A novel comprehensive procedure for determination of optimum operating conditions for cleaner energy production system

Cleaner energy production system such as direct alcohol fuel cells (DAFCs) are considered as an alternative source for generating cleaner energy. Studies based on design of catalysts, electrodes design, proton exchange membrane, and flow field were conducted for improving its performance characteristic such as power density. However, the less focus was paid on determining the operating conditions considering the uncertainties that will result in an increase of power density of DAFCs. Therefore, the present work proposes a novel comprehensive procedure involving experimental study and evolutionary approach of genetic programming (GP) in formulation of robust power density models for DAFCs. Two uncertainties such as the selection of objective function and variations in measurement of operating conditions are incorporated in framework of GP. The power density models incorporate the formulation of new objective function in GP that will result in higher accuracy of the models. Experiments performed on DAFCs validate performance of the models. Simulation profiler is then generated for models to verify its robustness in uncertain operating conditions. The inferences on relationships between power density and operating conditions for DAFCs are made by surface analysis of the models.     

Integration of direct carbon and hydrogen fuel cells for highly efficient power generation from hydrocarbon fuels

In view of impending depletion of hydrocarbon fuel resources and their negative environmental impact, it is imperative to significantly increase the energy conversion efficiency of hydrocarbon-based power generation systems. The combination of a hydrocarbon decomposition reactor with a direct carbon and hydrogen fuel cells (FC) as a means for a significant increase in chemical-to-electrical energy conversion efficiency is discussed in this paper. The data on development and operation of a thermocatalytic hydrocarbon decomposition reactor and its coupling with a proton exchange membrane FC are presented. The analysis of the integrated power generating system including a hydrocarbon decomposition reactor, direct carbon and hydrogen FC using natural gas and propane as fuels is conducted. It was estimated that overall chemical-to-electrical energy conversion efficiency of the integrated system varied in the range of 49.4–82.5%, depending on the type of fuel and FC used, and CO₂ emission per kW_elh produced is less than half of that from conventional power generation sources.     

Critical challenges in the system development of direct alcohol fuel cells as portable power supplies: An overview

Direct alcohol fuel cells (DAFCs) are considered a reasonable alternative power source because alcohol has a much higher energy density than hydrogen. Most DAFC development has focused on small portable application by using passive systems. DAFCs with active feed systems have appeared as potential portable power sources for larger applications, as they are easily handled, simple systems with smaller volumes than polymer electrolyte membrane fuel cells (PEMFCs). A general active DAFC system consists of a fuel and oxidant supplying system, product management and fuel concentration control. However, system development and commercialization are constrained by various critical challenges. This paper highlights the critical challenges of the fuel cell system rather than fundamental problems in the membrane electrode assembly (MEA), including fuel feed fluctuation, contaminant poisoning, two-phase flow, low power density, and heat and water management.     

Analysis and control of a hybrid fuel delivery system for a polymer electrolyte membrane fuel cell

A polymer electrolyte membrane fuel cell (PEM FC) system as a power source used in mobile applications should be able to produce electric power continuously and dynamically to meet the demand of the driver by consuming the fuel, hydrogen. The hydrogen stored in the tank is supplied to the anode of the stack by a fuel delivery system (FDS) that is comprised of supply and recirculation lines controlled by different actuators. Design of such a system and its operation should take into account several aspects, particularly efficient fuel usage and safe operation of the stack.     

Comparative performance analysis of a direct ammonia-fuelled anode supported flat tubular solid oxide fuel cell: A 3D numerical study

Solid oxide fuel cells that are designed in different geometrical structures (planar, tubular, flat-tubular, etc.) are dirt-free, quiet, and efficient cells that run using different fuels including contagions fuels. In this work, the performance of a 3D model of direct ammonia feed anode supported flat-tubular solid oxide fuel cell having six fuel supply channels was developed, investigated, and elucidated numerically in comparison with hydrogen fuels at different operating conditions using COMOSOL Multiphysics. The finding of this study is revealed that the performance of the developed model that is running with direct ammonia is better than hydrogen feed one using the same geometrical dimensions and operating parameters. It is also confirmed that direct ammonia feed anode supported flat-tubular solid oxide fuel cell has outstanding performance over the corresponding anode supported tubular solid oxide fuel cell using the same active cell surface area, gas channel length, and operating conditions. Parametric sweep analyses have been also performed on selected operating parameters and the outcomes revealed that the working temperature and the amount of reactant gases have a powerful impact on cell performance. Thus, ammonia is a green auspicious, and profitable candidate to use as a carbon-neutral fuel for anode supported flat-tubular solid oxide fuel cells in the near future.     

Exergy analysis of an integrated fuel processor and fuel cell (FP–FC) system

Fuel cells have great application potential as stationary power plants, as power sources in transportation, and as portable power generators for electronic devices. Most fuel cells currently being developed for use in vehicles and as portable power generators require hydrogen as a fuel. Chemical storage of hydrogen in liquid fuels is considered to be one of the most advantageous options for supplying hydrogen to the cell. In this case a fuel processor is needed to convert the liquid fuel into a hydrogen-rich stream. This paper presents a second-law analysis of an integrated fuel processor and fuel cell system. The following primary fuels are considered: methanol, ethanol, octane, ammonia, and methane. The maximum amount of electrical work and corresponding heat effects produced from these fuels are evaluated. An exergy analysis is performed for a methanol processor integrated with a proton exchange membrane fuel cell, for use as a portable power generator. The integrated FP–FC system, which can produce 100 W of electricity, is simulated with a computer model using the flow-sheeting program Aspen Plus. The influence of various operating conditions on the system efficiency is investigated, such as the methanol concentration in the feed, the temperature in the reformer and in the fuel cell, as well as the fuel cell efficiency. Finally, it is shown that the calculated overall exergetic efficiency of the FP–FC system is higher than that of typical combustion engines and rechargeable batteries.     

Analysis of performance parameters of an ethanol fueled spark ignition engine operating with hydrogen enrichment

Concerns with the environment and energy security have increased interest in phasing out fossil fuels in the automotive industry, as it transitions from conventional internal combustion engines (ICE) to electric and fuel cell powertrains. During this transition, ethanol is of particular interest as a renewable fuel option in ICE, despite drawbacks compared to gasoline. Adding hydrogen to ethanol could remedy the disadvantages associated with ethanol, while maintaining the benefits of using renewable fuels. There is a gap in the literature of both experimental and numerical studies considering hydrogen addition in turbocharged ethanol engines. Therefore, this paper presents an experimental and numerical study of a turbocharged ethanol engine operating with hydrogen enrichment at stoichiometric conditions under boosted conditions. It was concluded that hydrogen addition allowed spark ignition engines to achieve lower brake specific energy consumption, better performance, and lower emissions. Thus, after proper calibration, a simulation model was created and shown to be a suitable tool to predict engine performance of a spark ignition engine operating with hydrogen enrichment and reduce the overall number of experimental tests needed to tune engines operating with this fuel blend. Finally, some operating strategies are recommended based on these findings.     

An overview of the methanol reforming process: Comparison of fuels,catalysts, reformers,and systems

One of the main challenges facing power generation by fuel cells involves the difficulties related to hydrogen storage. Several methods have been suggested and studied by researchers to overcome this problem. Among these methods, using fuel reformers as a component of the fuel cell system is a practical and promising alternative to hydrogen storage. Among many hydrogen carrier fuels used in reformers, methanol is one of the most attractive ones because of its distinctive properties. To design and improve of the methanol reformate gas fuel cell systems, different aspects such as promising market applications for reformate gas–fueled fuel cell systems, and catalysts for methanol reforming should be considered. Therefore, our goal in this paper is to provide a comprehensive overview on the past and recent studies regarding methanol reforming technologies, while considering different aspects of this topic. Firstly, different fuel reforming processes are briefly explained in the first section of the paper. Then properties of various fuels and reforming of these fuels are compared, and the characteristics of commercial reformate gas–fueled systems are presented. The main objective of the first section of the paper is to give information about studies and market applications related to reformation of various fuels to understand advantages and disadvantages of using various fuels for different practical applications. In the next sections of the paper, advancements in the methanol reforming technology are explained. The methanol reforming catalysts and reaction kinetics studies by various researchers are reviewed, and the advantages and disadvantages of each catalyst are discussed, followed by presenting the studies accomplished on different types of reformers. The effects of operating parameters on methanol reforming are also discussed. In the last section of this paper, methanol reformate gas–fueled fuel cell systems are reviewed. Overall, this review paper provides insight to researchers on what has been accomplished so far in the field of methanol reforming for fuel cell power generation applications to better plan the next stage of studies in this field.     

A new method for dynamic performance improvement of a hybrid power system by coordination of converter's controller

In this paper, a new strategy for modeling and controlling a hybrid power generation system that contains a fuel cell (FC) and super capacitor (SC) system is proposed. The main drawback of FC systems is its slow dynamic because the FC current slope must be limited in order to prevent fuel starvation problems and to improve its efficiency and lifetime. To overcome this slow dynamic and to improve dynamic performance, a new control strategy is proposed to combine FC system with SC system. The proposed control strategy can be also used for cold starting and different types of FC systems with different dynamics. The control strategy is capable of determining the desired FC power to prolong FC system lifetime and keeps the AC and DC voltages around its nominal value in transient event by supplying propulsion power and recuperating FC energy. The minimum SC system is computed in new method and used to meet the load demand to constraint the DC bus voltage and enhances power regulation under various active and reactive load conditions. Two different case studies are used to obtain the simulation results using MATLAB/SIMULINK to verify the validity of the proposed control strategy.     

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.     

Experimental analysis of an integrated biomass gasification and PEM fuel cell system

PEM fuel cell is an electrochemical system that converts the chemical energy of hydrogen directly into electricity and is widely used as an energy source for ground vehicle applications. This paper aims to analyze the technical aspects of integrated biomass gasification and PEM fuel cell systems for electricity production which is focused on gasifier operating conditions and their effect on the cell voltage. To evaluate the effect of gasifier operating conditions (gasification temperature, steam/biomass ratio, equivalence ratio, and biomass particle size) on cell voltage, an experimental work has also been carried. The results show that for all catalysts, the cell voltage increased rapidly as the reaction temperature increased from 500 °C to 650 °C, then tended to a slow growth due to the increase of reaction rates, enabling the fast decomposition of biomass into clean syngas (H₂ and CO), especially at the initial stage of reaction.     

Carbonate fuel cells: Milliwatts to megawatts

The carbonate fuel cell power plant is an emerging high efficiency, ultra-clean power generator utilizing a variety of gaseous, liquid, and solid carbonaceous fuels for commercial and industrial applications. The primary mover of this generator is a carbonate fuel cell. The fuel cell uses alkali metal carbonate mixtures as electrolyte and operates at 650 °C. Corrosion of the cell hardware and stability of the ceramic components have been important design considerations in the early stages of development. The material and electrolyte choices are founded on extensive fundamental research carried out around the world in the 60s and early 70s. The cell components were developed in the late 1970s and early 1980s. The present day carbonate fuel cell construction employs commonly available stainless steels. The electrodes are based on nickel and well-established manufacturing processes. Manufacturing process development, scale-up, stack tests, and pilot system tests dominated throughout the 1990s. Commercial product development efforts began in late 1990s leading to prototype field tests beginning in the current decade leading to commercial customer applications. Cost reduction has been an integral part of the product effort. Cost-competitive product designs have evolved as a result. Approximately half a dozen teams around the world are pursuing carbonate fuel cell product development. The power plant development efforts to date have mainly focused on several hundred kW (submegawatt) to megawatt-class plants. Almost 40 submegawatt units have been operating at customer sites in the US, Europe, and Asia. Several of these units are operating on renewable bio-fuels. A 1 MW unit is operating on the digester gas from a municipal wastewater treatment plant in Seattle, Washington (US). Presently, there are a total of approximately 10 MW capacity carbonate fuel cell power plants installed around the world. Carbonate fuel cell products are also being developed to operate on coal-derived gases, diesel, and other logistic fuels. Innovative carbonate fuel cell/turbine hybrid power plant designs promising record energy conversion efficiencies approaching 75% have also emerged. This paper will review the historical development of this unique technology from milliwatt-scale laboratory cells to present megawatt-scale commercial power plants.     

Direct liquid-feed fuel cells: Thermodynamic and environmental concerns

The present paper briefly reviews the different direct liquid-feed fuel cells that have been regarded through the open literature. It especially focuses on thermodynamic-energetic data and toxicological–ecological hazards of the chemicals used as liquid fuels. The analysis of those two databases shows that borohydride, ethanol and 2-propanol would be the most adequate liquid fuels for the polymer electrolyte membrane fuel cell-type systems, even if they are inferior to hydrogen. All the fuels and also all the by-products stem from their decomposition are more or less harmful towards health and environment. More particularly, hydrazine should be avoided because it and its by-product are very dangerous. It is to note that the present paper does not intend to review and to compare the performances of those fuel cells because of great differences in the efforts devoted to each of them.     

Direct NaBH4/H2O2 fuel cells

A fuel cell (FC) using liquid fuel and oxidizer is under investigation. H₂O₂ is used in this FC directly at the cathode. Either of two types of reactant, namely a gas-phase hydrogen or an aqueous NaBH₄ solution, are utilized as fuel at the anode. Experiments demonstrate that the direct utilization of H₂O₂ and NaBH₄ at the electrodes results in >30% higher voltage output compared to the ordinary H₂/O₂ FC. Further, the use of this combination of all liquid fuels, provides numerous advantages (ease of storage, reduced pumping requirements, simplified heat removal, etc.) from an operational point of view. This design is inherently compact compared to other cells that use gas phase reactants. Further, regeneration is possible using an electrical input, e.g. from power lines or a solar panel. While the peroxide-based FC is ideally suited for applications such as space power where air is not available and a high energy density fuel is essential, other distributed and mobile power uses are of interest.     

Solid oxide fuel cell: Decade of progress,future perspectives and challenges

In an increasing demand of renewable energy resources, fuel cell represents the highly efficient, clean and sustainable energy conversion source. Broadly speaking, fuel cell can be divided into six different categories according to the types of electrolyte and fuels used. Each type of fuel cells has their own advantages and disadvantages. Among them, solid oxide fuel cell (SOFC) gains significant attentions due to their high efficiency, cost-effectiveness and the possibility to utilize variety of fuels other than hydrogen such as hydrocarbons, coal gas etc. As name implies, SOFC uses solid electrolyte for their operation. Indeed, in medium and large power requirement sectors, SOFC are highly suitable. In the present review article, recent advances and future perspectives of SOFC have been discussed via reviewing the literature over last five years. Most of the available review articles discussed the literature in terms of specific SOFC component such as anode, cathode, electrolytes and so on. In contrast, herein the literatures have been reviewed in the context of two types of SOFC stack designs i.e. planar and tubular that have been immensely used to fabricate efficient SOFC devices. Furthermore, fundamental of SOFC operation and its typical I–V characteristics and SOFC designs are also discussed in detail. Furthermore, preparation techniques for planar and tubular SOFC are briefly described. Finally, some of the recent trends in SOFC technology along with challenges and future perspectives are presented in this review article.     

Energetic life cycle assessment of fuel cell powertrain systems and alternative fuels in Germany

By means of energetic life cycle assessment, innovative fuel cell (FC) powertrain systems and the respective fuels are examined and compared with conventional systems. The basis for this research is process chain analyses for the supply of conventional and alternative fuels at the point of consumption in Germany, e.g. compressed natural gas, methanol or hydrogen. To complete the integrated view, the use of these fuels in vehicles with internal combustion engines and FCs is examined. Within the scope of this study, special attention is paid to a system breakdown and energetic assessment of the FC powertrain. For the purpose of a full life cycle assessment, energy requirements and CO₂-emissions for the production, maintenance and disposal of the vehicles are included.     

Exergy flow and energy utilization of direct methanol fuel cells based on a mathematic model

An exergetic analysis model for direct methanol fuel cell (DMFC) is established in the present paper. Expressions of electrical, thermal and total exergetic efficiencies have been deduced with consideration of methanol crossover and over potential in operation. Furthermore, energy utilization of a DMFC system is quantitatively calculated and changes of electrical efficiency and thermal efficiency at various current density, methanol concentration, operating temperature, and cathode pressure have been investigated. Some suggestions of optimal operating conditions of direct methanol fuel cell based on our findings are put forward. Results show that the thermal energy generated in a DMFC takes up a significant amount of exergy in total energy and should be sufficiently used to obtain high total efficiency in a DMFC, high methanol crossover rate is the predominant cause of energy loss when the fuel cell operates at low current density, and total exergetic efficiency of a DMFC reaches its peak value at relatively high current density.     

Ten years of solar hydrogen demonstration project at Neunburg vorm Wald,Germany

Major system components of possible future energy supply based on hydrogen generated by utilizing (solar) energy unaccompanied by release of carbon dioxide are installed on an industrial scale at a demonstration facility located in Neunburg vorm Wald, Germany. Initial technical aspects of stepwise transition from present-day energy supply aligned primarily to fossil fuels are considered. Most of the plant subsystems constitute prototypes of innovative technologies. Among others, the facility comprises: photovoltaic solar generators, water electrolyzers, catalytic and advanced conventional heating boilers, a catalytically heated absorption-type refrigeration unit, fuel cell plants for stationary and mobile application, and an automated LH₂ filling station for test vehicles.Focal points of the investigations being carried out under the project are performance of the plant subsystems and their interaction under practical operating conditions. Analysis of the work is yielding a reliable database for updated assessment of the prospects and challenges of (solar) hydrogen technology.The present review (current to October 1997) concerns primarily the technology and operation of the facility with regard to the objectives and perspectives of the project. Results of the test programs are not reported in explicit detail; rather, they are communicated by integrating them into the more practical records of overall plant operation.     

Energy and exergy analyses of a hybrid system containing solid oxide and molten carbonate fuel cells,a gas turbine,and a compressed air energy storage unit

Design of a hybrid system composed of a solid oxide fuel cell (SOFC), molten carbonate fuel cell (MCFC), gas turbine (GT), and an advanced adiabatic compressed air energy storage (AA-CAES) based on only energy analysis could not completely identify optimal operating conditions. In this study, the energy and exergy analyses of the hybrid fuel cell system are performed to determine suitable working conditions for stable system operation with load flexibility. Pressure ratios of the compressors and energy charging ratios are varied to investigate their effects on the performance of the hybrid system. The hybrid fuel cell system is found to produce electricity up to 60% of the variation in demand. A GT pressure ratio of 2 provides agreeable conditions for efficient operation of the hybrid system. An AA-CAES pressure ratio of 15 and charging ratio of 0.9 assist in lengthening the discharging time during a high load demand based on an electricity variation of 50%.