Study of the effect of noble metal promotion in Ni-based catalyst for the Sabatier reaction

This paper reports the preparation and the evaluation of the performance of Ni-based powder catalysts with low nickel loading on the CO2 methanation reaction, that is an integral part of the power-to-gas (PtG) technology. CeO₂, CeZrO₄ and CeO₂/SiO₂ were selected as possible supports, and the results of this first screening pointed out that 10%Ni/CeO₂ catalyst could offer the best reaction performances because of ceria's peculiar characteristics. Moreover, the promotion of this promising formulation with the addition of a small amount of noble metals (Pt, Ru, Rh) was investigated, showing that platinum in particular can enhance the catalyst performances. A further study related to the noble metal loading pointed out that platinum and ruthenium have a different optimum loading condition: this result, together with the activity tests performed on monometallic formulations with only the noble metal, suggested that the two metals are able to catalyse two different reactions, thus promoting two different reaction mechanisms.     

Energiepark Mainz: Technical and economic analysis of the worldwide largest Power-to-Gas plant with PEM electrolysis

The following paper is an analysis of the operating experiences during the initial phase of the 6 MW PEM electrolysis project “Energiepark Mainz”. The paper is divided into a technical and an economic evaluation. The technical evaluation contains the calculation of the efficiency of the Power-to-Gas plant based on the total power consumption, as well as the energy utilization factor. The economic evaluation analyses the different options of electricity procurement for the electrolysis. The three options, electricity purchase at the European power exchange, excess electricity from a direct marketing company, and participating in the control reserve market have been analysed. One first outcome shows, that economic feasibility can mainly be improved through participation in the secondary control reserve market.     

Renewable Power-to-Gas: A technological and economic review

The Power-to-Gas (PtG) process chain could play a significant role in the future energy system. Renewable electric energy can be transformed into storable methane via electrolysis and subsequent methanation.This article compares the available electrolysis and methanation technologies with respect to the stringent requirements of the PtG chain such as low CAPEX, high efficiency, and high flexibility.Three water electrolysis technologies are considered: alkaline electrolysis, PEM electrolysis, and solid oxide electrolysis. Alkaline electrolysis is currently the cheapest technology; however, in the future PEM electrolysis could be better suited for the PtG process chain. Solid oxide electrolysis could also be an option in future, especially if heat sources are available.Several different reactor concepts can be used for the methanation reaction. For catalytic methanation, typically fixed-bed reactors are used; however, novel reactor concepts such as three-phase methanation and micro reactors are currently under development. Another approach is the biochemical conversion. The bioprocess takes place in aqueous solutions and close to ambient temperatures.Finally, the whole process chain is discussed. Critical aspects of the PtG process are the availability of CO₂ sources, the dynamic behaviour of the individual process steps, and especially the economics as well as the efficiency.     

Parametric study of an efficient renewable power-to-substitute-natural-gas process including high-temperature steam electrolysis

Power-to-Substitute Natural Gas processes are investigated to offer solutions for renewable energy storing or transportation. In the present study, an original Power-to-SNG process combining high-temperature steam electrolysis and CO₂ methanation is implemented and simulated. A reference process is firstly defined, including a specific modelling approach of the electrolysis and a methanation modelling including a kinetic law. The process also integrates a unit to clean the gas from residual CO₂, H₂ and H₂O for gas network injection. Having set all the units, simulations are performed with ProsimPlus 3™ software for a reference case where the electrolyser and the methanation reactors are designed. The reference case allows to produce 67.5 Nm³/h of SNG with an electrical energy consumption of 14.4 kW h/Nm³. The produced SNG satisfies specifications required for network injection. From this reference process, two sensitivity analyses on electrolysis and methanation working points and on external parameters and constraints are considered. As a main result, we observe that the reference case maximises both process efficiency and SNG production when compared with other studied cases.     

Operational challenges for low and high temperature electrolyzers exploiting curtailed wind energy for hydrogen production

Understanding the system performance of different electrolyzers could aid potential investors achieve maximum return on their investment. To realize this, system response characteristics to 4 different summarized data sets of curtailed renewable energy is obtained from the Irish network and was investigated using models of both a Low Temperature Electrolyzer (LTE) and a High Temperature Electrolyzer (HTE). The results indicate that statistical parameters intrinsic to the method of data extraction along with the thermal response time of the electrolyzers influence the hydrogen output. A maximum hydrogen production of 5.97 kTonne/year is generated by a 0.5 MW HTE when the electrical current is sent as a yearly average. Additionally, the high thermal response time in a HTE causes a maximum change in the overall flowrate of 65.7% between the 4 scenarios, when compared to 7.7% in the LTE. This evaluation of electrolyzer performance will aid investors in determining scenario specific application of P2G for maximizing hydrogen production.     

The economic feasibility study of a 100-MW Power-to-Gas plant

Power-to-Gas (PtG) is a grid-scale energy storage technology by which electricity is converted into gas fuel as an energy carrier. PtG utilizes surplus renewable electricity to generate hydrogen from Solid-Oxide-Cell, and the hydrogen is then combined with CO₂ in the Sabatier process to produce the methane. The transportation of methane is mature and energy-efficient within the existing natural gas pipeline or town gas network. Additionally, it is ideal to make use of the reverse function of SOC, the Solid-Oxide-Fuel-Cell, to generate electricity when the grid is weak in power. This study estimated the cost of building a hypothetical 100-MW PtG power plant with energy storage and power generation capabilities. The emphasis is on the effects of SOC cost, fuel cost and capacity factor to the Levelized Cost of Energy of the PtG plant. The net present value of the plant is analyzed to estimate the lowest affordable contract price to secure a positive present value. Besides, the plant payback period and CO₂ emission are estimated.     

Power-to-SNG technologies by hydrogenation of CO2 and biomass resources: A comparative chemical engineering process analysis

Power to Synthetic-Natural-Gas (SNG) technology consists of two main steps: water electrolysis and methanation; the primary energy input is usually surplus power from renewable energy sources, while the electrolytic hydrogen and carbon oxides from different CO_x sources are converted into methane that can be fed in the natural gas grid. We focus on methanation technology, where the main criteria are the complexity of process setup and reactor sizes to achieve production and SNG quality for gas-grid injection. The processes are simulated using a plug-flow model for the reactors and a pseudo-homogeneous kinetic law describing the reaction of CO₂ (that is rate limiting). The results show that feeding biogas or syngas (instead of CO₂) for methanation has remarkable effects regarding the operation and design of the processes; it is concluded that Power-to-SNG technologies that use methane rich streams are favorable in terms of biogas upgrading, H₂ requirements, reactor volumes and process simplicity, as far as these resources are available: e.g., using a typical composition (60% CH₄) the required inputs are 0.96 kmol of biogas, 1.54 kmol of H₂ and 0.26 m³ of reactors (two adiabatic beds with recirculation, R/F = 0.695) per kmol/min of pipeline quality dry gas product (95% CH₄), which means 60% hydrogen saving, less than 26% reaction volumes and near 62% reduction of process throughput, when compared to the methanation process that uses pure CO₂; conversion of syngas can be also favorable, but it requires high recirculation due to the large proportions of CO_x; e.g. for syngas (47.3%H₂-25.9%CO-17.2%CO₂-9.6%CH₄), the required values mean a 53% hydrogen saving and less than 25% reaction volumes, but only 11% reduction of process throughput.     

H2NG environmental-energy-economic effects in hybrid energy systems for building refurbishment in future National Power to Gas scenarios

In order to comply to the ambitious targets of European Hydrogen Strategy, Member States will strongly encourage the deployment of Power-to-Gas (PtG) technologies. A significant fraction of produced green hydrogen will be injected into the existing natural gas networks, and the end-users will be served by Hydrogen enriched Natural Gas blends (H₂NG). The aim of this paper is to analyse the H₂NG effects on technical, economic and environmental parameters of hybrid energy systems for building refurbishment. Three hybrid energy systems for the existing plants replacement have been proposed, dynamically simulated and compared with the separate generation. Fuel supply has been simulated by varying the H₂ volumetric fraction in a range between 0 and 20%vol. The H₂NG blend employment will allow greater primary energy savings and avoided emissions. However, if the levelized cost of hydrogen (LCOH) due to electrolysis does not decrease, those benefits will be offset by a lower economic competitiveness.     

Impacts of the subsurface storage of natural gas and hydrogen mixtures

The subsurface storage of hydrogen (H₂) provides a potential solution for load-balancing of the intermittent electricity production from renewable energy sources. In such technical concept, surplus electricity is used to power electrolyzers that produce H₂, which is then stored in subsurface formations to be used at times when renewable electricity is not available. Blending H₂ with natural gas (NG) for injection into depleted gas/oil reservoirs, which are already used for NG storage, is considered a good option due to the lower initial capital cost and investment needed, and potential lower operating costs. In this study, the potential impact of storing a mixture of H₂ and NG in an existing NG storage field was investigated. Relevant reservoir, caprock and cement samples from a NG storage formation in California were characterized with respect to their permeability, porosity, surface area, mineralogy and other structural characteristics, before and after undergoing 3-month incubation experiments with H₂/NG gas mixtures at relevant temperature and pressure conditions. The results indicated relatively small changes in porosity and mineralogy due to incubation. However, the observed changes in permeability were more dramatic. In addition, polymeric materials, similar to those used in NG storage operations were also incubated, and their dimensions were measured before and after incubation. These measurements indicated swelling due to the exposure to H₂. However, direct evidence of geochemical reactions involving H₂ was not observed.