Accepted Manuscripts

Amir Hossein Davoodi and Mahmoud Reza Pishvaie
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4039043
This paper presents the design and part-load operation of a Molten Carbonate-Micro Gas Turbine (MCFC/MGT) hybrid system, and proposes a multi loop control strategy for the hybrid system. A mathematical model of the system is introduced. Then, the structure of process is changed and performance of hybrid systems at part-load operation is studied. The novelty includes utilizing some part of the main fuel instead of auxiliary fuel in the combustion stage. The results show that the new configuration has more efficiency (about 63%). In order to keep the operating system within safe limits, variables of the control system are determined. Those controlled variables are as follows: stack temperature, fuel utilization, turbine inlet temperature and output power of hybrid system. Base on relative gain array (RGA) analysis, control structures are suggested for two hybrid processes. Investigations on results of RGA analysis indicate that the new configuration has more interactions between inputs and outputs and so, has different control structure. The dynamic simulation results show that the proposed control structure is achievable for MCFC/MGT hybrid systems.
TOPICS: Molten carbonate fuel cells, Fuels, Stress, Temperature, Combustion, Control systems, Simulation results, Design, Gas turbines, Turbines
Samuel Majerus, Dirk Lauinger and Jan Van Herle
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4039045
In this study, the European biogas market and its potential is analysed. The four countries with the biggest biogas production and potential, namely Germany, Italy, France, and the United Kingdom, are studied in detail. Particular attention is paid to their agricultural characteristics (livestock population, average number of cattle per agricultural holding, number of farms), as well as their policy and market conditions (feed-in tariffs, average biogas investment costs). A financial model is built and used to compare the four countries, based on the net present value (NPV) as the performance indicator. Solid Oxide Fuel Cells (SOFCs) are considered as a more efficient alternative for valorising agricultural-derived biogas, which at the moment is vastly done with cheaper conventional engines. After an analysis of the economic merits, target farm sizes are recommended for each country. It is shown that the low valorisation of manure-derived biogas in Europe offers a big opportunity for the commercialisation of SOFCs and for a push towards mass-production. Considering the high installation costs, it is still primordial that policy-makers incentivize the installation of biogas plants throughout the EU.
TOPICS: Engines, Biogas, Fuel cells, Solid oxide fuel cells, Mass production
Lei Niu, Shan Geng, Hongliang Li, Songli Du, Xiaoling Cui and ShiYou Li
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4038799
Nano-micro spheres of LiNi0.5Mn1.5O4 materials are prepared by carbonate co-precipitation method. The effect of calcination temperatures on morphology and electrochemical property is explored. Results show that the structure of the material becomes more compact with the increase of the temperature, which is propitious to the improvement of electrical conductivity and activation level of the material. And the charge-discharge tests show that the sample obtained at 850 °C (LNMO850) exhibits optimal rate capability and cyclic stability, due to the fact that LNMO850 has a high diffusion coefficient, which is propitious to the improvement of electrical conductivity and activation level of the material.
TOPICS: Temperature, Roasting (Metallurgy), Lithium-ion batteries, Electrical conductivity, Stability, Diffusion (Physics), Coprecipitation
Jaka Dujc, Antoni Forner-Cuenca, Philip Marmet, Magali Cochet, Roman Vetter, Juergen Schumacher and Boillat Pierre
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4038626
We present a macrohomogeneous two-phase model of a proton exchange membrane fuel cell (PEMFC). The model takes into account the mechanical compression of the gas diffusion layer (GDL), the two-phase flow of water, the transport of the gas species and the electrochemical reaction of the reactant gases. The model was used to simulate the behavior of a PEMFC with a patterned GDL. The results of the reduced model, which considers only the mechanical compression and the two-phase flow, are compared to the experimental ex-situ imbibition data obtained by neutron radiography imaging. The results are in good agreement. Additionally, by using all model features, a simulation of an operating fuel cell has been performed to study the intricate couplings in an operating fuel cell and to examine the patterned GDL effects. The model confirms that the patterned GDL design liberates the pre-defined domains from liquid water and thus locally increases the oxygen diffusivity.
TOPICS: Water resource management, Modeling, Proton exchange membrane fuel cells, Gas diffusion layers, Water, Fuel cells, Two-phase flow, Compression, Couplings, Oxygen, Simulation, Neutron radiography, Electrochemical reactions, Design, Gases, Imaging
Luigino Capone, Philip Marmet, Lorenz Holzer, Jaka Dujc, Schumacher Juergen, Adrien Lamibrac, Dr. Felix Büchi and Jürgen Becker
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4038627
Water management in proton-exchange membrane fuel cells (PEFCs) has a large impact on the performance of the device, as liquid water affects the transport properties of the gas diffusion layer (GDL). In this study we develop an ensemble-based model of the liquid water distribution inside the GDL. Based on a water injection experiment, the wet structure of the porous medium is inspected via X-ray tomographic microscopy and, after an image segmentation process, a voxel-based meshing of the fiber, air and water domains is obtained. Starting from the obtained dry fiber structure, a Metropolis-Hastings Monte Carlo algorithm is used to obtain the equilibrium distribution of liquid water that minimizes the surface free energy of the ensemble. The different water distributions from the MC simulation and water injection experiment are identified as solution for different physical mechanisms which are both present in a running fuel cell. The wet structure is then used to calculate saturation-dependent effective transport properties, using the software GeoDict. Thereby, a strong influence of the saturation gradient on the macrohomogeneous transport properties is found.
TOPICS: Simulation, Water distribution, Proton exchange membrane fuel cells, Gas diffusion layers, Water, Fibers, Underground injection, Microscopy, Cities, Computer software, Image segmentation, Equilibrium (Physics), Algorithms, Fuel cells, X-rays, Water resource management, Porous materials
Stefan Keller, Tansu Özel, Anne-Christine Scherzer, Dietmar Gerteisen, Ulf Groos, Christopher Hebling and Yiannos Manoli
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4038632
Electrochemical Impedance Spectroscopy (EIS) is used during operation of different polymer electrolyte membrane fuel cell (PEMFC) stack assemblies at various conditions with special interest given to the characteristic time constant tlow-f derived from the low frequency arc of the spectra which is typically in the range of approx. 15 to 0.5 Hz. This was done by fitting an equivalent electrical circuit (EEC) to the data. Parameter variation performed on a 90 cell stack assembly suggests that conditions leading to different air flow velocities in the flow channels affect tlow-f while other parameters like humidity influence the impedance spectrum, but not tlow-f. Comparison of the stoichiometry variation between short stack and locally resolved single cell shows similar results with the stack´s time constant matching that of the cell´s segments which are located off-center towards the outlet. However, a nonlinear dependency between gas flow velocity and tlow-f especially at low stoichiometric values is obvious. Results from stoichiometry variations at different pressure levels suggest that this could be attributed to the different steady state oxygen partial pressures during the experiments. Comparison of the stoichiometry variation between different stack platforms result in similar dependencies of tlow-f on air flow rate with respect to a reference oxygen partial pressure regardless of size, flow field, geometry or cell count of the stack. The time constant caused by oxygen diffusion through the gas diffusion layer, tGDL was approximated and compared to tlow-f.
TOPICS: Spectra (Spectroscopy), Fuel cells, Oxygen, Stoichiometry, Electrochemical impedance spectroscopy, Proton exchange membrane fuel cells, Air flow, Pressure, Flow (Dynamics), Diffusion (Physics), Manufacturing, Circuits, Fittings, Geometry, Gas flow, Steady state, Gas diffusion layers
Liangfei Xu, Chuan Fang, Junming Hu, Siliang Cheng, Jianqiu Li, Minggao Ouyang and Werner Lehnert
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4038628
Water management is critical for the operation of a proton electrolyte membrane fuel cell (PEMFC). For the purposes of high power and long working-lifetime of PEMFCs, external humidifiers are always utilized as a necessary part of balance of plants to keep the imported air and fuel wet. However, they have several disadvantages, and it is beneficial to remove them so as to reduce system volume and to enhance the cold-starting capability. In this paper, a self-humidified PEMFC of an active area 250 cm2 and cell number 320 is proposed and investigated. The imported dry air on the cathode side is mixed with moisty exhaust gas by using a recirculation valve, and the dry hydrogen on the anode side is humidified by back-diffusion water through the membrane. A nonlinear model is set up based on mass transport and energy conservation equations to capture dynamics of gas gases in the supply and exhaust manifolds, the gas diffusion layers (GDLs) and the membrane. An analysis is conducted to investigate the influences of parameters on dynamic and stable performances. Simulation results show that, system performances can be greatly affected by parameters such as air stoichiometry, current density, exhaust gas recirculation ratio and membrane thickness. By accurately controlling the EGR ratio and carefully selecting design and operation parameters, it is possible for a PEMFC without an external humidifier to have similar system efficiency to a traditional system.
TOPICS: Protons, Fuel cells, Electrolytes, Membranes, Exhaust gas recirculation, Proton exchange membrane fuel cells, Humidifiers, Gas diffusion layers, System efficiency, Exhaust manifolds, Design, Energy conservation, Dynamics (Mechanics), Diffusion (Physics), Gases, Water resource management, Anodes, Fuels, Simulation results, Stoichiometry, Water, Exhaust systems, Hydrogen, Valves, Current density
Ken Darcovich, Dean MacNeil, Steven Recoskie, Quentin Cadic, Florin Ilinca and Ben Kenney
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4038631
This study combines an equivalent circuit approach for prismatic battery cells with the Single Particle Model (SPM) in order to model the thermal state of automotive battery packs. The objective here was to determine the effects of liquid cooling applied to the packs under standard driving cycles. The Kim model provided a means for determining a non-uniform current distribution over the surface of the current collectors. The Kim model is based on the application of Ohm's Law over a conducting medium, with empirical source terms representing current flowing into or out of an adjacent electrode layer. The Kim model was enhanced by replacing the empirical source terms with ones based on the chemistry and physics of the charge and discharge processes which occur in the electrode layers of a battery cell. As such, fundamental battery function was imparted to the model by integrating the SPM into the equivalent circuit model. The 2D procedure described above was carried out on electrode sheets at different positions inside the cell, and determined thermal generation values that were mapped volumetrically into a heat transfer simulation, which in turn, updated the electrochemical simulation. Capacity fade kinetics were determined by fitting experimental data to simulated results. With time-temperature profiles produced as described above for different pack cooling levels and varying degrees of cell degradation, a basic SPM simulation was then used with thermal overlays to estimate automotive cell life under various driving scenarios and a range of thermal management approaches.
TOPICS: Thermal management, Automotive batteries, Batteries, Simulation, Scanning probe microscopy, Electrodes, Cooling, Circuits, Cycles, Fittings, Particulate matter, Physics, Temperature, Heat transfer, Chemistry, Overlays (Materials engineering)
Alex J Tsai, David Tucker and Tooran Emami
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4038634
Operating points of a 300kW Solid Oxide Fuel Cell Gas Turbine (SOFC-GT) power plant simulator is estimated with the use of a Multiple Model Adaptive Estimation (MMAE) algorithm, aimed at improving the flexibility of controlling the system to changing operating conditions. Through a set of empirical Transfer Functions derived at two distinct operating points of a wide operating envelope, the method demonstrates the efficacy of estimating online the probability that the system behaves according to a predetermined dynamic model. By identifying which model the plant is operating under, appropriate control strategies can be switched and implemented upon changes in critical parameters of the SOFC-GT system - most notably the Load Bank (LB) disturbance and FC cathode airflow parameters. The SOFC-GT simulator allows testing of various fuel cell models under a cyber-physical configuration that incorporates a 120kW Auxiliary Power Unit, and Balance-of-Plant components in hardware, and a fuel cell model in software. The adaptation technique is beneficial to plants having a wide range of operation, as is the case for SOFC-GT systems. The practical implementation of the adaptive methodology is presented through simulation in the MATLAB/SIMULINK environment.
TOPICS: Gas turbines, Power stations, Solid oxide fuel cells, Fuel cells, Air flow, Simulation, Transfer functions, Hardware, Stress, Algorithms, Testing, Computer software, Matlab, Probability, Dynamic models
Tooran Emami, Alex Tsai and David Tucker
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4038635
The performance of a 300 kW Solid Oxide Fuel Cell Gas Turbine (SOFC-GT) pilot power plant simulator is evaluated by applying a set of robust Proportional Integral Derivative (PID) controllers that satisfy time delay and gain uncertainties of the SOFC-GT system. The actuators are a fuel valve (FV) that models the fuel cell thermal exhaust, and a cold-air (CA) valve which bypasses airflow rate from the fuel cell cathode. The robust PID controller results for the upper and lower boundary of uncertain gains are presented first, followed by a design for the upper and lower boundary of uncertain time delays process for both, FV and CA bypass valves. The final design incorporates the combined uncertain gain and the time delay modeling for the upper and lower boundary of both actuators. This Multiple-Input Multiple-Output (MIMO) technique is beneficial to plants having a wide range of operation and a strong parameter interaction. The practical implementation of the PID controllers and the set point responses are presented through simulation in the Matlab/Simulink environment.
TOPICS: Control equipment, Fuel cells, Gas turbines, Solid oxide fuel cells, Valves, Delays, Actuators, Design, Exhaust systems, Matlab, Uncertainty, Modeling, Power stations, Fuels, Air flow, Simulation
Maurizio Spinelli, Stefano Campanari, Stefano Consonni, Matteo C. Romano, Thomas G. Kreutz, Hossein Ghezel-Ayagh and Stephen Jolly
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4038601
The state-of-the-art conventional technology for post combustion capture of CO2 from fossil-fuelled power plants is based on chemical solvents, which requires substantial energy consumption for regeneration. A promising alternative, available in the near future, is the application of Molten Carbonate Fuel Cells (MCFC) for CO2 separation from post-combustion flue gases. Previous studies related to this technology showed high efficiency and high carbon capture rates, especially when the fuel cell is thermally integrated in the flue gas path of a natural gas-fired combined cycle or an integrated gasification combined cycle plant. This work compares the application of MCFC based CO2 separation process to pulverized coal fired steam cycles (PCC) and natural gas combined cycles (NGCC) as a 'retrofit' to the original power plant. Mass/energy balances are calculated through detailed models for both power plants, with MCFC behavior simulated using a 0D model calibrated against manufacturers' specifications and based on experimental measurements, carried out to support this study. The resulting analysis includes a comparison of the energy efficiency and CO2 separation efficiency as well as an economic comparison of the cost of CO2 avoided under several economic scenarios. The proposed configurations reveal promising performance, exhibiting very competitive efficiency and economic metrics in comparison with conventional CO2 capture technologies. Application as a MCFC retrofit yields a very limited (<3%) decrease in efficiency for both power plants (PCC and NGCC), a strong reduction (>80%) in CO2 emission and a competitive cost for CO2 avoided (25-40 €/ton).
TOPICS: Combustion, Coal, Economic analysis, Molten carbonate fuel cells, Thermal power stations, Carbon capture and storage, Combined cycles, Carbon dioxide, Power stations, Separation (Technology), Flue gases, Cycles, Fuel cells, Natural gas, Energy efficiency, Integrated gasification combined cycle power stations, Emissions, Steam, Energy consumption

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