Safety
Explosion Characteristics of Hydrogen-air and Hydrogen-Oxygen Mixtures at Elevated Pressures
Sep 2005
Publication
An essential problem for the operation of high pressure water electrolyzers and fuel cells is the permissible contamination of hydrogen and oxygen. This contamination can create malfunction and in the worst case explosions in the apparatus and gas cylinders. In order to avoid dangerous conditions the exact knowledge of the explosion characteristics of hydrogen/air and hydrogen/oxygen mixtures is necessary. The common databases e.g. the CHEMSAFE® database published by DECHEMA BAM and PTB contains even a large number of evaluated safety related properties among other things explosion limits which however are mainly measured according to standard procedures under atmospheric conditions.<br/>Within the framework of the European research project “SAFEKINEX” and other research projects the explosion limits explosion pressures and rates of pressure rise (KG values) of H2/air and H2/O2 mixtures were measured at elevated conditions of initial pressures and temperatures by the Federal Institute of Materials Research and Testing (BAM). Empirical equations of the temperature influence could be deduced from the experimental values. An anomaly was found at the pressure influence on the upper explosion limits of H2/O2 and H2/air mixtures in the range of 20 bars. In addition explosion pressures and also rates of pressure rises have been measured for different hydrogen concentrations inside the explosion range. Such data are important for constructive explosion protection measures. Furthermore the mainly used standards for the determination of explosion limits have been compared. Therefore it was interesting to have a look at the systematic differences between the new EN 1839 tube and bomb method ASTM E 681-01 and German DIN 51649-1.
Analysis Methodology for Hydrogen Behaviour in Accident Scenarios
Sep 2005
Publication
Hydrogen is not more dangerous than current fossil energy carriers but it behaves differently. Therefore hydrogen specific analyses and countermeasures will be needed to support the development of safe hydrogen technologies. A systematic step-by-step procedure for the mechanistic analysis of hydrogen behaviour and mitigation in accidents is presented. The procedure can be subdivided into four main parts:<br/>1) 3D modelling of the H2-air mixture generation<br/>2) hazard evaluation for this mixture based on specifically developed criteria for flammability flame acceleration and detonation on-set<br/>3) numerical simulation of the appropriate combustion regime using verified 3D-CFD codes and<br/>4) consequence analysis based on the calculated pressure and temperature loads.
Spontaneous Ignition of Hydrogen Leaks, a Review of Postulated Mechanisms
Sep 2005
Publication
Over the last century there have been reports of high pressure hydrogen leaks igniting for no apparent reason and several ignition mechanisms have been proposed. Although many leaks have ignited there are also reported leaks where no ignition has occurred. Investigations of ignitions where no apparent ignition source was present have often been superficial with a mechanism postulated which whilst appearing to satisfy the conditions prevailing at the time of the release simply does not stand up to rigorous scientific analysis. Some of these proposed mechanisms have been simulated in a laboratory under superficially identical conditions and appear to be rigorous and scientific but the simulated conditions often do not have the same large release rates or quantities mainly because of physical constraints of a laboratory. Also some of the release scenarios carried out or simulated in laboratories are totally divorced from the realistic situation of most actual leaks. Clearly there are gaps in the knowledge of the exact ignition mechanism for releases of hydrogen particularly at the high pressures likely to be involved in future storage and use. Mechanisms which have been proposed in the past are the reverse Joule-Thomson effect; electrostatic charge generation; diffusion ignition; sudden adiabatic compression; and hot surface ignition. Of these some have been characterized by means of computer simulation rather than by actual experiment and hence are not validated. Consequently there are discrepancies between the theories releases known to have ignited and releases which are known to have not ignited. From this postulated ignition mechanisms which are worthy of further study have been identified and the gaps in information have been highlighted. As a result the direction for future research into the potential for ignition of hydrogen escapes has been identified.
Validation of Flacs-Hydrogen CFD Consequence Prediction Model Against Large Scale H2 Explosion Experiments in the Flame Facility
Sep 2005
Publication
The FLACS CFD-tool for consequence prediction has been developed continuously since 1980. The initial focus was explosion safety on offshore oil platforms in recent years the tool is also applied to study dispersion hydrogen safety dust explosions and more. A development project sponsored by Norsk Hydro Statoil and Ishikawajima Heavy Industries (IHI) was carried out to improve the modelling and validation of hydrogen dispersion and explosions. In this project GexCon carried out 200 small-scale experiments on dispersion and explosion with H2 and mixtures with H2 and CO or N2. Experiments with varying confinement congestion concentration and ignition location were performed. Since the main purpose of the tests was to produce good validation data all tests were simulated with the FLACS-HYDROGEN tool. The simulations confirmed the ability to predict explosions effects for the wide range of scenarios studied. A few examples of comparisons will be shown. To build confidence in a consequence prediction model it is important that the scales used for validation are as close as possible to reality. Since the hazard to people and facilities and the risk will generally increase with scale validation against large-scale experiments is important. In the 1980s a series of large-scale explosion experiments with H2 was carried out in the Sandia FLAME facility and sponsored by the US Nuclear Regulatory Commission. The FLAME facility is a 30.5m x 1.83m x 2.44m channel tests were performed with H2 concentrations from 7% to 30% with varying degree of top venting (0% 13% and 50%) and congestion (with or without baffles blocking 33% of the channel cross-section). A wide range of flame speeds and overpressures were observed. Comparisons are made between FLACS simulations and FLAME tests. The main conclusion from this validation study is that the precision when predicting H2 explosion consequences with FLACS has been improved to a very acceptable level
An Inter-Comparison Exercise on the Capabilities of CFD Models to Predict the Short and Long Term Distribution and Mixing of Hydrogen in a Garage
Sep 2007
Publication
Alexandros G. Venetsanos,
E. Papanikolaou,
J. García,
Olav Roald Hansen,
Matthias Heitsch,
Asmund Huser,
Wilfried Jahn,
Jean-Marc Lacome,
Thomas Jordan,
H. S. Ledin,
Dmitry Makarov,
Prankul Middha,
Etienne Studer,
Andrei V. Tchouvelev,
Franck Verbecke,
M. M. Voort,
Andrzej Teodorczyk and
M. A. Delichatsios
The paper presents the results of the CFD inter-comparison exercise SBEP-V3 performed within the activity InsHyde internal project of the HYSAFE network of excellence in the framework of evaluating the capability of various CFD tools and modelling approaches in predicting the physical phenomena associated to the short and long term mixing and distribution of hydrogen releases in confined spaces. The experiment simulated was INERIS-TEST-6C performed within the InsHyde project by INERIS consisting of a 1 g/s vertical hydrogen release for 240 s from an orifice of 20 mm diameter into a rectangular room (garage) of dimensions 3.78x7.2x2.88 m in width length and height respectively. Two small openings at the front and bottom side of the room assured constant pressure conditions. During the test hydrogen concentration time histories were measured at 12 positions in the room for a period up to 5160 s after the end of release covering both the release and the subsequent diffusion phases. The benchmark was organized in two phases. The first phase consisted of blind simulations performed prior to the execution of the tests. The second phase consisted of post calculations performed after the tests were concluded and the experimental results made available. The participation in the benchmark was high: 12 different organizations (2 non-HYSAFE partners) 10 different CFD codes and 8 different turbulence models. Large variation in predicted results was found in the first phase of the benchmark between the various modelling approaches. This was attributed mainly to differences in turbulence models and numerical accuracy options (time/space resolution and discretization schemes). During the second phase of the benchmark the variation between predicted results was reduced.
Canadian Hydrogen Safety Program.
Sep 2005
Publication
This paper discusses the rationale structure and contents of the Canadian Hydrogen Safety Program developed by the Codes & Standards Working Group of the Canadian Transportation Fuel Cell Alliance consisting of representatives from industry academia government and regulators. The overall program objective is to facilitate acceptance of the products services and systems of the Canadian Hydrogen Industry by the Canadian Hydrogen Stakeholder Community to facilitate trade ensure fair insurance policies and rates ensure effective and efficient regulatory approval procedures and to ensure that the interests of the general public are accommodated. The Program consists of four projects including Comparative Quantitative Risk Assessment of Hydrogen and Compressed Natural Gas (CNG) Refuelling Stations; Computational Fluid Dynamics (CFD) Modelling Validation Calibration and Enhancement; Enhancement of Frequency and Probability Analysis and Consequence Analysis of Key Component Failures of Hydrogen Systems; and Fuel Cell Oxidant Outlet Hydrogen Sensor Project. The Program projects are tightly linked with the content of the IEA Task 19 Hydrogen Safety. The Program also includes extensive (destructive and non-destructive) testing of hydrogen components.
Hydrogen Refueling Stations: Safe Filling Procedures
Sep 2005
Publication
Safety is a high priority for a hydrogen refueling station. Here we propose a method to safely refuel a vehicle at optimised speed of filling with minimum information about it. Actually we identify two major risks during a vehicle refuelling: over filling and overheating. These two risks depend on the temperature increase in the tank during refuelling. But the inside temperature is a difficult information to get from the station point of view. It assumes a temperature sensor in a representative place of the tank and an additional connection between the vehicle and the station for data exchange. The refuelling control may not depend on this parameter only. Therefore out objective was to effectively control the filling particularly to avoid the two identified risks independently of optional and safety redundant information from the vehicle. For that purpose we defined a maximum filling pressure which corresponds to the most severe following conditions: if the maximum temperature is reached in the tank or if the maximum capacity is reached in the tank. This maximum pressure depends on a few filling parameters which are easily available. The method and its practical applications are depicted.
Effect of Carbon Dioxide, Argon and Hydrocarbon Fuels on the Stability of Hydrogen Jet Flames
Sep 2005
Publication
Experimental studies were carried out to examine the lift-off and blow-out stability of H2/CO2 H2/Ar H2/C3H8 and H2/CH4 jet flames. The experiments were carried out using a burner with a 2mm inner diameter. The flame structures were recorded by direct filming and also by a schlieren apparatus. The experiments showed that the four gases affected the lift-off and blow-out stability of the hydrogen differently. The experiments showed that propane addition to an initially attached flame always produced lifted flame and the flame was blown out at higher jet velocity. The blow-out velocity decreased as the increasing in propane concentration. Direct blow-off of hydrogen/propane was never observed. Methane addition resulted in a relatively stable flame comparing with the carbon dioxide and propane addition. Comparisons of the stability of H2/C3H8 H2/CH4 and H2/CO2 flames showed that H2/C3H8 produced the highest lift-off height. Propane is much more effective in lift-off and blow out hydrogen flames. The study carried out a chemical kinetic analysis of H2/CO2 H2/Ar H2/C3H8 and H2/CH4 flames for a comparison of effect of chemical kinetics on flame stability.
Development of Hydrogen Sensors and Recombiners
Sep 2005
Publication
Hydrogen energy is very promising as it ensures a high efficiency and ecological cleanliness of energy conversion. The goal of the present work is to provide the analysis of hydrogen safety aspects and to prescribe methods of safety operation with hydrogen. The authors conducted a hazard analysis of hydrogen operation and storage in comparison with other fuels. Good ventilation is the main hydrogen operation requirement. Besides an effective way of protection against propagation of hazards (for instance leaks) is neutralization of dangerous hydrogen-air mixtures by a method of controlled catalytic combustion inside special devices so-called recombiners [1-3]. The basis of these devices is a high porosity cell material (HPCM) activated by platinum deposition. Apart from recombiners HPCM was also applied for development of hydrogen detectors intended for measurement and analysis of hydrogen concentration for hydrogen-driven transport and objects of hydrogen infrastructure (including vapor-air media at high pressure and temperatures). A system of hydrogen safety based on hydrogen detectors and hydrogen catalytic recombiners was developed. Experimental and theoretical studies of hydrogen combustion processes heat- and mass transfer and also gas flows in catalytic-activated HPCM allowed for a design optimization of recombiners and their location. Pilot hydrogen detectors and hydrogen catalytic recombiners were fabricated and their laboratory tests were successfully performed. Thus it was indicated that on condition of following the appropriate passive and active safety measures hydrogen is just as safe as the other fuels. This conclusion represents another incentive for a transition to the hydrogen energy.
Wide Area and Distributed Hydrogen Sensors
Sep 2009
Publication
Recent advances in optical sensors show promise for the development of new wide area monitoring and distributed optical network hydrogen detection systems. Optical hydrogen sensing technologies reviewed here are: 1) open path Raman scattering systems 2) back scattering from chemically treated solid polymer matrix optical fiber sensor cladding; and 3) schlieren and shearing interferometry imaging. Ultrasonic sensors for hydrogen release detection are also reviewed. The development status of these technologies and their demonstrated results in sensor path length low hydrogen concentration detection ability and response times are described and compared to the corresponding status of hydrogen spot sensor network technologies.
Modeling of Hydrogen Flame Dynamics in Narrow Gap with Bendable Walls
Sep 2017
Publication
A concept of volume porosity together with model of moving walls were elaborated and implemented into the COM3D code. Additionally to that a support of real-time data exchange with finite-element code ABAQUS - © Dassault Systèmes provided possibility to perform simulations of the gas-dynamic simultaneously with geometrical adaptation of environmental conditions. Based on the data obtained in the KIT combustion experiments in narrow gaps the authors performed a series of the simulation on the combustion in the corresponding conditions. Obtained numerical results demonstrated good agreement with the observed experimental data. These data were also compared with those obtained in the simulation without wall bending where simulation showed considerably different combustion regime. Application of the developed technique allows to obtain results unreachable without accounting on wall displacements which demonstrates massive over-estimation of the pressures observed during flame propagation.
Hydrogen Compatibility of Austenitic Stainless Steel Tubing and Orbital Tube Welds
Sep 2013
Publication
Refueling infrastructure for use in gaseous hydrogen powered vehicles requires extensive manifolding for delivering the hydrogen from the stationary fuel storage at the refueling station to the vehicle as well as from the mobile storage on the vehicle to the fuel cell or combustion engine. Manifolds for gas handling often use welded construction (as opposed to compression fittings) to minimize gas leaks. Therefore it is important to understand the effects of hydrogen on tubing and tubing welds. This paper provides a brief overview of on-going studies on the effects of hydrogen precharging on the tensile properties of austenitic stainless tubing and orbital tube welds of several austenitic stainless steels.
Safety Design of Compressed Hydrogen Trailers with Composite Cylinders
Sep 2013
Publication
Compressed hydrogen is delivered by trailers in steel cylinders at 19.6 MPa in Japan. Kawasaki Heavy Industries Ltd. developed two compressed hydrogen trailers with composite cylinders in collaboration with JX Nippon Oil in a project of the New Energy and Industrial Technology Development Organization (NEDO).<br/>The first trailer which was the first hydrogen trailer with composite cylinder in Japan has 35 MPa cylinders and the second trailer has 45 MPa cylinders. These trailers have been operated transporting hydrogen and feedstock to hydrogen refuelling stations without the accident. This paper describes the safety design including compliance with regulations the influence of vibrations and safety verification in case of a collision.
Quantifying the Hydrogen Embrittlement of Pipeline Steels for Safety Considerations
Sep 2011
Publication
In a near future with an increasing use of hydrogen as an energy vector gaseous hydrogen transport as well as high capacity storage may imply the use of high strength steel pipelines for economical reasons. However such materials are well known to be sensitive to hydrogen embrittlement (HE). For safety reasons it is thus necessary to improve and clarify the means of quantifying embrittlement. The present paper exposes the changes in mechanical properties of a grade API X80 steel through numerous mechanical tests i.e. tensile tests disk pressure test fracture toughness and fatigue crack growth measurements WOL tests performed either in neutral atmosphere or in high-pressure of hydrogen gas. The observed results are then discussed in front of safety considerations for the redaction of standards for the qualification of materials dedicating to hydrogen transport.
State-of-the-Art and Research Priorities in Hydrogen Safety
Sep 2013
Publication
On October 16-17 2012 the International Association for Hydrogen Safety (HySafe) in cooperation with the Institute for Energy and Transport of the Joint Research Centre of the European Commission (JRC IET Petten) held a two-day workshop dedicated to Hydrogen Safety Research Priorities. The workshop was hosted by Federal Institute for Materials Research and Testing (BAM) in Berlin Germany. The main idea of the Workshop was to bring together stakeholders who can address the existing knowledge gaps in the area of the hydrogen safety including identification and prioritization of such gaps from the standpoint of scientific knowledge both experimental and theoretical including numerical. The experience highlighting these gaps which was obtained during both practical applications (industry) and risk assessment should serve as reference point for further analysis. The program included two sections: knowledge gaps as they are addressed by industry and knowledge gaps and state-of-the-art by research. In the current work the main results of the workshop are summarized and analysed.
Numerical Study of Spontaneous Ignition in Pressurized Hydrogen Release Through a Length of Tube with Local Contraction
Sep 2011
Publication
Numerical investigations have been conducted on the effect of the internal geometry of a local contraction on the spontaneous ignition of pressurized hydrogen release through a length of tube using a 5th-order WENO scheme. A mixture-averaged multi-component approach was used for accurate calculation of molecular transport. The auto-ignition and combustion chemistry were accounted for using a 21-step kinetic scheme. It is found that a local contraction can significantly facilitate the occurrence of spontaneous ignition by producing elevated flammable mixture and enhancing turbulent mixing from shock formation reflection and interaction. The first ignition kernel is observed upstream the contraction. It then quickly propagates along the contact interface and transits to a partially premixed flame due to the enhanced turbulent mixing. The partially premixed flames are highly distorted and overlapped with each other. Flame thickening is observed which is due to the merge of thin flames. The numerical predictions suggested that sustained flames could develop for release pressure as low as 25 bar. For the release pressure of 18 bar spontaneous ignition was predicted but the flame was soon quenched. To some extent this finding is consistent with Dryer et al.'s experimental observation in that the minimum release pressure required to induce a spontaneous ignition for the release through a tube with internal geometries is only 20.4 bar.
Hydrogen Storage: Recent Improvements and Industrial Perspectives
Sep 2019
Publication
Efficient storage of hydrogen is crucial for the success of hydrogen energy markets (early markets as well as transportation market). Hydrogen can be stored either as a compressed gas a refrigerated liquefied gas a cryo-compressed gas or in hydrides. This paper gives an overview of hydrogen storage technologies and details the specific issues and constraints related to the materials behaviour in hydrogen and conditions representative of hydrogen energy uses. It is indeed essential for the development of applications requiring long-term performance to have good understanding of long-term behaviour of the materials of the storage device and its components under operational loads.
Self-Ignition of Hydrogen Jet Fires By Electrostatic Discharge Induced By Entrained Particulates
Sep 2011
Publication
The potential for particulates entrained in hydrogen releases to generate electrostatic charge and induce electrostatic discharge ignitions was investigated. A series of tests were performed in which hydrogen was released through a 3.75-mm-diameter orifice from an initial pressure of 140 bar. Electrostatic field sensors were used to characterize the electrification of known quantities of iron oxide particulates deliberately entrained in the release. The ignition experiments focused on using charged particulates to induce spark discharges from isolated conductors and corona discharges. A total of 12 ignition events were observed. The results show that electrification of entrained particulates is a viable self-ignition mechanism of hydrogen releases.
Risk Based Safety Distances for Hydrogen Refuelling Stations
Sep 2017
Publication
This paper introduces a risk-based methodology for hydrogen refuelling stations. Momentarily four stations are present in the Netherlands. This number is expected to increase to around twenty in the next years. For these stations a quantitative risk analysis (QRA) must be carried out to account for spatial planning. The presented method identifies the loss of containment scenarios and failure frequencies. Additionally the results of this study may be used in legislative context in the form of fixed generic safety distances. Using the risk analysis tool Safeti-NL safety distances are determined for three different kinds of hydrogen refuelling stations distinguished by the supply method of the hydrogen. For the hydrogen refuelling stations a maximum safety distance of 35 m is calculated. However despite the relatively small safety distances the maximum effect distances (distance to 1% lethality) can be very large especially for stations with a supply and storage of liquid hydrogen. The research was overseen by an advisory committee which also provided technical information on the refuelling stations.
What is an Explosion?
Sep 2013
Publication
We are going to focus our discussion on “Explosions” its definitions from a scientific regulatory and societal perspective. We will point out that as defined these definitions are not consistent and lead to ambiguity. Of particular interest to this work is how this current ambiguity affects the emerging Regulation Codes and Standards (RCS) as applied to hydrogen technologies. While this manuscript has its roots in combustion science with extension to both the standard development and regulatory communities for hazards at large the unique behavior of hydrogen in many configurations motivates examining the relevant definitions and language used in these communities. We will point out the ambiguities how this leads to confusion in supporting definitions and how it leads to overly restrictive RCS for hydrogen applications. We will then suggest terminology which is not ambiguous internally self-consistent and allows appropriate RCS to be promulgated to ensure the safety of the public and capital to ensure the correct response of first responders and allow cost effective development of hydrogen technologies in our infrastructure.
A Turbulent Combustion Model for Ignition of Rapidly Expanding Hydrogen Jets
Mar 2013
Publication
A turbulent combustion model based on the Linear Eddy Model for Large Eddy Simulation (LEM- LES) is currently proposed to study self-ignition events of rapidly expanding hydrogen jets. The model is a one-dimensional treatment of a diffusion-reaction system within each multi-dimensional LES cell. This reduces the expense of solving a complete multi-dimensional problem while preserving micro-scale hotspots and their effects on ignition. The current approach features a Lagrangian description of fluid particles on the sub-grid for increased accuracy. Also Adaptive Mesh Refinement (AMR) is implemented for increased computational efficiency. In this paper the model is validated for various inviscid laminar 1-D mixing and ignition problems shock tube problems flames and detonations.
Experimental and Numerical Study on Spontaneous Ignition of Hydrogen-methane Jets in Air
Sep 2013
Publication
This paper is an investigation of the spontaneous ignition process of high-pressure hydrogen and hydrogen-methane mixtures injected into air. The experiments were conducted in a closed channel filled with air where the hydrogen or hydrogen–methane mixture depressurised through different tubes (diameters d = 6 10 and 14 mm and lengths L = 10 25 40 50 75 and 100 mm). The methane addition to the mixture was 5% and 10% vol. The results showed that only 5% methane addition may increase even 2.67 times the pressure at which the mixture may ignite in comparison to the pressure of the pure hydrogen flow. The 10% of methane addition did not provide an ignition for burst pressures up to 15.0 MPa in the geometrical configuration with the longest tube (100 mm). Additionally the simulations of the experimental configuration with pure hydrogen were performed with the use of KIVA numerical code with full kinetic reaction mechanism.
Experimental Investigation of Nozzle Aspect Ratio Effects on Under Expanded Hydrogen Jet Release Characteristics
Sep 2013
Publication
Most experimental investigations of underexpanded hydrogen jets have been limited to circular nozzles in an attempt to better understand the fundamental jet-exit flow physics and model this behaviour with pseudo source models. However realistic compressed storage leak exit geometries are not always expected to be circular. In the present study jet dispersion characteristics from rectangular slot nozzles with aspect ratios from 2 to 8 were investigated and compared with an equivalent circular nozzle. Schlieren imaging was used to observe the jet-exit shock structure while quantitative Planar Laser Rayleigh Scattering was used to measure downstream dispersion characteristics. These results provide physical insight and much needed model validation data for model development.
Pressure Cycling Of Type 1 Pressure Vessels with Gaseous Hydrogen
Sep 2011
Publication
Type 1 steel pressure vessels are commonly used for the transport of pressurized gases including gaseous hydrogen. In the majority of cases these cylinders experience relatively few pressure cycles over their lifetime perhaps in the hundreds. In emerging markets such as hydrogen-powered industrial trucks hydrogen fuel systems are expected to experience thousands of cycles over just a few year period. This study investigates the fatigue life of Type 1 steel pressure vessels by subjecting full- scale vessels to pressure cycles with gaseous hydrogen between nominal pressure of 3.5 and 43.8 MPa. In addition engineered defects were machined on the inside of several pressure vessels for comparison to fatigue crack growth measurements on materials sectioned from these pressure vessels. As-manufactured pressure vessels have sustained >35000 cycles with failure while vessels with machined defects leaked before bursting after 8000 to 15000 pressure cycles. The measured number of cycles to failure in these pressure vessels is two to three times greater than predicted using conservative methods based on fatigue crack growth rates measured in gaseous hydrogen.
Risk Assessment on Life Safety and Financial Loss for Road Accident of Fuel Cell Vehicles
Sep 2017
Publication
Vehicular use of hydrogen is the first attempt to apply hydrogen energy in consumers’ environment in large scale and has raised safety concerns in both public authorities and private bodies such as fire services and insurance companies. This paper analyzes typical accident progressions of hydrogen fuel cell vehicles in a road collision accident. Major hydrogen consequences including impinging jet fires and catastrophic tank ruptures are evaluated separately in terms of accident duration and hazard distances. Results show that in a 70 MPa fuel cell car accident the hazards associated with hydrogen releases would normally last for no more than 1.5 min due to the empty of the tank. For the safety of general public a perimeter of 100 m is suggested in the accident scene if no hissing sound is heard. However the perimeter can be reduced to 10 m once the hissing sound of hydrogen release is heard. Furthermore risks of fatalities injuries and damages are all quantified in financial terms to assess the impacts of the accident. Results show that costs of fatalities and injuries contribute most to the overall financial loss indicating that the insurance premium of fatalities and injuries should be set higher than that of property loss.
Hydrogen Safety Sensor Performance and Use Gap Analysis
Sep 2017
Publication
Hydrogen sensors are recognized as an important technology for facilitating the safe implementation of hydrogen as an alternative fuel and there are numerous reports of a sensor alarm successfully preventing a potentially serious event. However gaps in sensor metrological specifications as well as in their performance for some applications exist. The U.S. Department of Energy (DOE) Fuel Cell Technologies Office published a short list of critical gaps in the 2007 and 2012 Multiyear Project Plans; more detailed gap analyses were independently performed by the Joint Research Centre (JRC) and the National Renewable Energy Laboratory (NREL). There have been however some significant advances in sensor technologies since these assessments including the commercial availability of hydrogen sensors with fast response times (t90 < 1 s which had been an elusive DOE target since 2007) improved robustness to chemical poisons improved selectivity and improved lifetime and stability. These improvements however have not been universal and typically pertain to select platforms or models. Moreover as hydrogen markets grow and new applications are being explored more demands will be imposed on sensor performance. The hydrogen sensor laboratories at NREL and the JRC are currently updating the hydrogen safety sensor gap analysis through direct interaction with international stakeholders in the hydrogen community especially end users. NREL and the JRC are currently organizing a series of workshops (in Europe and the United States) with sensor developers end-users and other stakeholders in 2017 to identify technology gaps and to develop a path forward to address them. One workshop was held on May 10 in Brussels Belgium at the Headquarters of the Fuel Cell and Hydrogen Joint Undertaking. A second workshop is planned at NREL in Golden CO USA. This paper reviews improvements in sensor technologies in the past 5 to 10 years identifies gaps in sensor performance and use requirements and identifies potential research strategies to address the gaps. The outcomes of the Hydrogen Sensors Workshops are also summarized.
Numerical Investigation of Hydrogen Leakage from a High Pressure Tank and its Explosion
Oct 2015
Publication
We numerically investigated the initial behaviour of leakage and diffusion from high-pressure hydrogen storage tank assumed in hydrogen station. First calculations are carried out to validate the present numerical approach and compare with the theoretical distribution of hydrogen mass fraction to the direction which is vertical to the jet direction in the case of hydrogen leaking out from the circular injection port whose diameter is 0.25 mm. Then performing calculations about hydrogen leakage and diffusion behaviour on different tank pressures the effects are examined to reduce damage by gas explosion assumed in the hydrogen station. There is no significant difference in the diffusion distance to the jet direction from a start to 0.2 ms. After 0.2 ms it is seen the difference in the diffusion distance to the jet direction in different pressure. As tank pressures become large the hydrogen diffusion not only to the jet direction but also to the direction which is vertical to the jet direction is remarkably seen. Then according to histories of the percentage of the flammable mass to total one in the space it drastically increases up to 30%2between 0 and 0.05 ms. After 0.05 ms it uniformly increases so it is shown that the explosion risk becomes high over time. The place where mass within flammability range distributes at a certain time is shown. Hydrogen widely diffuses to jet direction and distributes in each case and time. Therefore it is found that when it is assumed that ignition occurs by some sources in place where high-pressure hydrogen is leaked and diffused the magnitude of the explosion damage can be predicted when and where ignition occurs.
Effects of the Injector Direction on the Temperature Distribution During Filling of Hydrogen Tanks
Sep 2017
Publication
The development of the temperature field in hydrogen tanks during the filling process has been investigated with Computational Fluid Dynamics (CFD). Measurements from experiments undertaken at the JRC GasTef facility have been used to develop and validate the CFD modelling strategy; by means of the CFD calculations the effect of the injector direction on the temperature distribution has been analysed. It has been found that the dynamics of the temperature field including the development of potentially detrimental phenomena like thermal stratification and temperature inhomogeneity e.g. hot spots can be significantly affected by the injector orientation.
Hydrogen Emergency Response Training for First Responders
Sep 2011
Publication
The U.S. Department of Energy supports the implementation of hydrogen fuel cell technologies by providing hydrogen safety and emergency response training to first responders. A collaboration was formed to develop and deliver a one-day course that uses a mobile fuel cell vehicle (FCV) burn prop designed and built by Kidde Fire Trainers. This paper describes the development of the training curriculum including the design and operation of the FCV prop; describes the successful delivery of this course to over 300 participants at three training centers in California; and discusses feedback and observations received on the course. Photographs and video clips of the training sessions will be presented.
Determination of Distribution Function Used in Monte Carlo Simulation on Safety Analysis of Hydrogen Vessels
Sep 2019
Publication
The test data of static burst strength and load cycle strength of composite pressure vessels are often described by GAUSSian normal or WEIBULL distribution function to perform safety analyses. The goodness of assumed distribution function plays a significant role in the inferential statistics to predict the population properties by using limited test data. Often GAUSSian and WEIBULL probability nets are empirical methods used to validate the distribution function; Anderson-Darling and Kolmogorov-Smirnov tests are the mostly favorable approaches for Goodness of Fit. However the different approaches used to determine the parameters of distribution function lead mostly to different conclusions for safety assessments.<br/>In this study six different methods are investigated to show the variations on the rates for accepting the composite pressure vessels according to GTR No. 13 life test procedure. The six methods are: a) Norm- Log based method b) Least squares regression c) Weighted least squares regression d) A linear approach based on good linear unbiased estimators e) Maximum likelihood estimation and f) The method of moments estimation. In addition various approaches of ranking function are considered. In the study Monte Carlo simulations are conducted to generate basic populations based on the distribution functions which are determined using different methods. Then the samples are extracted randomly from a population and evaluated to obtain acceptance rate. Here the “populations” and “samples” are corresponding to the burst strength or load cycle strength of the pressure vessels made from composite material and a plastic liner (type 4) for the storage of hydrogen. To the end the results are discussed and the best reliable methods are proposed.
Prediction of Pressure Reduction Rate in 30 m3 Liquid Hydrogen Tank Based on Experimental and Numerical Analysis
Sep 2019
Publication
Liquid hydrogen (LH2) compared to compressed gaseous hydrogen offers advantages for large scale transport and storage of hydrogen with higher densities and potentially better safety performance. Although the gas industry has good experience with LH2 only little experience is available for the new applications of LH2 as an energy carrier. Therefore the European FCH JU funded project PRESLHY conducts pre-normative research for the safe use of cryogenic LH2 in non-industrial settings. The work program consists of a preparatory phase where the state of the art before the project has been summarized and where the experimental planning was adjusted to the outcome of a research priorities workshop. The central part of the project consists of 3 phenomena oriented work packages addressing Release Ignition and Combustion with analytical approaches experiments and simulations. The results shall improve the general understanding of the behaviour of LH2 in accidents and thereby enhance the state-of-the-art what will be reflected in appropriate recommendations for development or revision of specific international standards. The paper presents the status of the project at the middle of its terms.
Influence of Doping Element in Distributed Hydrogen Optical Fiber Densors with Brillouin Scattering
Sep 2013
Publication
Distributed hydrogen optical fiber sensor with Brillouin scattering is an innovative solution to measure hydrogen in harsh environment as nuclear industry. Glass composition is the key point to enhance the sensing parameter of the fiber in the target application. Several optical fiber with different doping element were used for measuring hydrogen saturation. Permeability of optical plays a major role to the kinetic of hydrogen diffusion. Fluorine doped fiber increase the sorption and the desorption of hydrogen.
Lessons Learned from Safety Events
Sep 2011
Publication
The Hydrogen Incident Reporting and Lessons Learned website (www.h2incidents.org) was launched in 2006 as a database-driven resource for sharing lessons learned from hydrogen-related safety events to raise safety awareness and encourage knowledge-sharing. The development of this database its first uses and subsequent enhancements have been described at the Second and Third International Conferences on Hydrogen Safety [1] [2]. Since 2009 continuing work has not only highlighted the value of safety lessons learned but enhanced how the database provides access to another safety knowledge tool Hydrogen Safety Best Practices (http://h2bestpractices.org). Collaborations with the International Energy Agency (IEA) Hydrogen Implementing Agreement (HIA) Task 19 – Hydrogen Safety and others have enabled the database to capture safety event learning’s from around the world. This paper updates recent progress highlights the new “Lessons Learned Corner” as one means for knowledge-sharing and examines the broader potential for collecting analyzing and using safety event information.
Hydrogen Monitoring Requirements in the Global Technical Regulation on Hydrogen and Fuel Cell Vehicles
Oct 2015
Publication
The United Nations Economic Commission for Europe Global Technical Regulation (GTR) Number 13 (Global Technical Regulation on Hydrogen and Fuel Cell Vehicles) is the defining document regulating safety requirements in hydrogen vehicles and in particular fuel cell electric vehicles (FCEVs). GTR Number 13 has been formally adopted and will serve as the basis for the national regulatory standards for FCEV safety in North America (led by the United States) Japan Korea and the European Union. The GTR defines safety requirements for these vehicles including specifications on the allowable hydrogen levels in vehicle enclosures during in-use and post-crash conditions and on the allowable hydrogen emissions levels in vehicle exhaust during certain modes of normal operation. However in order to be incorporated into national regulations that is to be legally binding methods to verify compliance with the specific requirements must exist. In a collaborative program the Sensor Laboratories at the National Renewable Energy Laboratory in the United States and the Joint Research Centre Institute for Energy and Transport in the Netherlands have been evaluating and developing analytical methods that can be used to verify compliance with the hydrogen release requirements as specified in the GTR.
Threshold Stress Intensity Factor for Hydrogen Assisted Cracking of Cr-Mo Steel Used as Stationary Storage Buffer of a Hydrogen Refueling Station
Oct 2015
Publication
In order to determine appropriate value for threshold stress intensity factor for hydrogen-assisted cracking (KIH) constant-displacement and rising-load tests were conducted in high-pressure hydrogen gas for JIS-SCM435 low alloy steel (Cr-Mo steel) used as stationary storage buffer of a hydrogen refuelling station with 0.2% proof strength and ultimate tensile strength equal to 772 MPa and 948 MPa respectively. Thresholds for crack arrest under constant displacement and for crack initiation under rising load were identified. The crack arrest threshold under constant displacement was 44.3 MPa m1/2 to 44.5 MPa m1/2 when small-scale yielding and plane-strain criteria were satisfied and the crack initiation threshold under rising load was 33.1 MPa m1/2 to 41.1 MPa m1/2 in 115 MPa hydrogen gas. The crack arrest threshold was roughly equivalent to the crack initiation threshold although the crack initiation threshold showed slightly more conservative values. It was considered that both test methods could be suitable to determine appropriate value for KIH for this material.
Uncertainties in Risk Assessment of Hydrogen Discharges from Pressurized Storage Vessels Ranging from Cryogenic to Ambient Temperatures
Sep 2013
Publication
Evaluations of the uncertainties resulting from risk assessment tools to predict releases from the various hydrogen storage types are important to support risk informed safety management. The tools have to predict releases from a wide range of storage pressures (up to 80 MPa) and temperatures (at 20K) e.g. the cryogenic compressed gas storage covers pressures up to 35 MPa and temperatures between 33K and 338 K. Accurate calculations of high pressure releases require real gas EOS. This paper compares a number of EOS to predict hydrogen properties typical in different storage types. The vessel dynamics are modelled to evaluate the performance of various EOS to predict exit pressures and temperatures. The results are compared to experimental data and results from CFD calculations.
Strong and Mild Ignition Mechanism behind Reflected Shock Waves in Hydrogen Mixture
Sep 2013
Publication
A reflected shock wave in two-dimensional shock tube is studied numerically using Navier-Stokes equations with the detailed oxy-hydrogen reaction mechanism. The results show detailed process of mild ignition. The interaction between the reflected shock wave and the boundary layer yielded behind the incident shock wave produces clockwise and counter-clockwise vortices. These vortices generate compression waves. The future study related wall conditions (adiabatic or isothermal) will be shown at the conference site.
Socio-economic Analysis and Quantitative Risk Assessment Methodology for Safety Design of Onboard Storage Systems
Sep 2017
Publication
Catastrophic rupture of onboard hydrogen storage in a fire is a safety concern. Different passive e.g. fireproofing materials the thermally activated pressure relief device (TPRD) and active e.g. initiation of TPRD by fire sensors safety systems are being developed to reduce hazards from and associated risks of high-pressure hydrogen storage tank rupture in a fire. The probability of such low-frequency highconsequences event is a function of fire resistance rating (FRR) i.e. the time before tank without TPRD ruptures in a fire the probability of TPRD failure etc. This safety issue is “confirmed” by observed recently cases of CNG tanks rupture due to blocked or failed to operate TPRD etc. The increase of FRR by any means decreases the probability of tank rupture in a fire particularly because of fire extinction by first responders on arrival at an accident scene.<br/>This study of socio-economic effects of safety applies a quantitative risk assessment (QRA) methodology to an example of hydrogen vehicles with passive tank protection system on roads in London.<br/>The risk is defined here through the cost of human loss per fuel cell hydrogen vehicle (FCHV) fire accident and fatality rate per FCHV per year. The first step in the methodology is the consequence analysis based on validated deterministic engineering tools to estimate the main identified hazards: overpressure in the blast wave at different distances and the thermal hazards from a fireball in the case of catastrophic tank rupture in a fire. The population can be exposed to slight injury serious injury and fatality after an accident. These effects are determined based on criteria by Health and Safety Executive (UK) and a cost metrics is applied to the number of exposed people in these three harm categories to estimate the cost per an accident. The second step in the methodology is either the frequency or the probability analysis. Probabilities of a vehicle fire and failure of the thermally activated pressure relief device are taken from published sources. A vulnerability probit function is employed to calculate the probability of emergency operations’ failure to prevent tank rupture as a function of a storage tank FRR and time of fire brigade arrival. These later results are integrated to estimate the tank rupture frequency and fatality rate. The risk is presented as a function of fire resistance rating.<br/>The QRA methodology allows to calculate the cost of human loss associated with an FCHV fire accident and demonstrates how the increase of FRR of onboard storage as a safety engineering measure would improve socio-economics of FCHV deployment and public acceptance of the technology.
Development of a Generalized Integral Jet Model
Sep 2017
Publication
Integral type models to describe stationary plumes and jets in cross-flows (wind) have been developed since about 1970. These models are widely used for risk analysis to describe the consequences of many different scenarios. Alternatively CFD codes are being applied but computational requirements still limit the number of scenarios that can be dealt with using CFD only. The integral models however are not suited to handle transient releases such as releases from pressurized equipment where the initially high release rate decreases rapidly with time. Further on gas ignition a second model is needed to describe the rapid combustion of the flammable part of the plume (flash fire) and a third model has to be applied for the remaining jet fire. The objective of this paper is to describe the first steps of the development of an integral-type model describing the transient development and decay of a jet of flammable gas after a release from a pressure container. The intention is to transfer the stationary models to a fully transient model capable to predict the maximum extension of short-duration high pressure jets. The model development is supported by conducting a set of transient ignited and unignited spontaneous releases at initial pressures between 25bar and 400bar. These data forms the basis for the presented model development approach.
Helium Release in A Closed Enclosure- Comparisons Between Simple Models, CFD Calculations And Experimental Results
Sep 2011
Publication
In the prospect of a safe use of hydrogen in our society one important task is to evaluate under which conditions the storage of hydrogen systems can reach a sufficient level of safety. One of the most important issues is the use of such system in closed area for example a private garage or an industrial facility. In the scope of this paper we are mainly interested in the following scenario: a relatively slow release of hydrogen (around 5Nl/min) in a closed and almost cubic box representing either a fuel cell at normal scale or a private garage at a smaller scale. For practical reasons helium was used instead of hydrogen in the experiments on which are based our comparisons. This kind of situation leads to the fundamental problem of the dispersion of hydrogen due to a simple vertical source in an enclosure. Many numerical and experimental studies have already been conducted on this problem showing the formation of either a stably stratified distribution of concentration or the formation of a homogeneous layer due to high enough convective flows at the top of the enclosure. Nevertheless most of them consider the cases of accidental situation in which the flow rate is relatively important (higher than 10Nl/min). Numerical simulations carried out with the CEA code Cast3M and a LES turbulence model confirm the differences of results already observed in experimental helium concentration measurements for a same injection flow rate and two different injection nozzle diameters contradicting simple physical models used in safety calculations.
CFD Validation Against Large Scale Liquified Helium Release
Sep 2019
Publication
The ADREA-HF CFD code is validated against a large scale liquefied helium release experiment on flat ground performed by INERIS in the past. The predicted release and dispersion behavior is evaluated against the experimental using temperature time histories at sensors deployed at various distances and heights downstream the source. For the selected sensors the temperature predictions are generally in good agreement with the experimental with a tendency to under-predict temperature as the source is approached.
Risk Reduction Potential of Accident Prevention and Mitigation Features
Sep 2011
Publication
Quantitative Risk Assessment (QRA) can help to establish a set of design and operational requirements in hydrogen codes and standards that will ensure safe operation of hydrogen facilities. By analyzing a complete set of possible accidents in a QRA the risk drivers for these facilities can be identified. Accident prevention and mitigation features can then be analyzed to determine which are the most effective in addressing these risk drivers and thus reduce the risk from possible accidents. Accident prevention features/methods such as proper material selection and preventative maintenance are included in the design and operation of facilities. Accident mitigation features are included to reduce or terminate the potential consequences from unintended releases of hydrogen. Mitigation features can be either passive or active in nature. Passive features do not require any component to function in order to prevent or mitigate a hydrogen release. Examples of passive mitigation features include the use of separation distances barriers and flow limiting orifices. Active mitigation features initiate when specific conditions occur during an accident in order to terminate an accident or reduce its consequences. Examples of active mitigation features include detection and isolation systems fire suppression systems and purging systems. A concept being pursued by the National Fire Protection Association (NFPA) hydrogen standard development is to take credit for prevention and mitigation features as a means to reduce separation distances at hydrogen facilities. By utilizing other mitigation features the risk from accidents can be decreased and risk-informed separation distances can be reduced. This paper presents some preliminary QRA results where the risk reduction potential for several active and passive mitigation features was evaluated. These measures include automatic leak detection and isolation systems the use of flow limiting orifices and the use of barriers. Reducing the number of risk-significant components in a system was also evaluated as an accident prevention method. In addition the potential reduction in separation distances if such measures were incorporated at a facility was also determined.
The Effect of Tube Internal Geometry on the Propensity to Spontaneous Ignition in Pressurized Hydrogen Release
Sep 2013
Publication
Spontaneous ignition of compressed hydrogen release through a length of tube with different internal geometries is numerically investigated using our previously developed model. Four types of internal geometries are considered: local contraction local enlargement abrupt contraction and abrupt enlargement. The presence of internal geometries was found to significantly increase the propensity to spontaneous ignition. Shock reflections from the surfaces of the internal geometries and the subsequent shock interactions further increase the temperature of the combustible mixture at the contact region. The presence of the internal geometry stimulates turbulence enhanced mixing between the shock-heated air and the escaping hydrogen resulting in the formation of more flammable mixture. It was also found that forward-facing vertical planes are more likely to cause spontaneous ignition by producing the highest heating to the flammable mixture than backward-facing vertical planes.
Large Eddy Simulations of Asymmetric Turbulent Hydrogen Jets Issuing from Realistic Pipe Geometries
Sep 2017
Publication
In the current study a Large Eddy Simulation strategy is applied to model the dispersion of compressible turbulent hydrogen jets issuing from realistic pipe geometries. The work is novel as it explores the effect of jet densities and Reynolds numbers on vertical buoyant jets as they emerge from the outer wall of a pipe through a round orifice perpendicular to the mean flow within the pipe. An efficient Godunov solver is used and coupled with Adaptive Mesh Refinement to provide high resolution solutions only in areas of interest. The numerical results are validated against physical experiments of air and helium which allows a degree of confidence in analysing the data obtained for hydrogen releases. The results show that the jets investigated are always asymmetric. Thus significant discrepancies exist when applying conventional round jet assumptions to determine statistical properties associated with gas leaks from pipelines.
Ia-HySafe Standard Benchmark Exercise Sbep-V21- Hydrogen Release and Accumulation within a Non-Ventilated Ambient Pressure Garage at Low Release Rates
Sep 2011
Publication
The successful Computational Fluid Dynamics (CFD) benchmarking activity originally started within the EC-funded Network of Excellence HySafe (2004-2009) continues within the research topics of the recently established “International Association of Hydrogen Safety” (IA-HySafe). The present contribution reports the results of the standard benchmark problem SBEP-V21. Focus is given to hydrogen dispersion and accumulation within a non-ventilated ambient pressure garage both during the release and post-release periods but for very low release rates as compared to earlier work (SBEP-V3). The current experiments were performed by CEA at the GARAGE facility under highly controlled conditions. Helium was vertically released from the centre of the 5.76 m (length) x 2.96 m (width) x 2.42 m (height) facility 22 cm from the floor from a 29.7 mm diameter opening at a volumetric rate of 18 L/min (0.027 g/s equivalent hydrogen release rate compared to 1 g/s for SBEP-V3) and for a period of 3740 seconds. Helium concentrations were measured with 57 catharometric sensors at various locations for a period up to 1.1 days. The simulations were performed using a variety of CFD codes and turbulence models. The paper compares the results predicted by the participating partners and attempts to identify the reasons for any observed disagreements.
HIAD – Hydrogen Incident and Accident Database
Sep 2011
Publication
The Hydrogen Incident and Accident Database (HIAD) is being developed as a repository of systematic data describing in detail hydrogen-related undesired events (incidents or accidents). It is an open web-based information system serving various purposes such as a data source for lessons learnt risk communication and partly risk assessment. The paper describes the features of the three HIAD modules – the Data Entry Module (DEM) the Data Retrieval Module (DRM) and the Data Analysis Module (DAM) – and the potential impact the database may have on hydrogen safety. The importance of data quality assurance process is also addressed.
Radiation from Hydrogen Jet Fires Investigated by Time-resolved Spectroscopy
Sep 2013
Publication
Jet fires develop on release of hydrogen from pressurized storage depending on orifice pressures and volumes. Risks arise from flame contact dispersion of hot gases and heat radiation. The latter varies strongly in time at short scales down to milliseconds caused by turbulent air entrainment and fluctuations. These jets emit bands of OH in the UV and water in the NIR and IR spectral range. These spectra enable the temperature measurement and the estimation of the air number of the measuring spot which can be used to estimate the total radiation at least from the bright combustion zones. Compared to video and IR camera frames the radiation enables to estimate species and temperatures distributions and total emissions. Impurities generate continuum radiation and the emission of CO2 in the IR indicates air entrainment which can be compared to CHEMKIN II calculation of the reaction with air.
Experimental Investigation of Flame and Pressure Dynamics after Spontaneous Ignition in Tube Geometry
Sep 2013
Publication
Spontaneous ignition processes due to high pressure hydrogen releases into air are known phenomena. The sudden expansion of pressurized hydrogen into a pipe filled with ambient air can lead to a spontaneous ignition with a jet fire. This paper presents results of an experimental investigation of the visible flame propagation and pressure measurements in 4 mm extension tubes of up to 1 m length attached to a bulk vessel by a rupture disc. Transparent glass tubes for visual observation and shock wave pressure sensors are used in this study. The effect of the extension tube length on the development of a stable jet fire after a spontaneous ignition is discussed.
Materials Aspects Associated with the Addition of up to 20 mol% Hydrogen into an Existing Natural Gas Distribution Network
Sep 2019
Publication
The introduction of hydrogen into the UK natural gas main has been reviewed in terms of how materials within the gas distribution network may be affected by contact with up to 80% Natural Gas : 20 mol% hydrogen blend at up to 2 barg. A range of metallic polymeric and elastomeric materials in the gas distribution network (GDN) were assessed via a combination of literature review and targeted practical test programmes.
The work considered:
The work considered:
- The effect of hydrogen on metallic materials identified in the network
- The effect of hydrogen on polymeric materials identified in the network
- The effect of hydrogen exposure on polyethylene pipeline techniques (squeeze off and collar electrofusion)
Regulations, Codes, and Standards (RCS) For Large Scale Hydrogen Systems
Sep 2017
Publication
Hydrogen has potential applications that require larger-scale storage use and handling systems than currently are employed in emerging-market fuel cell applications. These potential applications include hydrogen generation and storage systems that would support electrical grid systems. There has been extensive work evaluating regulations codes and standards (RCS) for the emerging fuel cell market such as the infrastructure required to support fuel cell electric vehicles. However there has not been a similar RCS evaluation and development process for these larger systems. This paper presents an evaluation of the existing RCS in the United States for large-scale systems and identifies potential RCS gaps. This analysis considers large-scale hydrogen technologies that are currently being employed in limited use but may be more widely used as large-scale applications expand. The paper also identifies areas of potential safety research that would need to be conducted to fill the RCS gaps. U.S. codes define bulk hydrogen storage systems but do not define large-scale systems. This paper evaluates potential applications to define a large-scale hydrogen system relative to the systems employed in emerging technologies such as hydrogen fuelling stations. These large-scale systems would likely be of similar size to or larger than industrial hydrogen systems.
Hydrogen Bubble Dispersion and Surface Bursting Behaviour
Sep 2013
Publication
In many processes where hydrogen may be released from below a liquid surface there has been concern regarding how such releases might ultimately disperse in an ullage space. Knowledge of the extent and persistence of any flammable volume formed is needed for hazardous area classification as well as for validation of explosion modelling or experiments. Following an initial release of hydrogen the overall process can be subdivided into three stages (i) rise and possible break-up of a bubble in the liquid (ii) formation and bursting of a thin gas-liquid-gas interface at the liquid surface and (iii) dispersion of the released gas. An apparatus based on a large glass sided water tank has been constructed which employs two synchronised high-speed imaging systems to record the behaviour of hydrogen bubble release and dispersion. A high-speed digital video system records the rising of the bubbles and the formation and bursting of the gas-liquid-gas interface at the liquid surface. An additional schlieren system is used to visualise the hydrogen release as bubbles burst at the liquid surface. The bubble burst mechanism can clearly be described from the results obtained. Following the nucleation of a hole surface tension causes the liquid film to peel back rapidly forming a ring/torus of liquid around the enlarging hole. This process lasts only a few milliseconds. Although some hydrogen can be seen to be expelled from the bubble much seems to remain in place as the film peels away. To assess the extent of the flammable plume following a bubble burst the apparatus was modified to include an electric-arc igniter. In order to identify plumes coincident in space with the igniter a schlieren system was built capable of recording simultaneously in two orthogonal directions. This confirmed that clouds undetected by the schlerien imaging could not be ignited with the electric arc igniter.
Experimental Investigation of Nonideality and Nonadiabatic Effects Under High Pressure Releases
Sep 2013
Publication
Due to the nonideality of a high pressure hydrogen release the possibility of a two-phase flow and its effect on the dynamics of the discharge process was experimentally investigated. A small-scale facility was designed and constructed to simulate the transient blow-down of a cryogenic fluid through a small break. Gaseous and liquid nitrogen were planned to were used as a surrogate for GH2 and LH2. The results will complement the quasi-stationary safety regulation tests and will provide time-dependent data for verification of the theoretical models. Different orifice sizes (0.5 1 2 4 mm) and initial N2 pressures (30 – 200 bar) were used in the tests. The measured time-dependent data for vessel discharge pressure thrust discharge mass flow rate and gas temperatures were compared against a theoretical model for high pressure nitrogen release. This verification for nitrogen also assures the equation of state for hydrogen which is based on the same methodology.
Thermal Loading Cases of Hydrogen High Pressure Storage Cylinders
Sep 2007
Publication
Composite cylinders with metal liner are used for the storage of compressed hydrogen in automotive application. These hybrid pressure cylinders are designed for a nominal working pressure of up to 70 MPa. They also have to withstand a temperature range between -40°C and +85°C according GRPE draft [1] and for short periods up to a maximum temperature of 140°C during filling (fast filling) [2]. In order to exploit the material properties efficiently with a high degree of lightweight optimization and a high level of safety on the same time a better understanding of the structural behavior of hybrid designs is necessary. Work on this topic has been carried out in the frame of a work package on safety aspects and regulation (Subproject SAR) of the European IP StorHy (www.storhy.net). The temperature influence on the composite layers is distinctive due to there typical polymer material behavior. The stiffness of the composite layer is a function of temperature which influences global strains and stress levels (residual stresses) in operation. In order to do an accurate fatigue assessment of composite hybrid cylinders a realistic modeling of a representative temperature load is needed. For this climate data has been evaluated which were collected in Europe over a period of 30 years [3]. Assuming that the temperature follows a Gaussian (normal) distribution within the assessed period of 30 years it is possible to generate a frequency distribution for different temperature classes for the cold extreme and the hot extreme. Combining these distributions leads to the overall temperature range distribution (frequency over temperature classes). The climatic temperature influence the filling temperature and the pressure load have to be considered in combination with the operation profile of the storage cylinder to derive a complete load vector for an accurate assessment of the lifetime and safety level.
Combustion Modeling in Large Scale Volumes
Sep 2013
Publication
This paper is devoted to a benchmarking exercise of the EUROPLEXUS code against several large scale deflagration and detonation experimental data sets in order to improve its hydrogen combustion modeling capabilities in industrial settings. The code employs an algorithm for the propagation of reactive interfaces RDEM which includes a combustion wave as an integrable part of the Reactive Riemann problem propagating with a fundamental flame speed (being a function of initial mixture properties as well as gas dynamics parameters). An improvement of the combustion model is searched in a direction of transient interaction of flames with regions of elevated vorticity/shear in obstacle-laden channels and vented enclosures.
Experiments with Release and Ignition of Hydrogen Gas in a 3m Long Channel
Sep 2007
Publication
This paper presents results from laboratory experiments with hydrogen dispersions and explosions in a 3 m long channel. Our objective is to get a better understanding of the phenomena and to develop tools that can analyse hydrogen dispersions and explosions. A total of 5 test series were performed with flow rates of hydrogen from 1.8 dm³/min to 75 dm³/min. The propagation of the combustible hydrogen-air cloud in the channel was observed from high-speed video recordings. The hydrogen-air cloud in the channel behaves as a gravity current and the flow appears to be well described by Froude scaling with a length scale corresponding to the height of a layer of 100 % hydrogen. The Froude numbers observed in the experiments are in good agreement with the theory of "light-fluid intrusion" for gravity currents found in the literature. Numerical simulations with the Flacs code correlate well with the experimental results. The flame propagation indicated that approximately half the height of the channel was filled with combustible mixture. We believe that this Froude scaling can be useful as a tool to analyse the consequences of hydrogen release in buildings channels and tunnels.
Effectiveness of a Blower in Reducing the Hazard of Hydrogen Leaking from a Hydrogen-fueled Vehicle
Sep 2013
Publication
To handle a hydrogen fuel cell vehicle (HFCV) safely after its involvement in an accident it is necessary to provide appropriate emergency response information to the first responder. In the present study a forced wind of 10 m/s or faster with and without a duct was applied to a vehicle leaking hydrogen gas at a rate of 2000 NL/min. Then hydrogen concentrations were measured around the vehicle and an ignition test was conducted to evaluate the effectiveness of forced winds and the safety of emergency response under forced wind conditions. The results: 1) Forced winds of 10 m/s or faster caused the hydrogen concentrations in the vicinity of the vehicle to decline to less than the lower flammability limit and the hydrogen gas in the various sections of the vehicles were so diluted that even if ignition occurred the blast-wave pressure was moderate. 2) When the first responder had located the hydrogen leakage point in the vehicle it was possible to lower the hydrogen concentrations around the vehicle by aiming the wind duct towards the leakage point and blowing winds at 10 m/s from the duct exit.
Gas Detection of Hydrogen/Natural Gas Blends in the Gas Industry
Sep 2019
Publication
A key element in the safe operation of a modern gas distribution system is gas detection. The addition of hydrogen to natural gas will alter the characteristics of the fuel and therefore its impact on gas detection must be considered. It is important that gas detectors remain sufficiently sensitive to the presence of hydrogen and natural gas mixtures and that they do not lead to false readings. This paper presents analyses of work performed as part of the Office for Gas and Energy Markets (OFGEM) funded HyDeploy project on the response of various natural gas industry detectors to blended mixtures up to 20 volume percent (vol%) of hydrogen in natural gas. The scope of the detectors under test included survey instruments and personal monitors that are used in the gas industry. Four blend ratios were analysed (0 10 15 and 20 vol% hydrogen in natural gas). The laboratory testing undertaken investigated the following:
- Flammable response to blends in the ppm range (0-0.2 vol%);
- Flammable response to blends in the lower explosion limit range (0.2-5 vol%);
- Flammable response to blends in the volume percent range (5-100 vol%);
- Oxygen response to blends in the volume percent range (0-25 vol%); and
- Carbon monoxide response to blends in the ppm range (0-1000 ppm).
The Correlation Method to Analyze the Gas Mixing Process On The Basis Of BOS Method
Sep 2011
Publication
Structures formed during gas mixing following an injection of a gas into atmosphere are analyzed using optic methods based on the detection of density non-uniformities. Methods for determination of fractal parameters for a random distribution of these non-uniformities are described and information revealed on the gas mixing structure is analyzed. The BOS (background oriented schlieren) technique is utilized to obtain the optical image of the forming structures which afterward is processed using the correlation procedure allowing to extract the quantitative information on the mixing. Additionally a possibility to link the characteristics of the injected gas source and the system fractal parameters was demonstrated. The method can be used in the development of the non-contact methods for the evaluation of the gaseous system parameters based on the optical diagnostics and potentially for the obtaining more detailed information of the gaseous turbulence.
Ignition of Hydrogen-air Mixtures by Moving Heated Particles
Oct 2015
Publication
Studying thermal ignition mechanisms is a key step for evaluating many ignition hazards. In the present work two-dimensional simulations with detailed chemistry are used to study the reaction pathways of the transient flow and ignition of a stoichiometric hydrogen-air mixture by moving hot spheres. For temperatures above the ignition threshold ignition takes place after a short time between the front stagnation point and separation location depending upon the sphere's surface temperature. Closer to the threshold the volume of gas adjacent to the separation region ignites homogeneously after a longer time. These results demonstrate the importance of boundary layer development and flow separation in the ignition process.
Fast Turbulent Deflagration and DDT of Hydrogen-Air Mixtures in Small Obstructed Channel
Sep 2007
Publication
An experimental study of flame propagation acceleration and transition to detonation in hydrogen-air mixture in 2 m long rectangular cross section channel filled with obstacles located at the bottom wall was performed. The initial conditions of the hydrogen-air mixture were 0.1 MPa and 293 K. Three different cases of obstacle height (blockage ratio 0.25 0.5 and 0.75) and four cases of obstacle density were studied with the channel height equal to 0.08 m. The channel width was 0.11 m in all experiments. The propagation of flame and pressure waves was monitored by four pressure transducers and four in house ion probes. The pairs of transducers and probes were placed at various locations along the channel in order to get information about the progress of the phenomena along the channel. To examine the influence of mixture composition on flame propagation and DDT the experiments were performed for the compositions of 20% 25% and 29.6% of H2 in air by volume. As a result of the experiments the deflagration and detonation regimes and velocities of flame propagation in the obstructed channel were determined.
Simulation of Hydrogen Dispersion under Cryogenic Release Conditions
Sep 2013
Publication
The use of hydrogen as fuel should always be accompanied by a safety assessment in case of an accidental release. To evaluate the potential hazards in a spill accident both experiments and simulations are performed. In the present work the CFD code ADREA-HF is used to simulate the liquefied hydrogen (LH2) spill experiments (test 5 6 7) conducted by the Health and Safety Laboratory (HSL). In these tests LH2 was spilled at a fixed rate of 60lt/min in several directions and for several durations. The factors that influence the vapor dispersion under cryogenic release conditions that were examined in this study are: the air humidity the wind direction and the slip effect of droplets formed by both the cryogenic liquid and the condensation of air humidity. The numerical results were compared with the experimental measurements and the effect of each abovementioned factors in the vapor dispersion is being discussed.
Hydrogen Storage - Recent Improvements and Industrial Prospectives
Sep 2013
Publication
This paper gives a historical and technical overview of hydrogen storage vessels and details the specific issues and constraints of hydrogen energy uses. Hydrogen as an industrial gas is stored either as a compressed or as a refrigerated liquefied gas. Since the beginning of the last century hydrogen is stored in seamless steel cylinders. At the end of the 60s tubes also made of seamless steels were used; specific attention was paid to hydrogen embrittlement in the 70s. Aluminum cylinders were also used for hydrogen storage since the end of the 60s but their cost was higher compared to steel cylinders and smaller water capacity. To further increase the service pressure of hydrogen tanks or to slightly decrease the weight metallic cylinders can be hoop-wrapped. Then with specific developments for space or military applications fully-wrapped tanks started to be developed in the 80s. Because of their low weight they started to be used in for portable applications for vehicles (on-board storages of natural gas) for leisure applications (paint-ball) etc… These fully-wrapped composite tanks named types III and IV are now developed for hydrogen energy storage; the requested pressure is very high (from 700 to 1 000 bar) leads to specific issues which are discussed. Each technology is described in term of materials manufacturing technologies and approval tests. The specific issues due to very high pressure are depicted. Hydrogen can also be stored in liquid form (refrigerated liquefied gases). The first cryogenic vessels were used in the 60s. In the following the main characteristics of this type of storage will be indicated.
Numerical Investigation of Vented Hydrogen-air Deflagration in a Chamber
Oct 2015
Publication
This paper shows numerical investigation related to hydrogen-air deflagration venting. The aim of this study is to clarify the influence of concentration gradient on the pressure histories and peak pressures in a chamber. The numerical analysis target is a 27 m3 cubic chamber which has 2.6 m2 vent area on the sidewall. The vent opening pressure is set to be gauge 10 kPa. Two different conditions of the hydrogen concentration are assumed which are uniform and gradient. In the uniform case 15 20 25 30 and 35 vol.% concentrations are assumed. In the gradient case the concentration linearly increases from 0 vol.% (at the ground) to 30 40 50 60 70 vol.% (at the ceiling). The initial total mass of hydrogen inside the chamber is the same as the uniform case. Moreover three different ignition points are assumed: on the rear center and the front of the chamber relative to the vent. The deflagrations are initiated by a single ignition source. In most gradient cases the highest peak is lower than in the uniform case though the initial total mass of hydrogen inside the chamber is the same as in the uniform case. This is because the generated burned gas per time is smaller in the gradient case than in the uniform case. In 15 vol.% gradient case however the peak pressure gets higher than in the uniform case. This is because in 15 vol.% gradient case the burning velocity around the ignition point gets faster and the flame surface gets larger which induces larger amount of burned gas per time.
Let’s Go Green With Hydrogen! The General Public’s Perspective
Sep 2011
Publication
It is well known in socio-economics that the success of an innovation process depends to a great extent on public acceptance. The German HyTrust project analyzes the current state of public acceptance in hydrogen technology in the mobility sector. This paper focuses on cutting-edge results of interviews focus groups and a representative survey. Based on these results almost 80% of the Germans are in favor of introducing hydrogen vehicles. But from the perspective of the general public it is important that hydrogen is produced in an environmentally friendly way. HyTrust is the socio-scientific research project that accompanies the German Federal Government's National Innovation Programme.
Modelling of H2 Dispersion and Combustion Phenomena Using CFD Codes
Sep 2005
Publication
Computational Fluid Dynamics codes are increasingly being considered for safety assessment demonstrations in many industrial fields as tools to model accidental phenomena and to design mitigation (risk reducing) systems. Thus they naturally complement experimental programmes which may be expensive to run or difficult to set up. However to trust numerical simulations the validity of the codes must be firmly established and a certain number of error sources (user effect modelling errors discretization errors etc) reduced to the minimum. Code validation and establishment of “best practice guidelines” in the application of simulation tools to hydrogen safety assessment are some of the objectives pursued by the HYSAFE Network of Excellence. This paper will contribute to these goals by describing some of the validation efforts that CEA is making in the areas of release dispersion combustion and mitigation thereby proposing the outline of a validation matrix for hydrogen safety problems.
Detonability of Binary H2/Ch4 - Air Mixture
Sep 2009
Publication
Abatement of greenhouse gas emissions and diversification of energy sources will probably lead to an economy based on hydrogen. In order to evaluate safety conditions during transport and distribution experimental data is needed on the detonation of Hydrogen/Natural gas blend mixtures. The aim of this study is to constitute detonation and deflagration to detonation transition (DDT) database of H2/CH4-air mixtures. More precisely the detonability of such mixtures is evaluated by the detonation cell size and the DDT run up distance measurements. Large experimental conditions are investigated (i) various equivalence ratios from 0.6 to 3 (ii) various H2 molar fraction x ( ( )2 2 4x H H CH= + ) from 0.5 to 1 (iii) different initial pressure P0 from 0.2 to 2 bar at fixed ambient temperature T0=293 K. Detonation pressures P velocities D and cell sizes ? were measured in two smooth tubes with different i.d. d (52 and 106 mm). For DDT data minimum DDT run up distances LDDT were determined in the d=52 mm tube containing a 2.8 m long Schelkin spiral with a blockage ratio BR = 0.5 and a pitch equal to the diameter. Measured detonation velocities D are very close to the Chapman Jouguet values (DCJ). Concerning the effect of detonation cell size ? follows a classical U shaped- curve with a minimum close to =1 and concerning the effect of x ? decreases when x increases. The ratio ik L?= obtained from different chemical kinetics (Li being the ZND induction length) is well approximated by the value 40 in the range 0.5 < x < 0.9 and 50 for x 0.9. Minimum DDT run up distance LDDT varies from 0.36 to 1.1m when x varies from 1 to 0.8. The results show that LDDT obeys the linear law LDDT ~ 30-40? previously validated in H2/Air mixtures. Adding Hydrogen in Natural Gas promotes the detonability of the mixtures and for x 0.65 these mixtures are considered more sensitive than common heavy Alkane-Air mixtures.
Simulator Development of Virtual Experience and Accident Scenarios of Hydrogen Stations for Safety
Sep 2007
Publication
Nowadays 4 type hydrogen stations have been demonstrated in Korea for preparing hydrogen economy. This simulator is consists of virtual experience modules and virtual accident scenarios of 4 type hydrogen stations. Virtual experience modules show the performance properties through a movie or a virtual reality technology. Also they provide an explanation of hydrogen station equipment and a guide for operators immediately after the accident. Virtual accident scenario modules show accident simulations based on modelling equations as 3D virtual reality. These modules could choose the sham accident for every kind of a station after categorizing all possible accidents in a station A Commercialized CFD program based on hydrogen dispersion model theory shows a movie of accident simulations. The result of a simulator has been developed as web applications. And will be applied to training materials and public relations for a user concerned about hydrogen stations.
Hot Surface Ignition of Hydrogen-air Mixtures
Oct 2015
Publication
Hot surface ignition is relevant in the context of industrial safety. In the present work two-dimensional simulations with detailed chemistry and study of the reaction pathways of the buoyancy-driven flow and ignition of a stoichiometric hydrogen-air mixture by a rapidly heated surface (glowplug) are reported. Experimentally ignition is observed to occur regularly at the top of the glowplug; numerical results for hydrogen-air reproduce this trend and shed light on this behaviour. The simulations show the importance of flow separation in creating zones where convective losses are minimized and heat diffusion is maximized resulting in the critical conditions for ignition to take place.
Validation of CFD Modelling of LH2 Spread and Evaporation Against Large-Scale Spill Experiments
Sep 2009
Publication
Hydrogen is widely recognized as an attractive energy carrier due to its low-level air pollution and its high mass-related energy density. However its wide flammability range and high burning velocity present a potentially significant hazard. A significant fraction of hydrogen is stored and transported as a cryogenic liquid. Therefore loss of hydrogen containments may lead to the formation of a pool on the ground. In general very large spills will give a pool whereas moderate sized spills may evaporate immediately. Accurate hazard assessments of storage systems require a proper prediction of the liquid hydrogen pool evaporation and spreading. A new pool model handling the spread and the evaporation of liquid spills on different surfaces has recently been developed in the 3D Computational Fluid Dynamics (CFD) tool FLACS [1-4]. As the influence of geometry on the liquid spread is taken into account in the new pool model realistic industrial scenarios can be investigated. The model has been validated for LNG spills on water with the Burro and Coyote experiments [56]. The model has previously been tested for LH2 release in the framework of the EU-sponsored Network of Excellence HySafe where experiments carried out by BAM were modelled. In the large scale BAM experiments [7] 280 kg of liquid hydrogen was spilled in 6 tests adjacent to buildings. In these tests the pool spreading the evaporation and the cloud formation were investigated. Simulations of these tests are found to compare reasonably well with the experimental results. In the present work the model is extended and the liquid hydrogen spill experiments carried out by NASA are simulated with the new pool model. The large scale NASA experiments [89] consisted of 7 releases of liquefied hydrogen at White Sand New Mexico. The release test 6 is used. During these experiments cloud concentrations were measured at several distances downwind of the spill point. With the new pool model feature the FLACS tool is shown to be an efficient and accurate tool for the investigation of complex and realistic accidental release scenarios of cryogenic liquids.
Numerical Simulation of Diverging Detonation in Hydrogen Air Mixtures
Oct 2015
Publication
Propagation and stability of diverging cylindrical detonation in hydrogen air mixture is numerically simulated and the mechanism of the transverse waves is analysed. For the numerical modelling a new solver based on compressible transient reactive Navier–Stokes equations is developed which can the simulate detonation propagation and extinction in hydrogen-air mixture. A single step reaction mechanism is tuned to ensure the detonation and deflagration properties (in case of detonation failure) can be simulated accurately. The solver is used for modelling various detonation scenarios in particular cylindrical diverging-detonations because most of accidental industrial detonations start from a spark and then a diverging-detonation propagates outwards. The diverging detonation its cellular structure and adoption with the increased surface area at the detonation front as well as interactions with obstacles leading to detonation failure and re-initiation are studied.
Modelling Of Hydrogen Explosion on a Pressure Swing Adsorption Facility
Sep 2011
Publication
Computational fluid dynamic simulations have been performed in order to study the consequences of a hydrogen release from a pressure swing adsorption installation operating at 30 barg. The simulations were performed using FLACS-Hydrogen software from GexCon. The impact of obstruction partial confinement leak orientation and wind on the explosive cloud formation (size and explosive mass) and on explosion consequences is investigated. Overpressures resulting from ignition are calculated as a function of the time to ignition.
Compatibility and Suitability of Existing Steel Pipelines for Transport of Hydrogen and Hydrogen-natural Gas Blends
Sep 2017
Publication
Hydrogen is being considered as a pathway to decarbonize large energy systems and for utility-scale energy storage. As these applications grow transportation infrastructure that can accommodate large quantities of hydrogen will be needed. Many millions of tons of hydrogen are already consumed annually some of which is transported in dedicated hydrogen pipelines. The materials and operation of these hydrogen pipeline systems however are managed with more constraints than a conventional natural gas pipeline. Transitional strategies for deep decarbonization of energy systems include blending hydrogen into existing natural gas systems where the materials and operations may not have the same controls. This study explores the hydrogen compatibility of existing pipeline steels and the suitability of these steels in hydrogen pipeline systems. Representative fracture and fatigue properties of pipeline grade steels in gaseous hydrogen are summarized from the literature. These properties are then considered in idealized design life calculations to inform materials performance for a typical gas pipeline.
Benchmark Exercise on Risk Assessment Methods Applied to a Virtual Hydrogen Refuelling Station
Sep 2009
Publication
A benchmarking exercise on quantitative risk assessment (QRA) methodologies has been conducted within the project HyQRA under the framework of the European Network of Excellence (NoE) HySafe. The aim of the exercise was basically twofold: (i) to identify the differences and similarities in approaches in a QRA and their results for a hydrogen installation between nine participating partners representing a broad spectrum of background in QRA culture and history and (ii) to identify knowledge gaps in the various steps and parameters underlying the risk quantification. In the first step a reference case was defined: a virtual hydrogen refuelling station (HRS) in virtual surroundings comprising housing school shops and other vulnerable objects. All partners were requested to conduct a QRA according to their usual approach and experience. Basically participants were free to define representative release cases to apply models and frequency assessments according their own methodology and to present risk according to their usual format. To enable inter-comparison a required set of results data was prescribed like distances to specific thermal radiation levels from fires and distances to specific overpressure levels. Moreover complete documentation of assumptions base data and references was to be reported. It was not surprising that a wide range of results was obtained both in the applied approaches as well as in the quantitative outcomes and conclusions. This made it difficult to identify exactly which assumptions and parameters were responsible for the differences in results as the paper will show. A second phase was defined in which the QRA was determined by a more limited number of release cases (scenarios). The partners in the project agreed to assess specific scenarios in order to identify the differences in consequence assessment approaches. The results of this phase provide a better understanding of the influence of modelling assumptions and limitations on the eventual conclusions with regard to risk to on-site people and to the off-site public. This paper presents the results and conclusions of both stages of the exercise.
Safe Operation of Combined Cycle Gas Turbine and Gas Engine Systems Using Hydrogen Rich Fuels
Oct 2015
Publication
This paper describes work performed by a consortium led by the UK Health and Safety Laboratory(HSL)to identify the safe operating conditions for combined cycle power generating systems running on high hydrogen fuels. The work focuses on hydrogen and high hydrogen syngas and biogas waste-stream fuel mixtures which may prove hazardous in the event of a turbine or engine flame out resulting in a flammable fuel mixture entering the hot exhaust system and igniting. The paper describes the project presenting some initial results from this work including the development of large scale experimental facilities on the550 acre HSL site near Buxton Derbyshire UK. It describes the large scale experimental facility which utilises the exhaust gas from a Rolls-Royce Viper jet-engine (converted to run on butane) feeding into a 12 m long 0.60 m diameter instrumented tube at a pre-combustion velocity of 22 m/s. A variable geometry simulated heat exchanger with a 40 %2blockage ratio is present in the tube. Flammable mixtures injected into the tube close to the Viper outlet together with make-up oxygen are then ignited. Extensive optical ionisation temperature and pressure sensors are employed along the length of the tube to measure the pressures and flame speeds resulting from the combustion event. Some preliminary results from the test programme are discussed including deflagration to detonation transitions at high equivalence ratios.
A Numerical Simulation on the Leakage Event of a High-Pressure Hydrogen Dispenser
Dec 2021
Publication
For the sake of the increasing demand of hydrogen fuel cell vehicles there are more concerns on the safety of hydrogen refueling stations. As one of the key pieces of equipment the hydrogen dispenser has drawn attention on this aspect since it involves massive manual operations and may be bothered by a high probability of failure. In this paper a numerical study is conducted to simulate the possible leakage events of the hydrogen dispenser based on a prototype in China whose working pressure is 70 MPa. The leakage accident is analyzed with respect to leakage sizes leak directions and the time to stop the leakage. It is found that due to the large mass flow rate under such high pressure the leak direction and the layout of the components inside the dispenser become insignificant and the ignitable clouds will form inside the dispenser in less than 1 s if there is a leakage of 1% size of the main tube. The ignitable clouds will form near the vent holes outside the dispenser which may dissipate quickly if the leakage is stopped. On the other hand the gas inside the dispenser will remain ignitable for a long time which asks for a design with no possible ignition source inside. The results can be useful in optimizing the design of the dispenser regarding the reaction time and sensitivity requirements of the leakage detector the size and amount of vent holes etc.
Steam Condensation Effect in Hydrogen Venting from a BWR Reactor Building
Oct 2015
Publication
In the accident of Fukushima Daiichi nuclear power plants hydrogen was accumulated in the reactor buildings and exploded. To prevent such explosions hydrogen venting from reactor buildings is considered. When the gas mixture is released to a reactor building through a reactor containment together with the hydrogen some amount of steam might also be released. The steam condenses if the building atmosphere is below the saturation temperature and it affects the hydrogen behaviour. In this study the condensation effect to the hydrogen venting is evaluated using CFD analyses by comparing the case where a hydrogen-nitrogen mixture is released and the case where a hydrogen-steam mixture is released.
Public Perception on Hydrogen Infrastructure in Japan
Oct 2015
Publication
A public survey was conducted in March 2015 in Japan asking public awareness knowledge perception and acceptance regarding hydrogen hydrogen infrastructure and fuel cell vehicle adopting the same key questions contained in the public surveys conducted six and seven years ago. Changes in answers between two different times of survey implementation were analyzed by comparing results of current survey to those of the previous surveys. Regression analyses were conducted and revealed influence of respondents’ awareness knowledge and perception about hydrogen hydrogen infrastructure and fuel cell vehicle on their acceptance on hydrogen station. We found a large increase in the awareness and relatively a small improvement on knowledge on hydrogen energy hydrogen infrastructure and fuel cell vehicle from the previous surveys. In contrast we did not find much changes in perception of risk and benefit perception on hydrogen society and hydrogen station and public acceptance of hydrogen infrastructure. Through the regression analyses we found large influences of negative risk perception of hydrogen itself and technology of hydrogen station and perception of necessity of hydrogen station on public acceptance of hydrogen station and the small influence of time background on the acceptance. Through the results of analyses implications to public communication in building public infrastructure are presented.
Comparison of Two Simplified Models Predictions with Experimental Measurements for Gas Release Within an Enclosure
Sep 2009
Publication
In this work the validity of simplified mathematical models for predicting dispersion of turbulent buoyant jet or plume within a confined volume is evaluated. In the framework of the HYSAFE Network of Excellence CEA performed experimental tests in a full-scale Garage facility in order to reproduce accidental gas leakages into an unventilated residential garage. The effects of release velocities diameters durations mass flow rates and flow regimes on the vertical distribution of the gas concentration are investigated. Experimental data confirm the formation for the release conditions of an almost well-mixed upper layer and a stratified lower layer. The comparison of the measurements and the model predictions shows that a good agreement is obtained for a relatively long-time gas discharge for jet like or plume like flow behaviour.
Experimental Study on Vented Hydrogen Deflagrations in a Low Strength Enclosure
Oct 2015
Publication
This paper describes an experimental programme on vented hydrogen deflagrations which formed part of the Hyindoor project carried out for the EU Fuel Cells and Hydrogen Joint Undertaking. The purpose of this study was to investigate the validity of analytical models used to calculate overpressures following a low concentration hydrogen deflagration. Other aspects of safety were also investigated such as lateral flame length resulting from explosion venting. The experimental programme included the investigation of vented hydrogen deflagrations from a 31 m3 enclosure with a maximum internal overpressure target of 10 kPa (100 mbar). The explosion relief was provided by lightly covered openings in the roof or sidewalls. Uniform and stratified initial hydrogen distributions were included in the test matrix and the location of the ignition source was also varied. The maximum hydrogen concentration used within the enclosure was 14% v/v. The hydrogen concentration profile within the enclosure was measured as were the internal and external pressures. Infrared video images were obtained of the gases vented during the deflagrations. Findings show that the analytical models were generally conservative for overpressure predictions. Flame lengths were found to be far less than suggested by some guidance. Along with the findings the methodology test conditions and corresponding results are presented.
The Structure and Flame Propagation Regimes in Turbulent Hydrogen Jets
Sep 2009
Publication
Experiments on flame propagation regimes in a turbulent hydrogen jet with velocity and hydrogen concentration gradients have been performed at the FZK hydrogen test site HYKA. Horizontal stationary hydrogen jets released at normal and cryogenic temperatures of 290K and 80 and 35K with different nozzle diameters and mass flow rates in the range from 0.3 to 6.5 g/s have been investigated. Sampling probe method and laser PIV technique have been used to evaluate distribution of hydrogen concentration and flow velocity along and across the jet axis. High-speed photography (1000 fps) combined with a Background Oriented Schlieren (BOS) system was used for the visual observation of the turbulent flame propagation. In order to investigate different flame propagation regimes the ignition position was changed along the jet axis. It was found that the maximum flame velocity and pressure loads can only occur if the hydrogen concentration at the ignition point exceeds 11% of hydrogen in air. In this case the flame propagates in both directions up- and downstream the jet flow whereas in the opposite case the flame propagates only downstream. Such a behavior is consistent with previous experiments according to that the flame is able to accelerate effectively only if the expansion rate σ of the H2-air mixture is higher than a critical value σ* = 3.75 (like for the 11% hydrogen-air mixture). The measured data allow conservative estimates of the safety distance and risk assessment for realistic hydrogen leaks.
A Study on Dispersion Resulting From Liquefied Hydrogen Spilling
Oct 2015
Publication
For massive utilization of hydrogen energy it is necessary to transport a large quantity of hydrogen by liquefied hydrogen carriers. However the current rule on ships carrying liquefied hydrogen in bulks do not address the maritime transport of liquefied hydrogen and the safety assessment of liquefied hydrogen carriage is thus very important. In the present study we spilled liquefied hydrogen and LNG (Liquefied Natural Gas) on the surface of various materials and compared the difference of their spread and dispersion. Liquefied hydrogen immediately dispersed upward compared to LNG. Furthermore we also measured the flammability limit of low temperature hydrogen gas. Its range at low temperature was narrower than the range at normal temperature.
Application of Risk Assessment Approach on a Hydrogen Station
Sep 2013
Publication
An accident modelling approach is used to assess the safety of a hydrogen station as part of a ground transportation network. The method incorporates prevention barriers associated to human factors management and organizational failures in a risk assessment framework. Failure probabilities of these barriers and end-states events are predicted using Fault Tree Analysis and Event Tree Analysis respectively. Results from the case study considered revealed the capability of the proposed method in estimating the likelihood of various outcomes as well as predicting the future probability. In addition the scheme offers opportunity to provide dynamic adjustment by updating the failure probability with actual plant data. Results from the analysis can be used to plan maintenance and management of change as required by the plant condition.
Visualization of Auto-ignition Phenomenon Under the Controlled Burst Pressure
Oct 2015
Publication
A high-pressure hydrogen jet released into the air has the possibility of igniting in a tube without any ignition source. The mechanism of this phenomenon called spontaneous ignition is considered to be that hydrogen diffuses into the hot air caused by the shock wave from diaphragm rupture and the hydrogen-oxidizer mixed region is formed enough to start chemical reaction. Recently flow visualization studies on the spontaneous ignition process have been conducted to understand its detailed mechanism but such ignition has not yet been well clarified. In this study the spontaneous ignition phenomenon was observed in a rectangular tube. The results confirm the presence of a flame at the wall of the tube when the shock wave pressure reaches 1.2–1.5 MPa in more than 9 MPa burst pressure and that ignition occurs near the wall followed by multiple ignitions as the shock wave propagates with the ignitions eventually combining to form a flame.
Simulation of the Fast Filling of Hydrogen Tanks
Sep 2009
Publication
High pressure storage of hydrogen in tanks is a promising option to provide the necessary fuel for transportation purposes. The fill process of a high-pressure tank should be reasonably short but must be designed to avoid too high temperatures in the tank. The shorter the fill should be the higher the maximum temperature in the tank climbs. For safety reasons an upper temperature limit is included in the requirements for refillable hydrogen tanks (ISO 15869) which sets the limit for any fill optimization. It is crucial to understand the phenomena during a tank fill to stay within the safety margins.<br/>The paper describes the fast filling process of hydrogen tanks by simulations based on the Computational Fluid Dynamics (CFD) code CFX. The major result of the simulations is the local temperature distribution in the tank depending on the materials of liner and outer thermal insulation. Different material combinations (type III and IV) are investigated.<br/>Some measurements from literature are available and are used to validate the approach followed in CFX to simulate the fast filling of tanks. Validation has to be continued in future to further improve the predictability of the calculations for arbitrary geometries and material combinations.
Numerical Simulations of Spontaneous Ignition of High-pressure Hydrogen Based on Detailed Chemical Kinetics
Sep 2013
Publication
A two-dimensional (2-D) simulation of spontaneous ignition of high-pressure hydrogen in a length of duct is conducted in order to explore its underlying ignition mechanisms. The present study adopts a 2-D rectangular duct (i.e. not axisymmetric geometry) and focuses on the effects of initial diaphragm shape on the spontaneous ignitions. The Navier-Stokes equations with a detailed chemical kinetics mechanism are solved in a manner of direct numerical simulation. The detailed mechanisms of spontaneous ignition are discussed for each initial diaphragm shape. For a straight diaphragm shape it is found that the ignition occurs only near the wall due to the adiabatic wall condition while the three ignition events: ignitions due to leading shock wave reflection at the wall hydrogen penetration into shock-heated air near the wall and deep penetration of hydrogen into shock-heated air behind the leading shock wave are identified for a largely deformed diaphragm shape.
QRA Including Utility for Decision Support of H2 Infrastructure Licensing
Sep 2011
Publication
Rational decision making in land use planning and licensing of H2 infrastructure surrounded by other industrial activities and population should take account of individual and societal risks. QRA produces a risk matrix of potential consequences versus event probabilities that is shrouded in ambiguity and lacking transparency. NIMBY and conflict are lurking. To counter these issues risk analysts should therefore also determine the utilities of decision alternatives which describe desirability of benefits on a single scale. Rationally weighing risks versus benefits results in more transparent and defendable decisions. Example risk analyses of two types of refuelling stations and three hydrogen supply transportation types applying Influence Diagram/BBNs are worked out. Keywords: risk assessment influence diagram decision making land use planning
Numerical Study on Detailed Mechanism of H2-Air Flame Jet Ignition
Sep 2013
Publication
Jet ignition was recognized in the 1970s and has since been applied to automobile engines such as the Honda CVCC. In the 1990s jet ignition was observed in explosions and was seen as a problem that may relate to jet ignition. Our group presented jet ignition experimentally and numerically in 1999 and later using LIF measurements with the same experimental vessel as used in 1999. However the detailed mechanism of jet ignition was not clarified at that time. The target of this study is to clarify how jet ignition happens and to understand the detailed mechanism of flame jet ignition.
Safety Considerations for Hydrogen Test Cells
Sep 2009
Publication
The properties of hydrogen compared to conventional fuels such as gasoline and diesel are substantially different requiring adaptations to the design and layout of test cells for hydrogen fuelled engines and vehicles. A comparison of hydrogen fuel properties versus conventional fuels in this paper provides identification of requirements that need to be adapted to design a safe test cell. Design examples of actual test cells are provided to showcase the differences in overall layout and ventilation safety features fuel supply and metering and emissions measurements. Details include requirements for ventilation patterns the necessity for engine fume hoods as well as hydrogen specific intake and exhaust design. The unique properties of hydrogen in particular the wide flammability limits and nonvisible flames also require additional safety features such as hydrogen sensors and flame cameras. A properly designed and implemented fuel supply system adds to the safety of the test cell by minimizing the amount of hydrogen that can be released. Apart from this the properties of hydrogen also require different fuel consumption measurement systems pressure levels of the fuel supply system additional ventilation lines strategically placed safety solenoids combined with appropriate operational procedures. The emissions measurement for hydrogen application has to be expanded to include the amount of unburned hydrogen in the exhaust as a measurement of completeness of combustion. This measurement can also be used as a safety feature to avoid creation of ignitable hydrogen-air mixtures in the engine exhaust. The considerations provided in this paper lead to the conclusion that hydrogen IC engines can be safely tested however properly designed test cell and safety features have to be included to mitigate the additional hazards related to the change in fuel characteristics.
Ignited Releases of 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 (LH2) 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/>Several research projects have been undertaken already at HSL with the aim of identifying and addressing hazards relating to the storage and transport of bulk LH2 that are associated with hydrogen refuelling stations located in urban environments.<br/>The first phase of the research was to produce a position paper on the hazards of LH2 (Pritchard and Rattigan 2009). This was published as an HSE research report RR769 in 2010. <br/>The second phase developed an experimental and modelling strategy for issues associated with LH2 spills and was published as an internal report HSL XS/10/06. The subsequent experimental work is a direct implementation of that strategy. LH2 was first investigated experimentally (Royle and Willoughby 2012 HSL XS/11/70) as large-scale spills of LH2 at a rate of 60 litres per minute. Measurements were made on unignited releases which included the concentration of hydrogen in air thermal gradients in the concrete substrate liquid pool formation and temperatures within the pool. Computational modelling on the un-ignited spills was also performed (Batt and Webber 2012 HSL MSU/12/01).<br/>The experimental work on ignited releases of LH2 detailed in this report is a direct continuation of the work performed by Royle and Willoughby.<br/>The aim of this work was to determine the hazards and severity of a realistic ignited spill of LH2 focussing on; flammability limits of an LH2 vapour cloud flame speeds through an LH2 vapour cloud and subsequent radiative heat and overpressures after ignition. The results of the experimentation 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.
Safety Considerations and Approval Procedures for the Integration of Fuel Cells on Board of Ships
Sep 2009
Publication
The shipping industry is becoming increasingly visible on the global environmental agenda. Shipping's hare of emissions to air is regarded to be significant and public concern lead 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 additional 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 main propulsion. The presentation summarizes the legal background in international shipping related to the use for gas as ship fuel and fuel cells. The focus of the presentation will be on the safety principles for the use of gas as fuel and fuel cells on board of ships and boats. The examples given show the successful integration of such systems on board of ships. Furthermore a short outlook will be given to the ongoing and planed projects for the use of fuel cells on board of ships.
Experimental Study of the Effects of Vent Geometry on the Dispersion of a Buoyant Gas in a Small Enclosure
Sep 2011
Publication
We present an experimental study on the dispersion of helium in an enclosure of 1 m3 with natural ventilation through one vent. Three vent geometries have been studied. Injection parameters have been varied so that the injection Richardson number ranges from 2·10−6 to 9 and the volume Richardson number which gives the ability of the release to mix the enclosure content ranges from 8·10−4 to 900. It has been found that the vertical distribution of helium volume fraction can exhibit significant gradient. Nevertheless the results are compared to the simple analytical model based on the homogenous mixture hypothesis which gives fairly good estimates of the maximum helium volume fraction.
Delayed Explosion of Hydrogen High Pressure Jets in a Highly Obstructed Geometry
Sep 2017
Publication
Delayed explosions of accidental high pressure hydrogen releases are an important risk scenario in safety studies of production plants transportation pipelines and fuel cell vehicles charging stations. Such explosions were widely explored in multiple experimental and numerical investigations. Explosion of high pressure releases in highly obstructed geometries with high blockage ratio is a much more complicated phenomenon. This paper is dedicated to the experimental investigation of the influence of obstacles on a delayed deflagration of hydrogen jets. The computational fluid dynamics (CFD) code FLACS is used to reproduce experimental data. In the current study the computed overpressure signals are compared to the experimentally measured ones at different monitoring points. Simulations are in close agreement with experimental results and can be used to predict overpressure where experimental pressure detectors were saturated. For homogenous stationary clouds a new approach of equivalent mixture of H2/air (~16.5%) to stoichiometric mixture of CH4/air is suggested. This approach is validated versus experimental data from the literature in terms of overpressure maxima. A parametric study is performed using FLACS for various concentrations in the same geometry in order to identify a possible transition from deflagration to detonation.
A Numerical Simulation of Hydrogen Diffusion for the Hydrogen Leakage from a Fuel Cell Vehicle in an Underground Parking Garage
Sep 2011
Publication
In the present study the diffusion process of hydrogen leaking from a FCV (Fuel Cell Vehicle) in an underground parking garage is analyzed by numerical simulations in order to assess the risk of a leakage accident. The temporal and spatial evolution of the hydrogen concentration as well as the flammable region in the parking garage was predicted numerically. The effects of the leakage flow rate and an additional ventilation fan were investigated to evaluate the ventilation performance to relieve the accumulation of the hydrogen gas. The volume of the flammable region shows a non-linear growth in time and rapidly increases eventually. The present numerical analysis can provide a physical insight and quantitative data for safety of various hydrogen applications.
Allowable Hydrogen Permeation Rate From Road Vehicle Compressed Gaseous Storage Systems In Garages- Part 1- Introduction, Scenarios, and Estimation of an Allowable Permeation Rate
Sep 2009
Publication
The paper presents an overview of the main results of the EC NOE HySafe activity to estimate an allowable hydrogen permeation rate for automotive legal requirements and standards. The work was undertaken as part of the HySafe internal project InsHyde.<br/>A slow long term hydrogen release such as that due to permeation from a vehicle into an inadequately ventilated enclosed structure is a potential risk associated with the use of hydrogen in automotive applications. Due to its small molecular size hydrogen permeates through the containment materials found in compressed gaseous hydrogen storage systems and is an issue that requires consideration for containers with non-metallic (polymer) liners. Permeation from compressed gaseous hydrogen storage systems is a current hydrogen safety topic relevant to regulatory and standardisation activities at both global and regional levels.<br/>Various rates have been proposed in different draft legal requirements and standards based on different scenarios and the assumption that hydrogen dispenses homogeneously. This paper focuses on the development of a methodology by HySafe Partners (CEA NCSRD. University of Ulster and Volvo Technology) to estimate an allowable upper limit for hydrogen permeation in automotive applications by investigating the behaviour of hydrogen when released at small rates with a focus on European scenario. The background to the activity is explained. reasonable scenarios are identified a methodology proposed and a maximum hydrogen permeation rate from road vehicles into enclosed structures is estimated The work is based on conclusions from the experimental and numerical investigations described by CEA NCSRD and the University of Ulster in related papers.
The Hydrogen Economy - Evaluation of the Materials Science and Engineering Issues
Jan 2005
Publication
The main objectives were to identify materials issues relating to the widespread use of hydrogen as a fuel.
MAIN FINDINGS
MAIN FINDINGS
- Hydrogen is seen by many as the answer to the environmental problems of reliance on fossil fuels for energy needs. A great deal of effort is currently being invested in research into all areas of the hydrogen economy such as fuel cells hydrogen generation transportation and storage.
- Fuel cells have the potential to provide power for a very wide range of applications ranging from small portable electronics devices to large stationary electricity production and vehicles covering the whole range of road vehicles and possibly extending to rail marine and even aviation.
- The main obstacles to achieving a viable hydrogen economy are costs of producing hydrogen from renewable sources issues relating to transportation and storage due to the low energy density of hydrogen gas and the cost and reliability of fuel cells.
- The main material considerations relating to the use of hydrogen are hydrogen embrittlement material properties at cryogenic temperatures (due to use of liquid hydrogen) and permeability.
- A number of new materials are likely to come to prominence in a hydrogen economy; high performance composites are likely to be used extensively for high pressure hydrogen cylinders new materials or combinations of materials may be used for hydrogen pipelines and a range of new materials are currently being considered for hydrogen storage such as metal hydrides and carbon nanotubes.
- Due to the effect of hydrogen on materials it is important to test any materials in the environment in which they would be used. Depending on the type of test this could require the use of very specialist expensive equipment.
Status, Gaps and Recommendations Regarding Standardisation and the Use of Hydrogen in Sustainable Buildings
Sep 2013
Publication
The use of and interpretation of Regulations Codes and Standards is important input when developing hydrogen systems and applications. This paper presents the work related to standardisation undertaken by DNV as part of the EU supported project H2SusBuild. During the H2SusBuild project a renewable (solar and wind) based full scale energy system with components for hydrogen storage hydrogen production by electrolysis and hydrogen consumption by fuel cell and burner was built and integrated into an existing office building in Lavrion Greece. The relevant standards identified and applied the standardisation gaps identified and the recommendations made for further standardisation activities are presented.
H-Mat Hydrogen Compatibility of Polymers and Elastomers
Sep 2019
Publication
The H2@Scale program of the U.S. Department of Energy (DOE) Fuel Cell Technologies Office is supporting work on the hydrogen compatibility of polymers to improve the durability and reliability of materials for hydrogen infrastructure. The hydrogen compatibility program (H-Mat) seeks “to address the challenges of hydrogen degradation by elucidating the mechanisms of hydrogen-materials interactions with the goal of providing science-based strategies to design materials (micro)structures and morphology with improved resistance to hydrogen degradation.” This research has found hydrogen and pressure interactions with model rubber-material compounds demonstrating volume change and compression-set differences in the materials. The research leverages state-of-the-art capabilities of the DOE national labs. The materials were investigated using helium-ion microscopy which revealed significant morphological changes in the plasticizer incorporating compounds after exposure as evidenced by time-of-flight secondary ion mass spectrometry. Additional studies using transmission electron microscopy and nuclear magnetic resonance revealed that nanosized inclusions developed after gas decompression in rubber- and plasticizer-only materials; this is an indication of void formation at the nanometer level.
Comparisons of Helium and Hydrogen Releases in 1 M3 and 2 M3 Two Vents Enclosures: Concentration Measurements at Different Flow Rates and for Two Diameters of Injection Nozzle
Oct 2015
Publication
This work presents a parametric study on the similitude between hydrogen and helium distribution when released in the air by a source located inside of a naturally ventilated enclosure with two vents. Several configurations were experimentally addressed in order to improve knowledge on dispersion. Parameters were chosen to mimic operating conditions of hydrogen energy systems. Thus the varying parameters of the study were mainly the source diameter the releasing flow rate the volume and the geometry of the enclosure. Two different experimental set-ups were used in order to vary the enclosure's height between 1 and 2 m. Experimental results obtained with helium and hydrogen were compared at equivalent flow rates determined with existing similitude laws. It appears for the plume release case that helium can suitably be used for predicting hydrogen dispersion in these operating designs. On the other hand – when the flow turns into a jet – non negligible differences between hydrogen and helium dispersion appear. In this case helium – used as a direct substitute to hydrogen – will over predict concentrations we would get with hydrogen. Therefore helium concentration read-outs should be converted to obtain correct predictions for hydrogen. However such a converting law is not available yet.
Safety and Regulatory Challenges of Using Hydrogen/Natural Gas Blends in the UK
Sep 2019
Publication
The addition of hydrogen to natural gas for heating and cooking is being considered as a route to reducing carbon emissions in the United Kingdom (UK). The HyDeploy programme (hereafter referred to as HyDeploy) aims to demonstrate that hydrogen can be added to the natural gas supply without compromising public safety or appliance performance. This paper relates to the preparatory work for hydrogen injection on a live site at Keele University closed network comprising domestic premises multi-occupancy buildings and light commercial premises. The project is based around the injection of up to 20 %mol/mol hydrogen into mains natural gas at pressures below 2 barg. Work streams addressed during the pre-trial preparation included; assessment of material interaction with hydrogen blends for all distribution system components and appliances; understanding of gas appliance behaviour; review of: gas detection systems fire and explosion considerations routine and emergency procedural considerations; and the design of a new hydrogen injection grid entry unit. This paper describes the safety and regulatory challenges that were encountered during preparation of the project including obtaining the necessary regulatory permissions to blend hydrogen gas.
Effect of Temperature on Laminar Flame Velocity for Hydrogen-air Mixtures at Reduced Pressures
Sep 2013
Publication
The work was done with respect to hydrogen safety of ITER vacuum vessel in cases of loss of cooling and loss of vacuum accidents. Experiments were conducted at sub-atmospheric pressures from 1 bar to 200 mbar and elevated temperatures up to 300 oC. Hydrogen concentration was changed from lower to upper flammability limits in all the range of pressures and temperatures. The experiments were performed in a spherical explosion bomb equipped with two quartz windows. The flame propagation velocity was measured using pressure method and high speed shadow cinematography. The theoretical flame velocities were calculated by Cantera code using Lutz and Mueller mechanisms. The influence of the initial temperature and pressure conditions on the laminar flame speed SL overall reaction order n and Markstein length LM are presented in this work and compared with the results of a theoretical model.
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