Safety
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.
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