Simulation of High Temperature Fuel Cells for Carbon Capture

The aim of this doctoral thesis is to develop and apply a kinetic model for the simulation of High Temperature Fuel Cells for energy conversion and Carbon Capture applications. In particular, the work will focus on the analysis and the modeling of a newly discovered mechanism in Molten Carbonate Fuel Cells that sees the net migration of H2O from the cathode to the anode side in competition with the usually encountered migration of CO2. This mechanism was never reported in the literature and was named "dual-anion mechanism" to underline the parallel migration of carbonate and hydroxide ions. It is important because it can greatly affect the cell\u2019s performance in terms of both energy conversion and CO2 sequestration. The work was performed in collaboration with ExxonMobil that first observed this phenomenon during a campaign to test the use of molten carbonate fuel cells as Carbon Capture devices. The work was also done in partnership with FuelCell Energy, who through an agreement with ExxonMobil obtained all of the experimental data of this phenomenon. The analysis of the mechanism and the development of a model to simulate cells working at such conditions were conducted in a series of different steps. To start, based on experimental data, the mechanism was studied as a function of the reactant gases to understand the main dependences of the occurring phenomena. Consequently, as more data became available, additional dependences to improve the knowledge of the mechanism and the modeling were studied. In particular, the work was focused on the analysis of the effects that the diffusion resistance has on the extent on which one anionic path evolves over the other. Successively, the operating temperature and the carbonate/hydroxide equilibrium were studied and included in the model. The analysis of the experimental data also allowed to observe the effects that the gas atmosphere can have on the cell ohmic resistance as it was determined that the electrolyte melt can change based on equilibria between melt and gas phase. The developed kinetic formulation was implemented into the SIMFC code, a home-made Fortran program realized by the group PERT of the University of Genoa for the simulation of High Temperature Fuel Cells (Molten Carbonate and Solid Oxide). In this way, the model was successfully tested by simulating the experimental data. Additionally, a formulation to consider the direct internal steam reforming of CH4 on the performance of cells was also included into the SIMFC code. The formulation considers the reaction locally with dependence on catalyst loading. As such, it allows the study of the effect of catalyst distribution and degradation. This part of the thesis was developed on Solid Oxide Fuel Cells instead of Molten Carbonate. This choice was dictated by the fact that I spent a period of 8 months during the first year of the Ph.D. program at the Korea Institute of Science and Technology studying solid oxide fuel cells materials, specifically focused on the use of perovskite (a possible solid oxide fuel cells anode material) as catalysts for the CH4 reforming reaction which will be presented. The overall model developed and implemented into the SIMFC code was demonstrated to be very promising in simulating High Temperature Fuel Cells performance under a great range of operating conditions

2D Simulation for CH4 Internal Reforming-SOFCs: An Approach to Study Performance Degradation and Optimization

Solid oxide fuel cells (SOFCs) are a well-developed technology, mainly used for combined heat and power production. High operating temperatures and anodic Ni-based materials allow for direct reforming reactions of CH4 and other light hydrocarbons inside the cell. This feature favors a wider use of SOFCs that otherwise would be limited by the absence of a proper H2 distribution network. This also permits the simplification of plant design avoiding additional units for upstream syngas production. In this context, control and knowledge of how variables such as temperature and gas composition are distributed on the cell surface are important to ensure good long-lasting performance. The aim of this work is to present a 2D modeling tool able to simulate SOFC performance working with direct internal CH4 reforming. Initially thermodynamic and kinetic approaches are compared in order to tune the model assuming a biogas as feed. Thanks to the introduction of a matrix of coefficients to represent the local distribution of reforming active sites, the model considers degradation/poisoning phenomena. The same approach is also used to identify an optimized catalyst distribution that allows reducing critical working conditions in terms of temperature gradient, thus facilitating long-term applications

High temperature fuel cells to reduce CO

Recently the interest in the sustainability of the maritime sector has increased exponentially. The International Maritime Organization (IMO) set as objective the reduction of CO2 emissions by 2030 by a margin of 40% compared to 2008. Recent studies showed that, according to the ships and the emission mitigation method applied, only 15–25% of CO2 reduction is de facto needed. Fuel cells represent an answer to meet this regulation. We propose two different solutions: (i) produce with SOFCs instead of engines the minimum power necessary to cut 20% of the emissions, or (ii) reduce the engine power of about 10% balancing the power requirement using MCFCs with CO2 capture. Using Aspen Plus each solution was investigated. The analysis contemplated LNG steam reforming to produce the H2 necessary for cell operation and the separation and liquefaction of CO2. Two case studies were considered comparing existing passenger ships with engines working on HFO and on LNG respectively. Although both solutions showed potential for the reduction of CO2 emissions respecting the IMO regulations, the SOFC solution requires a major change in the design of the ship, while MCFCs are proposed as an urgent solution allowing ship retrofitting without demanding update

Preliminary model and validation of molten carbonate fuel cell kinetics under sulphur poisoning

MCFC represents an effective technology to deal with CO2 capture and relative applications. If used for these purposes, due to the working conditions and the possible feeding, MCFC must cope with a different number of poisoning gases such as sulphur compounds. In literature, different works deal with the development of kinetic models to describe MCFC performance to help both industrial applications and laboratory simulations. However, in literature attempts to realize a proper model able to consider the effects of poisoning compounds are scarce. The first aim of the present work is to provide a semi-empirical kinetic formulation capable to take into account the effects that sulphur compounds (in particular SO2) have on the MCFC performance. The second aim is to provide a practical example of how to effectively include the poisoning effects in kinetic models to simulate fuel cells performances. To test the reliability of the proposed approach, the obtained formulation is implemented in the kinetic core of the SIMFC (SIMulation of Fuel Cells) code, an MCFC 3D model realized by the Process Engineering Research Team (PERT) of the University of Genova. Validation is performed through data collected at the Korea Institute of Science and Technology in Seoul

Multiscale Modeling for Reversible Solid Oxide Cell Operation

Solid Oxide Cells (SOCs) can work efficiently in reversible operation, allowing the energy storage as hydrogen in power to gas application and providing requested electricity in gas to power application. They can easily switch from fuel cell to electrolyzer mode in order to guarantee the production of electricity, heat or directly hydrogen as fuel depending on energy demand and utilization. The proposed modeling is able to calculate effectively SOC performance in both operating modes, basing on the same electrochemical equations and system parameters, just setting the current density direction. The identified kinetic core is implemented in different simulation tools as a function of the scale under study. When the analysis mainly focuses on the kinetics affecting the global performance of small-sized single cells, a 0D code written in Fortran and then executed in Aspen Plus is used. When larger-scale single or stacked cells are considered and local maps of the main physicochemical properties on the cell plane are of interest, a detailed in-home 2D Fortran code is carried out. The presented modeling is validated on experimental data collected on laboratory SOCs of different scales and electrode materials, showing a good agreement between calculated and measured values and so confirming its applicability for multiscale approach studies