Internal Reforming Reactions Research Articles

GradientFunctionalLayerAnodeforCarbonate-SuperstructuredSolidFuelCellswithEthaneFuel.

Carbonate-superstructured solid fuel cells (CSSFCs) are an emerging type of fuel cells with high flexibility of fuels. However, using ethane fuel for solid fuel cells is a great challenge due to serious degradation of their anodes. Herein, this critical issue is solved by creating a novel gradient functional layer anode for CSSFCs. First, a finer-scale anode with a larger surface area is demonstrated to provide more active sites for the internal reforming reaction of ethane, achieving a 60% higher ethane conversion rate and 40% lower polarization resistance than conventional anodes. Second, incorporating a gradient functional layer into the anode results in an additional 50% enhancement in the peak power density of CSSFCs to a record high value (up to 241mW cm-2) with dry ethane fuel at a low temperature of 550°C, which is even comparable to the power density of conventional solid oxide fuel cellsabove 700°C. Furthermore, the CSSFC with the gradient anode exhibits excellent durability for over 200 h. This finding provides a new strategy to develop efficient anodes for hydrocarbon fuels.

Numerical study on effects of CH4–CO2 internal reforming on electrochemical performance and carbon deposition of solid oxide fuel cell

CH4–CO2 fueled solid oxide fuel cells (SOFCs) are the high-efficiency and low-carbon power generation technology. However, carbon deposition severely hinders its application. Here, the numerical model considering the complex anode CH4 internal reforming reactions, H2 electrochemical reaction, gas diffusion and charge transfer of SOFC using CH4–CO2 fuel has been established. The CH4–CO2 internal reforming and electrochemical reactions of SOFC under different CO2/CH4 ratios and temperatures are studied to reveal the optimal operating conditions. The distributions of different reaction rates, gas components and carbon deposition activity at the anode are analyzed. The results show that the increase of CO2 concentration can decrease the carbon activity but also cause the decrease of electrochemical performance. It is found that the good comprehensive performances including power density, carbon activity and methane conversion rate can be achieved under the CO2/CH4 molar ratio of 1. The thermodynamic calculation of three different methane reforming modes shows that CH4–CO2 reforming leads to the greatest carbon deposition risk compared with CH4–H2O and CH4–O2 reforming, implying the importance of anti-carbon for CH4–CO2 fueled SOFC.

Nanoengineering modification of Ni-YSZ anode using in-situ solvothermal process in solid oxide fuel cells with internally reformed fuel

The conventional Ni-Y0.16Zr0.84O1.92 anode in solid oxide fuel cells fueled with hydrocarbon fuels is prone to suffer from carbon deposition. In this work, we employed an in-situ solvothermal method to decorate the Ni-Y0.16Zr0.84O1.92 anode with Gd0.1Ce0.9O1.95-δ nanoparticles to improve its resistance to carbon deposition and thus improve the electrochemical performance of the cell. This method generates small Gd0.1Ce0.9O1.95-δ particles and at the same time does not block the gas diffusion channels. The Gd0.1Ce0.9O1.95-δ-decorated anode showed enhanced long-term stability in methane with no significant performance degradation after 700 at 750 °C, whereas an untreated Ni-Y0.16Zr0.84O1.92 anode only worked for less than 8 h under the same conditions. The addition of Gd0.1Ce0.9O1.95-δ nanoparticles was found to enhance internal reforming reactions of methane by the distribution of relaxation times technique. This work demonstrated that in-situ solvothermal modification strategy can provide anodes with excellent carbon deposition resistance.

Numerical Investigation of Heat/Flow Transfer and Thermal Stress in an Anode-Supported Planar SOFC

To elucidate the thermofluid reacting environment and thermal stress inside a solid oxide fuel cell (SOFC), a three-dimensional SOFC model is implemented by using the finite element method in the commercial software COMSOL Multiphysics®, which contains both a geometric model of the full-cell structure and a mathematical model. The mathematical model describes heat and mass transfer, electrochemical reactions, internal reforming reactions, and mechanical behaviors that occur within the cell. A parameter study is performed focusing on the inlet fuel composition, where humidified hydrogen and methane syngas (the steam-to-carbon ratio is 3) as well as the local distribution of temperature, velocity, gas concentrations, and thermal stress are predicted and presented. The simulated results show that the fuel inlet composition has a significant effect on the temperature and gas concentration distributions. The high-temperature zone of the hydrogen-fueled SOFC is located at the central part of units 5, 6, and 7, and the maximum value is about 44 K higher than that of methane syngas-fueled SOFC. The methane-reforming and electrochemical reactions in the anode active layer result in a significant concentration gradient between the anode support layer and the active layer of the methane syngas-fueled SOFC. It is also found that the thermal stress distributions of different fuel inlet compositions are rather different. The maximum stress variation gradient between electrode layers of hydrogen SOFC is larger (44.2 MPa) than that of methanol syngas SOFC (14.1 MPa), but the remaining components have a more uniform stress distribution. In addition, the electrode layer of each fuel SOFC produces a significant stress gradient in the y-axis direction, and stress extremes appear in the corner regions where adjacent assembly components are in contact.

Effect of electrochemical reaction on steam adsorption during methane reforming on a Ni-GDC anode

The influence of steam on the internal reforming reaction in solid oxide fuel cells is under debate based on previously reported results. Therefore, appropriate kinetic models that accurately describe the methane reforming behaviour in solid oxide fuel cells under various operating conditions are required. The objective of this study is to find the appropriate kinetic model to describe the effect of current density on steam adsorption behaviour. The Langmuir-Hinshelwood model considers the associative methane adsorption and the dissociative steam adsorption. The formation of catalyst-hydroxide complexes is directly influenced by the steam concentration and current drawn via the non-faradaic electrochemical modification of the catalysis effect. The steam adsorption constant appeared to significantly drop when a current was produced. Of the current densities investigated, the models seemed to provide a more accurate description of reforming rates at a 600 A/m2 current density relative to open-circuit and 1000 A/m2 conditions. The models are used to predict the reaction rate in the fuel cell channel where the in-situ measurement is not practical.

Simulation of a Flat-Tube Solid Oxide Fuel Cell with Symmetric Double-Sided Cathode Considering Different Fuel Compositions

Due to its high operating temperature, solid oxide fuel cells (SOFCs) can use a variant of hydrocarbon fuels. Then the methane steam reforming (MSR) and water gas shift (WGS) reactions are active within the anode during the energy conversion process. On one hand, the air velocity controls the heat within a SOFC, e.g., through control of heat convection, on the other hand, the internal endothermal reactions also have an impact on the heat balance through different fuel composition. It should be noted that the carbon deposition greatly reduces the catalytic property of the anode material.The reforming process can be synthetized by the following electrochemical reactions:2CO ↔ C(s)+ CO2 (1)CO+H2 ↔ C(s)+H2O (2)C n H2n+2 ↔ nC(s)+(n+1)H2 (3)Thus, it is important to investigate the effect of internal reforming reactions of different fuel composition on cell performance.Numerical simulations can reduce the cost of experimental design and achieve desirable accuracy. A flat-tube SOFC with a symmetric double-sided cathode is built using the commercial software COMSOL Multiphysics®. Our model includes the simulation of the ion, electron, momentum, heat, and mass transport phenomena. Also, MSR and WGS reactions are considered in the model. The geometric representation of the flat-tube SOFC anode is shown in Figure 1. Figure 1

Nickel–molybdenum catalysts for combined solid oxide fuel cell internal steam and dry reforming

A series of supported Ni-Mo catalysts were synthesised through a deposition-co-precipitation method (DcP) and investigated in combined steam and dry reforming. The prepared Ni-Mo catalysts supported by Yttria-Stabilised Zirconia (YSZ), Gadolinium-Doped Ceria (GDC) and Ceria Stabilised Zirconia (CSZ) with improved carbon tolerance have the potential to be used as anodes in Solid Oxide Fuel Cells (SOFC). These catalysts will be applied in the anode supporting layer where most of the internal reforming reaction takes place. The catalysts were compared to conventional reforming catalysts, where Al2O3 and TiO2 supports are typical for reforming catalysts. The catalytic performance of the Ni-Mo catalysts according to the support materials was observed in the sequence Al2O3 > YSZ > TiO2 > CSZ > GDC. Formation of Mo2C improved catalytic activity towards the steam reforming reaction. Increasing the Mo loading to Ni catalyst improved the coke resistance properties; however, it reduced the catalytic activity.

Measurement of transient temperature distribution behavior of a planar solid oxide fuel cell: Effect of instantaneous switching of power generation and direct internal reforming

The transient temperature distribution behavior of a planar, co-flow type anode supported solid oxide fuel cell is experimentally investigated under furnace temperatures of 670 °C, 720 °C, and 770 °C. An in-situ measurement is conducted by using a specially designed cell holder and a high-resolution infrared camera. The single and combined effects of electrochemical reactions and direct internal reforming (DIR) reactions are examined. The transient response of the cell temperature profile to a sudden change in the current density or reforming reaction rate is obtained. The results show the clear increase/decrease in the local temperature owing to the exothermic electrochemical reaction/endothermic reforming reaction. The analysis of the time constant shows that the response of the temperature distribution to a sudden change in the current density is faster than that to a change in the fuel gas composition. The time constant is smaller in the upstream region, indicating that the new steady state is first achieved near the flow inlet and gradually propagates downstream. The maximum temperature gradient along the operating cell is found to be lower under the DIR condition than under the non-DIR condition regardless of the furnace temperature.

Three-dimensional modeling of flow field optimization for co-electrolysis solid oxide electrolysis cell

Flow field optimization has an evident effect on the performance improvement of solid oxide electrolysis cells (SOEC). In this study, a novel flow field based on porous material is proposed to improve the electrolysis efficiency of SOEC. The internal reforming reactions, multi-component diffusion process and co-electrolysis of H2O and CO2 are numerically studied by establishing a three-dimensional model. The results show that the novel design with porous material instead of conventional rib-channel configuration can lower the electrolysis voltage demand up to 0.062 V. To understand the mechanisms for the improved performance of the new flow field design, the multi-physical field distributions and thermal process are investigated. It is found that the new flow field design can ensure more uniform distribution of species concentration and reduce the maximum temperature difference by 3.81 K at 1.5 A cm−2. The thermal analysis indicates that the ohmic loss is the most important factor for temperature distribution. In addition, the structure and configuration of porous flow field are further optimized to obtain a better performance.

Structure optimization and thermal field analysis of biogas derived methane fueled Solid Oxide Fuel Cell

The suitability for using various gaseous fuels makes the Solid Oxide Fuel Cell (SOFC) the most promising heat-electricity cogeneration device. Thermal field distribution of SOFC directly determines whether the cell is operating in sufficient catalytic activity and weakened by thermal stress. For biogas derived methane fueled SOFC, the internal reforming reactions can cause the inhomogeneous temperature distribution. So it is crucial to optimize the thermal field to achieve optimal cell operation state. In this paper, a 3D muti-physics model is developed to study the improvements of a new cathode flow field structure. When adopting new cathode structure, the power density increases by over 11%, and the maximum temperature gradient can be evidently reduced.

Study on Coal Syngas Applicability to SOFC Module

Solid oxide fuel cells (SOFCs) are expected to be applied to Integrated Coal Gasification Fuel Cell Combined Cycle (IGFC). However, most SOFC modules are designed with natural gas as fuel that means SOFC modules are cooled using the internal reforming reaction (endothermic reaction) of natural gas. In this research, a modified SOFC module manufactured by Mitsubishi Hitachi Power Systems, Ltd. (MHPS) was installed and power generation performance with assumed gas was verified. As a result, it was confirmed that the output of SOFC module was reduced by changing the fuel from natural gas to assumed coal gas. On the other hand, improvement of SOFC performance was possible by changing the operating conditions. In this paper, operation test results are introduced.

Modelling of effect of pressure on co-electrolysis of water and carbon dioxide in solid oxide electrolysis cell

As a promising renewable energy storage device, the solid oxide electrolysis cell (SOEC) attracts wide attention in the world. In this study, the effect of operating pressure on the co-electrolysis of water and carbon dioxide in SOEC is investigated by a three-dimensional model, in which the reversible water gas shift reaction and direct internal reforming reaction are considered. After comparison with experimental data, the influence of operating pressure on the polarization loss, electrolysis reaction rate, chemical reaction rate and thermal-neutral voltage is also studied in detail. The results show that the cell voltage increases below 8 atm and then decreases with the operating pressure. In addition, the effects of thermal insulation boundary condition, gas flow configuration and gas utilization rate under different operating pressures are also discussed. It is found that the reverse direct internal reforming reaction is activated under the operating pressure higher than 3 atm. Moreover, compared to co-flow arrangement, counter-flow arrangement is more helpful to cell performance improvement at high current densities.

Three-dimensional modeling of pressure effect on operating characteristics and performance of solid oxide fuel cell

A three-dimensional (3-D) model for planar, anode-supported, solid oxide fuel cell (SOFC) is developed to investigate the effect of operating pressure on cell characteristics. The results show that the elevated operating pressure can improve cell performance by increasing open circuit voltage and reducing activation overpotential, and enhance the electrochemical reaction in the vicinity of electrolyte. Besides, the high pressure can also change the distributions of species and internal reforming reactions. Compared to the case using syngas as fuel, the operating pressure has more significant effects on temperature gradient along flow direction when partly pre-reformed gas is supplied. In addition, efficient control of cell temperature could be achieved by decreasing fuel utilization in the case of partly pre-reformed gas, but this is achieved at the expense of cell efficiency, especially under high pressure condition. Another way to reduce the temperature gradient is to adopt higher air ratio. Moreover, when partly pre-reformed gas is used, the counter-flow configuration has a better performance due to the higher overall temperature.

Deactivation of SiO2 supported Ni catalysts by structural change in the direct internal reforming reaction of molten carbonate fuel cell

A direct internal reforming (DIR) reaction for a molten carbonate fuel cell (MCFC) is carried out using SiO2 supported catalysts, which are known to be a highly stable in catalytic reactions. The SiO2 supported Ni catalysts rapidly deactivate in DIR-MCFC. To elucidate the mechanism of the catalyst deactivation, various characteristic analyses (XRD, BET, H2-chemisorption, FT-IR, and SEM) of calcined and used catalysts are employed. The co-existence of H2O and K causes the formation of the non-active nickel oxide and silica hydrate resulting in the significant decrease of Ni dispersion and BET surface area.

Experimental and Detailed Kinetic Modeling Study of Carbon Deposition on Ni/YSZ Anode in SOFC

The nickel/yttria-stabilized zirconia (Ni/YSZ) has widely used as an anode for solid oxide fuel cells (SOFCs). The high operation temperature allows an SOFC to operate on a wide range of fuels, including hydrocarbons and coal syngas. Direct internal reforming reactions inside SOFC porous anodes enable the hydrocarbon fuel and steam into H2 and CO. The internal reforming fuel cells eliminate the requirement for a separate fuel reformer, leading to more efficient system. Meanwhile, Ni is also a catalyst for carbon deposition reactions such as methane cracking. The deposited carbon deactivates the Ni catalyst and causes rapid cell degradation. Although the high steam/carbon ratio is able to suppress carbon formation, it lowers the electrical efficiency by steam dilution of the fuel. Thus, an optimum steam/carbon ratio results in high performance of SOFC. This study aims to investigate mechanisms of carbon deposition on Ni/YSZ anode experimentally and numerically. First, the carbon deposition on Ni/YSZ was observed with SEM/EDX. Then, carbon deposition pathways on Ni surface were studied by detailed reaction kinetics. Moreover, the impact of steam carbon ratio on carbon deposition was investigated. An electrolyte-supported button cell was used. The disk-type electrolyte was composed of YSZ (8 mol% Y2O3-stabilized ZrO2). The diameter and thickness of the cell were 20 mm and 300 mm, respectively. To manufacture the anode, a mixture of NiO/YSZ powder, ethyl cellulose, α-terpineol, a dispersant and a plasticizer was prepared and coated on one side of the disk (Ni:YSZ = 50:50 vol%). The disk was dried at 90 oC for 12 h and sintered at a temperature of 1300 oC. The fabricated cell was put into a quartz reactor. The temperature near the cell was measured by K-type thermocouple. The cell was heated in the reactor to 900 oC by an electric furnace. CH4 and Ar were supplied to the cell at 10 and 90 ml/min, respectively. The mixture gas impinged on the cell. During the experiment, H2 concentration in off-gas from the reactor was measured with GC. Before the cell was pulled out from the quartz reactor for ex-situ observation, the gas line was switched from CH4/Ar to Ar, and the reactor was rapidly cooled for reaction quench. Then, the carbon deposition on the cell was performed by SEM-EDX and off-gas analysis. The carbon was supposed to form on Ni surface. Thus, the one-dimensional stagnation flow model in which CH4/Ar flow impinged on the Ni plate like experimental setup was used in the calculation. Catalytic heterogeneous reactions were modeled by elemental step based reaction mechanisms developed by Maier et al. (Top. Catal., 54 (2011) 845-858). The 42 surface reactions involving 12 surface-adsorbed species were used. The transient surface coverage of carbon was calculated, and the carbon formation pathways were computationally studied. As a result, the amount of carbon was increased as time proceeded in the experiment. The amount of deposited carbon measured with the balance corresponded to that estimated from H2 concentration, assuming that the carbon was formed through CH4 decomposition (CH4 → C + 2 H2). It was shown that the mass was well balanced in the experimental system. SEM-EDX analysis showed that carbon was deposited on not YSZ but Ni surface, indicating Ni acted as catalyst for carbon deposition as reported by previous studies. 20 min after CH4/Ar was supplied, the Ni/YSZ layer started to expand. A swelling ratio based on the initial cell thickness became over 100 % after 60 min. SEM observation showed that the porous anode structure was destroyed by the carbon growth. In fact, the recovery of the anode structure was difficult once the anode was expanded even if the carbon was removed by reforming. Calculation showed that the surface coverage of carbon became over 0.9 within 10 sec when CH4/Ar was supplied to Ni substrate at the same condition as the experiment. Carbon was formed on the surface subsequent to CH4 adsorption on Ni surface and dissociation reactions. CH4 adsorption reaction on Ni surface showed a high sensitivity against the carbon formation. Calculation also showed that the carbon was not formed when S/C (steam carbon ratio) was less than 1.0 where the carbon was formed in equilibrium condition, indicating kinetics of surface reaction played an important role in the carbon deposition than equilibrium.

Minimizing the Influence of Experimental Uncertainty for Delivered Methane/Steam Reforming Kinetic Equation by the Optimized Design of Experimentation

One of the important issues in the future development of Solid Oxide Fuel Cells (SOFC) is increasing the fuel flexibility of the commercially available units. In order to provide the accurate models for SOFC coupled with internal indirect reformer or with direct internal reforming reactions, it is necessary to provide the reliable description of the reaction kinetic of fuel reforming process. This research focuses on the methane/steam reforming process and method to develop effective experimental-calculation procedure to deliver the reliable kinetic reaction rate expression. The experimental studies were conducted on the NiO:YSZ (60:40vol%) catalyst, one of the most typical materials, for Solid Oxide Fuel Cell anodes. The experimental conditions included various temperatures, methane flow, steam-to-carbon ratios and nitrogen-to-carbon ratios, which defines each of the measurement points. The goal of this study was to decrease the number of necessary experimental measurements for the calculations of the empirical parameters defining the kinetic of methane/steam reforming reaction. By the analysis with the Orthogonal Least Squares Method and an analysis of a-posteriori covariance matrix, the experimentation process has been optimized. The proposed systematic approach was applied to evaluate the minimal number of measurements required to achieve the assumed accuracy of final solution and to reveal the influence of distribution of experimental condition for the quality of final reaction kinetic equation. It was proved that the number of experimental measurements can be reduced without significant deterioration in the quality of solution, if the dismissed measurements are properly chosen. In the paper the correlation between design experimental condition and quality of delivered model for the methane/steam reforming reaction is discussed. The proposed deliberation can be extended and provide useful strategy for the design of experimental procedures for the estimation of empirical reaction kinetic for various catalytic materials.

CFD Systems Level Modeling of a Protonic Ceramic Fuel Cell

There is a critical need for intermediate-temperature fuel cells that offer low-cost, distributed generation both at the system and device levels. Current development work at the Colorado School of Mines is being carried out for a mixed proton and oxygen-ion-conducting electrolyte that enables fuel-cell operation at temperatures less than 500°C. By using a proton- and oxygen-ion-conducting electrolyte, the fuel cell stack is able to reduce coking which clogs anodes with carbon deposits and enhance the process of turning hydrocarbon fuels into hydrogen. Today's solid-oxide fuel cells (SOFCs) are based on oxygen-ion conducting electrolytes and operate at high temperatures. Advanced mixed proton- and oxygen-ion-conducting fuel cells operate at lower temperatures, and have the capacity to utilize hydrogen, ethanol, methanol, or methane fuels. Additionally, an advanced single-step sintering process has been developed to reduce manufacturing costs of these protonic-ceramic fuel cells (PCFC). “Solid-state reactive sintering” reduces the number of manufacturing steps from 15 to 3, drastically decreasing costs. Understanding the systems-level behavior of the PCFC is critical to enable its emergence as a roll-out technology. The team at Calif. State Polytechnic Univ. at Pomona is performing numerical modeling of the PCFC system. The goal of this poster is to present results of Computational Fluid Dynamic (CFD) systems level modeling of a typical PCFC stack having a cylindrical shape factor. The configuration is modeled using commercial CFD software which can easily be benchmarked using experimental data. The flow is H2 on anode side and air on the cathode side. Flow rates are on the order of 100 sccm for each side. The interconnect between each cell is made of ferritic stainless steel (70% Fe, 27% Cr, 1% Y2O3). The operation of a PCFC is fundamentally different than SOFCs due to their ability to conduct protons as well as oxygen ions across a dense ceramic electrolyte. Two global electrochemical reactions are needed since the material is capable of conducting two charged defects. One global reaction is the result of proton conduction across the electrolyte, and the other is the result of oxygen-ion transport across the electrolyte. Similar to SOFCs, heterogeneous internal reforming of hydrocarbons such as methane and water-gas-shift reactions still occur on the nickel phase of the anode. However, since minimal water is generated in the anode from the electrochemical reactions, the reforming reactions must be supplied with an external water source, such as an external waste heat recovery boiler or via anode gas recycle. Additionally, the low temperature operation tends to shift the equilibrium composition of the fuel species toward higher methane content (i.e., lower conversion of internal reforming reaction) where hydrogen partial pressures in the anode will be limited by thermodynamics. The difference in operating temperatures and the removal of hydrogen from the anode via electrochemical oxidation can also influence the optimal steam-to-carbon ratio (S/C) required to avoid solid carbon deposition when compared to SOFCs. The above-described electromechanical kinetics are incorporated into the systems-level CFD model of the PCFC presented in this poster. Results for CFD based Multi-physics of the electro-mechanical PCFC behavior for mole fraction vs. temperature, fuel utilization vs. temperature, voltage potential vs. current density, and power density vs. current density are presented in the poster. Figure 1

Model-based evaluation of an integrated autothermal biomass gasification and solid oxide fuel cell combined heat and power system

Numerical analysis of combined heat and power plant consisting of a solid oxide fuel cell and autothermal gasification system has been made for several cases of different composition of fuel relevant to air and steam blown biomass gasification process. Wet wood is fed to the fixed-bed downdraft gasifier and gaseous fuel is produced then after gas cleaning and conditioning can be used in solid oxide fuel cells. The integrated plant is investigated by thermodynamic modeling combining a one-dimensional model of direct internal intermediate planar type solid oxide fuel cell which allows monitoring the temperature gradients along the cell length in different operating conditions and a zero-dimensional autothermal gasifier. The solid oxide fuel cell mathematical model is developed based on gas species mass balances, energy balance, and an electrochemical model beside the kinetics describing internal reforming and water-gas shift reactions. Such a model can be integrated with adiabatic gasification modeling which includes atom balance conservation for assumed gas species and a modified thermodynamic equilibrium analysis. Both gasifier and solid oxide fuel cell models are verified against experimental and previous numerical data available in the literature. Two main parameters, namely modified equivalence ratio and air-to-steam ratio are investigated and the most important cycle parameters such as power, electric and combined heat and power efficiencies, temperature gradients along the cell length, and mole fractions of gaseous species of the produced fuel are analyzed. It has been revealed that any increase in air-to-steam ratio at fixed modified equivalence ratio leads to penalty on cold gas efficiency of the gasifier and both solid oxide fuel cell and combined heat and power plant electric efficiencies. Increased air-to-steam ratio at constant modified equivalence ratio produces a mixture with lower low heating value, higher steam-to-carbon ratio, rich in CO and lower in CH4 content. Under this condition the operating temperature of the cycle and solid oxide fuel cell increases and consequently improves the operating voltage of the cell and combined heat and power efficiency of the plant. On the other hand, results show that gasification with increased modified equivalence ratio at constant air-to-steam ratio produces mixtures richer in CH4 and CO, poorer in H2 with higher low heating value and cold gas efficiency, and lower steam-to-carbon ratio. Such condition improves the electric efficiency of the solid oxide fuel cell and the integrated plant, but the combined heat and power efficiency of the cycle decreases due to decreased operating temperature of the solid oxide fuel cell and the cycle.

Optimization of manifold design for 1 kW-class flat-tubular solid oxide fuel cell stack operating on reformed natural gas

Abstract This study focuses on optimizing the manifold design for a 1 kW-class flat-tubular solid oxide fuel cell stack by performing extensive three-dimensional numerical simulations on numerous manifold designs. The stack flow uniformity and the standard flow deviation indexes are implemented to characterize the flow distributions in the stack and among the channels of FT-SOFC's, respectively. The results of the CFD calculations demonstrate that the remodeled manifold without diffuser inlets and 6 mm diffuser front is the best among investigated designs with uniformity index of 0.996 and maximum standard flow deviation of 0.423%. To understand the effect of manifold design on the performance of stack, both generic and developed manifold designs are investigated by applying electrochemical and internal reforming reactions modeling. The simulation results of the stack with generic manifold are validated using experimental data and then validated models are adopted to simulate the stack with the developed manifold design. The results reveal that the stack with developed manifold design achieves more uniform distribution of species, temperature, and current density with comparatively lower system pressure drop. In addition, the results also showed ∼8% increase in the maximum output power due to the implementation of uniform fuel velocity distributions in the cells.

Three-dimensional numerical and experimental investigation of an industrial-sized SOFC fueled by diesel reformat – Part II: Detailed reforming chemistry and carbon deposition analysis

As an important energy source, liquid diesel can be reformed in order to be used in high temperature solid oxide fuel cells (SOFCs) cleanly and efficiently. However, a big challenge of using carbon containing fuels, such as diesel reformat, is carbon deposition on the porous Ni/YSZ-anode structure caused by internal reforming reactions. In this work a planar industrial-sized 100 × 100 mm2 anode supported SOFC fueled with synthetic diesel reformat was numerically and experimentally investigated, in order to predict carbon depositions in the porous anode substrate. Gas phase as well as detailed wall-surface reactions were scrutinized in order to evaluate reforming mechanisms available in literature. Implementation and simulation was done by one single 3D CFD simulation tool, since such a comparison is missing in the scientific community. It was shown that global reforming mechanisms are capable of correctly predicting the occurring gas phase reactions, but only provide indicators for the thermodynamic equilibria of considered carbon formation pathways. Detailed information about surface adsorbed carbon can only be determined by a heterogeneous reaction mechanism. Elementary carbon was shown to be permanently adsorbed onto the catalytic active sites in the anode by the conducted steady state simulations. The investigations showed that the inlet region of the porous anodic structure is especially susceptible to coking. Simulation results were validated with in-house experimentally determined data. High cell current densities were reached during the single cell experiments, which determine good electrical contacting as well as electrochemical performance and therefore represent reliable validation data.