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•Thermal decoupling of methanation and electrolysis is an effective solution.•Power-to-Gas feasibility is strictly related on oxygen selling and local grants.•Highly efficient natural ...gas production with 75% conversion efficiency.•Optimization suggests reducing the capacity of the methanation reactor.
This work presents a numerical analysis of a fully renewable Power-to-Gas system driven by photovoltaic and anaerobic digestion technologies, to produce synthetic renewable natural gas. The anaerobic digester is supplied by municipal wastes and it produces biogas, including about 35 % of carbon dioxide. This carbon dioxide is separated by means of an upgrading unit and it is combined in a three stage multi-tubular methanation reactor with the hydrogen produced by solid oxide electrolysis. A novel control strategy is developed to achieve a stable, safe, and efficient operation of the reactor. Suitable zero-dimensional and one-dimensional steady state models are developed in MatLab for the solid oxide electrolyzer and the methanation reactor. Such MatLab models are subsequently integrated into TRNSYS environment to perform the dynamic simulation for one year of operation of the whole system. A suitable thermoeconomic analysis is also implemented, also considering the possibility of selling the oxygen produced by the electrolyzer for industrial purposes. The results show that the proposed system achieves a primary energy saving of 30.33 GWh per year with 6,330 tCO2eq per year saved. The economic profitability of the is also very good, showing a Simple Payback of 2.63 years. The income due to the selling of oxygen plays a crucial role in this result. The overall efficiency of the system is equal to 0.75, that is extremely high when compared to similar layouts. The results from the thermoeconomic optimization show that the lowest Simple Payback value, i.e. less than 2 years, is obtained when the capacity of the methanation reactor is reduced by five times.
The power-to-methane process using a solid-oxide electrolyser, followed by an exothermic methanation reactor, is effective for the production of an energy carrier (synthesis methane) that can be ...readily stored and transported at a large scale. A significant gain of the coupling is the steam generation from the heat produced by the methanation reaction for the more effective steam electrolysis (compared to liquid water electrolysis). This paper investigates, both theoretically and experimentally, the system integrability and operability of an evaporating water-cooled methanation reactor designed for thermal coupling with a solid-oxide electrolyser. The results show that the pressurized steam generation directly by the reactor’s cooling system improves the flexibility of the system design. Under certain conditions, an increase in overall power-to-methane efficiency of more than 3 % can be obtained from the use of a superheater and a turbine located after the evaporation process. The parametric study of the methanation reactor indicates that decreasing the flowrate of the H2 and CO2 mixture, increasing the reaction gas pressure and increasing the cooling system pressure (saturation temperature) shifts the hot spot towards the inlet and improves the H2 conversion rate, which can reach above 97 %. It was determined that, under steady-state operation, the steam generation can be sufficiently stable for injection into the solid-oxide electrolyser; rapid pulsations with a standard deviation under 10% were measured. The calibrated 1D pseudo-homogeneous plug flow reactor model captures many of the trends, though, the assessment is limited without the exact kinetic model of the catalyst pellets.
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•A partially evaporating water-cooled fixed-bed methanation reactor was built.•>97% H2 conversion reached within available pressure ranges.•The second CO2 injection has limited hot spot control potential within tested range.•Sufficiently stable steam generation for the coupling with solid-oxide electrolysers.
The present work studies the effect of reagent preheat temperature on methanation while maintaining the initial temperature of the catalytic bed constant. An adiabatic packed bed reactor was used ...with 193 g of commercial 10% Ni/Al2O3 catalyst. The tested preheat temperatures were 25 °C, 100 °C, 180 °C, and 280 °C, while the initial catalytic bed temperature was 280 °C. Two tests were performed in which the effect of preheat temperature was evaluated: the first comparing gas hourly space velocities (GHSVs) of 935 h−1 and 1559 h−1, and the second comparing gauge pressures of 0 bar, 1 bar, and 4 bar. Similar behavior was observed for the temperature inside the reactor and final CO2 conversion for preheating temperatures of 100 °C, 180 °C, and 280 °C at a gauge pressure of 0 bar. However, at this pressure, conversion was considerably reduced for the preheat temperature of 25 °C, due to a large part of the catalytic bed serving to preheat the reactants to the minimum reaction temperature. This effect can be partially attenuated by decreasing the GHSV, due to the increased residence time. Finally, increased pressure significantly improved the final CO2 conversion for all preheating temperatures (Tin), and attenuates the effect of Tin. These results show that certain operating conditions do not require as high a reactant preheat temperature for methanation, which offers energy savings in certain processes such as power-to-gas (P2G), where the hydrogen is produced from electrolysis and can leave the process at a lower temperature than that required for methanation.
•Under high pressure, no high reactant preheating temperature is required in a methanation reaction.•The CO2 conversion is highly dependent on preheating temperature in atmospheric methanation reaction.•CO production is highly dependent on the reactant preheating temperature under low pressures.
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•A directly solar-driven power-to-methane system is proposed.•The detailed distributed parameter method is used to model the system.•A comprehensive thermodynamic and economic ...analysis is performed.•Energy and exergy efficiencies are 9.88% and 11.08% with 914.51 MWh/y SNG yield.•Unit cost is 186.57 $/MWh in 2020 and will be reduced to 91.51 $/MWh in 2050.
The transformation of solar energy into easily transportable and storable fuel brings a prospective solution to the issue caused by its intermittency and non-dispatching. Relying on well-established infrastructures and mature technologies for application, methane can be an attractive energy carrier for improving the penetration of solar energy in the future energy structure. To evaluate the feasibility of solar-to-methane from technical and economic views, this paper proposes a directly solar-driven power-to-methane system integrating photovoltaic plant, solid oxide electrolysis cell, methanation reactor, and membrane module. The detailed distributed parameter method is employed for thermodynamically modeling the core components of the system to consider the profiles of current density, temperatures, and composition concentrations. A comprehensive thermodynamic and economic analysis is further conducted for the system, and the results indicate that the power-to-methane efficiency, total energy efficiency, and total exergy efficiency of the system can reach 68.41%, 9.88%, and 11.08%, respectively. With the annual average solar radiation of 557.43 W/m2, the system achieves an annual synthetic natural gas yield of 914.51 MWh/y. A high total product unit cost of 186.57 $/MWh is obtained in 2020, whereas it is predicted to decrease to 91.51 $/MWh (about 51% reduction) in a future scenario with a payback period of 4.66 years due to the significant decrement of the photovoltaic investment cost. The present work reveals the engineering realizability and economic viability of solar-to-methane and provides a competitive option for the development of solar energy.
•Optimal design is determined for a power-to-methane system.•Performance analysis is performed for the system under off-design conditions.•ANN model is established for off-design performance ...prediction.•ANN-based optimization is conducted to obtain optimal off-design performances.
Power-to-methane (PtM) is a prospective solution to the mismatching between the supply and consumption of renewable energy resources (RES) by converting renewable power into methane. However, the continuous fluctuation of RES causes the PtM system to deviate from the design condition in the vast majority of cases, and thus it is significantly vital to study the operating characteristics of the PtM system under off-design conditions. This paper proposes a comprehensive investigation framework from design to off-design steps for the performance improvement of a PtM system combining solid oxide electrolysis cell with methanation reactor, and solar energy is selected as renewable energy input. Firstly, the system with the total exergy efficiency (ηEX,tot) of 11.83% and levelized cost of exergy (LCOE) of 150.76 $/MWh is selected as the optimal design condition based on the homogeneous assessment from both thermodynamic and economic aspects, by means of Non-dominated sorting genetic algorithm-II. Then, based on the optimal design point, the off-design performances are quantitatively investigated under varying solar radiation and key operating parameters, in terms of synthetic natural gas (SNG) yield and ηEX,tot. The results indicate that with the increment in solar radiation, the SNG yield rises, while the ηEX,tot increases first and then decreases. Finally, the multi-objective optimization based on the Artificial Neural Network models is implemented for the system under off-design conditions to acquire the best trade-off between hourly SNG yield and ηEX,tot. The off-design optimization solutions reveal that the hourly optimal SNG yield is located in the range of 275.06 kW to 946.53 kW, achieving a total annual SNG yield of 1697 MWh/y, and the hourly optimal ηEX,tot mainly varies in the range of 10.40-11.40%.
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•Carbon neutral methane production by chemical conversion of CO2 waste flue gases.•Using renewable energy in a circular economy scheme.•Plasmas generation by electrical discharges on ...CO2+H2 gas mixtures.•New emerging catalysts development in chemical engineering.•Plasma-assisted CO2 conversion on CH4 fuel.
An experimental study aiming at reusing CO2 and implementing a validated laboratory technology based on a prototype methanation reactor (ProGeo) producing carbon neutral methane through the chemical conversion of CO2 waste flue gases using renewable energy in a circular economy scheme, is presented. ProGeo is able to produce a CH4 flux of 1 Nm3/h, using the Sabatier reaction at high pressure (1.5–3 bar) and temperature (200–400 °C) with a solid phase catalyst. Furthermore, the investigation of a new methanation pathway by exploring mechanisms involving a plasma generation by electrical discharges on CO2+H2 gas mixtures has been undertaken. Obtained results indicate the formation of hydrocarbons as methane, formic acid and/or dimethyl ether as well as small amounts of HCO+, H2CO+, H3CO+, HCO2+ ions. These ionic species together with CO+ and O+ ions, having a very high kinetic energy content, should increase the chemical reactivity of generated plasmas playing a pivotal role in the plasma-assisted CO2 conversion on CH4 fuel. Further experimental work is in progress to optimize the experimental conditions of the CO2 methanation process via alternative microscopic mechanisms, using plasma assisted catalyzed reactions that are of great importance in new emerging catalysts development in chemical engineering.
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•A prototype experimental apparatus reusing CO2 to produce CH4 was assembled.•Experiments and simulations run to a better understanding of the reaction mechanism.•An alternative path ...to a gas-phase-only process to the reduction of CO2 to CH4 has been outlined.
Leveraging on the experience gained by designing and assembling a prototype experimental apparatus reusing CO2 to produce methane in a reaction with H2, we are developing an alternative innovative cost effective and contaminant resistant synthetic strategy based on the replacement of the solid phase catalysis with a homogeneous gas phase process going through the forming CO22+molecular dications.
The need to decarbonize industrial processes and to increase the utilization of renewable resources, either energy and raw materials, has led to the development of new production processes. The focus ...of this paper is to evaluate the environmental impacts of an innovative 1 kW pilot plant for methane production, following the life cycle thinking approach. The process is based on the coupling of an alkaline water electrolysis, which generates syngas using a carbon source, with a methanation reactor that converts the syngas to methane. The life cycle assessment (LCA) takes into account the pilot plant construction materials, electricity and reactants used, for a functional model of a mole of methane produced per hour of operation. Data from the pilot plant, in particular reaction conversions, were used complemented with data from the literature and inventory databases. Energy and the construction materials used to build the experimental unit are the main factors influencing the environmental performance. Several scenarios were defined varying the electricity source and the carbon source, showing the results that the energy source is more relevant to reduce the process environmental impacts. The results can be used to scale-up and to better implement the combined electrolysis methanation process in industrial practice.
•A Life Cycle Assessment of methane production in an innovative combined electrolyzer/methanation reactor process was done.•Energy and construction materials are the main factors influencing the environmental performance.•Several scenarios were analyzed varying the energy source and carbon source.•Replacing the energy source to fully renewable has the largest reduction of the environmental impact.
Biomass-based synthetic natural gas (Bio-SNG) has attracted extensive attention in recent years. In order to analyze the energy efficiency of Bio-SNG production system, a simulation model of this ...system via interconnected fluidized beds and fluidized bed methanation reactor is built and validated. Then, the influences of operating conditions and biomass categories on the energy efficiency are studied. The results show that the Bio-SNG production process can achieve energy efficiency higher than 64 %. There exists an appropriate gasification temperature (around 750 °C), gasification pressure (about 0.3 MPa), ratio of steam to biomass (ranging from 0.4 to 0.8), methanation temperature (around 350 °C), and pressure (around 0.3 MPa) to maximize the energy efficiency. With respect to the typical biomass, the highest energy efficiency is found in sawdust, while the lowest is in rice straw. After comparing with the hydrogen production and diesel oil production from biomass, the Bio-SNG production is more competitive in the energy efficiency.
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