Hydrogen Blending

Hydrogen energy represents a crucial pathway towards achieving carbon neutrality and is a pivotal facet of future strategic emerging industries. The safe and efficient transportation of hydrogen is a key link in the entire chain development of the hydrogen energy industry’s “production storage and transportation”. Mixing hydrogen into natural gas pipelines for transportation is the potential best way to achieve large-scale long-distance safe and efficient hydrogen transportation. Welds are identified as the vulnerable points in natural gas pipelines and compatibility between hydrogen-doped natural gas and existing pipeline welds is a critical technical challenge that affects the global-scale transportation of hydrogen energy. Therefore this article systematically discusses the construction and weld characteristics of hydrogen-doped natural gas pipelines the research status of hydrogen damage mechanism and mechanical property strengthening methods of hydrogen-doped natural gas pipeline welds and points out the future development direction of hydrogen damage mechanism research in hydrogen-doped natural gas pipeline welds. The research results show that: 1 Currently there is a need for comprehensive research on the degradation of mechanical properties in welds made from typical pipe materials on a global scale. It is imperative to systematically elucidate the mechanism of mechanical property degradation due to conventional and hydrogeninduced damage in welds of high-pressure hydrogen-doped natural gas pipelines worldwide. 2 The deterioration of mechanical properties in welds of hydrogen-doped natural gas pipelines is influenced by various components including hydrogen carbon dioxide and nitrogen. It is necessary to reveal the mechanism of mechanical property deterioration of pipeline welds under the joint participation of multiple damage mechanisms under multi-component gas conditions. 3 Establishing a fundamental database of mechanical properties for typical pipeline steel materials under hydrogen-doped natural gas conditions globally is imperative to form a method for strengthening the mechanical properties of typical high-pressure hydrogen-doped natural gas pipeline welds. 4 It is essential to promptly develop relevant standards for hydrogen blending transportation welding technology as well as weld evaluation testing and repair procedures for natural gas pipelines.

The increasing demand for energy and the urgent need to reduce carbon emissions have positioned hydrogen as a promising alternative. This review paper explores the potential of hydrogen blending in natural gas pipelines focusing on the compatibility of pipeline materials and the associated safety challenges. Hydrogen blending can significantly reduce carbon emissions from homes and industries as demonstrated by various projects in Canada and globally. However the introduction of hydrogen into natural gas pipelines poses risks such as hydrogenassisted materials degradation which can compromise the integrity of pipeline materials. This study reviews the effects of hydrogen on the mechanical properties of both vintage and modern pipeline steels cast iron copper aluminum stainless steel as well as plastics elastomers and odorants that compose an active natural gas pipeline network. The review highlights the need for updated codes and standards to ensure safe operation and discusses the implications of hydrogen on material selection design and safety considerations. Overall this manuscript aims to provide a comprehensive resource on the current state of pipeline materials in the context of hydrogen blending emphasizing the importance of further research to address the gaps in current knowledge and to develop robust guidelines for the integration of hydrogen into existing natural gas infrastructure.

Hydrogen transportation through a new pipeline poses significant economic barriers and blending hydrogen into existing natural gas pipelines offers promising alternative. However hydrogen’s low energy density and potential material compatibility challenges necessitate modifications to existing infrastructure. This study conducts a comprehensive thermo-economic analysis of natural gas and hydrogen mixtures with and without gaseous inhibitors evaluating the impact on thermophysical properties (Wobbe index density viscosity energy density higher and lower heating values) compression power economic feasibility and storage volume requirement. A pipeline transmission model was developed in Aspen HYSYS to assess these properties considering major and minor infrastructure modifications. The findings suggest that the addition of 5% carbon monoxide and 2% ethylene as gaseous inhibitors in maintaining desired properties ensuring compatibility with existing infrastructure and operational processes. The findings also indicate that blending 30% hydrogen increases storage volume by 30–55% while reducing higher and lower heating values by 20–25%. However the addition of 5% carbon monoxide and 2% ethylene improves the pipeline performance and reduces the carbon emissions by 23–26% supporting the transition to low-carbon energy systems. The results suggest that hydrogen blending is viable under specific infrastructure modifications providing critical insights for optimizing pipeline repurposing for sustainable hydrogen transportation.

Hydrogen is blended with natural gas to form hydrogenated natural gas (HCNG) which is a new efficient and clean energy. CHEMKIN-PRO 19.0 software was combined with the GRI-Mech 3.0 mechanism to evaluate the capacity of H2 blending in reducing CO and CO2 emissions. Influences of H2 blending on combustion reactions of the CH4-air mixture were investigated. The results showed that the main reactants and products (CH4 CO and CO2) decreased in gradient with increasing H2 blending ratio accompanied by a shorter reaction duration and a faster reaction rate. After adding H2 important key radicals H O and OH increase significantly so that the combustion reactions become more violent. Sensitivity analysis reveals that among relevant elementary reactions of CO and CO2 R38 (with its promotional effect) and R158 (with its inhibitory effect) show the greatest sensitivity. As the H2 concentration increases the sensitivity of the two reactions (separately with promotional and inhibitory effects) decreases. Blending H2 in the natural gas can improve the combustion rate and reduce the generation of emissions CO and CO2 which is of important significance for realizing low-carbon goals and reducing air pollution.

Hydrogen is increasingly recognized as a key solution for decarbonizing the Dutch energy system particularly within the industrial sector. A national hydrogen network is under development to serve the five major industrial clusters in the Netherlands. However meeting the hydrogen needs of the industries outside these clusters which are collectively known as “Cluster 6” remains difficult. Regulatory unclarity and ambiguity around the hydrogen distribution infrastructure including restrictions on distribution system operators (DSOs) compound these challenges. This study investigates the complex and evolving regulatory landscape for hydrogen distribution across Cluster 6 in the Netherlands using a two-step approach of Institutional Network Analysis (INA) and stakeholder interviews. Findings outline possible pathways for delegating distribution responsibilities in current and future regulatory frameworks while stakeholders report structural and outcome uncertainty limiting their willingness to invest in hydrogen distribution initiatives. The research findings highlight the need for a more coherent regulatory and technical framework to support more effective development of physical hydrogen systems. Policy recommendations include clarification of distributor roles targeted support mechanisms and flexible regulations that can adapt to the rapidly developing hydrogen market.

An experimental study was devised to assess the technical environmental and economic impact of incorporating hydrogen into natural gas. The experimental tests were conducted on a GUNT ET 792 demonstration unit characterized by operating on a gas cycle in a twin-shaft configuration. The equipment was adapted to accommodate natural gas and mixtures of natural gas with hydrogen in volumetric fractions of 5% 10% and 20%. The tests carried out ensured the viability of using these mixtures from a safety perspective. On the other hand it was possible to evaluate the main differences in the use of these fuel gases in terms of the temperatures and pressures that characterize the main points of the gas cycle fuel injection pressures air/fuel ratios excess air power output overall cycle efficiencies NOX and CO2 emissions and operational cost.

In order to study the flow blending and transporting process of hydrogen that injects into the natural gas pipelines a three-dimensional T-pipe blending model is established and the flow characteristics are investigated systematically by the large eddy simulation (LES). Firstly the mathematical formulation of hydrogen-methane blending process is provided and the LES method is introduced and validated by a benchmark gas blending model having experimental data. Subsequently the T-pipe blending model is presented and the effects of key parameters such as the velocity of main pipe hydrogen blending ratio diameter of hydrogen injection pipeline diameter of main pipe and operating pressure on the hydrogen-methane blending process are studied systematically. The results show that under certain conditions the gas mixture will be stratified downstream of the blending point with hydrogen at the top of the pipeline and methane at the bottom of the pipeline. For the no-stratified scenarios the distance required for uniformly mixing downstream the injection point increases when the hydrogen mixing ratio decreases the diameter of the hydrogen injection pipe and the main pipe increase. Finally based on the numerical results the underlying physics of the stratification phenomenon during the blending process are explored and an indicator for stratification is proposed using the ratio between the Reynolds numbers of the natural gas and hydrogen.

Hydrogen-blended natural gas (NG) pipeline network transport is the most effective approach for solving the problem of large-scale hydrogen use. Hydrogen-blended NG that contains water vapour is prone to water vapour condensation when it passes through complex NG pipeline networks leading to pipeline network failures. To analyse the condensation behaviour of hydrogenblended NG containing water vapour in a Laval nozzle a condensation model of water vapour was established. A computational fluid dynamics approach was used to calculate the condensation process of hydrogen-blended NG containing water vapour in Laval nozzles for four countries: Iran USA Russia and Australia. Hydrogen-blended NG components affect the flow characteristics of the gas mixture in the nozzle. The gas components have the greatest effect on the Mach number. The difference between the maximum and minimum Mach numbers at the outlet was 0.02 Mach. Hydrogen-blended NG containing water vapour condenses downstream of the throat of the Laval nozzle. Hydrogen-blended NG from Russia had the largest condensation ratio (79.63%). The largest droplet radius and liquid mass fraction were observed in the hydrogen-blended NG from Australia. The condensation process can accelerate the future research and engineering application of water vapour into hydrogen-blended NG.

New flow metering challenges are presented by the energy transition program since the available and new infrastructures might be used to transport energy using energy vectors such as hydrogen-enriched natural gas mixtures including blends never adopted before in current distribution lines. In this framework it is necessary to have the possibility to verify the performance of flowmeters which are currently calibrated using natural gas and nitrogen as reference fluids even when operating with fluids that are not yet in use. For this reason a commercial clamp-on ultrasonic flowmeter was used to measure the speed of sound in a mixture of hydrogen and iso-butane after being calibrated using helium as reference fluid. Helium is actually much more expensive than nitrogen but in our case it is advantageous because in the temperature and pressure ranges considered in this work the speeds of sound of helium are more comparable with those of the binary mixture of hydrogen and isobutane than the speeds of sound of nitrogen under the same thermodynamic conditions. A specifically developed control apparatus was designed to adjust the temperature and the pressure of the gas filling a DN50-PN100 spool where the ultrasonic meter was mounted on. The instrument was calibrated for temperatures between (270 and 320) K and for pressures up to 3 MPa by using the prediction of the reference equation of state for helium of Ortiz-Vega et al. The measurements of the speed of sound were obtained in a binary mixture containing mainly hydrogen with a small content of iso-butane since for these compounds new results are necessary to validate and improve the predictions of thermodynamic models installed in flowmeters and in flow computers. The expanded relative uncertainty was evaluated to be of 0.09% ( = 2) that was estimated by considering the contributions of the main influence quantities repeatability and reproducibility of the measurements. The obtained results were compared with the AGA-8-92DC and GERG-2008 equations of state and found to be consistent with the values predicted by both models demonstrating the feasibility of using a clamp-on ultrasonic flowmeter to determine the speed of sound and possibility to verify the performance of flowmeter installed on the gas networks using the speed of sound as transfer quantity.

It is likely that blending hydrogen into natural gas grids could contribute to economy-wide decarbonization while retaining some of the benefits that natural gas networks offer energy systems. Hydrogen injection into existing natural gas infrastructure is recognised as a key solution for energy storage during periods of low electricity demand or high variable renewable energy penetration. In this scenario natural gas networks provide an energy vector parallel to the electricity grid offering additional energy transmission capacity and inherent storage capabilities. By incorporating green hydrogen into the NG network it becomes feasible to (i) address the current energy crisis (ii) reduce the carbon intensity of the gas grid and (iii) promote sector coupling through the utilisation of various renewable energy sources. This study gives an overview of various interchangeability indicators and investigates the permissible ratios for hydrogen blending with two types of natural gas distributed in Tunisia (ANG and MNG). Additionally it examines the impact of hydrogen injection on energy content variation and various combustion parameters. It is confirmed by the data that ANG and MNG can withstand a maximum hydrogen blend of up to 20%. The article’s conclusion emphasises the significance of evaluating infrastructure and safety standards related to Tunisia’s natural gas network and suggests more experimental testing of the findings. This research marks a critical step towards unlocking the potential of green hydrogen in Tunisia.

A thorough investigation of the thermodynamics and economic performance of a cogeneration system based on solid oxide fuel cells that provides heat and power to homes has been carried out in this study. Additionally different percentages of green hydrogen have been blended with natural gas to examine the techno-economic performance of the suggested cogeneration system. The energy and exergy efficiency of the system rises steadily as the hydrogen blending percentage rises from 0% to 20% then slightly drops at 50% H2 blending and then rises steadily again until 100% H2 supply. The system’s minimal levelised cost of energy was calculated to be 4.64 £/kWh for 100% H2. Artificial Neural Network (ANN) model was also used to further train a sizable quantity of data that was received from the simulation model. Heat power and levelised cost of energy estimates using the ANN model were found to be extremely accurate with coefficients of determination of 0.99918 0.99999 and 0.99888 respectively.

Methane is a significant contributor to anthropogenic greenhouse gas emissions. Blending hydrogen with natural gas in existing networks presents a promising strategy to reduce these emissions and support the transition to a carbon-neutral energy system. However hydrogen’s potential for atmospheric release raises safety and environmental concerns necessitating an assessment of its impact on methane emissions and leakage behavior. This study introduces a methodology for estimating how fugitive emissions change when a natural gas network is shifted to a 10% hydrogen blend by combining analytical flowrate models with data from sampled leaks across a natural gas network. The methodology involves developing conversion factors based on existing methane emission rates to predict corresponding hydrogen emissions across different sections of the network including mainlines service lines and facilities. Our findings reveal that while the overall volumetric emission rates increase by 5.67% on the mainlines and 3.04% on the service lines primarily due to hydrogen’s lower density methane emissions decrease by 5.95% on the mainlines and 8.28% on the service lines. However when considering the impact of a 10% hydrogen blend on the Global Warming Potential the net reduction in greenhouse gas emissions is 5.37% for the mainlines and 7.72% for the service lines. This work bridges the gap between research on hydrogen leakage and network readiness which traditionally focuses on safety and environmental sustainability studies on methane emission.

The weather-dependent nature of renewable energy production has led to periodic overproduction making hydrogen production a practical solution for storing excess energy. In addition to conventional storage methods such as physical tanks or chemical bonding using the existing natural gas network as a storage medium has also proven to be effective. Households can play a role in this process as well. The purpose of these experiments is to evaluate the parameters of a household heating device currently in use but not initially designed for hydrogen operation. The appliance used in the tests has a closed combustion chamber with a natural draft induced by a density difference which is a common type. The tests were conducted at nominal load with a mix of 0–40 V/V% hydrogen and natural gas; no flashbacks or other issues occurred. As the hydrogen ratio increased from 0 to 40 V/V% the input heat decreased from 3.9 kW to 3.4 kW. The NOx concentration in the flue gas dropped from 26.2 ppm to 14.2 ppm and the CO2 content decreased from 4.5 V/V% to 3.4 V/V%. However the CO con centration slightly increased from 40.0 ppm to 44.1 ppm. Despite these changes efficiency remained stable fluctuating between 86.9% and 87.0%. The internal flame cone height was 3.27 mm when using natural gas but reduced sharply to just 0.38 mm when using 62 V/V% hydrogen. In addition to the fact that the article examines a group of devices that has been rarely investigated but is also widely distributed it also provides valuable experience for other experiments since the experiments were carried out with a higher hydrogen ratio compared to previous works.

Blending hydrogen in existing natural gas pipelines compromises steel integrity because it increases fatigue crack growth promotes subcritical cracking and decreases fracture toughness. In this regard several laboratories reported that the fracture toughness measured in a hydrogen containing gaseous atmosphere KIH can be 50% or less than KIC the fracture toughness measured in air. From a pipeline integrity perspective fracture mechanics predicts that injecting hydrogen in a natural gas pipeline decreases the failure pressure and the size of the critical flaw at a given pressure level. For a pipeline with a given flaw size as shown in this work the effect of hydrogen embrittlement (HE) in the predicted failure pressure is largest when failure occurs by brittle fracture. The HE effect on failure pressure diminishes with a decreasing crack size or increasing fracture toughness. The safety margin after a successful hydrostatic test is reduced and therefore the time between hydrotests should be decreased. In this work all those effects were quantified using a crack assessment methodology (level 2 API 579-ASME FFS) considering literature values for KIH and KIC reported for an API 5L X52 pipeline steel. To characterize different scenarios various crack sizes were assumed including a small crack with a size close to the detection limit of current in-line inspection techniques and a larger crack that represents the largest crack size that could survive a hydrotest to 100% of the steel specified minimum yield stress. The implications of a smaller failure pressure and smaller critical crack size on pipeline integrity are discussed in this paper.

Hydrogen blending offers significant potential for decarbonizing natural gas-based thermal processes particularly in the steel and cement sectors. Due to its distinct combustion properties compared to natural gas – such as lower minimum air requirements and altered flame speeds – the hydrogen fraction of the fuel must be monitored for combustion control. In this study we present an ultrasonic time-of-flight measurement system for hydrogen concentrations of 0–40% in natural gas. The system is verified with test gas mixtures at laboratory scale and validated in a technical-scale setup using a real blower burner (< 60 kW). We evaluate uncertainty of the hydrogen fraction measurement and analyze the influence of varying natural gas compositions. We show that standard uncertainties below 4% can be achieved without knowledge of the specific natural gas composition. Our results provide insights for measurement system design and support the safe application of hydrogen in thermal systems for industrial processes.

This study employs first principles calculations and thermodynamic analyses to investigate the dissociative adsorption of hydrogen on the Fe(110) surface. The results show that the adsorption energies of hydrogen at different sites on the iron surface are −1.98 eV (top site) −2.63 eV (bridge site) and −2.98 eV (hollow site) with the hollow site being the most stable adsorption position. Thermodynamic analysis further reveals that under operational conditions of 25 ◦C and 12 MPa the Gibbs free energy change (∆G) for hydrogen dissociation is −1.53 eV indicating that the process is spontaneous under pipeline conditions. Moreover as temperature and pressure increase the spontaneity of the adsorption process improves thus enhancing hydrogen transport efficiency in pipelines. These findings provide a theoretical basis for optimizing hydrogen transport technology in natural gas pipelines and offer scientific support for mitigating hydrogen embrittlement improving pipeline material performance and developing future hydrogen transportation strategies and safety measures.

The blending of hydrogen significantly impacts the diffusion and safety characteristics of natural gas within indoor environments. This study employs ANSYS Fluent 2021 R1 to numerically investigate the diffusion and ventilation characteristics of hydrogen-blended natural gas (HBNG) leakage in indoor spaces. A physical and mathematical model of gas leakage from pipelines is established to study hazardous areas flammable regions ventilation characteristics alarm response times safe ventilation rates and the concentration distribution of leaked gas. The effects of hydrogen blending ratio (HBR) ventilation conditions and space dimensions on leakage diffusion and safety are analyzed. Results indicate that HBNG leakage forms vertical concentration stratification in indoor spaces with ventilation height being negatively correlated with gas concentration and flammable regions. In the indoor space conditions of this study by improving ventilation conditions the hazardous area can be reduced by up to 92.67%. Increasing HBR substantially expands risk zones—with pure hydrogen producing risk volumes over five times greater than natural gas. Mechanical ventilation significantly enhances indoor safety. Safe ventilation rates escalate with hydrogen content providing quantitative safety criteria for HBNG implementation. The results underscore the critical influence of HBR and ventilation strategy on risk assessment providing essential insights for the safe indoor deployment of HBNG.

In response to the global need to reduce greenhouse gas emissions and advance the decarbonization of thermal energy systems this study evaluates the performance of a tankless water heater operating with hydrogen–natural gas blends. The objective is to improve thermal efficiency and reduce pollutant emissions without requiring major modifications to existing equipment. Experimental tests were conducted at three thermal power levels (35 40 and 45 kW) and four hydrogen volume fractions (0% 20% 40% and 60%) analyzing operational variables such as temperatures flow rates efficiency and NOx emissions. Results show that efficiency increases with hydrogen content particularly at lower power levels reaching a maximum of 56%. NOx emissions tend to rise with both power and hydrogen fraction although this effect can be mitigated by controlling the water flow rate. In addition machine learning models were trained to predict efficiency and emissions with the scaled Support Vector Regression (SVR) model achieving R² values above 90% for both outputs. This approach not only enables system optimization but also represents a step toward the implementation of digital twins and opens the door to monitoring indirect variables offering broad potential for predictive applications in thermal equipment.