Safety
Initial Assessment of the Impact of Jet Flame Hazard from Hydrogen Cars in Road Tunnels and the Implication on Hydrogen Car Design
Sep 2007
Publication
Underground or partial underground tunnels form a very important part of modern road transportation systems. As the development of hydrogen cars advancing into the markets it is unavoidable in the near future that hydrogen cars would become the users of ordinary road tunnels. This paper discusses potential fire scenarios and fire hazards of hydrogen cars in road tunnels and implications on the fire safety measures and ventilation systems in existing tunnels. The information needed for carry out risk assessment of hydrogen cars in road tunnels are discussed. hydrogen has a low ignition energy and wide flammable range suggesting that leaks have a high probability of ignition and result hydrogen flame. CFD simulations of hydrogen fires in a full scale 5m by 5m square cross-section tunnel were carried out. The effect of the ventilation on controlling the back-layering and the downstream flame are discussed.
Assessment and Evaluation of 3rd Party Risk for Planned Hydrogen Demonstration Facility
Sep 2007
Publication
Potential risk exposure of 3rd parties i.e. people not involved in the actual operation of a plant is often a critical factor to gain authority approval and public acceptance for a development project. This is also highly relevant for development of demonstration facilities for hydrogen production and refuelling infrastructure. This paper presents and discusses results for risk exposure of 3rd parties based on risk assessment studies performed for the planned Hydrogen Technology Research Centre Hytrec in Trondheim. The methodology applied is outlined. Key assumptions and study uncertainties are identified and how these might affect the results are discussed.<br/>The purpose of Hytrec is to build a centre for research development and demonstration of hydrogen as an energy carrier. Hydrogen will be produced both by reforming of natural gas with CO2 capture and by electrolysis of water. The plant also includes a SOFC that will run on natural gas or hydrogen and produce heat and electricity for the Hytrec visitor centre. Hytrec will be located in a populated area without access control. Most of the units will be located within cabinets and modules.<br/>The authors acknowledge the Hytrec project and the Hytrec project partners Statoil Statkraft and DNV for their support and for allowing utilisation of results from the Hytrec QRA in this paper.
Study of Hydrogen Diffusion and Deflagration in a Closed System
Sep 2007
Publication
A total of 12 ventilation experiments with various combinations of hydrogen release rates and ventilation speeds were performed in order to study how ventilation speed and release rate effect the hydrogen concentration in a closed system. The experiential facility was constructed out of steel plates and beams in the shape of a rectangular enclosure. The volume of the test facility was about 60m3. The front face of the enclosure was covered by a plastic film in order to allow visible and infrared cameras to capture images of the flame. The inlet and outlet vents were located on the lower front face and the upper backside panel respectively. Hydrogen gas was released toward the ceiling from the center of the floor. The hydrogen gas was released at constant rate in each test. The hydrogen release rate ranged from 0.002 m3/s to 0.02 m3/s. Ventilation speeds were 0.1 0.2 and 0.4 m3/s respectively. Ignition was attempted at the end of the hydrogen release by using multiple continuous spark ignition modules on the ceiling and next to the release point. Time evolution of hydrogen concentration was measured using evacuated sample bottles. Overpressure and impulse inside and outside the facility were also measured. The mixture was ignited by a spark ignition module mounted on the ceiling in eight of eleven tests. In the other three tests the mixture was ignited by spark ignition modules mounted next to the nozzle. Overpressures generated by the hydrogen deflagration in most of these tests were low and represented a small risk to people or property. The primary risk associated with the hydrogen deflagrations studied in these tests was from the fire. The maximum concentration is proportional to the ratio of the hydrogen release rate to the ventilation speed within the range of parameters tested. Therefore a required ventilation speed can be estimated from the assumed hydrogen leak rate within the experimental conditions described in this paper.
Molecular Transport Effects of Hydrocarbon Addition on Turbulent Hydrogen Flame Propagation
Sep 2007
Publication
We analytically investigated the influence of light hydrocarbons on turbulent premixed H2/air atmospheric flames under lean conditions in view of safe handling of H2 systems applications in H2 powered IC engines and gas turbines and also with an orientation towards modelling of H2 combustion. For this purpose an algebraic flame surface wrinkling model included with pressure and fuel type effects is used. The model predictions of turbulent premixed flames are compared with the set of corresponding experimental data of Kido et al. (Kido Nakahara et al. 2002). These expanding spherical flame data include H2–air mixtures doped with CH4 and C3H8 while the overall equivalence ratio of all the fuel/air mixtures is fixed at 0.8 for constant unstretched laminar flame speed of 25 cm/s by varying N2 composition. The model predictions show that there is little variation in turbulent flame speed ST for C3H8 additions up to 20-vol%. However for 50 vol% doping flame speed decreases by as much as 30 % from 250 cm/s that of pure H2–air mixtures for turbulence intensity of 200 cm/s. With respect to CH4 for 50 vol% doping ST reduces by only 6 % cf. pure H2/air mixture. In the first instance the substantial decrease of ST with C3H8 addition may be attributed to the increase in the Lewis number of the dual-fuel mixture and proportional restriction of molecular mobility of H2. That is this decrease in flame speed can be explained using the concept of leading edges of the turbulent flame brush (Lipatnikov and Chomiak 2005). As these leading edges have mostly positive curvature (convex to the unburned side) preferential-diffusive-thermal instabilities cause recognizable impact on flame speed at higher levels of turbulence with the effect being very strong for lean H2 mixtures. The lighter hydrocarbon substitutions tend to suppress the leading flame edges and possibly transition to detonation in confined structures and promote flame front stability of lean turbulent premixed flames. Thus there is a necessity to develop a predictive reaction model to quantitatively show the strong influence of molecular transport coefficients on ST.
Novel Wide-area Hydrogen Sensing Technology
Sep 2007
Publication
Element One Inc. is developing novel indicators for hydrogen gas for applications as a complement to conventional electronic hydrogen sensors or as a low-cost alternative in situations where an electronic signal is not needed. The indicator consists of a thin film coating or a pigment of a transition metal oxide such as tungsten oxide or molybdenum oxide with a catalyst such as platinum or palladium. The oxide is partially reduced in the presence of hydrogen in concentrations as low as 300 parts per million and changes from transparent to a dark colour. The colour change is fast and easily seen from a distance. In air the colour change reverses quickly when the source of hydrogen gas is removed in the case of tungsten oxide or is nearly irreversible in the case of molybdenum oxide. A number of possible implementations have been successfully demonstrated in the laboratory including hydrogen indicating paints tape cautionary decals and coatings for hydrogen storage tanks. These and other implementations may find use in vehicles stationary appliances piping refuelling stations and in closed spaces such as maintenance and residential garages for hydrogen-fuelled vehicles. The partially reduced transition metal oxide becomes semi conductive and increases its electrical conductivity by several orders of magnitude when exposed to hydrogen. The integration of this electrical resistance sensor with an RFID tag may extend the ability of these sensors to record and transmit a history of the presence or absence of leaked hydrogen over long distances. Over long periods of exposure to the atmosphere the indicator’s response may slow due to catalyst degradation. Our current emphasis is on controlling this degradation. The kinetics of the visual indicators is being investigated along with their durability in collaboration with the NASA Kennedy Space Center.
CFD Simulation on Diffusion of Leaked Hydrogen Caused by Vehicle Accident in Tunnels
Sep 2005
Publication
Hydrogen fuel cell vehicles are expected to come into widespread use in the near future. Accordingly many hydrogen carrying vehicles will begin to pass through tunnels. It is therefore important to predict whether risk from leaked hydrogen accidents in tunnels can be avoided. CFD simulation was carried out on diffusion of leaked hydrogen in tunnels. Three areas of tunnels were chosen for study. One is the typical longitudinal and lateral areas of tunnels and the others are underground ventilation facilities and electrostatic dust collectors which were simulated with an actual tunnel. The amount of hydrogen leaked was 60m3 (approximately 5.08 kg) which corresponds to the amount necessary for future fuel cell vehicles to achieve their desired running distance. Analytical periods were the time after leaks began until regions of hydrogen above the low flammability limit had almost disappeared or thirty minutes. We found that leaked hydrogen is immediately carried away from leaking area under existing ventilation conditions. We also obtained basic data on behaviour of leaked hydrogen.
Recent Progress in Hydrogen Flammability Prediction for the Safe Energy Systems
Nov 2020
Publication
Many countries consider hydrogen as a promising energy source to resolve the energy challenges over the global climate change. However the potential of hydrogen explosions remains a technical issue to embrace hydrogen as an alternate solution since the Hindenburg disaster occurred in 1937. To ascertain safe hydrogen energy systems including production storage and transportation securing the knowledge concerning hydrogen flammability is essential. In this paper we addressed a comprehensive review of the studies related to predicting hydrogen flammability by dividing them into three types: experimental numerical and analytical. While the earlier experimental studies had focused only on measuring limit concentration recent studies clarified the extinction mechanism of a hydrogen flame. In numerical studies the continued advances in computer performance enabled even multi-dimensional stretched flame analysis following one-dimensional planar flame analysis. The different extinction mechanisms depending on the Lewis number of each fuel type could be observed by these advanced simulations. Finally historical attempts to predict the limit concentration by analytical modelling of flammability characteristics were discussed. Developing an accurate model to predict the flammability limit of various hydrogen mixtures is our remaining issue.
Hydrogen Tank Rupture in Fire in the Open Atmosphere: Hazard Distance Defined by Fireball
Feb 2021
Publication
The engineering correlations for assessment of hazard distance defined by a size of fireball after either liquid hydrogen spill combustion or high-pressure hydrogen tank rupture in a fire in the open atmosphere (both for stand-alone and under-vehicle tanks) are presented. The term “fireball size” is used for the maximum horizontal size of a fireball that is different from the term “fireball diameter” applied to spherical or semi-spherical shape fireballs. There are different reasons for a fireball to deviate from a spherical shape e.g. in case of tank rupture under a vehicle the non-instantaneous opening of tank walls etc. Two conservative correlations are built using theoretical analysis numerical simulations and experimental data available in the literature. The theoretical model for hydrogen fireball size assumes complete isobaric combustion of hydrogen in air and presumes its hemispherical shape as observed in the experiments and the simulations for tank rupturing at the ground level. The dependence of the fireball size on hydrogen mass and fireball’s diameter-to-height ratio is discussed. The correlation for liquid hydrogen release fireball is based on the experiments by Zabetakis (1964). The correlations can be applied as engineering tools to access hazard distances for scenarios of liquid or gaseous hydrogen storage tank rupture in a fire in the open atmosphere
Hydrogen Jet Fire from a Thermally Activated Pressure Relief Device (TPRD) from Onboard Storage in a Naturally Ventilated Covered Car Park
Aug 2021
Publication
Hydrogen jet fires from a thermally activated pressure relief device (TPRD) on onboard storage are considered for a vehicle in a naturally ventilated covered car park. Computational Fluid Dynamics was used to predict behaviour of ignited releases from a 70 MPa tank into a naturally ventilated covered car park. Releases through TPRD diameters 3.34 2 and 0.5 mm were studied to understand effect on hazard distances from the vehicle. A vertical release and downward releases at 0° 30° and 45° for TPRD diameters 2 and 0.5 mm were considered accounting for tank blowdown. direction of a downward release was found to significantly contribute to decrease of temperature in a hot cloud under the ceiling. Whilst the ceiling is reached by a jet exceeding 300 °C for a release through a TPRD of 2 mm for inclinations of either 0° 30° or 45° an ignited release through a TPRD of 0.5 mm and angle of 45° did not produce a cloud with a temperature above 300 °C at the ceiling during blowdown. The research findings specifically regarding the extent of the cloud of hot gasses have implications for the design of mechanical ventilation systems.
Construction of Natural Gas Energy-measuring System in China: A Discussion
Feb 2022
Publication
During the 13th Five-Year Plan China's natural gas industry developed rapidly and a diversified supply and marketing pattern was formed including domestic conventional gas unconventional gas (shale gas tight sandstone gas coalbed methane etc.) coal-based synthetic natural gas imported LNG and imported pipeline gas. The gross calorific value of gas sources ranged from 34 MJ/m3 to 43 MJ/m3 and the maximum difference of calorific value between different gas sources exceeded 20%. On May 24th 2019 the National Development and Reform Commission and other three ministries/commissions jointly issued the Supervision Regulation on the Fair Access of Oil and Gas Pipeline Network Facilities and required that a natural gas energy measuring and pricing system shall be established within 24 months from the implementation date of this Regulation. In order to speed up the construction of China's natural gas energy measuring system this paper summarizes domestic achievements in the construction of natural gas energy measuring system from the aspects of value traceability and energy measurement standard and analyzes natural gas flowrate measurement technology calorific value determination technology value traceability localization intelligentization and application technology of key energy measurement equipment natural gas pipeline network energy balancing technology based on big data analysis multi-source quality tracking and monitoring technology and energy measurement standard system the need of new energy detection and measurement technology and put forward strategy for the development of natural gas measuring in China. And the following research results are obtained. First China's natural gas energy measuring system can basically meet the requirements of implementing natural gas energy measurement but it still falls behind the international leading level in terms of calibration and application of high-level flowmeter (such as 0.5 class) high-accuracy gas reference material level of calorific value reference equipment and measurement standard system and needs to be further improved. Second it is necessary for China to speed up the research and application of the localization and intelligentization technologies of key energy measurement equipment. Third natural gas pipeline network shall be equipped with measurement check method energy balancing system based on big data analysis and multi-source quality tracking and monitoring system so that the energy transmission loss index of natural gas pipeline network can be superior to the international leading level (0.10%). Fourth to realize the large-scale application of hydrogen energy and bio-energy and the mixed transportation of hydrogen bio-methane and natural gas it is necessary to carry out research on new technology and standardization of hydrogen/bio-methane blended natural gas detection and measurement.
Fundamentals and Principles of Solid-State Electrochemical Sensors for High Temperature Gas Detection
Dec 2021
Publication
The rapid development of science technology and engineering in the 21st century has offered a remarkable rise in our living standards. However at the same time serious environmental issues have emerged such as acid rain and the greenhouse effect which are associated with the ever-increasing need for energy consumption 85% of which comes from fossil fuels combustion. From this combustion process except for energy the main greenhouse gases-carbon dioxide and steam-are produced. Moreover during industrial processes many hazardous gases are emitted. For this reason gas-detecting devices such as electrochemical gas sensors able to analyze the composition of a target atmosphere in real time are important for further improving our living quality. Such devices can help address environmental issues and inform us about the presence of dangerous gases. Furthermore as non-renewable energy sources run out there is a need for energy saving. By analyzing the composition of combustion emissions of automobiles or industries combustion processes can be optimized. This review deals with electrochemical gas sensors based on solid oxide electrolytes which are employed for the detection of hazardous gasses at high temperatures and aggressive environments. The fundamentals the principle of operation and the configuration of potentiometric amperometric combined (amperometric-potentiometric) and mixed-potential gas sensors are presented. Moreover the results of previous studies on carbon oxides (COx) nitrogen oxides (NOx) hydrogen (H2 ) oxygen (O2 ) ammonia (NH3 ) and humidity (steam) electrochemical sensors are reported and discussed. Emphasis is given to sensors based on oxygen ion and proton-conducting electrolytes.
Fire Safety of Hydrogen-Fuelled Vehicles- System-Level Bonfire Test
Sep 2005
Publication
The European Community requires a vehicle-level bonfire test for vehicles using plastic fuel tanks for conventional fuels (ECE R-34 Annex 5). A similar test could be applied to hydrogen-fuelled vehicles. It would test a realistic vehicle with its complete fuel and safety systems. An advantage of such a test is that the same test could be applied independent of the hydrogen storage technology (compressed gas liquid or hydride). There are currently standards for bonfire testing of a bare Compressed Natural Gas (CNG) tank and its Pressure Relief Device (PRD). This standard is FMVSS 304 in the U.S. and ISO 15869-1 in Europe. Japan has a similar standard. It requires that a bare tank and its associated PRD be subjected to a propane flame for 20 minutes. The tank must either survive or safely vent its contents. No modern composite wound tank is expected to survive for 20 minutes – so this is not a tank test but really a PRD test. The test procedure requires the PRD to be shielded from direct impingement of the flames – but the shield is not well specified. If it shields the PRD too well the PRD will not activate and the tank will burst. This paper describes the results of a CNG and a hydrogen tank burst from such tests. The mechanical energy released is enormous. It is simply unacceptable to allow the tank to burst – the PRD and venting system must work. Organizations in the U.S Europe and Japan are in the process of modifying the CNG tank bonfire test for compressed hydrogen storage. A bare tank with a single PRD is not a good simulation of a hydrogen fuel system installed in an actual vehicle. There will usually be multiple tanks plumbed together at either the tank pressure or at the intermediate pressure (after the pressure regulator). There may be more than one PRD. The tank may be shielded (from debris) or insulated to protect it from an underbody pool fire. Also the heat transfer from the simulated pool fire (propane flame) will be very different when mounted in a vehicle versus the bare tank test. A vehicle-level pool fire test will alleviate these problems. It is therefore recommended that the bare tank test be replaced by or augmented with a vehicle-level bonfire test similar to ECE R-34 Annex 5.
Risk Assessment Method Combining Independent Protection Layers (IPL) of Layer of Protection Analysis (LOPA) and RISKCURVES Software: Case Study of Hydrogen Refueling Stations in Urban Areas
Jul 2021
Publication
The commercialization of eco-friendly hydrogen vehicles has elicited attempts to expand hydrogen refueling stations in urban areas; however safety measures to reduce the risk of jet fires have not been established. The RISKCURVES software was used to evaluate the individual and societal risks of hydrogen refueling stations in urban areas and the F–N (Frequency–Number of fatalities) curve was used to compare whether the safety measures satisfied international standards. From the results of the analysis it was found that there is a risk of explosion in the expansion of hydrogen refueling stations in urban areas and safety measures should be considered. To lower the risk of hydrogen refueling stations this study applied the passive and active independent protection layers (IPLs) of LOPA (Layer of Protection Analysis) and confirmed that these measures significantly reduced societal risk as well as individual risk and met international standards. In particular such measures could effectively reduce the impact of jet fire in dispensers and tube trailers that had a high risk. Measures employing both IPL types were efficient in meeting international standard criteria; however passive IPLs were found to have a greater risk reduction effect than active IPLs. The combination of RISKCURVES and LOPA is an appropriate risk assessment method that can reduce work time and mitigate risks through protective measures compared to existing risk assessment methods. This method can be applied to risk assessment and risk mitigation not only for hydrogen facilities but also for hazardous materials with high fire or explosion risk.
Critical Morphological Phenomena During Ultra-lean Hydrogen-air Combustion in Closed Horizontal Hele-Shaw Cell
Sep 2021
Publication
Free quasi-two-dimensional outward propagation of the ultra-lean hydrogen-air flames was studied in a horizontal closed flat channel in order to minimize the influences of gravity and natural convection. Experiments were carried out with a sequential change of initial hydrogen concentration in the premixed gaseous hydrogen-air mixtures in the range from 3 to 12 vol. % H2 under normal pressure and temperature conditions. Two types of critical (in term of concentration threshold behavior) morphological phenomena were observed - formation of a pre-flame kernel and primary bifurcation of the pre-flame kernel and the higher order (secondary tertiary etc.) bifurcations of the individual locally spherical and restricted in space flame fronts. For the given initial ambient conditions (channel thickness initial gas mixture pressure and temperature) variation of initial mixture stoichiometry results in a few substantial changes in overall flame shape. These changes were recorded at the specific concentration limits which delineate three characteristic macroscopic morphological forms (morphotypes) of the ultra-lean hydrogen-air flame's ""trails"" - ""ray-like"" ""dendritic"" and ""quasi-uniform"". Transitions between the revealed basic flame morphotypes took place in different ways. The ""pre-flame kernel-to- rays"" and ""rays-to-dendrites"" transitions were abrupt and resembled the first order transitions in physics. -to-quasi-uniform morphology"" were significantly blurred and can be regarded as analogue to the second order transitions.
Current Research and Development Activities on Fission Products and Hydrogen Risk after the Accident at Fukushima Daiiichi Nuclear Power Station
Jan 2015
Publication
After the Fukushima Daiichi nuclear power plant (NPP) accident new regulatory requirements were enforced in July 2013 and a backfit was required for all existing nuclear power plants. It is required to take measures to prevent severe accidents and mitigate their radiological consequences. The Regulatory Standard and Research Department Secretariat of Nuclear Regulation Authority (S/NRA/R) has been conducting numerical studies and experimental studies on relevant severe accident phenomena and countermeasures. This article highlights fission product (FP) release and hydrogen risk as two major areas. Relevant activities in the S/NRA/R are briefly introduced as follows: 1. For FP release: Identifying the source terms and leak mechanisms is a key issue from the viewpoint of understanding the progression of accident phenomena and planning effective countermeasures that take into account vulnerabilities of containment under severe accident conditions. To resolve these issues the activities focus on wet well venting pool scrubbing iodine chemistry (in-vessel and ex-vessel) containment failure mode and treatment of radioactive liquid effluent. 2. For hydrogen risk: because of three incidents of hydrogen explosion in reactor buildings a comprehensive reinforcement of the hydrogen risk management has been a high priority topic. Therefore the activities in evaluation methods focus on hydrogen generation hydrogen distribution and hydrogen combustion.
Differentiating Gas Leaks from Normal Appliance Use
Jun 2021
Publication
DNV has carried out an investigation into potential uses for smart gas meter data as part of Phase 1 of the Modernising Energy Data Applications competition as funded by UK Research & Innovation. In particular a series of calculations have been carried out to investigate the possibility of differentiating accidental gas leaks from normal appliance use in domestic properties. This is primarily with the aim of preventing explosions but the detection of leaks also has environmental and financial benefits.
Three gases have been considered in this study:
An examination of detailed historical incident information suggests that the explosions that lead to fatalities or significant damage to houses are typically of the type that would be more likely to be detected and prevented. It is estimated that between 25% and 75% of the more severe explosions could be prevented depending on which potential improvements are implemented.
Based on the conservative estimates of explosion prevention a cost benefit analysis suggests that it is justifiable to spend between around £1 and £10 per meter installed to implement the proposed technology. This is based purely on lives saved and does not take account of other benefits.
Three gases have been considered in this study:
- A representative UK natural gas composition.
- A blend of 80% natural gas and 20% hydrogen.
- Pure hydrogen.
- Small holes of up to 1 mm rarely reach flammable gas/air concentrations for any gas except under the most unfavourable conditions such as small volumes combined with low ventilation rates. These releases would likely be detected within 6 to 12 hours.
- Medium holes between 1 mm and 6 mm give outflow rates equivalent to a moderate to high level of gas use by appliances. The ability to detect these leaks is highly dependent on the hole size the time at which the leak begins and the normal gas use profile in the building. The larger leaks in this category would be detected within 30 to 60 minutes while the smaller leaks could take several hours to be clearly differentiated from appliance use. This is quick enough to prevent some explosions.
- Large holes of over 6 mm give leak rates greater than any gas use by appliances. These releases rapidly reach a flammable gas/air mixture in most cases but would typically be detected within the first 30-minute meter output period. Again some explosions could be prevented in this timescale.
An examination of detailed historical incident information suggests that the explosions that lead to fatalities or significant damage to houses are typically of the type that would be more likely to be detected and prevented. It is estimated that between 25% and 75% of the more severe explosions could be prevented depending on which potential improvements are implemented.
Based on the conservative estimates of explosion prevention a cost benefit analysis suggests that it is justifiable to spend between around £1 and £10 per meter installed to implement the proposed technology. This is based purely on lives saved and does not take account of other benefits.
Safety Standard for Hydrogen and Hydrogen Systems Guidelines for Hydrogen System Design, Materials Selection, Operations, Storage and Transportation
Jan 1997
Publication
The NASA Safety Standard which establishes a uniform process for hydrogen system design materials selection operation storage and transportation is presented. The guidelines include suggestions for safely storing handling and using hydrogen in gaseous (GH2) liquid (LH2) or slush (SLH2) form whether used as a propellant or non-propellant. The handbook contains 9 chapters detailing properties and hazards facility design design of components materials compatibility detection and transportation. Chapter 10 serves as a reference and the appendices contained therein include: assessment examples; scaling laws explosions blast effects and fragmentation; codes standards and NASA directives; and relief devices along with a list of tables and figures abbreviations a glossary and an index for ease of use. The intent of the handbook is to provide enough information that it can be used alone but at the same time reference data sources that can provide much more detail if required.
Hydrogen Safety Prediction and Analysis of Hydrogen Refueling Station Leakage Accidents and Process Using Multi-Relevance Machine Learning
Oct 2021
Publication
Hydrogen energy vehicles are being increasingly widely used. To ensure the safety of hydrogenation stations research into the detection of hydrogen leaks is required. Offline analysis using data machine learning is achieved using Spark SQL and Spark MLlib technology. In this study to determine the safety status of a hydrogen refueling station we used multiple algorithm models to perform calculation and analysis: a multi-source data association prediction algorithm a random gradient descent algorithm a deep neural network optimization algorithm and other algorithm models. We successfully analyzed the data including the potential relationships internal relationships and operation laws between the data to detect the safety statuses of hydrogen refueling stations.
Experimental Study and Model Predictions on Helium Release in an Enclosure with Single or Multiple Vents
Sep 2021
Publication
This paper presents experiments performed at Canadian Nuclear Laboratories (CNL) to examine the dispersion behaviour of helium in a polycarbonate enclosure that was representative of a residential parking garage. The purpose was to gain a better understanding of the effect of buoyancy- or winddriven natural ventilation on hydrogen dispersion behaviour. Although hydrogen dispersion studies have been reported extensively in the literature gaps still exist in predictive methods for hazard analysis. Helium a simulant for hydrogen was injected near the centre of the floor with a flow rate ranging from 5 to 75 standard litres per minute through an upward-facing nozzle resulting in an injection Richardson number ranging between 10-1 and 102. The location of the nozzle varied from the bottom of the enclosure to near the ceiling to examine the impact of the nozzle elevation on the development of a stratified layer in the upper region of the enclosure. When the injection nozzle was placed at a sufficiently low elevation the vertical helium profile always consisted of a homogenous layer at the top overlaying a stratified layer at the bottom. To simulate outdoor environmental conditions a fan was placed in front of each vent to examine the effect of opposing or assisting wind on the dispersion. The helium transients in the uniform layer predicted with analytical models were in good agreement with the measured transients for the tests with injection at lower elevations or with no wind. Model improvements are required for adequately predicting transients with significantly stratified profiles or with wind.
Detonation Wave Propagation in Semi-confined Layers of Hydrogen-air and Hydrogen-oxygen Mixtures
Oct 2015
Publication
This paper presents results of an experimental investigation on detonation wave propagation in semi-confined geometries. Large scale experiments were performed in layers up to 0.6 m filled with uniform and non-uniform hydrogen–air mixtures in a rectangular channel (width 3 m; length 9 m) which is open from below. A semi confined driver section is used to accelerate hydrogen flames from weak ignition to detonation. The detonation propagation was observed in a 7 m long unobstructed part of the channel. Pressure measurements ionization probes soot-records and high speed imaging were used to observe the detonation propagation. Critical conditions for detonation propagation in different layer thicknesses are presented for uniform H2/air-mixtures as well as experiments with uniform H2/O2 mixtures in a down scaled transparent channel. Finally detail investigations on the detonation wave propagation in H2/air-mixtures with concentration gradients are shown.
Computational Analysis of Hydrogen Diffusion in Polycrystalline Nickel and Anisotropic Polygonal Micro, Nano Grain Size Effects
Sep 2013
Publication
The effect of irregular polygonal grain size and random grain boundary on hydrogen diffusion in polycrystalline nickel is investigated. Hydrogen diffusion behavior in micropolycrystalline nickel is compared with that in nanopolycrystalline nickel through numerical analysis. The two dimensional computational finite element microstructural and nanostructural analyses are based on Fick's law corresponding to heterogeneous polycrystalline model geometry. The heterogeneous polycrystalline model consists of random irregular polygonal grains. These grains are divided into internal grain and grain boundary regions the size of which is determined from the grain size. The computational analysis results show that hydrogen diffusion in nanostructural irregular polycrystalline nickel is higher in magnitude than the microstructural irregular polycrystalline nickel. However models of voids traps and micro and nano clustered grains are yet to be included.
An Analysis of the Experiments Carried Out by HSL in the HyIndoor European Project Studying Accumulation of Hydrogen Released into a Semi-confined Enclosure
Oct 2015
Publication
Experimental work on hydrogen releases consequences in a 31-m3 semi-confined enclosure was performed in the framework of the collaborative European Hyindoor project. Natural ventilation effectiveness on hydrogen build-up limitation in a confined area was studied for several configurations of ventilation openings and of release conditions in real environmental conditions [1]; influence of wind on gas build-up was observed as well. This paper proposes a critical analysis of these experiments carried out by HSL and compares results with analytical approaches available in open scientific literature. The validity of these models in presence of wind was broached.
Fuel Cell in Maritime Applications Challenges, Chances and Experiences
Sep 2011
Publication
The shipping industry is becoming increasingly visible on the global environmental agenda. Shipping's share of air pollution is becoming significant and public concern has led to ongoing political pressure to reduce shipping emissions. International legislation at the IMO governing the reduction of SOx and NOx emissions from shipping is being enforced and both the European Union and the USA are planning to introduce further regional laws to reduce emissions. Therefore new approaches for more environmental friendly and energy efficient energy converter are under discussion. One possible solution will be the use of fuel cell systems for auxiliary power or even main propulsion. The paper summarizes the legal background in international shipping related to the use of fuel cells and gas as fuel in ships. The focus of the paper will be on the first experiences on the use of fuel cell systems on board of ships. In this respect an incident on a fuel cell ship in Hamburg will be discussed. Moreover the paper will point out the potential for the use of fuel cell systems on board. Finally an outlook is given on ongoing and planed projects for the use of fuel cells on board of ships.
Numerical Prediction of Forced-ignition Limit in High-pressurized Hydrogen Jet Flow Through a Pinhole
Sep 2017
Publication
The numerical simulations on the high-pressure hydrogen jet are performed by using the unsteady three-dimensional compressible Navier-Stokes equations with multi-species conservation equations. The present numerical results show that the highly expanded hydrogen free jet observes and the distance between the Mach disc and the nozzle exit agrees well with the empirical equation. The time-averaged H2 concentration of the numerical simulations agrees well with the experimental data and the empirical equation. The numerical simulation of ignition in a hydrogen jet is performed to show the flame behaviour from the calculated OH iso surface. We predicted the ignition and no-ignition region from the present numerical results about the forced ignition in the high-pressurized hydrogen jet.
Time Response of Hydrogen Sensors
Sep 2013
Publication
The efficiency of gas sensor application for facilitating the safe use of hydrogen depends to a considerable extent on the response time of the sensor to change in hydrogen concentration. The response and recovery times have been measured for five different hydrogen sensors three commercially available and two promising prototypes which operate at room temperature. Experiments according to ISO 26142 show that most of the sensors surpass much for a concentration change from clean to hydrogen containing air the demands of the standard for the response times t(90) and values of 2 to 16 s were estimated. For an opposite shift to clean air the recovery times t(10) are from 7 to 70 s. Results of transient behaviour can be fitted with an exponential approach. It can be demonstrated that results on transient behaviour depend not only from investigation method and the experimental conditions like gas changing rate and concentration jump as well as from operating parameters of sensors. In comparison to commercial MOS and MIS-FET hydrogen sensors new sensor prototypes operating at room temperature possesses in particular longer recovery times.
A Comparative CFD Assessment Study of Cryogenic Hydrogen and Liquid Natural Gas Dispersion
Sep 2017
Publication
The introduction of hydrogen to the commercial market as alternative fuel brings up safety concerns. Its storage in liquid or cryo-compressed state to achieve volumetric efficiency involves additional risks and their study is crucial. This work aims to investigate the behaviour of cryogenic hydrogen release and to study factors that affect the vapor dispersion. We focus on the effect of ambient humidity and air's components (nitrogen and oxygen) freezing in order to identify the conditions under which these factors have considerable influence. The study reveals that the level of influence depends highly on the release conditions and that humidity can reduce conspicuously the longitudinal distance of the Lower Flammability Limit (LFL). Low Froude (Fr) number (<1000) at the release allows the generated by the humidity phase change buoyancy to affect the dispersion while for higher Fr number - that usually are met in cryo-compressed releases - the momentum forces are the dominant forces and the buoyancy effect is trivial. Simulations with liquid methane release have been also performed and compared to the liquid hydrogen simulations in order to detect the differences in the behaviour of the two fuels as far as the humidity effect is concerned. It is shown that in methane spills the buoyancy effect in presence of humidity is smaller than in hydrogen spills and it can be considered almost negligible.
Numerical Investigation on the Dispersion of Hydrogen Leaking from a Hydrogen Fuel Cell Vehicle in Seaborne Transportation
Oct 2015
Publication
The International Maritime Organization under the United Nations has developed safety requirements for seaborne transportation of hydrogen fuel cell vehicles in consideration of a recent increase in such transportation. Japan has led the development of new regulations in the light of some research outcomes including numerical simulations on hydrogen dispersion in a cargo space of a vehicle carrier in case of accidental leakage of hydrogen from the vehicle. Numerical results indicate that the region of space occupied by flammable hydrogen/air mixture strongly depends on the direction of ventilation openings. These findings have contributed to the development of new international regulations.
Hydrogen Systems Component Safety
Sep 2013
Publication
The deployment of hydrogen technologies particularly the deployment of hydrogen dispensing systems for passenger vehicles requires that hydrogen components perform reliably in environments where they have to meet the following performance parameters:
The paper will use incident frequency data from NREL’s Technology Validation project to more quantitatively identify safety concerns in hydrogen dispensing and storage systems.
- Perform safely where the consumer will be operating the dispensing equipment
- Dispense hydrogen at volumes comparable to gasoline dispensing stations in timeframes comparable to gasoline stations
- Deliver a fueling performance that is within the boundaries of consumer tolerance
- Perform with maintenance/incident frequencies comparable to gasoline dispensing systems
The paper will use incident frequency data from NREL’s Technology Validation project to more quantitatively identify safety concerns in hydrogen dispensing and storage systems.
Numerical Simulation and Experiments of Hydrogen Diffusion Behaviour for Fuel Cell Electric Vehicle
Sep 2011
Publication
Research was conducted on hydrogen diffusion behaviour to construct a simulation method for hydrogen leaks into complexly shaped spaces such as around the hydrogen tank of a fuel cell electric vehicle (FCEV). To accurately calculate the hydrogen concentration distribution in the vehicle underfloor space it is necessary to take into account the effects of hydrogen mixing and diffusion due to turbulence. The turbulence phenomena that occur in the event that hydrogen leaks into the vehicle underfloor space were classified into the three elements of jet flow wake flow and wall turbulence. Experiments were conducted for each turbulence element to visualize the flows and the hydrogen concentration distributions were measured. These experimental values were then compared with calculated values to determine the calculation method for each turbulence phenomenon. Accurate calculations could be performed by using the k-ω Shear Stress Transport (SST) model for the turbulence model in the jet flow calculations and the Reynolds Stress Model (RSM) in the wall turbulence calculations. In addition it was found that the large fluctuations produced by wake flow can be expressed by unsteady state calculations with the steady state calculation solutions as the initial values. Based on the above information simulations of hydrogen spouting were conducted for the space around the hydrogen tank of an FCEV. The hydrogen concentration calculation results matched closely with the experimental values which verified that accurate calculations can be performed even for the complex shapes of an FCEV.
Characteristic of Cryogenic Hydrogen Flames from High-aspect Ratio Nozzles
Sep 2019
Publication
Unintentional leaks at hydrogen fuelling stations have the potential to form hydrogen jet flames which pose a risk to people and infrastructure. The heat flux from these jet flames are often used to develop separation distances between hydrogen components and buildings lot-lines etc. The heat flux and visible flame length is well understood for releases from round nozzles but real unintended releases would be expected to be be higher aspect-ratio cracks. In this work we measured the visible flame length and heat-flux characteristics of cryogenic hydrogen flames from high-aspect ratio nozzles. We compare this data to flames of both cryogenic and compressed hydrogen from round nozzles. The aspect ratio of the release does not affect the flame length or heat flux significantly for a given mass flow under the range of conditions studied. The engineering correlations presented in this work that enable the prediction of flame length and heat flux can be used to assess risk at hydrogen fuelling stations with liquid hydrogen and develop science-based separation distances for these stations.
A Comparative Study of Detonability and Propensity to Sustain High-speed Turbulent Deflagrations in Hydrogen and Methane Mixtures
Sep 2013
Publication
We’ve studied the conditions enabling a detonation to be quenched when interacting with an obstruction and the propensity for establishing subsequent fast-flame. Oxy-hydrogen detonations were found quench more easily than oxy-methane detonations when comparing the ratio of gap size and the detonation cell size. High-speed turbulent deflagrations that re-accelerate back to a detonation were only observed in methane-oxygen mixtures. Separate hot-spot ignition calculations revealed that the higher detonability of methane correlates with its stronger propensity to develop localized hot-spots. The results suggest that fast-flames are more difficult to form in hydrogen than in methane mixtures.
ISO 19880-1, Hydrogen Fueling Station and Vehicle Interface Safety Technical Report
Oct 2015
Publication
Hydrogen Infrastructures are currently being built up to support the initial commercialization of the fuel cell vehicle by multiple automakers. Three primary markets are presently coordinating a large build up of hydrogen stations: Japan; USA; and Europe to support this. Hydrogen Fuelling Station General Safety and Performance Considerations are important to establish before a wide scale infrastructure is established.
This document introduces the ISO Technical Report 19880-1 and summarizes main elements of the proposed standard. Note: this ICHS paper is based on the draft TR 19880 and is subject to change when the document is published in 2015. International Standards Organisation (ISO) Technical Committee (TC) 197 Working Group (WG) 24 has been tasked with the preparation of the ISO standard 19880-1 to define the minimum requirements considered applicable worldwide for the hydrogen and electrical safety of hydrogen stations. This report includes safety considerations for hydrogen station equipment and components control systems and operation. The following systems are covered specifically in the document as shown in Figure 1:
This document introduces the ISO Technical Report 19880-1 and summarizes main elements of the proposed standard. Note: this ICHS paper is based on the draft TR 19880 and is subject to change when the document is published in 2015. International Standards Organisation (ISO) Technical Committee (TC) 197 Working Group (WG) 24 has been tasked with the preparation of the ISO standard 19880-1 to define the minimum requirements considered applicable worldwide for the hydrogen and electrical safety of hydrogen stations. This report includes safety considerations for hydrogen station equipment and components control systems and operation. The following systems are covered specifically in the document as shown in Figure 1:
- H2 production / supply delivery system
- Compression
- Gaseous hydrogen buffer storage;
- Pre-cooling device;
- Gaseous hydrogen dispensers.
- Hydrogen Fuelling Vehicle Interface
Hazards of Liquid Hydrogen: Position paper
Jan 2010
Publication
In the long term the key to the development of a hydrogen economy is a full infrastructure to support it which include means for the delivery and storage of hydrogen at the point of use eg at hydrogen refuelling stations for vehicles. As an interim measure to allow the development of refuelling stations and rapid implementation of hydrogen distribution to them liquid hydrogen is considered the most efficient and cost effective means for transport and storage.
The Health and Safety Executive have commissioned the Health and Safety Laboratory to identify and address issues relating to bulk liquid hydrogen transport and storage and update/develop guidance for such facilities. This position paper the first part of the project assesses the features of the transport and storage aspects of the refuelling stations that are now being constructed in the UK compares them to existing guidance highlights gaps in the regulatory regime and identifies outstanding safety issues. The findings together with the results of experiments to improve our understanding of the behaviour of liquid hydrogen will inform the development of the guidance for refuelling facilities
link to Report
The Health and Safety Executive have commissioned the Health and Safety Laboratory to identify and address issues relating to bulk liquid hydrogen transport and storage and update/develop guidance for such facilities. This position paper the first part of the project assesses the features of the transport and storage aspects of the refuelling stations that are now being constructed in the UK compares them to existing guidance highlights gaps in the regulatory regime and identifies outstanding safety issues. The findings together with the results of experiments to improve our understanding of the behaviour of liquid hydrogen will inform the development of the guidance for refuelling facilities
link to Report
Releases of Unignited Liquid Hydrogen
Jan 2014
Publication
If the hydrogen economy is to progress more hydrogen fuelling stations are required. In the short term in the absence of a hydrogen distribution network these fuelling stations will have to be supplied by liquid hydrogen road tanker. Such a development will increase the number of tanker offloading operations significantly and these may need to be performed in close proximity to the general public.<br/>The aim of this work is to identify and address hazards relating to the storage and transport of bulk liquid hydrogen (LH2) that are associated with hydrogen refuelling stations located in urban environments. Experimental results will inform the wider hydrogen community and contribute to the development of more robust modelling tools. The results will also help to update and develop guidance for codes and standards.<br/>The first phase of the project was to develop an experimental and modelling strategy for the issues associated with liquid hydrogen spills; this was documented in HSL report XS/10/06[1].<br/>The second phase of the project was to produce a position paper on the hazards of liquid hydrogen which was published in 2009 XS/09/72[2]. This was also published as a HSE research report RR769 in 2010[3].<br/>This report details experiments performed to investigate spills of liquid hydrogen at a rate of 60 litres per minute. Measurements were made on unignited releases which included concentration of hydrogen in air thermal gradient in the concrete substrate liquid pool formation and temperatures within the pool. Computational modelling of the unignited releases has been undertaken at HSL and reported in MSU/12/01 [4]. Ignited releases of hydrogen have also been performed as part of this project; the results and findings from this work are reported in XS/11/77[5].
CFD design of protective walls against the effects of vapor cloud fast deflagration of hydrogen
Oct 2015
Publication
Protective walls are a well-known and efficient way to mitigate overpressure effects of accidental explosions (detonation or deflagration). For detonation there are multiple published studies whereas for deflagration no well-adapted and rigorous method has been reported in the literature. This article describes the validation of a new modelling approach for fast deflagrations of H2. This approach includes two steps. At the first step the combustion phase of vapor cloud explosion (VCE) involving a fast deflagration is substituted by equivalent vessel burst problem. The purpose of this step is to avoid the reactive flow computations. At the second step CFD is used for computations of pressure propagation from the equivalent (non reactive) vessel burst problem. After verifying the equivalence of the fast deflagration and the vessel burst problem at the first step the capability of two CFD codes such as FLACS and Europlexus are examined for modelling of the vessel burst problem (with and without barriers). Finally the efficiency of finite and infinite barriers used for mitigation of the shock is investigated
Pressure Effects of an Ignited Release from Onboard Storage in a Garage with a Single Vent
Sep 2017
Publication
This work is driven by the need to understand the hazards resulting from the rapid ignited release of hydrogen from onboard storage tanks through a thermally activated pressure relief device (TPRD) inside a garage-like enclosure with low natural ventilation i.e. the consequences of a jet fire which has been immediately ignited. The resultant overpressure is of particular interest. Previous work [1] focused on an unignited release in a garage with minimum ventilation. This initial work demonstrated that high flow rates of unignited hydrogen through a thermally activated pressure relief device (TPRD) in ventilated enclosures with low air change per hour can generate overpressures above the limit of 10- 15 kPa which a typical civil structure like a garage could withstand. This is due to the pressure peaking phenomenon. Both numerical and phenomenological models were developed for an unignited release and this has been recently validated experimentally [2]. However it could be expected that the majority of unexpected releases through a TPRD may be ignited; leading to even greater overpressures and to date whilst there has been some work on fires in enclosures the pressure peaking phenomenon for an ignited release has yet to be studied or compared with that for an equivalent unignited release. A numerical model for ignited releases in enclosures has been developed and computational fluid dynamics has then been used to examine the pressure dynamics of an ignited hydrogen release in a real scale garage. The scenario considered involves a high mass flow rate release from an onboard hydrogen storage tank at 700 bar through a 3.34 mm diameter orifice representing the TPRD in a small garage with a single vent equivalent in area to small window. It is shown that whilst this vent size garage volume and TPRD configuration may be considered “safe” from overpressures in the event of an unignited release the overpressure resulting from an ignited release is two orders of magnitude greater and would destroy the structure. Whilst further investigation is needed the results clearly indicate the presence of a highly dangerous situation which should be accounted for in regulations codes and standards. The hazard relates to the volume of hydrogen released in a given timeframe thus the application of this work extends beyond TPRDs and is relevant where there is a rapid ignited release of hydrogen in an enclosure with limited ventilation.
Safety Issues of the Liquefaction, Storage and Transportation of Liquid Hydrogen
Sep 2013
Publication
The objectives of the IDEALHY project which receives funding from the European Union’s 7th Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement No. 278177 are to design a novel process that will significantly increase the efficiency of hydrogen liquefaction and be capable of delivering liquid hydrogen at a rate that is an order of magnitude greater than current plants. The liquid hydrogen could then be delivered to refueling stations in road tankers. As part of the project the safety management of the new large scale process and the transportation of liquid hydrogen by road tanker into urban areas are being considered. Effective safety management requires that the hazards are identified and well understood. This paper describes the scope of the safety work within IDEALHY and presents the output of the work completed so far. Initially a review of available experimental data on the hazards posed by releases of liquid hydrogen was undertaken which identified that generally there is a dearth of data relevant to liquid hydrogen releases. Subsequently HAZIDs have been completed for the new liquefaction process storage of liquid hydrogen and its transportation by road. This included a review of incidents relevant to these activities. The principal causes of the incidents have been analysed. Finally the remaining safety work for the IDEALHY project is outlined.
Flame Characteristics of Ignited under-expanded Cryogenic Hydrogen Jets
Sep 2021
Publication
The anticipated upscaling of hydrogen energy applications will involve the storage and transport of hydrogen in a cryogenic state. Understanding the potential hazard arising from small leaks in pressurized storage and transport systems is needed to assist safety analysis and development of mitigation measures. The current knowledge of the ignited pressurized cryogenic hydrogen jet flame is limited. Large eddy simulation (LES) with detailed hydrogen chemistry is applied for the reacting flow. The effects of ignition locations are considered and the initial development of the transient flame kernel from the ignition hot spots is analysed. The flame structures namely side flames and envelop flames are observed in the study which are due to the complex interactions between turbulence fuel-air mixing at cryogenic temperature and chemical reactions.
Safe Storage of Compressed Hydrogen at Ambient and Cryogenic Temperatures in Flexible Glass Capillaries
Sep 2013
Publication
We have demonstrated that the strength of produced flexible quartz capillaries can be high enough to withstand the internal hydrogen pressure up to 233 MPa at normal and cryogenic temperature. According to the experimental results the cryo-compressed storage of hydrogen in the capillaries at moderate pressure can enable one to reach DOE 2015 aims for the gravimetric and volumetric capacities of vessels for the safe mobile hydrogen storage. Furthermore flexible capillaries in a bundle can probably serve as a high-pressure pipes for the transportation of gases over long distances. The developed technology of hydrogen storage can be applied to methane and hythane (H₂ - CH₄ mixture) which bridge the gap between conventional fossil fuels and the clean future of a hydrogen economy. It can be also applied to other gases i.e. air oxygen and helium-oxygen mixtures widely used in autonomic breathing devices.
Fatigue Behavior of AA2198 in Liquid Hydrogen
Aug 2019
Publication
Tensile and fatigue tests were performed on an AA2198 aluminum alloy in the T851 condition in ambient air and liquid hydrogen (LH2). All fatigue tests were performed under load control at a frequency of 20 Hz and a stress ratio of R=0.1. The Gecks-Och-Function [1] was fitted on the measured cyclic lifetimes.<br/><br/>The tensile strength in LH2 was measured to be 46 % higher compared to the value determined at ambient conditions and the fatigue limit was increased by approximately 60 %. Both S-N curves show a distinct S-shape but also significant differences. Under LH2 environment the transition from LCF- to HCF-region as well as the transition to the fatigue limit is shifted to higher cyclic lifetimes compared to ambient test results. The investigation of the crack surfaces showed distinct differences between ambient and LH2 conditions. These observed differences are important factors in the fatigue behavior change.
Simulation-based Safety Investigation of a Hydrogen Fueling Station with an On-site Hydrogen Production System Involving Methylcyclohexane
Jan 2017
Publication
Adequate safety measures are crucial for preventing major accidents at hydrogen fuelling stations. In particular risk analysis of the domino effect at hydrogen fuelling stations is essential because knock-on accidents are likely to intensify the consequences of a relatively small incident. Several risk assessment studies have focused on hydrogen fuelling stations but none have investigated accidental scenarios related to the domino effect at such stations. Therefore the purpose of this study is to identify a domino effect scenario analyze the scenario by using simulations and propose safety measures for preventing and mitigating of the scenario. In this hazard identification study we identified the domino effect scenario of a hydrogen fuelling station with an on-site hydrogen production system involving methylcyclohexane and investigated through simulations of the scenario. The simulations revealed that a pool fire of methylcyclohexane or toluene can damage the process equipment and that thermal radiation may cause the pressurized hydrogen tanks to rupture. The rupture-type vent system can serve as a critical safety measure for preventing and mitigating the examined scenario.
Test Methodologies for Hydrogen Sensor Performance Assessment: Chamber vs. Flow-through Test Apparatus
Sep 2017
Publication
Certification of hydrogen sensors to meet standards often prescribes using large-volume test chambers. However feedback from stakeholders such as sensor manufacturers and end-users indicates that chamber test methods are often viewed as too slow and expensive for routine assessment. Flow-through test methods are potentially an efficient and cost-effective alternative for sensor performance assessment. A large number of sensors can be simultaneously tested in series or in parallel with an appropriate flow-through test fixture. The recent development of sensors with response times of less than 1s mandates improvements in equipment and methodology to properly capture the performance of this new generation of fast sensors; flow methods are a viable approach for accurate response and recovery time determinations but there are potential drawbacks. According to ISO 26142 flow-through test methods may not properly simulate ambient applications. In chamber test methods gas transport to the sensor is dominated by diffusion which is viewed by some users as mimicking deployment in rooms and other confined spaces. Conversely in flow-through methods forced flow transports the gas to the sensing element. The advective flow dynamics may induce changes in the sensor behaviour relative to the quasi-quiescent condition that may prevail in chamber test methods. The aim of the current activity in the JRC and NREL sensor laboratories is to develop a validated flow-through apparatus and methods for hydrogen sensor performance testing. In addition to minimizing the impact on sensor behaviour induced by differences in flow dynamics challenges associated with flow-through methods include the ability to control environmental parameters (humidity pressure and temperature) during the test and changes in the test gas composition induced by chemical reactions with upstream sensors. Guidelines on flow-through test apparatus design and protocols for the evaluation of hydrogen sensor performance have been developed. Various commercial sensor platforms (e.g. thermal conductivity catalytic and metal semiconductor) were used to demonstrate the advantages and issues with the flow-through methodology.
Hydrogen-enhanced Fatigue Crack Growth in Steels and its Frequency Dependence
Jun 2017
Publication
In the context of the fatigue life design of components particularly those destined for use in hydrogen refuelling stations and fuel cell vehicles it is important to understand the hydrogen-induced fatigue crack growth (FCG) acceleration in steels. As such the mechanisms for acceleration and its influencing factors are reviewed and discussed in this paper with a special focus on the peculiar frequency dependence of the hydrogen-induced FCG acceleration. Further this frequency dependence is debated by introducing some potentially responsible elements along with new experimental data obtained by the authors.
This article is part of the themed issue ‘The challenges of hydrogen and metals’.
Link to document download on Royal Society Website
This article is part of the themed issue ‘The challenges of hydrogen and metals’.
Link to document download on Royal Society Website
Experimental Study of Light Gas Dispersion in a Channel
Sep 2019
Publication
Usage of hydrogen as fuel gives rise to possible accidental risks due to leakage and dispersion. A risk from hydrogen leak is the formation of a large volume of the hydrogen-air mixture which could be ignited and leading up to a severe explosion. Prevention and control of formation and ignition of combustible hydrogen cloud necessitate sufficient knowledge of mechanisms of the hydrogen leak dispersion ignition and over-pressures generated during combustion. This paper aims to investigate the momentum-controlled jet the buoyancy-controlled wave and the parameters influencing hydrogen concentration distribution in an elongated space. It demonstrates experimental results and analysis from helium and hydrogen dispersion in a channel. A set of experiments were carried out for the release of helium and hydrogen jets in a 3 m long channel to record their concentrations in the cloud by concentration sensors at different horizontal and vertical positions. Flow visualization technique was applied using shadowgraph to image the mixing process next to the release point and the helium- hydrogen-air cloud shape at the middle of the channel. Moreover results were used for comparison of helium and hydrogen concentration gradients. The results of the experiments show that swift mixing occurs at higher flow rates smaller nozzle sizes and downward release direction. Higher concentration recorded in the channel with negative inclination. Results also confirmed that hydrogen/helium behavior pattern in the channel accords with mutual intrusion theory about gravity currents.
Impact Assessments on People and Buildings for Hydrogen Pipeline Explosions
Sep 2019
Publication
Hydrogen has the potential to act as the energy carrier of the future. It will be then produced in large amounts and will certainly need to be transported for long distances. The safest way to transport hydrogen is through pipelines. Failure of pipelines carrying gaseous hydrogen can have several effects some of which can pose a significant threat of damage to people and buildings in the immediate proximity of the failure location. This paper presents a probabilistic risk assessment procedure for the estimation of damage to people and buildings endangered by high-pressure hydrogen pipeline explosions. The procedure provides evaluation of annual probability of damage to people and buildings under an extreme event as a combination of the conditional probability of damage triggered by an explosion and the probability of occurrence of the explosion as a consequence of the pipeline failure. Physical features such as the gas jet release process flammable cloud size blast generation and explosion effects on people and buildings are considered and evaluated through the SLAB integral model TNO model Probit equations and Pressure-Impulse diagrams. For people both direct and indirect effects of overpressure events are considered. For buildings a comparison of the damage to different types of buildings (i.e. reinforced concrete buildings and tuff stone masonry buildings) is made. The probabilistic procedure presented may be used for designing a new hydrogen pipeline network and will be an advantageous tool for safety management of hydrogen gas pipelines.
Pressure Peaking Phenomena: Unignited Hydrogen Releases in Confined Spaces – Large-scale Experiments
Sep 2020
Publication
The aim of this study was to validate a model for predicting overpressure arising from accidental hydrogen releases in areas with limited ventilation. Experiments were performed in a large-scale setup that included a steel-reinforced container of volume 14.9 m3 and variable ventilation areas and mass flow rates. The pressure peaking phenomenon characterized as transient overpressure with a characteristic peak in a vented enclosure was observed during all the experiments. The model description presented the relationship between the ventilation area mass flow rate enclosure volume and discharge coefficient. The experimental results were compared with two prediction models representing a perfect mix and the real mix. The perfect mix assumed that all the released hydrogen was well stirred inside the enclosure during the releases. The real mix prediction s used the hydrogen concentration and temperature data measured during experiments. The prediction results with both perfect mix and real mix showed possible hazards during unignited hydrogen releases.
A Large-Scale Study on the Effect of Ambient Conditions on Hydrogen Recombiner Induced Ignition
Sep 2019
Publication
Hydrogen recombiners (known in the nuclear industry as passive autocatalytic recombiners-PARs) in general can be utilized for mitigation of hydrogen in controlled areas where there is potential for hydrogen release and ventilation is not practical. Recombiners are widely implemented in the nuclear industry however there are other applications of recombiners outside the nuclear industry that have not yet been explored practically. The most notable benefit of recombiners over conventional hydrogen mitigation measures is their passive capability where power or operator actions are not needed for the equipment to remove hydrogen when it is present.
One of most significant concerns regarding the use of hydrogen recombiners in industry is their potential to ignite hydrogen at elevated concentrations (>6 vol%). The catalyst heated by the exothermal H2–O2 reaction is known to be a potential ignition source to cause hydrogen burns. An experimental program utilizing a full-size PAR at the Large-Scale Vented Combustion Test Facility (LSVCTF) has been carried out by Canadian Nuclear Laboratories (CNL) to investigate and understand the behaviour of hydrogen combustion induced by a PAR on a large-scale basis. A number of parameters external to the PAR have been explored including the effect of ambient humidity (steam) and temperature. The various aspects of this investigation will be discussed in this paper and examples of results are provided.
One of most significant concerns regarding the use of hydrogen recombiners in industry is their potential to ignite hydrogen at elevated concentrations (>6 vol%). The catalyst heated by the exothermal H2–O2 reaction is known to be a potential ignition source to cause hydrogen burns. An experimental program utilizing a full-size PAR at the Large-Scale Vented Combustion Test Facility (LSVCTF) has been carried out by Canadian Nuclear Laboratories (CNL) to investigate and understand the behaviour of hydrogen combustion induced by a PAR on a large-scale basis. A number of parameters external to the PAR have been explored including the effect of ambient humidity (steam) and temperature. The various aspects of this investigation will be discussed in this paper and examples of results are provided.
Numerical study of the release and dispersion of a light gas using 3D CFD code GASFLOW-MPI
Sep 2017
Publication
With the development of the hydrogen economy it requires a better understanding of the potential for fires and explosions associated with the unintended release of hydrogen within a partially confined space. In order to mitigate the hydrogen fire and explosion risks effectively accurate predictions of the hydrogen transport and mixing processes are crucial. It is well known that turbulence modelling is one of the key elements for a successful simulation of gas mixing and transport. GASFLOW-MPI is a scalable CFD software solution used to predict fluid dynamics conjugate heat and mass transfer chemical kinetics aerosol transportation and other related phenomena. In order to capture more turbulence information the Large Eddy Simulation (LES) model and LES/RANS hybrid model Detached Eddy Simulation (DES) have been implemented and validated in 3-D CFD code GASFLOW-MPI. The standard Smagorisky SGS model is utilized in LES turbulence model. And the k-epsilon based DES model is employed. This paper assesses the capability of algebraic k-epsilon DES and LES turbulence model to simulate the mixing and transport behavior of highly buoyant gases in a partially confined geometry. Simulation results agree well with the overall trend measured in experiments conducted in a reduced scale enclosure with idealized leaks which shows that all these four turbulent models are validated and suitable for the simulation of light gas behavior. Furthermore the numerical results also indicate that the LES and DES model could be used to analysis the turbulence behavior in the hydrogen safety problems.
LES Simulation of Buoyancy Jet From Unintended Hydrogen Release with GASFLOW-MPI
Sep 2017
Publication
Hydrogen leakage is a key safety issue for hydrogen energy application. For hydrogen leakage hydrogen releases with low momentum hence the development of the leakage jet is dominated by both initial momentum and buoyancy. It is important for a computational code to capture the flow characteristics transiting from momentum-dominated jet to buoyancy dominated plume during leakage. GASFLOW-MPI is a parallel computational fluid dynamics (CFD) code which is well validated and widely used for hydrogen safety analysis. In this paper its capability for small scale hydrogen leakage is validated with unintended hydrogen release experiment. In the experiment pure hydrogen is released into surrounding stagnant air through a jet tube on a honeycomb plate with various Froude numbers (Fr). The flow can be fully momentum-dominated at the beginning while the influence of buoyancy increases with the Fr decreases along the streamline. Several quantities of interest including velocity along the centerline radial profiles of the time-averaged H2 mass fraction are obtained to compare with experimental data. The good agreement between the numerical results and the experimental data indicates that GASFLOW-MPI can successfully simulate hydrogen turbulent dispersion driven by both momentum and buoyant force. Different turbulent models i.e. k-ε LES and DES model are analyzed for code performance the result shows that all these three models are adequate for hydrogen leakage simulation k-ε simulation is sufficient for industrial applications while LES model can be adopted for detail analysis for a jet/plume study like entrainment. The DES model possesses both characters of the former two model only the performance of its result depends on the grid refinement.
On the Response of a Lean-premixed Hydrogen Combustor to Acoustic and Dissipative-dispersive Entropy Waves
May 2019
Publication
Combustion of hydrogen or hydrogen containing blends in gas turbines and industrial combustors can activate thermoacoustic combustion instabilities. Convective instabilities are an important and yet less investigated class of combustion instability that are caused by the so called “entropy waves”. As a major shortcoming the partial decay of these convective-diffusive waves in the post-flame region of combustors is still largely unexplored. This paper therefore presents an investigation of the annihilating effects due to hydrodynamics heat transfer and flow stretch upon the nozzle response. The classical compact analysis is first extended to include the decay of entropy waves and heat transfer from the nozzle. Amplitudes and phase shifts of the responding acoustical waves are then calculated for subcritical and supercritical nozzles subject to acoustic and entropic forcing. A relation for the stretch of entropy wave in the nozzle is subsequently developed. It is shown that heat transfer and hydrodynamic decay can impart considerable effects on the entropic response of the nozzle. It is further shown that the flow stretching effects are strongly frequency dependent. The results indicate that dissipation and dispersion of entropy waves can significantly influence their conversion to sound and therefore should be included in the entropy wave models.
Interaction of Hydrogen Jets with Hot Surfaces of Various Sizes and Temperatures
Sep 2019
Publication
The formation of hydrogen jets from pressurized sources and ignition has been studied by many projects also when hitting hot devices. In the paper presented at the conference 2 years ago the ignition was caused by glow plug a “point like source” at various temperatures distances of igniter and source and source pressures. In continuation of that work ignition now occurred by 1 or 3 platelets of size 45 x 18 mm at a temperatures of 1223 K. When hitting these hot platelets the resulting flame explosions and flame jets show interesting characteristics in contrast to the point like ignition where the explosions drifts downstream with the jet. Parameters of the experiments vary in initial pressure of the tubular source (10 20 and 40 MPa) distance between the nozzle and the hot surface (3 5 and 7 m) and temperature of the hot surface (1223 K). The initial explosions stabilize already at the stagnation point or the wake of the hot platelets. Furthermore flames propagate upstream and downstream depending on the pressure of the hydrogen reservoir and the distance. The achieved flame velocities vary strongly from 30 to 240 m/s. With all investigated hydrogen pressures strong reactions v > 40 m/s occur at platelet distances of 3 and 5 m. The higher values are mainly achieved with jets with 40 MPa pressure at 3 m distance. In these cases the initial explosion contours show irregular shapes. Various effects are found like explosion separation further independently initiated explosions and two parallel flame jets upstream as well as downstream.
Comparison of Two-layer Model for High Pressure Hydrogen Jets with Notional Nozzle Model Predictions and Experimental Data
Oct 2015
Publication
A two-layer reduced order model of high pressure hydrogen jets was developed which includes partitioning of the flow between the central core jet region leading to the Mach disk and the supersonic slip region around the core. The flow after the Mach disk is subsonic while the flow around the Mach disk is supersonic with a significant amount of entrained air. This flow structure significantly affects the hydrogen concentration profiles downstream. The predictions of this model are compared to previous experimental data for high pressure hydrogen jets up to 20 MPa and to notional nozzle models and CFD models for pressures up to 35 MPa using ideal gas properties. The results show that this reduced order model gives better predictions of the mole fraction distributions than previous models for highly underexpanded jets. The predicted locations of the 4% lower flammability limit also show that the two-layer model much more accurately predicts the measured locations than the notional nozzle models. The comparisons also show that the CFD model always underpredicts the measured mole fraction concentrations.
Large Scale Experiments and Model Validation of Pressure Peaking Phenomena-ignited Hydrogen Releases
Jan 2021
Publication
The Pressure Peaking Phenomena (PPP) is the effect of introducing a light gas into a vented volume of denser gas. This will result in a nonequilibrium pressure as the light gas pushes the dense gas out at the vent. Large scale experiments have been performed to produce relevant evidence. The results were used to validate an analytical model. Pressure and temperature were measured inside a constant volume while the mass flow and vent area were varied. The analytical model was based on the conservation of mass and energy. The results showed that increasing the mass flow rate the peak pressure increases and with increasing the ventilation area the peak pressure decreases. Peak pressure was measured above 45 kPa. Longer combustion time resulted in higher temperatures increasing an underpressure effect. The experimental results showed agreement with the analytical model results. The model predicts the pressures within reasonable limits of+/-2 kPa. The pressure peaking phenomena could be very relevant for hydrogen applications in enclosures with limited ventilation. This could include car garages ship hull compartments as well as compressor shielding. This work shows that the effect can be modeled and results can be used in design to reduce the consequences.
Development of a Model Evaluation Protocol for CFD Analysis of Hydrogen Safety Issues – The SUSANA Project
Oct 2015
Publication
The “SUpport to SAfety aNAlysis of Hydrogen and Fuel Cell Technologies (SUSANA)” project aims to support stakeholders using Computational Fluid Dynamics (CFD) for safety engineering design and assessment of FCH systems and infrastructure through the development of a model evaluation protocol. The protocol covers all aspects of safety assessment modelling using CFD from release through dispersion to combustion (self-ignition fires deflagrations detonations and Deflagration to Detonation Transition - DDT) and not only aims to enable users to evaluate models but to inform them of the state of the art and best practices in numerical modelling. The paper gives an overview of the SUSANA project including the main stages of the model evaluation protocol and some results from the on-going benchmarking activities.
Numerical Prediction of Cryogenic Hydrogen Vertical Jets
Sep 2019
Publication
Comparison of Computational Fluid Dynamics (CFD) predictions with measurements is presented for cryo-compressed hydrogen vertical jets. The stagnation conditions of the experiments are characteristic of unintended leaks from pipe systems that connect cryogenic hydrogen storage tanks and could be encountered at a fuel cell refuelling station. Jets with pressure up to 5 bar and temperatures just above the saturation liquid temperature were examined. Comparisons are made to the centerline mass fraction and temperature decay rates the radial profiles of mass fraction and the contours of volume fraction. Two notional nozzle approaches are tested to model the under-expanded jet that was formed in the tests with pressures above 2 bar. In both approaches the mass and momentum balance from the throat to the notional nozzle are solved while the temperature at the notional nozzle was assumed equal to the nozzle temperature in the first approach and was calculated by an energy balance in the second approach. The two approaches gave identical results. Satisfactory agreement with the measurements was found in terms of centerline mass fraction and temperature. However for test with 3 and 4 bar release the concentration was overpredicted. Furthermore a wider radial spread was observed in the predictions possibly revealing higher degree of diffusion using the k-ε turbulence model. An integral model for cryogenic jets was also developed and provided good results. Finally a test simulation was performed with an ambient temperature jet and compared to the cold jet showing that warm jets decay faster than cold jets.
An Investigation of Mobile Hydrogen and Fuel Cell Technology Applications
Sep 2019
Publication
Safe practices in the production storage distribution and use of hydrogen are essential for the widespread acceptance of hydrogen and fuel cell technologies. A significant safety incident in any project could damage public perception of hydrogen and fuel cells. A recent incident involving a hydrogen mobile storage trailer in the United States has brought attention to the potential impacts of mobile hydrogen storage and transport. Road transport of bulk hydrogen presents unique hazards that can be very different from those for stationary equipment and new equipment developers may have less experience and expertise than seasoned gas providers. In response to the aforementioned incident and in support of hydrogen and fuel cell activities in California the Hydrogen Safety Panel (HSP) has investigated the safety of mobile hydrogen and fuel cell applications (mobile auxiliary/emergency fuel cell power units mobile fuellers multi-cylinder trailer transport unmanned aircraft power supplies and mobile hydrogen generators). The HSP examined the applications requirements and performance of mobile applications that are being used extensively outside of California to understand how safety considerations are applied. This paper discusses the results of the HSP’s evaluation of hydrogen and fuel cell mobile applications along with recommendations to address relevant safety issues.
Validation of Two-Layer Model for Underexpanded Hydrogen Jets
Sep 2019
Publication
Previous studies have shown that the two-layer model more accurately predicts hydrogen dispersion than the conventional notional nozzle models without significantly increasing the computational expense. However the model was only validated for predicting the concentration distribution and has not been adequately validated for predicting the velocity distributions. In the present study particle imaging velocimetry (PIV) was used to measure the velocity field of an underexpanded hydrogen jet released at 10 bar from a 1.5 mm diameter orifice. The two-layer model was the used to calculate the inlet conditions for a two-dimensional axisymmetric CFD model to simulate the hydrogen jet downstream of the Mach disk. The predicted velocity spreading and centerline decay rates agreed well with the PIV measurements. The predicted concentration distribution was consistent with data from previous planar Rayleigh scattering measurements used to verify the concentration distribution predictions in an earlier study. The jet spreading was also simulated using several widely used notional nozzle models combined with the integral plume model for comparison. These results show that the velocity and concentration distributions are both better predicted by the two-layer model than the notional nozzle models to complement previous studies verifying only the predicted concentration profiles. Thus this study shows that the two-layer model can accurately predict the jet velocity distributions as well as the concentration distributions as verified earlier. Though more validation studies are needed to improve confidence in the model and increase the range of validity the present work indicates that the two-layer model is a promising tool for fast accurate predictions of the flow fields of underexpanded hydrogen jets.
Thermal Radiation Properties of Large Hydrogen Leaks from Gas Distribution Networks
Sep 2019
Publication
Determination of the behaviour of hydrogen when leaking from pipework on gas distribution assets is essential in assessing the comparative risk associated with using pure hydrogen in place of natural gas in existing assets. Experimental work considering the behaviour of gaseous hydrogen when released in large volumes from gas distribution pipework at pressures of up to 7 barg through holes of up to 200mm in diameter in both buried and unburied scenarios is currently underway. The present paper presents and briefly discusses the results from a set of ignited 20mm diameter releases of hydrogen at pressures up to 7 barg vertically upwards from a pipe in an open excavation. Gaseous releases which find a direct route to atmosphere have the potential to create significant volumes of flammable gas and subsequently significant fires in the case of ignition. It is important to understand both the dispersion distances and thermal hazard field to be able to understand the comparative risk posed when compared to natural gas releases in similar situations. Results of current work completed to date are presented alongside comparisons with known properties of natural gas releases and the potential implications to the comparative risk of hydrogen network operation. The work has been conducted at the DNV GL Spadeadam Testing and Research Centre UK as part of the UK Gas Distribution Networks and Ofgem National Innovation Competition funded H21 project.
Experimental Measurements, CFD Simulations and Model for a Helium Release in a Two Vents Enclosure
Sep 2017
Publication
The present work proposes improvements on a model developed by Linden to predict the concentration distribution in a 2 vented cavities. Recent developments on non constant entrainment coefficient from Carazzo et al as well as a non constant pressure distribution at the vents-the vents being vertical-are included in the Linden approach. This model is compared with experimental results from a parametric study on the influence of the height of the release source on the helium dispersion regimes inside a naturally ventilated 2 vents enclosure. The varying parameters of the study were mainly the height of the release the releasing flow rate and the geometry of the vents. At last Large Eddy Simulations of the flow and Particle Image Velocimetry measurements performed on a small 2 vented cavity are presented. The objective is to have a better understanding of the flow structure which is at the origin of the 2 layers concentration distribution described by Linden.
Numerical Modelling of Unconfined and Confined Hydrogen Explosion
Sep 2019
Publication
Numerical studies were conducted with the objective of gaining a better understanding of the consequences of potential explosion that could be associated with release of hydrogen in a confined and unconfined environment. This paper describes the work done by us in modelling explosion of accidental releases of hydrogen using our Fire Explosion Release Dispersion (FRED) software. CAM and SCOPE models in FRED is used for validation of congested/uncongested unconfined and congested/uncongested confined vapour cloud explosion respectively. In the first step CAM is validated against experiments of varying gas cloud size blockage ratio equivalence ratio of the mixture and blockage configuration. The model predictions of explosion overpressure are in good agreement with experiments. The results obtained from FRED i.e. overpressure as a function of distance match well in comparison to the experiments. In the second step SCOPE is validated against vented explosion experiments available in open literature. In general SCOPE reproduces the maximum overpressure within the factor of 2. Moreover it well predicts the trends of increase in overpressure with change in type of the fuel increase in number of obstacles blockage ratio and decrease in the vent size.
Compliance Measurements of Fuel Cell Electric Vehicle Exhaust
Sep 2019
Publication
The NREL Sensor Laboratory has been developing an analyzer that can verify compliance to the international United Nations Global Technical Regulation number 13 (GTR 13--Global Technical Regulation on Hydrogen and Fuel Cell Vehicles) prescriptive requirements pertaining to allowable hydrogen levels in the exhaust of fuel cell electric vehicles (FCEV) [1]. GTR 13 prescribes that the FCEV exhaust shall remain below 4 vol% H2 over a 3-second moving average and shall not at any time exceed 8 vol% H2 as verified with an analyzer with a response time (t90) of 300 ms or faster. GTR 13 has been implemented and is to serve as the basis for national regulations pertaining to hydrogen powered vehicle safety in the United States Canada Japan and the European Union. In the U.S. vehicle safety is overseen by the Department of Transportation (DOT) through the Federal Motor Vehicle Safety Standards (FMVSS) and in Canada by Transport Canada through the Canadian Motor Vehicle Safety Standard (CMVSS). The NREL FCEV exhaust analyzer is based upon a low-cost commercial hydrogen sensor with a response time (t90) of less than 250 ms. A prototype analyzer and gas probe assembly have been constructed and tested that can interface to the gas sampling system used by Environment and Climate Change Canada’s (ECCC) Emission Research and Measurement Section (ERMS) for the exhaust gas analysis. Through a partnership with Transport Canada ECCC will analyze the hydrogen level in the exhaust of a commercial FCEV. ECCC will use the NREL FCEV Exhaust Gas analyzer to perform these measurements. The analyzer was demonstrated on a FCEV operating under simulated road conditions using a chassis dynamometer at a private facility.
Effect of the Time Dependent Loading of Type IV Cylinders Using a Multi-scalemodel
Sep 2019
Publication
The current requirements for composite cylinders are still based on an arbitrary approach derived from the behaviour of metal structures that the designed burst pressure should be at least 2.5 times the maximum in-service pressure. This could lead to an over-designed composite cylinder for which the weight saving would be less than optimum. Moreover predicting the lifetime of composite cylinders is a challenging task due to their anisotropic characteristics. A federal research institute in Germany (BAM) has proposed a minimum load-cycle requirement that mitigates this issue by using a MonteCarlo analysis of the burst test results. To enrich this study more experiments are required however they are normally limited by the necessity of long duration testing times (loading rate and number of cylinders) and the design (stacking sequence of the composite layer). A multi-scale model incorporating the micromechanical behaviour of composite structures has been developed at Mines ParisTech. The model has shown similar behaviour to that of composite cylinders under different loading rates. This indicates that the model could assist the Monte-Carlo analysis study. An evaluation of the multi-scale model therefore has been carried out to determine its limitations in predicting lifetimes of composite cylinders. The evaluation starts with the comparison of burst pressures with type IV composite cylinders under different loading rates. A μCT-Scan of a type IV cylinder has been carried out at the University of Southampton. The produced images were analysed using the Fast-Fourier Transform (FFT) technique to determine the configuration of the composite layers which is required by the model. Finally the time dependent effect studied by using the multi scale model has been described. In the long-term this study can be used to conduct a parametric study for creating more efficient design of type IV cylinders.
Numerical Analysis for Hydrogen Flame Acceleration during a Severe Accident in the APR1400 Containment Using a Multi-Dimensional Hydrogen Analysis System
Nov 2020
Publication
Korea Atomic Energy Research Institute (KAERI) established a multi-dimensional hydrogen analysis system to evaluate hydrogen release distribution and combustion in the containment of a Nuclear Power Plant (NPP) using MAAP GASFLOW and COM3D. In particular KAERI developed an analysis methodology for a hydrogen flame acceleration on the basis of the COM3D validation results against measured data of the hydrogen combustion tests in the ENACCEF and THAI facilities. The proposed analysis methodology accurately predicted the peak overpressure with an error range of approximately ±10% using the Kawanabe model used for a turbulent flame speed in the COM3D. KAERI performed a hydrogen flame acceleration analysis using the multi-dimensional hydrogen analysis system for a severe accident initiated by a station blackout (SBO) under the assumption of 100% metal–water reaction in the Reactor Pressure Vessel (RPV) to evaluate an overpressure buildup in the containment of the Advanced Power Reactor 1400 MWe (APR1400). The magnitude of the overpressure buildup in the APR1400 containment might be used as a criterion to judge whether the containment integrity is maintained or not when the hydrogen combustion occurs during a severe accident. The COM3D calculation results using the established analysis methodology showed that the calculated peak pressure in the containment was lower than the fracture pressure of the APR1400 containment. This calculation result might have resulted from a large air volume of the containment a reduced hydrogen concentration owing to passive auto-catalytic recombiners installed in the containment during the hydrogen release from the RPV and a lot of stem presence during the hydrogen combustion period in the containment. Therefore we found that the current design of the APR1400 containment maintained its integrity when the flame acceleration occurred during the severe accident initiated by the SBO accident.
Vented Hydrogen-air Deflagrations in Low Strength Equipment and Buildings
Sep 2013
Publication
This paper aims to improve prediction capability of the vent sizing correlation presented in the form of functional dependence of the dimensionless deflagration overpressure on the turbulent Bradley number similar to our previous studies. The correlation is essentially upgraded based on recent advancements in understanding and modelling of combustion phenomena relevant to hydrogen-air vented deflagrations and unique large-scale tests carried out by different research groups. The focus is on hydrogen-air deflagrations in low-strength equipment and buildings when the reduced pressure is accepted to be below 0.1 MPa. The combustion phenomena accounted for by the correlation include: turbulence generated by the flame front itself; leading point mechanism stemming from the preferential diffusion of hydrogen in air in stretched flames; growth of the fractal area of the turbulent flame surface; initial turbulence in the flammable mixture; as well as effects of enclosure aspect ratio and presence of obstacles. The correlation is validated against the widest range of experimental conditions available to date (76 experimental points). The validation covers a wide range of test conditions: different shape enclosures of volume up to 120 m3; initially quiescent and turbulent hydrogen-air mixtures; hydrogen concentration in air from 6% to 30% by volume; ignition source location at enclosure centre near and far from a vent; empty enclosures and enclosures with obstacles.
Highly Resolve Large Eddy Simulations of a Transitional Air-helium Buoyant Jet in a Two Vented Enclosure: Validation Against Particle Image Velocimetry Experiments
Sep 2017
Publication
The article deals with LES simulations of an air-helium buoyant jet in a two vented enclosure and their validation against particle image velocimetry experiments. The main objective is to test the ability of LES models to simulate such scenarios. These types of scenarios are of first interest considering safety studies for new hydrogen systems. Three main challenges are identified. The two first are the ability of the LES model to account for a rapid laminar-to-turbulence transition mainly due to the buoyancy accelerations and the Rayleigh-Taylor instabilities that can develop due to sharp density gradients. The third one is the outlet boundary conditions to be imposed on the vent surfaces. The influence of the classical pressure boundary condition is studied by comparing the simulations results when an exterior region is added in the simulations. The comparisons against particle image velocimetry experiments show that the use of an exterior domain gives more accurate results than the classical pressure boundary condition. This result and the description of the phenomena involved are the main outlets of the article.
Hydrogen Venting Under Variable Flow Conditions
Sep 2011
Publication
Safety distances for hydrogen plumes are currently derived using models developed for hydrocarbon releases. It is well known that hydrogen behaves in a significantly different manner to that of hydrocarbons when released to atmosphere. There are two main aspects involved with the development of safety distances for credible hydrogen releases; the intensity of the thermal radiation from such a plume should it be ignited and the distance downwind from the release point to the point where a flammable mixture with air no longer exists. A number of distinct areas of venting behaviour were investigated; Thermal radiation from ignited plumes from vertical open ended vent pipes Far field radiation measurements for direct comparison with models Thermal radiation from ignited plumes from vertical vent pipes terminating in a T-piece Thermal radiation measurements from ignited hydrogen with a 45 vent termination Hydrogen concentration measurements with a T-piece.
High-Order Perturbation Solutions to a Lh2 Spreading Model With Continuous Spill
Sep 2011
Publication
High-order perturbation solutions have been obtained for the simple physical model describing the LH2 spreading with a continuous spill and are shown to improve over the first-order perturbation solutions. The non-dimensional governing equations for the model are derived to obtain more general solutions. Non-dimensional parameters are sought as the governing parameters for the non-dimensional equations and the non-dimensional evaporation rate is used as the perturbation parameter. The results show that the second-order solutions exhibit an improvement over the first-order solutions with respect to the pool volume; however there is still a difference between numerical solutions and second-order solutions in the late stage of spread. Finally it is revealed that the third-order solutions almost agree with numerical solutions.
Hydrogen Risk Assessment in Sao Paulo State, Brazil
Sep 2011
Publication
Sao Paulo State Environmental Protection Agency CETESB Brazil adopts a so called Reference Distance (RD) from hazardous substances storage facilities to populated places as a decision making tool for the application of a simplified or a full Risk Analysis (RA). As for hydrogen RD was set up based on instantaneous release scenarios where consequences reaching off-site population were estimated for delayed ignition ending up in vapor cloud explosion (VCE) with a 0.1 bar blast wave overpressure as a chosen endpoint corresponding to a 1%2of death probability range. Procedures for RD evaluation and further adoption by CETESB are presented in this paper.
Analysis of Acoustic Pressure Oscillation During Vented Deflagration
Oct 2015
Publication
In industrial buildings explosion relief panels or doors are often used to reduce damages caused by gas explosion. Decades of research produced a significant contribution to the understanding of the phenomena involved nevertheless among the aspects that need further research interaction between acoustic oscillation and the flame front is one of the more important. Interaction between the flame front and acoustic oscillation has raised technical problem in lots of combustion applications as well and had been studied theoretically and experimentally in such cases. Pressure oscillation had been observed in vented deflagration and in certain cases they are responsible for the highest pressure peak generated during the event. At Scalbatraio laboratory of Pisa University CVE test facility was built in order to investigate vented hydrogen deflagration. This paper is aimed to present an overview of the results obtained during several experimental campaigns which tests are analysed with the focus on the investigation of flame acoustic interaction phenomenon. Qualitative and quantitative analysis is presented and the possible physic generating the phenomenon investigated.
Risk Informed Separation Distances For Hydrogen Refuelling Stations
Sep 2011
Publication
The lay-out requirements developed for hydrogen systems operated in industrial environment are not suitable for the operating conditions specific to hydrogen refuelling stations (service pressure of up to 95 MPa facility for public use). A risk informed rationale has been developed to define and substantiate separation distance requirements in ISO 20100 Gaseous hydrogen – refuelling stations [1]. In this approach priority is given to preventing escalation of small incidents into majors ones with a focus on critical exposures such as places of occupancy (fuelling station retail shop) while optimizing use of the available space from a risk perspective a key objective for being able to retrofit hydrogen refuelling in existing stations.
A Study of Hydrogen Flame Length with Complex Nozzle Geometry
Sep 2017
Publication
The growing number of hydrogen fillings stations and cars increases the need for accurate models to determine risk. The effect on hydrogen flame length was measured by varying the diameter of the spouting nozzle downstream from the chocked nozzle upstream. The results was compared with an existing model for flame length estimations. The experimental rig was setup with sensors that measured accurately temperature mass flow heat radiation and the pressure range from 0.1 to 11 MPa. The flame length was determined with an in-house developed image-processing tool which analyzed a high-speed film of the each experiment. Results show that the nozzle geometry can cause a deviation as high as 50% compared to estimated flame lengths by the model if wrong assumptions are made. Discharge coefficients for different nozzles has been calculated and presented.
Numerical and Experimental Investigation of H2-air and H2-O2 Detonation Parameters in a 9 m Long Tube, Introduction of a New Detonation Model
Sep 2017
Publication
Experimental and numerical investigation of hydrogen-air and hydrogen-oxygen detonation parameters was performed. A new detonation model was introduced and validated against the experimental data. Experimental set-up consisted of 9 m long tube with 0.17 m in diameter where pressure was measured with piezoelectric transducers located along the channel. Numerical simulations were performed within OpenFoam code based on progress variable equation where the detonative source term accounts for autoignition effects. Autoignition delay times were computed at a simulation run-time with the use of a multivariate regression model where independent variables were: pressure temperature and fuel concentration. The dependent variable was the autoignition delay time. Range of the analyzed gaseous mixture composition varied between 20% and 50% of hydrogen-air and 50%–66% of hydrogen in oxygen. Simulations were performed using LES one-equation eddy viscosity turbulence model in 2D and 3D. Calculations were validated against experimental data.
Safety Concept of Nuclear Cogeneration of Hydrogen and Electricity
Oct 2015
Publication
There is a significant potential for nuclear combined heat and power (CHP) in quite a number of industries. The reactor concepts of the next generation would be capable to open up in particular the high temperature heat market where nuclear energy is applicable to the production processes of hydrogen (or liquid fuels) by steam reforming or water splitting. Due to the need to locate a nuclear facility near the hydrogen plant an overall safety concept has to deal with the question of safety of the combined nuclear/industrial system by taking into account a qualitatively new class of events characterized by interacting influences. Specific requirements will be determined by such factors as the reactor type the nature of the industrial process the separation distances of the industrial facility and population centers from the nuclear plant and prevailing public attitudes. Based on the Japanese concept of the GTHTR300C nuclear reactor for electricity and hydrogen cogeneration theoretical studies were conducted on the release dispersive transport and explosion of a hydrogen cloud in the atmosphere for the sake of assessing the required minimum separation distance to avoid any risk to the nuclear plant's safety systems. In the case of sulfur-iodine water splitting the accidental release of process intermediates including large amounts of sulfur dioxide sulfur trioxide and sulfuric acid need to be investigated as well to estimate the potential risk to nuclear installations like the operators' room and estimate appropriate separation distances against toxic gas propagation. Results of respective simulation studies will be presented.
Effect of Initial Turbulence on Vented Explosion Over Pressures from Lean Hydrogen-air Deflagrations
Sep 2013
Publication
To examine the effect of initial turbulence on vented explosions experiments were performed for lean hydrogen–air mixtures with hydrogen concentrations ranging from 12 to 15% vol. at elevated initial turbulence. As expected it was found that an increase in initial turbulence increased the overall flame propagation speed and this increased flame propagation speed translated into higher peak overpressures during the external explosion. The peak pressures generated by flame–acoustic interactions however did not vary significantly with initial turbulence. When flame speeds measurements were examined it was found that the burning velocity increased with flame radius as a power function of radius with a relatively constant exponent over the range of weak initial turbulence studied and did not vary systematically with initial turbulence. Instead the elevated initial turbulence increased the initial flame propagation velocities of the various mixtures. The initial turbulence thus appears to act primarily by generating higher initial flame wrinkling while having a minimal effect on the growth rate of the wrinkles. For practical purposes of modelling flame propagation and pressure generation in vented explosions the increase in burning velocity due to turbulence is suggested to be approximated by a single constant factor that increases the effective burning velocity of the mixture. When this approach is applied to a previously developed vent sizing correlation the correlation performs well for almost all of the peaks. It was found however that in certain situations this approach significantly under predicts the flame–acoustic peak. This suggests that further research may be necessary to better understand the influence of initial turbulence on the development of flame–acoustic peaks in vented explosions.
Leakage-type-based Analysis of Accidents Involving Hydrogen Fueling Stations in Japan and USA
Aug 2016
Publication
To identify the safety issues associated with hydrogen fuelling stations incidents at such stations in Japan and the USA were analyzed considering the regulations in these countries. Leakage due to the damage and fracture of main bodies of apparatuses and pipes in Japan and the USA is mainly caused by design error that is poorly planned fatigue. Considering the present incidents in these countries adequate consideration of the usage environment in the design is very important. Leakage from flanges valves and seals in Japan is mainly caused by screw joints. If welded joints are to be used in hydrogen fuelling stations in Japan strength data for welded parts should be obtained and pipe thicknesses should be reduced. Leakage due to other factors e.g. external impact in Japan and the USA is mainly caused by human error. To realize self-serviced hydrogen fuelling stations safety measures should be developed to prevent human error by fuel cell vehicle users.
Measurements of Effective Diffusion Coefficient of Helium and Hydrogen Through Gypsum
Sep 2011
Publication
An experimental apparatus which was based on the ¼-scale garage previously used for studying helium release and dispersion in our laboratory was used to obtain effective diffusion coefficients of helium and hydrogen (released as forming gas for safety reasons) through gypsum panel. Two types of gypsum panel were used in the experiments. Helium or forming gas was released into the enclosure from a Fischer burner1 located near the enclosure floor for a fixed duration and then terminated. Eight thermal-conductivity sensors mounted at different vertical locations above the enclosure floor were used to monitor the temporal and spatial gas concentrations. An electric fan was used inside the enclosure to mix the released gas to ensure a spatially uniform gas concentration to minimize stratification. The temporal variations of the pressure difference between the enclosure interior and the ambience were also measured. An analytical model was developed to extract the effective diffusion coefficients from the experimental data.
Non-steady Characteristics of Dispersion and Ignitability for High-pressurized Hydrogen Jet Discharged From a Pinhole
Sep 2017
Publication
Hydrogen gas concentrations and jet velocities were measured downstream by a high response speed flame ionization detector and PIV (Particle Image Velocimetry) in order to investigate the characteristics of dispersion and ignitability for 40–82 MPa high-pressurized hydrogen jet discharged from a nozzle with 0.2 mm diameter. The light emitted from both OH radical and water vapor species yielded from hydrogen combustion ignited by an electric spark were recorded by two high speed cameras. From the results the empirical formula concerning the relationships for time-averaged concentrations concentration fluctuations and ignition probability were obtained to suggest that they would be independent of hydrogen discharge pressure.
Closing the Regulatory Gaps and Advancing Hydrogen Infrastructure Deployment in Australia
Sep 2019
Publication
With downward trends in Australian equipment manufacturing there are increased numbers of overseas designed manufactured and certified hydrogen systems being introduced into Australia. In parallel there are also opportunities for hydrogen and its carriers to be exported to overseas. Certainty of reputable codes and standards is important to meet regulatory requirements and community safety expectations locally and overseas.
This paper is a progress report of Hydrogen Mobility Australia’s (HMA) Technical Committee on mapping the regulatory codes and standards (RCS) gaps in Australia and establishing a pathway together with Standards Australia and Commonwealth and State Governments. This paper will discuss the benefits of the pathway covering the areas of:
This paper is a progress report of Hydrogen Mobility Australia’s (HMA) Technical Committee on mapping the regulatory codes and standards (RCS) gaps in Australia and establishing a pathway together with Standards Australia and Commonwealth and State Governments. This paper will discuss the benefits of the pathway covering the areas of:
- Safety – Enable Australia to implement consensual rules to minimise avoidable risks to persons and goods to an acceptable level
- Environment – Ensure protection of the environment from unacceptable damage due to the operation and effects of products processes and services linked to hydrogen
- Elimination of barriers to trade – Provide consistency between international jurisdictions enabling streamlined entry of hydrogen related equipment from overseas
- Upskilling of Australian industry participants – Gain useful learnings from countries more advanced in their progress in implementing ISO standards and hydrogen sector development
Helios- A New Method for Hydrogen Permeation Test
Sep 2013
Publication
Hydrogen induced cracking is still a severe and current threat for several industrial applications. With the aim of providing a simple and versatile device for hydrogen detection a new instrument was designed based on solid state sensor technology. New detection technique allows to execute hydrogen permeation measurement in short time and without material surface preparation. Thanks to this innovation HELIOS offers a concrete alternative to traditional experimental methods for laboratory permeability tests. In addition it is proposed as a new system for Non Destructive Testing of components in service in hydrogenating environment. Hydrogen flux monitoring is particularly relevant for risk mitigation of elements involved in hydrogen storage and transportation. Hydrogen permeation tests were performed by means of HELIOS instruments both on a plane membrane and on the wall of a gas cylinder. Results confirmed the extreme sensitivity of the detection system and its suitability to perform measurements even on non metallic materials by means of an easy-to-handle instrument.
A Study on the Continuous Spill with Limited Period of Release
Sep 2013
Publication
In this study the spread of cryogenic liquid due to a limited period of release is investigated for the first time to clarify the unclear conventional concept regarding two release types continuous and instantaneous release. In describing instantaneous release a discharge time has been assumed to be infinitesimally small; however such an assumption is unreal because there exists a finite period of release no matter how rapid it is. If the discharge time is less than the entire time domain the instantaneous release model should be added to the continuous model from the end of the time. This combined release that consists of the initial continuous model and subsequent instantaneous model is more realistic than the instantaneous release. The physical phenomenon is governed by three parameters: the evaporation rate per unit area release time and spill quantity. Third-order perturbation solutions are obtained and compared with a numerical solution to verify the perturbation solution. For the same spill quantity the combined model that consists of continuous and subsequent instantaneous model is necessary for small release times whereas the continuous model is only required for large release times. Additionally the combined release model is necessary for a small spill quantity at a fixed release time. These two release models are clearly distinguished using the perturbation solution.
Uncertainties in Explosion Risk Assessment for a Hydrogen Refuelling Station
Sep 2011
Publication
The project “Towards a Hydrogen Refuelling Infrastructure for Vehicles” (THRIVE) aimed at the determination of conditions to stimulate the building of a sustainable infrastructure for hydrogen as a car fuel in The Netherlands. Economic scenarios were constructed for the development of such an infrastructure for the next one to four decades. The eventual horizon will require the erection of a few hundred to more than a thousand hydrogen refuelling stations (HRS) in The Netherlands. The risk acceptability policy in The Netherlands implemented in the External Safety Establishments decree requires the assessment and management of safety risks imposed on the public by car fuelling stations. In the past a risk-informed policy has been developed for the large scale introduction of liquefied petroleum gas (LPG) as a car fuel and a similar policy will also be required if hydrogen is introduced in the public domain. A risk assessment methodology dedicated to cope with accident scenarios relevant for hydrogen applications is to be developed. Within the THRIVE project a demo risk assessment was conducted for the possible implementation of an HRS within an existing station for conventional fuels. The studied station is located in an urban area occupied with housing and commercial activities. The HRS is based on delivery and on-site storage of liquid hydrogen and dispensing of high pressure gaseous hydrogen into vehicles. The main challenges in the risk assessment were in the modelling of release and dispersion of liquid hydrogen. Definition of initial conditions for computational fluid dynamics (CFD) modelling to evaluate dispersion of a cold hydrogen air mixture appears rather complex and is not always fully understood. The modelling assumptions in the initial conditions determine to a large extent the likelihood and severity of potential explosion effects. The paper shows the results of the investigation and the sensitivity to the basic assumptions in the model input.
Updated Jet Flame Radiation Modelling with Corrections for Buoyancy and Wind
Sep 2013
Publication
Radiative heat fluxes from small to medium-scale hydrogen jet flames (<10 m) compare favorably to theoretical predictions provided the product species thermal emittance and optical flame thickness are corrected for. However recent heat flux measurements from two large-scale horizontally orientated hydrogen flames (17.4 and 45.9 m respectively) revealed that current methods underpredicted the flame radiant fraction by 40% or more. Newly developed weighted source flame radiation models have demonstrated substantial improvement in the heat flux predictions particularly in the near-field and allow for a sensible way to correct potential ground surface reflective irradiance. These updated methods are still constrained by the fact that the flame is assumed to have a linear trajectory despite buoyancy effects that can result in significant flame deformation. The current paper discusses a method to predict flame centerline trajectories via a one-dimensional flame integral model which enables optimized placement of source emitters for weighted multi-source heat flux prediction methods. Flame shape prediction from choked releases was evaluated against flame envelope imaging and found to depend heavily on the notional nozzle model formulation used to compute the density weighted effective nozzle diameter. Nonetheless substantial improvement in the prediction of downstream radiative heat flux values occurred when emitter placement was corrected by the flame integral model regardless of the notional nozzle model formulation used.
Consequence Models for Vented Hydrogen Deflagrations: CFD vs. Engineering Models
Sep 2017
Publication
This paper compares two approaches for predicting the consequences of vented hydrogen deflagrations: empirical engineering models (EMs) and computational fluid dynamics (CFD) simulations. The study is part of the project ‘Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations’ (HySEA) funded by the Fuel Cells and Hydrogen 2 Joint Undertaking (FCH JU) under grant agreement No 671461. The HySEA project focuses on vented hydrogen deflagrations in containers and smaller enclosures with internal congestion representative of industrial applications. Data from experiments conducted as part of the HySEA project are used to evaluate predictions from a selection of EMs and the CFD tool FLACS. The experiments involve various obstacle and venting configurations and initially quiescent homogeneous hydrogen-air mixtures with hydrogen concentrations in the range 15–24 vol%. There is a significant scatter in the maximum reduced overpressures predicted by the different EMs in the present study. For certain configurations there is an order of magnitude difference between the different EM predictions. Two versions of the CFD tool FLACS are used in the present study: i) the standard commercial release FLACS v10.7r2 and ii) an in-house development version termed FLACS-beta. The commercial release generally over-predicts the maximum overpressures measured in the experiments while the development version of FLACS gives improved results for several configurations.
Tests of the Vehicle’s Powertrain with Hydrogen Fuel Cells at a Low Temperature
Sep 2019
Publication
The article discusses issues related to the operation of fuel cells stack fed with hydrogen at low temperature. The test object was a Toyota Mirai passenger car equipped with this type of powertrain. Tests were carried out in a thermoclimatic chamber at the Cracow University of Technology. They had an initial character and their aim was to evaluate the work of individual subassemblies of the propulsion system including the hydrogen supply system in terms of operational safety.
Development of a Realistic Hydrogen Flammable Atmosphere Inside a 4-m3 Enclosure
Sep 2017
Publication
To define a strategy of mitigation for containerized hydrogen systems (fuel cells for example) against explosion the main characteristics of flammable atmosphere (size concentration turbulence…) shall be well-known. This article presents an experimental study on accidental hydrogen releases and dispersion into an enclosure of 4 m3 (2 m x 2 m x 1 m). Different release points are studied: two circular releases of 1 and 3 mm and a system to create ring-shaped releases. The releases are operated with a pressure between 10 and 40 bars in order to be close to the process conditions. Different positions of the release inside the enclosure i.e. centred on the floor or along a wall are also studied. A specific effort is made to characterize the turbulence in the enclosure during the releases. The objectives of the experimental study are to understand and quantify the mechanisms of formation of the explosive atmosphere taking into account the geometry and position of the release point and the confinement. Those experimental data are analyzed and compared with existing models and could bring some new elements to improve them.
Removing the Disrupting Wind Effect in Single Vented Enclosure Exposed to External Wind
Oct 2015
Publication
We are addressing hydrogen release into a single-vented facility with wind blowing onto the opposite side of the vent wall. Earlier work based on tests performed by HSL with wind (within the HyIndoor project) and comparative CFD simulations with and without wind ([1]within the H2FC project) has shown that the hydrogen concentrations inside the enclosure are increased compared to the case with no wind. This was attributed to the fact that wind is disrupting the passive ventilation. The present work is based on the GAMELAN tests (within the HyIndoor project) performed with one vent and no wind. For this enclosure simulations were performed with and without wind and reproduced the disrupting wind effect. In order to remove this effect and enhance the ventilation additional simulations were performed by considering different geometrical modifications near the vent. A simple geometrical layout around the vent is here proposed that leads to elimination of the disrupting wind effect. The analysis has been performed using the ADREA-HF code earlier validated both for the HSL and the GAMELAN tests. The current work was performed partly within HyIndoor project
Sample Scale Testing Method to Prevent Collapse of Plastic Liners in Composite Pressure Vessels
Sep 2017
Publication
Type IV pressure vessels are commonly used for hydrogen on-board stationary or bulk storages. When pressurised hydrogen permeates through the materials and solves into them. Emptying then leads to a difference of pressure at the interface between composite and liner possibly leading to a permanent deformation of the plastic liner called “collapse” or “buckling”. This phenomenon has been studied through French funded project Colline allowing to better understand its initiation and long-term effects. This paper presents the methodology followed using permeation tests hydrogen decompression tests on samples and gas diffusion calculation in order to determine safe operating conditions such as maximum flow rate or residual pressure level.
In Situ X-ray Absorption Spectroscopy Study on Water Formation Reaction of Palladium Metal Nanoparticle Catalysts
Oct 2015
Publication
Proper management of hydrogen gas is very important for safety security of nuclear power plants. Hydrogen removal by water formation reaction on a catalyst is one of the candidates for creating hydrogen free system. We observed in situ and time-resolved structure change of palladium metal nanoparticle catalyst during the water formation reaction by using X-ray absorption spectroscopy technique. A poisoning effect by carbon monoxide on catalytic activity was also studied. We have found that the creation of oxidized surface layer on palladium metal nanoparticles plays an important role for the water formation reaction process.
Experimental Study on Accumulation of Helium Released into a Semi-confined Enclosure without Ventilation
Sep 2019
Publication
This paper examines the helium dispersion behaviour in a 16.6 m3 enclosure with a small opening in the floor and distributed leaks along the edges. Helium a simulant for hydrogen was injected near the center of the floor with an injection rate ranging from 2 to 50 standard liters per minute (Richardson number of 0.3–134) through an upward-facing nozzle. In a short-term transient the helium distribution predicted with the models of Baines & Turner (1969) and Worster & Huppert (1983) matched the measured distributions reasonably well. In a long-term transient the vertical helium profile always reached a steady state which consisted of a homogenous layer at the top overlaying a stratified layer at the bottom. The helium transients in the uniform layer predicted with the models of Lowesmith (2009) and Prasad & Yang (2010) assuming a vent was located in the ceiling were in good agreement with the measured transients.
A Chicken and Egg Situation: Enhancing Emergency Service Workers' Knowledge of Hydrogen
Sep 2021
Publication
This paper reports on the results of interviews conducted with 21 representatives from emergency services organisations within Australia and New Zealand. With a relative emergent industry such as future fuels a chicken and egg situation does emerge with regards to how much training needs to be in place in advance of large-scale industry development or not. These respondents were employed in a variety of roles being directly involved in research and training of emerging technologies frontline operational managers and other senior roles across the emergency services sector. Participants' responses to a series of questions were able to provide insights into the state of knowledge and training requirements within their organisations in relation to hydrogen and other future fuels. The findings suggest that formal and informal processes currently exist to support the knowledge development and transferal around the adoption of hydrogen and other future fuels. From the interviews it became clear that there are a number of processes that have emerged from the experiences gained through the implementation of rooftop solar PV and battery storage that provide some background context for advancing future fuels information across the sector. Because safety is a critical component for securing a social licence to operate engagement and knowledge sharing with any representatives from across this sector will only help to build confidence in the industry. Similarly because interviewees were very keen to access information they expressed a clear willingness to learn more through more formalised relationships rather than an ad hoc information seeking that has been employed to date. The presentation will identify key recommendations and also highlight the importance of QR Codes in the emergency responder landscape. Implications for industry and policy makers are discussed.
Study of Hydrogen Enriched Premixed Flames
Sep 2005
Publication
In the present paper the theoretical study of the un-stretched laminar premixed flames of hydrogen-methane mixtures is carried out by using the detailed reaction mechanism GRI-Mech 3.0 implemented in the CHEMKIN software to find out the effect of hydrogen addition on the hybrid fuel burning velocity. The model results show that the laminar burning velocity of the hydrogen-methane mixtures is not the linear regression of those of the pure fuels since it results substantially less than the proportional averaging of the values for the fuel constituents. Moreover the effect of hydrogen addition in terms of enhancement of the mixture laminar burning velocity with respect to the methane is relevant only at very high values of the hydrogen content in the hybrid mixtures (> 70 % mol.). The performed sensitivity analysis shows that these results can be attributed to kinetics and in particular to the concentration of H radicals: depending on the hydrogen content in the fuels mixture the production of the H radicals can affect the limiting reaction step for methane combustion. Two regimes are identified in the hydrogen-methane combustion. The first regime is controlled by the methane reactivity the hydrogen being not able to significantly affect the laminar burning velocity (< 70 % mol.). In the second regime the hydrogen combustion has a relevant role as its high content in the hybrid fuel leads to a significant H radicals pool thus enhancing the reaction rate of the more slowly combusting methane.
Vented Hydrogen-air Explosion in a Small Obstructed Rectangular Container- effect of the Blockage Ratio
Sep 2019
Publication
The explosion venting is an effective way to reduce hydrogen-air explosion hazards but the explosion venting has been hardly touched in an obstructed container. Current experiments focused on the effects of different blockage ratios on the explosion venting in a small obstructed rectangular container. Experimental results show that three overpressure peaks are formed in the case with the obstacle while only two can be observed in the case of no obstacle. The obstacle blockage ratio has a significant influence on the peak overpressure induced by the obstacle-acoustic interactions but it has an ignorable effect on the peak overpressure caused by the rupture of the vent film. The obstacle-induced overpressure peak first increases and then decreases with the increase of the blockage ratio. In addition all overpressure peaks inside the container decreases with the increase of the vent area and its appearance time is relatively earlier for larger vent area.
Development of a Flashback Correlation for Burner-stabilized Hydrogen-air Premixed Flames
Feb 2022
Publication
With a growing need for replacing fossil fuels with cleaner alternatives hydrogen has emerged as a viable candidate for providing heat and power. However stable and safe combustion of hydrogen is not simple and as such a number of key issues have been identified that need to be understood for a safe design of combustion chambers. One such issue is the higher propensity of hydrogen flames to flashback compared to that for methane flames. The flashback problem is coupled with higher burner temperatures that could cause strong thermal stresses in burners and could hinder their performance. In order to systematically investigate flashback in premixed hydrogen-air flames for finding a global flashback criteria in this study we use numerical simulations as a basic tool to study flashback limits of slit burners. Flashback limits are found for varying geometrical parameters and equivalence ratios and the sensitivity of each parameter on the flashback limit and burner temperatures are identified and analyzed. It is shown that the conventional flashback correlation with critical velocity gradient does not collapse the flashback data as it does not take into account stretch induced preferential diffusion effects. A new Karlovitz number definition is introduced with physical insights that collapses the flashback data at all tested conditions in an excellent manner.
Hydrogen Safety Aspects Related to High Pressure - PEM Water Electrolysis
Sep 2007
Publication
Polymer electrolyte membrane (PEM) water electrolysis has demonstrated its potentialities in terms of cell efficiency (energy consumption ≈ 4.0-4.2 kW/Nm3 H2) and gas purity (> 99.99% H2). Current research activities are aimed at increasing operating pressure up to several hundred bars for direct storage of hydrogen in pressurized vessels. Compared to atmospheric pressure electrolysis high-pressure operation yields additional problems especially with regard to safety considerations. In particular the rate of gases (H2 and O2) cross-permeation across the membrane and their water solubility both increase with pressure. As a result gas purity is affected in both anodic and cathodic circuits and this can lead to the formation of explosive gas mixtures. To prevent such risks two different solutions reported in this communication have been investigated. First the chemical modification of the solid polymer electrolyte in order to reduce cross-permeation phenomena. Second the use of catalytic H2/O2 recombiners to maintain H2 levels in O2 and O2 levels in H2 at values compatible with safety requirements.
Simulation Analysis on the Risk of Hydrogen Releases and Combustion in Subsea Tunnels
Oct 2015
Publication
Hydrogen is considered to be a very promising potential energy carrier due to its excellent characteristics such as abundant resources high fuel value clean and renewable. Its safety features greatly influence the potential use. Several safety problems need to be analyzed before using in transportation industry. With the development of the tunnel transportation technology the safe use of hydrogen in tunnels will receive a lot of research attentions. In this article the risk associated with hydrogen release from onboard high-pressure vessels and the induced combustion in tunnels was analyzed using the Partially Averaged Navier–Stokes (PANS) turbulence model. The influences of the tunnel ventilation facilities on the hydrogen flow characteristics and the flammable hydrogen cloud sizes were studied. The tunnel layouts were designed according to the subsea tunnel. And a range of longitudinal ventilation conditions had been considered to investigate the hydrogen releases and the sizes of the flammable hydrogen cloud. Then the hydrogen combustion simulation was carried out after the fixed leaking time. The overpressures induced after the ignition of leaking hydrogen were studied. The influences of ventilation and ignition delay time on the overpressure were also investigated. The main aim was to research the phenomena of hydrogen releases and combustion risk inside subsea tunnels and to lay the foundation of risk assessment methodology developed for hydrogen energy applications on transportation.
A Barrier Analysis of a Generic Hydrogen Refuelling Station
Sep 2009
Publication
Any technical installation need appropriate safety barriers installed to prevent or mitigate any adverse effects concerning people property and environment. In this context a safety barrier is a series of elements each consisting of a technical system or human action that implement a planned barrier function to prevent control or mitigate the propagation of a condition or event into an undesired condition or event. This is also important for new technologies as hydrogen refuelling stations being operated at very high pressures up to 900bar. In order to establish the needed barriers a hazard identification of the installation has to be carried out to identify the possible hazardous events. In this study this identification was done using the generic layout of a future large hydrogen refuelling station that has been developed by the EU NoE HySafe. This was based on experiences with smaller scale refuelling stations that has been in operation for several years e.g. being used in the former CUTE and ECTOS projects. Using this approach the object of the study is to support activities to further improve the safety performance of future larger refuelling stations. This will again help to inform the authorities and the public to achieve a proper public awareness and to support building up a realistic risk and safety perception of the safety on such future refuelling stations. In the second step the hazardous events that may take place and the barriers installed to stop hazards and their escalation are analysed also using in-house developed software to model the barriers and to quantify their performance. The paper will present an overview and discuss the state-of-the-art of the barriers established in the generic refuelling station.
Materials Considerations in Hydrogen Production
Sep 2007
Publication
Correct selection and application of materials is essential to ensure safety and economy in production transportation and storage of hydrogen. There are several sources of materials challenges related to hydrogen. Established component producers may have limited experience in this specific field. Process developments may involve new process conditions with new demands on the materials. Further new materials will be added to the engineering toolbox to be used. The behaviour of these materials for hydrogen service may need additional documentation. Finally focus on hydrogen susceptibility and hydrogen damages alone may take away awareness of other subjects as trace elements by-products and change in raw materials which may be of as high importance for safety and quality. This overview of challenges and recommendations is made with emphasis on water electrolysis.
Experimental Study on a Hydrogen Stratification Induced by PARs Installed in a Containment
Oct 2020
Publication
Hydrogen can be produced in undesired ways such as a high temperature metal oxidation during an accident. In this case the hydrogen must be carefully managed. A hydrogen mitigation system (HMS) should be installed to protect a containment of a nuclear power plant (NPP) from hazards of hydrogen produced by an oxidation of the fuel cladding during a severe accident in an NPP. Among hydrogen removal devices passive auto-catalytic recombiners (PARs) are currently applied to many NPPs because of passive characteristics such as not requiring a power supply nor an operators’ manipulations. However they offer several disadvantages resulting in issues related to hydrogen control by PARs. One of the issues is a hydrogen stratification in which hydrogen is not well-mixed in a compartment due to the high temperature exhaust gas of PARs and accumulation in the lower part. Therefore experimental simulation on hydrogen stratification phenomenon by PARs is required. When the hydrogen stratification by PARs is observed in the experiment the verification and improvement of a PAR analysis model using the experimental results can be performed and the hydrogen removal characteristics by PARs installed in an NPP can be evaluated using the improved PAR model. View Full-Text
A Temperature Controlled Mechanical Test Facility to Ensure Safe Materials Performance in Hydrogen at 1000 Bar
Sep 2007
Publication
Increasingly car manufacturers are turning to high pressure hydrogen storage for on-board power applications. Many prototypes use costly materials and fabrication methods such as Type 316L austenitic stainless steel and processes such as TIG (GTA) welding. There is a need to move to less expensive options without compromising safety to assist in developing economic vehicles. It is important that the behaviour of new/modified materials and joints (including those fabricated by new technologies) is understood at anticipated service temperatures and hydrogen pressure as the consequences of poor material choice could be severe. The greatest detrimental effect of gaseous hydrogen on the mechanical properties of metallic materials is commonly observed under conditions of dynamic plastic strain. Under such conditions an atomically clean surface is produced where hydrogen molecules will dissociate and penetrate the material. Thus static load test methods with hydrogen charging are not reliable for engineering data generation. To meet the need for dynamically straining material in a pressurised hydrogen environment TWI has developed a facility to load specimens in a high pressure environment for tensile toughness and fatigue testing. The design of this has involved a number of innovative steps. This paper outlines the requirements and the design and construction issues that were encountered when installing a facility which can not only perform tests at up to 1000bar (100MPa) but also for temperatures between –150°C to +85°C.
Risk Analysis of the Storage Unit in Hydrogen Refuelling Station
Sep 2007
Publication
Nowadays consumer demand for local and global environmental quality in terms of air pollution and in particular greenhouse gas emissions reduction may help to drive to the introduction of zero emission vehicles. At this regard the hydrogen technology appears to have future market valuablepotential. On the other hand the use of hydrogen vehicles which requires appropriate infrastructures for production storage and refuelling stages presents a lot of safety problems due to the peculiar chemicophysical hydrogen characteristics. Therefore safe at the most practices are essential for the successful proliferation of hydrogen vehicles. Indeed to avoid limit hazards it is necessary to implement practices that if early adopted in the development of a fuelling station project can allow very low environmental impact safety being incorporated in the project itself. Such practices generally consist in the integrated use of Failure Mode and Effect Analysis (FMEA) HAZard OPerability (HAZOP) and Fault Tree Analysis (FTA) which constitute well established standards in reliability engineering. At this regard however a drawback is the lack of experience and the scarcity of the relevant data collection. In this work we present the results obtained by the integrated use of FMEA HAZOP and FTA analyses relevant for the moment the high-pressure storage equipment in a hydrogen gas refuelling station. The study that is intended to obtain elements for improving safety of the system can constitute a basis for further more refined works.
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