1,721,050 research outputs found
Modeling an alkaline electrolysis cell through reduced-order and loss-estimate approaches
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Power-to-gas plants and gas turbines for improved wind energy dispatchability: Energy and economic assessment
Full text linkComparative assessment and safety issues in state-of-the-art hydrogen production technologies
Full text linkThis work discusses the development of a benchmark comparison among hydrogen production technologies, focussing on the assessment of their operating conditions by the point of view of the potential impact on safety. The analysis focuses on state-of-the-art, fully industrialized and commercial technologies, or at least with established early-market availability, not considering unconventional or emerging technologies still featuring a low technology readiness level. After a selection of hydrogen production technologies and their classification according to the possible feedstock, hydrogen purity and plant size, operating conditions and relative component sizes were calculated. Temperatures, pressures and chemical features are given in the most important points, as well as relative size of components, considering that these factors can be important by the point of view of safety. The qualitative comparison of the investigated technologies evidenced the presence of flammable and toxic mixtures at high temperature common to all the natural gas fed technologies, while gasifiers generally operates at lower temperature. ATR and gasifiers exhibit flammable and toxic gases at high pressure, as well as highly reactive streams (i.e. pure oxygen). This last is an aspect common also to electrolysis and POX. Common ranges for operating conditions are provided as a support for subsequent safety evaluation on how critical is a certain plant by the point of view of safety
Long-term P2G and hydrogen potential in an integrated energy system: coupling of power grid and mobility in Italy
No full textThis work analyses future high-RES energy scenarios at country scale, focusing on the interaction between the power grid and the mobility sector, where Power-to-Gas (P2G) is a key technology. A multi-node model is developed to represent the energy system, including additional load form plug-in electric vehicles and clean hydrogen generation from excess electricity (P2G) for fuel cell vehicles. Energy from RES is prioritised, either covering the load or feeding the storage. Italy is investigated as case study, considering the possible evolution up to 2030 and 2050. The simulations of the Italian energy system behaviour in 2050 yield a maximum of 57% RES share in the electricity mix, while biomass could account for a further 5%. The introduction of P2G technology results in a good exploitation of excess energy, thus increasing the overall RES share. High coverage of hydrogen mobility demand (about 81%) is achieved in presence of large installation of RES plants; however, the e-RES share stays far from the high targets proposed
Dynamic Quality Tracking of Natural Gas and Hydrogen Mixture in a Portion of Natural Gas Grid
Full text linkAbstractDirect injection of alternative fuels (biomethane, hydrogen) in the natural gas grid appears to be a promising solution to reach environmental objectives of CO2 emission reduction in the current energy scenario. This approach is justified by the large amount of biogas producible, which can be upgraded to biomethane; while another proposed solution to increase renewable energy sources exploitation lies in producing hydrogen from excess wind energy, followed by injection in the natural gas grid. Nevertheless, compliance with composition limitsand quality constraints in the resulting natural gas mixture has to be analysed in both stationary and dynamic operations, tracking the gas quality downstream the injection point of the alternative fuels. A model was developed to simulate unsteady operation of a portion of gas grid dealing with realistic industrial and residential consumptions concentrated in offtake points. Two case studies were investigated focusing on the comparison between different amounts of hydrogen injectionin the pure natural gasflow, yieldingcomposition, flow rate and pressure profiles. The analysis shows how imposed quality thresholds can berespected, although the hydrogen fraction within the natural gas mixture is highly sensitive to the profile and size of the loads connected to the gas pipeline
Dynamic modeling of natural gas quality within transport pipelines in presence of hydrogen injections
No full textIn the near future, the natural gas grid could face an increasing share of alternative fuels (biomethane, hydrogen) injected in addition to the traditional mixture. Indeed, this pathway is particularly promising in order to reach environmental objectives of CO2 emissions reduction, in both thermal and electrical final uses. Biogas is already abundantly produced and could be easily upgraded to biomethane; hydrogen technologies are still under development, but they can help the exploitation of the increasing availability of renewable energy sources. A promising solution to problems due to unpredictable fluctuations of renewable energy production (in particular related to wind parks) or excess energy with respect to the load lies in hydrogen production by electrolysis and further injection in the natural gas grid. In this scenario, the effects on design and management of the transport infrastructure should be investigated, and the compliance with composition limits and quality constraints has to be analyzed in both stationary and dynamic operation, tracking the gas quality downstream the injection point of the alternative fuels. A model was developed to simulate the unsteady operation of a portion of the gas grid; with respect to traditional volume-based approaches, a novel energy-based approach is developed, including variable composition along the pipes and allowing to consider a given energy delivery to customers as a constraint. After the validation against available operational data, a case study considering concentrated realistic domestic and industrial offtakes is simulated. The effects of hydrogen injection, usually not considered in NG grid design and operation analyses, are investigated in terms of composition, flow rate and pressure profiles with comparison to the reference natural gas case. The analysis shows how imposed quality thresholds can be respected, although the effects on calorific value, Wobbe index and density are not negligible; results indicate that the allowed hydrogen fractions are limited and highly sensitive to the profile and size of the offtakes connected to the pipeline. The discussion also evidences the potential impact of hydrogen injection on gas metering and measurements errors
Wind power plant and power-to-gas system coupled with natural gas grid infrastructure: Techno-economic optimization of operation
No full textIn this work, the coupled operation of a wind park and a hydrogen power-to-gas (P2G) technology is addressed in order to improve dispatchability and profitability of the wind resource. Among many available storage technologies currently under development, the P2G was chosen because of its large storage capacity and fast response. In particular, oppositely to traditional storage approaches, the solution that considers the direct injection of hydrogen in the natural gas grid infrastructure could reduce investment costs and improve the renewable fraction of fuels. Economic optimal operation and installed P2G power are calculated solving a mixed-integer linear programming (MILP) problem. Performances of the main component (electrolysis unit) are modeled, including additional costs for start-up and partial load operation losses. Technical limits on both electric and natural gas grids are also included. Some assumptions on the economic rules governing the electric grid unbalance are made, according to possible evolutions of the regulation framework focused on EU and Italian system. The simulation is performed on hourly basis, assuming realistic forecasted and real power production profiles from an actual mid-size (30 MW) wind power plant, together with prices of electricity markets and gas production. A sensitivity analysis is also performed varying both economic and technical parameters. Whereas in some scenarios the technology is profitable with the current investment costs, a reduction of electrolyzer costs down to expected mid-term targets would lead to a stronger competitiveness in each scenario. The study aims at identifying the influence of main technical and economic parameters on the effectiveness of the power-to-gas technology. Results show how the proposed solution allows better exploiting the wind resource, although the net electricity production can decrease due to the production of hydrogen, suggesting the possibility to substantially oversize the wind park in order to cover the same electric load
Investigating the partial load of reversible solid oxide cell systems: A focus on balance of plant and thermal integration
Full text linkSolid oxide cells are promising electrochemical devices capable of operating in both electrolysis and fuel cell modes with high electrical efficiency. This work investigates the design and partial-load operation of a reversible solid oxide cell (rSOC) system for steam electrolysis and hydrogen-based power generation, when adopting a unified balance of plant for both modes and molten salt thermal energy storage for thermal integration. Different configurations are compared with the aim of widening the part-load window, taking into account the electrochemical behavior as well as the changes in heat exchange properties. The definition of system efficiency losses with respect to the stack efficiency is proposed, helping in identifying the main causes of efficiency degradation throughout the part-load window. Results show that pre- or post-stack heaters are required when switching from exothermic to endothermic conditions. Moreover, they prove essential in keeping the rSOC in thermal balance also when the reaction is slightly exothermic. The use of electric heaters and hydrogen combustors is compared, and electric heaters appear to have the least impact on system efficiency at lower loads. For all configurations, the highest efficiency is obtained close to the thermoneutral point, which optimizes the trade-off between stack efficiency and system efficiency losses. Heat recovery in fuel cell mode is prominent at nominal load and could be beneficial in facilitating thermal integration between the two operational modes. However, the magnitude of its reduction at partial load is greater than the corresponding reduction in heat demand in electrolysis mode, leading to increased thermal imbalances between fuel cell and electrolysis modes
Techno-economic evaluation of biomass-to-methanol production via circulating fluidized bed gasifier and solid oxide electrolysis cells: A comparative study
Full text linkMethanol is considered a promising solution for decarbonizing the transportation and chemical industry sectors, being a worldwide traded commodity that can be synthesized from biomass, renewable electricity, CO2 and other carbon-rich gases. This study investigates the potential of Solid Oxide Electrolysis Cells (SOEC) in enhancing the performance of bio-methanol production from biomass gasification. The research explores three distinct biomass-to-methanol plant configurations, incorporating an oxygen-blown Circulating Fluidized Bed Gasifier (CFBG) and different SOEC systems, namely: (i) steam electrolysis for hydrogen generation, (ii) co-electrolysis of steam and CO2 separated from syngas and (iii) direct supply of purified bio-syngas to the SOEC. The study reveals that, although the choice of SOEC type and system configuration could impact energy conversion efficiency and carbon efficiency, all plants show similar performance. In terms of Levelized Cost of Fuel (LCOF) and total efficiency, the syngas-electrolysis configuration exhibits the lowest LCOF, 21.56 €/GJ, and comparable total efficiency of around 80 % to the steam-electrolysis configuration. On the other hand, the CO2-H2O-electrolysis configuration showed the highest LCOF due to higher electricity consumption and capital investment
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