Solid Oxide Fuel Cell Model Research Articles

The performance of thermal based modified solid oxide fuel cell (SOFC) model under different DC load conditions

In this paper, a thermal-baseddynamic model of a Solid Oxide Fuel Cell under different direct current loadconditions is improved by using our previous developed fuel cell model, whichincludes ohmic, activation and concentration voltage losses, thermal dynamics,and methanol reformer. The modified SolidOxide Fuel Cell model covers restriction of fuel utilization factor. Hence, the voltage and power of the Solid OxideFuel Cell stack are limited to avoid excessive fuel flow and temperature. The SolidOxide Fuel Cell model is developed in a Matlab/Simulink environment and testedfor different direct current load conditions, which are step, ramp, random and stair-caseloads. The simulation results show that the modified Solid Oxide Fuel Cellmodel can be used to precisely follow the direct current load variations. Thisis true because reaching thesteady state of the system takes a shorter time for the ramp load, and takes a longertime for the step load. Besides, the limitation of the fuel utilizationfactor can be seen more clearly from the system with the stair-case load.

Three-Dimensional Computational Fluid Dynamics Modelling for a Planar Solid Oxide Fuel Cell of a New Design

The aim of the work is to investigate the electrochemical processes of a planar Solid Oxide Fuel Cell (SOFC) and to estimate the performance of a novel SOFC design. The design involves cross-flow bipolar plates. Flow channels were designed to connect pairs of four orifices at the corners of the SOFC plates. Each of the bipolar plates has an air channel system on one side and a fuel channel system on the other side. One pair of channels in adjacent plates is used for the air flow along the cathode electrode, the other for the fuel flow along the anode of each cell. A schematic of the design proposed by Bossel [1] is shown in Fig. 1. Figure 1. A schematic of the proposed planar SOFC design: (a) cathode side view, (b) anode side view [1] A three-dimensional Computational Fluid Dynamics (CFD) model for an anode-supported planar SOFC with complex bipolar plates has been developed using the ANSYS Fluent code with additional Fuel Cell Tools module. The conservation equations of mass, momentum, energy and species as well as electrochemical models were solved for the fuel cell. The distributions of temperature and gas flow through the gas channels and PEN (positive electrode/electrolyte/negative electrode) structure were studied. The results identified the most susceptible areas for significant increase of the temperature at high current density, which can lead to hot spots formation and destruction of the electrodes. Knowledge of such parameters as the flow fields, pressure losses or temperature variation over the fuel cell area allowed to validate the effectiveness of the new SOFC design and is useful in further design modification. Acknowledgments The research programme leading to these results received funding from the European Union’s Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement no [325323]. Acknowledgments are due to the partners of SAFARI project. The work was also financed from the Polish research funds awarded for the project No. 3043/7.PR/2014/2 of international cooperation within SAFARI in years 2014-2016. [1] U. Bossel, Rapid startup SOFC modules, Energy Procedia, 28, 2012, 48-56. DOI: 10.1016/j.egypro.2012.08.039. Figure 1

Performance Characteristics of a Micro-tubular Solid Oxide Fuel Cell Operated with a Fuel-rich Methane Flame

A micro-tubular solid oxide fuel cell (SOFC) is directly combined with a fuel-rich methane flame in a simple, "no-chamber" setup. The multi-element diffusion flat flame burner (MEDB) is served as a fuel reformer and implements the quick starting process for the flame fuel cell. Experiments are performed based on novel anode supported micro-tubular SOFC cells and a multi-element diffusion flame burner for various equivalence ratios and flow rates. The SOFC is directly heated up by the flame from room temperature to operating temperature in less than 120 s. The maximum power generated by the fuel cell reached 0.45 W at the equivalence ratio of 1.2. The cell was operated for 8 hours at the equivalence ratio of 1.2 at a fixed voltage of 0.45 V without significant performance degradation. A transient two-dimensional SOFC model is developed to analyze the transient temperature field and the associated thermal stresses of the SOFC when the cell is suddenly exposed to a high temperature flame. The thermal shock resistance of the direct flame micro-tubular SOFC is analyzed and the result shows the excellent performance characteristics of the micro-tubular cell in the aspect of thermal shock resistance. Figure 1

The Performance of SOFC Model Under Different Three‐phase Load Conditions

AbstractIn this paper, the dynamic performance of a modified thermal based dynamic model of a solid oxide fuel cell (SOFC) is presented under different three‐phase load conditions. The modified thermal based fuel cell model contains ohmic, activation and concentration voltage losses, thermal dynamics, methanol reformer and fuel utilization factor limiting stage. SOFC model and the power conditioning unit (PCU), which consists of a DC‐DC boost converter, a DC‐AC inverter, their controller, transformer and filter, are developed on Matlab/Simulink environment. The simulation results show that the real and reactive power management of the inverter is performed successfully in an AC power system with the proposed thermal based SOFC model under three‐phase load conditions such as ohmic loads, switched ohmic−inductive loads and a three‐phase induction motor. Finally, the three‐phase induction motor is performed both no load and load conditions. The simulation results show that the modified thermal based fuel cell model provides an accurate representation of the dynamic and steady state behavior of the fuel cell under different three‐phase load conditions.

Mathematical modeling of synthesis gas fueled electrochemistry and transport including H2/CO co-oxidation and surface diffusion in solid oxide fuel cell

Fuel flexibility is a significant advantage of solid oxide fuel cell (SOFC). A comprehensive macroscopic framework is proposed for synthesis gas (syngas) fueled electrochemistry and transport in SOFC anode with two main novelties, i.e. analytical H2/CO electrochemical co-oxidation, and correction of gas species concentration at triple phase boundary considering competitive absorption and surface diffusion. Staring from analytical approximation of the decoupled charge and mass transfer, we present analytical solutions of two defined variables, i.e. hydrogen current fraction and enhancement factor. Giving explicit answer (rather than case-by-case numerical calculation) on how many percent of the current output contributed by H2 or CO and on how great the water gas shift reaction plays role on, this approach establishes at the first time an adaptive superposition mechanism of H2-fuel and CO-fuel electrochemistry for syngas fuel. Based on the diffusion equivalent circuit model, assuming series-connected resistances of surface diffusion and bulk diffusion, the model predicts well at high fuel utilization by keeping fixed porosity/tortuosity ratio. The model has been validated by experimental polarization behaviors in a wide range of operation on a button cell for H2–H2O–CO–CO2–N2 fuel systems. The framework could be helpful to narrow the gap between macro-scale and meso-scale SOFC modeling.

Multiscale model for solid oxide fuel cell with electrode containing mixed conducting material

Solid oxide fuel cells (SOFCs) with electrodes that contain mixed conducting materials usually show very different relationships among microstructure parameters, effective electrode characteristics, and detailed working processes from conventional ones. A new multiscale model for SOFCs using mixed conducting materials, such as LSCF or BSCF, was developed. It consisted of a generalized percolation micromodel to obtain the electrode properties from microstructure parameters and a multiphysics single cell model to relate these properties to performance details. Various constraint relationships between the activation overpotential expressions and electric boundaries for SOFC models were collected by analyzing the local electrochemical equilibrium. Finally, taking a typical LSCF‐SDC/SDC/Ni‐SDC intermediate temperature SOFC as an example, the application of the multiscale model was illustrated. The accuracy of the models was verified by fitting 25 experimental I‐V curves reported in literature with a few adjustable parameters; additionally, and several conclusions were drawn from the analysis of simulation results. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3786–3803, 2015

<b>The modeling and simulation of thermal based modified solid oxide fuel cell (SOFC) for grid-connected systems

This paper presents a thermal based modified dynamic model of a Solid Oxide Fuel Cell (SOFC) for grid-connected systems. The proposed fuel cell model involves ohmic, activation and concentration voltage losses, thermal dynamics, methanol reformer, fuel utilization factor and power limiting module. A power conditioning unit (PCU), which consists of a DC-DC boost converter and a DC-AC voltage-source inverter (VSI), their controller, transformer and filter, is designed for grid-connected systems. The voltage-source inverter with six Insulated Gate Bipolar Transistor (IGBT) switches inverts the DC voltage that comes from the converter into a sinusoidal voltage synchronized with the grid. The simulations and modeling of the system are developed on Matlab/Simulink environment. The performance of SOFC with converter is examined under step and random load conditions. The simulation results show that the designed boost converter for the proposed thermal based modified SOFC model has fairly followed different DC load variations. Finally, the AC bus of 400 Volt and 50 Hz is connected to a single-machine infinite bus (SMIB) through a transmission line. The real and reactive power managements of the inverter are analyzed by an infinite bus system. Thus, the desired nominal values are properly obtained by means of the inverter controller.

Energy and exergy analyses of an ethanol-fueled solid oxide fuel cell for a trigeneration system

This paper examines an integrated SOFC (solid oxide fuel cell) system with an absorption chiller that uses heat recovery of the SOFC exhaust gas for combined cooling, heating, and power production (trigeneration) through energy and exergy analyses. The system consists of an ethanol reformer, SOFCs, an air pre-heater, a steam generator and a double-effect LiBr/H2O absorption chiller. Validation of the SOFC and absorption chiller models is performed by comparison with published data. To assess the system performance and determine the irreversibility in each component, a parametric study of the effects of changing the current density, SOFC temperature, fuel utilization ratio and SOFC anode recirculation ratio on the net electrical efficiency and the efficiency of heating cogeneration, cooling cogeneration and trigeneration is presented. The study shows that in the trigeneration plant, there is at least a 32% gain in efficiency, compared to the conventional power cycle. This study also demonstrates that the proposed trigeneration system represents an attractive option to improve the heat recovery and enhance the exergetic performance of the system.

Parameter extraction of different fuel cell models with transferred adaptive differential evolution

To improve the design and control of FC (fuel cell) models, it is important to extract their unknown parameters. Generally, the parameter extraction problems of FC models can be transformed as nonlinear and multi-variable optimization problems. To extract the parameters of different FC models exactly and fast, in this paper, we propose a transferred adaptive DE (differential evolution) framework, in which the successful parameters of the adaptive DE solving previous problems are properly transferred to solve new optimization problems in the similar problem-domains. Based on this framework, an improved adaptive DE method (TRADE, in short) is presented as an illustration. To verify the performance of our proposal, TRADE is used to extract the unknown parameters of two types of fuel cell models, i.e., PEMFC (proton exchange membrane fuel cell) and SOFC (solid oxide fuel cell). The results of TRADE are also compared with those of other state-of-the-art EAs (evolutionary algorithms). Even though the modification is very simple, the results indicate that TRADE can extract the parameters of both PEMFC and SOFC models exactly and fast. Moreover, the V–I characteristics obtained by TRADE agree well with the simulated and experimental data in all cases for both types of fuel cell models. Also, it improves the performance of the original adaptive DE significantly in terms of both the quality of final solutions and the convergence speed in all cases. Additionally, TRADE is able to provide better results compared with other EAs.

Accelerated Degradation for Hardware in the Loop Simulation of Fuel Cell-Gas Turbine Hybrid System

The U.S. Department of Energy (DOE)-National Energy Technology Laboratory (NETL) in Morgantown, WV has developed the hybrid performance (HyPer) project in which a solid oxide fuel cell (SOFC) one-dimensional (1D), real-time operating model is coupled to a gas turbine hardware system by utilizing hardware-in-the-loop simulation. To assess the long-term stability of the SOFC part of the system, electrochemical degradation due to operating conditions such as current density and fuel utilization have been incorporated into the SOFC model and successfully recreated in real time. The mathematical expression for degradation rate was obtained through the analysis of empirical voltage versus time plots for different current densities and fuel utilizations.

Thermal modeling and efficiency assessment of an integrated biomass gasification and solid oxide fuel cell system

Performance assessment of a novel energy system integrating both biomass gasification and fuel cell systems is performed thermodynamically through energy and exergy efficiencies. Steam gasification for rich hydrogen gas production as a useful gasification output is considered. Energy and exergy thermodynamics model of the gasification process is introduced. A thermal model of bubbling fluidized bed gasifier, operating at atmospheric pressure, is also considered to investigate the temperature profile through the gasifier. Direct internal reforming solid oxide fuel cell model is introduced and it is integrated with the system for power production. The presented models are validated, and the effects of different operating parameters on the system performance are studied under various conditions. Different values of gasification operating temperature and moisture content of the supplied fuel are also considered in parametric studies. The results show that steam biomass ratio has a significant effect on the hydrogen production efficiency and optimal value of 0.677 is calculated for maximum exergy efficiency at the base case condition.

Effect of operating parameters on performance of an integrated biomass gasifier, solid oxide fuel cells and micro gas turbine system

An integrated power system of biomass gasification with solid oxide fuel cells (SOFC) and micro gas turbine has been investigated by thermodynamic model. A zero-dimensional electrochemical model of SOFC and one-dimensional chemical kinetics model of downdraft biomass gasifier have been developed to analyze overall performance of the power system. Effects of various parameters such as moisture content in biomass, equivalence ratio and mass flow rate of dry biomass on the overall performance of system have been studied by energy analysis.It is found that char in the biomass tends to be converted with decreasing of moisture content and increasing of equivalence ratio due to higher temperature in reduction zone of gasifier. Electric and combined heat and power efficiencies of the power system increase with decreasing of moisture content and increasing of equivalence ratio, the electrical efficiency of this system could reach a level of approximately 56%.Regarding entire conversion of char in gasifier and acceptable electrical efficiency above 45%, operating condition in this study is suggested to be in the range of moisture content less than 0.2, equivalence ratio more than 0.46 and mass flow rate of biomass less than 20 kg h−1.

Engine-integrated solid oxide fuel cells for efficient electrical power generation on aircraft

This work investigates the use of engine-integrated catalytic partial oxidation (CPOx) reactors and solid oxide fuel cells (SOFCs) to reduce fuel burn in vehicles with large electrical loads like sensor-laden unmanned air vehicles. Thermodynamic models of SOFCs, CPOx reactors, and three gas turbine (GT) engine types (turbojet, combined exhaust turbofan, separate exhaust turbofan) are developed and checked against relevant data and source material. Fuel efficiency is increased by 4% and 8% in the 50 kW and 90 kW separate exhaust turbofan systems respectively at only modest cost in specific power (8% and 13% reductions respectively). Similar results are achieved in other engine types. An additional benefit of hybridization is the ability to provide more electric power (factors of 3 or more in some cases) than generator-based systems before encountering turbine inlet temperature limits. A sensitivity analysis shows that the most important parameters affecting the system's performance are operating voltage, percent fuel oxidation, and SOFC assembly air flows. Taken together, this study shows that it is possible to create a GT-SOFC hybrid where the GT mitigates balance of plant losses and the SOFC raises overall system efficiency. The result is a synergistic system with better overall performance than stand-alone components.

Parallel Constrained Control for Solid Oxide Fuel Cell Based on PID and CMAC Neural Network

This paper proposes a cerebellar model articulation controller (CMAC) based parallel adaptive constrained PID control scheme for a solid oxide fuel cell (SOFC). Conventional PID controller with fixed parameters can hardly adapt to time varying of characteristics in wide range. To improve the control performance, CMAC is used to learn the controller through parallel structure. At same time, in order to solve the input saturation problem, we design an anti‐windup compensator for accommodating the reference. Finally, the simulation results on the dynamic model of SOFC are provided to demonstrate the effectiveness of the proposed constrained control approach.

Modelling of gradual internal reforming process over Ni‐YSZ SOFC anode with a catalytic layer

AbstractMethane appears to be a fuel of great interest for solid oxide fuel cell (SOFC) systems because it can be directly converted into hydrogen by Internal Reforming within the SOFC anode. To cope with carbon formation, a new SOFC cell configuration combining a catalyst layer with a classical anode was developed. The rate of the CH4 consumption in the catalyst layer (Ir‐CGO) was determined experimentally for small values of steam to carbon ratios. This paper proposes a modelling and a simulation, using the CFD‐Ace software package, of the behaviour of a SOFC operated in Gradual Internal Reforming (GIR) conditions. This model of SOFC takes into account the kinetics of the steam reforming reaction in the catalyst layer in order to assess the influence of the steam to carbon ratio and the cell polarization. Because the risk of carbon formation is greater under GIR operation, a detailed thermodynamic analysis was carried out. Thermodynamic equilibrium calculations allowed us to predict the conditions of carbon formation occurrence.

Validation of a Solid Oxide Fuel Cell Model on the International Energy Agency Benchmark Case with Hydrogen Fuel

AbstractA detailed model of a solid oxide fuel cell was developed with an object‐oriented open‐source computational fluid dynamics code based on a finite‐volume method. The methodology is derived from a local Nernst equation with associated irreversible losses. Calculations were performed with the International Energy Agency benchmark case #1 with hydrogen as fuel, for co‐flow, counter‐flow, and cross‐flow. While agreement with the results of previous workers was satisfactory, a number of shortcomings with the benchmark case were identified and highlighted. These include over‐simplified electro‐chemical kinetics, neglect of porous transport layers, and ambiguities associated with the very low flow rates prescribed for the benchmark case.

A nonlinear sliding mode observer for the estimation of temperature distribution in a planar solid oxide fuel cell

Compliance to certain temperature constraints is essential for the long life and stable operation of solid oxide fuel cells (SOFCs). However, it is difficult and costly to measure the temperature inside a high temperature, well-sealed cell directly. A nonlinear sliding mode observer has been designed in this paper for estimating the temperature distribution in a hydrogen fed SOFC stack. The observer design is based on a finite-volume parameter SOFC model, which is simplified by quasi-static mass balance assumption. In the observer design, a decoupling pole placement method that applies to multi-timescale systems is proposed to obtain a suitable observer gain. And a quasi-sliding mode control method is adopted to eliminate the chatter caused by the discontinuous control actions of sliding mode control. Theoretical analysis and simulation results are presented to prove the convergence and good performance of the designed observer for estimating the temperature distribution in a SOFC stack during steady-state and transient operation.

Peak Power Optimization of Solid Oxide Fuel Cells with Particle Size and Porosity Grading

Solid oxide fuel cells (SOFCs) are blessed with high efficiency, the capability of using a variety of hydrocarbon fuels, and high impurity tolerance. Functionally graded electrodes have previously been investigated to improve SOFCs performance with controlled microstructure. However, little investigation has been focused on the cell-level optimization of power output for nonlinearly graded electrode microstructures. In this work, a multiscale electrode polarization model of SOFCs has been expanded and developed to a cell-level model. The cell-level SOFCs model has been utilized to disclose the complex relationship among the transport phenomena, which include the transports of electron, ion and gas molecules through the electrode and the electrochemical reaction at the triple phase boundaries. The work advances the understanding of the cell performance with graded microstructures. The performance of functionally graded electrodes has been analyzed to understand the effects of tailored electrode microstructures on cell power output.

Investigation of the electrochemical active thickness of solid oxide fuel cell anode

Determination of the electrochemical active thickness (EAT) is of paramount importance for optimizing the solid oxide fuel cell (SOFC) electrode. However, very different EAT values are reported in the previous literatures. This paper aims to systematically study the EAT of SOFC anode numerically. An SOFC model coupling electrochemical reactions with transport of gas, electron and ion is developed. The microstructure features of the electrode are modeled based on the percolation theory and coordinate number theory. Parametric analysis is performed to examine the effects of various operating conditions and microstructures on EAT. Results indicate that EAT increases with decreasing exchange current density (or decreasing TPB length) and increasing effective ionic conductivity. In addition to the numerical simulations, theoretical analysis is conducted including various losses in the electrode, which clearly shows that the EAT highly depends on the ratio of concentration related activation loss Ract,con to ohmic loss Rohmic. The theoretical analysis explains very well the different EATs reported in the literature and is different from the common understanding that the EAT is controlled mainly by the ionic conductivity of electrode.

Small-Scale Biogas-SOFC Plant: Technical Analysis and Assessment of Different Fuel Reforming Options

This paper investigates simulation results of the thermodynamic performance of a 25 kWel small-scale solid oxide fuel cell model fuelled with biogas. Hereby, biogas is produced from a predefined group of substrates, namely, livestock effluents, energy crops, agricultural waste, and organic waste. For the analysis, average methane (CH4) content is assumed to lie between 50 and 60 mol % as large seasonal and daily variations are observed which are independent of used matter. The main biogas contaminants are sulfur compounds, mostly in the form of H2S. Sulfur leads to fast catalyst deactivation in the reformer and fuel cell, which is why an effective gas-cleaning system is established. For this, ZnO and activated carbon are the most practical gas-cleaning solutions for small-scale plants. The energy model of the solid oxide fuel cell plant is designed and analyzed through detailed energy and mass balance calculations throughout all system components and streams. The above-mentioned model is set up in in such...