Hydrogen Leakage Research Articles

Estimating Greenhouse Gas Emissions from Hydrogen-Blended Natural Gas Networks

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.

Simulation and Quantitative Assessment of Sensor Placement in a Hydrogen Bus for Risk Mitigation

The cleanliness of hydrogen energy throughout its life cycle has enabled its applications in transportation and buildings. However, such scenarios often involve the storage and use of hydrogen in enclosed spaces. Ensuring the facility’s safety during hydrogen accidental leakage through rapid detection and emergency measures has been a long-standing topic. In this work, we analyze hydrogen leakage in a hydrogen bus through CFD simulation. By extracting the hydrogen diffusion time and combining it with the leakage frequency and ignition probability, we quantitatively evaluate the placement of the sensors and propose an index for detection system assessment named the average detection delay index (ADDI). A near-field detection sensor was introduced to the system, which reduced the lower ADDI limit of the detection system by up to 10 times while reducing the system cost without changing the level of performance.

Dynamic risk analysis of fire and explosion domino accidents at hydrogen refueling stations using Dynamic Bayesian Network

Hydrogen is a promising energy source and hydrogen refueling stations (HRS) are the main hydrogen supply infrastructures. Unwanted hydrogen leaks and releases at the hydrogen station may cause serious explosion accidents and even induce domino effects due to intensive hazardous equipment in the station. However, scant attention has been accorded to the dynamic risks of fire, explosion, and domino effects at HRS, posing a threat to the safe functioning of HRS and the advancement of the hydrogen energy. This study thus first develops Dynamic Bayesian networks to model the primary fire and explosion accidents as well as domino effects at HRS. By the developed models, the critical factors that lead to accidents and the critical equipment that contributes to the initiation or propagation of domino effects can be identified. Moreover, the failure probability of different equipment exposed to possible accidents can also be obtained, supporting safety management of HRS.

Hydrogen Leakage Risks and Mitigation Measures in Large Underground Garages

Abstract Hydrogen fuel cell vehicles, characterized by zero emissions, pollution-free operation, and high efficiency, have emerged as a key focus in the development of the global automotive industry. The operating pressure for onboard hydrogen storage tanks commonly ranges from 30 to 70 MPa. Due to hydrogen's wide combustion and explosion concentration range and its exceptionally rapid combustion rate, there is a high risk of explosions and other accidents once equipment failure happens during storage and transportation. The research presented in this paper focuses on the analysis of hydrogen leakage from storage tanks in an underground garage using FLUENT simulations. The findings reveal that released hydrogen forms a jet from the storage tank under high pressure, dispersing along the ceiling upon reaching it and accumulating at the edges and corners. Moreover, larger leakage ports on the storage tank result in a greater mass flow of hydrogen, leading to an expanded diffusion range of the hydrogen cloud and decreased local concentration. To mitigate the risk of hydrogen combustion and explosion within the garage, this study introduces 16 extraction vents on the garage ceiling and 6 natural vents on its sides. The validation of the proposed hydrogen risk mitigation measures demonstrates their effectiveness in reducing the concentration and range of flammable clouds within the garage, especially when dealing with larger leakage ports.

Methodological approaches to carbon footprint assessment and certification of low carbon hydrogen

The article reviews existing approaches to low-carbon hydrogen certification and offers recommendations for their improvement based on an assessment of the carbon footprint across the entire life cycle. A comprehensive assessment of the carbon footprint of hydrogen produced from water and methane during steam reforming is presented. The assessment concluded that approximately 50% of hydrogen is produced from water, meets the requirements of low-carbon hydrogen (emission levels in the range of 4.2–4.5 kg CO2eq/kg H2) and can be considered for certification as renewable hydrogen. The results of estimating the carbon footprint of hydrogen from hydrogen sulfide demonstrate that for hydrogen sulfide methane reforming and thermal decomposition of hydrogen sulfide, carbon dioxide emissions will be on the order of 1.842 and 2.244 kg CO2/kg H2, respectively. Taking into account associated emissions from natural gas production, the total greenhouse gas emissions for the processes under consideration are 4.649 and 6.129 kg CO2eq/kg H2, respectively, when using grid electricity. When using electricity from hydropower, the total greenhouse gas emissions from hydrogen production through hydrogen sulfide methane reforming and thermal decomposition of hydrogen sulfide will be 2.33 and 2.78 kg CO2/kg H2, respectively, and for an alkaline electrolyzer they are about 2.60 kg CO2/kg H2. Thus, when using low-carbon sources of electricity to power processes, hydrogen sulfide technologies perform comparable to water electrolysis processes, and in some cases even show lower emissions.Additionally, the impact of hydrogen leaks on the greenhouse effect is considered and analyzed, which allows us to conclude that hydrogen is an indirect greenhouse gas.

Research on hydrogen diffusion and sensor arrangement strategy in a marine engine room

This paper investigates the diffusion behavior and spatiotemporal concentration distribution of hydrogen in the marine engine room under different leakage conditions. By analyzing the response times and alarm rates of sensors, it identifies the optimal positions for sensor installation. When hydrogen leaks in the upper and lower layer sequentially, the maximum diffusion volumes within 150s are 1804.0 m3 and 2281.9 m3, while the minimum diffusion volumes are 784.7 m3 and 1377.9 m3. These findings reveal significant differences in hydrogen diffusion behavior under different leakage locations and directions. Sensor arrangement recommendations are made for specific height ratios (h/H) where alarm rates are highest and response times shortest. The recommended installation positions are S4∼S6, S11∼S12 at h/H = 0.30, and S6, S12∼S11, S16, S25 at h/H = 0.52, and S3, S19, S2, S5, S10, S14, S20∼S22 at h/H = 0.97, as well as near the interfaces of hydrogen pipelines, valves, and gas equipment interfaces with a high risk of leakage.

A hybrid expert neural network for predicting hydrogen concentration under the ceiling in underground garage

In the event of a hydrogen leak, the build-up of hydrogen near the ceiling of an underground garage poses a significant safety risk. Fast and accurate estimation of hydrogen concentration distribution is crucial for risk assessment. This study proposes a novel neural network named multi-expert variational hybrid network (MEVHN) to predict the distribution of hydrogen concentration under the ceiling when the peak concentration reaches its maximum value during a leakage event. The model utilizes data from discrete sensors to make predictions. It incorporates a mixture of experts (MoE) framework to transform the sensor data into latent variables, which are then used by a variational autoencoder (VAE) decoder to predict the hydrogen concentration distribution. Constraints are added to the loss function to improve the prediction accuracy further. The results show that the MEVHN has an inference time of 1.3 seconds, a coefficient of determination (R²) of 0.977, a mean absolute error (MAE) of 1.86E-3, and a mean squared error (MSE) of 3.15E-5. These results indicate that the model performs well in predicting the 2D hydrogen concentration distribution.

Nano‐Patterned CuO Nanowire Nanogap Hydrogen Gas Sensor with Voids

AbstractHydrogen (H2) is increasingly employed in industrial applications, such as developing hydrogen fuel cells for vehicles and power plants. However, H2 explodes at a concentration limit of 4%, necessitating the development of ultrasensitive hydrogen sensors capable of early‐stage detection of hydrogen leaks. In this study, nano‐patterned polycrystalline cupric oxide (CuO) nanowire array nanogap gas sensors with voids are fabricated using electron‐beam lithography and ex situ oxidization by annealing, which could detect 5 ppb H2 and show response and recovery times of less than 10 s without a baseline shift. Combining a pre‐H2 annealing process in Ar/H2 for Cu nanowires and a low‐rate oxidation process enhances the crystallinity of CuO nanowires, facilitating the preparation of polycrystalline CuO nanowires with voids, which is a significantly practical approach for the improvements of gas sensing properties. Response and recovery times of <10 s can be obtained for a gap separation of ≈30 nm. These improvements are discussed based on a high electric field of ≈1.3 MV cm−1. The relationship between the normalized response and H2 concentration is discussed based on the power law. This paper presents highly reliable and fast H2 sensors without a baseline shift to meet the demands of the hydrogen industry.

Study on characterization of flame propagation of spontaneous ignition caused by high-pressure hydrogen leakage

As an ideal energy source, hydrogen is highly susceptible to spontaneous ignition once leaked, which is an urgent issue that needs to be addressed. Based on the shock tube model, this paper investigates flame propagation under various pressures, tube lengths, and diameters by employing the LES approach and a detailed hydrogen/air combustion mechanism. The results indicate that within the tube, the ignition kernels gradually evolve into tulip flames when specific conditions are satisfied. As pressure and tube length increase, the likelihood of forming a complete flame rises significantly; with the increase of tube diameter, the flame front is flatter and the flame intensity is more uniformly distributed. Furthermore, this paper develops a model to predict the formation of a complete flame: Pb/Pa=570.64(L/D)−0.6. Outside the tube, once the intact flame passes out of the tube and evolves into a jet flame, structures such as flame envelopes and jet vortices will appear. Higher release pressures make it more difficult for the flame to propagate steadily, whereas increasing tube length and diameter promotes combustion and sustains the flame outside the tube.

Experimental study on the distributioncharacteristics of hydrogen leakage in three-dimensional parking garages

Experimental study on the distributioncharacteristics of hydrogen leakage in three-dimensional parking garages

Analysis of hydrogen leakage characteristics and hazard assessment of hydrogen production container

The compactness and flexibility of hydrogen production containers make them suitable for integration in photovoltaic or wind power stations, yielding versatile applications. However, these enclosed spaces pose a high risk of hydrogen leakage, necessitating thorough analysis of leakage characteristics and exhaust strategies. This study employs a three-dimensional CFD simulation to assess the hazards of hydrogen leakage within a 42 m3 hydrogen production container. Considering its operational context, we examine scenarios of minor and severe hydrogen leaks, evaluating vent fan effects and supplementary ventilation during slight and heavy leaks. Two common scenarios are studied: routine operations with slight hydrogen leakage and emergency situations involving minor leaks. By comparing single longitudinal and combined ventilation approaches, we derive the optimal strategy. Results reveal negligible combustion risk for slight leaks (≤0.6 g/s), with the top exhaust fan reducing combustible area by >99.5 %. Conversely, heavy leaks (>24 g/s) necessitate additional ventilation beyond top fan enhancement. However, maintaining stable room temperature during daily operations requires managed ventilation areas. Ultimately, for significant hydrogen leaks, the optimal solution entails combined ventilation with a blower directed at the leak source. This research underscores the critical importance of addressing hydrogen leakage hazards in enclosed spaces for enhanced safety and efficient operations.

Research on Jet Structure and the Virtual Nozzle Model for High-pressure Hydrogen Leakage from Rectangular Nozzles

The shockwave structure generated after high-pressure hydrogen leakage presents a challenge for simulations. To simplify the shockwave structure, virtual nozzle models have been proposed. However, these models are based on circular leak openings, lacking research on rectangular nozzles. This study utilizes OpenFOAM to investigate the characteristics of high-pressure rectangular nozzle hydrogen leakage with pressures up to 90 MPa. A real gas model and a new thermophysical model are adopted to better demonstrate the shock wave structure of the jet under high pressure. The study examines the characteristics of jet structures after leakage from rectangular nozzles with different pressures, aspect ratios, and diameters. The critical conditions for forming Mach disks in rectangular jets are proposed, and an empirical relationship for the position of the central compression wave is summarized. By combining the isentropic expansion equation, mass conservation, momentum conservation, energy conservation, and shock wave relationship before and after, a virtual nozzle model for rectangular nozzles is proposed. Using this model as the boundary condition for calculating large-scale diffusion and comparing the results with previous experimental and simulation data demonstrates its accuracy.

Simulation of hydrogen leakage and diffusion in an enclosed garage of mixed parking of fuel-cell vehicles

The numerical simulation is used to investigate the spread and diffusion behaviors of hydrogen leaks during mixed parking of two different models of fuel cell vehicle in a closed garage. Simultaneously, the impact of different adjacent vehicle models on hydrogen diffusion behaviors is also investigated. It is shown that for vehicles with a higher chassis, hydrogen diffuses rapidly along the ground after striking it. Conversely, vehicle with a lower chassis exhibit slower diffusion of hydrogen along the ground, owing to the limitations imposed by the chassis height. The development of the flammable zones caused by hydrogen leakage can be clearly distinguished into three stages. Each stage is influenced by distinct factors, including the model of leaking vehicle, the model of adjacent vehicles, and the presence of larger vehicles nearby. Notably, the chassis height has a significant impact on the volume of flammable zones, with vehicles possessing lower chassis exhibiting larger volumes. For a given vehicle model, parking near a fuel cell vehicle of the same model facilitates hydrogen diffusion more effectively than parking near a vehicle of a different model.

Gasochromic WO3/MoO3 sensors prepared by co-sputtering for hydrogen leak detection with long-lasting visible signal

Gasochromic WO3/MoO3 sensors prepared by co-sputtering for hydrogen leak detection with long-lasting visible signal

Numerical investigation of hydrogen vapor cloud explosion from a conceptual offshore hydrogen production platform

Offshore hydrogen production platforms have the potential to become significant components in the upcoming large-scale offshore hydrogen production, contributing to the global commitment to carbon neutrality. However, the risk of hydrogen leaks is inherent, and the ignition of released flammable mixture can lead to catastrophic explosion, endangering both structures and nearby personnel. This study aims to numerically investigate the hydrogen vapor cloud explosion from offshore hydrogen production platform. The solvers published within the OpenFOAM framework are validated against two public tests involving hydrogen gas explosions within obstacles. A numerical model of the hydrogen vapor cloud explosion from a conceptual offshore hydrogen production platform is then constructed. The effect of offshore facility layout configuration on flame propagation mechanism and overpressure characteristics is analyzed. Results indicate that the presence of compressor equipment and cylindrical hydrogen storage tank leads to accelerated flame propagation and higher overpressure peaks. By reducing the cross-sectional area of the compressor equipment by 68% perpendicular to the flame propagation direction, the maximum flame propagation speed and overpressure are reduced by 88.6% and 94.2%, respectively. With an appropriate layout that maintains a cross-sectional area of 0.008, the presence of compressor equipment may not exacerbate the consequences compared to scenarios without any compressor equipment. This study provides a foundational basis for the safety design of offshore hydrogen production platforms, aiming to mitigate potential hydrogen explosion hazards.

Discovery of large-scale natural hydrogen leakage in the Zhangbei Basin, North China

Discovery of large-scale natural hydrogen leakage in the Zhangbei Basin, North China

Numerical study on leakage, diffusion and accident consequences of liquid hydrogen jet and analysis of influencing factors

Key equipment in liquid hydrogen refueling stations (LHRS), such as liquid hydrogen (LH2) storage tanks or cryogenic pumps, are usually equipped with multiple protective measures. The likelihood of a catastrophic explosion is minimal. More commonly, valve or pipeline failures occur, leading to LH2 jet release. This study utilizes three-dimensional computational fluid dynamics (CFD) software FLACS to develop a numerical simulation method for LH2 jet release. A simple open environment scenario was created, and experimental data were used to verify the feasibility of the numerical simulation principles. The study analyzed the effects of parameters such as wind speed and direction, presence of barrier walls, and the height and distance of these walls on the consequences of LH2 jet release incidents. Results indicate that for LH2 impingement jet, the longitudinal dispersion distance is greatest under downwind conditions. Under crosswind conditions, the horizontal dispersion distance, flammable volume, and flammable mass are highest. Under upwind conditions, the equivalent stoichiometric cloud volume, explosion overpressure, and damage area are the largest, resulting in the most severe consequences. As wind speed increases, the explosion overpressure and damage area under upwind conditions initially increase and then decrease, with the most dangerous wind speed being 5m/s. Walls can effectively reduce the hazard range of explosions and fires following liquid hydrogen leakage from small holes. The optimal wall height is between 3m and 4m, and the optimal distance from the leakage point is around 9m. These findings provide crucial engineering guidelines for optimizing barrier wall design and wind mitigation strategies in LHRS. Furthermore, by improving safety standards and reducing the risks of explosions, this research plays a pivotal role in fostering public trust and promoting the broader use of LH2 as a clean energy source.

On the chemistry of the global warming potential of hydrogen

Hydrogen (H2) is considered a promising fuel to contribute to net-zero carbon emission goals. While hydrogen itself is not a greenhouse gas, leakage of hydrogen fuels causes indirect warming due to hydrogen’s influence on methane, tropospheric ozone, and stratospheric water vapor, with the methane term dominating the impact. Some studies consider a simple four-equation box model to explore the climate consequences of leakage from hydrogen fuel use relative to methane, while others have employed much more detailed global photochemical models. Here we use a comprehensive photochemical box model including 66 reactions to show and quantify how the analogous four-equation system is missing a critical OH feedback, leading it to overestimate the time-integrated methane response to a pulse of hydrogen by over 100%. We estimate a hydrogen global warming potential (GWP) relative to carbon dioxide of 28−11+18 on the 20-year time horizon and 10−4+7 on the 100-year time horizon based on the 66-reaction model and information from the literature. GWPs provide a measure of the relative global warming impact of emission of one gas compared to a selected reference gas per unit mass emitted. While CO2 is generally chosen for the reference, any gas can be used. We present the GWP of H2 using CH4 as the reference, as this choice cancels out some uncertainties that are common to both H2 and CH4. The GWP for H2 relative to CH4 from fossil fuel sources is 0.35−0.06+0.13 on time horizons beyond 15 years; put differently, we find that relative to an equivalent mass of emission of fossil CH4, hydrogen emission has a climate impact about three times smaller. These global warming potentials underscore that hydrogen leakage does contribute to climate change, emphasizing the importance of limiting both hydrogen and methane leakage if global net-zero greenhouse gas emissions are to be achieved by 2050.

Microscale chemiresistive hydrogen sensors: Current status and recent developments

Hydrogen is known for its efficient combustion, abundant natural availability, and environmentally friendly characteristics. It is recognized as a promising energy source for the future and is already utilized in various industries, including petrochemicals, electronics, food processing, aerospace, and new energy vehicles. However, challenges arise in the storage and use of hydrogen owing to its tendency to leak, its potential for explosion within a specific concentration range of 4%–75%, and itslow ignition energy requirements. Consequently, there is a demand for hydrogen sensors capable of quickly and accurately detecting low levels of hydrogen leaks. Microelectromechanical systems-based chemiresistive hydrogen sensors offer advantages such as low cost, compact size, low energy consumption, and superior sensing performance, making them a major focus of recent research. This article provides a comprehensive overview and comparison of the sensing principles of various hydrogen sensors, including chemiresistive sensors, electrochemical sensors, thermocatalytic sensors, acoustic sensors, and mechanical sensors. Micro-chemiresistive hydrogen sensors exhibit high sensitivity, low cost, and ease of integration, making them highly promising for practical applications. In response to the challenges encountered in practical applications of chemiresistive hydrogen sensors, such as high operating temperatures and high power consumption, this review explores emerging trends in chemiresistive hydrogen sensor technology from the perspectives of novel materials and activation methods. Finally, it discusses the applications and potential further developments of chemiresistive hydrogen sensors.

Miniaturized Electrochemical Gas Sensor with a Functional Nanocomposite and Thin Ionic Liquid Interface for Highly Sensitive and Rapid Detection of Hydrogen.

Hydrogen has been widely used in industrial and commercial applications as a carbon-free, efficient energy source. Due to the high flammability and explosion risk of hydrogen-air mixtures, it is vital to develop sensors featuring fast-responding and high sensitivity for hydrogen leakage detection. This paper presents a miniaturized electrochemical gas sensor by elaborately establishing a nanocomposite and thin ionic liquid interface for highly sensitive and rapid electrochemical detection of hydrogen, in which a remarkable response time and recovery time of approximately 6 s was achieved at room temperature. A screen-printed carbon electrode was modified with a reduced graphene oxide-carbon nanotube (rGO-CNT) hybrid and platinum-palladium (Pt-Pd) bimetallic nanoparticles to realize high sensitivity. To achieve miniaturization and high stability of the sensor, a thin-film room-temperature ionic liquid (RTIL) was employed as the electrolyte with a significantly decreased response time. The fast-responding hydrogen sensor demonstrates excellent performance with high sensitivity, linearity, and repeatability at concentrations below the lower explosive limit of 4 vol %. The engineered high-performance interface and gas sensor provide a promising and effective strategy for gas sensor design and rapid hazardous gas monitoring.