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Hofmann Ph.,Laboratory of Steam Boilers and Thermal Plants | Panopoulos K.D.,Center for Research and Technology Hellas
Journal of Power Sources

This paper presents a detailed flexible mathematical model for planar solid oxide fuel cells (SOFCs), which allows the simulation of steady-state performance characteristics, i.e. voltage-current density (V-j) curves, and dynamic operation behavior, with a special capability of simulating electrochemical impedance spectroscopy (EIS). The model is based on physico-chemical governing equations coupled with a detailed multi-component gas diffusion mechanism (Dusty-Gas Model (DGM)) and a multi-step heterogeneous reaction mechanism implicitly accounting for the water-gas-shift (WGS), methane reforming and Boudouard reactions. Spatial discretization can be applied for 1D (button-cell approximation) up to quasi-3D (full size anode supported cell in cross-flow configuration) geometries and is resolved with the finite difference method (FDM). The model is built and implemented on the commercially available modeling and simulations platform gPROMS™. Different fuels based on hydrogen, methane and syngas with inert diluents are run. The model is applied to demonstrate a detailed analysis of the SOFC inherent losses and their attribution to the EIS. This is achieved by means of a step-by-step analysis of the involved transient processes such as gas conversion in the main gas chambers/channels, gas diffusion through the porous electrodes together with the heterogeneous reactions on the nickel catalyst, and the double-layer current within the electrochemical reaction zone. The model is an important tool for analyzing SOFC performance fundamentals as well as for design and optimization of materials' and operational parameters. © 2010 Elsevier B.V. All rights reserved. Source

Nikolopoulos N.,Center for Research and Technology Hellas | Violidakis I.,Center for Research and Technology Hellas | Karampinis E.,Center for Research and Technology Hellas | Agraniotis M.,Mitsubishi Hitachi Power Systems Europe GmbH | And 5 more authors.

Lignite constitutes a major energy source and has long been used for energy production despite its contribution in greenhouse gas (GHG) emissions, as a fossil fuel. For example, 27.4% of Germany's electricity originates from lignite power plants, while in Greece more than 55% of its electric energy consumption is provided by lignite. 45% of the total global coal reserves consist of low-rank coals (LRCs) such as lignite. With this background, the utilization of lignite for energy production is expected to remain a common practice in the decades to come since the availability of lignite is considerable in many countries of Europe and the world (e.g. Germany, Poland, Greece, USA, and Australia). Therefore, problems regarding the combustion and use of lignite should be addressed in a more efficient and environmentally friendly way. One of the main existing problems is the high moisture contained in raw lignite as received from the mine. The high moisture content results in higher CO2 emissions per unit of energy produced and is responsible for high capital and transport costs as well as other technical problems such as reduction in coal friability and difficulties in its blending and pneumatic transportation. Therefore, processing of lignite through drying is considered of great interest in the implementation of energy production in lignite power plants. Taking into account the significance of the subject and the usefulness of such an attempt, an overview of the currently existing drying technologies, including both evaporative and non-evaporative drying methods is reported in the present paper. © 2015 Elsevier Ltd. Source

Drosatos P.,Center for Research and Technology Hellas | Nikolopoulos N.,Center for Research and Technology Hellas | Agraniotis M.,Center for Research and Technology Hellas | Itskos G.,Center for Research and Technology Hellas | And 3 more authors.

In this work, we simulated the convective section of Unit I of Meliti Power Plant (330 MWel) in Florina, Greece, using the macro heat exchanger model (MHEM). As boundary conditions, previous temperature and velocity field data have been used, referring to the exit surface of combustion chamber. The MHEM approximates the pressure losses, using the porous media model, and the heat transfer, using the number of transfer units (NTU) model. The results have been validated against standard operating data, provided by the plant manufacturer. The working fluid outlet temperature for each heat exchanger, the total heat transfer, and the temperature distribution throughout the whole convective section have been calculated, showing good agreement with the respective data, under full operational load. Further, a parametric investigation of the level has been conducted, in order to validate the applied boundary conditions. Overall, we evidence that the MHEM can be a quite effective alternative for heat exchanger simulations. © 2013 Elsevier Ltd. All rights reserved. Source

Perdikaris N.,Laboratory of Steam Boilers and Thermal Plants | Panopoulos K.D.,Center for Research and Technology Hellas | Hofmann Ph.,Laboratory of Steam Boilers and Thermal Plants | Spyrakis S.,Laboratory of Steam Boilers and Thermal Plants | And 2 more authors.
International Journal of Hydrogen Energy

The Solid Oxide Cells (SOCs) are able to operate in two modes: (a) the Solid Oxide Fuel Cells (SOFCs) that produce electricity and heat and (b) the Solid Oxide Electrolyser Cells (SOEC) that consume electricity and heat to electrolyse water and produce hydrogen and oxygen. The present paper presents a carbon free SOEC/SOFC combined system for the production of hydrogen, electricity and heat (tri-generation) from natural gas fuel. Hydrogen can be locally used as automobile fuel whereas the oxygen produced in the SOEC is used to combust the depleted fuel from the SOFC, which is producing electricity and heat from natural gas. In order to achieve efficient carbon capture in such a system, water steam should be used as the SOEC anode sweep gas, to allow the production of nitrogen free flue gases. The SOEC and SOFC operations were matched through modeling of all components in Aspenplus™. The exergetic efficiency of the proposed decentralised system is 28.25% for power generation and 18.55% for production of hydrogen. The system is (a) carbon free because it offers an almost pure pressurised CO2 stream to be driven for fixation via parallel pipelines to the natural gas feed, (b) does not require any additional water for its operation and (c) offers 26.53% of its energetic input as hot water for applications. © 2009 Professor T. Nejat Veziroglu. Source

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