Publications

The potential for particulates entrained in hydrogen releases to generate electrostatic charge and induce electrostatic discharge ignitions was investigated. A series of tests were performed in which hydrogen was released through a 3.75-mm-diameter orifice from an initial pressure of 140 bar. Electrostatic field sensors were used to characterize the electrification of known quantities of iron oxide particulates deliberately entrained in the release. The ignition experiments focused on using charged particulates to induce spark discharges from isolated conductors and corona discharges. A total of 12 ignition events were observed. The results show that electrification of entrained particulates is a viable self-ignition mechanism of hydrogen releases.

There will be significant temperature rise within hydrogen vehicle cylinder during the fast filling process. The temperature rise should be controlled under the temperature limit (85 °C) of the structure material (set by ISO/TS 15869) because it may lead to the failure of the structure. In this paper a 2-dimensional axisymmetric computational fluid dynamics (CFD) model for fast filling of 70 MPa hydrogen vehicle cylinder is presented. The numerical simulations are based on the modified standard k − ɛ turbulence model. In addition both the equation of state for hydrogen gas and the thermodynamic properties are calculated by National Institute of Standards and Technology (NIST) database: REFPROP 7.0. The thermodynamic responses of fast filling with different pressure-rise patterns and filling times within type III cylinder have been analyzed in detail.

In the event of a fire the TPRD (Thermally activated Pressure Relief Device) prevents the high-pressure full composite cylinder from bursting by detecting high temperatures and releasing the pressurized gas. The current safety performance of both the vessel and the TPRD is demonstrated by an engulfing bonfire test. However there is no requirement concerning the effect of the TPRD release which may produce a hazardous hydrogen flame due to the high flow-rate of the TPRD. It is necessary to understand better the behavior of an unprotected composite cylinder exposed to fire in order to design appropriate protection for it and to be able to reduce the length of any potential hydrogen flame. For that purpose a test campaign was performed on a 36 L cylinder with a design pressure of 70 MPa. The time from fire exposure to the bursting of this cylinder (the burst delay) was measured. The influence of the fire type (partial or global) and the influence of the pressure in the cylinder during the exposure were studied. It was found that the TPRD orifice diameter should be significantly reduced compared to current practice.

High injection pressures are used during the re-fuelling process of vehicle tanks with compressed hydrogen and consequently high temperatures are generated in the tank potentially jeopardizing the system safety. Computational Fluid Dynamics (CFD) tools can help in predicting the temperature rise within vehicle tanks providing complete and detailed 3D information on flow features and temperature distribution. In this framework CFD simulations of hydrogen fast filling at different working conditions are performed and the accuracy of the numerical models is assessed against experimental data for a type 4 tank up to 70 MPa. Sensitivity analyses on the main modelling parameters are carried out in compliance with general CFD Best Practice Guidelines.

Type 1 steel pressure vessels are commonly used for the transport of pressurized gases including gaseous hydrogen. In the majority of cases these cylinders experience relatively few pressure cycles over their lifetime perhaps in the hundreds. In emerging markets such as hydrogen-powered industrial trucks hydrogen fuel systems are expected to experience thousands of cycles over just a few year period. This study investigates the fatigue life of Type 1 steel pressure vessels by subjecting full- scale vessels to pressure cycles with gaseous hydrogen between nominal pressure of 3.5 and 43.8 MPa. In addition engineered defects were machined on the inside of several pressure vessels for comparison to fatigue crack growth measurements on materials sectioned from these pressure vessels. As-manufactured pressure vessels have sustained >35000 cycles with failure while vessels with machined defects leaked before bursting after 8000 to 15000 pressure cycles. The measured number of cycles to failure in these pressure vessels is two to three times greater than predicted using conservative methods based on fatigue crack growth rates measured in gaseous hydrogen.

There are new safety challenges with an increased use of hydrogen e.g. that people may not see dangerous jet flames in case of an incident. Compared to conventional fuels hydrogen has very different characteristics and physical properties and is stored at very high pressure or at very low temperatures. Thus the nature of hazard scenarios will be very different. Consequence modelling of ventilation releases explosions and fires can be used to predict and thus understand hazards. In order to describe the detailed development of a hazard scenario and evaluate ways of mitigation 3D Computational Fluid Dynamics (CFD) models will be required. Even with accurate modelling the communication of risk can be challenging. For this visualization in virtual reality (VR) may be of good help in which the CFD model predictions are presented in a realistic 3D environment with the possibility to include sounds like noise from a high pressure release explosion or fire. In cooperation with Statoil Christian Michelsen Research (CMR) and GexCon have developed the VRSafety application. VRSafety can visualize simulation results from FLACS (and another CFD-tool KFX) in an immersive VR-lab or on a PC. VRSafety can further be used to interactively control and start new CFD-simulations during the sessions. The combination of accurate CFD-modelling visualization and interactive use through VRSafety represents a powerful toolbox for safety training and risk communication to first-responders employees media and other stakeholders. It can also be used for lessons learned sessions studying incidents and accidents and to demonstrate what went wrong and how mitigation could have prevented accidents from happening. This paper will describe possibilities with VRSafety and give examples of use.

Two-dimensional numerical simulations of deflagration-to-detonation transition (DDT) in hydrogen–air mixtures are presented and compared with experiments. The investigated geometry was a 3 m long square channel. One end was closed and had a single obstacle placed 1 m from the end and the other end was open to the atmosphere. The mixture was ignited at the closed end. Experiments and simulations showed that DDT occurred within 1 m behind the obstacle. The onset of detonation followed a series of local explosions occurring far behind the leading edge of the flame in a layer of unburned reactants between the flame and the walls. A local explosion was also seen in the experiments and the pressure records indicated that there may have been more. Furthermore local explosions were observed in the experiments and simulations which did not detonate. The explosions should have sufficient strength and should explode in a layer of sufficient height to result in a detonation. The numerical resolution was 0.5 mm per square cell and further details of the combustion model used are provided in the paper.

In this paper the accidental release of hydrogen from cryogenic liquid storage tank and the subsequent consequences are studied including hydrogen cold cloud fire ball jet fire flash fire and vapor cloud explosion. The cold effect thermal effects and explosion overpressures from the above consequences are evaluated using IGC and TNO harm criteria. Results show that for instantaneous releases of liquid hydrogen the sequence of harm effect distances is that vapor cloud explosion>flash fire>cold cloud> fireball. For continuous releases of liquid hydrogen the sequence of harm effect distances is that vapor cloud explosion>jet fire>flash fire>cold cloud. The vapor cloud explosion is the leading consequence of both instantaneous and continuous releases and may be used for the determination of safety distances of a liquid hydrogen tank. Besides the harm effect distances of liquid hydrogen tank are compared with those of compressed hydrogen storages with equivalent mass. Results show that the liquid hydrogen storage may be safer than 70MPa gaseous storage in case of leak scenario but may be more dangerous than 70MPa storage in case of catastrophic rupture. It is difficult to tell which storage is safer from a consequence perspective. Further investigation need to be made from a standpoint of risk which combined both consequences and the likelihood of scenarios.

Hydrogen is seen as an ideal energy carrier for stationary and mobile applications. However the use of high energy density condensed hydrogen storage materials such as NH3BH3 comes with risks associated with their high reactivity with water exposure and their decomposition products reactivity in air. To predict their behaviour under these circumstances idealized finite element models of hypothetical accident scenarios have been developed. Empirical thermodynamic calculations based on precise thermal gravimetric analysis (TGA) and calorimetric experiments have been performed in order to quantify the energy and hydrogen release rates and to quantify the reaction products resulting from water and air exposure.

Hydrogen (H2 ) can be a promising energy carrier for decarbonizing the economy and especially the transport sector which is considered as one of the sectors with high carbon emissions due to the extensive use of fossil fuels. H2 is a nontoxic energy carrier that could replace fossil fuels. Fuel Cell Electric Vehicles (FCEVs) can decrease air pollution and reduce greenhouse gases when H2 is produced from Renewable Energy Sources (RES) and at the same time being accessible through a widespread network of Hydrogen Refueling Stations (HRSs). In this study both the sizing of the equipment and financial analysis were performed for an HRS supplied with H2 from the excess electrical energy of a 10 MW wind park. The aim was to determine the optimum configuration of an HRS under the investigation of six different scenarios with various numbers of FCEVs and monthly demands as well as ascertaining the economic viability of each examined scenario. The effect of the number of vehicles that the installation can refuel to balance the initial cost of the investment and the fuel cost in remote regions was investigated. The results showed that a wind-powered HRS could be a viable solution when sized appropriately and H2 can be used as a storage mean for the rejected wind energy. It was concluded that scenarios with low FCEVs penetration have low economic performance since the payback period presented significantly high values.

A two-dimensional (2-D) simulation of spontaneous ignition of high-pressure hydrogen in a length of duct is conducted in order to explore its underlying ignition mechanisms. The present study adopts a 2-D rectangular duct (i.e. not axisymmetric geometry) and focuses on the effects of initial diaphragm shape on the spontaneous ignitions. The Navier-Stokes equations with a detailed chemical kinetics mechanism are solved in a manner of direct numerical simulation. The detailed mechanisms of spontaneous ignition are discussed for each initial diaphragm shape. For a straight diaphragm shape it is found that the ignition occurs only near the wall due to the adiabatic wall condition while the three ignition events: ignitions due to leading shock wave reflection at the wall hydrogen penetration into shock-heated air near the wall and deep penetration of hydrogen into shock-heated air behind the leading shock wave are identified for a largely deformed diaphragm shape.

Hydrogen is seen as an ideal energy carrier for stationary and mobile applications. However the use of high energy density materials such as hydrides comes with the drawback of risks associated to their high reactivity towards air and water exposure. We have developed novel strategies to mitigate these risks. These strategies were evaluated using standard UN tests and isothermal calorimetric measurements. Cycling experiments were conducted to assess the impact of the mitigants on the modified materials derived from 8LiH•3Mg(NH2)2 system. In some cases our results show an improvement in kinetics when compared to the unmodified material.  Effective mitigants were also discovered for aluminium hydride (alane) and lithium borohydride completely inhibiting ignition.

The  storage  of  hydrogen  poses  inherent  weight  volume  and  safety  obstacles.  An  innovative technology which allows for the storage of hydrogen in thin sealed glass capillaries ensures the safe infusion storage and controlled release of hydrogen gas under pressures up to 100 MPa. Glass is a non-flammable material which also guarantees high burst pressures. The pressure resistance of single and multiple capillaries has been determined for different glass materials. Borosilicate capillaries have been proven to have the highest pressure resistance and have therefore been selected for further series of  advanced testing.  The innovative  storage  system  is  finally  composed of  a  variable number  of modules. As such in the case of the release of hydrogen this modular arrangement allows potential hazards to be reduced to a minimum. Further advantage of a modular system is the arrangement of single modules in every shape and volume dependent on the final application. Therefore the typical locations of storage systems e.g. the rear of cars can be modified or shifted to places of higher safety and not directly involved in crashes. The various methods of refilling and releasing capillaries with compressed hydrogen the increase of burst pressures through pre-treatment as well as the theoretical analysis and  experimental results of  the resistance  of glass  capillaries will further  be discussed  in detail.

Vehicular use of hydrogen is the first attempt to apply hydrogen energy in consumers’ environment in large scale and has raised safety concerns in both public authorities and private bodies such as fire services and insurance companies. This paper analyzes typical accident progressions of hydrogen fuel cell vehicles in a road collision accident. Major hydrogen consequences including impinging jet fires and catastrophic tank ruptures are evaluated separately in terms of accident duration and hazard distances. Results show that in a 70 MPa fuel cell car accident the hazards associated with hydrogen releases would normally last for no more than 1.5 min due to the empty of the tank. For the safety of general public a perimeter of 100 m is suggested in the accident scene if no hissing sound is heard. However the perimeter can be reduced to 10 m once the hissing sound of hydrogen release is heard. Furthermore risks of fatalities injuries and damages are all quantified in financial terms to assess the impacts of the accident. Results show that costs of fatalities and injuries contribute most to the overall financial loss indicating that the insurance premium of fatalities and injuries should be set higher than that of property loss.

In this work we evaluate the consequences of the combustion of a stoichiometric mixture of hydrogen-air on a mechanical device which can be considered as a long tube. In order to choose the most dangerous combustion regime for the mechanical device we devote a particular attention to the investigation of the 1D deflagration-to-detonation transition. Then once established the most dangerous combustion regime we compute the reacting  flow and the stress and strain in the mechanical device. Analyses are performed using both semi-analytical solutions and Europlexus a computer program for the simulation of  fluid-structure systems under transient dynamic loading.

In a near future with an increasing use of hydrogen as an energy vector gaseous hydrogen transport as well as high capacity storage may imply the use of high strength steel pipelines for economical reasons. However such materials are well known to be sensitive to hydrogen embrittlement (HE). For safety reasons it is thus necessary to improve and clarify the means of quantifying embrittlement. The present paper exposes the changes in mechanical properties of a grade API X80 steel through numerous mechanical tests i.e. tensile tests disk pressure test fracture toughness and fatigue crack growth measurements WOL tests performed either in neutral atmosphere or in high-pressure of hydrogen gas. The observed results are then discussed in front of safety considerations for the redaction of standards for the qualification of materials dedicating to hydrogen transport.

A reflected shock wave in two-dimensional shock tube is studied numerically using Navier-Stokes equations with the detailed oxy-hydrogen reaction mechanism. The results show detailed process of mild ignition. The interaction between the reflected shock wave and the boundary layer yielded behind the incident shock wave produces clockwise and counter-clockwise vortices. These vortices generate compression waves. The future study related wall conditions (adiabatic or isothermal) will be shown at the conference site.

Hydrogen gas explosions in homogeneous reactive mixtures have been widely studied both experimentally and numerically. However in practice combustible mixtures are usually inhomogeneous and subject to both vertical and horizontal concentration gradients. There is still very limited understanding of the hydrogen explosion characteristics in such situations. The present numerical investigation aims to study the effect of mixture concentration gradient on the process of Deflagration to Detonation Transition and the effect of different hydrogen concentration gradient in the obstructed channel of hydrogen/air mixtures. An obstructed channel with 30% blockage ratio (BR=30) and three different average hydrogen concentrations of 20 % 30% and 35% have been considered using a specially developed density-based solver within the OpenFOAM toolbox. A high-resolution grid was built with the using adaptive mesh refinement technique providing 10 grid points in half reaction length. The numerical results are in reasonably good agreement with the experimental  observations [1]. These studies show that the concentration gradient has a considerable effect on the accelerated flame tip speed and the location of transition to detonation in the obstructed channel. In all the three cases the first localised explosion occurred near the bottom wall where the shock and flame interacted and the mixture was most lean; and the second localised explosion occurred at the top wall due to the reflection of shock and flame front and later develops to form the leading detonation wave. The increase in the fuel concentration was found to increase the flame acceleration (FA) and having a faster transition to detonation.

This paper introduces a risk-based methodology for hydrogen refuelling stations. Momentarily four stations are present in the Netherlands. This number is expected to increase to around twenty in the next years. For these stations a quantitative risk analysis (QRA) must be carried out to account for spatial planning. The presented method identifies the loss of containment scenarios and failure frequencies. Additionally the results of this study may be used in legislative context in the form of fixed generic safety distances. Using the risk analysis tool Safeti-NL safety distances are determined for three different kinds of hydrogen refuelling stations distinguished by the supply method of the hydrogen. For the hydrogen refuelling stations a maximum safety distance of 35 m is calculated. However despite the relatively small safety distances the maximum effect distances (distance to 1% lethality) can be very large especially for stations with a supply and storage of liquid hydrogen. The research was overseen by an advisory committee which also provided technical information on the refuelling stations.

Zero Emission Vehicles (ZEVs) are necessary to help reduce the emissions in the transportation sector which is responsible for 40% of overall greenhouse gas emissions. There are two types of ZEVs Battery Electric Vehicles (BEVs) and Fuel Cell Electric Vehicles (FCEVs) Commercial Success of BEVs has been challenging thus far also due to limited range and very long charging duration. FCEVs using H2 infrastructure with SAE J2601 and J2799 standards can be consistently fuelled in a safe manner fast and resulting in a range similar to conventional vehicles. Specifically fuelling with SAE J2601 with the SAE J2799 enables FCEVs to fill with hydrogen in 3-5 minutes and to achieve a high State of Charge (SOC) resulting in 300+ mile range without exceeding the safety storage limits. Standardized H2 therefore gives an advantage to the customer over electric charging. SAE created this H2 fuelling protocol based on modelling laboratory and field tests. These SAE standards enable the first generation of commercial FCEVs and H2 stations to achieve a customer acceptable fueling similar to today's experience. This report details the advantages of hydrogen and the validation of H2 fuelling for the SAE standards.

Delayed explosions of accidental high pressure hydrogen releases are an important risk scenario in safety studies of production plants transportation pipelines and fuel cell vehicles charging stations. Such explosions were widely explored in multiple experimental and numerical investigations. Explosion of high pressure releases in highly obstructed geometries with high blockage ratio is a much more complicated phenomenon. This paper is dedicated to the experimental investigation of the influence of obstacles on a delayed deflagration of hydrogen jets. The computational fluid dynamics (CFD) code FLACS is used to reproduce experimental data. In the current study the computed overpressure signals are compared to the experimentally measured ones at different monitoring points. Simulations are in close agreement with experimental results and can be used to predict overpressure where experimental pressure detectors were saturated. For homogenous stationary clouds a new approach of equivalent mixture of H2/air (~16.5%) to stoichiometric mixture of CH4/air is suggested. This approach is validated versus experimental data from the literature in terms of overpressure maxima. A parametric study is performed using FLACS for various concentrations in the same geometry in order to identify a possible transition from deflagration to detonation.

Hydrogen behavior at elevated pressures and temperatures was intensively studied by numerous investigators. Nevertheless there is a lack of experimental data on hydrogen ignition and combustion at reduced sub-atmospheric pressures. Such conditions are related to the facilities operating under vacuum or sub-atmospheric conditions for instance like ITER vacuum vessel. Main goal of current work was an experimental evaluation of such fundamental properties of hydrogen–air mixtures as flammability limits and laminar flame speed at sub-atmospheric pressures. A spherical explosion chamber with a volume of 8.2 dm3 was used in the experiments. A pressure method and high-speed camera combined with schlieren system for flame visualization were used in this work. Upper and lower flammability limits and laminar flame velocity have been experimentally evaluated in the range of 4–80% hydrogen in air at initial pressures 25–1000 mbar. An extraction of basic flame properties as Markstein length overall reaction order and activation energy was done from experimental data on laminar burning velocity.

NaBH4-based hydrogen generator for fuel cell Unmanned Aerial Vehicle (UAVs) with movable fuel cartridge was developed in the present study. The main fuel of hydrogen generator is Sodium borohydride (NaBH4) that is a kind of chemical hydride and has a high hydrogen storage density. In the previous studies hydrogen generators were developed in which hydrogen was directly generated from solid state NaBH4. However it was a prototype so inconvenient to replace the fuel after used up and lacked user convenience. Therefore the performance evaluation and the development procedure of NaBH4-based hydrogen generator that was designed taking user convenience in consideration for commercialization were described in this paper.

We report the development and testing of a novel hydrogen sensor that shows a very peculiar response to hydrogen exposure due to its micro-structured palladium surface. The fabrication of the wrinkled Pd surface is obtained using an innovative fast and cheap technique based on the deposition of a thin Pd film on to a thermo-retractable polystyrene sheet that shrinks to 40% of its original size when heated. The buckling of the Pd surface induced by shrinking of the substrate produces nano and micro-wrinkles on the sensor surface. The micro-structured sensor surface is very stable even after repeated hydrogen sorption/desorption cycles. The hydrogen sensing mechanism is based on the transitory absorption of hydrogen atoms into the Pd layer leading to the reversible change of its electrical resistance. Interestingly depending on hydrogen concentration the proposed sensor shows the concurrent effect of both the usually described behaviors of increase or decrease of resistance related to different phenomena occurring upon hydrogen exposure and formation of palladium hydride. The study reports and discusses evidences for an activation threshold of hydrogen concentration in air switching the behavior of sensor performances from e.g. poor negative to large positive sensitivity and from slow to fast detection.

Although many studies have looked at safety issues relating to hydrogen fuelling stations few studies have analyzed the security risks such as deliberate attack of the station by threats such as terrorists and disgruntled employees. The purpose of this study is to analyze security risks for a hydrogen fuelling station with an on-site production of hydrogen from methylcyclohexane. We qualitatively conducted a security risk analysis using American Petroleum Institute Standard 780 as a reference for the analysis. The analysis identified 93 scenarios including pool fires. We quantitatively simulated a pool fire scenario unique to the station to analyze attack consequences. Based on the analysis and the simulation we recommend countermeasures to prevent and mitigate deliberate attacks.

The HyDeploy project has undertaken a programme of work to assess the effect of hydrogen addition on the safety and performance of gas appliances and installations. A representative set of eight appliances have been assessed in laboratory experiments with a range of test gases that explored high and low Wobbe Number and hydrogen concentrations up to 28.4 % mol/mol. Tests have demonstrated that the addition of hydrogen does not affect the key hazard areas of CO production light back flame out or the operation of flame failure devices. It was identified that for some designs of gas fire appliances the operation of the oxygen depletion sensors may be affected by the addition of hydrogen and further studies in this area are planned. A laboratory based study was supported by an onsite testing programme where 133 installations were assessed for gas tightness appliance combustion safety and operation against normal line natural gas G20 reference gas and two hydrogen blended gases. Where installations were gas tight for natural gas analysis showed that no additional leakage occurred with hydrogen blended gases. There were also no issues identified with the combustion performance of appliances and onsite results were in line with those obtained in the laboratory testing programme.

In Japan 82 commercial Hydrogen Refuelling Stations (HRSs) were constructed as of March 1 2017 but few impact assessments have been reported on the surroundings at HRS. In addition as HRSs become more widespread the number of HRSs around narrow urban areas will also increase. Thus the necessity of impact assessments on the surroundings of HRSs is expected to increase. In order to confirm that the influence from our HRS is not problematic to the surrounding residences we conducted an impact assessment on the surroundings at HRS by using the actual HRS construction plan. Although safety is one of the objects of an impact assessment in Japan the safety of an HRS is guaranteed by observing the High Pressure Gas Safety Act its Technical Standards and other related regulations. On the other hand if an accident such as a hydrogen leak or hydrogen fire occurs at an HRS it becomes important to prevent secondary disasters and to minimize influence on the surroundings by means of an initial response by the operators of the HRS. Therefore we have conducted training to improve the emergency response capability of the HRS operators and to prevent secondary disasters. In this paper we describe the abovementioned information with regard to an impact assessment on the surroundings and for emergency response training.

The storage of excess electrical generation enabled through the electrolytic production of hydrogen from water would allow “load-shifting” of power generation. This paves the way for hydrogen as an energy carrier to be further used as a zero‑carbon fuel for land air and sea transportation. However challenges in hydrogen storage and transportation ultimately pose restrictions on its wider adaption along horizontal and vertical vectors. This paper investigates chemical energy carriers ranging from small molecules such as ammonia and methane to formic acid as well as other more complex hydrocarbons in response to this timely engineering problem. The hydrogenation and dehydrogenation of such carrier molecules require energy lowering the effective net heating value of hydrogen up to 32 %. Different carrier approaches are discussed in the light of availability energetics water requirements and suitability for applications in power generation shipping trucking and aviation supplemented by a comprehensive safety review making this study unique in its field. It is found that hydrogen delivered without a carrier is ideal for power generation applications due to the large quantities required. Aviation would benefit from either ammonia or hydrogen and is generally a field challenging to decarbonize. Ammonia appears also to be a good medium for shipping hydrogen between continents and to power container ships due to its high energy density and lower liquid temperature compared with hydrogen. At the same time ammonia can also be used to power the ship's engine. Long-haul trucking would benefit the most from cryogenic or compressed hydrogen due to the lower quantities required and purity requirements of the fuel cells.

Liquid hydrogen (LH2) storage is viewed as a viable approach to assure sufficient hydrogen capacity at commercial fuelling stations. Presently LH2 is produced at remote facilities and then transported to the end-use site by road vehicles (i.e. LH2 tanker trucks). Venting of hydrogen to depressurize the transport storage tank is a routine part of the LH2 delivery and site transfer process. The behaviour of cold hydrogen plumes has not been well characterized because of the sparsity of empirical field data which can lead to overly conservative safety requirements. Committee members of the National Fire Protection Association (NFPA) Standard 2 [1] formed the Hydrogen Storage Safety Task Group which consists of hydrogen producers safety experts and computational fluid dynamics modellers has identified the lack of understanding of hydrogen dispersion during LH2 venting of storage vessels as a critical gap for establishing safety distances at LH2 facilities especially commercial hydrogen fuelling stations. To address this need the National Renewable Energy Laboratory Sensor Laboratory in collaboration with the NFPA Hydrogen Storage Task Group developed a prototype Cold Hydrogen Plume Analyzer to empirically characterize the hydrogen plume formed during LH2 storage tank venting. The prototype analyzer was field deployed during an actual LH2 venting process. Critical findings included

• Hydrogen above the lower flammable limit (LFL) was detected as much as 2 m lower than the release point which is not predicted by existing models.
• Personal monitors detected hydrogen at ground level although at levels below the LFL.
• A small but inconsistent correlation was found between oxygen depletion and the hydrogen concentration.
• A negligible to non-existent correlation was found between in-situ temperature measurements and the hydrogen concentration.

The prototype analyzer is being upgraded for enhanced metrological capabilities including improved real-time spatial and temporal profiling of hydrogen plumes and tracking of prevailing weather conditions. Additional deployments are planned to monitor plume behaviour under different wind humidity and temperature conditions. The data will be shared with the Hydrogen Storage Task Group and ultimately will be used support theoretical models and code requirements prescribed in NFPA 2.

The formation of hydrogen jets from pressurized sources and its ignition when hitting hot devices has been studied by many projects. The transient jets evolve with high turbulence depending on the configuration of the nozzle and especially the pressure in the hydrogen reservoir. In addition the length of the jets and the flames generated by ignition at a hot surface varies. Parameters to be varied were initial pressure of the source (2.5 10 20 and 40 MPa) distance between the nozzle and the hot surface (3 5 and 7 m) and temperature of the hot surface (between 400 and 1000 K). The interaction of the hydrogen jets is visualized by high-speed cinematography techniques which allow analysing the jet characteristics. By combination of various methods of image processing the visibility of the phenomena on the videos taken at 15 000 fps was improved. In addition high-speed NIR spectroscopy was used to obtain temperature profiles of the expanding deflagrations. The jets ignite already above 450 K for conditions mainly from the tubular source at 40 MPa. In addition the propagation of the flame front depends on all three varied parameters: temperature of the hot surface pressure in the reservoir and distance between nozzle and hot surface. In most cases also upstream propagation occurs. A high turbulence seems to lead to the strong deflagrations. At high temperatures of the ignition sources the interaction leads to fast deflagration and speeds up- and downstream of the jet. The deflagration velocity is close to velocity of sound and emission of pressure waves occurs.

Buoyancy effects and nozzle geometry can have a significant impact on turbulent jet dispersion. This work was motivated by applications involving hydrogen. Using helium as an experimental proxy buoyant horizontal jets issuing from a round orifice on the side wall of a circular tube were analyzed experimentally using particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) techniques simultaneously to provide instantaneous and time-averaged flow fields of velocity and concentration. Effects of buoyancy and asymmetry on the resulting flow structure were studied over a range of Reynolds numbers and gas densities. Significant differences were found between the centreline trajectory spreading rate and velocity decay of conventional horizontal round axisymmetric jets issuing through flat plates and the pipeline leak-representative jets considered in the present study. The realistic pipeline jets were always asymmetric and found to deflect about the jet axis in the near field. In the far field it was found that the realistic pipeline leak geometry causes buoyancy effects to dominate much sooner than expected compared to horizontal round jets issuing through flat plates.

Vented deflagration tests were conducted by UNIPI at B. Guerrini Laboratory during the experimental campaign for HySEA project. Experiments included homogeneous hydrogen-air mixture in a 10-18% vol. range of concentrations contained in an about 1 m3 enclosure called SSE (Small Scale Enclosure). Displacement measurements of a test plate were taken in order to acquire useful data for the validation of FE model developed by IMPETUS Afea. In this paper experimental facility displacement measurement system and FE model are briefly described then comparison between experimental data and simulation results is discussed.

Hydrogen safety is a relevant topic for both nuclear fission and fusion power plants. Hydrogen generated in the course of a severe accident may endanger the integrity of safety barriers and may result in radioactive releases. In the case of the ITER fusion facility accident scenarios with water ingress consider the release of hydrogen into the suppression tank (ST) of the vacuum vessel pressure suppression system (VVPSS). Under the assumption of additional air ingress the formation of flammable gas mixtures may lead to explosions and safety component failure.<br/>The installation of passive auto-catalytic recombiners (PARs) inside the ST which are presently used as safety devices inside the containments of nuclear fission reactors is one option under consideration to mitigate such a scenario. PARs convert hydrogen into water vapor by means of passive mechanisms and have been qualified for operation under the conditions of a nuclear power plant accident since the 1990s.<br/>In order to support on-going hydrogen safety considerations simulations of accident scenarios using the CFD code ANSYS-CFX are foreseen. In this context the in-house code REKO-DIREKT is coupled to CFX to simulate PAR operation. However the operational boundary conditions for hydrogen recombination (e.g. temperature pressure gas mixture) of a fusion reactor scenario differ significantly from those of a fission reactor. In order to enhance the code towards realistic PAR operation a series of experiments has been performed in the REKO-4 facility with specific focus on ITER conditions. These specifically include operation under sub-atmospheric pressure (0.2–1.0 bar) gas compositions ranging from lean to rich H2/O2 mixtures and superposed flow conditions.<br/>The paper gives an overview of the experimental program presents results achieved and gives an outlook on the modelling approach towards accident scenario simulation.

Delayed explosions of accidental high pressure hydrogen releases are an important risk scenario for safety studies of production plants transportation pipelines and fuel cell vehicles charging stations. As a consequence the assessment of the associated consequences requires accurate and validated prediction based on modelling and experimental approaches. In the frame of the French working group dedicated to the evaluation of computational fluid dynamics (CFD) codes for the modelling of explosion phenomena this study is dedicated to delayed explosions of high pressure releases. Two participants using two different codes have evaluated the capacity of CFD codes to reproduce explosions of high pressure hydrogen releases. In the first step the jet dispersion is modelled and simulation results are compared with experimental data in terms of axial and radial concentration dilution velocity decay and turbulent characteristics of jets. In the second step a delayed explosion is modelled and compared to experimental data in terms of overpressure at different monitor points. Based on this investigation several recommendations for CFD modelling of high pressure jets explosions are suggested.

This session concerned the political economic and environmental impact on the hydrogen economy due to hydrogen embrittlement.

This article is a transcription of the recorded discussion of ‘Political economic and environmental concerns’ at the Royal Society Scientific Discussion Meeting Challenges of Hydrogen and Metals 16–18 January 2017. The text is approved by the contributors. G.C.G.S. transcribed the session and F.F.D. assisted in the preparation of the manuscript.

Link to document download on Royal Society Website 

This paper describes a methodology for simulating the structural response of vented enclosures during hydrogen deflagrations. The paper also summarises experimental results for the structural response of 20-foot ISO (International Organization for Standardization) containers in a series of vented hydrogen deflagration experiments. The study is part of the project Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations (HySEA). The project is funded by the Fuel Cells and Hydrogen 2 Joint Undertaking 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. The structural response modelling involves one-way coupling of pressure loads taken either directly from experiments or from simulations with the computational fluid dynamics (CFD) tool FLACS to the non-linear finite element (FE) IMPETUS Afea Solver. The performance of the FE model is evaluated for a range of experiments from the HySEA project in both small-scale enclosures and 20-foot ISO containers. The paper investigates the sensitivity of results from the FE model to the specific properties of the geometry model. The performance of FLACS is evaluated for a selected set of experiments from the HySEA project. Furthermore the paper discusses uncertainties associated with the combined modelling approach.

Laboratory measurements were made on the concentration and temperature fields of cryogenic hydrogen jets. Images of spontaneous Raman scattering from a pulsed planar laser sheet were used to measure the concentration and temperature fields from varied releases. Jets with up to 5 bar pressure with near-liquid temperatures at the release point were characterized in this work. This data is relevant for characterizing unintended leaks from piping connected to cryogenic hydrogen storage tanks such as might be encountered at a hydrogen fuel cell vehicle fuelling station. The average centerline mass fraction was observed to decay at a rate similar to room temperature hydrogen jets while the half-width of the Gaussian profiles of mass fraction were observed to spread more slowly than for room temperature hydrogen. This suggests that the mixing and models for cryogenic hydrogen may be different than for room temperature hydrogen. Results from this work were also compared to a one-dimensional (streamwise) model. Good agreement was seen in terms of temperature and mass fraction. In subsequent work a validated version of this model will be exercised to quantitatively assess the risk at hydrogen fuelling stations with cryogenic hydrogen on-site.

An integrated system for H2 production from microalgae and its storage is proposed employing enhanced process integration technology (EPI). EPI consists of two core technologies i.e. exergy recovery and process integration. The proposed system includes a supercritical water gasification H2 separation hydrogenation and combined cycle. Microalga Chlorella vulgaris is used as a material for evaluation. The produced syngas is separated to produce highly pure H2. Furthermore to store the produced H2 liquid organic H2 carrier of toluene-and-methylcyclohexane cycle is adopted. The remaining gas is used as fuel for combustion in combined cycle to generate electricity. The effects of fluidization velocity and gasification pressure to energy efficiency are evaluated. From process modelling and calculation it is shown that high total energy efficiency about 60% can be achieved. In addition about 40% of electricity generation efficiency can be realized.

A hydrogen leak from a facility which uses highly compressed hydrogen gas (714 bar 800 K) during operation was studied. The investigated scenario involves supersonic hydrogen release from a 10 cm2 leak of the pressurized reservoir turbulent hydrogen dispersion in the facility room followed by an accidental ignition and burn-out of the resulting H2-air cloud. The objective is to investigate the maximum possible flame velocity and overpressure in the facility room in case of a worst-case ignition. The pressure loads are needed for the structural analysis of the building wall response. The first two phases namely unsteady supersonic release and subsequent turbulent hydrogen dispersion are simulated with GASFLOW-MPI. This is a well validated parallel all-speed CFD code which solves the compressible Navier-Stokes equations and can model a broad range of flow Mach numbers. Details of the shock structures are resolved for the under-expanded supersonic jet and the sonic-subsonic transition in the release. The turbulent dispersion phase is simulated by LES. The evolution of the highly transient burnable H2-air mixture in the room in terms of burnable mass volume and average H2-concentration is evaluated with special sub-routines. For five different points in time the maximum turbulent flame speed and resulting overpressures are computed using four published turbulent burning velocity correlations. The largest turbulent flame speed and overpressure is predicted for an early ignition event resulting in 35–71 m/s and 0.13–0.27 bar respectively.

Hydrogen sulfide corrosion is one of the main reasons of steels destruction in the oil and gas industry. Damages appear as a result of corrosion and hydrogen embrittlement and corrosion cracking occurs when the load is applied. The influence of the steels structure on its stress corrosion cracking under the loads in hydrogen sulfide environment is insufficiently studied. The aim of the study is to determine the influence of the steels structure on its corrosion hydrogenation and corrosion cracking in the NACE hydrogen sulfide solution.<br/>It was established that the corrosion rate and hydrogenation of steel У8 in the NACE solution grows when the structure dispersion increases from perlite to sorbite troostite and martensite. The corrosion rate and hydrogenation of steel 45 are the greatest in pearlite-ferrite while the smallest - in sorbite.<br/>The corrosion of steels У8 and 45 in the NACE solution is localized: the average size of the ulcers is 50 ... 80 μm on the steel У8 and 45 ... 65 μm on steel 45. The depth of ulcers is maximal on the steel У8 with the martensite structure (~ 260 μm) and on the steel 45 with the troostite structure (~ 210 μm).<br/>Static load (σ = 300 MPa) increases the hydrogenation of steels in the hydrogen sulfide environment. The concentration of hydrogen in steel У8 with troostite structure increases by ~ 1.8 times. The concentration of hydrogen in steel 45 with troostite and martensite structures increases by ~ 1.2...1.3 and by ~ 1.4...1.6 times respectively.<br/>The steel У8 with martensite and perlite structures and steel 45 with troostite structure has the lowest resistance to corrosion cracking. Steels destruction depends on both hydrogen permeation and the corrosion localization which leads to the increase of the microelectrochemical heterogeneity of the surfaces.

In this work a mixed-cation borohydride (K2Mn(BH4)4) with P21/n structure was successfully synthesized by mechanochemical milling of the 2KBH4–MnCl2 sample under argon. The structural and thermal decomposition properties of the borohydride compounds were investigated using XRD Raman spectroscopy FTIR TGA-MS and DSC. Apart from K2Mn(BH4)4 the KMnCl3 and unreacted KBH4 compounds were present in the milled 2KBH4–MnCl2. The two mass loss regions were observed for the milled sample: one was from 100 to 160 °C with a 1.6 ± 0.1 wt% loss (a release of majority hydrogen and trace diborane) which was associated with the decomposition of K2Mn(BH4)4 to form KBH4 boron and finely dispersed manganese; the other was from 165 to 260 °C with a 1.9 ± 0.1 wt% loss (only hydrogen release) which was due to the reaction of KBH4 with KMnCl3 to give KCl boron finely dispersed manganese. Simultaneously the formed KCl could dissolve in KBH4 to yield a K(BH4)xCl1−x solid solution and also react with KMnCl3 to form a new compound K4MnCl6.

Experiments in an obstructed semi-confined vertical combustion channel with a height of 6 m (cross-section 0.4 × 0.4 m) inside a safety vessel of the hydrogen test center HYKA at the Karlsruhe Institute of Technology (KIT) are reported. In the work homogeneous hydrogen-air-mixtures as well as mixtures with different well-defined H2-concentration gradients were ignited either at the top or at the bottom end of the channel. The combustion characteristics were recorded using pressure sensors and sensors for the detection of the flame front that were distributed along the complete channel length. In the tests slow subsonic and fast sonic deflagrations as well as detonations were observed and the conditions for the flame acceleration (FA) to speed of sound and deflagration-to-detonation transition (DDT) are compared with the results of similar experiments performed earlier in a larger semi-confined horizontal channel.

Consequence modelling of high potential risks of usage and transportation of cryogenic liquids yet requires substantial improvements. Among the cryogenics liquid hydrogen (LH2) needs especial treatments and a comprehensive understanding of spill and spread of liquid and dispersion of vapor. Even though many of recent works have shed lights on various incidents such as spread dispersion and explosion of the liquid over land less focus was given on spill and spread of LH2 onto water. The growing trend in ship transportation has enhanced risks such as ships’ accidental releases and terrorist attacks which may ultimately lead to the release of the cryogenic liquid onto water. The main goal of the current study is to present a computational fluid dynamic (CFD) approach using OpenFOAM to model release and spread of LH2 over water substrate and discuss previous approaches. It also includes empirical heat transfer equations due to boiling and computation of evaporation rate through an energy balance. The results of the proposed model will be potentially used within another coupled model that predicts gas dispersion]. This work presents a good practice approach to treat pool dynamics and appropriate correlations to identify heat flux from different sources. Furthermore some of the previous numerical approaches to redistribute or in some extend manipulate the LH2 pool dynamic are brought up for discussion and their pros and cons are explained. In the end the proposed model is validated by modelling LH2 spill experiment carried out in 1994 at the Research Centre Juelich in Germany.

Catastrophic rupture of onboard hydrogen storage in a fire is a safety concern. Different passive e.g. fireproofing materials the thermally activated pressure relief device (TPRD) and active e.g. initiation of TPRD by fire sensors safety systems are being developed to reduce hazards from and associated risks of high-pressure hydrogen storage tank rupture in a fire. The probability of such low-frequency highconsequences event is a function of fire resistance rating (FRR) i.e. the time before tank without TPRD ruptures in a fire the probability of TPRD failure etc. This safety issue is “confirmed” by observed recently cases of CNG tanks rupture due to blocked or failed to operate TPRD etc. The increase of FRR by any means decreases the probability of tank rupture in a fire particularly because of fire extinction by first responders on arrival at an accident scene.<br/>This study of socio-economic effects of safety applies a quantitative risk assessment (QRA) methodology to an example of hydrogen vehicles with passive tank protection system on roads in London.<br/>The risk is defined here through the cost of human loss per fuel cell hydrogen vehicle (FCHV) fire accident and fatality rate per FCHV per year. The first step in the methodology is the consequence analysis based on validated deterministic engineering tools to estimate the main identified hazards: overpressure in the blast wave at different distances and the thermal hazards from a fireball in the case of catastrophic tank rupture in a fire. The population can be exposed to slight injury serious injury and fatality after an accident. These effects are determined based on criteria by Health and Safety Executive (UK) and a cost metrics is applied to the number of exposed people in these three harm categories to estimate the cost per an accident. The second step in the methodology is either the frequency or the probability analysis. Probabilities of a vehicle fire and failure of the thermally activated pressure relief device are taken from published sources. A vulnerability probit function is employed to calculate the probability of emergency operations’ failure to prevent tank rupture as a function of a storage tank FRR and time of fire brigade arrival. These later results are integrated to estimate the tank rupture frequency and fatality rate. The risk is presented as a function of fire resistance rating.<br/>The QRA methodology allows to calculate the cost of human loss associated with an FCHV fire accident and demonstrates how the increase of FRR of onboard storage as a safety engineering measure would improve socio-economics of FCHV deployment and public acceptance of the technology.

In order to facilitate the application of hydrogen energy and ensure its safety the compressed hydrogen storage tank on board needs to be full of hydrogen gas within 3 minutes. Therefore to meet this requirement the effects of refueling parameters on the filling time need to be investigated urgently. For the purpose of solving this issue a novel analytical solution of filling time is obtained from a lumped parameter model in this paper. According to the equation of state for real gas and dimensionless numbers Nu and Re the function relationships between the filling time and the refueling parameters are presented. These parameters include initial temperature initial pressure inflow temperature final temperature and final pressure. These equations are used to fit the reference data the results of fitting show good agreement. Then the values of fitting parameters are further utilized so as to verify the validity of these formulas. We believe this study can contribute to control the hydrogen filling time and ensure the safety during fast filling process.

Stationary pressure vessels for the storage of large volumes of gaseous hydrogen at high pressure (>70 MPa) are typically manufactured from Cr-Mo steels. These steels display hydrogen-enhanced fatigue crack growth but pressure vessels can be manufactured using defect-tolerant design methodologies. However storage volumes are limited by the wall thickness that can be reliably manufactured for quench and tempered Cr-Mo steels typically not more than 25-35 mm. High-hardenability steels can be manufactured with thicker walls which enables larger diameter pressure vessels and larger storage volumes. The goal of this study is to assess the fracture and fatigue response of high hardenability Ni-Cr-Mo pressure vessel steels for use in high-pressure hydrogen service at pressure in excess of 1000 bar. Standardized fatigue crack growth tests were performed in gaseous hydrogen at frequency of 1Hz and for R-ratios in the range of 0.1 to 0.7. Elastic-plastic fracture toughness measurements were also performed. The measured fatigue and fracture behavior is placed into the context of previous studies on fatigue and fracture of Cr-Mo steels for gaseous hydrogen.

Explosion relief panels or doors are often used in industrial buildings to reduce damages caused by gas explosions. Decades of research have contributed to the understanding of the phenomena involved in gas explosions in order to establish an effective method to predict reliably the explosion overpressure. All the methods predict a monotonic increase of the overpressure with the concentration of the gas in the range from the lower explosion limit to the stoichiometric one. Nevertheless in few cases a non-monotonic behaviour of the maximum developed pressure as a function of hydrogen concentration was reported in the literature. The non-monotonic behaviour was also observed during experimental tests performed at the Scalbatraio laboratory at the University of Pisa in a 25 m3 vented combustion test facility with a vent area of 112 m2. This paper presents the results obtained during the tests and investigates the possible explanations of the phenomena.

Studying thermal ignition mechanisms is a key step for evaluating many ignition hazards. In the present work two-dimensional simulations with detailed chemistry are used to study the reaction pathways of the transient flow and ignition of a stoichiometric hydrogen-air mixture by moving hot spheres. For temperatures above the ignition threshold ignition takes place after a short time between the front stagnation point and separation location depending upon the sphere's surface temperature. Closer to the threshold the volume of gas adjacent to the separation region ignites homogeneously after a longer time. These results demonstrate the importance of boundary layer development and flow separation in the ignition process.

Since the rapid development of hydrogen stationary and vehicle fuel cells the last decade it is of importance to improve the prediction of overpressure generated during an accidental explosion which could occur in a confined part of the system. To this end small-scale vented hydrogen–air explosions were performed in a transparent cubic enclosure with a volume of 3375 cm3. The flame propagation was followed with a high speed camera and the overpressure inside the enclosure was recorded using high frequency piezoelectric transmitters. The effects of vent area and ignition location on the amplitude of pressure peaks in the enclosed volume were investigated. Indeed vented deflagration generates several pressures peaks according to the configuration and each peak can be the dominating pressure. The parametric study concerned three ignition locations and five square vent sizes.