Role of methane as a cushion gas for hydrogen storage in depleted gas reservoirs

Depleted natural gas reservoirs play an important role as a viable option for large-scale hydrogen storage and production. However, its deployment depends on the accurate knowledge of the cushion gas (such as CH₄, CO₂, and N₂) compositions, which are key components affecting the rock-fluid interfacial phenomenon. In addition, there are currently few reported studies on rock/brine/gas-mixture wettability and gas-mixture/brine surface tension representing this type of reservoir. Hence, we report the feasibility of using CH₄ as a cushion gas (in the presence of CO₂ and N₂) for H₂ storage at various pressures (500 up to 3000 psi), temperatures (30 up to 70) ^oC, and salinities (2 up to 20) wt.% using drop shape analyzer equipment. Contact angle (CA) and surface tension (ST) experiments were extensively conducted for the different gas mixtures (H₂–CH₄–CO₂–N₂) to establish relevant data for H₂ storage in depleted gas reservoirs.Our result indicates that unless when the rock's initial wetting state is altered, the studied gas-mixture compositions (Test case 1: 80% H₂ – 10% CH₄ – 5% CO₂ – 5% N₂; case 2: 70% H₂ – 20% CH₄ – 5% CO₂ – 5% N₂; case 3: 60% H₂ – 30% CH₄ – 5% CO₂ – 5% N₂; case 4: 50% H₂ – 40% CH₄ – 5% CO₂ – 5% N₂; case 5: 40% H₂ – 50% CH₄ – 5% CO₂ – 5% N₂; case 6: 30% H₂ – 60% CH₄ – 5% CO₂ – 5% N₂; and case 7: 20% H₂ – 70% CH₄ – 5% CO₂ – 5% N₂) will exhibit comparable wettability behavior as the CAs ranged between [20 to 41°] irrespective of the reservoir pressure, temperature, and salinity. ST decreases with increasing temperature and linearly with increasing pressure. ST for each gas mixture increased with salinity. ST decreases systematically with increasing CH₄ fraction (at any given salinity, temperature, and pressure) with the highest observed in Test case 1 and the lowest in Test case 7 compositions. Test cases 3 and 4 with H₂ (50–60%) and CH₄ (30–40%) fractions was selected as the optimal gas mixture based on CA and ST for H₂ storage and withdrawal. The study's findings offer precise and useful input data for the reservoir-scale simulation used in geo-storage optimization in depleted natural gas reservoirs.     

Ab initio mechanistic insights into the stability,diffusion and storage capacity of sI clathrate hydrate containing hydrogen

Gas hydrates are non-conventional materials offering great potential in capturing, storage, and sequestration of different gases. The weak van der Waals interactions between a gas molecule and the pore walls stabilize these non-stoichiometric structures. The present article reports an ab initio improved van der Waals density functional (vdW-DF2) study devoted to the interactions associated with H₂, CH₄, and CO₂ adsorption in sI clathrate hydrate. The study provides the clathrate stability, diffusion, and energy storage of possible mixed gas occupancy in sI cages in the presence of H₂. The results also provided the hydrogen energy landscapes and the estimated diffusion activation energy barriers to the large and small cage to be 0.181 and 0.685 eV, respectively. In addition, the results showed that the presence of CH₄ or CO₂ could enhance the storage capacity, thermodynamic stability, and hydrogen diffusion in sI clathrates. The volumetric storage, gravimetric storage, and molecular hydrogen content in H₂–CH₄ binary sI clathrate are calculated to be 2.0 kW h/kg, and 1.8 kW h/L, and 5.0 wt%, respectively. These results are comparable to DOE targets of hydrogen storage.     

Influence of capillary threshold pressure and injection well location on the dynamic CO2 and H2 storage capacity for the deep geological structure

The subject of this study is the analysis of influence of capillary threshold pressure and injection well location on the dynamic CO₂ and H₂ storage capacity for the Lower Jurassic reservoir of the Sierpc structure from central Poland. The results of injection modeling allowed us to compare the amount of CO₂ and H₂ that the considered structure can store safely over a given time interval. The modeling was performed using a single well for 30 different locations, considering that the minimum capillary pressure of the cap rock and the fracturing pressure should not be exceeded for each gas separately.Other values of capillary threshold pressure for CO₂ and H₂ significantly affect the amount of a given gas that can be injected into the reservoir. The structure under consideration can store approximately 1 Mt CO₂ in 31 years, while in the case of H₂ it is slightly above 4000 tons. The determined CO₂ storage capacity is limited; the structure seems to be more prospective for underground H₂ storage. The CO₂ and H₂ dynamic storage capacity maps are an important element of the analysis of the use of gas storage structures. A much higher fingering effect was observed for H₂ than for CO₂, which may affect the withdrawal of hydrogen. It is recommended to determine the optimum storage depth, particularly for hydrogen. The presented results, important for the assessment of the capacity of geological structures, also relate to the safety of use of CO₂ and H₂ underground storage space.     

Measurement of hydrogen dispersion in rock cores using benchtop NMR

Electrolysis followed by underground hydrogen storage (UHS) in both salt caverns and depleted oil and gas reservoirs is widely considered as a potential option to overcome fluctuations in energy provision from intermittent renewable sources. Particularly in the case of depleted oil and gas reservoirs, a denser layer of cushion gas (N₂, CH₄ or CO₂) can be accommodated in these storage volumes to allow for sufficient system pressure control as hydrogen is periodically injected and extracted. These gases/fluids are however fully soluble with hydrogen and thus with sufficient mixing can undesirably contaminate the extracted hydrogen product. Fluid mixing in a porous medium is typically characterized by a dispersion coefficient (K_L), which is hence a critical input parameter into reservoir simulations of underground hydrogen storage. Such dispersion data is however not readily available in the literature for hydrogen at relevant storage conditions. Here we have developed and demonstrated novel methodology for the measurement of K_L between hydrogen and nitrogen in a Berea sandstone at 50 bar as a function of displacement velocity (0.007–0.722 mm/s). This leverages off previous work quantifying K_L between carbon dioxide and methane in rock cores relevant to enhanced gas recovery (EGR). This used infrared (IR) spectroscopy to differentiate the two fluids, hydrogen is however IR invisible. Hence the required time-resolved quantification of hydrogen concentration emerging from the rock core is uniquely performed here using bench-top nuclear magnetic resonance (NMR). The resultant hydrogen-nitrogen dispersion data as a function of displacement velocity allows for the determination of dispersivity (α = 0.31 mm). This intrinsic rock property compares favorably with previous CO₂ dispersion measurements on similar sandstones, hence validating our methodology to some extent. In addition, at very low velocities, determination of the rock core tortuosity (τ, another intrinsic rock property) produces a value (τ = 10.9) that is similar to that measurement independently using pulsed field gradient NMR methods (τ = 11.3).     

Effect of low concentration of impurity gases on the hydrogen absorption performance of uranium

The performance of uranium as a hydrogen storage material has attracted much attention. Herein, the hydrogen absorption properties of depleted uranium in impure hydrogen containing He, Ar, CH₄, N₂, CO, CO₂ and O₂ were studied by PVT method and XPS analysis. When these impurity gases were mixed in H₂ at low concentrations (0.1%∼1.5%), their behavior can be classified into three categories. The He, CH₄ and Ar were chemically inert to the activated uranium powder under room condition. These three gases inhibited the absorption kinetics during the whole stage by hindering the diffusion of H₂ molecules, showing a blanketing effect. The N₂ and O₂ did not affect the absorption kinetics but reduced the capacity by forming nitrides and oxides. The poisoning effect of N₂ was weaker than that of O₂. The CO and CO₂ not only affected the hydrogen absorption capacity, but also strongly inhibited the absorption kinetics. These two gases are chemically adsorbed on the uranium surface to form passivation layers, thus inhibiting the adsorption and dissociation of H₂ molecules and the diffusion of H atoms. The poisoning and retardation effect of CO₂ were much stronger than that of CO. The above conclusions are important to further study the reactivity of mixed gas with uranium, and can also be used as a reference for other hydrogen storage systems.     

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.     

Storage of hydrogen,natural gas,and carbon dioxide – Geological and legal conditions

The analysis of geological and reservoir conditions of the underground storage of hydrogen, methane, and carbon dioxide, that are important when choosing rock formations for the storage of gas, was presented. Physico-chemical properties of the discussed gases, affecting underground storage, were taken into account. Aquifers, hydrocarbon reservoirs, and caverns leached in salt rocks were analyzed. Legal aspects of underground gas storage were indicated.The physico-chemical conditions of the gases considered (especially molecular mass, and dynamic viscosity) are important for the selection of geological structures for their storage. The reservoir tightness is one of the most important geological and reservoir conditions when taking the appropriate porosity and permeability of rocks building underground storage sites into account. Salt caverns should be mainly used for hydrogen storage due to the tightness of rock salt. Geochemical and microbiological interactions affecting the operation of the underground storage site and its tightness are especially important and should be taken into account. The size of the underground storage site, while not as crucial in the case of H₂ storage, is important for CO₂ storage. When it comes to reservoir conditions, the amount of cushion gas and storage efficiency are important. The legal status of gas storage sites is highly variable. While there are existing regulations regarding natural gas storage, CO₂ storage requires further legislation. In the case of H₂ storage legal regulations need to be developed based on the experience of storage of other gases. The potential competition from other entities focused on the use of underground space for gas storage should be taken into account.     

The role of hydrogen in microwave plasma valorization of producer gas

Plasma methods are given significant attention in the context of conditioning the producer gas derived from biomass gasification. The goal of this work is to present the impact of hydrogen on the other producer gas compounds during microwave plasma valorization. These compounds include main producer gas components (CO, CO₂, CH₄, N₂) and minor impurities (tar compounds, H₂S and NH₃). The results prove a beneficial impact of hydrogen addition on the conversion of CH₄ and toluene, increasing it from ca. 68%–95% and ca. 97%–100%, respectively. Additionally, the presence of hydrogen changes the distribution of the products, inhibiting soot and aromatics production and promoting C₂ compounds. In the case of CO₂, the conversion increases from ca. 18%–63% when compared to nitrogen plasma, with CO being the resulting product. The presence of hydrogen inhibits H₂S conversion and does not affect CO and NH₃     

Augmented hydrogen adsorption on metal (Mg,Mn) doped α-phase TeO2: A DFT investigation

TeO₂, as a promising gas sensor material, has been extensively studied for its capacity to detect hydrogen with high sensitivity. First-principles calculations were applied to explore the adsorption properties of hydrogen (H₂), carbon dioxide (CO₂), methane (CH₄), and hydrogen sulfide (H₂S) on TeO₂ doped with either Mg or Mn to explore this compound's potential as hydrogen sensors. Hydrogen is more readily adsorbed on pure-TeO₂, Mg–TeO₂ and Mn–TeO₂ than CO₂, CH₄ and H₂S molecules by calculating their adsorption energy and charge transfer; the sequence of adsorption strength is H₂>H₂S > CO₂>CH₄. The hydrogen molecules and pure-TeO₂, Mg–TeO₂ and Mn–TeO₂ form H–O bonds with lengths of 0.98, 0.98 and 0.99 Å, respectively, indicating that chemical adsorption is dominant between them. The adsorption of hydrogen leads to significant changes in the density of states (DOSs) of pure-TeO₂, Mg–TeO₂ and Mn–TeO₂, which may lead to changes in their electrical conductivity. Moreover, the larger diffusion coefficients for hydrogen on the surfaces of pure-TeO₂, Mg–TeO₂ and Mn–TeO₂ relative to other gases indicates that hydrogen diffuses readily in TeO₂-based sensing materials, and the higher gas concentration contributes to improvements in response performance. This finding offers a theoretical basis for experimental explorations of the influence of metal dopants on TeO₂ hydrogen sensing performance.     

A framework for assessing economics of blue hydrogen production from steam methane reforming using carbon capture storage & utilisation

Hydrogen (H₂) generation using Steam Methane Reforming (SMR) is at present the most economical and preferred pathway for commercial H₂ generation. This process, however, emits a considerable amount of CO₂, ultimately negating the benefit of using H₂ as a clean industrial feedstock and energy carrier. That has prompted growing interest in enabling CO₂ capture from SMR for either storage or utilisation and producing zero-emission “blue H₂”. In this paper, we propose a spatial techno-economic framework for assessing blue hydrogen production SMR hubs with carbon capture, utilisation and storage (CCUS), using Australia as a case study. Australia offers a unique opportunity for developing such ‘blue H₂’ hubs given its extensive natural gas resources, availability of known carbon storage reservoirs and an ambitious government target to produce clean/zero-emission H₂ at the cost of <A$2 kg^?1 by 2030. Our results highlight that the H₂ production costs are unsurprisingly dominated by natural gas, with the additional capital requirement of carbon capture and storage (CCS) also playing a critical role. These outcomes are especially pertinent for eastern Australian states, as they are experiencing high natural gas costs and would generally require extensive CO₂ transport and storage infrastructure to tap potential storage reservoirs, ultimately resulting in a higher cost of producing H₂ (>A$2.7 kg_H2^?1). On the other hand, Western Australia offers lower gas pricing and relatively lesser storage costs, which would lead to more economically favourable hydrogen production (<A$2.2 kg_H2^?1). We further explore the possibility of utilising the emissions captured at blue SMR hubs by converting them into formic acid through CO₂ electroreduction, yielding revenue that will decrease the cost of blue H₂ and reduce the reliance on CO₂ storage. Our analysis reveals that formic acid production utilising a 10 MW CO₂ electrolyser can potentially reduce H₂ production costs by between 4 and 9%. Further cost reduction is possible by scaling the CO₂ electrolyser capacity to convert a larger portion of the emissions captured, albeit at the cost of higher capital investment, electricity consumption and saturating the market for formic acid. Thus, carbon utilisation for a range of products with high market demand represents a more promising approach to replacing the need for costly carbon storage. Overall, our modelling framework can be adapted for global application, particularly for regions interested in generating blue H₂ and extended to include other CO₂ utilisation opportunities and evaluate other hydrogen production technologies.     

H2 permeation and its influence on gases through a SAPO-34 zeolite membrane

This work analysed the permeation of binary and ternary H₂-containing mixtures through a SAPO-34 membrane, aiming at investigating how hydrogen influences and its permeation is influenced by the presence of the other gaseous species, such as CO₂ and CH₄. We considered the behaviour of various gas mixtures in terms of permeability and selectivity at various temperatures (25–300 °C), feed pressures (400–1000 kPa) and compositions by means of an already validated mass transport model, which is based on surface and gas translation diffusion. We found that the presence of CO₂ and CH₄ in the H₂-containing mixtures influences in a similar way the H₂ permeation, reducing its permeability of about 80% compared to the single-gas value because of their stronger adsorption. On the other hand, H₂ promotes the permeation of CO₂ and CH₄, causing an increment of their permeability with respect to those as single gases. These combined effects reflected in interesting selectivity values in binary mixture (e.g., CO₂/H₂ about 11 at 25 °C, H₂/CH₄ about 9 at 180 °C), which showed the potential of SAPO-34 membranes in treating of H₂-containing mixtures.     

Investigation of combustion and emission characteristics in a TBC diesel engine fuelled with CH4–CO2–H2 mixtures

In this study, an experimental investigation was performed to reveal combustion and emission characteristics of common-rail four-cylinder diesel engine run with CH₄, CO₂ and H₂ mixtures. The engine pistons were thermally coated with zirconia and Ni–Al bond coat by plasma spray method. With a small amount of the pilot diesel, port fuelled methane (100% CH₄), synthetic biogas (80% CH₄ + 20% CO₂), and hydrogen presented (80% CH₄+10% CO₂+10% H₂) mixtures were used as main fuel at different loads (50 Nm, 75 Nm, and 100 Nm) at a constant speed of 1750 min^?1. Comparative analysis of the combustion (cylinder pressure, PRR, HRR, CHR, ringing intensity, CA10, CA50, and CA90), BSFC, and emissions (CO₂, HC, NO_x, smoke, and oxygen) at the various engine loads with and without piston coating was made for all fuel combinations. It was found that coating the engine pistons enhanced the examining combustion characteristics, whereas it slightly changed BSFC and most of the emissions. As compared to the sole diesel fuel, the gaseous fuel operations showed higher in-cylinder pressure, PRR, and ringing intensity values, earlier combustion starting and CAs, and lower diesel injection pressure at the same engine operating conditions. Dramatic increase in the ringing intensity was particularly found by the hydrogen introduced mixture under the tests with coated piston. HC and CO₂ emissions increased in operation with the synthetic biogas; however, hydrogen introduction reduced HC emissions by 4.97–30.92%, and CO₂ emissions by 5.16–10%.     

Effect of food to microorganisms (F/M) ratio on biohythane production via single-stage dark fermentation

Hythane is a mixture of hydrogen and methane gases which are generally produced in separate ways. This work studied mesophilic biohythane gas (H₂+CH₄+CO₂) production in a bioreactor via single-stage dark fermentation. The fermentation was conducted in batch mode using mixed anaerobic microflora and food waste and condensed molasses fermentation soluble to elucidate the effects of food to microorganisms (F/M) ratio (ranging from 0.2 to 38.2) on gas production, metabolite variation, kinetics and biohythane-composition indicator performances. The experimental results indicate that the F/M ratio and fermentation time affect biohythane production efficiency with values of peak maximum hydrogen production rate 9.60 L/L-d, maximum methane production rate 0.72 L/L-d, and hydrogen yield (HY) of 6.17 mol H₂/kg COD_added. Depending on the F/M ratios, the H₂, CH₄ and CO₂ biogas components were 10–60%, 5–20% and 35–70%, respectively. Prospects for the further real application for single-stage biohythane fermentation based on the experimental data are proposed. This work characterizes an important reactor operation factor F/M ratio for innovative single-stage dark fermentation.     

Two-stage PSA/VSA to produce H2 with CO2 capture via steam methane reforming (SMR)

A two-stage pressure/vacuum swing adsorption (PSA/VSA) process was proposed to produce high purity H₂ from steam methane reforming (SMR) gas and capture CO₂ from the tail gas of the SMR-H₂-PSA unit. Notably, a ten-bed PSA process with activated carbon and 5A zeolite was designed to produce 99.99+% H₂ with over 85% recovery from the SMR gas (CH₄/CO/CO₂/H₂ = 3.5/0.5/20/76 vol%). Moreover, a three-bed VSA system was constructed to recover CO₂ from the tail gas using silica gel as the adsorbent. CO₂ product with 95% purity and over 90% recovery could be attained. Additionally, the effects of various operating parameters on the process performances were investigated in detail.     

Hydrogen permeation studies of composite supported alumina-carbon molecular sieves membranes: Separation of diluted hydrogen from mixtures with methane

One alternative for the storage and transport of hydrogen is blending a low amount of hydrogen (up to 15 or 20%) into existing natural gas grids. When demanded, hydrogen can be then separated, close to the end users using membranes. In this work, composite alumina carbon molecular sieves membranes (Al-CMSM) supported on tubular porous alumina have been prepared and characterized. Single gas permeation studies showed that the H₂/CH₄ separation properties at 30 °C are well above the Robeson limit of polymeric membranes. H₂ permeation studies of the H₂–CH₄ mixture gases, containing 5–20% of H₂ show that the H₂ purity depends on the H₂ content in the feed and the operating temperature. In the best scenario investigated in this work, for samples containing 10% of H₂ with an inlet pressure of 7.5 bar and permeated pressure of 0.01 bar at 30 °C, the H₂ purity obtained was 99.4%.     

Selective and efficient hydrogen separation of Pd–Au–Ag ternary alloy membrane

The widespread demand for clean energy stimulates great interest to hydrogen energy with high energy density and conversion efficiency. Separation technologies by membranes are increasingly applied for hydrogen separation because of its excellent performance and low consumption. In this work, density functional theory simulations is used to study hydrogen separation of Pd–Au–Ag membrane, and the performance of Pd–Au alloy is also compared and discussed. The results indicate that Pd–Au alloy shows superior selectivity to H₂ gas over CO, N₂, CH₄, CO₂ and H₂S gases, which is in line with experimental results. In particular, the separation selectivity of Pd–Au–Ag to H₂ is significantly greater than those for Pd–Au alloy and several currently reported materials. Moreover, the permeability of H₂ in Pd–Au–Ag exceeds the limits for industrial production at deferent temperatures. Our calculations demonstrate that Pd–Au–Ag alloy present excellent performance as a promising membrane for hydrogen separation.     

A synergistic effect of physisorption and chemisorption: Multiple H2 molecules on the ScC6H6 complex

Investigation of the H₂ dissociation and H migration on the 3d transition metal modified carbon nanomaterials is very important for better understanding the hydrogen storage mechanism. Herein, the adsorption processes including H₂ dissociation and H migration on ScC₆H₆ complex are studied systematically. The optimal adsorption pathway indicates that five H₂ molecules are continuously adsorbed on ScC₆H₆ until six adjacent CH₂ groups is reached. The corresponding hydrogen storage capacity is up to 7.50 wt %. The optimal adsorption pathway is ScC₆H₆ → 1d → 1a → 2a → 3b → 3e → 3c → 3d → 3a → 4a → 5b → 5c → 5a (ScC₆H₁₂(H₂)–2H), and the whole reaction is exothermic by 6.19 kcal/mol and 1.89 kcal/mol using B3LYP and CCSD(T) functional, respectively. It indicates that the adsorption of multiple H₂ molecules on the ScC₆H₆ complex is a synergistic process of physisorption and chemisorption.     

Solar-driven pyrolysis and gasification of low-grade carbonaceous materials

Three low-grade carbonaceous materials from biomass (Scenedesmus algae and wheat straw) and waste treatment (sewage sludge) have been selected as feedstock for solar-driven thermochemical processes. Solar-driven pyrolysis and gasification measurements were conducted directly irradiating the samples in a 7 kW_e high flux solar simulator and the released gases H₂, CO, CO₂ and CH₄ and the sample temperature were continuously monitored.Solar-driven experiments showed that H₂ and CO evolved as important product gases demonstrating the high quality of syngas production for the three feedstocks. Straw is the more suitable feedstock for solar-driven processes due to the high gas production yields. Comparing the solar-driven experiments, gasification generates higher percentage of syngas (mix of CO and H₂) respect to total gas produced (sum of H₂, CO, CO₂ and CH₄) than pyrolysis. Thus, solar-driven gasification generates better quality of syngas production than pyrolysis.     

Dry and steam reforming of biomass pyrolysis gas for rich hydrogen gas

Biomass pyrolysis gas (including H₂, CO, CH₄, CO₂, C₂H₄, C₂H₆ and etc.) reforming for hydrogen production over Ni/Fe/Ce/Al₂O₃ catalysts was presented in this study. This study investigated how the operating conditions, such as the calcinations temperature of catalysts, the reaction temperature, the gas hourly space velocity (GHSV) and the ratio of H₂O/C, affect the conversion of CH₄ and CO₂ and the selectivity of hydrogen from dry and steam reforming of pyrolysis gas. The experimental results indicated that, under the conditions: the reaction temperature of 600 °C, the GHSV of 900 h⁻¹ and H₂O/C of 0.92, the reaction efficiency is the optimal. Especially, the concentration of H₂, CO, CH₄, CO₂, and C₂H_n (C₂H₄ and C₂H₆) were 36.80%, 10.48%, 9.61%, 42.62%, 0.49% respectively. The conversion of CH₄ and CO₂ reached 45.9% and 51.09%, respectively. There were all kinds of reactions during the processing of reforming of pyrolysis gas. And the main reactions changed with the operation condition. It was due to the promoting or inhibiting interaction among different constituents in the pyrolysis gas and the different activity of catalysts in the different operation condition.