Safety
Interaction of Hydrogen Jets with Hot Surfaces of Various Sizes and Temperatures
Sep 2019
Publication
The formation of hydrogen jets from pressurized sources and ignition has been studied by many projects also when hitting hot devices. In the paper presented at the conference 2 years ago the ignition was caused by glow plug a “point like source” at various temperatures distances of igniter and source and source pressures. In continuation of that work ignition now occurred by 1 or 3 platelets of size 45 x 18 mm at a temperatures of 1223 K. When hitting these hot platelets the resulting flame explosions and flame jets show interesting characteristics in contrast to the point like ignition where the explosions drifts downstream with the jet. Parameters of the experiments vary in initial pressure of the tubular source (10 20 and 40 MPa) distance between the nozzle and the hot surface (3 5 and 7 m) and temperature of the hot surface (1223 K). The initial explosions stabilize already at the stagnation point or the wake of the hot platelets. Furthermore flames propagate upstream and downstream depending on the pressure of the hydrogen reservoir and the distance. The achieved flame velocities vary strongly from 30 to 240 m/s. With all investigated hydrogen pressures strong reactions v > 40 m/s occur at platelet distances of 3 and 5 m. The higher values are mainly achieved with jets with 40 MPa pressure at 3 m distance. In these cases the initial explosion contours show irregular shapes. Various effects are found like explosion separation further independently initiated explosions and two parallel flame jets upstream as well as downstream.
Comparison of Two-layer Model for High Pressure Hydrogen Jets with Notional Nozzle Model Predictions and Experimental Data
Oct 2015
Publication
A two-layer reduced order model of high pressure hydrogen jets was developed which includes partitioning of the flow between the central core jet region leading to the Mach disk and the supersonic slip region around the core. The flow after the Mach disk is subsonic while the flow around the Mach disk is supersonic with a significant amount of entrained air. This flow structure significantly affects the hydrogen concentration profiles downstream. The predictions of this model are compared to previous experimental data for high pressure hydrogen jets up to 20 MPa and to notional nozzle models and CFD models for pressures up to 35 MPa using ideal gas properties. The results show that this reduced order model gives better predictions of the mole fraction distributions than previous models for highly underexpanded jets. The predicted locations of the 4% lower flammability limit also show that the two-layer model much more accurately predicts the measured locations than the notional nozzle models. The comparisons also show that the CFD model always underpredicts the measured mole fraction concentrations.
Large Scale Experiments and Model Validation of Pressure Peaking Phenomena-ignited Hydrogen Releases
Jan 2021
Publication
The Pressure Peaking Phenomena (PPP) is the effect of introducing a light gas into a vented volume of denser gas. This will result in a nonequilibrium pressure as the light gas pushes the dense gas out at the vent. Large scale experiments have been performed to produce relevant evidence. The results were used to validate an analytical model. Pressure and temperature were measured inside a constant volume while the mass flow and vent area were varied. The analytical model was based on the conservation of mass and energy. The results showed that increasing the mass flow rate the peak pressure increases and with increasing the ventilation area the peak pressure decreases. Peak pressure was measured above 45 kPa. Longer combustion time resulted in higher temperatures increasing an underpressure effect. The experimental results showed agreement with the analytical model results. The model predicts the pressures within reasonable limits of+/-2 kPa. The pressure peaking phenomena could be very relevant for hydrogen applications in enclosures with limited ventilation. This could include car garages ship hull compartments as well as compressor shielding. This work shows that the effect can be modeled and results can be used in design to reduce the consequences.
Development of a Model Evaluation Protocol for CFD Analysis of Hydrogen Safety Issues – The SUSANA Project
Oct 2015
Publication
The “SUpport to SAfety aNAlysis of Hydrogen and Fuel Cell Technologies (SUSANA)” project aims to support stakeholders using Computational Fluid Dynamics (CFD) for safety engineering design and assessment of FCH systems and infrastructure through the development of a model evaluation protocol. The protocol covers all aspects of safety assessment modelling using CFD from release through dispersion to combustion (self-ignition fires deflagrations detonations and Deflagration to Detonation Transition - DDT) and not only aims to enable users to evaluate models but to inform them of the state of the art and best practices in numerical modelling. The paper gives an overview of the SUSANA project including the main stages of the model evaluation protocol and some results from the on-going benchmarking activities.
Numerical Prediction of Cryogenic Hydrogen Vertical Jets
Sep 2019
Publication
Comparison of Computational Fluid Dynamics (CFD) predictions with measurements is presented for cryo-compressed hydrogen vertical jets. The stagnation conditions of the experiments are characteristic of unintended leaks from pipe systems that connect cryogenic hydrogen storage tanks and could be encountered at a fuel cell refuelling station. Jets with pressure up to 5 bar and temperatures just above the saturation liquid temperature were examined. Comparisons are made to the centerline mass fraction and temperature decay rates the radial profiles of mass fraction and the contours of volume fraction. Two notional nozzle approaches are tested to model the under-expanded jet that was formed in the tests with pressures above 2 bar. In both approaches the mass and momentum balance from the throat to the notional nozzle are solved while the temperature at the notional nozzle was assumed equal to the nozzle temperature in the first approach and was calculated by an energy balance in the second approach. The two approaches gave identical results. Satisfactory agreement with the measurements was found in terms of centerline mass fraction and temperature. However for test with 3 and 4 bar release the concentration was overpredicted. Furthermore a wider radial spread was observed in the predictions possibly revealing higher degree of diffusion using the k-ε turbulence model. An integral model for cryogenic jets was also developed and provided good results. Finally a test simulation was performed with an ambient temperature jet and compared to the cold jet showing that warm jets decay faster than cold jets.
An Investigation of Mobile Hydrogen and Fuel Cell Technology Applications
Sep 2019
Publication
Safe practices in the production storage distribution and use of hydrogen are essential for the widespread acceptance of hydrogen and fuel cell technologies. A significant safety incident in any project could damage public perception of hydrogen and fuel cells. A recent incident involving a hydrogen mobile storage trailer in the United States has brought attention to the potential impacts of mobile hydrogen storage and transport. Road transport of bulk hydrogen presents unique hazards that can be very different from those for stationary equipment and new equipment developers may have less experience and expertise than seasoned gas providers. In response to the aforementioned incident and in support of hydrogen and fuel cell activities in California the Hydrogen Safety Panel (HSP) has investigated the safety of mobile hydrogen and fuel cell applications (mobile auxiliary/emergency fuel cell power units mobile fuellers multi-cylinder trailer transport unmanned aircraft power supplies and mobile hydrogen generators). The HSP examined the applications requirements and performance of mobile applications that are being used extensively outside of California to understand how safety considerations are applied. This paper discusses the results of the HSP’s evaluation of hydrogen and fuel cell mobile applications along with recommendations to address relevant safety issues.
Validation of Two-Layer Model for Underexpanded Hydrogen Jets
Sep 2019
Publication
Previous studies have shown that the two-layer model more accurately predicts hydrogen dispersion than the conventional notional nozzle models without significantly increasing the computational expense. However the model was only validated for predicting the concentration distribution and has not been adequately validated for predicting the velocity distributions. In the present study particle imaging velocimetry (PIV) was used to measure the velocity field of an underexpanded hydrogen jet released at 10 bar from a 1.5 mm diameter orifice. The two-layer model was the used to calculate the inlet conditions for a two-dimensional axisymmetric CFD model to simulate the hydrogen jet downstream of the Mach disk. The predicted velocity spreading and centerline decay rates agreed well with the PIV measurements. The predicted concentration distribution was consistent with data from previous planar Rayleigh scattering measurements used to verify the concentration distribution predictions in an earlier study. The jet spreading was also simulated using several widely used notional nozzle models combined with the integral plume model for comparison. These results show that the velocity and concentration distributions are both better predicted by the two-layer model than the notional nozzle models to complement previous studies verifying only the predicted concentration profiles. Thus this study shows that the two-layer model can accurately predict the jet velocity distributions as well as the concentration distributions as verified earlier. Though more validation studies are needed to improve confidence in the model and increase the range of validity the present work indicates that the two-layer model is a promising tool for fast accurate predictions of the flow fields of underexpanded hydrogen jets.
Thermal Radiation Properties of Large Hydrogen Leaks from Gas Distribution Networks
Sep 2019
Publication
Determination of the behaviour of hydrogen when leaking from pipework on gas distribution assets is essential in assessing the comparative risk associated with using pure hydrogen in place of natural gas in existing assets. Experimental work considering the behaviour of gaseous hydrogen when released in large volumes from gas distribution pipework at pressures of up to 7 barg through holes of up to 200mm in diameter in both buried and unburied scenarios is currently underway. The present paper presents and briefly discusses the results from a set of ignited 20mm diameter releases of hydrogen at pressures up to 7 barg vertically upwards from a pipe in an open excavation. Gaseous releases which find a direct route to atmosphere have the potential to create significant volumes of flammable gas and subsequently significant fires in the case of ignition. It is important to understand both the dispersion distances and thermal hazard field to be able to understand the comparative risk posed when compared to natural gas releases in similar situations. Results of current work completed to date are presented alongside comparisons with known properties of natural gas releases and the potential implications to the comparative risk of hydrogen network operation. The work has been conducted at the DNV GL Spadeadam Testing and Research Centre UK as part of the UK Gas Distribution Networks and Ofgem National Innovation Competition funded H21 project.
Experimental Measurements, CFD Simulations and Model for a Helium Release in a Two Vents Enclosure
Sep 2017
Publication
The present work proposes improvements on a model developed by Linden to predict the concentration distribution in a 2 vented cavities. Recent developments on non constant entrainment coefficient from Carazzo et al as well as a non constant pressure distribution at the vents-the vents being vertical-are included in the Linden approach. This model is compared with experimental results from a parametric study on the influence of the height of the release source on the helium dispersion regimes inside a naturally ventilated 2 vents enclosure. The varying parameters of the study were mainly the height of the release the releasing flow rate and the geometry of the vents. At last Large Eddy Simulations of the flow and Particle Image Velocimetry measurements performed on a small 2 vented cavity are presented. The objective is to have a better understanding of the flow structure which is at the origin of the 2 layers concentration distribution described by Linden.
Numerical Modelling of Unconfined and Confined Hydrogen Explosion
Sep 2019
Publication
Numerical studies were conducted with the objective of gaining a better understanding of the consequences of potential explosion that could be associated with release of hydrogen in a confined and unconfined environment. This paper describes the work done by us in modelling explosion of accidental releases of hydrogen using our Fire Explosion Release Dispersion (FRED) software. CAM and SCOPE models in FRED is used for validation of congested/uncongested unconfined and congested/uncongested confined vapour cloud explosion respectively. In the first step CAM is validated against experiments of varying gas cloud size blockage ratio equivalence ratio of the mixture and blockage configuration. The model predictions of explosion overpressure are in good agreement with experiments. The results obtained from FRED i.e. overpressure as a function of distance match well in comparison to the experiments. In the second step SCOPE is validated against vented explosion experiments available in open literature. In general SCOPE reproduces the maximum overpressure within the factor of 2. Moreover it well predicts the trends of increase in overpressure with change in type of the fuel increase in number of obstacles blockage ratio and decrease in the vent size.
Compliance Measurements of Fuel Cell Electric Vehicle Exhaust
Sep 2019
Publication
The NREL Sensor Laboratory has been developing an analyzer that can verify compliance to the international United Nations Global Technical Regulation number 13 (GTR 13--Global Technical Regulation on Hydrogen and Fuel Cell Vehicles) prescriptive requirements pertaining to allowable hydrogen levels in the exhaust of fuel cell electric vehicles (FCEV) [1]. GTR 13 prescribes that the FCEV exhaust shall remain below 4 vol% H2 over a 3-second moving average and shall not at any time exceed 8 vol% H2 as verified with an analyzer with a response time (t90) of 300 ms or faster. GTR 13 has been implemented and is to serve as the basis for national regulations pertaining to hydrogen powered vehicle safety in the United States Canada Japan and the European Union. In the U.S. vehicle safety is overseen by the Department of Transportation (DOT) through the Federal Motor Vehicle Safety Standards (FMVSS) and in Canada by Transport Canada through the Canadian Motor Vehicle Safety Standard (CMVSS). The NREL FCEV exhaust analyzer is based upon a low-cost commercial hydrogen sensor with a response time (t90) of less than 250 ms. A prototype analyzer and gas probe assembly have been constructed and tested that can interface to the gas sampling system used by Environment and Climate Change Canada’s (ECCC) Emission Research and Measurement Section (ERMS) for the exhaust gas analysis. Through a partnership with Transport Canada ECCC will analyze the hydrogen level in the exhaust of a commercial FCEV. ECCC will use the NREL FCEV Exhaust Gas analyzer to perform these measurements. The analyzer was demonstrated on a FCEV operating under simulated road conditions using a chassis dynamometer at a private facility.
Effect of the Time Dependent Loading of Type IV Cylinders Using a Multi-scalemodel
Sep 2019
Publication
The current requirements for composite cylinders are still based on an arbitrary approach derived from the behaviour of metal structures that the designed burst pressure should be at least 2.5 times the maximum in-service pressure. This could lead to an over-designed composite cylinder for which the weight saving would be less than optimum. Moreover predicting the lifetime of composite cylinders is a challenging task due to their anisotropic characteristics. A federal research institute in Germany (BAM) has proposed a minimum load-cycle requirement that mitigates this issue by using a MonteCarlo analysis of the burst test results. To enrich this study more experiments are required however they are normally limited by the necessity of long duration testing times (loading rate and number of cylinders) and the design (stacking sequence of the composite layer). A multi-scale model incorporating the micromechanical behaviour of composite structures has been developed at Mines ParisTech. The model has shown similar behaviour to that of composite cylinders under different loading rates. This indicates that the model could assist the Monte-Carlo analysis study. An evaluation of the multi-scale model therefore has been carried out to determine its limitations in predicting lifetimes of composite cylinders. The evaluation starts with the comparison of burst pressures with type IV composite cylinders under different loading rates. A μCT-Scan of a type IV cylinder has been carried out at the University of Southampton. The produced images were analysed using the Fast-Fourier Transform (FFT) technique to determine the configuration of the composite layers which is required by the model. Finally the time dependent effect studied by using the multi scale model has been described. In the long-term this study can be used to conduct a parametric study for creating more efficient design of type IV cylinders.
Numerical Analysis for Hydrogen Flame Acceleration during a Severe Accident in the APR1400 Containment Using a Multi-Dimensional Hydrogen Analysis System
Nov 2020
Publication
Korea Atomic Energy Research Institute (KAERI) established a multi-dimensional hydrogen analysis system to evaluate hydrogen release distribution and combustion in the containment of a Nuclear Power Plant (NPP) using MAAP GASFLOW and COM3D. In particular KAERI developed an analysis methodology for a hydrogen flame acceleration on the basis of the COM3D validation results against measured data of the hydrogen combustion tests in the ENACCEF and THAI facilities. The proposed analysis methodology accurately predicted the peak overpressure with an error range of approximately ±10% using the Kawanabe model used for a turbulent flame speed in the COM3D. KAERI performed a hydrogen flame acceleration analysis using the multi-dimensional hydrogen analysis system for a severe accident initiated by a station blackout (SBO) under the assumption of 100% metal–water reaction in the Reactor Pressure Vessel (RPV) to evaluate an overpressure buildup in the containment of the Advanced Power Reactor 1400 MWe (APR1400). The magnitude of the overpressure buildup in the APR1400 containment might be used as a criterion to judge whether the containment integrity is maintained or not when the hydrogen combustion occurs during a severe accident. The COM3D calculation results using the established analysis methodology showed that the calculated peak pressure in the containment was lower than the fracture pressure of the APR1400 containment. This calculation result might have resulted from a large air volume of the containment a reduced hydrogen concentration owing to passive auto-catalytic recombiners installed in the containment during the hydrogen release from the RPV and a lot of stem presence during the hydrogen combustion period in the containment. Therefore we found that the current design of the APR1400 containment maintained its integrity when the flame acceleration occurred during the severe accident initiated by the SBO accident.
Vented Hydrogen-air Deflagrations in Low Strength Equipment and Buildings
Sep 2013
Publication
This paper aims to improve prediction capability of the vent sizing correlation presented in the form of functional dependence of the dimensionless deflagration overpressure on the turbulent Bradley number similar to our previous studies. The correlation is essentially upgraded based on recent advancements in understanding and modelling of combustion phenomena relevant to hydrogen-air vented deflagrations and unique large-scale tests carried out by different research groups. The focus is on hydrogen-air deflagrations in low-strength equipment and buildings when the reduced pressure is accepted to be below 0.1 MPa. The combustion phenomena accounted for by the correlation include: turbulence generated by the flame front itself; leading point mechanism stemming from the preferential diffusion of hydrogen in air in stretched flames; growth of the fractal area of the turbulent flame surface; initial turbulence in the flammable mixture; as well as effects of enclosure aspect ratio and presence of obstacles. The correlation is validated against the widest range of experimental conditions available to date (76 experimental points). The validation covers a wide range of test conditions: different shape enclosures of volume up to 120 m3; initially quiescent and turbulent hydrogen-air mixtures; hydrogen concentration in air from 6% to 30% by volume; ignition source location at enclosure centre near and far from a vent; empty enclosures and enclosures with obstacles.
Highly Resolve Large Eddy Simulations of a Transitional Air-helium Buoyant Jet in a Two Vented Enclosure: Validation Against Particle Image Velocimetry Experiments
Sep 2017
Publication
The article deals with LES simulations of an air-helium buoyant jet in a two vented enclosure and their validation against particle image velocimetry experiments. The main objective is to test the ability of LES models to simulate such scenarios. These types of scenarios are of first interest considering safety studies for new hydrogen systems. Three main challenges are identified. The two first are the ability of the LES model to account for a rapid laminar-to-turbulence transition mainly due to the buoyancy accelerations and the Rayleigh-Taylor instabilities that can develop due to sharp density gradients. The third one is the outlet boundary conditions to be imposed on the vent surfaces. The influence of the classical pressure boundary condition is studied by comparing the simulations results when an exterior region is added in the simulations. The comparisons against particle image velocimetry experiments show that the use of an exterior domain gives more accurate results than the classical pressure boundary condition. This result and the description of the phenomena involved are the main outlets of the article.
Hydrogen Venting Under Variable Flow Conditions
Sep 2011
Publication
Safety distances for hydrogen plumes are currently derived using models developed for hydrocarbon releases. It is well known that hydrogen behaves in a significantly different manner to that of hydrocarbons when released to atmosphere. There are two main aspects involved with the development of safety distances for credible hydrogen releases; the intensity of the thermal radiation from such a plume should it be ignited and the distance downwind from the release point to the point where a flammable mixture with air no longer exists. A number of distinct areas of venting behaviour were investigated; Thermal radiation from ignited plumes from vertical open ended vent pipes Far field radiation measurements for direct comparison with models Thermal radiation from ignited plumes from vertical vent pipes terminating in a T-piece Thermal radiation measurements from ignited hydrogen with a 45 vent termination Hydrogen concentration measurements with a T-piece.
High-Order Perturbation Solutions to a Lh2 Spreading Model With Continuous Spill
Sep 2011
Publication
High-order perturbation solutions have been obtained for the simple physical model describing the LH2 spreading with a continuous spill and are shown to improve over the first-order perturbation solutions. The non-dimensional governing equations for the model are derived to obtain more general solutions. Non-dimensional parameters are sought as the governing parameters for the non-dimensional equations and the non-dimensional evaporation rate is used as the perturbation parameter. The results show that the second-order solutions exhibit an improvement over the first-order solutions with respect to the pool volume; however there is still a difference between numerical solutions and second-order solutions in the late stage of spread. Finally it is revealed that the third-order solutions almost agree with numerical solutions.
Hydrogen Risk Assessment in Sao Paulo State, Brazil
Sep 2011
Publication
Sao Paulo State Environmental Protection Agency CETESB Brazil adopts a so called Reference Distance (RD) from hazardous substances storage facilities to populated places as a decision making tool for the application of a simplified or a full Risk Analysis (RA). As for hydrogen RD was set up based on instantaneous release scenarios where consequences reaching off-site population were estimated for delayed ignition ending up in vapor cloud explosion (VCE) with a 0.1 bar blast wave overpressure as a chosen endpoint corresponding to a 1%2of death probability range. Procedures for RD evaluation and further adoption by CETESB are presented in this paper.
Analysis of Acoustic Pressure Oscillation During Vented Deflagration
Oct 2015
Publication
In industrial buildings explosion relief panels or doors are often used to reduce damages caused by gas explosion. Decades of research produced a significant contribution to the understanding of the phenomena involved nevertheless among the aspects that need further research interaction between acoustic oscillation and the flame front is one of the more important. Interaction between the flame front and acoustic oscillation has raised technical problem in lots of combustion applications as well and had been studied theoretically and experimentally in such cases. Pressure oscillation had been observed in vented deflagration and in certain cases they are responsible for the highest pressure peak generated during the event. At Scalbatraio laboratory of Pisa University CVE test facility was built in order to investigate vented hydrogen deflagration. This paper is aimed to present an overview of the results obtained during several experimental campaigns which tests are analysed with the focus on the investigation of flame acoustic interaction phenomenon. Qualitative and quantitative analysis is presented and the possible physic generating the phenomenon investigated.
Risk Informed Separation Distances For Hydrogen Refuelling Stations
Sep 2011
Publication
The lay-out requirements developed for hydrogen systems operated in industrial environment are not suitable for the operating conditions specific to hydrogen refuelling stations (service pressure of up to 95 MPa facility for public use). A risk informed rationale has been developed to define and substantiate separation distance requirements in ISO 20100 Gaseous hydrogen – refuelling stations [1]. In this approach priority is given to preventing escalation of small incidents into majors ones with a focus on critical exposures such as places of occupancy (fuelling station retail shop) while optimizing use of the available space from a risk perspective a key objective for being able to retrofit hydrogen refuelling in existing stations.
A Study of Hydrogen Flame Length with Complex Nozzle Geometry
Sep 2017
Publication
The growing number of hydrogen fillings stations and cars increases the need for accurate models to determine risk. The effect on hydrogen flame length was measured by varying the diameter of the spouting nozzle downstream from the chocked nozzle upstream. The results was compared with an existing model for flame length estimations. The experimental rig was setup with sensors that measured accurately temperature mass flow heat radiation and the pressure range from 0.1 to 11 MPa. The flame length was determined with an in-house developed image-processing tool which analyzed a high-speed film of the each experiment. Results show that the nozzle geometry can cause a deviation as high as 50% compared to estimated flame lengths by the model if wrong assumptions are made. Discharge coefficients for different nozzles has been calculated and presented.
Numerical and Experimental Investigation of H2-air and H2-O2 Detonation Parameters in a 9 m Long Tube, Introduction of a New Detonation Model
Sep 2017
Publication
Experimental and numerical investigation of hydrogen-air and hydrogen-oxygen detonation parameters was performed. A new detonation model was introduced and validated against the experimental data. Experimental set-up consisted of 9 m long tube with 0.17 m in diameter where pressure was measured with piezoelectric transducers located along the channel. Numerical simulations were performed within OpenFoam code based on progress variable equation where the detonative source term accounts for autoignition effects. Autoignition delay times were computed at a simulation run-time with the use of a multivariate regression model where independent variables were: pressure temperature and fuel concentration. The dependent variable was the autoignition delay time. Range of the analyzed gaseous mixture composition varied between 20% and 50% of hydrogen-air and 50%–66% of hydrogen in oxygen. Simulations were performed using LES one-equation eddy viscosity turbulence model in 2D and 3D. Calculations were validated against experimental data.
Safety Concept of Nuclear Cogeneration of Hydrogen and Electricity
Oct 2015
Publication
There is a significant potential for nuclear combined heat and power (CHP) in quite a number of industries. The reactor concepts of the next generation would be capable to open up in particular the high temperature heat market where nuclear energy is applicable to the production processes of hydrogen (or liquid fuels) by steam reforming or water splitting. Due to the need to locate a nuclear facility near the hydrogen plant an overall safety concept has to deal with the question of safety of the combined nuclear/industrial system by taking into account a qualitatively new class of events characterized by interacting influences. Specific requirements will be determined by such factors as the reactor type the nature of the industrial process the separation distances of the industrial facility and population centers from the nuclear plant and prevailing public attitudes. Based on the Japanese concept of the GTHTR300C nuclear reactor for electricity and hydrogen cogeneration theoretical studies were conducted on the release dispersive transport and explosion of a hydrogen cloud in the atmosphere for the sake of assessing the required minimum separation distance to avoid any risk to the nuclear plant's safety systems. In the case of sulfur-iodine water splitting the accidental release of process intermediates including large amounts of sulfur dioxide sulfur trioxide and sulfuric acid need to be investigated as well to estimate the potential risk to nuclear installations like the operators' room and estimate appropriate separation distances against toxic gas propagation. Results of respective simulation studies will be presented.
Effect of Initial Turbulence on Vented Explosion Over Pressures from Lean Hydrogen-air Deflagrations
Sep 2013
Publication
To examine the effect of initial turbulence on vented explosions experiments were performed for lean hydrogen–air mixtures with hydrogen concentrations ranging from 12 to 15% vol. at elevated initial turbulence. As expected it was found that an increase in initial turbulence increased the overall flame propagation speed and this increased flame propagation speed translated into higher peak overpressures during the external explosion. The peak pressures generated by flame–acoustic interactions however did not vary significantly with initial turbulence. When flame speeds measurements were examined it was found that the burning velocity increased with flame radius as a power function of radius with a relatively constant exponent over the range of weak initial turbulence studied and did not vary systematically with initial turbulence. Instead the elevated initial turbulence increased the initial flame propagation velocities of the various mixtures. The initial turbulence thus appears to act primarily by generating higher initial flame wrinkling while having a minimal effect on the growth rate of the wrinkles. For practical purposes of modelling flame propagation and pressure generation in vented explosions the increase in burning velocity due to turbulence is suggested to be approximated by a single constant factor that increases the effective burning velocity of the mixture. When this approach is applied to a previously developed vent sizing correlation the correlation performs well for almost all of the peaks. It was found however that in certain situations this approach significantly under predicts the flame–acoustic peak. This suggests that further research may be necessary to better understand the influence of initial turbulence on the development of flame–acoustic peaks in vented explosions.
Leakage-type-based Analysis of Accidents Involving Hydrogen Fueling Stations in Japan and USA
Aug 2016
Publication
To identify the safety issues associated with hydrogen fuelling stations incidents at such stations in Japan and the USA were analyzed considering the regulations in these countries. Leakage due to the damage and fracture of main bodies of apparatuses and pipes in Japan and the USA is mainly caused by design error that is poorly planned fatigue. Considering the present incidents in these countries adequate consideration of the usage environment in the design is very important. Leakage from flanges valves and seals in Japan is mainly caused by screw joints. If welded joints are to be used in hydrogen fuelling stations in Japan strength data for welded parts should be obtained and pipe thicknesses should be reduced. Leakage due to other factors e.g. external impact in Japan and the USA is mainly caused by human error. To realize self-serviced hydrogen fuelling stations safety measures should be developed to prevent human error by fuel cell vehicle users.
Measurements of Effective Diffusion Coefficient of Helium and Hydrogen Through Gypsum
Sep 2011
Publication
An experimental apparatus which was based on the ¼-scale garage previously used for studying helium release and dispersion in our laboratory was used to obtain effective diffusion coefficients of helium and hydrogen (released as forming gas for safety reasons) through gypsum panel. Two types of gypsum panel were used in the experiments. Helium or forming gas was released into the enclosure from a Fischer burner1 located near the enclosure floor for a fixed duration and then terminated. Eight thermal-conductivity sensors mounted at different vertical locations above the enclosure floor were used to monitor the temporal and spatial gas concentrations. An electric fan was used inside the enclosure to mix the released gas to ensure a spatially uniform gas concentration to minimize stratification. The temporal variations of the pressure difference between the enclosure interior and the ambience were also measured. An analytical model was developed to extract the effective diffusion coefficients from the experimental data.
Non-steady Characteristics of Dispersion and Ignitability for High-pressurized Hydrogen Jet Discharged From a Pinhole
Sep 2017
Publication
Hydrogen gas concentrations and jet velocities were measured downstream by a high response speed flame ionization detector and PIV (Particle Image Velocimetry) in order to investigate the characteristics of dispersion and ignitability for 40–82 MPa high-pressurized hydrogen jet discharged from a nozzle with 0.2 mm diameter. The light emitted from both OH radical and water vapor species yielded from hydrogen combustion ignited by an electric spark were recorded by two high speed cameras. From the results the empirical formula concerning the relationships for time-averaged concentrations concentration fluctuations and ignition probability were obtained to suggest that they would be independent of hydrogen discharge pressure.
Closing the Regulatory Gaps and Advancing Hydrogen Infrastructure Deployment in Australia
Sep 2019
Publication
With downward trends in Australian equipment manufacturing there are increased numbers of overseas designed manufactured and certified hydrogen systems being introduced into Australia. In parallel there are also opportunities for hydrogen and its carriers to be exported to overseas. Certainty of reputable codes and standards is important to meet regulatory requirements and community safety expectations locally and overseas.
This paper is a progress report of Hydrogen Mobility Australia’s (HMA) Technical Committee on mapping the regulatory codes and standards (RCS) gaps in Australia and establishing a pathway together with Standards Australia and Commonwealth and State Governments. This paper will discuss the benefits of the pathway covering the areas of:
This paper is a progress report of Hydrogen Mobility Australia’s (HMA) Technical Committee on mapping the regulatory codes and standards (RCS) gaps in Australia and establishing a pathway together with Standards Australia and Commonwealth and State Governments. This paper will discuss the benefits of the pathway covering the areas of:
- Safety – Enable Australia to implement consensual rules to minimise avoidable risks to persons and goods to an acceptable level
- Environment – Ensure protection of the environment from unacceptable damage due to the operation and effects of products processes and services linked to hydrogen
- Elimination of barriers to trade – Provide consistency between international jurisdictions enabling streamlined entry of hydrogen related equipment from overseas
- Upskilling of Australian industry participants – Gain useful learnings from countries more advanced in their progress in implementing ISO standards and hydrogen sector development
Helios- A New Method for Hydrogen Permeation Test
Sep 2013
Publication
Hydrogen induced cracking is still a severe and current threat for several industrial applications. With the aim of providing a simple and versatile device for hydrogen detection a new instrument was designed based on solid state sensor technology. New detection technique allows to execute hydrogen permeation measurement in short time and without material surface preparation. Thanks to this innovation HELIOS offers a concrete alternative to traditional experimental methods for laboratory permeability tests. In addition it is proposed as a new system for Non Destructive Testing of components in service in hydrogenating environment. Hydrogen flux monitoring is particularly relevant for risk mitigation of elements involved in hydrogen storage and transportation. Hydrogen permeation tests were performed by means of HELIOS instruments both on a plane membrane and on the wall of a gas cylinder. Results confirmed the extreme sensitivity of the detection system and its suitability to perform measurements even on non metallic materials by means of an easy-to-handle instrument.
A Study on the Continuous Spill with Limited Period of Release
Sep 2013
Publication
In this study the spread of cryogenic liquid due to a limited period of release is investigated for the first time to clarify the unclear conventional concept regarding two release types continuous and instantaneous release. In describing instantaneous release a discharge time has been assumed to be infinitesimally small; however such an assumption is unreal because there exists a finite period of release no matter how rapid it is. If the discharge time is less than the entire time domain the instantaneous release model should be added to the continuous model from the end of the time. This combined release that consists of the initial continuous model and subsequent instantaneous model is more realistic than the instantaneous release. The physical phenomenon is governed by three parameters: the evaporation rate per unit area release time and spill quantity. Third-order perturbation solutions are obtained and compared with a numerical solution to verify the perturbation solution. For the same spill quantity the combined model that consists of continuous and subsequent instantaneous model is necessary for small release times whereas the continuous model is only required for large release times. Additionally the combined release model is necessary for a small spill quantity at a fixed release time. These two release models are clearly distinguished using the perturbation solution.
Uncertainties in Explosion Risk Assessment for a Hydrogen Refuelling Station
Sep 2011
Publication
The project “Towards a Hydrogen Refuelling Infrastructure for Vehicles” (THRIVE) aimed at the determination of conditions to stimulate the building of a sustainable infrastructure for hydrogen as a car fuel in The Netherlands. Economic scenarios were constructed for the development of such an infrastructure for the next one to four decades. The eventual horizon will require the erection of a few hundred to more than a thousand hydrogen refuelling stations (HRS) in The Netherlands. The risk acceptability policy in The Netherlands implemented in the External Safety Establishments decree requires the assessment and management of safety risks imposed on the public by car fuelling stations. In the past a risk-informed policy has been developed for the large scale introduction of liquefied petroleum gas (LPG) as a car fuel and a similar policy will also be required if hydrogen is introduced in the public domain. A risk assessment methodology dedicated to cope with accident scenarios relevant for hydrogen applications is to be developed. Within the THRIVE project a demo risk assessment was conducted for the possible implementation of an HRS within an existing station for conventional fuels. The studied station is located in an urban area occupied with housing and commercial activities. The HRS is based on delivery and on-site storage of liquid hydrogen and dispensing of high pressure gaseous hydrogen into vehicles. The main challenges in the risk assessment were in the modelling of release and dispersion of liquid hydrogen. Definition of initial conditions for computational fluid dynamics (CFD) modelling to evaluate dispersion of a cold hydrogen air mixture appears rather complex and is not always fully understood. The modelling assumptions in the initial conditions determine to a large extent the likelihood and severity of potential explosion effects. The paper shows the results of the investigation and the sensitivity to the basic assumptions in the model input.
Updated Jet Flame Radiation Modelling with Corrections for Buoyancy and Wind
Sep 2013
Publication
Radiative heat fluxes from small to medium-scale hydrogen jet flames (<10 m) compare favorably to theoretical predictions provided the product species thermal emittance and optical flame thickness are corrected for. However recent heat flux measurements from two large-scale horizontally orientated hydrogen flames (17.4 and 45.9 m respectively) revealed that current methods underpredicted the flame radiant fraction by 40% or more. Newly developed weighted source flame radiation models have demonstrated substantial improvement in the heat flux predictions particularly in the near-field and allow for a sensible way to correct potential ground surface reflective irradiance. These updated methods are still constrained by the fact that the flame is assumed to have a linear trajectory despite buoyancy effects that can result in significant flame deformation. The current paper discusses a method to predict flame centerline trajectories via a one-dimensional flame integral model which enables optimized placement of source emitters for weighted multi-source heat flux prediction methods. Flame shape prediction from choked releases was evaluated against flame envelope imaging and found to depend heavily on the notional nozzle model formulation used to compute the density weighted effective nozzle diameter. Nonetheless substantial improvement in the prediction of downstream radiative heat flux values occurred when emitter placement was corrected by the flame integral model regardless of the notional nozzle model formulation used.
Consequence Models for Vented Hydrogen Deflagrations: CFD vs. Engineering Models
Sep 2017
Publication
This paper compares two approaches for predicting the consequences of vented hydrogen deflagrations: empirical engineering models (EMs) and computational fluid dynamics (CFD) simulations. The study is part of the project ‘Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations’ (HySEA) funded by the Fuel Cells and Hydrogen 2 Joint Undertaking (FCH JU) under grant agreement No 671461. The HySEA project focuses on vented hydrogen deflagrations in containers and smaller enclosures with internal congestion representative of industrial applications. Data from experiments conducted as part of the HySEA project are used to evaluate predictions from a selection of EMs and the CFD tool FLACS. The experiments involve various obstacle and venting configurations and initially quiescent homogeneous hydrogen-air mixtures with hydrogen concentrations in the range 15–24 vol%. There is a significant scatter in the maximum reduced overpressures predicted by the different EMs in the present study. For certain configurations there is an order of magnitude difference between the different EM predictions. Two versions of the CFD tool FLACS are used in the present study: i) the standard commercial release FLACS v10.7r2 and ii) an in-house development version termed FLACS-beta. The commercial release generally over-predicts the maximum overpressures measured in the experiments while the development version of FLACS gives improved results for several configurations.
Tests of the Vehicle’s Powertrain with Hydrogen Fuel Cells at a Low Temperature
Sep 2019
Publication
The article discusses issues related to the operation of fuel cells stack fed with hydrogen at low temperature. The test object was a Toyota Mirai passenger car equipped with this type of powertrain. Tests were carried out in a thermoclimatic chamber at the Cracow University of Technology. They had an initial character and their aim was to evaluate the work of individual subassemblies of the propulsion system including the hydrogen supply system in terms of operational safety.
Development of a Realistic Hydrogen Flammable Atmosphere Inside a 4-m3 Enclosure
Sep 2017
Publication
To define a strategy of mitigation for containerized hydrogen systems (fuel cells for example) against explosion the main characteristics of flammable atmosphere (size concentration turbulence…) shall be well-known. This article presents an experimental study on accidental hydrogen releases and dispersion into an enclosure of 4 m3 (2 m x 2 m x 1 m). Different release points are studied: two circular releases of 1 and 3 mm and a system to create ring-shaped releases. The releases are operated with a pressure between 10 and 40 bars in order to be close to the process conditions. Different positions of the release inside the enclosure i.e. centred on the floor or along a wall are also studied. A specific effort is made to characterize the turbulence in the enclosure during the releases. The objectives of the experimental study are to understand and quantify the mechanisms of formation of the explosive atmosphere taking into account the geometry and position of the release point and the confinement. Those experimental data are analyzed and compared with existing models and could bring some new elements to improve them.
Removing the Disrupting Wind Effect in Single Vented Enclosure Exposed to External Wind
Oct 2015
Publication
We are addressing hydrogen release into a single-vented facility with wind blowing onto the opposite side of the vent wall. Earlier work based on tests performed by HSL with wind (within the HyIndoor project) and comparative CFD simulations with and without wind ([1]within the H2FC project) has shown that the hydrogen concentrations inside the enclosure are increased compared to the case with no wind. This was attributed to the fact that wind is disrupting the passive ventilation. The present work is based on the GAMELAN tests (within the HyIndoor project) performed with one vent and no wind. For this enclosure simulations were performed with and without wind and reproduced the disrupting wind effect. In order to remove this effect and enhance the ventilation additional simulations were performed by considering different geometrical modifications near the vent. A simple geometrical layout around the vent is here proposed that leads to elimination of the disrupting wind effect. The analysis has been performed using the ADREA-HF code earlier validated both for the HSL and the GAMELAN tests. The current work was performed partly within HyIndoor project
Sample Scale Testing Method to Prevent Collapse of Plastic Liners in Composite Pressure Vessels
Sep 2017
Publication
Type IV pressure vessels are commonly used for hydrogen on-board stationary or bulk storages. When pressurised hydrogen permeates through the materials and solves into them. Emptying then leads to a difference of pressure at the interface between composite and liner possibly leading to a permanent deformation of the plastic liner called “collapse” or “buckling”. This phenomenon has been studied through French funded project Colline allowing to better understand its initiation and long-term effects. This paper presents the methodology followed using permeation tests hydrogen decompression tests on samples and gas diffusion calculation in order to determine safe operating conditions such as maximum flow rate or residual pressure level.
In Situ X-ray Absorption Spectroscopy Study on Water Formation Reaction of Palladium Metal Nanoparticle Catalysts
Oct 2015
Publication
Proper management of hydrogen gas is very important for safety security of nuclear power plants. Hydrogen removal by water formation reaction on a catalyst is one of the candidates for creating hydrogen free system. We observed in situ and time-resolved structure change of palladium metal nanoparticle catalyst during the water formation reaction by using X-ray absorption spectroscopy technique. A poisoning effect by carbon monoxide on catalytic activity was also studied. We have found that the creation of oxidized surface layer on palladium metal nanoparticles plays an important role for the water formation reaction process.
Experimental Study on Accumulation of Helium Released into a Semi-confined Enclosure without Ventilation
Sep 2019
Publication
This paper examines the helium dispersion behaviour in a 16.6 m3 enclosure with a small opening in the floor and distributed leaks along the edges. Helium a simulant for hydrogen was injected near the center of the floor with an injection rate ranging from 2 to 50 standard liters per minute (Richardson number of 0.3–134) through an upward-facing nozzle. In a short-term transient the helium distribution predicted with the models of Baines & Turner (1969) and Worster & Huppert (1983) matched the measured distributions reasonably well. In a long-term transient the vertical helium profile always reached a steady state which consisted of a homogenous layer at the top overlaying a stratified layer at the bottom. The helium transients in the uniform layer predicted with the models of Lowesmith (2009) and Prasad & Yang (2010) assuming a vent was located in the ceiling were in good agreement with the measured transients.
A Chicken and Egg Situation: Enhancing Emergency Service Workers' Knowledge of Hydrogen
Sep 2021
Publication
This paper reports on the results of interviews conducted with 21 representatives from emergency services organisations within Australia and New Zealand. With a relative emergent industry such as future fuels a chicken and egg situation does emerge with regards to how much training needs to be in place in advance of large-scale industry development or not. These respondents were employed in a variety of roles being directly involved in research and training of emerging technologies frontline operational managers and other senior roles across the emergency services sector. Participants' responses to a series of questions were able to provide insights into the state of knowledge and training requirements within their organisations in relation to hydrogen and other future fuels. The findings suggest that formal and informal processes currently exist to support the knowledge development and transferal around the adoption of hydrogen and other future fuels. From the interviews it became clear that there are a number of processes that have emerged from the experiences gained through the implementation of rooftop solar PV and battery storage that provide some background context for advancing future fuels information across the sector. Because safety is a critical component for securing a social licence to operate engagement and knowledge sharing with any representatives from across this sector will only help to build confidence in the industry. Similarly because interviewees were very keen to access information they expressed a clear willingness to learn more through more formalised relationships rather than an ad hoc information seeking that has been employed to date. The presentation will identify key recommendations and also highlight the importance of QR Codes in the emergency responder landscape. Implications for industry and policy makers are discussed.
Study of Hydrogen Enriched Premixed Flames
Sep 2005
Publication
In the present paper the theoretical study of the un-stretched laminar premixed flames of hydrogen-methane mixtures is carried out by using the detailed reaction mechanism GRI-Mech 3.0 implemented in the CHEMKIN software to find out the effect of hydrogen addition on the hybrid fuel burning velocity. The model results show that the laminar burning velocity of the hydrogen-methane mixtures is not the linear regression of those of the pure fuels since it results substantially less than the proportional averaging of the values for the fuel constituents. Moreover the effect of hydrogen addition in terms of enhancement of the mixture laminar burning velocity with respect to the methane is relevant only at very high values of the hydrogen content in the hybrid mixtures (> 70 % mol.). The performed sensitivity analysis shows that these results can be attributed to kinetics and in particular to the concentration of H radicals: depending on the hydrogen content in the fuels mixture the production of the H radicals can affect the limiting reaction step for methane combustion. Two regimes are identified in the hydrogen-methane combustion. The first regime is controlled by the methane reactivity the hydrogen being not able to significantly affect the laminar burning velocity (< 70 % mol.). In the second regime the hydrogen combustion has a relevant role as its high content in the hybrid fuel leads to a significant H radicals pool thus enhancing the reaction rate of the more slowly combusting methane.
Vented Hydrogen-air Explosion in a Small Obstructed Rectangular Container- effect of the Blockage Ratio
Sep 2019
Publication
The explosion venting is an effective way to reduce hydrogen-air explosion hazards but the explosion venting has been hardly touched in an obstructed container. Current experiments focused on the effects of different blockage ratios on the explosion venting in a small obstructed rectangular container. Experimental results show that three overpressure peaks are formed in the case with the obstacle while only two can be observed in the case of no obstacle. The obstacle blockage ratio has a significant influence on the peak overpressure induced by the obstacle-acoustic interactions but it has an ignorable effect on the peak overpressure caused by the rupture of the vent film. The obstacle-induced overpressure peak first increases and then decreases with the increase of the blockage ratio. In addition all overpressure peaks inside the container decreases with the increase of the vent area and its appearance time is relatively earlier for larger vent area.
Development of a Flashback Correlation for Burner-stabilized Hydrogen-air Premixed Flames
Feb 2022
Publication
With a growing need for replacing fossil fuels with cleaner alternatives hydrogen has emerged as a viable candidate for providing heat and power. However stable and safe combustion of hydrogen is not simple and as such a number of key issues have been identified that need to be understood for a safe design of combustion chambers. One such issue is the higher propensity of hydrogen flames to flashback compared to that for methane flames. The flashback problem is coupled with higher burner temperatures that could cause strong thermal stresses in burners and could hinder their performance. In order to systematically investigate flashback in premixed hydrogen-air flames for finding a global flashback criteria in this study we use numerical simulations as a basic tool to study flashback limits of slit burners. Flashback limits are found for varying geometrical parameters and equivalence ratios and the sensitivity of each parameter on the flashback limit and burner temperatures are identified and analyzed. It is shown that the conventional flashback correlation with critical velocity gradient does not collapse the flashback data as it does not take into account stretch induced preferential diffusion effects. A new Karlovitz number definition is introduced with physical insights that collapses the flashback data at all tested conditions in an excellent manner.
Hydrogen Safety Aspects Related to High Pressure - PEM Water Electrolysis
Sep 2007
Publication
Polymer electrolyte membrane (PEM) water electrolysis has demonstrated its potentialities in terms of cell efficiency (energy consumption ≈ 4.0-4.2 kW/Nm3 H2) and gas purity (> 99.99% H2). Current research activities are aimed at increasing operating pressure up to several hundred bars for direct storage of hydrogen in pressurized vessels. Compared to atmospheric pressure electrolysis high-pressure operation yields additional problems especially with regard to safety considerations. In particular the rate of gases (H2 and O2) cross-permeation across the membrane and their water solubility both increase with pressure. As a result gas purity is affected in both anodic and cathodic circuits and this can lead to the formation of explosive gas mixtures. To prevent such risks two different solutions reported in this communication have been investigated. First the chemical modification of the solid polymer electrolyte in order to reduce cross-permeation phenomena. Second the use of catalytic H2/O2 recombiners to maintain H2 levels in O2 and O2 levels in H2 at values compatible with safety requirements.
Simulation Analysis on the Risk of Hydrogen Releases and Combustion in Subsea Tunnels
Oct 2015
Publication
Hydrogen is considered to be a very promising potential energy carrier due to its excellent characteristics such as abundant resources high fuel value clean and renewable. Its safety features greatly influence the potential use. Several safety problems need to be analyzed before using in transportation industry. With the development of the tunnel transportation technology the safe use of hydrogen in tunnels will receive a lot of research attentions. In this article the risk associated with hydrogen release from onboard high-pressure vessels and the induced combustion in tunnels was analyzed using the Partially Averaged Navier–Stokes (PANS) turbulence model. The influences of the tunnel ventilation facilities on the hydrogen flow characteristics and the flammable hydrogen cloud sizes were studied. The tunnel layouts were designed according to the subsea tunnel. And a range of longitudinal ventilation conditions had been considered to investigate the hydrogen releases and the sizes of the flammable hydrogen cloud. Then the hydrogen combustion simulation was carried out after the fixed leaking time. The overpressures induced after the ignition of leaking hydrogen were studied. The influences of ventilation and ignition delay time on the overpressure were also investigated. The main aim was to research the phenomena of hydrogen releases and combustion risk inside subsea tunnels and to lay the foundation of risk assessment methodology developed for hydrogen energy applications on transportation.
A Barrier Analysis of a Generic Hydrogen Refuelling Station
Sep 2009
Publication
Any technical installation need appropriate safety barriers installed to prevent or mitigate any adverse effects concerning people property and environment. In this context a safety barrier is a series of elements each consisting of a technical system or human action that implement a planned barrier function to prevent control or mitigate the propagation of a condition or event into an undesired condition or event. This is also important for new technologies as hydrogen refuelling stations being operated at very high pressures up to 900bar. In order to establish the needed barriers a hazard identification of the installation has to be carried out to identify the possible hazardous events. In this study this identification was done using the generic layout of a future large hydrogen refuelling station that has been developed by the EU NoE HySafe. This was based on experiences with smaller scale refuelling stations that has been in operation for several years e.g. being used in the former CUTE and ECTOS projects. Using this approach the object of the study is to support activities to further improve the safety performance of future larger refuelling stations. This will again help to inform the authorities and the public to achieve a proper public awareness and to support building up a realistic risk and safety perception of the safety on such future refuelling stations. In the second step the hazardous events that may take place and the barriers installed to stop hazards and their escalation are analysed also using in-house developed software to model the barriers and to quantify their performance. The paper will present an overview and discuss the state-of-the-art of the barriers established in the generic refuelling station.
Materials Considerations in Hydrogen Production
Sep 2007
Publication
Correct selection and application of materials is essential to ensure safety and economy in production transportation and storage of hydrogen. There are several sources of materials challenges related to hydrogen. Established component producers may have limited experience in this specific field. Process developments may involve new process conditions with new demands on the materials. Further new materials will be added to the engineering toolbox to be used. The behaviour of these materials for hydrogen service may need additional documentation. Finally focus on hydrogen susceptibility and hydrogen damages alone may take away awareness of other subjects as trace elements by-products and change in raw materials which may be of as high importance for safety and quality. This overview of challenges and recommendations is made with emphasis on water electrolysis.
Experimental Study on a Hydrogen Stratification Induced by PARs Installed in a Containment
Oct 2020
Publication
Hydrogen can be produced in undesired ways such as a high temperature metal oxidation during an accident. In this case the hydrogen must be carefully managed. A hydrogen mitigation system (HMS) should be installed to protect a containment of a nuclear power plant (NPP) from hazards of hydrogen produced by an oxidation of the fuel cladding during a severe accident in an NPP. Among hydrogen removal devices passive auto-catalytic recombiners (PARs) are currently applied to many NPPs because of passive characteristics such as not requiring a power supply nor an operators’ manipulations. However they offer several disadvantages resulting in issues related to hydrogen control by PARs. One of the issues is a hydrogen stratification in which hydrogen is not well-mixed in a compartment due to the high temperature exhaust gas of PARs and accumulation in the lower part. Therefore experimental simulation on hydrogen stratification phenomenon by PARs is required. When the hydrogen stratification by PARs is observed in the experiment the verification and improvement of a PAR analysis model using the experimental results can be performed and the hydrogen removal characteristics by PARs installed in an NPP can be evaluated using the improved PAR model. View Full-Text
A Temperature Controlled Mechanical Test Facility to Ensure Safe Materials Performance in Hydrogen at 1000 Bar
Sep 2007
Publication
Increasingly car manufacturers are turning to high pressure hydrogen storage for on-board power applications. Many prototypes use costly materials and fabrication methods such as Type 316L austenitic stainless steel and processes such as TIG (GTA) welding. There is a need to move to less expensive options without compromising safety to assist in developing economic vehicles. It is important that the behaviour of new/modified materials and joints (including those fabricated by new technologies) is understood at anticipated service temperatures and hydrogen pressure as the consequences of poor material choice could be severe. The greatest detrimental effect of gaseous hydrogen on the mechanical properties of metallic materials is commonly observed under conditions of dynamic plastic strain. Under such conditions an atomically clean surface is produced where hydrogen molecules will dissociate and penetrate the material. Thus static load test methods with hydrogen charging are not reliable for engineering data generation. To meet the need for dynamically straining material in a pressurised hydrogen environment TWI has developed a facility to load specimens in a high pressure environment for tensile toughness and fatigue testing. The design of this has involved a number of innovative steps. This paper outlines the requirements and the design and construction issues that were encountered when installing a facility which can not only perform tests at up to 1000bar (100MPa) but also for temperatures between –150°C to +85°C.
Risk Analysis of the Storage Unit in Hydrogen Refuelling Station
Sep 2007
Publication
Nowadays consumer demand for local and global environmental quality in terms of air pollution and in particular greenhouse gas emissions reduction may help to drive to the introduction of zero emission vehicles. At this regard the hydrogen technology appears to have future market valuablepotential. On the other hand the use of hydrogen vehicles which requires appropriate infrastructures for production storage and refuelling stages presents a lot of safety problems due to the peculiar chemicophysical hydrogen characteristics. Therefore safe at the most practices are essential for the successful proliferation of hydrogen vehicles. Indeed to avoid limit hazards it is necessary to implement practices that if early adopted in the development of a fuelling station project can allow very low environmental impact safety being incorporated in the project itself. Such practices generally consist in the integrated use of Failure Mode and Effect Analysis (FMEA) HAZard OPerability (HAZOP) and Fault Tree Analysis (FTA) which constitute well established standards in reliability engineering. At this regard however a drawback is the lack of experience and the scarcity of the relevant data collection. In this work we present the results obtained by the integrated use of FMEA HAZOP and FTA analyses relevant for the moment the high-pressure storage equipment in a hydrogen gas refuelling station. The study that is intended to obtain elements for improving safety of the system can constitute a basis for further more refined works.
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