Solid Oxide Fuel Cell Configurations Research Articles

Nanoparticle exsolutionviaelectrochemical switching in perovskite fibers for solid oxide fuel cell electrodes

Metal nanoparticles supported on powder and fiber perovskitesviaexsolution. The fiber shows a weight loss about 4.4 times higher than the powder sample. These have been applied in solid oxide fuel cell configuration.

Thermo-economic analysis of solid oxide fuel cell using human waste as a source of fuel

The production of fuel cell technology for commercial purposes is hindered by limited durability and cost. Hence, we focused on the thermo-economic analysis of solid oxide fuel cell (SOFC) that is fuelled with hydrogen produced from human waste to generate 200 kW power. This was achieved through computer simulation using Thermolib 5.4 version (a MATLAB/Simulink's software). Two configurations were adopted for biomass production and are based on gasification and slow pyrolysis. The results obtained revealed that producer gas from gasification and slow pyrolysis have a thermal efficiency of 82.2 % and 34.69 respectively. Lower heating value (LHV) of 113.14 kJ/mole and 466.37 kJ/mole accounted for the variation. Additional energy requirements of 571.50 kW for gasification and 353.04 kW for slow pyrolysis would be needed to achieve the set power output. Exergy analysis further showed that producer gas (slow pyrolysis) had the highest exergy input of 11848.86 kW and corresponding output of 11160.91 kW which was far higher than that of producer gas (gasification) with exergy input as 5,992.17 kW, and exergy output of 5698.44 kW. The difference was due to the presence of ethane which had the highest standard exergy of 1437.2 kJ/mole in addition to the methane content of the gas. The exergy efficiency indicated that auto-thermal reformer (ATR) had an efficiency of 99.71% and 99.6% for gasification and slow pyrolysis respectively. The SOFC from producer gas gasification had an efficiency of 57.59 % with the reformate stream having a mole fraction of 0.3543 and 0.0028 for hydrogen and carbon monoxide respectively whereas producer gas from slow pyrolysis had 72.50% exergy efficiency with mole fractions of 0.5194 of hydrogen and 0.1288 of carbon monoxide in the reformate. The cost analysis indicated that the total annual cost for producer gas from slow pyrolysis configuration was $190,380.70, which is higher than that of producer gas from gasification configuration by 52.66%. Exergy and economic performance favoured the choice of gasification configuration as the preferred route to produce hydrogen gas for Solid Oxide Fuel Cell configuration. We concluded that fuelling of Solid Oxide Fuel Cell with producer gas from human waste is viable, efficient, and highly economical.

Thermodynamic analysis of 100% system fuel utilization solid oxide fuel cell (SOFC) system fueled with ammonia

The system efficiency of solid oxide fuel cells (SOFCs) fueled with ammonia or pure hydrogen always underperforms compared to the SOFCs fueled with carbon-based fuels. Hence, improving the efficiency of SOFCs fueled with pure hydrogen or hydrogen carriers such as ammonia is required to promote hydrogen economy. This study deals with the thermodynamic analyses of SOFC with 100% system fuel utilization configuration achieved by a dead-end anode (DEA) loop. The results are compared with the conventional SOFC configuration with the afterburner setup. It is shown that the energy efficiency and exergy efficiency of ammonia-fueled recirculation system are 12.17% points and 11.39% points higher than the conventional system. Energy balance comparison shows that the reduction in heat loss through exhaust gas is one of the significant factors for improving the system efficiency. The improvement in the exergy efficiency of the recirculation system is attributed to the reduction in exergy destructions in air preheaters and the elimination of exergy destruction at the afterburner. In addition, a parametric analysis and artificial neural network– genetic algorithm (ANN-GA) based optimization are performed to understand the effects of stack fuel utilization, current density, stack operating temperature, radiation loss, the pressure ratio across the membrane, and species removal rate in anode off-gas on system efficiency. The system efficiency as high as 75% lower heating value (LHV) can be achieved by the DEA loop configuration with operating the system at lower stack fuel utilizations.

Flat-chip flame fuel cell operated on a catalytically enhanced porous media combustor

The flame fuel cell is a novel kind of fuel cell that directly combines a fuel-rich flame and solid oxide fuel cells together. Because of their simple setup, low cost, quick start-up and shut-down as well as no extra thermal management, flame fuel cells have great potential in micro-combined heat and power systems and portable applications. However, the conventional solid oxide fuel cell configurations including planar ones and tubular ones, may cause some problems when used in flame fuel cells such as thermal stress, secondary flame front, and difficulty for mass production. To solve these problems, a newly developed flat-chip solid oxide fuel cell is proposed to be used in the flame fuel cell in this study. Combining the merits of both planar and tubular solid oxide fuel cells, the flat-chip fuel cell is advantageous for its simple fabrication technology, good thermal shock resistance and feasibility to scale up. A flat-chip solid oxide fuel cell is fabricated and then integrated with a catalytically enhanced porous media combustor, demonstrating a novel flat-chip flame fuel cell system. The heating time for the flat-chip solid oxide fuel cell by the fuel-rich flame is less than 10 min from room temperature to 800 °C, with a temperature change rate of 5 °C/s in the first stage. The start-up time of the flat-chip flame fuel cell is less than 10 s. When the gas velocity is 6.0 cm/s and the equivalence ratio is 2.0, a peak power density of 179 mW/cm2 is obtained for a single cell. Although there exists a remarkable temperature gradient, a small current degradation of 0.01 A/h is observed after a constant-voltage discharging at 0.5 V for 8 hrs. In addition, the flat-chip solid oxide fuel cell can be further scaled up in dimension, resulting in higher fuel utilization of flame fuel cell.

Multidimensional Reversible Solid Oxide Fuel Cell Modeling for Embedded Applications

This paper presents a multiphysical modeling of a two-dimensional (2-D) reversible tubular solid oxide cell. The developed model can represent both a solid oxide electrolysis cell (SOEC) and solid oxide fuel cell (SOFC) operations. By taking into account of the electrochemical, fluidic, and thermal physical phenomena, the presented model can accurately describe the multiphysical effects inside a cell for both fuel cell and electrolysis cell operation under entire working range of cell current and temperature. In addition, an iterative solver is proposed which is used to solve the 2-D distribution of physical quantities along the tubular cell. The proposed model is suitable for embedded applications, such as real-time simulation or online diagnostic control. The reversible solid oxide cell model is then validated experimentally in both SOEC and SOFC configurations under different species partial pressures, operating temperatures, and current densities conditions.

Solid oxide fuel cell reactor analysis and optimisation through a novel multi-scale modelling strategy

The simulation of a solid oxide fuel cell (SOFC) that incorporates a detailed user-developed model was performed within the commercial flowsheet simulator Aspen Plus. It allows modification of the SOFC's governing equations, as well as the configuration of the cell's fuel-air flow pattern at the flowsheet level. Initially, the dynamic behaviour of single compartment of a cell was examined with a 0D model, which became the building block for more complex SOFC configurations. Secondly, a sensitivity analysis was performed at the channel (1D) scale for different flow patterns. Thirdly, the effect of fuel and air flow rates on the predominant distributed variables of a cell was tested on a 2D assembly. Finally, an optimisation study was carried out on the 2D cell, leading to a robust, optimal air distribution profile that minimises the internal temperature gradient. This work forms the foundation of future stack and system scale studies.

Configuration Development of Autothermal Solid Oxide Fuel Cell: A Review

Solid Oxide Fuel Cell (SOFC) is typically operated at high temperature. Both electricity and heat are generated during operation. Therefore, SOFC can be efficiently designed to integrate the endothermic reformer with the cell for optimizing heated utilization, as called autothermal operation. However, the mismatch between rate of exothermic electrochemical reaction and endothermic reforming reaction is easily resulted in material cracking of those integrated structure. In order to overcome the thermal mismatch limitation, various approaches for autothermal SOFC configurations have been widely developed; these configurations can be classified into 2 main groups including direct internal reforming (as called DIR-SOFC) and indirect internal reforming (as called IIR-SOFC) operations. This review focuses on the technological progress of these various configurations. In detail, computer simulation technique has been applied to study the thermal behavior inside the autothermal SOFC configurations using various primary hydrocarbon fuels. In addition, the advantage and disadvantage on thermal stress reduction of each configuration are also discussed.

Thermodynamic analysis of SOFC (solid oxide fuel cell)–Stirling hybrid plants using alternative fuels

A novel hybrid power system (∼10 kW) for an average family home is proposed. The system investigated contains a solid oxide fuel cell (SOFC) on top of a Stirling engine. The off-gases produced in the SOFC cycle are fed to a bottoming Stirling engine, at which additional power is generated. Simulations of the proposed system were conducted using different fuels, which should facilitate the use of a variety of fuels depending on availability. Here, the results for natural gas (NG), ammonia, di-methyl ether (DME), methanol and ethanol are presented and analyzed. The system behavior is further investigated by comparing the effects of key factors, such as the utilization factor and the operating conditions under which these fuels are used. Moreover, the effect of using a methanator on the plant efficiency is also studied. The combined system improves the overall electrical efficiency relative to that of a stand-alone Stirling engine or SOFC plant. For the combined SOFC and Stirling configuration, the overall power production was increased by approximately 10% compared to that of a stand-alone SOFC plant. System efficiencies of approximately 60% are achieved, which is remarkable for such small plant sizes. Additionally, heat is also produced to heat the family home when necessary.

ChemInform Abstract: Mathematical Modeling of Solid Oxide Fuel Cells: A Review

AbstractReview: 198 refs.

Technical and economic study of integrated system of solid oxide fuel cell, palladium membrane reactor, and CO 2 sorption enhancement unit

This paper deals with the integrated system of solid oxide fuel cell (SOFC), palladium membrane reactor (PMR), and CO 2 sorption enhancement (SE) unit. Three configurations of the SOFC systems fed by biogas are considered, i.e., PMR–SOFC, SE–PMR–SOFC, and SE–PMR–SOFC with a retentate gas recycling (SER–PMR–SOFC). The SOFC system equipped with a conventional reformer (CON–SOFC) is considered as a base case. The simulation results show that the capture of CO 2 in biogas before being fed to PMR (SE–PMR–SOFC) can improve H 2 recovery. The performance of SE–PMR–SOFC can be further enhanced by recycling retentate gas from PMR to CO 2 sorption enhancement unit (SER–PMR–SOFC). Compared to CON–SOFC, both SE–PMR–SOFC and SER–PMR–SOFC give higher power density and thus require smaller stack size (the stack size reduction of 1.55% and 8.27% are observed for SE–PMR–SOFC and SER–PMR–SOFC, respectively). The economic analysis is performed to identify the potential benefits of each SOFC configuration. The results indicate that SE–PMR–SOFC and SER–PMR–SOFC are not cost-effective systems compared with CON–SOFC; however, the capture of CO 2 in these SOFC systems offers an environmental benefit. High %total CO 2 capture and low cost of CO 2 capture are achieved under these SOFC systems.

Thermodynamic performance study of biomass gasification, solid oxide fuel cell and micro gas turbine hybrid systems

A system level modelling study of three combined heat and power systems based on biomass gasification is presented. Product gas is converted in a micro gas turbine (MGT) in the first system, in a solid oxide fuel cell (SOFC) in the second system and in a combined SOFC–MGT arrangement in the third system. An electrochemical model of the SOFC has been developed and calibrated against published data from Topsoe Fuel Cells A/S and the Risø National Laboratory. The modelled gasifier is based on an up scaled version (∼500 kW th) of the demonstrated low tar gasifier, Viking, situated at the Technical University of Denmark. The SOFC converts the syngas more efficiently than the MGT, which is reflected by the energetic electrical efficiency of the gasifier and MGT system in opposition to the gasifier and SOFC configuration – η el = 28.1% versus η el = 36.4%. By combining the SOFC and MGT, the unconverted syngas from the SOFC is utilised in the MGT to produce more power and the SOFC is pressurised, which improves the efficiency to as much as η el = 50.3%. Variation of the different operating conditions reveals an optimum for the chosen pressure ratio with respect to the resulting electrical efficiency. Furthermore, the SOFC operating temperature should be kept high and the cathode temperature gradient maximised.

Modeling of thermal stresses and lifetime prediction of planar solid oxide fuel cell under thermal cycling conditions

A typical operating temperature of a solid oxide fuel cell (SOFC) is above 600 °C, which leads to severe thermal stresses caused by the difference in material mechanical properties during thermal cycling. Interfacial shear stress and peeling stress are the two types of thermal stresses that can cause the mechanical failure of the SOFC. Two commonly used SOFC configurations (electrolyte-supported and anode-supported) were considered for this study. The paper developed a mathematical model to estimate the thermal stresses and to predict the lifetime of the cell (Ni/8YSZ–YSZ–LSM). Due to the mismatch of the material mechanical properties of the cell layers, a crack nucleation induced by thermal stresses can be predicted by the crack damage growth rate and the initial damage distribution in the interfacial layer for each thermal cycle. It was found that the interfacial shear stress and peeling stress were more concentrated near the electrode free edge areas. The number of cycles needed for failure decreased with the increase in the porosity of electrode. The number of cycle for failure decreased with increase in electrolyte thickness for both anode- and electrolyte-supported SOFC. The model provides insight into the distribution of interfacial shear stress and peeling stress and can also predict damage evolution in a localized damage area in different SOFC configurations.

Modeling of solid oxide fuel cells for dynamic simulations of integrated systems

Solid oxide fuel cell (SOFC) stacks are at the core of complex and efficient energy conversion systems for distributed power generation. Such systems are currently in various stages of development. These power plants of the future feature complicated configurations, because the fuel cell demands for a complex balance of plant. Moreover, proposed SOFC-based systems for stationary applications are often connected to additional components and subsystems, such as a gasifier with its gas-cleaning section, a gas turbine, and a heat recovery system for thermal cogeneration or additional power production. For the simplest SOFC configurations, and more so for complex integrated systems, the dynamic operation of the power plant is challenging, especially because the fluctuating electrical load of distributed energy systems demand for reliable transient operation. Issues related to dynamic operation must be studied in the early design stage and simulation results can be used to optimize the system configuration, taking into account transient behavior. This paper presents the development and the validation of a non-linear dynamic lumped-parameters model of a SOFC stack suitable for integration into models of complex power plants. Particular emphasis is placed on the systematic approach to model development. The model is implemented using the open-source Modelica language, which allows for a high degree of flexibility and modularity, the main features of the model herein presented. The SOFC stack model will be incorporated into ThermoPower, a freely distributed library of reusable software components for the modeling of thermo-hydraulic processes and power plants.

Thermal-stress analyses of an operating planar solid oxide fuel cell with the bonded compliant seal design

A thermo-electrochemical-structure model has been proposed in the present work to investigate the thermal behavior and the thermal-stress of a solid oxide fuel cell (SOFC) with the bonded compliant seal (BCS) design. A comprehensive numerical simulation model, employing the finite-volume approach, has been developed for the three-dimensional, multi-component, electrochemically, and chemically reacting flow of a single planar SOFC unit cell. The cell temperature predicted by the finite-volume model is imported to a finite-element model to estimate the thermal-stress with the BCS design. Effects of the cell voltage and the temperature non-uniformity on the thermal-stress of the SOFC have been investigated. Numerical results obtained from the present study show that an assumed isothermal SOFC configuration leads to an underestimate of the thermal-stress by 28% for the cell and 37% for the metal frame in comparison with those in practical operating conditions. Two factors are identified to be responsible for the thermal-stress. One is the residual stress, and the other is the temperature gradient. The dominant factor for the thermal-stress depends on the location and the cell voltage.

Novel SOFC Tubular Design Configurations

A novel tubular solid oxide fuel cell configuration with high volumetric power packing density is discussed. With good thermal shock resistance, high mechanical strength, easy sealing, and high volume manufacturing ability, tubular SOFC designs offer many advantages over planar designs. One shortcoming is the lower volumetric power packing density. As a result, for a given stack power, planar SOFC stacks will be smaller than tubular SOFC stacks. For a tubular design, tube size is one of the critical parameters to be determined. Small diameter tubes, less than 3 mm for example, will cause assembling problems due to the feasible nature of the tubes. The power of each cell is directly related to the cell active area. Obviously the bigger the tube, the larger the surface area results in more cell power. However, increasing the size in single tubular fuel cell will lead to lower power packing density and lower fuel utilization. Multiple Tubular Fuel Cell design (MTFC) is a potential solution. MTFC design arranges a group of different sized tubular cells together as a basic module. One can assemble these basic modules to make a stack with high volumetric packing density. Comparing with a single tube design, the MTFC design increases volumetric packing power density by over 40% for a 2-tube assembly, over 80% for a 3-tube assembly, and 116% for a 5-tube assembly. MTFC design also increases the fuel utilization rate and the stack reliability. The module can be standardized and controlled individually. If one individual module fails, it can be switched off and replaced. This concept can be applied to any tubular design, for example electrolyte-, anode-, or cathode-supported designs. This concept of using MTFC design to increase volumetric power densities can also be extended to other type fuel cells.

Synthesis and properties of dense nickel and cobalt zirconia cermet anodes for solid oxide fuel cells

Porous Ni/Zirconia cermets have been traditionally used as anodes in solid oxide fuel cell configurations. They show excellent catalytic activity towards hydrogen oxidation as well as a number of other attributes. However, they are prone to sintering during long term operation, thus causing a drop in the efficiency of the cell. This paper describes the fabrication and properties of a dense cermet which, we suggest, may act as an intermediate layer between the electrolyte and the porous anode and possibly reduce anode degradation. Co and Ni based cermet systems were investigated and a 30 vol % Co/zirconia system could be fabricated with less than 20% porosity after being sintered at 1300°C.

Properties of Partially Stabilized Zirconia Fuel Cell

not Available.