Roberto Bove

Modeling Solid Oxide Fuel Cells: Methods, Procedures and Techniques

This book fills the need for a practical reference for all scientists and graduate students who are seeking to define a mathematical model for Solid Oxide Fuel Cell (SOFC) simulation. Structured in two parts, part one presents the basic theory, and the general equations describing SOFC operation phenomena. Part two deals with the application of the theory to practical examples, where different SOFC geometries, configurations, and different phenomena are analyzed in detail.

Analysis and optimization of hybrid MCFC gas turbines plants

Abstract High temperature fuel cells are electricity producers that guarantee relevant energetic and environmental performances. They feature high electricity to input chemical energy ratios and availability of high temperature heat. Notwithstanding, the search for a further increase in electric efficiency, especially when applying a CHP solution is not feasible, has brought to plant integration with gas turbines (GTs) in several studies and some pilot installations. While for pressurized fuel cells the choice of internal combustion gas turbines seem to be the only one feasible, in ambient pressure fuel cells it seems useful to analyze the combination with indirect heated GT. This choice allows to optimize turbine pressure ratio and cell size. In this work, a parametric performance evaluation of a hybrid molten carbonate fuel cell (MCFC) indirect heated gas turbine has been performed by varying the fuel cell section size and the fuel utilization coefficient. The analysis of performance variation with the latter parameter shows how a cell that is optimized for stand alone operation is not necessarily optimized for the integration in a hybrid cycle. Working with reduced utilization factors, in fact can reduce irreversible losses and does not necessarily yield to less electricity production since the heat produced in the post combustor is recovered by the gas turbine section. This aspect has not been taken into sufficient consideration in literature. The analysis illustrates the methodology to define new operating conditions so to allow global output and global efficiency maximization.

Performance Enhancement of Fuel Cells Systems Through Series and Parallel Connections of Multi Stack Arrays

Fuel cells have been known theoretically for more than a century. Recently conceived high temperature fuel cells, by guaranteeing higher degrees of efficiencies and greater fuel flexibility, have the potential to yield a radical change in the future of distributed electricity market promising high efficient and ultra-clean power generation. In the last years progress has been so relevant that they seem to be on the verge of commercialization. All plants commissioned seem to consider the parallel flow solution i.e. in which primary fuel flow splits to enter all the stacks that works with nominally equal operational parameters. The present work analysed the possibility of disposing stacks in an array, thus leading to a combination of series and parallel fluid dynamic connection so that one cell anode may have as input the exhaust of another cell anode. The aim is to allow some cells to work with low utilization factors and therefore at greater voltages. Different solutions have been analysed with a tool obtained from the integration of a proprietary code for cells simulation, with Aspen+ flowsheet. Code predictions of cells performances have been validated by experimental campaigns [Lunghi and Burzacca 2002]. The results showed that a noticeable performance increase can be obtained with the proposed configuration without any significant complication in the process. The authors believe that this should be considered as a very interesting research field and strongly encourage participation of the scientific community.Copyright

Solid Oxide Fuel Cells

A Solid Oxide Fuel Cell (SOFC) is typically composed of two porous electrodes, interposed between an electrolyte made of a particular solid oxide ceramic material. The system originates from the work of Nernst in the nineteenth century. In his patent [1], Nernst proposed that a solid electrolyte could be made to electrically conduct, using a heater; the system then “glowed” by the passage of an electric current. The systems originally studied by Nernst were based on simple metal oxides. In 1937, Bauer and Preis [2] operated the first ceramic fuel cell at 1000°C, showing that the so-called “Nernst Mass” (85% zirconia and 15% yttria), and other zirconia-based materials present a reasonable ionic conduction at high temperature (600–1000°C). These works were really the prelude to the modern SOFC.

A Methodology for Assessing Fuel Cell Performance Under a Wide Range of Operational Conditions: Results for Single Cells

Testing the performance of fuel cells is an important key for verifying technology improvements and for demonstrating their potential. However, due to the novelty of this technology, there is not a standardized procedure for testing fuel cell performance. In order to fully investigate fuel cell performance, the behavior must be known under a wide range of operational conditions. Furthermore, in order to compare results coming from different test teams, a set of procedures and parameters to evaluate single cell performance should be defined. The research group of the Fuel Cell Laboratory of the University of Perugia is conducting performance tests on single cells, focusing on defining test procedures to find effective parameters to be used to compare tests performed by different teams. This work demonstrates how the testing parameters developed by the team allow one to perform advanced control on test procedures, to understand test results, and to compare them with tests carried out under different operational conditions. The entire analysis is easily conducted by using a single parameter variation hyperspace approach. The experimental results obtained on single fuel cells are reported.

Thermodynamic Analysis of SOFC Systems Using Different Fuel Processors

Solid oxide fuel cells operate at high temperature and consequently the internal reforming of hydrocarbons, for example methane, can easily be achieved. Nevertheless, since the reforming process is strongly endothermic, internal temperature gradients can be generated, thus producing considerable limitations to the fuel cell operation. Moreover, total internal reforming can lead to carbon deposition in the anode component. In order to avoid these problems total internal reforming is generally not conducted, and part of the fuel is externally pre-reformed. In the present study, different options for the pre-conversion process are considered. The relative system performances are evaluated through a thermodynamic analysis and numerical simulations.Copyright

Analysis and Optimization of a Hybrid MCFC-Steam Turbine Plant

Fuel Cells are high efficiently chemical energy conversion devices and their promising high performance are recognized by all the scientific community. Their conversion efficiency can be further enhanced recycling the heat content of the exhaust gas for CHP applications or for a bottoming cycle. For this kind of application, high temperature fuel cells (MCFC and SOFC) particularly suit, because outlet gas temperature is relatively high. In previous works (Desideri U. et al. 2001, Lunghi P. and Ubertini S. 2001, Lunghi P., Bove R. and Desideri U. 2002) the possibility of combining an ambient pressure MCFC with a gas turbine has been deeply investigated. Results showed very promising performance only if new designed turbines will be available for an optimised plants combination. The inlet temperature for gas turbine, in fact, is sensible higher than exhaust gas from fuel cell anode and so additional fuel is needed in the bottoming cycle, leading a system efficiency reducing. For this reason, in a previous work (Lunghi P. and Bove R. 2003) it was analyzed the possibility using as bottoming cycle a Steam Turbine Plant equipped with a HRSG for steam generation. In the present work suitable MCFC and Steam Turbine sizes are chosen and a performance analysis is conducting, through numerical simulations. Results showed very high electric efficiency reachable with this plant configuration.Copyright

Comparison Between MCFC/Gas Turbine and MCFC/Steam Turbine Combined Power Plants

Worldwide, the main power source to produce electric energy is represented by fossil fuels, principally used at the present time in large combustion power plants. The main environmental impacts of fossil fuel-fired power plants are the use of non-renewable resources and pollutants emissions. An improvement in electric efficiency would yield a reduction in emissions and resources depletion. In fact, if efficiency is raised, in order to produce an amount unit of electric energy, less fuel is required and consequently less pollutants are released. Moreover, higher efficiency leads to economic savings in operating costs. A generally accepted way of improving efficiency is to combine power plants’ cycles. If one of the combined plants is represented by a fuel cell, both thermodynamic efficiency and emissions level are improved. Fuel cells, in fact, are ultra-clean high efficiency energy conversion devices because no combustion occurs in energy production, but only electrochemical reactions and consequently no NOx and CO are produced inside the cell. Moreover, the final product of the reaction is water that can be released into the atmosphere without particular problems. Second generation fuel cells (Solid Oxide FC and Molten Carbonate FC) are particularly suitable for combining cycles, due to their high operating temperature. In previous works, the authors had analyzed the possibility of combining Molten Carbonate Fuel Cell (MCFC) plant with a Gas Turbine and then a MCFC with a Steam Turbine Plant. Results obtained show that both these configurations allow to obtain high conversion efficiencies and reduced emissions. In the present work, a comparison between MCFC-Gas Turbine and MCFC-Steam Turbine is conducted in order to evaluate the main advantages and disadvantages in adopting one solution instead of the other one.Copyright

Energy Recovery From Wastewater Treatment Biogas: Integration of an Anaerobic Digester With a High Temperature Fuel Cell

Wastewater treatment facilities operating with anaerobic digesters produce a methane-rich gas as by-product of the process. In most cases, this gas is released into the atmosphere, thus increasing the greenhouse effect, due to the presence of methane. At the same time, the methane content makes the biogas an interesting source of energy. An efficient energy recovery presents the dual benefits of reducing greenhouse gas emissions and of producing a usable form of energy (typically electric current or heat), using a renewable source of energy, thus diminishing fossil fuel consumption. Due to the high operating temperature, Molten Carbonate Fuel Cells (MCFCs) and Solid Oxide Fuel Cells (SOFCs) present the advantage of being able to operate with a wide variety of fuels, of achieving high energy efficiency and of releasing near-zero emissions. In the present study, the possibility of integrating an anaerobic digester with a high temperature fuel cell is presented. The result of the study illustrates the options, opportunities and the relative benefits and disadvantages related to this energy recovery option.Copyright