Fuel Processor Efficiency Research Articles

In-depth characterization through dimensional analysis of the performance of a membrane-integrated fuel processor for high purity hydrogen generation

Efficient production of high purity hydrogen from reforming of natural or synthetic hydrocarbons is an enabling technology for the competitiveness of hydrogen-based systems. Specifically, fuel processors based on membrane-integrated reformers are one of the most promising technologies being potentially more efficient than state-of-the-art fuel processors. The effects of the operating parameters on the performance of the complete membrane-integrated fuel processor are relevant and have not been properly investigated, especially in terms of mutual interactions. Therefore, we analyze the effects of the pressure and temperature of the steam reforming reactor as well as of the steam to fuel and air to fuel ratios, on the system efficiency. To this aim, we use a steady state model developed in Aspen Plus® that implements a hybrid lumped-distributed parameter approach. To generalize our results to diverse system sizes and fuel compositions we conduct a dimensional analysis to express all the parameters in non-dimensional form.The results show that the fuel processor efficiency based on lower heating value varies between 75% and 84% as a function of the operating parameters. Notably, it always exceeds 75% that is the reference value for a state-of-the-art fuel processor based on pressure swing adsorption purification. We also note that the retentate composition has a relevant impact on the fuel processor operation. Specifically, when the retentate is rich in fuel content the fuel processor can turn in exothermic regime or can suffer oxygen starvation in the catalytic oxidation reaction. However, when the fuel processor operates in regular conditions the only relevant mutual interaction is between the steam to fuel and air to fuel ratios. Also, the fuel processor efficiency is mostly sensitive to the operating temperature and to the steam to fuel ratio. The 770 °C optimal temperature implies that only dense ceramic membranes can be used to build a fuel processor that operates at the maximum possible efficiency. Finally, leveraging on such results we evaluate the preliminary design of an innovative tubular plug flow reactor with layer catalysts.

Experimental and theoretical analysis of a natural gas fuel processor

In this study, a natural gas fuel processor was experimentally and theoretically investigated. The constructed 2.0 kWth fuel processor is suitable for a residential-scale high temperature proton exchange membrane fuel cell. The system consists of an autothermal reformer; gas clean-up units, namely high and low-temperature water-gas shift reactors; and utilities including feeding unit, burner, evaporator and heat exchangers. Commercial monolith catalysts were used in the reactors. The simulation was carried out by using ASPEN HYSYS program. A validated kinetic model and adiabatic equilibrium model were both presented and compared with experimental data. The nominal operating conditions which were determined by the kinetic model were the steam-to-carbon ratio of 3.0, the oxygen-to-carbon ratio of 0.5 and the inlet temperatures of 450 °C for autothermal reformer, 400 °C for high-temperature water-gas shift reactor and 310 °C for low-temperature water-gas shift reactor. Experimental results at the nominal condition showed that the performance criteria of the hydrogen yield, the fuel conversion and the efficiency were 2.53, 93.5% and 82.3% (higher heating value-HHV), respectively. The validated kinetic model was further used for the determination of 2–10kWthermal fuel processor efficiency which was increasing linearly up-to 86.3% (HHV).

Thermo-economic analysis of PEM fuel cell fuelled with biomethane obtained from human waste by computer simulation

Fuel cells, especially Proton Exchange Membrane (PEMFC) is considered as perfect alternative energy source that can either replace or complement existing energy source which is fossil fuel. However, the technology is still at developmental stage due to the lack of availability of fuel sources that is safe and economical. This study, therefore focused on thermo-economic analysis of PEMFC fuelled with biogas from human waste. To achieve the purpose of this study, thermo-economic analysis was used to analyse PEMFC designed to generate 1.45 MW of electricity from domestic human waste. The stages involved are biogas generation, hydrogen production and fuel cell application. The processes were modelled using Aspen HYSYS V8.8, a software developed by Aspen Tech®. The Hydrogen was produced at a rate of 358 kgmole/h, temperature of 330 K, pressure of 4.8 bar and 99% purity from the Preferential oxidation (PrOx) exit stream. Data generated from the simulation model were subsequently used for the thermodynamic and economic analysis and a fuel processor efficiency of 83.5% was obtained. Energy analysis of the process showed that the principle of energy conservation was satisfied, requiring and producing energy simultaneously and a net electrical efficiency of 42.32% was realized, while the result of exergy analysis showed that the unit associated with high irreversibilities and maximum exergy destruction is the steam generator. From the economic analysis, a rate of return of 20% was realized which is an indication that the investment is safe and profitable. The general overview of the processes based on economic and thermodynamics performance shows that the investment is worthwhile and indeed waste can be turned to wealth.

Impact of Ni-based catalyst patterning on hydrogen production from MSR: External steam reformer modelling

Wall-coated Methane Steam Reformers (MSR) are commonly used as fuel processing in the hydrogen production chain. In such devices, the catalyst which is generally nickel-based is coated on the walls, and the heat supply influences directly the fuel processing efficiency. In this work, two-dimensional CFD study is carried out to explore an enhancement on MSR thermal behavior. Two configurations in terms of catalyst coating are investigated. The first MSR configuration is equipped with continuous catalytic layer, while in the second, discrete catalyst layers separated by an inert gap are imposed. The effect of the catalyst patterning on the thermal and mass behavior of MSR is discussed. The results show that the MSR efficiency can be improved by extending the catalytic zone and discretizing the catalyst coating. Comparing to conventional MSR with continuous catalytic layers, enhancement of 28.71% in CH4 conversion and 88.574% in H2 production is realized by using discretized catalytic layers.

Comparative analysis of biomass and coal based co-gasification processes with and without CO2 capture for HT-PEMFCs

With the seasonal availability and low energy density of biomass and the high environmental impact of coal, the co-gasification of biomass and coal is an alternative approach facilitating a trade-off between renewable and non-renewable resources. The aim of this study was to investigate hydrogen production from the co-gasification of biomass and coal integrated by means of the sorption-enhanced water gas shift reactor (G-SEWGS) for a high temperature proton exchange membrane fuel cell (HT-PEMFC). The effects of the gasifier temperature, the steam to fuel ratio (S/F ratio), and the equivalence ratio (ER) on the hydrogen production performance and environmental impact of the G-SEWGS were theoretically analysed and compared with the conventional gasifier integrated with the water gas shift reactor (G-WGS) and the sorption-enhanced gasifier integrated with the water gas shift reactor (SEG-WGS). As compared to the conventional water gas shift reactor, the addition of a CaO sorbent in the modified water gas shift reactor not only reduces the amount of the CO2 emission but also leads to an increase in the hydrogen concentration and hydrogen content. The G-SEWGS provides better performance in terms of its fuel processor efficiency and CO2 emission than the G-WGS and the SEG-WGS. Also, the problem of sulphur compound in the hydrogen-rich gas can be reduced by using of the sorption-enhanced water gas shift reactor (SEWGS). The best system exergy efficiency, which was around 22% for the power generation, was determined from the HT-PEMFC integrated with the G-SEWGS. The main exergy destruction of around 70% of the total loss was caused by hydrogen production processes.

Investigation of a novel & integrated simulation model for hydrogen production from lignocellulosic biomass

Process simulation and modeling works are very important to determine novel design and operation conditions. In this study; hydrogen production from synthesis gas obtained by gasification of lignocellulosic biomass is investigated. The main motivation of this work is to understand how biomass is converted to hydrogen rich synthesis gas and its environmentally friendly impact. Hydrogen market development in several energy production units such as fuel cells is another motivation to realize these kinds of activities. The initial results can help to contribute to the literature and widen our experience on utilization of the CO2 neutral biomass sources and gasification technology which can develop the design of hydrogen production processes. The raw syngas is obtained via staged gasification of biomass, using bubbling fluidized bed technology with secondary agents; then it is cleaned, its hydrocarbon content is reformed, CO content is shifted (WGS) and finally H2 content is separated by the PSA (Pressure Swing Adsorption) unit. According to the preliminary results of the ASPEN HYSYS conceptual process simulation model; the composition of hydrogen rich gas (0.62% H2O, 38.83% H2, 1.65% CO, 26.13% CO2, 0.08% CH4, and 32.69% N2) has been determined. The first simulation results show that the hydrogen purity of the product gas after PSA unit is 99.999% approximately. The mass lower heating value (LHVmass) of the product gas before PSA unit is expected to be about 4500 kJ/kg and the overall fuel processor efficiency has been calculated as ∼93%.

Increasing wood fuel processing efficiency by fine-tuning chipper settings

Latest chipper models feature new in-feed and evacuation systems that can be adjusted on the fly to match variable work conditions. Proper adjustments of the two systems are expected to produce significant effects in terms of productivity, diesel fuel consumption and chip quality. The study verified such claims by testing one of these new machines in a controlled experiment, conducted under two alternative in-feed and evacuation system settings on two different feedstock types (2×2×2=8 treatment combinations). Each treatment was repeated 5 to 10 times, depending on feedstock availability. The study showed that feedstock type has a dominant effect on all the studied parameters, whereas in-feed mode has no effect on any of them. In contrast, blower setting has a significant effect and offers a strong potential for increased wood fuel processing efficiency. In particular, decreasing blower speed when full ejection power is not necessary allows reducing diesel fuel consumption between 6 and 16%, while increasing chip integrity by 20%.

Enhancement of dilute bio-ethanol steam reforming for a proton exchange membrane fuel cell system by using methane as co-reactant: Performance and life cycle assessment

The fuel processor and a proton exchange membrane fuel cell (PEMFC) integrated process fueled by cassava based bio-ethanol and methane as co-reactant is theoretically investigated and compared with that run by dehydrated bio-ethanol in this work. The methane is added to bio-ethanol reformer as co-reactant to reduce dilution effect of crude bio-ethanol and adjust very high steam to carbon ratio of this system. The hydrogen fraction increases with the reformer temperature and methane to bio-ethanol ratio until reaching a maximum point. In addition, the optimal operating conditions of mixed bio-ethanol and methane reformer and dehydrated bio-ethanol reformer, which achieve the highest reformer efficiency, are presented. The results show that superior fuel processor efficiency, fuel cell efficiency and system efficiency are obtained when the mixed bio-ethanol and methane is used to generate hydrogen. The mixed bio-ethanol and methane reforming integrated with PEMFC system has the lower environmental impact, compared to the dehydrated bio-ethanol reforming integrated with PEMFC system.

Solar fuel processing efficiency for ceria redox cycling using alternative oxygen partial pressure reduction methods

Solar-driven non-stoichiometric thermochemical redox cycling of ceria for the conversion of solar energy into fuels shows promise in achieving high solar-to-fuel efficiency. This efficiency is significantly affected by the operating conditions, e.g. redox temperatures, reduction and oxidation pressures, solar irradiation concentration, or heat recovery effectiveness. We present a thermodynamic analysis of five redox cycle designs to investigate the effects of working conditions on the fuel production. We focused on the influence of approaches to reduce the partial pressure of oxygen in the reduction step, namely by mechanical approaches (sweep gassing or vacuum pumping), chemical approaches (chemical scavenger), and combinations thereof. The results indicated that the sweep gas schemes work more efficient at non-isothermal than isothermal conditions, and efficient gas phase heat recovery and sweep gas recycling was important to ensure efficient fuel processing. The vacuum pump scheme achieved best efficiencies at isothermal conditions, and at non-isothermal conditions heat recovery was less essential. The use of oxygen scavengers combined with sweep gas and vacuum pump schemes further increased the system efficiency. The present work can be used to predict the performance of solar-driven non-stoichiometric redox cycles and further offers quantifiable guidelines for system design and operation.

Evaluation of an integrated methane autothermal reforming and high-temperature proton exchange membrane fuel cell system

The aim of this study was to investigate the performance and efficiency of an integrated autothermal reforming and HT-PEMFC (high-temperature proton exchange membrane fuel cell) system fueled by methane. Effect of the inclusion of a CO (carbon monoxide) removal process on the integrated HT-PEMFC system was considered. An increase in the S/C (steam-to-carbon) ratio and the reformer temperature can enhance the hydrogen fraction while the CO formation reduces with increasing S/C ratio. The fuel processor efficiency of the methane autothermal reformer with a WGS (water gas shift reactor) reactor, as the CO removal process, is higher than that without a WGS reactor. A higher fuel processor efficiency can be obtained when the feed of the autothermal reformer is preheated to the reformer temperature. Regarding the cell performance, the reformate gas from the methane reformer operated at Tin = TR and with a high S/C ratio is suitable for the HT-PEMFC system without a WGS reactor. When considering the HT-PEMFC system with a WGS reactor, the CO poisoning has less significant impact on the cell performance and the system can be operated over a broader range to minimize the required total active area. A WGS reactor is necessary for the methane autothermal reforming and HT-PEMFC integrated system with regard to the system efficiency.

Hydrogen production by onboard gasoline processing – Process simulation and optimization

Fuel cell vehicles have reached the commercialization stage and hybrid vehicles are already on the road. While hydrogen storage and infrastructure remain critical issues in stand alone commercialization of the technology, researchers are developing onboard fuel processors, which can convert a variety of fuels into hydrogen to power these fuel cell vehicles. The feasibility study of a 100kW on board fuel processor based on gasoline fuel is carried out using process simulation. The steady state model has been developed with the help of Aspen HYSYS to analyze the fuel processor and total system performance. The components of the fuel processor are the fuel reforming unit, CO clean-up unit and auxiliary units. Optimization studies were carried out by analyzing the influence of various operating parameters such as oxygen to carbon ratio, steam to carbon ratio, temperature and pressure on the process equipments. From the steady state model optimization using Aspen HYSYS, an optimized reaction composition in terms of hydrogen production and carbon monoxide concentration corresponds to: oxygen to carbon ratio of 0.5 and steam to carbon ratio of 0.5. The fuel processor efficiency of 95.98% is obtained under these optimized conditions. The heat integration of the system using the composite curve, grand composite curve and utility composite curve were studied for the system. The most appropriate heat exchanger network from the generated ones was chosen and that was incorporated into the optimized flow sheet of the100kW fuel processor. A completely heat integrated 100kW fuel processor flow sheet using gasoline as fuel was thus successfully simulated and optimized.

Steam and partial oxidation reforming options for hydrogen production from fossil fuels for PEM fuel cells

Proton exchange membrane fuel cell (PEM) generates electrical power from air and from hydrogen or hydrogen rich gas mixtures. Therefore, there is an increasing interest in converting current hydrocarbon based marine fuels such as natural gas, gasoline, and diesel into hydrogen rich gases acceptable to the PEM fuel cells on board ships. Using chemical flow sheeting software, the total system efficiency has been calculated. Natural gas appears to be the best fuel for hydrogen rich gas production due to its favorable composition of lower molecular weight compounds. This paper presents a study for a 250kW net electrical power PEM fuel cell system utilizing a partial oxidation in one case study and steam reformers in the second. This study has shown that steam-reforming process is the most competitive fuel processing option in terms of fuel processing efficiency. Partial oxidation process has proved to posses the lowest fuel processing efficiency. Among the options studied, the highest fuel processing efficiency is achieved with natural gas steam reforming system.

On-board reforming of biodiesel and bioethanol for high temperature PEM fuel cells: Comparison of autothermal reforming and steam reforming

In the 21st century biofuels will play an important role as alternative fuels in the transportation sector. In this paper different reforming options (steam reforming (SR) and autothermal reforming (ATR)) for the on-board conversion of bioethanol and biodiesel into a hydrogen-rich gas suitable for high temperature PEM (HTPEM) fuel cells are investigated using the simulation tool Aspen Plus. Special emphasis is placed on thermal heat integration. Methyl-oleate (C19H36O2) is chosen as reference substance for biodiesel. Bioethanol is represented by ethanol (C2H5OH). For the steam reforming concept with heat integration a maximum fuel processing efficiency of 75.6% (76.3%) is obtained for biodiesel (bioethanol) at S/C=3. For the autothermal reforming concept with heat integration a maximum fuel processing efficiency of 74.1% (75.1%) is obtained for biodiesel (bioethanol) at S/C=2 and λ=0.36 (0.35). Taking into account the better dynamic behaviour and lower system complexity of the reforming concept based on ATR, autothermal reforming in combination with a water gas shift reactor is considered as the preferred option for on-board reforming of biodiesel and bioethanol. Based on the simulation results optimum operating conditions for a novel 5kW biofuel processor are derived.

A simulated auto‐thermal membrane reformer process for a PEM fuel cell micro cogeneration unit

AbstractThere are several methods of producing hydrogen‐rich gas from fossil resources such as natural gas or naphtha, for example, steam reforming, partial oxidation and auto‐thermal reforming. In this paper, an integrated ATR membrane reactor system was simulated. The effect of operating parameters on the product distribution, fuel cell hydrogen utilization and the net electric efficiency of the overall system were discussed. The overall system was integrated with a 1‐kWe PEM fuel cell. The ASPEN‐HYSIS 3.2 software has been utilized for the simulations and calculations of the fuel processing reactions. Natural gas fuel has been used as feedstock and applied to the simulated flow‐sheet model. It was desired to produce hydrogen‐rich gas with a low CO formation using an autothermal membrane reformer. A very low CO content with higher content of hydrogen was provided by the membrane reformer, eliminating the use of the conventional preferential oxidation (PrOx) reactor. Different combinations of TATR, S/C, O2/C ratios and UH2 have been parametrically studied. Fuel processing efficiency and net electrical efficiency of all selected operating conditions have been calculated as well. Results indicate that the system parameters are very critical for the appropriate operation of the residential cogeneration system with ATR membrane unit. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

Operating line analysis of fuel processors for PEM fuel cell systems

At least three different definitions of fuel processor efficiency are in widespread use in the fuel cell industry. In some instances the different definitions are qualitatively the same and differ only in their quantitative values. However, in certain limiting cases, the different efficiency definitions exhibit qualitatively different trends as system parameters are varied. In one limiting case that will be presented, the use of the wrong efficiency definition can lead a process engineer to believe that a theoretical maximum in fuel processor efficiency exists at a particular operating condition, when in fact no such efficiency optimum exists. For these reasons, the objectives of this paper are to: (1) quantitatively compare and contrast these different definitions, (2) highlight the advantages and disadvantages of each definition and (3) recommend the correct definition of fuel processor efficiency.

Compact gasoline fuel processor for passenger vehicle APU

Due to the increasing demand for electrical power in today's passenger vehicles, and with the requirements regarding fuel consumption and environmental sustainability tightening, a fuel cell-based auxiliary power unit (APU) becomes a promising alternative to the conventional generation of electrical energy via internal combustion engine, generator and battery. It is obvious that the on-board stored fuel has to be used for the fuel cell system, thus, gasoline or diesel has to be reformed on board. This makes the auxiliary power unit a complex integrated system of stack, air supply, fuel processor, electrics as well as heat and water management. Aside from proving the technical feasibility of such a system, the development has to address three major barriers:start-up time, costs, and size/weight of the systems. In this paper a packaging concept for an auxiliary power unit is presented. The main emphasis is placed on the fuel processor, as good packaging of this large subsystem has the strongest impact on overall size. The fuel processor system consists of an autothermal reformer in combination with water–gas shift and selective oxidation stages, based on adiabatic reactors with inter-cooling. The configuration was realized in a laboratory set-up and experimentally investigated. The results gained from this confirm a general suitability for mobile applications. A start-up time of 30 min was measured, while a potential reduction to 10 min seems feasible. An overall fuel processor efficiency of about 77% was measured. On the basis of the know-how gained by the experimental investigation of the laboratory set-up a packaging concept was developed. Using state-of-the-art catalyst and heat exchanger technology, the volumes of these components are fixed. However, the overall volume is higher mainly due to mixing zones and flow ducts, which do not contribute to the chemical or thermal function of the system. Thus, the concept developed mainly focuses on minimization of those component volumes. Therefore, the packaging utilizes rectangular catalyst bricks and integrates flow ducts into the heat exchangers. A concept is presented with a 25 l fuel processor volume including thermal isolation for a 3 kW el auxiliary power unit. The overall size of the system, i.e. including stack, air supply and auxiliaries can be estimated to 44 l.

Modelling an experimental methane fuel processor

Steady-state models are developed to describe an experimental methane fuel processor that is intended to provide hydrogen for a fuel cell system for power generation (2–3 kW). First-principle reactor models are constructed to describe a series of reactions, i.e., steam and autothermal reforming (SR/ATR), high- and low-temperature water–gas shift (HTS/LTS) reactions and preferential oxidation (PROX) reactions, at different sectors of the reactor system for methane reforming as well as gas cleaning. The pre-exponential factors of the rate constants are adjusted to fit the experimental data and the resultant reactor model provides a reasonably good description of steady-state behaviour. Next, sensitivity analyses are performed to locate the optimum operating point of the fuel processor. The objective function of the optimization is fuel processor efficiency. The dominating optimization variables include: the ratios of water and oxygen to the hydrocarbon feed to the autothermal reforming reactor and the inlet temperature of the reactor. The results indicate that further improvement in fuel processor efficiency can be made with a reliable process model.

Development of a soldier-portable fuel cell power system: Part I: A bread-board methanol fuel processor

A 15-W e portable power system is being developed for the US Army that consists of a hydrogen-generating fuel reformer coupled to a proton-exchange membrane fuel cell. In the first phase of this project, a methanol steam reformer system was developed and demonstrated. The reformer system included a combustor, two vaporizers, and a steam reforming reactor. The device was demonstrated as a thermally independent unit over the range of 14–80 W t output. Assuming a 14-day mission life and an ultimate 1-kg fuel processor/fuel cell assembly, a base case was chosen to illustrate the expected system performance. Operating at 13 W e, the system yielded a fuel processor efficiency of 45% (LHV of H 2 out/LHV of fuel in) and an estimated net efficiency of 22% (assuming a fuel cell efficiency of 48%). The resulting energy density of 720 Wh/kg is several times the energy density of the best lithium-ion batteries. Some immediate areas of improvement in thermal management also have been identified, and an integrated fuel processor is under development. The final system will be a hybrid, containing a fuel reformer, a fuel cell, and a rechargeable battery. The battery will provide power for start-up and added capacity for times of peak power demand.

Fuel processors for automotive fuel cell systems: a parametric analysis

An autothermally-reformed, gasoline-fueled automotive polymer electrolyte fuel cell (PEFC) system has been modeled and analyzed for the fuel processor and total system performance. The purpose of the study is to identify the influence of various operating parameters on the system performance and to investigate related tradeoff scenarios. Results of steady-state analyses at the design rated power level are presented and discussed. The effects of the following parameters are included in the analysis: operating pressure (3 and 1 atm), reforming temperature (1000–1300 K), water-to-fuel and air-to-fuel reactant feed ratios, electrochemical fuel utilization, and thermal integration of the fuel processor and the fuel cell stack subsystems. The analyses are also used to evaluate the impact of those parameters on the concentrations of methane and carbon monoxide in the processed reformate. Both of these gases can be reduced to low levels with adequate water-to-carbon used in the fuel processor. Since these two species represent corresponding amounts of hydrogen that would not be available for electrochemical oxidation in the fuel cell stack, it is important to maintain them at low levels. Subject to the assumptions used in the analyses, particularly that of thermodynamic equilibrium, it was determined that reforming temperatures of 1100 K, a water-to-carbon mole ratio of 1.5–2.5, and the use of fuel cell exhaust energy in the fuel processor subsystem can yield fuel processor efficiencies of 82–84%, and total system efficiencies of 40–42% can be achieved. For the atmospheric pressure system, if the exhaust energy is not used in the fuel processor subsystem, the fuel processor efficiency would drop to 75–82% and the total system efficiency would drop below 40%. At higher reforming temperatures, say 1300 K, the fuel processor efficiency would decrease to 78%, and the total system efficiency would drop below 39%, even with the use of the fuel cell stack exhaust energy.