1,721,022 research outputs found
Design, development and testing of SOEC-based Power-to-Gas systems for conversion and storage of RES into synthetic methane
Full text linkInternational and national initiatives are promoting the worldwide transition of energy systems towards power production mixes increasingly based on Renewable Energy Sources (RES). The integration of large shares of RES into the actual electricity infrastructure is representing a challenge for the power grids due to the fluctuating characteristics of RES. The adoption of long-term, large-scale Electric Energy Storage (EES) is envisaged as the key-option for promoting the integration of RES in the electricity sector by overcoming the issue of temporal and spatial decoupling of electricity supply and demand. Among the several EES options, one of the most promising is the conversion of energy from the electrical into the chemical form through the synthesis of H2 and synthetic natural gas (SNG) in Power-to-Gas (P2G) systems based on the electrolysis of water (and also CO2) in Solid Oxide Cells (SOCs). The application of SOC technology in P2G solutions shows attractiveness for the high efficiency of high-temperature electrolysis and the flexibility of SOCs that can operate reversibly as electrolyzers or fuel cells (rSOC) and can directly perform the electrochemical conversion of CO2 and H2O to syngas by co-electrolysis. The capability of reversible operation also allows the application of SOC-based systems to Power-to-Power (P2P) concepts designed for deferred electricity production. This dissertation is focused on the investigation of electricity storage using Power-to-Gas/Power systems based on SOCs. The aim of this Thesis has been the investigation of the thermo-electrochemical behavior of SOCs integrated P2G/P2P systems, with the purpose to identify the system configuration and the operating conditions that ensure the most efficient electricity-to-SNG (P2G) or electricity-to-electricity (P2P) conversion within the thermal limits imposed by state-of-the art SOC materials. To this purpose, a detailed thermo-electrochemical model of an SOC has been developed at cell level, validated on experimental data, extended at stack level and coupled with models of the main P2G/P2P components for the system analysis. Model validation was performed through the characterization of planar commercial SOCs in the reversible operation as electrolyzers (SOEC) and fuel cells (SOFC) with H2/H2O and CO/CO2 fuel mixtures at different reactant fractions and temperatures. The physical consistency of electrode kinetic parameters evaluated from the model was verified with the support of literature studies. The investigation of SOC-based P2P and P2G solutions was performed using the models developed. Three different configurations were analyzed and simulated: 1) hydrogen-based P2P with rSOC, 2) SOEC-based electricity storage into hydrogen with subsequent SNG production by methanation with CO2 and 3) electricity storage by co-electrolysis of water and carbon dioxide with SOEC for syngas production and subsequent upgrading to SNG by methanation. The performance of the P2P system was thoroughly assessed by analyzing the effects of rSOC stack operating parameters (inlet gas temperature, oxidant-to-fuel ratio, oxidant recirculation rate, cell current) and system configurations (pressurized/ambient rSOC operation, air/oxygen as oxidant/sweep fluid) on stack and system efficiency. The analysis allowed to identify the most efficient configuration of the P2P system, and to select the feasible operating currents (i.e., the currents included within the limits given by the physical thermal constraints of SOC materials) for which the highest roundtrip efficiency is achieved. Pressurized rSOC operation (10 bar) with pure oxygen as oxidant/sweep gas and full recirculation of the oxidant flow ensured the highest charging and discharging effectiveness, with a system roundtrip efficiency of 72% when the stack is operating at the maximum efficiency currents (-1.3 A/cm2 in SOEC and 0.3 A/cm2 in SOFC). A dynamic analysis was performed on the rSOC to determine the characteri
Thermodynamic assessment of non-catalytic Ceria for syngas production by methane reduction and CO2 + H2O oxidation
Full text linkChemical looping syngas production is a two-step redox cycle with oxygen carriers (metal oxides) circulating between two interconnected reactors. In this paper, the performance of pure CeO2/Ce2O3 redox pair was investigated for low-temperature syngas production via methane reduction together with identification of optimal ideal operating conditions. Comprehensive thermodynamic analysis for methane reduction and water and CO2 splitting was performed through process simulation by Gibbs free energy minimization in ASPEN Plus®. The reduction reactor was studied by varying the CH4/CeO2 molar ratio between 0.4 and 4 along with the temperature from 500 to 1000 °C. In the oxidation reactor, steam and carbon dioxide mixture oxidized the reduced metal back to CeO2, while producing simultaneous streams of CO and H2 respectively. Within the oxidation reactor, the flow and composition of the mixture gas were varied, together with reactor temperature between 500 and 1000 °C. The results indicate that the maximum CH4 conversion in the reduction reactor is achieved between 900 and 950 °C with CH4/CeO2 ratio of 0.7–0.8, while, for the oxidation reactor, the optimal condition can vary between 600 and 900 °C based on the requirement of the final product output (H2/CO). The system efficiency was around 62% for isothermal operations at 900 °C and complete redox reaction of the metal oxide
Investigation of a novel concept for hydrogen production by PEM water electrolysis integrated with multi-junction solar cells
No full textA 2D finite element model of a high-pressure PEM water electrolyzer is developed and validated over experimental data obtained from a demonstration prototype. The model includes the electrochemical, fluidic and thermal description of the repeating unit of a PEM electrolyzer stack. The model is applied to the simulation of a novel system composed by a high-temperature, high-pressure PEM electrochemical cell coupled with a photovoltaic multi-junction solar cell installed in a solar concentrator. The thermo-electrochemical characterization of the solar-driven PEM electrolysis system is presented and the advantages of the high-temperature operation and of the direct coupling of electrolyzer and solar cell are assessed. The results show that the integration of the multi-junction cell enhances the performance of the electrolyzer and allows to achieve higher system efficiency compared to separated photovoltaic generation and hydrogen production by electrolysis
Optimal design of stand-alone solutions based on RES + hydrogen storage feeding off-grid communities
Full text linkNumerical study on performance enhancement of a solid oxide fuel cell using gas flow field with obstacles and metal foam
Full text linkThis study investigates the impact of gas flow field design on the performance of a solid oxide fuel cell (SOFC). A three-dimensional numerical model of the cell and channel is developed to simulate the use of metal foam as flow distributor, along with the presence of obstacles in the gas flow channels. The model is calibrated using experimental data and applied to simulate four relevant cases combining metal foam and obstacles, compared to a straight channel structure. The results demonstrate the positive impact of flow-field modifications on the distribution of species along the cell’s active layers. It is found that, even though the pressure drops are affected, reactant gases are more uniformly distributed across the active electrode of the cell, reducing mass transport losses and enhancing current density. Simulations performed at a cell voltage of 0.7 V indicate that incorporating a metal foam as flow distributor increases the maximum current density by 26 % compared to the conventional straight flow design. Furthermore, combining metal foam with obstacles results in the best performance, achieving a 34 % increase in the maximum current density
Reversible operation of planar solid oxide cells with H2/H2O and CO/CO2 mixtures: Modeling and experimental validation
No full textSystem efficiency analysis of dual interconnected bubbling fluidized bed reactors for solar fuel production
No full textBenefits from heat pipe integration in H2/H2O fed SOFC systems
No full textThe Solid oxide fuel cell (SOFC) is an electrochemical energy-conversion device considered as a promising solution because of its high electrical efficiency, fuel flexibility and modularity with relevant environmental benefits. However, high temperatures and thermal gradients cause significant problems for the practical application of SOFC systems. SOFC operating conditions have to be maintained within specific bounds with limitation in the maximum achievable current density in order to avoid excessive degradation. Relevant air flow rate values are also required for a correct thermal management, dealing with the highly exothermicity of the SOFC operation. In this context, the integration of planar liquid metal heat pipes into the stack structure can contribute to reduce thermal gradients within the stack itself while lowering the parasitic consumption of the air blower since less convective cooling is required. In the present work, a model implementing different SOFC cells interposed between two planar heat pipe plates filled with sodium is developed. In particular, an SOFC system fed with a H2/H2O mixture is assessed (the most stringent thermal condition because of the absence of internal reforming). The maximum permissible current density is then evaluated by varying the air utilization factor (AU). The limiting operating conditions are identified by taking into account the following constraints: maximum cell temperature, maximum global and local temperature gradients and heat pipe transport limits. A comparison of the system with and without the presence of heat pipes is then carried out with the aim of highlighting the positive effects derived from their integration. Results from simulations show a remarkable improvement of the system performance with heat pipes, which allow to reach higher values of current densities (and so power densities) with a consequent economic benefit
H2-based energy storage systems in remote areas: the REMOTE project
Full text linkThe REMOTE project has the objective to demonstrate the techno-economic feasibility of hydrogen-based energy storage solutions in isolated micro-grids and off-grid remote areas. Four DEMOs will be installed in four different location across Europe: Ginostra (South of Italy), Agkistro (Greece), Ambornetti (North of Italy) and Froan Island (Norway). The four sites will be characterized by different types of renewable sources (i.e., solar, wind, biomass and water fall) and user loads (i.e., residential and/or industrial), which will affect differently the design and management of the hybrid storage solution. The variety of the DEMO cases can thus provide a robust demonstration of the benefits derived from these innovative storage systems paving way for their deployment at large.
According to the ‘Power-to-Power (P2P)’ solution, renewable energy exceeding the electric demand, rather than being curtailed, is supplied to an electrolyzer for hydrogen production. In the four cases under consideration, the alkaline and PEM technology are considered for the electrolysis section. In case of renewable power shortages, PEM fuel cell stacks are then employed for hydrogen conversion into electricity. A battery bank is also coupled with the hydrogen section because of its short-term and quick response capability. Local Renewable Energy Sources (RES) can be therefore better used allowing to reduce or even eliminate the intervention of traditional diesel generators and avoid unstable connections to the grid, if present.
The aim of the presented work is to demonstrate the effectiveness of the H2-based P2P solution in reducing the usage of external sources (e.g., diesel genset) by maximizing the exploitation of local RES. Operation strategy models have been developed in order to perform energy balance simulations on a yearly basis. Results showed the usefulness of the P2P operation: in Ginostra, for example, the intervention of diesel generators can be reduced to less than 5% of the total load. Hydrogen was found to be particularly effective as a longer term energy storage solution. Economic considerations are also provided to outline the economic viability of the suggested RES and H2-based scenario
Numerical study of electrode permeability influence on planar SOFC performance
No full textA solid oxide fuel cell (SOFC) is a clean and very efficient electrochemical conversion device, which generates electricity directly from fuel electrochemical oxidation. In this paper, a three dimensional numerical model has been developed in order to analyse the role of some thermophysical and morphological parameters on the performance of the SOFC cell. In particular, we studied the effect of the variation of permeability of the electrodes: fuel distribution, ionic and electric current density, pressure and diffusion flux are analyzed and compared. The volume fraction of the ionic and electronic phase in the electrodes is studied using a parametric study. It was shown that the current density enhanced by decreasing the permeability, up to a defined value, and it diminished with very small permeability. A remarkable influence of pressure and diffusion of species on the performance of the cell, with the variation of permeability, has been recognized. Varying the permeability in the active layer of electrodes has a large impact on the current density, connected to the volume fraction of ionic phase. This study permits to comprehend the relationship between the performance and microstructure of SOFCs. Meanwhile, it furnishes theoretical guidance for an optimum design of the electrode permeability
- …
