69 research outputs found
Comparison of the solid oxide fuel cell system for micro CHP using natural gas with a system using a mixture of natural gas and hydrogen
No full textSolid oxide fuel cell systems for combined heat and power production (SOFC μCHP) fueled by natural gas are attractive because of their high electrical and total efficiency even at small scale. The development of a hydrogen economy will increase the availability of distributed hydrogen as a pure gas. Alternatively, hydrogen may be blended with natural gas in the grid. This study investigates the performance of SOFC μCHP systems, while using a fuel varying from pure hydrogen to pure methane via mixtures of hydrogen and methane called Hythane. Flowsheet models of external as well as internal reforming fuel cell systems were developed in Cycle-Tempo simulation software. Results show that both the external as well as the internal reforming system can operated on all fuel gas compositions varying from pure hydrogen to pure methane, thus allowing for a transition towards a hydrogen economy via the mixing of hydrogen into the natural gas grid. Although the natural gas based systems have a higher electrical efficiency, the introduction of hydrogen into the gas leads to a higher total efficiency of the combined heat and power system. The addition of hydrogen into the fuel minimizes the problems of thermal stress and thermal shock associated with the use of methane in internal reforming fuel cell systems. The internal reforming system showed a higher performance compared to the external reforming system for all Hythane gas mixtures in terms of not only electrical efficiency but also in terms of thermal and total efficiency.Economics of Technology and Innovatio
Gas-fired wind power and electric hydrogen
No full textIn the seemingly endless discussions about the pros and cons of wind power even its advocates have to agree that though wind can fly, with offshore wind farms soon to become reality, this only exacerbates the problem of the winds changeability. Even now the major producers of electricity and power grid companies foresee grave difficulties from the peaks and dips in supply of this green power source. Dr Kas Hemmes of the faculty of Systems Engineering, Policy Analysis, and Management at TU Delft has managed to adapt wind power for use in the current power grid system by combining a fuel cell with a wind turbine, and by better use of the heat released by a fuel cell. Wind turbines will be producing hydrogen after all, albeit mainly from natural gas.Technology, Policy and Managemen
A personal retrospect on three decades of high temperature fuel cell research: ideas and lessons learned
No full textIn 1986 the Dutch national fuel cell program started. Fuel cells were developed under the paradigm of replacing conventional technology. Coal-fired power plants were to be replaced by large-scale MCFC power plants fuelled by hydrogen in a full-scale future hydrogen economy. With today's knowledge we will reflect on these and other ideas with respect to high temperature fuel cell development including the choice for the type of high temperature fuel cell. It is explained that based on thermodynamics proton conducting fuel cells would have been a better choice and the direct carbon fuel cell even more so, with electrochemical gasification of carbon as the ultimate step. The specific characteristics of fuel cells and multisource multiproduct systems were not considered, whereas we understand now that these can provide huge driving forces for the implementation of fuel cells compared to just replacing conventional combined heat and power production technology.Economics of Technology and Innovatio
The integration of molten carbonate fuel cells with coal fired steam power plants for CO2 capture
No full textLAUREA SPECIALISTICAConsiderando che la riduzione delle emissioni dei gas serra è un delle più grandi sfide dell’epoca moderna, questo lavoro è volto a ridurre lo scarico di anidride carbonica nell’atmosfera da parte di centrali elettriche attraverso l’utilizzo di celle a combustibile ad alta temperatura. Infatti, le celle ad alta temperatura, in particolare del tipo a carbonati fusi oltre a produrre elettricità, possono essere utilizzate per concentrare e successivamente catturare la CO2. Aggiungendo una cella a combustibile a carbonati fusi (MCFC) all’interno di una centrale a carbone si prova a conciliare un metodo economico per catturare l’anidride carbonica con una fonte di produzione di energia di grossa scala. Lo scopo dell’analisi è quello di ridurre i costi elevati che caratterizzano le tecniche di cattura della CO2 convenzionali sfruttando le caratteristiche della cella a combustibile. Inoltre, il calore presente allo scarico della cella può essere recuperato nel ciclo a vapore aumentandone l’efficienza. Il lavoro di tesi punta a valutare i benefici legati all’integrazione di una cella a combustibile relativamente piccola rispetto alle dimensioni della centrale a carbone, in modo da trovare una tecnologia per catturare la CO2 fattibile sul breve-medio periodo. Nello studio viene assunto che una porzione di gas di scarico sia estratta dal generatore di vapore, pulito dalle sostanze dannose per il funzionamento della cella e mandato all’ingresso del catodo, dopo una diluizione con aria, per assicurarsi la proporzione ossidante/combustibile corretta. Dal lato opposto, l’anodo viene alimentato a gas naturale precedentemente riscaldato fino alla temperatura richiesta. Grazie alle condizioni di funzionamento della cella, allo scarico anodo il gas sarà composto principalmente da CO2 e in percentuali minori da idrogeno e monossido di carbonio. Dopo la combustione in ossigeno dei residui di questi ultimi, il flusso viene raffreddato per condensare l’acqua e rimuovere il contenuto di CO2. Il calore contenuto nel flusso uscente dal lato catodo è inviato al ciclo a vapore che, per mezzo di uno scambiatore, riscalda una porzione di vapore in maniera da permettere un incremento di efficienza e di potenza della centrale originaria. Il lavoro è stato svolto durante un periodo di stage presso TU Delft, considerata una delle università più importanti a livello mondiale nel campo di tecnologie energetiche sostenibili. La tesi è stata sviluppata sotto la guida del Dr. Kas Hemmes che ha definito le linee guida e gli argomenti del progetto, contribuendo attivamente all’esecuzione per l’intero svolgimento del progetto, in collaborazione con il Group of Energy Convesion Systems (Gecos) del Politecnico di Milano.Considering that the mitigation of greenhouse emission is one of the biggest challenges of the modern age, this work aims to reduce the carbon dioxide emission from a pre-existing power plant by means the integration of high temperature fuel cells. In fact, high temperature fuel cells of the molten carbonate type can produce electricity while also acting as carbon dioxide concentrator. The addition of Molten Carbonate Fuel Cell (MCFC) in a standard coal-fired power plant might represent an economic way for capturing CO2 from a large scale power plant. The analysis proposes to reduce the typical high costs of conventional techniques for capturing carbon dioxide, exploiting the properties of MCFCs. Moreover, the heat excess coming out from the cell can be recovered in the steam cycle increasing the plant efficiency.
The work aims to evaluate the potential benefits obtained by integrating a relatively small size fuel cell (with respect to the power plant size) in order to find a technology for capturing CO2 which could be applied in the short or medium term. The study assumes that a portion of flue gases is extracted from the steam generator, cleaned up from detrimental elements for the MCFC and then sent to the cathode inlet. Before feeding the cathode the flue gas is diluted with air in order to respect oxidant requirements of the fuel cell. On the other side, preheated natural gas is used as fuel for the anode. Due to MCFC operating conditions, the out coming gas from the anode side is mainly composed by carbon dioxide, water, hydrogen and carbon monoxide in smaller percentage. After the combustion with oxygen of residual fuels (namely H2 and CO) for preheating the cell system, the flow is cooled down in order to separate the carbon dioxide content from water by condensation. The heat contained in the flow exiting from cathode side is recovered in the steam cycle by means of a heat exchanger which preheat a portion of steam flow in order to increase plant efficiency and electric power output.
The work has been developed during a stage period at TU Delft considered one of the most prestigious universities in the world in the field of Sustainable Energy Technology. The thesis has been carried out thanks to the guidance of Dr. Kas Hemmes that defined the guidelines and the main topics of the project, supporting us during the entire development of the work, in cooperation with the Group of Energy COnversion Systems (GECOS) at Politecnico di Milano
Exploring the Possibility of Using Molten Carbonate Fuel Cell for the Flexible Coproduction of Hydrogen and Power
No full textFuel cells are electrochemical devices that are conventionally used to convert the chemical energy of fuels into electricity while producing heat as a byproduct. High temperature fuel cells such as molten carbonate fuel cells and solid oxide fuel cells produce significant amounts of heat that can be used for internal reforming of fuels such as natural gas to produce gas mixtures which are rich in hydrogen, while also producing electricity. This opens up the possibility of using high temperature fuel cells in systems designed for flexible coproduction of hydrogen and power at very high system efficiency. In a previous study, the flowsheet software Cycle-Tempo has been used to determine the technical feasibility of a solid oxide fuel cell system for flexible coproduction of hydrogen and power by running the system at different fuel utilization factors (between 60 and 95%). Lower utilization factors correspond to higher hydrogen production while at a higher fuel utilization, standard fuel cell operation is achieved. This study uses the same basis to investigate how a system with molten carbonate fuel cells performs in identical conditions also using Cycle-Tempo. A comparison is made with the results from the solid oxide fuel cell study.Economics of Technology and InnovationProcess and Energ
Hydrogen Production by Internal Reforming Fuel Cells
No full textInternal reforming fuel cells have been developed based on the Molten Carbonate Fuel Cell as well as on the Solid Oxide Fuel Cell. In these concepts effective use is made of the high temperature of the fuel cell and the surplus of heat produced by the fuel cell. The high temperature allows the reforming of hydrocarbons to hydrogen by a reaction with steam. This is an endothermic reaction consuming part of the (waste) heat produced in the fuel cell, which thereby increases the fuel cell's efficiency. The capability of internal reforming fuel cells to reform hydrocarbons can be exploited further by producing more hydrogen than necessary for their own consumption.This can be done by decreasing electric power output or by increasing the input of hydrocarbons. By producing hydrogen the Nernst loss of the fuel cell decreases since also the area near the fuel exit still contains a high partial pressure of hydrogen contrary to standard operation. Total efficiency in terms of hydrogen and power output can reach 95% as was shown by flowsheet calculations. Furthermore since waste heat can be converted into hydrogen the fuel cell can be operated in higher power density compared to standard operation and still obtain relatively high efficiencies in terms of hydrogen and power production. Overall a very flexible system is obtained in which operation can be optimized depending on (local) demand and market prices for power, hydrogen and heat.
A very interesting but more exotic form of hydrogen production using fuel cells is a concept in which carbon is electrochemically converted into carbon monoxide and subsequently reacted with steam to form carbon dioxide and hydrogen in the well known shift reaction. The electrochemical reaction takes place in a Direct Carbon Fuel Cell operated at high temperature to promote the formation of CO above CO2 following the temperature dependance of the Boudouard equilibrium.
The reaction is characterized by a negative enthalpy change and a positive entropy change. Therefor the reversible electrochemical reaction is endothermic and next to chemical energy also heat is converted into electric power. The conversion process can be called ‘electrochemical gasification’ and is a true Multi Source Multi Product conversion system in which chemical energy and heat are converted into electric power and CO (to hydrogen).</jats:p
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