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Comparison of different system layouts to generate a substitute of natural gas from biomass and electrolytic hydrogen
No full textThe production of electrolytic hydrogen is considered among the best solution to mitigate the grid instability problems which arise from the widespread distribution of renewable energy sources, such as wind and solar. However, hydrogen is not easy to stock and distribute. Possible solutions are represented by its direct injection into the existing pipeline for natural gas distribution or its utilisation for the production of a substitute of natural gas. In this last case, which follows the so called approach of “power to gas”, a source of carbon is required. Preferably the carbon should come from biomass, since it can be considered “renewable carbon”. Starting from this idea, this study analyses two different approaches, depending on the grid power demand. In a first layout, biomass is gasified with electrolytic hydrogen to generate directly a methane rich syngas. After water condensation, the syngas is fed to a methanation process to convert almost completely carbon in methane. In the second layouts the biomass is gasified with electrolytic oxygen and the syngas is fed, together with other electrolytic oxygen, to a power unit, such as an internal combustion engine, a gas turbine or a high temperature fuel cells (SOFC). The exhaust gas from these power units is composed almost exclusively by carbon dioxide and water vapour. After water condensation, the carbon dioxide is fed together electrolytic hydrogen to a methanation process to obtain the substitute of natural gas. An overall best efficiency of roughly 74% is obtained when the plant is not connected to the grid. On the contrary, when electricity can be absorbed by the grid, best efficiency of 59.4% is reached utilising, as power unit, a SOFC fed at 6 bars. In all cases the input is low value energy (biomass and unstable electric power) and the output is high value energy constituted by a substitute of natural gas and stable electric power
From biomass and electrolytic hydrogen to substitute natural gas and power: The issue of intermediate gas storages
Full text linkThe possibility to upgrade biomass and intermittent power from renewable energy sources generating stable power and substitute natural gas (SNG) has been discussed in previous papers. Such papers focussed mainly on the choice and design of the most suitable power units to generate power and a high purity carbon dioxide stream to feed the methanation section; moreover, heat recovery strategies to improve the plant efficiency were investigated and implemented. In the proposed plant, power for electrolysis potentially comes from renewable energy sources (RES), thus arises the need to introduce gas storages in order to fully decouple the outputs (SNG flow and stable electric power) from the input intermittency. This paper analyses some different possible layouts for intermediate gas storages and compares them from an energy consumption point of view
A thermodynamic cycle with a quasi-isothermal expansion
No full textThe combustion of hydrogen and oxygen makes feasible a steam re-heating by mixing rather than by surface exchange. In such a way the use of several re-heaters is possible as well as the increase of re-heating temperature. The performances of steam power-plants with a large number of super-heaters (5-15) have been analyzed. Some theoretical considerations are also given in order to explain expectations, results and perspectives. Using so many super-heaters makes the expansion gradually approach isothermal conditions. A significant reduction of the efficiency gap with respect to the Carnot cycle was therefore expected. A thermal efficiency of 49.2% is achievable. Although this is far from the 61.6% of the Carnot cycle, the study points out some interesting aspects and suggests the basis for further development. © 1997 International Association for Hydrogen Energy
Hydrogen energy storage: Hydrogen and oxygen storage subsystems
No full textHydrogen seems to possess all the characteristics to store the excess of electrical energy produced during off-peak periods. Hydrogen energy storage plants could be environmentally non-polluting, easy to place, not sensible to load variation, unbounded in size, efficient and safe. These last two features seem to contradict one another. An option that could give a reliable solution is the storage of hydrogen in metal hydride and the storage of oxygen as a liquid. Such a choice is probably the safest one to make and allows the achievement of efficiencies comparable to those obtainable with gaseous storage of both electrolytic products. The power consumption for H2and O2storage is only 3% of the total energy stored and the charging ratio approaches the values obtained with hydro-pumped storage plants. © 1997 International Association for Hydrogen Energy
Cogeneration of power and substitute of natural gas using biomass and electrolytic hydrogen
Full text linkStoring renewable energy sources is becoming a very important issue to allow a further reduction of greenhouse gas emissions. Most of such energy sources generate electric power which not always can be conveniently transferred to the grid and also its conversion to hydrogen presents some critical aspects connected mainly to hydrogen distribution and storage. Electrolysis generates not only hydrogen, but also oxygen which could be used to burn biomass or waste products (oxycombustion) in power plants with the result to obtain an exhaust gas containing mainly water and CO2. This last can be converted into a mixture of methane and hydrogen by reacting with electrolytic hydrogen, so that the power used for electrolysis is stored into a fuel which can be distributed and stored just like natural gas. In this paper, an innovative biomass fuelled plant has been designed and simulated for different layouts with an internal combustion engine as a main power system. Utilizing hydrogen and oxygen produced through electrolysis and applying a hydrogasification process, the plant produces electricity and a substitute of natural gas. The result of such simulations is that the electricity can be stored in a useful and versatile fuel with a marginal efficiency up to 60%
Life Cycle Assessment of Substitute Natural Gas production from biomass and electrolytic hydrogen
Full text linkThe synthesis of a Substitute Natural Gas (SNG) that is compatible with the gas grid composition requirements by using surplus electricity from renewable energy sources looks a favourable solution to store large quantities of electricity and to decarbonise the gas grid network while maintaining the same infrastructure. The most promising layouts for SNG production and the conditions under which SNG synthesis reduces the environmental impacts if compared to its fossil alternative is still largely untapped. In this work, six different layouts for the production of SNG and electricity from biomass and fluctuating electricity are compared from the environmental point of view by means of Life Cycle Assessment (LCA) methodology. Global Warming Potential (GWP), Cumulative Energy Demand (CED) and Acidification Potential (AP) are selected as impact indicators for this analysis. The influence of key LCA methodological aspects on the conclusions is also explored. In particular, two different functional units are chosen: 1 kg of SNG produced and 1 MJ of output energy (SNG and electricity). Furthermore, different approaches dealing with co-production of electricity are also applied. The results show that the layout based on hydrogasification has the lowest impacts on all the considered cases apart from the GWP and the CED with SNG mass as the functional unit and the avoided burden approach. Finally, the selection of the multifunctionality approach is found to have a significant influence on technology ranking
MHD plants: A comparison between two-level and three-level systems
No full textThe present paper aims to analyse a way to improve the performance of magnetohydrodynamic systems by introducing a third level in a classic MHD/steam plant. The task of this further level is to reduce the energy loss between the MHD outlet (T > 2000 K) and the steam turbine inlet. Two layouts have been considered: the first one with an air open cycle and the second one with an air closed cycle. This last layout shows the best current efficiency, close to 60%, having an improvement of about 10% with respect to the two-level system. © 1997 Elsevier Science Ltd. All rights reserved
Parametric analysis of a steam cycle with a quasi-isothermal expansion
No full textUsing a hydrogen/oxygen steam generator it is possible to carry out many steam mixing re-heatings without increasing the complexity of a traditional steam power-plant: steam is not required to re-enter the boiler for each re-heating. An isothermal expansion could thus be approached by means of several adiabatic expansions and several steam mixing re-heatings. A theoretical investigation showed that an isothermal expansion could achieve high efficiency (up to 70% of HHV) when the waste heat at the turbine outlet is recovered for pre-heating water, hydrogen and oxygen. In a real plant the number of re-heatings that can be carried out, although high, is limited and we can therefore expect an efficiency drop which varies as a function of the number of re-heatings, the re-heating temperature and the maximum pressure. In order to evaluate real cycle performance, a numerical code, specifically created, was implemented
Characterization of hydrogen in metallic alloys suitable for electrolysis
Full text linkIn this work we determine some fundamental microscopic and macroscopic properties of metals and metallic alloys-hydrogen systems. We deal with simple hydride such as LiH, NaH e CaH 2, which react with water producing hydrogen. Using a calculus program based on the density functional formalism, we obtain values of important properties in the determination of the behaviour of the system, such as the variation of the electronic density and of the induced density of states due to the presence of hydrogen in the matrix. The general features of these methods are discussed and the corresponding results are compared with experimental data.Fil: Gervasoni, Juana Luisa. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Segui Osorio, Silvina Inda Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; ArgentinaFil: Spazzafumo, G.. Universidad de Cassino y del Lazio Meridional (u. de C. y del L. Meridional); Itali
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