Safety
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.
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