydrogen is produced via methane autothermal reforming, separated with a membrane unit coupled with a water gas shift reactor and then converted into electric energy by means of the PEM fuel cell.     

Thermally integrated fuel processor design for fuel cell applications

Effective thermal integration could enable the use of compact fuel processors with PEM fuel cell-based power systems. These systems have potential for deployment in distributed, stationary electricity generation using natural gas. This paper describes a concept wherein the latent heat of vaporization of H₂O is used to control the axial temperature gradient of a fuel processor consisting of an autothermal reformer (ATR) with water gas shift (WGS) and preferential oxidation (PROX) reactors to manage the CO exhaust concentration. A prototype was experimentally evaluated using methane fuel over a range of external heat addition and thermal inputs. The experiments confirmed that the axial temperature profile of the fuel processor can be controlled by managing only the vapor fraction of the premixed reactant stream. The optimal temperature profile is shown to result in high thermal efficiency and a CO concentration less than 40 ppm at the exit of the PROX reactor.     

Design and demonstration of an ethanol fuel processor for HT-PEM fuel cell applications

This work describes the development of a compact ethanol fuel processor for small scale high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) systems with 200–500 W electrical power output. Promising markets for reformer fuel cell systems based on ethanol are mobile or portable leisure and security power supply applications as well as small scale stationary off grid power supply and backup power. Main components of the fuel processor to be developed were the reformer reactor, the shift converter, a catalytic burner and heat exchangers. Development focused in particular on the homogeneous evaporation of the liquid reactants ethanol and water for the reformer and burner and on the development of an efficient and autarkic start-up method, respectively. Theoretical as well as experimental work has been carried out for all main components separately including for example catalyst screening and evaporator performance tests in a first project period. Afterwards all components have been assembled to a complete fuel processor which has been qualified with various operation parameter set-ups. A theoretically defined basic operation point could practically be confirmed. The overall start-up time to receive reformate gas with appropriate quality to feed an HT-PEMFC (x_CO < 2%) takes around 30 min. At steady state operation the hydrogen power output is around 900 W with H₂ and CO fractions of 41.2% and 1.5%, respectively.     

Investigations on the behaviour of 2 kW natural gas fuel processor

In this paper, the first experimental investigations on a pre-commercial natural gas steam reformer have been presented. The fuel processor unit contains the elements as follows: desulfurizer, steam reformer reactor, CO shift converter, CO preferential oxidation (PROX) reactor, steam generator, burner and heat exchangers.The fuel processor produces 45 Nl/min of syngas in which the hydrogen concentration is about 75 vol.% and the other chemical species are nitrogen, carbon dioxide and methane. The CO concentration is below 1 ppmv, so that this reforming system is suitable for the integration with a PEM fuel cell stack.The experimental activity has been conducted in a test station, properly designed to measure the behaviour of the fuel processor. The laboratory test facility is equipped by a National Instruments Compact DAQ real-time data acquisition and control system running Labview™ software. Several measurement instruments and controlling devices have been installed. Furthermore, a gas chromatograph is used to measure the product gas composition during the tests.The aim of this work has been to analyze the behaviour of this pre-commercial steam reforming unit during its operation cycle in different operating conditions (full and partial loads) in order to study its integration with a PEM fuel cell for developing a high efficiency microcogeneration system for residential applications.     

A diesel fuel processor for stable operation of solid oxide fuel cells system: II. Integrated diesel fuel processor for the operation of solid oxide fuel cells

Post-reforming experimental results for the complete removal of light hydrocarbons from diesel reformate are introduced in part I. In part II of the paper, an integrated diesel fuel processor is investigated for the stable operation of SOFCs. Several post-reforming processors have been operated to suppress both sulfur poisoning and carbon deposition on the anode catalyst. The integrated diesel fuel processor is composed of an autothermal reformer, a desulfurizer, and a post-reformer. The autothermal reforming section in the integrated diesel fuel processor effectively decomposes aromatics, and converts fuel into H₂-rich syngas. The subsequent desulfurizer removes sulfur-containing compounds present in the diesel reformate. Finally, the post-reformer completely removes the light hydrocarbons, which are carbon precursors, in the diesel reformate. We successfully operate the diesel reformer, desulfurizer, and post-reformer as microreactors for about 2500 h in an integrated mode. The degradation rate of the overall reforming performance is negligible for the 2000 h, and light hydrocarbons and sulfur-containing compounds are completely removed from the diesel reformate.     

Self-sustained operation and durability testing of a 300 W-class micro-structured LPG fuel processor

A miniaturized fuel processor for LPG has been developed and put into operation as compact hydrogen supply system for low power applications. The fuel processor consists of an integrated micro-structured evaporator and a micro-structured reformer both integrated with micro-structured catalytic burners, heat exchangers, and a micro-structured water-gas shift (WGS) stage. In the current paper, performance data of a coupled LPG steam reformer/catalytic burner are presented, which has been running stably over 1060 h with repeated start-up and shut-down cycles. On top of that, some performance data of complete LPG fuel processors will be shown, which have been operated up to 3500 h in combination with high temperature PEM fuel cell stacks. These fuel processing systems are capable to convert LPG with a nominal hydrogen production rate of 0.263 Nm³ h⁻¹. It could be demonstrated, that the micro-structured devices are not only compact but show also high reliability and durability.     

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.     

Thermal integration of a cylindrically symmetric methanol fuel processor for portable fuel cell power

The realization of a proven approach combining small hydrogen fuel cells with reformed methanol has continued to be elusive. This is so because of the overwhelming challenge of thermally integrating a chemical process involving many steps, each at a unique temperature, within a confined volume. In addition, heat loss to the environment becomes correspondingly higher as overall size shrinks due to increasing surface-to-volume ratio, requiring an inordinate use of system volume on thermal insulation. To address these challenges, we present a study based on extrapolation of experiment which incorporates novel cylindrical symmetry of the methanol fuel processor based on microchemical system technology. Models for two different fuel processor-proton exchange fuel cell systems of 4-W and 20-W scale are presented. ASPEN process simulation was used to establish basic system operating parameters. Finite difference modeling of the axisymmetric configuration was used to establish the heat flows in the systems. The results indicate strong potential for the cylindrical arrangement to provide viable self-contained small form factor battery replacements.     

A complete miniaturized microstructured methanol fuel processor/fuel cell system for low power applications

A complete miniaturized methanol fuel processor/fuel cell system was developed and put into operation as compact hydrogen supplier for low power application. The whole system consisting of a micro-structured evaporator, a micro-structured reformer and two stages of preferential oxidation of CO (PROX) reactor, micro-structured catalytic burner, and fuel cell was operated to evaluate the performance of the whole production line from methanol to electricity. The performance of micro methanol steam reformer and PROX reactor was systematically investigated. The effect of reaction temperature, steam to carbon ratio, and contact time on the methanol steam reformer performance is presented in terms of catalytic activity, selectivity, and reformate yield. The performance of PROX reactor fed with the reformate produced by the reformer reactor was evaluated by the variation of reaction temperature and oxygen to CO ratio. The results demonstrate that micro-structured device may be an attractive power source candidate for low power application.     

Water-gas shift assisted autothermal reforming of methane gas – transient and cold start studies

A study has been carried out to investigate the dynamic behaviour of water-gas shift assisted autothermal reforming (ATR-WGS) utilising a 2-D heterogeneous kinetic model. The purpose of this study is to gain insights to the dynamic changes of ATR-WGS during cold start and when subjected to a sudden change in square-pulse flow rate. In addition to analysis of ATR-WGS, the model can also aid in guiding the design of a feedback controller aimed at improving the dynamic response of the system. Cold start time for ATR-WGS reactor was found to be longer than autothermal reforming (ATR) reactor due to the addition of a slower water-gas shift (WGS) process. It was also observed that WGS plays an important role in the final products of the reaction. In addition to these findings, the investigations in the transient performance of ATR-WGS showed that there are serious overshoot/undershoot of performance related parameters in the transients, whose values are quite different from those under steady state conditions.     

Autothermal reforming of gasoline for fuel cell applications: Controller design and analysis

In this work, we address the control system options available to an autothermal reforming (ATR) reactor. The targeted application is within an on-board fuel processor for a hydrogen-fed low-temperature fuel cell. The feedback controller employs air feed rate as the manipulated variable and a measurement of catalyst temperature as the control variable. Disturbances include significant fluctuations in the measured temperature as well as large throughput changes, owning to the on-board application. Our investigation includes an analysis of a simple feedback configuration as well as feed-forward control structure. It is concluded that the feedback only method is insufficient for the unique challenges associated with on-board operation, which include fast start-up and quick load changes. While the feed-forward configuration improves performance, we found a fair amount of sensitivity with respect to model mismatch. The general conclusion is that some form of advanced control will be needed to meet the stringent performance requirements of the on-board fuel processor application.