Safety
Computational Fluid Dynamic (CFD) Analysis of a Cold-adsorbed Hydrogen Tank During Refilling
Sep 2023
Publication
Hydrogen has the potential to be an important source of clean energy but the development of efficient and cost-effective methods for storing hydrogen is a key challenge that needs to be addressed in order to make widespread use of hydrogen as a possible energy sourc. There are different methods for storing hydrogen (i.e. compressed it at high pressures liquefied by cooling the hydrogen to a temperature of -253°C and stored with a chemical compound) each with its own advantages and disadvantages.<br/>MAST3RBoost (Maturing the Production Standards of Ultraporous Structures for High Density Hydrogen Storage Bank Operating on Swinging Temperatures and Low Compression) is a European project which aims to provide a solid benchmark of cold-adsorbed H2 storage (CAH2) at low compression (100 bar or below) by maturation of a new generation of ultraporous materials for mobility applications i.e. H2-powered vehicles including road and railway air-borne and waterborne transportation. Based on a new generation of Machine Learning-improved ultraporous materials – such as Activated Carbons (ACs) and high-density MOFs (Metal-organic Frameworks) – MAST3RBoost project will enable a disruptive path to meet the industry goals by developing the first worldwide adsorption-based demonstrator at the kg-scale.<br/>The design of the tank is supported by numerical investigation by mean of the use of Computational Fluid Dynamic (CFD) commercial code. In this a paper a preliminary analysis of the refilling of tank is presented focused on the effect of different tank configurations on the hydrogen temperature and on the hydrogen adsorption.
Safety Aspects Related to the Underground Hydrogen Storage
Sep 2023
Publication
The transition from fossil fuels to the renewable energies (wind solar) is a key factor to face climate change and build a sustainable reliable and secure energy system. To balance the intermittent energy demand and supply affecting the renewable sources the surplus of electrical energy may be converted in hydrogen and then storage in geological formations. While the risks associated to the natural gas storage in the sub-surface are well known from decades those associated with hydrogen underground storage (UHS) are relatively underexplored. This paper presents an inventory of risks related to large H2-storage in depleted gas and oil fields salt caverns and aquifers. Different issues such as integrity and durability of materials H2 leakages and interaction with the reservoir H2 uncontrolled outflow from the wellhead with potential combustion of air-hydrogen mixture (fire and explosion) soil subsidence and induced seismicity are analyzed.
Numerical Simulations of the Critical Diameter and Flame Stability for the Hydrogen Jet Flames
Sep 2023
Publication
This study focuses on development of a CFD model able to simulate the experimentally observed critical nozzle diameter for hydrogen non-premixed flames. The critical diameter represents the minimum nozzle size through which a free jet flame will remain stable at all driving pressures. Hydrogen non-premixed flames will not blow-out at diameters equal to or greater than the critical diameter. Accurate simulation of this parameter is important for assessment of thermally activated pressure relief device (TPRD) performance during hydrogen blowdown from a storage tank. At TPRD diameters below the critical value there is potential for a hydrogen jet flame to blow-out as the storage tank vents potentially leading to hydrogen accumulation in an indoor release scenario. Previous experimental studies have indicated that the critical diameter for hydrogen is approximately 1 mm. In this study flame stability is considered across a range of diameters and overpressures from 0.1 mm to 2 mm and from 0.2 MPa to 20 MPa respectively. The impact of turbulent Schmidt number Sct which is the ratio of momentum diffusivity (kinematic viscosity) and mass diffusivity on the hydrogen concentration profile in the region near the nozzle exit and subsequent influence on critical diameter was investigated and discussed. For lower Sct values the enhanced mass mixing resulted in smaller predicted critical diameters. The use of value Sct=0.61 in the model demonstrated the best agreement with experimental values of the critical diameter. The model reproduced the critical diameter of 1 mm and then was applied to predict flame stability for under-expanded hydrogen jets.
CO2 Effect on the Fatigue Crack Growth of X80 Pipeline Steel in Hydrogen-Enriched Natural Gas: Experiment vs Density Functional Theory Calculation
Sep 2023
Publication
The influence of hydrogen-enriched natural gas (HENG) and CO2 on the mechanical property of X80 pipeline steel were investigated via fatigue crack growth rate (FCGR) tests and density functional theory (DFT) calculations. The results show that the FCGR in H2 was slightly faster than that in HENG while it was slower than that in the N2/CO2/H2 mixtures. The enhanced FCGR by CO2 further increased with the increasing CO2 content. DFT calculation results show that the adsorbed CO2 on the iron surface significantly increased the migration rate of H atoms from surface to subsurface. This promotes the entry of hydrogen into the steel.
Ignition and Flow Stopping Considerations for the Transmission of Hydrogen in the Existing Natural Gas Network
Sep 2023
Publication
This work formed part of the H21 programme whose objective is to reach the point whereby it is feasible to convert the existing natural gas (NG) distribution network to 100% hydrogen (H2) and provide a contribution to decarbonising the UK’s heat and power sectors with the focus on decarbonised fuel at point of use. Hydrogen has an ATEX Gas Group of IIC compared to IIA for natural gas which means further precautions are necessary to prevent the ignition of hydrogen during network operations. Both electrostatic and friction ignition risks were considered. Network operations considered include electrostatic precautions for polyethylene (PE) pipe and cutting and drilling of metallic pipes. As a result of the updated basis of safety from ignition considerations existing flow stopping methods were reviewed to see if they were compatible. Commonly used flow stopping methods were tested under laboratory conditions with hydrogen following the methodologies specified in the Gas Industry Standards (GIS). A new basis of safety for flow stopping has been proposed that looks at the flow past the secondary stop as double isolations are recommended for use with hydrogen.
Investigation of the Suitability of Viper: Blast CFD Software for Hydrogen and Vapor Cloud Explosions
Sep 2023
Publication
Many simplified methods for estimating blast loads from a hydrogen or vapor cloud explosion are unable to take into account the accurate geometry of confining spaces obstacles or landscape that may significantly interact with the blast wave and influence the strength of blast loads. Computation fluid dynamics (CFD) software Viper::Blast which was originally developed for the simulation of the detonation of high explosives is able to quickly and easily model geometry for blast analyses however its use for vapor cloud explosions and deflagrations is not well established. This paper describes the results of an investigation into the suitability of Viper::Blast for use in modeling hydrogen deflagration and detonation events from various experiments in literature. Detonation events have been captured with a high degree of detail and relatively little uncertainty in inputs while deflagration events are significantly more complex. An approach is proposed that may allow for a reasonable bounding of uncertainty potentially leading to an approach to CFD-based Monte Carlo analyses that are able to address a problem’s true geometry while remaining reasonably pragmatic in terms of run-time and computational investment. This will allow further exploration of practical CFD application to inform hydrogen safety in the engineering design assessment and management of energy mobility and transport systems infrastructure and operations.
CFD Simulation and ANN Prediction of Hydrogen Leakage and Diffusion Behavior in a Hydrogen Refuelling Station
Sep 2023
Publication
Hydrogen refuelling stations are an important part of the infrastructure for promoting the hydrogen economy. Since hydrogen is a flammable and explosive gas hydrogen released from high-pressure hydrogen storage equipment in hydrogen refuelling stations will likely cause combustion or explosion accidents. Studying high-pressure hydrogen leakage in hydrogen refuelling stations is a prerequisite for promoting hydrogen fuel cell vehicles and hydrogen refuelling stations. In this work an actual-size hydrogen refuelling station model was established on the ANSYS FLUENT software platform. The computational fluid dynamics (CFD) models for hydrogen leakage simulation were validated by comparing the simulation results with experimental data in the literature. The effects of ambient wind speed wind direction leakage rate and leakage direction on the diffusion behaviors of the released hydrogen were investigated. The spreading distances of the flammable hydrogen cloud were predicted using an artificial neural network for horizontal leakage. The results show that the leak direction strongly affected the flammable cloud flow. The ambient wind speed has complicated effects on spreading the flammable cloud. The wind makes the flammable cloud move in certain directions and the higher wind speed accelerates the diffusion of the flammable gas in the air. The results of the study can be used as a reference for the study of high-pressure hydrogen leakage in hydrogen refuelling stations.
A New Dimensionless Number for Type IV Composite Pressure Vessel Designer to Increase Efficiency and Reduce Cost
Sep 2023
Publication
A new dimensionless number (DN) is proposed in order to evaluate the performance of a high-pressure vessel composite structure. It shows that very few composite part is used at its maximum loading potential during bursting. Today for 70 MPa on-board type IV composite tanks DN values close to 20%. The suggested DN will be a useful indicator for an industrial application. By maximizing the DN at the design phase it is possible to minimize the mass of the composite structure of a CPV to reduce the manufacturing time and cost. To increase the DN as close as possible to 100% it is necessary to succeed in increasing the overall loading of the composite structure to have better oriented fibre. For this it seems necessary to find new processes which make it possible to better orient the fibre.
Experimental Study on the Effect of the Ignition Location on Vented Deflagration of Hydrogen-air Mixtures in Enclosure
Sep 2023
Publication
No countermeasures exist for accidents that might occur in hydrogen-based facilities (leaks fires explosions etc.). In South Korea discussions are underway regarding measures to ensure safety from such accidents such as the construction of underground hydrogen storage tank facilities. However explosion vents with a minimum ventilation area are required in such facilities to minimize damage to buildings and other structures due to accidental explosions. These explosion vents allow the generated overpressure and flames to be safely dispersed outside; however a safe separation distance must be secured to minimize damage to humans. This study aimed to determine the safe separation distance to minimize human damage after analyzing the dispersed overpressure and flame behavior following a vent explosion. Explosion experiments were conducted to investigate the influence of the ignition source location on internal and external overpressure and external flame behavior using a cuboid concrete structure with a volume of 20.33 m3 filled with a hydrogen-air mixture (29.0 vol.%). The impact on overpressure and flame was increased with the increasing distance of the ignition source from the vent. Importantly depending on the ignition location the incident pressure was up to 24.4 times higher while the reflected pressure was 8.7 times higher. Additionally a maximum external overpressure of 30.01 kPa was measured at a distance of 2.4 m from the vent predicting damage to humans at the “Injury” level (1 % fatality probability). Whereas no significant damage would occur at a distance of 7.4 m or more from the vent.
Modelling of Hydrogen Dispersion with Effects
Sep 2023
Publication
The paper shows the latest developments of Gexcon’s consequence modelling software EFFECTS with validation based on hydrogen experimental data for different storage conditions and scenarios including liquid hydrogen two-phase jet releases. The effect of atmospheric turbulence on the dispersion and potential worst-case scenarios of hydrogen which are very different from heavy gas releases are discussed. Beside validation for gaseous hydrogen releases a validation study for pressurised liquid hydrogen jet releases including a sensitivity analysis is performed and the results are compared with experimental data.
GT Enclosure Dispersion Analysis with Different CFD Tools
Sep 2023
Publication
A gas turbine is usually installed inside an acoustic enclosure where the fuel gas supply system is also placed. It is common practice using CFD analysis to simulate the accidental fuel gas release inside the enclosure and the consequent dispersion. These numerical studies are used to properly design the gas detection system according to specific safety criteria which are well defined when the fuel gas is a conventional natural gas. Package design is done to prevent that any sparking items and hot surfaces higher than auto-ignition temperature could be a source of ignition in case of leak. Nevertheless it is not possible to exclude that a leakage from a theoretical point of view could be ignited and for this reason a robust design requires that the enclosure structure is able to withstand the overpressure generated by a gas cloud ignition. Moving to hydrogen as fuel gas makes this design constraint much more relevant for its known characteristics of reactiveness large range of flammability maximum burning velocity etc. In such context gas leak and dispersion analysis become even more crucial because a correct prediction of these scenarios can guide the design to a safe configuration. The present work shows a comparison of the dispersion of different leakages inside a gas turbine enclosure carried out with two different CFD tools Ansys CFX and FLACS. This verification is considered essential since dispersion analysis results are used as initial conditions for gas cloud ignition simulations strictly necessary to predict the consequence in term of overpressure without doing experimental tests.
Study on Liquid Hydrogen Leakage and Diffusion Behavior in a Hydrogen Production Station
Jun 2024
Publication
Liquid hydrogen storage is an important way of hydrogen storage and transportation which greatly improves the storage and transportation efficiency due to the high energy density but at the same time brings new safety hazards. In this study the liquid hydrogen leakage in the storage area of a hydrogen production station is numerically simulated. The effects of ambient wind direction wind speed leakage mass flow rate and the mass fraction of gas phase at the leakage port on the diffusion behavior of the liquid hydrogen leakage were investigated. The results show that the ambient wind direction directly determines the direction of liquid hydrogen leakage diffusion. The wind speed significantly affects the diffusion distance. When the wind speed is 6 m/s the diffusion distance of the flammable hydrogen cloud reaches 40.08 m which is 2.63 times that under windless conditions. The liquid hydrogen leakage mass flow rate and the mass fraction of the gas phase have a greater effect on the volume of the flammable hydrogen cloud. As the leakage mass flow rate increased from 5.15 kg/s to 10 kg/s the flammable hydrogen cloud volume increased from 5734.31 m3 to 10305.5 m3 . The installation of a barrier wall in front of the leakage port can limit the horizontal diffusion of the flammable hydrogen cloud elevate the diffusion height and effectively reduce the volume of the flammable hydrogen cloud. This study can provide theoretical support for the construction and operation of hydrogen production stations.
Numerical Simulation and Field Experimental Study of Combustion Characteristics of Hydrogen-Enriched Natural Gas
Jun 2024
Publication
For the safe and efficient utilization of hydrogen-enriched natural gas combustion in industrial gas-fired boilers the present study adopted a combination of numerical simulation and field tests to investigate its adaptability. Firstly the combustion characteristics of hydrogen-enriched natural gas with different hydrogen blending ratios and equivalence ratios were evaluated by using the Chemkin Pro platform. Secondly a field experimental study was carried out based on the WNS2- 1.25-Q gas-fired boiler to investigate the boiler’s thermal efficiency heat loss and pollutant emissions after hydrogen addition. The results show that at the same equivalence ratio with the hydrogen blending ratio increasing from 0% to 25% the laminar flame propagation speed of the fuel increases the extinction strain rate rises and the combustion limit expands. The laminar flame propagation speed of premixed methane/air gas reaches the maximum value when the equivalence ratio is 1.0 and the combustion intensity of the flame is the highest at this time. In the field tests as the hydrogen blending ratio increases from 0% to nearly 10% with the increasing excess air ratio the boiler’s thermal efficiency decreases as well as the NOx emission. This indicates that there exists a tradeoff between the boiler thermal efficiency and NOx emission in practice.
The Economical Repurposing Pipeliness to Hydrogen - Why Performance Testing of Representative Line Pipes is Key?
Sep 2023
Publication
The introduction of hydrogen in natural gas pipeline systems introduces integrity challenges due to the nature of interactions between hydrogen and line pipe steel materials. However not every natural gas pipeline is equal in regards to the challenges potentially posed by the repurposing to hydrogen. Existing codes and practices penalise high-grade materials on the basis of a perceived higher susceptibility to hydrogen embrittlement in regards to their increased strength. This philosophy challenges the realisation of a hydrogen economy because it puts at economical and technical risk the conversion of almost half of the natural gas transmission systems in western countries.
The paper addresses the question whether pipe grade is actually a good proxy to strength and predictor to assess the performance of steel line pipes in hydrogen. Drivers that could affect the suitability of pipeline conversion in hydrogen from an integrity management perspective and industry experience of other hydrogen-charging applications are reviewed. In doing so the paper challenges the basis of the assumption that low-grade steels (up to X52 / L360) are automatically safer for hydrogen repurposing while at the other end of the spectrum higher-grade materials (>X52 / L360) are inevitably less suitable for hydrogen service.
Ultimately the paper discusses that materials sampling and testing of representative line pipes populations should be placed at the core of hydrogen repurposing strategies in order to safely address conversion and to maximize the hydrogen chain value. The paper addresses alternatives to make the sampling smart and cost-effective.
The paper addresses the question whether pipe grade is actually a good proxy to strength and predictor to assess the performance of steel line pipes in hydrogen. Drivers that could affect the suitability of pipeline conversion in hydrogen from an integrity management perspective and industry experience of other hydrogen-charging applications are reviewed. In doing so the paper challenges the basis of the assumption that low-grade steels (up to X52 / L360) are automatically safer for hydrogen repurposing while at the other end of the spectrum higher-grade materials (>X52 / L360) are inevitably less suitable for hydrogen service.
Ultimately the paper discusses that materials sampling and testing of representative line pipes populations should be placed at the core of hydrogen repurposing strategies in order to safely address conversion and to maximize the hydrogen chain value. The paper addresses alternatives to make the sampling smart and cost-effective.
Hydrogen Jet Flame Simulation and Thermal Radiation Damage Estimation for Leakage Accidents in a Hydrogen Refueling Station
Jun 2024
Publication
With the rapid development of hydrogen energy worldwide the number of hydrogen energy facilities such as hydrogen refueling stations has grown rapidly in recent years. However hydrogen is prone to leakage accidents during use which could lead to hazards such as fires and explosions. Therefore research on the safety of hydrogen energy facilities is crucial. In this paper a study of high-pressure hydrogen jet flame accidents is conducted for a proposed integrated hydrogen production and refueling station in China. The effects of leakage direction and leakage port diameter on the jet flame characteristics are analyzed and a risk assessment of the flame accident is conducted. The results showed that the death range perpendicular to the flame direction increased from 2.23 m to 5.5 m when the diameter of the leakage port increased from 4 mm to 10 mm. When the diameter of the leakage port is larger than 8 mm the equipment on the scene will be within the boundaries of the damage. The consequences of fire can be effectively mitigated by a reasonable firewall setup to ensure the overall safety of the integrated station.
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