This paper presents a comprehensive overview on the current status of solid oxide fuel cell (SOFC) energy systems technology with a deep insight into the techno-energy performance. In recent years, SOFCs have received growing attention in the scientific landscape of high efficiency energy technologies. They are fuel flexible, highly efficient, and environmentally sustainable. The high working temperature makes it possible to work in cogeneration, and drive downstream bottomed cycles such as Brayton and Hirn/Rankine ones, thus configuring the hybrid system of a SOFC/turbine with very high electric efficiency. Fuel flexibility makes SOFCs independent from pure hydrogen feeding, since hydrocarbons can be fed directly to the SOFC and then converted to a hydrogen rich stream by the internal thermochemical processes. SOFC is also able to convert carbon monoxide electrochemically, thus contributing to energy production together with hydrogen. SOFCs are much considered for being supplied with biofuels, especially biogas and syngas, so that biomass gasifiers/SOFC integrated systems contribute to the “waste to energy” chain with a significant reduction in pollution. The paper also deals with the analysis of techno-energy performance by means of ad hoc developed numerical modeling, in relation to the main operating parameters. Ample prominence is given to the aspect of fueling, emphasizing fuel processing with a deep discussion on the impurities and undesired phenomena that SOFCs suffer. Constituent materials, geometry, and design methods for the balance of plant were studied. A wide analysis was dedicated to the hybrid system of the SOFC/turbine and to the integrated system of the biomass gasifier/SOFC. Finally, an overview of SOFC system manufacturing companies on SOFC research and development worldwide and on the European roadmap was made to reflect the interest in this technology, which is an important signal of how communities are sensitive toward clean, low carbon, and efficient technologies, and therefore to provide a decisive and firm impulse to the now outlined energy transition.
Renewable sources and electric distribution network can produce or make available a surplus of electric and thermal energies. The Intermediate Temperature Solid Oxide Electrolyzer (IT-SOE) fed by CO2-steam mixtures can store these electric and thermal energies producing CO-H2 mixtures with high conversion efficiency. Inside the IT-SOE, the CO2-steam mixtures are converted into CO-H2 mixtures and O2 through cathodic and anodic electrochemical reactions and reverse water gas shift chemical reactions. In this article an IT-SOE stack fed by different types of steam mixtures was tested at different operating temperatures and the stack polarization and electric power curves were detected experimentally. At the highest hydrogen production operating temperature of the stack fed by steam mixtures, the experimental polarization and electric power curves of the stack fed by steam and CO2-steam mixtures were compared. A simulation model of the IT-SOE system (stack and furnace) fed by CO2-steam mixtures was formulated ad hoc and implemented in a MatLab environment and experimentally validated. At the highest hydrogen production stack operating temperature, the IT-SOE system thermal equilibrium current was evaluated through the simulation model. Moreover, the influence of this current on the IT-SOE system efficiency and the CO-H2 mixture degree of purity was highlighted.
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