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Gas explosions mostly occur in turbulent environments in practical situations. Meanwhile, the current research on the explosion characteristics of hydrogen-doped natural gas is mostly methane/hydrogen mixed fuel, ignoring the influence of other components of natural gas on the explosion characteristics of the actual situation. Therefore, the effects of different jet intensities (P jet), hydrogen-doping ratios (X H2) and equivalence ratios (φ) on the explosion characteristics of multi-component natural gas/hydrogen mixed fuel are experimentally investigated in cylindrical tanks of 30 L. Additionally, it extensively explored the dual influence of jet disturbance and gas inerting effect on the flame propagation characteristics of multi-component natural gas/hydrogen mixed fuel. With the increase of P jet , both P max and (d p/ d t) max initially increase and then decrease, while τ continuously decreases. When P jet = 0.4 MPa, the promotion effect on P max and (d p/ d t) max is most significant. The lifting of X H2 leads to a gradual increase in P max and decreasing τ. (d p/ d t) max exhibits a trend of initially increasing and then decreasing with the elevation of X H2 , reaching its maximum at X H2 = 40%. The introduction of jet flow significantly reduces the promotion or inhibition effect on explosions of high hydrogen blending ratio mixtures. Furthermore, the introduction of jet flow is more effective in promoting the explosive performance of multi-component natural gas/hydrogen mixed fuel with high equivalence ratios and low hydrogen doping ratios under rich fuel conditions. This study can provide a key reference for the explosion hazard assessment during the practical application of natural gas/hydrogen mixed fuel. • Hydrogen-doped natural gas is used in explosion experiments collected in real environments. • A gas jet disturbance experimental platform has been established. • The flame propagation characteristics under turbulent conditions have been summarized. • The promotion effect on the explosion is most significant when the jet intensity reaches 0.4 MPa. [ABSTRACT FROM AUTHOR]

Methane pyrolysis is emerging as an attractive clean hydrogen production method. As its commercialization proceeds, the pyrolysis of natural gas (NG) becomes pertinent. In this work, the decomposition of pure methane and a realistic NG mixture are compared experimentally and numerically. Methane and NG pyrolysis are performed between 600 and 1200 °C over a fluidized bed of carbon particles heated by microwaves. Experimentally, no conclusive difference is observed in methane conversion between methane and NG pyrolysis. Numerically, the methane conversion rate is 8.5% higher for NG at 950 °C. The difference diminishes past 950 °C, becoming 0 past 1050 °C. The simulations showed that the enhanced methane decomposition in NG pyrolysis is due to an attack on methane by radicals generated during ethane and propane decomposition. The CO 2 in our NG mixture decomposes into CO. This work validates the longstanding use of methane pyrolysis as a surrogate for NG pyrolysis. • Experimentally, no conclusive difference between NG and pure CH 4 pyrolysis. • Numerically, NG pyrolysis had at most 8.5% higher methane conversion. • Radicals from ethane decomposition attacked methane and increased methane conversion. • Inlet C 2 H 6 > 10 vol% increased the outlet CH 4 rather than aiding its decomposition. • CO 2 in the NG mixture decomposed into CO, implying non-zero GHG emissions. [ABSTRACT FROM AUTHOR]

The energy gap between primary sources of energy like coal, oil, and natural gas will be 14 TW by 2050, hence finding sustainable sources of energy is the need of the day to bridge this gap. Hydrogen (H 2) in water is freely and abundantly available in nature, thus, the effective combination of light energy and water to produce hydrogen in an environmentally acceptable manner has a great potential to meet the current as well as future world's energy demand. Several semiconductors (SC's) have been employed to catalyze the formation of hydrogen from water (H 2 O). But the practical and feasible applicability of this system is limited due to photocatalyst high energy demand via wide band gap, quick recombination of photoexcited charge carriers (electron/hole pairs), easy nanoparticles agglomeration in solution and low photocatalyst surface area for adsorption. The incorporation of the majestic graphene material with the SC alone or in multiple SC's system can improve photocatalytic H 2 -production. Therefore, this review systematically presents an overview of, to shape graphene into a photocatalyst, graphene role in water splitting and in the interfacial charge-migration dynamics at surface contacts. We also focused on the built-in mechanism of the heterostructures comprises of photocatalyst (mainly TiO 2 , ZnO and WO 3) and graphene-based nanomaterials (pure graphene (G), graphene oxide (GO), reduced graphene oxide (r-GO)) and their combination thereof for H 2 generation in aqueous system. Composite comprised of SC's/graphene could potentially be a promising green light in the future of solar energy-led photocatalysis, specifically aimed at energy production. • This article provides a comprehensive overview on SC's/G composites for H 2 production. • The charge carrier's mechanism was thoroughly discussed in different SC's/G hybrids. • Ternary SC's/G heterostructure performed well for H 2 evaluation. • Future research directions for SC's/G heterostructures are outlined. [ABSTRACT FROM AUTHOR]

Injecting hydrogen into natural gas pipelines for direct use by end users is an economical and effective method to realize long-distance transportation of hydrogen. However, the density of hydrogen is much lower than natural gas, and it tends to accumulate at the top of the pipeline, resulting in significant different flow characteristics of pure natural gas. Therefore, mixing hydrogen into natural gas pipelines will affect the accuracy of calorific value and flow rate measurement in the existing natural gas metering system. This article studies the flow characteristics of injecting hydrogen into natural gas using a T-shaped pipe and its impact on energy measurement through CFD numerical simulation. The results show that the energy metering equipment should be installed where the gas reaches a uniform mixture and the radial section velocity is centrally symmetrical. Injecting hydrogen with a lower position, and smaller main stream velocity will shorten the distance between the metering pipeline section and the mixing point, but a distance of at least 100 times the pipe diameter is still required. Thus, a mixing process combining a static mixer and flow straightener is proposed, which reduces this distance to within 40 times the pipe diameters. [Display omitted] • Composition and velocity changes in natural gas pipelines after hydrogen injection. • Define coefficient of variation velocity to quantify velocity central symmetry. • Static mixers have negative impact on HBNG flow measurement. • A high-efficient combined structure reduces the mixing distance from 100D to 40D. • Improve the existing measurement process to enable measurement of HBNG. [ABSTRACT FROM AUTHOR]

One of the primary concerns with fuel combustion in internal combustion engines is the significant quantity of energy that is dissipated as waste heat, which leads to thermal pollution and reduced engine efficiency. To address this issue, a new integrated system incorporating a natural gas fueled homogeneous charge compression ignition (HCCI) engine for different hydrogen fractions (0%–20%) in fuel blends and its exhaust heat is recovered to drive the NH 3 –H 2 O based absorption refrigeration cycle (ARC) and process heat exchanger has been developed, which encompasses the generation of electricity, heating, and cooling. A comprehensive energy-exergy model was built and the impact of some key operating variables on the performance of combined system are investigated. Simulation of the proposed system was performed using Engineering Equation Solver (EES) software and REFPROP toolbox library data. The energy and exergy efficiencies of HCCI engine resulted in an increase from 45.26% to 55.45% and from 41.15% to 46.14%, whereas the combined system efficiencies were increased by 15.90% and 10.13% when hydrogen addition is promoted from 0% to 20%. Utilization of 10% hydrogen resulted in energy efficiency of 49.57% for electrical, 11.89% for cooling, and 4.51% for heating. Illustration of exergy flow diagram identified HCCI engine (118.29 kW, 32.11%) as the most fuel exergy destructive component, followed by ARC cycle (30.86 kW, 8.37%), catalytic converter (27.24 kW, 7.39%) and process heat exchanger (11.103 kW, 3.01%). Impressive exergetic results from the system include a power exergy of 158.91 kW (43.14%), heating exergy 10.697 kW (2.90%), and cooling exergy 3.92 kW (1.06%). • H 2 enriched natural gas fueled HCCI engine based trigeneration system was developed. • HCCI engine's exhaust waste heat was harnessed through the ARC cycle and PHE. • A single effect NH 3 –H 2 O absorption chiller was employed for cold production. • Energy and exergy-based assessment was carried out to analyze the proposed system. • HCCI engine (32.11%) were identified as the primary exergy destructive components. [ABSTRACT FROM AUTHOR]

The utilization of hydrogen (H 2) instead of natural gas (NG) in high-temperature industries has the potential to significantly reduce global greenhouse gas emissions. To obtain detailed information on the combustion characteristics in a semi-industrial air–fuel setup, comprehensive experiments and 3D CFD simulations are performed on a low-swirl burner inside a combustion chamber. The H 2 enrichment in NG of 0–100 vol % is analyzed at burner powers of 75–120 kW and temperatures of 900–1400 ° C. The process efficiency increases by up to 10 percentage points due to higher temperatures and enhanced heat transfer. Furthermore, up to 20% lower NO x emissions are observed, which is attributed to a significant change in the flow and flame characteristics. For the first time, OH* chemiluminescence imaging is successfully applied to validate RANS simulations of an industrial turbulent flame. Further research should be directed toward evaluating OH* reaction kinetics in both laminar and turbulent NG/H 2 combustion setups. • H 2 enrichment of up to 100 vol% at powers of 75–120 kW and temperatures of 900–1400 °C. • Effect on furnace temperatures, heat transfer characteristics and NO x emissions. • Accurate and efficient 3D RANS simulation model for a detailed flame evaluation. • Novel validation method for industrial-type flame simulation using OH* imaging. • Correspondence of NG/H 2 induced OH*-chemiluminescence with 3D numerical OH*-results. [ABSTRACT FROM AUTHOR]

We investigate the challenges and options for repurposing existing natural gas pipelines for hydrogen transportation. Challenges of re-purposing are mainly related to safety and due to the risk of hydrogen embrittlement of pipeline steels and the smaller molecular size of the gas. From an economic perspective, the lower volumetric energy density of hydrogen compared to natural gas is a challenge. We investigate three pipeline repurposing options in depth: a) no modification to the pipeline but enhanced maintenance, b) use of gaseous inhibitors, and c) the pipe-in-pipe approach. The levelized costs of transportation of these options are compared for the case of the German Norddeutsche Erdgasleitung (NEL) pipeline. We find a similar cost range for all three options. This indicates that other criteria such as the sunk costs, public acceptance, and consumer requirements are likely to shape the decision making for gas pipeline repurposing. • Three options for repurposing a natural gas pipeline to use with hydrogen are considered. • The levelized costs of hydrogen transport of each option are calculated. • The calculations are for the case study of the NEL pipeline in Germany. • Levelized costs of hydrogen transport are similar between the three options. [ABSTRACT FROM AUTHOR]

Hydrogen has enormous potential for sustainable future mobility. However, current challenges include high production costs and storage issues, necessitating further engineering advancements. Compressed Natural Gas is also a viable alternative, as it is easily produced and stored but suffers from slow flame speed-related issues. Improving its combustion characteristics by enrichment using a small fraction of hydrogen holds significant promise. Inducting hydrogen directly into the combustion chamber improves the engine's volumetric efficiency, eliminating the backfire issues. However, it is crucial to understand the test fuel's jet and mixing characteristics before engine investigations. This study aims to analyse the macroscopic jet characteristics of hydrogen, compressed natural gas and hydrogen-enriched compressed natural gas in realistic engine-like conditions in a constant volume spray chamber at various fuel injection pressures and varying ambient pressures and temperatures. Fuel injection pressures for hydrogen and CNG were varied at 16, 32, and 48 bar, and ambient pressures in the constant volume spray chamber were set at 4- and 8-bar and ambient temperatures at 25 and 100 °C. The results showed hydrogen exhibited ∼2% shorter jet penetration length than compressed natural gas. Depending on the test conditions, hydrogen showed a ∼1–3% higher jet area than CNG due to its higher diffusivity and faster mixing. This higher jet area improved fuel-air mixing of hydrogen with air compared to CNG. The effect of hydrogen enrichment with CNG on their jet characteristics was also analysed for 8 bar FIP. 10% (v/v), 20%, and 40% hydrogen-enriched compressed natural gas did not significantly alter the macroscopic jet characteristics from baseline compressed natural gas. [Display omitted] • Macroscopic spray characterization of hydrogen and CNG in CVSC using Schlieren. • FIP for hydrogen and CNG was varied at varying ambient pressures/temperatures. • Hydrogen exhibited a ∼2% shorter spray jet penetration length than CNG. • Hydrogen showed a larger spray area than CNG. • Hydrogen enrichment of CNG didn't alter macroscopic spray characteristics. [ABSTRACT FROM AUTHOR]

The addition of hydrogen in a dual-fuel mode based on natural gas and diesel offers great potential for improving engine efficiency and reducing emissions. Therefore, detailed numerical simulations have been used to explore the effects of soot formation characteristics of natural gas-diesel dual-fuel engines doped by hydrogen at elevated pressure. Numerical simulations are compared with available experimental data, the effects of H 2 addition on soot formation in laminar CH 4 + n-heptane, H 2 + CH 4 + n-heptane, FH 2 + CH 4 + n-heptane diffusion flames at 2, 4, 6 and 8 atm are simulated, FH 2 is added to separate the H 2 chemical effects. The results show that the dilution and thermal effects of H 2 inhibit soot formation, while the chemical effects of H 2 promote soot formation under different pressures. The addition of H 2 increases the concentration of H and OH radicals, which promotes the formation of C 2 H 2 and benzene (A1). By simplifying the reaction path and analyzing the production rate of A1, the mechanism of H 2 addition to promote A1 formation is illustrated. The concentrations of polycyclic aromatic hydrocarbon (PAH) pyrene (A4), benzo(ghi)fluoranthene (BGHIF) and benzo(a)pyrene (BAPYR) are inhibited at higher pressures that result in lower inception and condensation rates. Therefore, the increase of hydrogen abstraction acetylene addition (HACA) rate is the main reason for the increase of soot formation under chemical effects. While the O 2 oxidation rate decreases and the OH oxidation rate increases, that is due to the decrease of O 2 concentration and the increase of OH concentration in the soot formation area under chemical effects. • The dilution, thermal and chemical effects of H 2 addition on soot formation in methane/n-heptane flame were investigated at high pressures. • Key specie A1 formation pathways and related reactions were confirmed when H 2 addition. • The changes of soot formation and oxidation mechanisms with H 2 addition in different pressure were explained. [ABSTRACT FROM AUTHOR]

In this study, three premixed swirl gas turbine nozzles with different fuel injection hole sizes were designed to optimize combustion characteristics influenced by changes in the hydrogen mixing ratio. Experiments involved increasing the hydrogen volume fraction of the fuel from 0 to 60%. The amount of fuel supplied through the pilot flow was increased to suppress combustion instability. The OH* chemiluminescence technique was introduced to analyze flame structure. To understand combustion instability, time delay and time-delay distribution were derived from flame structure analysis and applied to the 1D thermoacoustic model. The results indicated that the amount of fuel required for pilot injection with increasing hydrogen ratio varied with fuel hole size. It was also observed that changes in fuel hole size significantly affected flame characteristic length. Findings from the 1D thermoacoustic analysis confirmed that fuel hole size variation altered combustion instability characteristics by influencing time delay and time-delay distribution variation. [Display omitted] • This study investigated the impact of fuel hole size for H 2 co-firing. • Increase in H 2 fraction reduced flame length and heat release distribution. • Fuel hole size variation affected time delay and its distribution. • Changing the time delay and its distribution influenced combustion instability. [ABSTRACT FROM AUTHOR]

Blending a specific proportion of hydrogen into a natural gas (NG) pipeline network is an effective strategy for achieving long-distance, large-scale, and cost-effective hydrogen transport. Static mixers played a crucial role in this process. In this study, a coaxial shear static mixer with ring-shaped structures instead of turbulence elements is proposed. The mixer exhibited favorable mixing performance and low pressure loss. The flow characteristics of NG and hydrogen within the mixer were investigated with computational fluid dynamics (CFD) methods. The effects of the number of cavities, hydrogen pipe diameter, hydrogen blending ratio and pressure on the mixer performances were investigated, taking into account both mixing uniformity and pressure loss. When the number of cavities in the coaxial shear mixer increases to 48, the mixing uniformity reaches 95.43% (SMX is 95%), and the pressure loss is 67.02 Pa (SMX is 500 Pa). • High mixing uniformity and low pressure loss in the new coaxial shear mixer. • Effects of structural and operating parameters on mixer performance analyzed. • Coaxial shear mixer performs better than SMX mixer. [ABSTRACT FROM AUTHOR]

Although low emission hydrogen has the prospect of huge growth in the future, the cost challenge hinders the deployment and makes it weak in the global market share. Green hydrogen has the advantage of zero carbon emission and has achieved rapid development with the support of renewable energy. Limited by investment, electricity and technology, the large-scale application of green hydrogen faces challenges in the short term. Blue hydrogen comes from natural gas reforming, and its output is guaranteed. However, its production reaction requires high energy consumption and additional carbon emission treatment, resulting in insufficient sustainability. To solve the problem of high-efficiency and large-scale production of low emission hydrogen, a hydrogen co-production scheme combining photovoltaic electrolysis and natural gas reforming with CCS was proposed in this study. Electrolytic hydrogen production, natural gas autothermal reforming, CO 2 sequestration and saline purification in the cogeneration hydrogen production system are coupled by energy and materials such as electricity, O 2 , CO 2 and water. The scheme is applied in Sichuan-Chongqing region to verify the feasibility and effectiveness. The results show that the proposed hydrogen co-production scheme can achieve cost reduction of up to 16.4%, and has long-term development prospects. [Display omitted] • Identifies the development status and bottlenecks of low-emission hydrogen. • Proposes a zero carbon emission co-production scheme of green and blue hydrogen. • Verifies the feasibility and benefit of the scheme in Sichuan-Chongqing region. [ABSTRACT FROM AUTHOR]

Chemical looping dry reforming of methane (CLDRM) using perovskites as a catalyst is considered a promising option for producing hydrogen from biogas. In this work, the life-cycle performance of a system compiling a CLDRM unit paired with a water gas shift unit, a pressure swing adsorption unit, and a combined cycle scheme to provide steam and electricity was assessed. The main data needed to reflect the behavior of the reforming reaction was obtained experimentally and implemented in an Aspen Plus® simulation. Inventory data was obtained through process simulation and used to assess the environmental performance of the process in terms of carbon footprint, acidification, freshwater eutrophication, ozone depletion, photochemical ozone formation, and depletion of minerals and metals. Overall, the environmental viability of the production of green hydrogen from biogas was found to be heavily dependent on the biogas leakage in anaerobic digestion plants. The CLDRM system was benchmarked against a conventional DRM implementation for the same feedstock. While the conventional DRM plant environmentally outperformed the perovskite-based CLDRM, the latter might present advantages from an implementation point of view. [Display omitted] • Scaled-up chemical looping dry reforming of biogas for hydrogen production was simulated. • The life-cycle performance of the configuration with a perovskite catalyst was assessed. • Environmental hotspots refer to biogas leakage, natural gas processes, and catalyst metals. • Environmental advantages of conventional dry reforming were linked to heat integration. • Green hydrogen qualification requires avoiding leakages from anaerobic digestion plants. [ABSTRACT FROM AUTHOR]

In this work, we investigate the electrochemical separation of hydrogen from a 10% H 2 /methane natural gas blend using a single cell experimental setup for electrochemical hydrogen pumping (EHP). Results show that the overall efficiency for hydrogen separation is high, ranging from about 87% at 0.2 A/cm2 to 75% at 0.6 A/cm2. In addition, we develop a zero-dimensional model for the hydrogen separation process including the membrane permeation of H 2 as well as CH 4 , N 2 , and CO 2 as the main components in natural gas. We derive analytical expressions for the permeability of these gases as a function of temperature and membrane humidity using available permeability data. Although the presence of dilutive inert gases poses a challenge, the modelled data indicate that it should be possible to produce fuel cell quality hydrogen using a single hydrogen separation stage. Importantly, this indicates technological feasibility of distributing hydrogen for use in fuel cells through existing natural gas infrastructure. Extension of this research to combined hydrogen separation and compression within the same EHP unit is recommended as future work. • An analytical electrochemical hydrogen pump (EHP) model is developed and validated. • Single cell EHP experiments show high overall hydrogen separation efficiency. • Expressions are developed for the permeability of H 2 , N 2 , CH 4 , and CO 2 in Nafion. • The effects of EHP membrane and operating parameters on H 2 purity are examined. • Fuel cell grade hydrogen extraction is shown to be feasible through system tuning. [ABSTRACT FROM AUTHOR]

In this work, three mathematical models were developed to study the laminar jet diffusion flame in mixtures of natural gas, hydrogen, and CO2 by extending and applying Roper's theory. Model M1 consists of derivation of the Roper's original equation described in the two-dimensional steady state without convection, thus showing the theoretical equations for the length of the diffusion flame for burners with circular, square, and rectangular cross sections and for regimes in which the flames are dominated by the momentum effects, the buoyancy effect, and in the transition regime. Models M2 and M3 extend the Roper's original theory by deriving analytical solutions of the two- and three-dimensional diffusion flame equation with convection in steady and transient states, taking into account the spatially variable velocity and diffusion coefficients. The flame lengths obtained with models M1 and M2 were compared with model M3 by Relative Percentage Difference (RPD) considering 5 mixtures of NG-H2-CO2. For t = 0.1, the maximum RPD in the circular cross-section for M1 in Gas20:60%NG-25%H 2 –15%CO 2 was 14.75%, while for M2 in Gas14:70%NG-15%H 2 –15%CO 2 was 6.47% and the minimum RPD in Gas1:100%NG was 9.78% and 4.83% for M1 and M2, respectively. The same analysis was developed for the square and rectangular (Fr ≪ 1) cross-sections and showed good agreement. The model M3 was tested under transient conditions, studying the effects of time and velocity on the distribution of the profile in the radial direction, in order to better understand the flame phenomenon, which cannot be observed with the Roper's original model M1. Finally, the models M2 and M3 were validated with experimental results and other analytical solutions showing a good performance considering the characteristics of each mixture. • Three mathematical models were developed to study the laminar diffusion flame. • The Roper's original equation was derived and named model M1. • Models M2 and M3 extend the original theory to 2 and 3 dimensions. • Models M2 and M3 were derived for steady and transient states, respectively. • The three models were compared and flame behavior in NG-H2 mixtures was explored. [ABSTRACT FROM AUTHOR]

In this study, the combustion and emission characteristics of natural gas/diesel dual-fuel engines under low load in diesel pilot ignition (DPI) and reactivity controlled compression ignition (RCCI) combustion modes were compared and analyzed by parametric study. The results show that compared with DPI mode, RCCI mode has lower NOx, CO and HC emissions and relatively higher thermal efficiency. However, under low load conditions, the in-cylinder mean temperature and combustion efficiency were reduced, and HC and CO emissions were still high in the RCCI combustion mode. The combustion characteristics of the fuel in the cylinder are changed by adding argon, hydrogen and syngas into the cylinder. The ability of additives to expand the low load operation range of natural gas/diesel RCCI engine was discussed and compared from the aspects of macroscopic combustion process and microscopic chemical reaction kinetics. The results show that argon, hydrogen and syngas can change the combustion characteristics of fuel. When argon, hydrogen and syngas are added, the gross indicated efficiency (GIE) can be increased from 38.1% to more than 50% compared to the basic condition. Maximum GIE and low HC emissions can be achieved with the introduction of 10% argon mass fraction, while a 20% hydrogen or syngas mass fraction is required to maintain low HC emissions. Therefore, argon has the greatest potential to improve the performance of natural gas/diesel RCCI engines under low load conditions. [Display omitted] • The effect of using Ar, H 2 and syngas on natural gas/diesel RCCI engine at low load. • The RCCI mode has lower NOx, HC, and CO emissions than the DPI mode. • The use of Ar, H 2 and syngas can improve the combustion of RCCI engine at low load. • Ar has the greatest potential to improve the performance of RCCI engines at low load. [ABSTRACT FROM AUTHOR]

The usage of liquefied hydrogen (LH 2) is growing fast as the EU aims to be climate-neutral by 2050. Therefore, reliable and consistent measurements of LH 2 amounts (as determined by flow meters) will become increasingly important for custody transfers. Reliability and consistency of measurements is established from calibration. Due to the lack of facilities being able to calibrate flow meters directly with LH 2 as calibration fluid, the question arises whether the measurement error of the calibration performed on a different fluid and different process conditions are representative for the errors when measuring LH 2. An on-site calibration of two turbine meters measuring LH 2 flow was performed. A Coriolis mass flow meter calibrated on water was used as a reference in conjunction with a dedicated flow meter model, which was validated by a directly SI-traceable calibration on liquefied natural gas. LH 2 flow rates were within 1000 kg/h and 3000 kg/h, which are relevant to hydrogen transport by LH 2 trailers. The analysis of the measurement data reveal errors on totalized mass ranging from 2.0 % to 2.9 % with a total calibration uncertainty of 1.3 % (k = 2), where the main uncertainty source was identified as the on-site density estimate necessary to convert the volume flow measurements into mass flow measurements. The results indicate the need for reliable and accurate temperature measurements (the latter allowing for an accurate density estimate), so that volume based and mass based amount measurements can be compared with smaller uncertainties. • Reliable measurements of liquefied hydrogen amounts will be crucial for custody transfer. • Direct calibration of flow meters on liquefied hydrogen is currently not possible. • Novel results of liquefied hydrogen flow measurement of an on-site calibration are presented. • The analysis reveals errors between 2.0 % and 2.9 % with an uncertainty of 1.3 % (coverage factor = 2). • The main uncertainty source was identified as the on-site density estimate. [ABSTRACT FROM AUTHOR]

Converting surplus electricity into hydrogen is considered a promising way for accommodating large-scale wind or solar power. However, it is expensive to establish a new-built hydrogen network or storage facilities at the current stage. Hydrogen-enriched compressed natural gas (HCNG), a mixture of natural gas and hydrogen, can be an alternative approach to consuming surplus renewable energy in the short-medium term. This paper investigates the feasibility of establishing an electricity-gas-hydrogen coupled energy system by modeling the HCNG network, power grid, and hydrogen electrolyzer in Ireland with consideration of pipeline characteristics. The economic analysis based on the planning results of the coupled system is presented in detail. When the hydrogen injection ratio reaches 20% at the HCNG stations, the system operating cost and carbon emission can be reduced by 24.2% and 6.4%, and 100% wind can be consumed. • A detailed modeling method for HCNG pipeline pressure drop and line pack is proposed. • An EGH-IES planning model encompassing entire HCNG supply chain is established. • A case study is conducted based on the real energy system in Ireland. [ABSTRACT FROM AUTHOR]

This study investigated the flame combustion of gas-containing pipe cutting operations by combining experimental and numerical simulation techniques. Based on the empirical flame length formula and experimental and numerical simulation flame length data, a flame length formula for gas outlet with large aspect ratio was proposed. In the experimental phase, cutting experiments were conducted with cutting slit lengths of 1–11 cm for pipe pressures of 10–550 Pa and hydrogen doping ratios of 0%, 10%, and 20%. The flame lengths were then measured. A hydrogen-doped natural gas combustion model based on the vortex dissipation conceptual model and Grimech-3.0 mechanism was established to simulate the experimental conditions. The flame lengths derived from the numerical simulation were in good agreement with the experimentally measured flame lengths, with an average error of 7.02%. This indicates that the reliability of the numerical model can be verified. The effects of hydrogen doping ratio, tube pressure, and cutting slit length on flame length and thermal radiation range were investigated using the control variable method. The results demonstrated that hydrogen doping reduced flame length and flame length away from the flame. Furthermore, an increase in pipe pressure and single cut length also resulted in an increase in flame length. It was observed that under normal operating conditions, a safe intensity of thermal radiation could be maintained within the operating distance when the operator wore protective clothing. • The reveal that hydrogen blending enhances combustion stability and reduces the jet flame height and flame resistance height. [ABSTRACT FROM AUTHOR]

In recent times, there has been an amplified interest in exploring fresh applications of biogas, attributed to the rising concerns surrounding climate change and an enhanced emphasis on the utilization of renewable energy sources. This manuscript undertakes a comprehensive assessment of recent advancements in the domains of dry, bi-, and tri-reforming. Notably, it emphasizes situations in which the CO 2 present in biogas assumes the role of an oxidant or partial oxidant. A comparative evaluation of various techniques and the exploration of recent catalysts employed in the reforming process and techno-economic biogas conversion applications are also deliberated in this analysis. Biogas conversion exhibits economic feasibility, typically with a payback period ranging from 4 to 8 years. Opting for a higher reaction temperature within the range of 830–900 °C is typically favored as it results in increased CH 4 and CO 2 conversions within the bi-reforming of the biogas process. Similarly, the temperature range is maintained between 750 and 850 °C and 850–1000 °C or above (depending on various factors) for dry reforming and tri reforming respectively. In general, biogas can undergo conversion processes to produce hydrogen, methanol, compressed natural gas, liquid fuel, wax, and form of heat. The inclusive conversion of biogas efficiency ranges from around 35%–80%, depending on the specific type of product being generated. [Display omitted] • Study investigates biogas valorization for H 2 production. • Desire H 2 /CO molar ratio decreases for H 2 production above 2.2. • Ni/CeO 2 –ZrO 2 nanoparticles appear promising as a catalyst. • Bi, dry, and tri-reforming optimize at 830–900 °C, 750–850 °C, and 850–1000 °C or higher, respectively. • Biogas conversion is 35–80% efficient, with a 4–8 year average payback period based on economic analysis. [ABSTRACT FROM AUTHOR]

To reveal the deflagration hazard and propagation law of hydrogen-enriched natural gas (H 2 NG) in closed spaces, this paper studied the deflagration characteristic parameters under different H 2 blended ratio (λ) and inert gas dilution fraction (X dilution) in slender closed pipelines with steel circular hole obstacles. The results indicate that the positive feedback mechanism's sustained effect, failure, and re-action leads to a "three-zone" distribution of H 2 NG explosion overpressure along the pipeline, namely the acceleration, attenuation, and rebound zones. The maximum explosion overpressure (P max), maximum pressure rise rate ((dP/dt) max), and peak shock wave propagation velocity (V p) all increase with the increase of λ. The rise of λ has the most significant enhancement effect on (dP/dt) max , while the enhancement effect on V p is the smallest. This is because the main reasons affecting their increase are different. P max , (dP/dt) max , and V p exhibit exponential decay with increased N 2 and CO 2. However, CO 2 has a more significant inhibitory effect on the H 2 NG deflagration process. When X CO2 = 25% and X CO2 = 30%, the deflagration process of H 2 NG with λ = 20% and λ = 80% can be inhibited entirely, respectively, which has important guiding significance for the safe application of H 2 NG. • The evolution law of deflagration shock waves in slender closed pipelines by H 2 NG was researched. • Effects of H 2 blended ratio and N 2 /CO 2 dilution fraction on H 2 NG deflagration characteristics were revealed. • The effects of N 2 /CO 2 dilution fraction on the P max , (dP/dt) max , and V p were predicted by an exponential model. [ABSTRACT FROM AUTHOR]

In the context of a global shift towards clean energy, the integration of hydrogen into existing natural gas pipeline networks is essential for facilitating the energy transition. Specifically, low-pressure natural gas pipeline networks are crucial for transporting gas efficiently and with minimal losses from the source to end-users in nearby cities. The physical properties of hydrogen differ significantly from those of natural gas, which implies that introducing hydrogen into the pipeline network will modify operational parameters and impact the safety and efficiency of gas transmission. Therefore, this study concentrates on the efficiency of transporting and scheduling hydrogen-blended natural gas through existing low-pressure direct pipelines. Utilizing the BWRS (Benedict-Webb-Rubin-Starling) equation of state, mathematical models were developed to calculate gas properties and to simulate both the steady and transient states of hydrogen-blended natural gas networks. These models were then validated with TGNET software. This study examines a low-pressure natural gas transmission and distribution network that transports gas directly from a production site in Sichuan to urban areas. It conducts simulations of hydrogen blending and analyzes the impact of various hydrogen blend ratios on the transport and scheduling responses of the network. Research suggests that maintaining the hydrogen blend below 30% ensures the safe operation of low-pressure gas pipelines and prevents the transmission pressure from exceeding 3 MPa. Additionally, under a fixed energy flow output, blending hydrogen intensifies the challenges associated with pressure drops and temperature increases due to high flows in small diameter pipes, and further complicates the management of interruptions resulting from faults. Therefore, it is recommended that the hydrogen blend ratio be maintained at no more than 30%, and that accident handling procedures be established in advance to control pressure variations following a shutdown. • Development of a model for a low-pressure hydrogen-doped pipeline network for direct delivery from the source to the city. • The minimum inlet pressure requirements for different hydrogen doping ratios are presented. • Elevated hydrogen levels can exacerbate temperature rise and pressure drop phenomena in small diameter, high flow pipes. • With the addition of hydrogen, the incident response time for a transient shutdown of transmission was reduced. [ABSTRACT FROM AUTHOR]

In this study, we developed a diagnosis method for combustion instability and validated its performance using experimental data obtained from a hydrogen/natural gas co-firing gas turbine combustor. Four criteria, namely temporal kurtosis, permutation entropy, energy entropy, and zero-crossing rate, were considered. First, the performance of each criterion was compared with that of the conventional method for determining combustion instability using the root mean square (RMS) of dynamic pressure. Temporal kurtosis the best performance in terms of detection speed (instability onset detected 0.71 s earlier than the RMS method). Permutation entropy yielded the best performance in terms of accuracy and precision with accuracy, recall, precision, and F1-score values of 96.6%, 100%, 92.6%, and 96.2%, respectively. The performances of combinations of these criteria were investigated using AND and OR gates. Twenty-two cases were considered and the combination of permutation entropy and zero-crossing rate (best case) achieved detection time, accuracy, precision, recall, and F1-score values of 8.49 s, 97.2%, 93.9%, 100%, and 96.8%, respectively. Other combinations exhibited competitive performance; however, the method combining two criteria was selected to simplify the computing process. The proposed method is expected to contribute to the safe and stable operation of hydrogen/natural gas co-firing gas turbines. • A Novel diagnostic method for detecting the onset of combustion instability is proposed. • The detection speeds and accuracies of TK, PE, EoE, and ZCR are assessed. • TK can detect instability onset 0.71 s earlier than the root mean square method. • PE achieved superior performance with 96.6% accuracy and 92.6% recall. • The PE∩STD ZCR combination improved accuracy (97%) and recall (100%). [ABSTRACT FROM AUTHOR]

In urban pipelines, blending hydrogen into natural gas has been considered as an effective way of hydrogen usage to reduce carbon emission on household appliances. However, few studies, especially experimental ones are dedicated to address the characteristics of a typical domestic cooker due to the transition from natural gas to 20%hydrogen-enriched natural gas. This study experimentally investigated the changes in terms of the gas flow rate, flame temperature, heat transfer and emission characteristics of a domestic cooker as a result of such transition. Using a self-developed gas blending system, the flow rates of the both the mixed fuel and its components are obtained. The data shows that after blending hydrogen, the mixed gas flow rate becomes higher. Compared to the original cooker burning natural gas, hydrogen blending results in a decreased natural gas flow rate, leading to lower carbon emission. In addition, the thermal input to the cooker is lowered and hydrogen blending leads both the inner and outer combustion zones of the flame to shorten while the flame temperature to increase. As an attempt to optimize the performance of the cooker, the effects of wok stand height on heat transfer efficiency and NO/NO x /CO emissions are examined. It is found that the cooker fueled by 20%hydrogen-enriched natural gas exhibits lower heat transfer efficiency, higher NO/NO x emissions and lower CO emission. According to the fact that the heat transfer efficiency increases at lower wok stand height, the wok stand height is lowered from its original 7 cm–6 cm and 5 cm. The finding indicates that when the wok stand height is moderately decreased to 6 cm, NO/NO x emissions decrease and CO emission is only marginally increased. This study proposes that when natural gas is replaced by 20%hydrogen-enriched natural gas on a swirl flame cooker, the wok stand height can be slightly lowered to exploit the advantages of blended hydrogen combustion. • A systematic experimental study of the flow/temperature/emission/heat transfer of a cooker. • The changed flow rates are measured by using a self-developed device. • The height of the swirling flame shortens after blending hydrogen to natural gas. • The flame temperature/NOx emission increase while CO emission decrease. • Lowering the wok leads to higher heat transfer efficiency, lower NO x while only marginally higher CO. [ABSTRACT FROM AUTHOR]

Hydrogen-enriched compressed natural gas (HCNG) technology is one of the most critical developments in the natural gas industry. To ensure the safe utilization of HCNG, the mixing effect of the two gases must be characterized and evaluated. In this paper, five types of static mixers were developed and numerically simulated. The results showed that the velocity, hydrogen blending ratio (HBR), mixer types, element aspect ratio, torsion angle, and number of elements affected the mixing effect to different degrees. Specifically, the increase in velocity and HBR improved the mixing uniformity of hydrogen and methane, but with a limited impact. Additionally, the mixing uniformity increased with the increase in the torsion angle and the number of elements, as well as the decrease in the element aspect ratio. Overall, the torsion angle had the most significant effect on mixing uniformity. Comparing the five types of static mixers, it was found that the new LPD static mixers yielded the best mixing effect, while the Y-type static mixers had the worst mixing effect. It is noted here that all the static mixers could satisfy the mixing uniformity requirements of industrial production. [Display omitted] • The influence of five models on the gas mixing effect is comprehensively analyzed. • The gas mixing effect is analyzed by three evaluation indexes. • The effects of operating conditions and spoilers on the mixing effect are studied. • The new LPD static mixer has the best effect on gas mixing. [ABSTRACT FROM AUTHOR]

Accurate control of natural gas flow and pressure is essential to achieving multi-gas combined production of the natural gas hydrates. In this study, a downhole stratification control tool for controlling natural gas flow rate and pressure with a multi-stage throttling structure was innovatively proposed. The multi-stage throttling structure combined an adjustable cage sleeve and a fixed nozzle. The numerical model of the internal flow field of the downhole stratification control tool was established. Through the computer fluid dynamics numerical simulation, the flow field change law inside the spool module of the downhole stratification control tool under different spool structures, different outlet pressures, and different spool openings was analyzed. Moreover, the spool module prototype was processed, and the indoor experiment of the spool's performance of reducing pressure and regulating production was carried out. The results show that the multi-stage throttling structure has the advantages of adjustable spool opening and moderate cooling range and the mass flow of gas inside the spool changes linearly with the opening of the spool. The spool module can accurately control the mass flow of natural gas under high-pressure conditions, and meet the needs of the downhole stratification control tool for accurate gas control. • A DSCT with multi-stage throttling structure is proposed. • The throttling structure composed of a cage sleeve and a fixed nozzle. • The flow field of multi-stage throttling structure is analyzed. • The DSCT can precisely control the gas mass flow under high-pressure conditions. • The pressure drop performance of the multi-stage throttling structure is the best. [ABSTRACT FROM AUTHOR]

The injection of hydrogen into the natural-gas grid is an alternative during the process of a gradual decarbonization of the heat and power supply. When dealing with hydrogen-enriched natural gas mixtures, the performance of the reference equations of state habitually used for natural gas should be validated by using high-precision experimental thermophysical data from multicomponent reference mixtures prepared with the lowest possible uncertainty in composition. In this work, we present experimental density data for an 11-compound high-calorific (hydrogen-free) natural gas mixture and for two derived hydrogen-enriched natural gas mixtures prepared by adding (10 and 20) mol-% of hydrogen to the original standard natural gas mixture. The three mixtures were prepared gravimetrically according to ISO 6142–1 for maximum precision in their composition and thus qualify for reference materials. A single-sinker densimeter was used to determine the density of the mixtures from (250–350) K and up to 20 MPa. The experimental density results of this work have been compared to the densities calculated by three different reference equations of state for natural gas related mixtures: the AGA8-DC92 EoS, the GERG-2008 EoS, and an improved version of the GERG-2008 EoS. While relative deviations of the experimental density data for the hydrogen-free natural gas mixture are always within the claimed uncertainty of the three considered equations of state, larger deviations can be observed for the hydrogen-enriched natural gas mixtures from any of the three equations of state, especially for the lowest temperature and the highest pressures. • H 2 -enriched NG is an alternative to the introduction of hydrogen into our energy infrastructure. • A high-calorific natural gas mixture of reference-quality was prepared. • Another two H2NG mixtures were prepared by adding 10 mol-% and 20 mol-% of H 2 to the original NG sample. • Density for these mixtures was measured using a single sinker densimeter over an extended p , T region. • Experimental density was compared with two different equations of state, GERG-2008 and AGA8-DC92. [ABSTRACT FROM AUTHOR]

Ammonia is a vital chemical with numerous applications. Currently, the primary methods for generating the necessary reactants for ammonia production involve steam methane reforming (SMR) and cryogenic air separation unit (CASU), while the Haber-Bosch process converts these reactants into ammonia. However, the SMR process releases substantial amounts of CO 2 , making it imperative to employ an efficient and cost-effective CO 2 capture technology to mitigate emissions. This investigation focuses on evaluating the cryogenic CO 2 capture (CCC) process for blue ammonia production and provides a thorough economic analysis, estimating both the initial investment costs and operational expenses involved in producing blue ammonia. The results indicated that the CCC process can capture 90% of the CO 2 content in the flue gas emitted by the SMR, incurring an energy penalty of 0.724 M J e / k g C O 2 while capturing CO 2 in the liquid phase with purities exceeding 99.9%. In this case, the estimated CO 2 capture costs would be 18.05, 45.1, and 16.65 USD/ton in 2021, 2022, and 2023, respectively. This represents a 40% reduction compared to the CO 2 capture costs associated with conventional amine-based technology. The results of this study indicate that the annual electricity costs for ammonia production increase by 38.5% and 64.2% when employing the CCC and amine-based processes, respectively. This investigation employed an isothermal reactor for ammonia synthesis, using the heat from the exothermic reaction in a water ammonia absorption refrigeration cycle (ARC) to condense and purify ammonia. The results show that the ARC system can effectively condense ammonia at −6 °C, producing a liquid ammonia stream with 99.3% purity. This leads to a 95% reduction in power consumption compared to a vapor compression refrigeration cycle (VCRC). Consequently, this method has the potential to decrease the annual operational costs for ammonia production by 2.92%, 2.69%, and 3.13% in 2021, 2022, and 2023, respectively. This study indicated that the hydrogen production unit incurs the highest initial investment costs, as well as operating costs, in the blue ammonia production process, followed by CASU and the Haber-Bosch process. • The performance of the CCC process for blue NH 3 production was thoroughly evaluated. • The economic impacts of CCC process were compared with those of amine-based method. • An energy efficient method for condensation of NH 3 in Haber-Bosch process is given. • Natural gas costs mainly influence the operating costs of blue NH 3 production. [ABSTRACT FROM AUTHOR]

Natural Hydrogen Gas (H 2) is producing a new golden rush worldwide due to its clean energetic features. The potential of natural hydrogen gas (H 2) in the southernmost regions of Brazil, specifically Rio Grande do Sul and Santa Catarina, remains largely unexplored. We found free H 2 occurrences identified in the intracratonic Mesozoic Paraná Basin, recognized in four formation tests performed in former exploratory wells. The data revealed H 2 concentrations ranging from 0.14% to 8.79%, albeit associated with noncommercial volumes of natural gas. These occurrences of H 2 exhibit a curious negative correlation with Helium (He), distinguishing it from many Eurasian occurrences associated with mantle sources. The Paraná Basin hosts the largest Brazilian coal reserves and organic-rich rocks. We posit that the hydrogen gas presence can be attributed to the maturation processes affecting mainly Rio Bonito, Taciba, and Ponta Grossa formations in this basin. Also, we identified hydrogen system elements in the rift-type Precambrian Camaquã Basin, which host potential source rocks, reservoirs, and seals. Until now, no H 2 measurements have been carried out in this basin. To solve this lack, it is fundamental to execute a systematic sampling survey; it will enable the identification of the potential of H 2 deposits in the Southernmost Brazilian region. This work lays the foundations for future research in the region, which is demanded to realize this economic potential. [Display omitted] • We present a review of the southmost Brazil geology from the perspective of hydrogen geology. • We summarize data from four wells with anomalous values of Hydrogen gas in the Paraná Basin. • We summarize all the elements of a hydrogen system in the Paraná and Camaquã basins. • Paraná Basin shows a concentration of up to 8% of H 2. [ABSTRACT FROM AUTHOR]

The utilization of H 2 blended natural gas has great significance for advancing large-scale applications of hydrogen energy. Numerical simulation can provide valuable insights into the combustion characteristics of H 2 blended natural gas. To calculate the radiative characteristics of H 2 O/CO 2 mixed gas under complex conditions efficiently and accurately in CFD simulation, new multi-parametrical pressurized WSGG correlations were proposed in this study, which introduced a set of parameters that can simultaneously adapt to variations in temperature, pressure and H 2 O/CO 2 molar ratio. The model coefficients are applicable across a wide range of conditions, including a total pressure range of 1∼10 bar, a temperature range of 400∼2500 K, H 2 O/CO 2 molar ratio from 3–5 and partial pressure path lengths from 0.001 to 60 bar·m. The new correlations were validated under one- and two-dimensional cases. The average error of radiative heat flux was less than 3.92% and the average error of radiative heat source was less than 4.32%, while traditional WSGG models developed under standard pressure failed to comprehensively meet the demands. The calculation results indicated that the new multi-parametrical pressurized WSGG correlations can effectively simulate radiative calculations in combustion media under varying pressures and are suitable for the fuel with high H 2 blending ratios, which is significant for hydrogen energy utilization. • New radiation model is designed for H 2 blended natural gas combustion in 1∼10 bar. • Multi-parameters of temperature, pressure and molar ratio are compatible with the model. • Proposed model shows great agreement with benchmark in radiation transfer cases. • Comparison between the proposed and previous WSGG models is conducted. • Detailed parameters and fitting methods are given. [ABSTRACT FROM AUTHOR]

The blending of hydrogen and natural gas (H 2 -NG) has emerged as a crucial and cost-effective means for processing hydrogen fluids through natural gas networks thereby aiding transition to net-zero energy. Nonetheless, the effective adaptation of H 2 -NG mixtures, especially up to 20% hydrogen concentrations, to existing natural gas distribution and storage facilities relies heavily on a comprehensive understanding of their thermophysical properties. We measured densities of three binary mixtures of hydrogen and methane (xH 2 = 0.0532, 0.0858, and 0.2031) at temperatures between 278 and 398 K, and pressures up to 56 MPa using a vibrating tube densimeter (VTD). The VTD was calibrated using H 2 and H 2 O. The measured densities were in reasonable agreements with the predictions of two thermodynamic equations of states (EoSs), Multi-Fluid Helmholtz Energy Approximation (MFHEA) and Peng-Robinson (PR). The average absolute relative deviation (AARD) for the measured density against the predictions of the PR EoS are 1.07%, 1.09%, and 0.89% for xH 2 = 0.0532, 0.0858, and 0.2031 mol fractions respectively. While the AARD for the measured density against the predictions of MFHEA EoS are 0.16%, 0.16%, and 0.32% for xH 2 = 0.0532, 0.0858, and 0.2031 mol fractions respective. The MFHEA EoS, which has the structure of GERG-2008, has better agreements with our density data than the PR EoS. The relative high deviations with PR EoS results from the PR's simple structure making it deficient in calculating thermal properties of natural gas in saturated-liquid and homogeneous states. In addition, the uncertainty of the measured density was determined, and the experimental data were compared with available literature data. Finally, the compressibility factor (Z), speed of sound (w), specific heat capacity at constant volume (C V), and specific heat capacity at constant pressure (C p) were obtained from the experimental results and were compared with the predictions of MFHEA EoS. This work provides accurate density and other thermophysical data useful for engineering/process designs and modelling of H 2 and natural gas systems thereby enhancing energy transition strategy. [Display omitted] • Density measurements for H 2 + CH 4 (xH 2 = 0.0532, 0.0858, and 0.2031) binary mixtures between 278 and 397 K and up to 56 MPa using VTD. • The measured densities were compared with the predictions of MFHEA and PR EoSs. • Determination of compressibility factors and other derived properties such w , C V , and C P for the mixtures. [ABSTRACT FROM AUTHOR]

In this paper, a diabatic compressed air energy storage system fueled by a natural gas/hydrogen mixture that integrates heating and power generation is proposed. A comprehensive thermodynamic analysis has been conducted to identify the key factors influencing system performance and elucidate the detailed formation and distribution patterns of irreversible losses when utilizing a hydrogen-natural gas blend as fuel in the proposed system. The research results indicate that increasing the hydrogen blending ratio from 0.5 to 1 lead to greater enhancements in roundtrip efficiency (∼1.08% vs. ∼0.33%), exergy efficiency (∼3.88% vs. ∼1.15%), and energy density (∼1.24% vs. ∼0.42%) compared to an increase from 0 to 0.5. The combustor suffers the largest exergy destruction proportion, with a notable reduction in exergy destruction achieved through increased hydrogen blending. System performance benefits significantly from higher combustor outlet temperatures and expansion ratios at various hydrogen blending ratios. The rate of change in exergy efficiency (∼42.76% vs. ∼83.17%) and energy density (∼58.83%) demonstrates an inverse correlation with the varied parameters (1100–1500K, 4–8), except for the rate of change in energy density (∼6.76%), which displays a positive relationship with the combustor outlet temperature. Notably, a significant decrease in the rate of change in roundtrip efficiency (∼1.87% vs. ∼6.64%) is observed within a specific parameter range (1400–1500K, 5–6). Sensitivity analysis identifies the combustor outlet temperature as the most influential factor in enhancing system performance, consistently showing positive effects of the hydrogen blending ratio. [Display omitted] • A natural gas/hydrogen-fueled CAES system combined heating and power is proposed. • Increasing the hydrogen contents significantly reduces combustor exergy destruction. • Higher hydrogen content (>0.5) yields notable performance boosts, especially in EXE. • The ROC s infected by ER display a remarkable correlation compared to the COT. • The COT is the crucial parameter on system performance via sensitivity analysis. [ABSTRACT FROM AUTHOR]

In the future, hydrogen will be more frequently injected into natural gas networks for storage and transportation purposes. A diffusion jet flame forms when gaseous fuel leakage occurs during the transportation or utilization of hydrogen-enriched natural gas, and the fuel is ignited by an ignition source in still air. In the study, methane was chosen to simulate natural gas. Experiments with the hydrogen addition fraction reaching up to 20% were performed to study the effects of the initial flame angle (θ = 90°, 60°, 30°, 0°, and −30°), variable nozzle diameter (d e = 3.15, 4, 4.94, 5.65, and 6 mm) and a multitude of fuel flow rates (10, 20, 30, 40, 50, and 60 L/min) on the morphological parameters of the gas jet flames. The geometrical features of the jet flame were determined via video processing for each experiment. The geometrical parameters of hydrogen-enriched natural gas were quantified under different conditions. The experimental results indicate that a dimensionless prediction model was established for the flame height of hydrogen-enriched natural gas by modifying the flame Froude number ( F r f) for vertical jet flames. For upward jet flames, the normalized flame horizontal projection length (L x) of hydrogen-enriched natural gas is well correlated with Q ∗. A global prediction model for inclination angles of 0° ≤ θ ≤ 60° and 2000 < Q ∗<20,000 was proposed based on the experimental data. For downward jet flames, the normalized horizontal projection length and downward extension length (L d) of the hydrogen-enriched natural gas jet flame are correlated with Q ∗, with powers of 2/5 and 3/5, respectively. Dimensionless prediction models for the horizontal projection length and downward extension length are given by modifying the flame Froude number. Quantitative results were proposed in order to gain insight into the development of the key parameters and the effects on the environment, from which extinguishing concepts and safety areas can be directly derived. • Hydrogen-enriched natural gas jet fire under various conditions was studied. • Macroscopic characteristics of hydrogen-enriched natural gas jet fire were quantified. • A unified empirical model was established to predict the horizontal extension length of hydrogen-enriched natural gas jet fire. • The normalized flame height and downward extension length correlated to the modified Froude number. [ABSTRACT FROM AUTHOR]

The rapid depletion of fossil fuels has become the worst scenario as most of the energy needed still depends on the use of fossil energy, oil, natural gas, and coal. The combustion of crude oil and coal has contributed to the major anthropogenic carbon dioxide (CO 2) gas in the atmosphere and has worsened climate change and global warming. Therefore, the abundant CO 2 in the surrounding has opened the door to many studies to convert CO 2 into the next generation of fuels and indirectly reduce the greenhouse effect. Transition metal dichalcogenides (TMDs) nanomaterials have appeared as a practical and reliable catalyst for CO 2 conversion to sustainable fuels under normal atmospheric conditions. Having fascinating electronic and catalytic properties, these earth-abundant element-based materials are being explored and developed for real-world application. This paper reviews the recent insight into the synthesis, properties and application of TMDs as catalysts in electrocatalysis, photocatalysis and thermal catalysis for CO 2 reduction and conversion. The role of type of sulfide (S), selenide (Se) and telluride (Te)-based TMDs in the production of various valuable products such as formate (HCO 2 −), formic acid (CH 2 O 2), methanol (CH 3 OH), and ethanol (CH 3 CH 2 OH), amongst others, will be discussed in detail. The possible reaction pathways and mechanisms and the relationship between tailoring the catalysts properties and CO 2 activation towards high CO 2 reduction and conversion efficiency will also be evaluated. • TMD catalysts have demonstrated promising performance in converting CO 2. • TMD catalyst can be used for electro-, photo- and thermal-catalytic CO 2 conversion. • The synthesis and characterization methods of TMD catalysts has been reviewed. • The different types of TMD catalysts and their potential have been investigated. • The mechanisms of all catalytic reactions have been examined. [ABSTRACT FROM AUTHOR]

Storing hydrogen gas in natural gas storage sites could help provide the large-scale energy storage required to decarbonize global energy supply. Here, we determine that active natural gas storage sites in the United States (U.S.) can store 312 TWh of hydrogen working gas, which is most of the hydrogen storage energy required for a 100% renewable energy grid in the country. We also provide the first assessment of the geologic reservoir quality for hydrogen and static storage capacity of inactive natural gas storage sites in the U.S. Our analysis evaluates each site for conversion to hydrogen storage based on their reservoir properties, and we find that these sites can store 3.9 TWh of hydrogen working gas. We conclude that these inactive sites provide a favorable route to commence seasonal hydrogen storage, but larger storage volumes, such as those provided by active sites, will be required in the future. • Storing hydrogen gas in natural gas storage sites can provide seasonal energy storage. • Active natural gas storage sites could store 312 TWh of hydrogen working gas. • Inactive natural gas storage sites could store 3.9 TWh of hydrogen working gas. • Active sites could store most of the hydrogen gas needed in a future electrical grid. • Inactive sites with good reservoir quality are strong candidate hydrogen storage sites. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H 2 S) methane (CH 4) reforming (H 2 SMR) is a promising process for sustainable energy production from conventional fuels, offering triple benefits for generating clean hydrogen (H 2), consuming toxic H 2 S, and producing an economically valuable by-product carbon disulfide (CS 2). In this work, we studied the optimal operating conditions and assessed the economic feasibility of the non-catalytic H 2 SMR process, employing a combination of kinetic modeling, process modeling, and techno-economic analysis. Plug flow reactor simulations were performed with our newly developed mechanism to shed light on the optimal operating conditions. It was concluded that a H 2 S/CH 4 molar feed ratio of 2 results in the highest hydrogen production rate, and a feed ratio of 1–2 and a temperature of 1100–1300 °C are needed to maximize the CS 2 production rate. However, feed ratios higher than 2 increase the conversion rate of CH 4 and therefore benefit the purity of the H 2 product. Comparing the cases for a feed ratio of 2 at 1300 °C and a feed ratio of 9 at 1200 °C, the cost is significantly higher for the feed ratio of 9, mainly attributed to the higher electricity cost for higher inlet flow rate and H 2 S recycling, as well as the cost for the additional steam required during the preheating process. The cost of hydrogen production by H 2 SMR process could be as low as $1.47/kgH 2 for a feed ratio of 2 and solar PV as an energy source, which is more competitive than a cost of $1.97/kgH 2 for the steam methane reforming process. Furthermore, since CS 2 is a valuable by-product, the higher amount of CS 2 formed at a feed ratio of 2 becomes the main source of revenue, which completely covers the cost of hydrogen production. This study demonstrates the huge potential of H 2 SMR process as a clean and economic-competitive way to produce hydrogen. • Studied H 2 SMR process using kinetic, process modeling, and techno-economic analysis. • Discussed optimal operating conditions for maximizing H 2 and CS 2 yields. • Conducted sensitivity analysis of power source and feed ratio on H 2 production cost. • Concluded that CS 2 yield in H 2 SMR could cover the cost of H 2 production. [ABSTRACT FROM AUTHOR]

This review article provides a comprehensive overview of the fundamentals, modelling approaches, experimental studies, and challenges associated with hydrogen gas flow in pipelines. It elucidates key aspects of hydrogen gas flow, including density, compressibility factor, and other relevant properties crucial for understanding its behavior in pipelines. Equations of state are discussed in detail, highlighting their importance in accurately modeling hydrogen gas flow. In the subsequent sections, one-dimensional and three-dimensional modelling techniques for gas distribution networks and localized flow involving critical components are explored. Emphasis is placed on transient flow, friction losses, and leakage characteristics, shedding light on the complexities of hydrogen pipeline transportation. Experimental studies investigating hydrogen pipeline transportation dynamics are outlined, focusing on the impact of leakage on surrounding environments and safety parameters. The challenges and solutions associated with repurposing natural gas pipelines for hydrogen transport are discussed, along with the influence of pipeline material on hydrogen transportation. Identified research gaps underscore the need for further investigation into areas such as transient flow behavior, leakage mitigation strategies, and the development of advanced modelling techniques. Future perspectives address the growing demand for hydrogen as a clean energy carrier and the evolving landscape of hydrogen-based energy systems. [Display omitted] • Hydrogen gas characteristics are useful to model flow in pipelines. • Flammability, embrittlement, and leak risks associated with hydrogen pose challenges in transportation. • Temperature variation and pressure drop across critical components are important aspects of pipeline design. [ABSTRACT FROM AUTHOR]

A green hydrogen (H 2) economy requires a sustainable, efficient, safe, and widespread infrastructure for transporting and distributing H 2 from production to consumption sites. Transporting a hydrogen/natural gas (H2NG) mixture, including pure H 2 , through the existing European natural gas (NG) infrastructure is considered a cost-effective solution, particularly in the transitional phase. Several reasons justify the H2NG blending option. The NG infrastructure can be efficiently repurposed to transport H 2 , by blending H 2 with NG, to operate as H 2 daily storage, matching production and demand and to enable large-scale seasonal H 2 storage. Although many benefits exist, the potential of existing NG grids for transporting and distributing green H 2 may face limitations due to technical, economic, or normative concerns. This paper focuses on the state of the art of the European NG transmission and distribution metrology normative framework and identifies the gaps to be filled in case of H2NG flowing into the existing grids. The paper was revised to provide a comprehensive analysis of the practical implications resulting from the H2NG blend option. [Display omitted] • The RePowerEU planned hydrogen production and utilization to achieve decarbonization targets. • The existing gas grid is considered for transporting and distribute large hydrogen amounts. • The European Committee for Standardization defined Standards on gas grid instrumentation. • A review of the European natural gas grid metrology normative was carried out in THOTH2 Project. • Standards need to be revised to account for hydrogen-natural gas mixtures transportation. [ABSTRACT FROM AUTHOR]

Integrating hydrogen (H 2) production systems within natural gas (NG) supply chains can support smoothening transition to cleaner energy resources by utilizing existing infrastructures. This work investigates the dynamic conversion of boil-off gas (BOG) using steam methane reforming (SMR) to produce H 2 within liquified natural gas (LNG) process. The study extends beyond technical considerations to encompass a socio-economic approach, exploring optimal H 2 allocation to different monetization techniques (e.g., ammonia and methanol) subject to final market price and demand data. Dynamic simulation showed an excellent ability to address the variations in BOG flow, change in LNG temperature and pressure drop within the LNG supply chain, highlighting the need for adaptive flowrate and process setpoints. The H 2 productivity and yield are dependent on steam flow rates, steam to carbon ration (S/C) and energy input to the system. Optimizing the reformer temperature is the best practice to enhanced the conversion of BOG to H 2. Allocating approximately 74% of the produced H 2 to CO 2 -free ammonia production, and the remainder to methanol via CO 2 hydrogenation, achieves an annual profitability of $1.36 billion. However, when considering variable demand and price data over ten years, the model proposes flexible annual H 2 allocation to both monetization routes, resulting in an average yearly profitability of $6.84 billion. These findings underscore the importance of integrating interactive simulation approaches to address exogenous and endogenous uncertainties, providing a robust strategy against risks. The comprehensive approach presented in this study contributes to the understanding and strategic planning of H 2 production within LNG supply chains, emphasizing adaptability and economic viability in the dynamic landscape of the energy transition. • Integrating hydrogen generation into LNG supply networks helps move to cleaner energy. • Economic/technical feasibility of SMR for H 2 production from BOG was presented. • Aspen HYSYS model was developed to ensure reliable, safe, and optimal H 2 production. • Implementing flexible H 2 allocation strategies in response to market conditions generates significant economic gains. • Annual allocation flexibility for economic performance increased profitability by 80% ($6.84B). [ABSTRACT FROM AUTHOR]

The transport of hydrogen in used natural gas pipelines is a strategic key element of a pan-European hydrogen infrastructure. At the same time, accurate knowledge of the hydrogen quality is essential in order to be able to address a wide application range. Therefore, an experimental investigation was carried out to find out which contaminants enter into the hydrogen from the used natural gas pipelines. Pipeline elements from the high pressure gas grid of Austria were exposed to hydrogen. Steel pipelines built between 1960 and 2018, which were operated with odorised and pure natural gas, were examined. The hydrogen was analysed according to requirements of ISO14687: 2019 Grade D measurement standard. The results show that based on age, odorization and sediments, different contimenants are introduced. Odorants, hydrocarbons but also sulphur compounds, ammonia and halogenated hydrogen compounds were identified. Sediments are identified as the main source of impurities. However, the concentrations of the introduced contaminants were low (6 nmol/mol to 10 μmol/mol). Quality monitoring with a wide range of detection options for different components (sulphur, halogenated compounds, hydrocarbons, ammonia and atmospheric components) is crucial for real operation. The authors deduce that a Grade A hydrogen quality can be safely achieved in real operation. • Adequate hydrogen quality can be achieved in used natural gas pipes. • Grade A would be reached safely in normal operation of the sampled pipelines. • Detection of odorants from natural gas operations can be confirmed. • Sediments in the pipe are found to be the main source of contamination. • Newer pipes without solid deposits hardly carry any detectable impurities in hydrogen. [ABSTRACT FROM AUTHOR]

Utilizing the existing natural gas grid presents a promising method for transporting hydrogen on a large scale. However, the effects of natural gas and its impurities on hydrogen-assisted cracking in pipeline steel have not been adequately studied. This study aims to investigate the fatigue performance of X80 pipeline steel in hydrogen-enriched natural gas (HENG) environments and in mixtures containing the impurity CO 2. This is achieved through fatigue crack growth rate (FCGR) tests and density functional theory (DFT) calculations. The experimental results show that the FCGR in H 2 is slightly faster than that in HENG, whereas it is slower than that in the N 2 /CO 2 /H 2 mixtures. The enhanced FCGR by CO 2 further increases with the increasing CO 2 content. DFT computational results indicate that the adsorbed CO 2 on the iron surface significantly accelerates the migration of H atoms from surface to subsurface. This promotes the entry of hydrogen into the steel. [Display omitted] • CO 2 promotes fatigue crack growth rate of X80 in the hydrogen environment. • Fatigue crack growth rate further enhances with the increasing CO 2 content. • CO 2 has little effect on the H 2 adsorption and dissociation on the Fe(110). • CO 2 accelerates the surface H atom migration to the subsurface of the Fe(110). [ABSTRACT FROM AUTHOR]

This paper suggests a Recalling Enhanced Recurrent Neural Network (RERNN) method for accurately predicting the performance and emissions of spark ignition (SI) engines. The RERNN method is an efficient neural network technique. The RERNN model is also trained using a better conjugate method that speeds up convergence by using a generalized Armijo search technique. The proposed method analyzes combustion phasing, exhaust temperature, engine-out emissions, burn duration, mean effective pressure, ignition lag, and maximum pressure rise rate. By then, the proposed technique is implemented on the MATLAB platform and is evaluated for its performance against existing techniques. The proposed RERNN method achieves a better outcome than other existing Seagull Optimization Algorithm (SOA), Grasshopper Optimization Algorithm (GOA), and Wild Horse Optimizer (WHO) techniques. The proposed method shows the error in carbon monoxide (CO) is 0.18% and carbon dioxide (CO2) is 0.29% at a high speed of 900 rpm compared with other existing approaches. • RERNN method designed for accurately predicting performance in SI engines. • The RERNN method is highlighted as an efficient neural network technique. • The RERNN model is trained using an improved conjugate method. • This approach contributes to a more holistic evaluation of engine performance. • The proposed RERNN method, implemented on the MATLAB platform. [ABSTRACT FROM AUTHOR]

Hydrogen-enriched natural gas is regarded as a promising low-carbon fuel in clean energy field. A hydrogen-enriched natural gas oxy-fuel combustion power plant is established to study the effect of hydrogen content on system thermodynamic performance. Three different diluents including recycled flue gas (RFG), H 2 O, and CO 2 are used to moderate the high combustion temperature. The transcritical CO 2 cycle is adopted to efficiently utilize flue gas waste heat. As the hydrogen blending ratio increases from 0 to 0.5, the efficiency of the O 2 /RFG system, O 2 /H 2 O system and O 2 /CO 2 system increases by 1.45%, 1.13% and 1.16%, respectively. The RFG system is preferable to realize high efficiency that can reach 50.23%. In the proposed systems, the carbon capture rate (CCR) decreases while specific CO 2 emission ( S E C O 2 ) increases with the hydrogen addition. In O 2 /RFG system, the CCR reaches a minimum of 99.09% when S E C O 2 is 3.81. The study results can have a positive influence on the utilization of hydrogen energy. • A hydrogen-enriched natural gas oxy-fuel combustion power plant is proposed. • Transcritical CO 2 cycle is employed to recover the waste heat of the system. • The effect of hydrogen content and the diluent on the system performance are studied. • The maximum system efficiency of RFG, H 2 O and CO 2 is 50.23%, 38.73% and 38.03%. [ABSTRACT FROM AUTHOR]

Green hydrogen has become more attractive as a fuel for engines to reduce greenhouse gas emissions. By mixing it with natural gas (NG), the modification work on the engine can be minimized but the carbon dioxide emissions from combustion can still be decreased. In this paper, an experimental study was accomplished to investigate the performance of a spark-ignition engine fueled with hydrogen-natural gas blends by either keeping a constant ignition timing or changing it. Up to 25 mol-% hydrogen was mixed into natural gases with different compositions and the methane number and Wobbe index were calculated and compared to the requirements set by Euromot. The results show that up to 15 mol-% hydrogen can be blended into NG to meet the limits of Euromot. However, when 25 mol-% hydrogen was mixed into NG the methane number varied between 56 and 64 depending on the gas composition. This would most likely cause knock for a mixture consisting of higher hydrocarbons but during the executed tests knock was never a problem. Furthermore, it was detected that the methane number alone cannot tell the knock tendency of a gas in a certain engine and an additional condition is needed such as the hydrogen level. An adjusted ignition timing was also preferable compared to a constant one to keep the engine component temperature at a moderate level. • A SI-engine was fueled with different hydrogen-natural gas (H 2 -NG) mixtures. • Wobbe index and methane number (MN) were calculated for all test points. • Efficiency was improved and emissions were decreased with higher hydrogen content. • No tendency of knock when 25 mol-% hydrogen was mixed into natural gas with a low MN. • Additional condition is needed for MN eg. H 2 -level to be sure if knock can happen. [ABSTRACT FROM AUTHOR]

Combustion of hydrogen-enriched natural gas is a valuable short-term strategy for reducing CO 2 emissions from high temperature industrial heating. This paper presents several experiments on combustion characteristics and the formation of nitrogen oxides. The experiments included hydrogen contents up to 100% and fuel heat inputs up to 75 kW. Water-cooled lances were used to influence the furnace temperature. The analysis includes the distribution of furnace temperatures, the composition of flue gas, the cooling capacity of the lances under steady-state operating conditions, and OH*-chemiluminescence imaging of the near burner region. The presented results demonstrate the dependence of furnace conditions and NO X formation on various factors, such as different air inlet fluxes, furnace temperature, and fuel composition, for constant heat inputs. Efficiency increased by up to 5.5% and significant changes in flame shaped along with a maximum increase in NO X emissions when comparing natural gas to hydrogen was measured at 167%. [Display omitted] • Combustion of hydrogen-enriched natural gas with 0 to 100% H 2 • Experimental analysis of an industrial burner in a steady state, false air-free furnace. • Converged measurements for temperature, flue gas composition and cooling heat fluxes. • Dependence of NO X in mg/kWh on flame shape, temperature, fuel blend and air ratio. • Imaging of self-emitted OH*-chemiluminescence from turbulent jet flames. [ABSTRACT FROM AUTHOR]

The rapid development of electric vehicles has drawn extensive attention to using rotary engines as small-scale power generation devices. However, their wide application has been limited by drawbacks such as low combustion efficiency and high emissions. Therefore, to obtain rotary engines with high combustion efficiency and low emissions, this study explored the strengthening effect of natural gas/hydrogen hybrid fuel (NHHF) and Triangular Rotor Piston (TRP) structure on the combustion in the turbulent jet ignition rotary engine (TJI-RE) at different ignition advance angles (IAAs). Additionally, an experimental platform and a three-dimensional computational model for TJI-RE fueled by natural gas/hydrogen hybrid fuel (NHHF) were established in this study. The research results indicated that the TRP structure altered the combustion process by affecting the ignition area in the ignition stage and the turbulence kinetic energy during the combustion stroke. Furthermore, the SC-shaped cylinder exhibited the highest peak pressure for any fixed IAA. When the IAA was fixed at 30°CA (BTDC), the TJI-RE with the SC-shaped cylinder experienced a 12.12% increase in peak pressure and a 4.1% increase in indicated work compared to the FP-shaped cylinder. Additionally, the CO emission was reduced by 13.79%, while the NO emission showed a significant increase. • NHHF was used to reduce the carbon emissions of the RE. • A three-dimensional computational model of the TJI-RE was established. • The effect of piston structure on combustion in TJI-RE was systematically studied. • The optimal combination of piston structure and IAA for the TJI-RE was given. [ABSTRACT FROM AUTHOR]

Massive storage of dihydrogen (H 2) in underground geological storage (UGSs) will be necessary to meet future H 2 production ambitions. Such storage in deep aquifers was simulated in a high-pressure reactor, and the evolution of the 3 phases (natural gas/H 2 , formation water and rock) with autochthonous microorganisms was monitored over several weeks. These results show that methanogens do not necessarily dominate the community, but that sulfate-reducing activity and formate bioproduction are systematically present. The experimental data were fed into a biochemical model in PHREEQC to better understand the interplay between the phenomena observed. In particular, it was shown that the microbial activities associated with H 2 consumption led to alkalinisation, which could explain, at least in part, the slower rate at which H 2 disappeared, even if sufficient CO 2 and sulfate remained in the system. Combined with a supposed local nutrient depletion, these results are encouraging for H 2 storage in deep aquifers. • Injection of H 2 in three deep aquifers was studied in a high-pressure reactor. • Multidisciplinary approach including experiment analyses and biochemical modeling. • Low sulfate content sites should be favored for H 2 storage in deep aquifers. • Storage behavior needs to be studied site-specifically. [ABSTRACT FROM AUTHOR]

With the continuous development of hydrogen energy technology, mixing hydrogen has become a potential method to enhance the performance of natural gas engines and reduce emissions. Aiming to offer guidance for optimizing strategies for mixing hydrogen from the perspectives of knock control and thermal efficiency enhancement, a three-dimensional model of a commercial heavy-duty natural gas engine is constructed based on the actual boundary conditions from a high load bench test. In this study, simulations were conducted under conditions where the hydrogen volume fraction ranged from 0% to 40%. The study explored the effects of two injection strategies, port fuel injection of hydrogen-enriched natural gas (PFI) and port fuel injection of natural gas combined with direct injection of hydrogen into the cylinder (PFI + DI), on engine knocking, performance, and emissions. Results indicate that for various injection strategies, there is an increasing trend in knock intensity (KI) with the higher hydrogen mixing ratio. When the hydrogen volume fraction exceeds 20%, the timing of direct hydrogen injection significantly affects KI. This effect is mainly caused by the distribution of unburned hydrogen at the knock onset crank angle (KOCA). Compared to other injection strategies, the PFI + DI strategy when the direct hydrogen injection time at 120°CA BTDC results in a high concentration of hydrogen near the spark plug at the ignition moment, combined with good mixture uniformity in the cylinder. This leads to the shortest CA0-10 and CA10-90, and achieves a maximum indicated thermal efficiency (ITE) of 44.68% under 20% hydrogen volume fraction. Compared to the original natural gas engine, the ITE increased by 2.9% and the NO x emissions increased by 166%, while the HC and CO emissions decreased by 88% and 53%. • Effects of different hydrogen mixing strategies on a natural gas engine are studied. • Knock intensity correlates with unburned hydrogen distribution at knock onset crank angle. • Hydrogen mixing methods affect mixture uniformity and TKE in cylinder. • At 20% hydrogen volume fraction, direct hydrogen injection timing of 120°CA BTDC maximizes ITE. [ABSTRACT FROM AUTHOR]

The urgent need for sustainable energy solutions has been underscored by escalating greenhouse gas emissions and the global commitment to net-zero emissions. Clean hydrogen energy, despite its potential for the global low-carbon transition, faces challenges such as high production and transport costs and significant carbon emissions. Herein, we investigate the molten-medium-catalyzed pyrolysis of natural gas (MPN) for hydrogen production and refueling. We highlight the urgent environmental and economic motivations for cleaner energy, specifically addressing the existing challenges faced by traditional hydrogen production methods. Our research introduces an innovative integrated system for onsite hydrogen production, showcasing its economic advantages, carbon emission reduction potential, and compatibility with current infrastructures. The study meticulously evaluates the MPN technology's economic feasibility, including a detailed analysis of cost drivers and the market value of by-product carbon materials. Furthermore, we stress the importance of further research to optimize the technology and promote its adoption for a low-carbon future. This investigation presents MPN as a promising alternative, potentially revolutionizing the hydrogen supply chain and contributing significantly to global decarbonization efforts. • Introduces molten-medium-catalyzed pyrolysis for clean hydrogen production. • Evaluates economic and environmental benefits for sustainable energy. • Showcases compatibility with existing energy infrastructures. • Analyzes cost drivers and market value of by-product carbon materials. • Advocates for research to optimize technology for low-carbon transition. [ABSTRACT FROM AUTHOR]

The exploitation of green hydrogen blending with natural gas (NG) is expected to contribute in lowering greenhouse gas emissions and fostering the share of renewable energy sources (RES). The NG infrastructure, in fact, can act as a storage facility for green hydrogen produced from excess RES, also providing flexibility to the electric system. However, the unbalance of the networks and the raise of protection issues for consumers may occur as a consequence of the potential decay of the metrological performance of gas meters operating with natural gas and hydrogen blends. In this paper, the authors present the results of an experimental campaign aimed at analysing the effect of hydrogen blending on the accuracy of smart domestic gas meters. Experimental tests were performed in the laboratory using air, natural gas and gas-hydrogen blends up to 23%vol. The results show no criticalities occur for diaphragm and ultrasonic gas meters, regardless of the hydrogen content. On the other hand, thermal mass gas meters show good reliability when hydrogen blends are within 2%vol, whereas for higher hydrogen contents, reliability is demonstrated only when they are equipped with a specific new design routine capable to address the gas quality changes. • Hydrogen blending with natural gas is becoming a spread practice for green energy storage and use. • Issues related to the readiness of the gas infrastructure to distribute hydrogen blends and appliances still have to be investigated. • Consumer protection and fairness of the billing is a crucial issue for domestic gas meters. • Accuracy tests of domestic gas meters of different measuring principles with hydrogen admixture up to 23% are presented. [ABSTRACT FROM AUTHOR]