Safety
Risk Analysis on Mobile Hydrogen Refueling Stations in the World Expo Shanghai
Sep 2013
Publication
During the World Expo Shanghai there were one hundred fuel-cell sight-seeing cars in operation at the Expo Site. The sight-seeing cars were not allowed to drive out of the Expo Site and the stationary hydrogen refuelling station was not permitted to build at the Expo Site for the sake of safety. A flexible solution to refuel the cars was the application of mobile hydrogen refuelling stations. To better understand the hazards and risks associated with the mobile hydrogen refueling stations a risk analysis was preformed to improve the safety of the operations. The risks to the station personnel and to the public were discussed separately. Results show that the stationary risks of the mobile stations to the personnel and refueling customers are lower than the risk acceptance criteria over an order of magnitude so occupational risks and risks to customers are completely acceptable. The third party risks can be acceptable as long as the appropriate mitigation measures are implemented especially well designed parking area and operation time. Leak from boosters is the main risk contributor to the stationary risks because of its highest failure rates according to the generic data and its worst harm effects based on the consequence evaluations. As for the road risks of the mobile stations they can be acceptable as long as the appropriate mitigation measures are implemented especially well-designed moving path and transportation time.
Deploying Fuel Cell Systems, What Have We Learned
Sep 2013
Publication
The Hydrogen Safety Panel brings a broad cross-section of expertise from the industrial government and academic sectors to help advise the U.S. Department of Energy's (DOE) Fuel Cell Technologies Office through its work in hydrogen safety codes and standards. The Panel's initiatives in reviewing safety plans conducting safety evaluations identifying safety-related technical data gaps and supporting safety knowledge tools and databases cover the gamut from research and development to demonstration. The Panel's recent work has focused on the safe deployment of hydrogen and fuel cell systems in support of DOE efforts to accelerate fuel cell commercialization in early market applications: vehicle refuelling material handling equipment backup power for warehouses and telecommunication sites and portable power devices. This paper summarizes the work and learnings from the Panel's early efforts the transition to its current focus and the outcomes and conclusions from recent work on the deployment of hydrogen and fuel cell systems.
TPR-XAFS Study for Hydrogen Recombination Reaction of Platinum Metal Nanoparticle Catalysts
Sep 2017
Publication
Proper management of hydrogen gas is very important for safety of nuclear power plants. Hydrogen removal system by hydrogen recombination reaction (water formation reaction) on a catalyst is one of the candidates for avoiding hydrogen explosion. We have observed in situ and time-resolved structure change of platinum metal nanoparticle catalyst during hydrogen recombination reaction by using simultaneous measurement of temperature-programmed reaction and X-ray absorption fine structure (TPR-XAFS). A poisoning effect by carbon monoxide on catalytic activity was focused. It was found that the start of hydrogen recombination reaction is closely connected with the occurrence of the decomposition of adsorbed carbon monoxide molecules and creation of surface oxide layer on platinum metal nanoparticles.
Outward Propagation Velocity and Acceleration Characteristics in Hydrogen-air Deflagration
Oct 2015
Publication
Propagation characteristics of hydrogen-air deflagration need to be understood for an accurate risk assessment. Especially flame propagation velocity is one of the most important factors. Propagation velocity of outwardly propagating flame has been estimated from burning velocity of a flat flame considering influence of thermal expansion at a flame front; however this conventional method is not enough to estimate an actual propagation velocity because flame propagation is accelerated owing to cellular flame front caused by intrinsic instability in hydrogen-air deflagration. Therefore it is important to understand the dynamic propagation characteristics of hydrogen-air deflagration. We performed explosion tests in a closed chamber which has 300 mm diameter windows and observed flame propagation phenomena by using Schlieren photography. In the explosion experiments hydrogen-air mixtures were ignited at atmospheric pressure and room temperature and in the range of equivalence ratio from 0.2 to 1.0. Analyzing the obtained Schlieren images flame radius and flame propagation velocity were measured. As the result cellular flame fronts formed and flame propagations of hydrogen–air mixture were accelerated at the all equivalence ratios. In the case of equivalent ratio φ = 0.2 a flame floated up and could not propagate downward because the influence of buoyancy exceeded a laminar burning velocity. Based upon these propagation characteristics a favorable estimation method of flame propagation velocity including influence of flame acceleration was proposed. Moreover the influence of intrinsic instability on propagation characteristics was elucidated.
Spontaneous Ignition of Hydrogen- Literature Review
Jan 2008
Publication
Objectives
The aim of this review is to establish which available literature may be of use as part of the HSE funded project which will investigate spontaneous ignition of accidental hydrogen releases (JR02071). It will identify phenomena that have the potential to cause spontaneous ignition of releases of pressured hydrogen and identify literature that may be of use when formulating the experimental program.
Main Findings
The identification of important work that shows conclusive evidence of spontaneous ignition of hydrogen due to the failure of a boundary layer.
The aim of this review is to establish which available literature may be of use as part of the HSE funded project which will investigate spontaneous ignition of accidental hydrogen releases (JR02071). It will identify phenomena that have the potential to cause spontaneous ignition of releases of pressured hydrogen and identify literature that may be of use when formulating the experimental program.
Main Findings
The identification of important work that shows conclusive evidence of spontaneous ignition of hydrogen due to the failure of a boundary layer.
The Effect of Iron on the Solubility Behavior of Hydrogen in Tantalum
Sep 2013
Publication
The separation storage and recovery of hydrogen are key requirements for the efficient development of advanced hydrogen fuel technologies. The ideal hydrogen separation membrane should have high hydrogen permeability and good mechanical properties at a range of temperatures and pressures. Tantalum is a potential candidate with highest permeability to hydrogen among pure materials for hydrogen separation membrane. Isothermal as well as isobaric PCT equilibrium studies have been done in the temperature range of 673 – 873 K and hydrogen pressure range of 0.60 – 1.20 atmospheres for pure Ta and its solid solution alloys with Fe in different compositions. Results are presented.
A Simple Model for Calculating Peak Pressure in Vented Explosions of Hydrogen and Hydrocarbons
Apr 2019
Publication
The authors presented a basic mathematical model for estimating peak overpressure attained in vented explosions of hydrogen in a previous study (Sinha et al. [1]). The model focussed on idealized cases of hydrogen and was not applicable for realistic accidental scenarios like presence of obstacles initial turbulent mixture etc. In the present study the underlying framework of the model is reformulated to overcome these limitations. The flame shape computations are simplified. A more accurate and simpler formulation for venting is also introduced. Further by using simplifying assumptions and algebraic manipulations the detailed model consisting of several equations is reduced to a single equation with only four parameters. Two of these parameters depend only on fuel properties and a standard table provided in the Appendix can be used. Therefore to compute the overpressure only the two parameters based on enclosure geometry need to be evaluated. This greatly simplifies the model and calculation effort. Also since the focus of previous investigation was hydrogen properties of hydrocarbon fuels which are much more widely used were not accounted for. The present model also accounts for thermo-physical properties of hydrocarbons and provides table for fuel parameters to be used in the final equation for propane and methane. The model is also improved by addition of different sub-models to account for various realistic accidental scenarios. Moreover no adjustable parameters are used; the same equation is used for all conditions and all gases. Predictions from this simplified model are compared with experimentally measured values of overpressure for hydrogen and hydrocarbons and found to be in good agreement. First the results from experiments focussing on idealized conditions of uniformly mixed fuel in an empty enclosure under quiescent conditions are considered. Further the model applicability is also tested for realistic conditions of accidental explosion consisting of obstacles inside the enclosure non-uniform fuel distribution initial turbulent mixture etc. For all the cases tested the new simple model is found to produce reasonably good predictions.
Cell Failure Mechanisms in PEM Water Electrolyzers
Sep 2011
Publication
PEM water electrolysis offers an efficient and flexible way to produce “green-hydrogen” from renewable (intermittent) energy sources. Most research papers published in the open literature on the subject are addressing performances issues and to date very few information is available concerning the mechanisms of performance degradation and the associated consequences. Results reported in this communication have been used to analyze the failure mechanisms of PEM water electrolysis cells which can ultimately lead to the destruction of the electrolyzer. A two-step process involving firstly the local perforation of the solid polymer electrolyte followed secondly by the catalytic recombination of hydrogen and oxygen stored in the electrolysis compartments has been evidenced. The conditions leading to the onset of such mechanism are discussed and some preventive measures are proposed to avoid accidents.
Explosion Venting of Rich Hydrogen-air Mixtures in a Cylindrical Vessel with Two Symmetrical Vents
Oct 2015
Publication
The safety issues related to explosion venting of hydrogen-air mixtures are significant and deserve more detailed investigation. Vented hydrogen-air explosion has been studied extensively in vessels with a single vent. However little attention has been paid to the cases with more than one vent. In this paper experiments about explosion venting of rich hydrogen-air mixtures were conducted in a cylindrical vessel with two symmetrical vents to investigate the effect of vent area and distribution on pressure build up and flame behaviours. Venting accelerates the flame front towards the vent but has nearly no effect on the opposite side. The maximum internal overpressure decreases and the maximum external flame length increases with the increase of vent area. Two pressure peaks can be identified outside of vessel which correspond to the external explosion and the burnt gas jet respectively. Compared with single vent two vents with same total vent area leads to nearly unchanged maximum internal and external overpressure but much smaller external flame length.
Cost Effective Inherent Safety Index for Polymer Electrolyte Membrane Fuel Cell Systems
Sep 2013
Publication
There have been many indices available in the process industries to describe rank or quantify hazards to people properties and environments. Most of the developed methods were meant to be applied to large scale and complex systems of process industries. Development of a swift and simple inherent safety index method which is relevant to small scale less complex membrane fuel cell system particularly the one in which to be applied during an early design stage is essential as an alternative to current comprehensive and yet time-consuming indices. In this work a modified version of PIIS modified prototype index for inherent safety (m-PIIS) was developed with the objectives of identifying indicating and estimating inherent safety of fuel cell system at an early design stage. The developed index was tested at four proton exchange membrane (PEM) fuel cell systems namely high pressure PEMFC system low pressure PEMFC system LH2 PEMFC system and on-board Me-OH PEMFC system. The developed index was also benchmarked against the original PIIS and ISI using the published results for the selection of process routes in MMA production. Results have indicated that m-PIIS has strong positive relationship with PIIS and ISI on most of the reaction step in MMA with the most significant are the C4 TBA and C3 reaction steps. Other reaction steps such as C2/MP C2/PA and ACH showed a strong positive relationship as well.
Consequences of Catastrophic Releases of Ignited and Unignited Hydrogen Jet Releases
Sep 2009
Publication
The possibility of using a risk based approach for the safe installation and siting of stationary fuel cell systems depends upon the availability of normative data and guidance on potential hazards and the probabilities of their occurrence. Such guidance data is readily available for most common hydrocarbon fuels. For hydrogen however data is still required on the hazards associated with different release scenarios. This data can then be related to the probability of different types of scenarios from historical fault data to allow safety distances to be defined and controlled using different techniques. Some data on releases has started to appear but this data generally relates to hydrogen vehicle refuelling systems that are designed for larger throughput higher pressures and the general use of larger pipe diameters than are likely to be used for small fuel cell systems.
Prediction of Third Party Damage Failure Frequency for Pipelines Transporting Mixtures of Natural Gas and Hydrogen
Sep 2009
Publication
As Europe is gradually moving towards a hydrogen based society it has been acknowledged that adding certain amount of hydrogen as a clean energy carrier to the existing natural gas pipeline will help reduce the CO2 emissions which contribute to the greenhouse effect. On the other hand hydrogen has been demonstrated to be able to change the behaviour of the pipeline steel such as lower toughness and faster crack growth due to hydrogen embrittlement. Therefore it is necessary that the risks associated with the failure of the pipeline carrying mixtures of natural gas and hydrogen be assessed.<br/>The study reported in this paper is part of European NATURALHY project whose aim is to investigate the possibility of using the existing natural gas transmission pipelines to convey natural gas/hydrogen mixtures. According to the EGIG database the most common cause of failure for the existing natural gas pipelines is third party damage which mainly refers to a gouge a dent/gouge combination of known geometry. Among third party damage failures 90% are the result of immediate failure i.e. leakage or rupture of the pipeline and only 10% of them are the result of delayed failure. While its not expected that hydrogen will impact the immediate failure it could increase the vulnerability of the pipe to delayed failure through the initiation or activation of crack like defects.<br/>This paper will present a methodology to predict the probability of increased failures and describe a software tool that has been developed to perform the calculations.
Fatigue and Fracture of High-hardenability Steels for Thick-walled Hydrogen Pressure Vessels
Sep 2017
Publication
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.
Dispersion and Burning Behavior of Hydrogen Released in a Full-scale Residential Garage in the Presence and Absence of Conventional Automobiles
Sep 2011
Publication
Experiments are described in which hydrogen was released at the center of the floor of a real-scale enclosure having dimensions of a typical two-car residential garage. Real-time hydrogen concentrations were monitored at a number of locations. The hydrogen/air mixtures were ignited at pre-determined local volume fractions ranging from 8% to 29%. The combustion behavior and structural effects were monitored using combinations of high-speed pressure transducers and ionization gauges standard thermocouples hydrogen sensors and digital infrared and high-speed video cameras. Experiments were performed both for empty garages and garages with conventional automobiles parked above the hydrogen release location.
Validation Strategy for CFD Models Describing Safety-relevant Scenarios Including LH2/GH2 Release and the Use of Passive Autocatalytic Recombiners
Sep 2013
Publication
An increase in use of hydrogen for energy storage and clean energy supply in a future energy and mobility market will strengthen the focus on safety and the safe handling of hydrogen facilities. The ability to simulate the whole chain of physical phenomena that may occur during an accident is mandatory for future safety studies on an industrial or urban scale. Together with the RWTH Aachen University Forschungszentrum Jülich (JÜLICH) develops numerical methods to predict safety incidents connected with the release of either LH2 or GH2 using the commercial CFD code ANSYS CFX. The full sequence from the release distribution or accumulation of accidentally released hydrogen till the mitigation of accident consequences by safety devices is considered. For specific phenomena like spreading and vaporization of LH2 pools or the operational behavior of passive auto-catalytic recombiners (PAR) in-house sub-models are developed and implemented. The paper describes the current development status gives examples of the validation and concludes with future work to provide the full range of hydrogen release and recombination simulation.
Numerical Simulation on Low-speed Hydrogen Jet Diffusion
Oct 2015
Publication
The numerical simulation for the hydrogen jet experiments performed by Schefer et al. is conducted using the compressible multicomponent Navier-Stokes equations with the preconditioning method. The simulated results for the hydrogen jet agree with the theoretical results of Tollmien. As far as comparing with the experiments by Schefer et al. the concentration profiles along the radial direction agree with the present numerical results and that along the centerline also agree well with the experimental results after the data are normalized by the equivalent nozzle diameter. It is confirmed that the spread of the jet width from the jet exit to downstream is affected by the Kelvin-Helmholtz instability. It is also confirmed that the jet flow field is formed alternately by the high pressure region and the low pressure one to cause the jet flow fluctuation.
Health and safety in the new energy economy
Dec 2010
Publication
Over the next decade and beyond the UK is set to take significant steps towards a new energy economy. This will be an economy where the technologies meeting<br/>our electricity heat and fuel needs have to deliver against three key criteria: sustainability security and affordability.<br/><br/>In this context a wide range of emerging energy technologies are expected to play an important role in reshaping the way we satisfy our energy requirements. The extent to which they do so however will depend fundamentally on their ability to be harnessed safely.<br/><br/>Compiled by HSE’s Emerging Energy Technologies Programme this report provides a current assessment of the health and safety hazards that key emerging energy technologies could pose both to workers and to the public at large. (Nuclear energy technologies fall outside the scope of this report.) But it also highlights how an appropriate framework can be and is being put in place to help ensure that these hazards are managed and controlled effectively – an essential<br/>element in enabling the technologies to make a major contribution to the UK’s energy future.
Indoor Use of Hydrogen, Knowledge Gaps and Priorities for the Improvement of Current Standards on Hydrogen, a Presentation of HyIndoor European Project
Sep 2013
Publication
To develop safety strategies for the use of hydrogen indoors the HyIndoor project is studying the behaviour of a hydrogen release deflagration or non-premixed flame in an enclosed space such as a fuel cell or its cabinet a room or a warehouse. The paper proposes a safety approach based on safety objectives that can be used to take various scenarios of hydrogen leaks into account for the safe design of Hydrogen and Fuel Cell (HFC) early market applications. Knowledge gaps on current engineering models and unknown influence of specific parameters were identified and prioritized thereby re-focusing the objectives of the project test campaign and numerical simulations. This approach will enable the improvement of the specification of openings and use of hydrogen sensors for enclosed spaces. The results will be disseminated to all stakeholders including hydrogen industry and RCS bodies.
Effect of Rotation on Ignition Thresholds of Stoichiometric Hydrogen Mixtures
Sep 2017
Publication
Successful transition to a hydrogen economy calls for a deep understanding of the risks associated with its widespread use. Accidental ignition of hydrogen by hot surfaces is one of such risks. In the present study we investigated the effect that rotation has on the reported ignition thresholds by numerically determining the minimum surface temperature required to ignite stoichiometric hydrogen-air using a hot horizontal cylinder rotating at various angular velocities ω. Numerical experiments showed a weak but interesting dependence of the ignition thresholds on rotation: the ignition thresholds increased by 8 K from 931 K to 939 K with increasing angular velocity (0 ≤ ω ≤ 240 rad/s). A further increase to ω = 480 rad/s resulted in a decrease in ignition surface temperature to 935 K. Detailed analysis of the flow patterns inside the vessel and in close proximity to the hot surface brought about by the combined effect of buoyancy and rotation as well as of the distribution of the wall heat flux along the circumference of the cylinder support our previous findings in which regions where temperature gradients are small were found to be prone to ignition.
Regulations, Codes, and Standards (RCS) for Multi-fuel Motor Vehicle Dispensing Station
Sep 2017
Publication
In the United States requirements for liquid motor vehicle fuelling stations have been in place for many years. Requirements for motor vehicle fuelling stations for gaseous fuels including hydrogen are relatively new. These requirements have in the United States been developed along different code and standards paths. The liquid fuels have been addressed in a single document and the gaseous fuels have been addressed in documents specific to an individual gas. The result of these parallel processes is that multi-fuel stations are subject to requirements in several fuelling regulations codes and standards (RCS). This paper describes a configuration of a multi-fuel motor vehicle fuelling station and provides a detailed breakdown of the codes and standards requirements. The multi-fuel station would dispense what the U.S. Department of Energy defines as the six key alternative fuels: biodiesel electricity ethanol hydrogen natural gas and propane. The paper will also identify any apparent gaps in RCS and potential research projects that could help fill these gaps.
Effectiveness Evaluation of Facilities Protecting from Hydrogen-air Explosion Overpressure
Sep 2011
Publication
The physical processes of the explosion of the hydrogen cloud which is formed as a result of the instantaneous destruction of high-pressure cylinder in the fuelling station are investigated. To simulate the formation of hydrogen-air mixture and its combustion a three-dimensional model of an instantaneous explosion of the gas mixture based on the Euler equations supplemented by the conservation laws of mixture components solved by Godunov method is used. To reduce the influence of the overpressure effects in the shock wave on the surrounding environment it is proposed to use a number of protective measures. An estimation of the efficiency of safety devices is carried out by monitoring the overpressure changes in several critical points. To reduce the pressure load on the construction of protective devices a range of constructive measures is also offered.
Safety Concept of a self-sustaining PEM Hydrogen Electrolyzer System
Sep 2013
Publication
Sustainable electricity generation is gaining importance across the globe against the backdrop of ever- diminishing resources and to achieve significant reductions in CO2 emissions. One of the challenges is storing excess energy generated from wind and solar power. Siemens developed an electrolysis system based on proton exchange membrane (PEM) technology enabling large volumes of energy to be stored through the conversion of electrical energy into hydrogen. In developing this new product range Siemens worked intensively on safe operation with a special focus on safety measures (primary secondary and tertiary). Indeed hydrogen is not only a rapidly diffusing gas with a wide range of flammability but frequent lack of information leads to insecurity among the public. Siemens PEM water electrolyzer operates at a working pressure of 50 bar / 5 MPa. The current product generation is being used for demonstration purposes and fits into a 30 ft. / 9.14 m container. Further industrialized product lines up to double-digit medium voltage ranges will be available on the market short- and mid-term. The system is designed to operate self-sustaining. Therefore special features such as back-up and fail-safe mode supported by remote monitoring and access have been implemented. This paper includes Siemens' approach to develop and implement a safety concept for the PEM water electrolyzer leading into the approval and certification by a Notified Body as well as the lessons learnt from test stand and field experience in this new application field
IGEM/SR/23 Review of Thermal Radiation and Noise for Hydrogen Venting
Nov 2021
Publication
IGEM/SR/23 (“Venting of natural gas”) provides recommendations for the conceptual design operation and safety aspects of permanent temporary and emergency venting of natural gas. The document was originally developed many years ago and the current edition dates to 1995. The document is due to be reviewed and updated for application to natural gas but the aim of this study is not to review the applicability of the document for natural gas but to assess the possible impact of 100% hydrogen on specific aspects of the existing guidance.<br/>A key element of the guidance concerns the safe dispersion distances for natural gas as vents are intended to provide a means of safely dispersing gas in the atmosphere without ignition. Guidance on safe dispersion distances for venting are provided in Section 6.6 accompanied by graphs showing the relationship between the mass flow rate through the vent and the safe (horizontal) dispersion distance. Details of the model used to predict the dispersion distances are given in Appendix 1. However for dispersion the guidance in IGEM/SR/23 has been superseded by similar guidance on hazard distances for unignited releases in IGEM/SR/25 (“Hazardous area classification of natural gas installations”) [2]. A comprehensive review of the applicability of IGEM/SR/25 to hydrogen is already underway for the LTS Futures project and is not duplicated here.<br/>However IGEM/SR/23 contains guidance on other important aspects relevant to the safe design and operation of vents which are not addressed elsewhere in the IGEM suite of standards; in particular guidance on hazard ranges for thermal radiation (in the event of an unplanned ignition of the venting gas) and noise.<br/>The main aim of this report is to assess the potential impact of replacing natural gas with 100% hydrogen on the guidance in IGEM/SR/23 concerned with thermal hazards with a secondary objective of assessing the available information to comment on the possible influence of hydrogen on noise.
Characterization of the Hazards from Jet Releases of Hydrogen
Sep 2005
Publication
Hydrogen is a convenient energy storage medium; it can be produced from fossil fuels and biomass via chemical conversion processes or from intermittent renewable sources like wind and solar via electrolysis. It is the fuel of choice for the clean fuel-cell vehicles of the future. If the general public are to use hydrogen as a vehicle fuel customers must be able to handle hydrogen with the same degree of confidence and with comparable risk as conventional liquid and gaseous fuels. For the safe design of retail facilities through the development of appropriate codes and standards it is essential to understand all the hazards that could arise following an accidental release of hydrogen. If it is to be stored and used as a high-pressure gas the hazards associated with jet releases from accidental leaks must be considered. This paper describes work by Shell and the Health and Safety Laboratory to characterise the hazards from jet releases of hydrogen. Jet release experiments have been carried out using small leaks (circular holes ranging from 1 mm to 12 mm diameter) at system pressures up to 150 barg. Concentration measurements were made in the unignited free jets to determine the extent of the flammable cloud generated. Ignited jets were observed both in the visible and infrared to determine the flame size and shape. The experimental results for the extent of the flammable cloud and jet flame length were found to be in good agreement with model predictions.
Numerical Characterization of Under-expanded Cryogenic Hydrogen Gas Jets
Sep 2022
Publication
High-resolution direct numerical simulations are conducted for under-expanded cryogenic hydrogen gas jets to characterize the nearfield flow physics. The basic flow features and jet dynamics are analyzed in detail revealing the existence of four stages during early jet development namely (a) initial penetration (b) establishment of near-nozzle expansion (c) formation of downstream compression and (d) wave propagation. Complex acoustic waves are formed around the under-expanded jets. The jet expansion can also lead to conditions for local liquefaction from the pressurized cryogenic hydrogen gas release. A series of simulations are conducted with systematically varied nozzle pressure ratios and systematically changed exit diameters. The acoustic waves around the jets are found to waken with the decrease in the nozzle pressure ratio. The increase in the nozzle pressure ratio is found to accelerate hydrogen dispersion and widen the regions with hydrogen liquefaction potential. The increase in the nozzle exit diameter also widens the region with hydrogen liquefaction potential but slows down the evolution of the flow structures.
Development of Dispensing Hardware for Safe Fueling of Heavy Duty Vehicles
Sep 2021
Publication
The development of safe dispensing equipment for the fueling of heavy duty (HD) vehicles is critical to the expansion of this newly and quickly expanding market. This paper discusses the development of a HD dispenser and nozzles assembly (nozzle hose breakaway) for these new larger vehicles where flow rates are more than double compared to light duty (LD) vehicles. This equipment must operate at nominal pressures of 700 bar -40o C gas temperature and average flow rate of 5-10 kg/min at a high throughput commercial hydrogen fueling station without leaking hydrogen. The project surveyed HD vehicle manufacturers station developers and component suppliers to determine the basic specifications of the dispensing equipment and nozzle assembly. The team also examined existing codes and standards to determine necessary changes to accommodate HD components. From this information the team developed a set of specifications which will be used to design the dispensing equipment. In order to meet these goals the team performed computational fluid dynamic pressure modelling and temperature analysis in order to determine the necessary parameters to meet existing safety standards modified for HD fueling. The team also considered user operational and maintenance requirements such as freeze lock which has been an issue which prevents the removal of the nozzle from LD vehicles. The team also performed a failure mode and effects analysis (FMEA) to identify the possible failures in the design. The dispenser and nozzle assembly will be tested separately and then installed on an innovative HD fueling station which will use a HD vehicle simulator to test the entire system.
Numerical Study of the Effects of Tunnel Inclination and Ventilation on the Dispersion of Hydrogen Released from a Car
Sep 2021
Publication
Hydrogen cars are expected to play an important role in a decarbonised clean-transport future. Safety issues arise though in tunnels due to the possibility of accidental release and accumulation of hydrogen. This Computational Fluid Dynamics (CFD) study focuses on the effect of tunnel inclination and ventilation on hydrogen dispersion. A horseshoe shaped tunnel of 200 m length is considered in all seventeen cases examined. In most cases hydrogen is released from the bottom of a car placed at the center of the tunnel. Various inclinations in-tunnel wind speeds and fuel tank Pressure Relief Device (PRD) diameters were considered in order to assess their influence on safety. It was found that even if the long-term influence of the inclination is positive there is no systematic effect at initial stages nor at the most dangerous ‘nearly-stoichiometric’ cloud volumes (25% - 35% v/v). Adverse effects may also exist like the occasionally higher flammable cloud (4% - 75% v/v). Regarding ventilation it was found that even low wind speeds (e.g. 1 m/s) can reduce the flammable cloud by several times. However no significant effect on the total nearly-stoichiometric volumes was found for most of the cases examined. Ventilation can also cause adverse effects as for example at mid-term of the release duration in some cases. Concerning the PRD diameter a reduction from 4 mm to 2 mm resulted in about five times smaller maximum of the nearly-stoichiometric cloud volume. In addition the effect of release orientation on hydrogen cloud was examined and it was found that the downwards direction presents drawbacks compared to the backwards and upwards release directions.
The Influence of Grain Boundary and Hydrogen on the Indetation of Bi-crystal Nickel
Sep 2021
Publication
Three different types of symmetrical tilt grain boundaries Ȉ3 Ȉ11 and Ȉ27 were constructed to study the dislocation behavior under the indentation on bi-crystal nickel. After hydrogen charging the number of hydrogen atoms in the Ȉ3 sample is the smallest and gradually increases in Ȉ11 and Ȉ27 samples. The force-displacement curve of indentation shows that the deformation resistance of the Ȉ3 sample is significantly higher than that of Ȉ11 and Ȉ27 samples. With the presence of grain boundaries the deformation resistance of Ȉ11 and Ȉ27 samples is significantly improved while the deformation resistance of the Ȉ3 VDPSOH is weakened. The indentation depth during the formation of dislocations in single crystals is significantly greater than that of bi-crystals. Grain boundaries slow down the dislocation propagation speed. Compared with the bi-crystals without hydrogen the presence of hydrogen reduces the deformation resistance and accelerates the dislocation propagation.
CFD Simulations of the Refueling of Long Horizontal H2 Tanks
Sep 2021
Publication
The understanding of physical phenomena occurring during the refueling of H2 tanks used for hydrogen mobility applications is the key point towards the most optimal refueling protocol. A lot of experimental investigations on tank refueling were performed in the previous years for different types and sizes of tank. Several operating conditions were tested through these experiments. For instance the HyTransfer project gave one of the major outputs on the understanding of the physical phenomena occurring during a tank refueling. From a numerical perspective the availability of accurate numerical tools is another key point. Such tools could be used instead of the experimental set-ups to test various operating conditions or new designs of tanks and injectors. The use of these tools can reduce the cost of the refueling protocol development in the future. However they first need to be validated versus experimental data. This work is dedicated to CFD (Computational Fluid Dynamics) modeling of the hydrogen refueling of a long horizontal 530L type IV tank. As of now the number of available CFD simulations for such a large tank is low as the computational cost is significant which is often considered as a bottleneck for this approach. The simulated operating conditions correspond to one of the experimental campaigns performed in the framework of the HyTransfer project. The 3D CFD model is presented. In a first validation step the CFD results are compared with experimental data. Then a deeper insight into the physics predicted by the CFD is provided. Finally two other methodologies with the aim to reduce the computational cost have been tested.
Study of Attenuation Effect of Water Droplets on Shockwaves from Hydrogen Explosion
Sep 2021
Publication
The increasing demand for renewable energy storage may position hydrogen as one of the major players in the future energy system. However to introduce such technology high level of safety must be offered. In particular for the accident scenarios with combustion or explosion of the unintendedly released hydrogen in partially or fully confined volumes such as e.g. road tunnel the effective countermeasures preventing or reducing the risk of equipment damages and person injuries should be established. A mitigation strategy could be the use of existing fire suppression system which can inject water as a spray. The shock waves resulted from hydrogen explosion could be weakened by the water droplets met on the shock path. In the presented work an attenuation effect of water droplets presence on the strength of the passing shock was studied. The analysis of the different attenuation mechanisms was performed and estimation of the effect of spray parameters such as droplet size and spray density on the shock wave was carried out. For the quantitative evaluation of the attenuation potential a numerical model for the COM3D combustion code was developed. The novel model for the droplet behavior accounting for the realistic correlations for the fluid (water) particle drag force linked with the corresponding droplet breakup model describing droplet atomization is presented. The model was validated against literature experimental data and was used for the blind simulations of the hydrogen test facility in KIT.
Hydrogen Sensing Properties of UV Enhanced Pd-SnO2 Nano-Spherical Composites at Low Temperature
Sep 2021
Publication
Metal oxide semiconductor (MOS) is promising in developing hydrogen detectors. However typical MOS materials usually work between 200-500°C which not only restricts their application in flammable and explosive gases detection but also weakens sensor stability and causes high power consumption. This paper studies the sensing properties of UV enhanced Pd-SnO2 nano-spherical composites at 80-360 ℃. In the experiment Pd of different molar ratios (0.5 2.5 5.0 10.0) was doped into uniform spherical SnO2 nanoparticles by a hydrothermal synthesis method. A xenon lamp with a filter was used as the ultraviolet excitation light source to examine the response of the spherical Pd- SnO2 nanocomposite to 50-1000 ppm H2 gas. The influence of different intensities of ultraviolet light on the gas-sensing properties of composite materials compared with dark condition was analyzed. The experiments show that the conductivity of the composites can be greatly stabilized and the thermal excitation temperature can be reduced to 180 ℃ under the effect of UV enhancement. A rapid response (4.4/ 17.4 s) to 200 ppm of H2 at 330 °C can be achieved by the Pd-SnO2 nanocomposites with UV assistance. The mechanism may be attributed to light motivated electron-hole pairs due to built-in electric fields under UV light illumination which can be captured by target gases and lead to UV controlled gas sensing performance. Catalytic active sites of hydrogen are provided on the surface of the mixed material by Pd. The results in this study can be helpful in reducing the response temperature of MOS materials and improving the performance of hydrogen detectors."
Spontaneous Ignition of Cryo-Compressed Hydrogen in a T-Shaped Channel System
Aug 2022
Publication
Sudden releases of pressurised hydrogen may spontaneously ignite by the so-called “diffusion ignition” mechanism. Several experimental and numerical studies have been performed on spontaneous ignition for compressed hydrogen at ambient temperature. However there is no knowledge of the phenomenon for compressed hydrogen at cryogenic temperatures. The study aims to close this knowledge gap by performing numerical experiments using a computational fluid dynamics model validated previously against experiments at atmospheric temperatures to assess the effect of temperature decrease from ambient 300 K to cryogenic 80 K. The ignition dynamics is analysed for a T-shaped channel system. The cryo-compressed hydrogen is initially separated from the air in the T-shaped channel system by a burst disk (diaphragm). The inertia of the burst disk is accounted for in the simulations. The numerical experiments were carried out to determine the hydrogen storage pressure limit leading to spontaneous ignition in the configuration under investigation. It is found that the pressure limit for spontaneous ignition of the cryo-compressed hydrogen at temperature 80 K is 9.4 MPa. This is more than 3 times larger than pressure limit for spontaneous ignition of 2.9 MPa in the same setup at ambient temperature of 300 K.
Why Ultrasonic Gas Leak Detection?
Sep 2021
Publication
Technologies that have traditionally been used in fixed installations to detect hydrogen gas leaks such as Catalytic and Electrochemical Point Sensors have one limitation: in order for a leak to be detected the gas itself must either be in close proximity to the detector or within a pre-defined area. Unfortunately outdoor environmental conditions such as changing wind directions and quick dispersion of the gas cloud from a leaking outdoor installation often cause that traditional gas detection systems may not alert to the presence of gas simply because the gas never reaches the detector. These traditional gas detection systems need to wait for the gas to form a vapor cloud which may or may not ignite and which may or may not allow loss prevention by enabling shutting down the gas facility in time. Ultrasonic Gas Leak Detectors (UGLD) respond at the speed of sound at gas leak initiation unaffected by changing wind directions and dilution of the gas. Ultrasonic Gas Leak Detectors are based on robust microphone technology; they detect outdoor leaks by sensing the distinct high frequency ultrasound emitted by all high pressure gas leaks. With the ultrasonic sensing technology leaking gas itself does not have to reach the sensor – just the sound of the gas leaking. By adding Ultrasonic Gas Leak Detectors for Hydrogen leak detection faster response times and lower operation costs can be obtained.
Simulation of a Hydrogen-Air Diffusion Flame under Consideration of Component-Specific Diffusivities
Mar 2022
Publication
This work deals with the numerical investigation of a three-dimensional laminar hydrogenair diffusion flame in which a cylindrical fuel jet is surrounded by in-flowing air. To calculate the distribution of gas molecules the model solves the species conservation equation for N-1 components using infinity fast chemistry and irreversible chemical reaction. The consideration of the component-specific diffusion has a strong influence on the position of the high-temperature zone as well as on the concentration distribution of the individual gas molecules. The calculations of the developed model predict the radial and axial species and temperature distribution in the combustion chamber comparable to those from previous publications. Deviations due to a changed burner geometry and air supply narrow the flame structure by up to 50% and the high-temperature zones merge toward the central axis. Due to the reduced inflow velocity of the hydrogen the high-temperature zones develop closer to the nozzle inlet of the combustion chamber. As the power increases the length of the cold hydrogen jet increases. Furthermore the results show that the axial profiles of temperature and mass fractions scale quantitatively with the power input by the fuel.
The Evolution and Structure of Ignited High-pressure Cryogenic Hydrogen Jets
Jun 2022
Publication
The anticipated upscaling of hydrogen energy applications will involve the storage and transport of hydrogen at cryogenic conditions. Understanding the potential hazard arising from leaks in high-pressure cryogenic storage is needed to improve hydrogen safety. The manuscript reports a series of numerical simulations with detailed chemistry for the transient evolution of ignited high-pressure cryogenic hydrogen jets. The study aims to gain insight of the ignition processes flame structures and dynamics associated with the transient flame evolution. Numerical simulations were firstly conducted for an unignited jet released under the same cryogenic temperature of 80 K and pressure of 200 bar as the considered ignited jets. The predicted hydrogen concentrations were found to be in good agreement with the experimental measurements. The results informed the subsequent simulations of the ignited jets involving four different ignition locations. The predicted time series snapshots of temperature hydrogen mass fraction and the flame index are analyzed to study the transient evolution and structure of the flame. The results show that a diffusion combustion layer is developed along the outer boundary of the jet and a side diffusion flame is formed for the near-field ignition. For the far-field ignition an envelope flame is observed. The flame structure contains a diffusion flame on the outer edge and a premixed flame inside the jet. Due to the complex interactions between turbulence fuel-air mixing at cryogenic temperature and chemical reactions localized spontaneous ignition and transient flame extinguishment are observed. The predictions also captured the experimentally observed deflagration waves in the far-field ignited jets.
Hydrogen Stratification in Enclosures in Dependence of the Gas Release Momentum
Sep 2021
Publication
The hydrogen dispersion phenomenon in an enclosure depends on the ratio of the gas buoyancy induced momentum. Random diffusive motions of individual gas particles become dominative when the release momentum is low. Then a uniform hydrogen concentration appears in the enclosure instead of the gas stratification below the ceiling. The paper justifies this hypothesis by demonstrating fullscale experimental results of hydrogen dispersion within a confined space under six different release variations. During the experiments hydrogen was released into the test room of 60 m3 volume in two methods: through a nozzle and through 21 points evenly distributed on the emission box cover (multipoint release). Each release method was tested with three different hydrogen volume flow rates (3.17·10−3 m3/s 1.63·10−3 m3/s 3.34·10−4 m3/s). The tests confirm the increase of hydrogen convective upward flow and its stratification tendency relative to increased volume flow. A tendency of more uniform hydrogen cloud distribution when Mach Reynolds and Froud number values decreased was demonstrated. Because the hydrogen dispersion phenomena impact fire and explosive hazards the presented experimental results could help fire protection systems be in an enclosure designed allowing their effectiveness optimization.
Quantitative Risk Assessment Methodology for Hydrogen Tank Rupture in a Tunnel Fire
Dec 2022
Publication
This study presents a methodology of a quantitative risk assessment for the scenario of an onboard hydrogen storage tank rupture and tunnel fire incident. The application of the methodology is demonstrated on a road tunnel. The consequence analysis is carried out for the rupture of a 70 MPa 62.4-litre hydrogen storage tank in a fire that has a thermally activated pressure relief device (TPRD) failed or blocked during an incident. Scenarios with two states of charge (SoC) of the tank i.e. SoC = 99% and SoC = 59% are investigated. The risks in terms of fatalities per vehicle per year and the cost per incident are assessed. It is found that for the reduction in the risk with the hydrogen-powered vehicle in a road tunnel fire incident to the acceptable level of 10−5 fatality/vehicle/year the fireresistance rating (FRR) of the hydrogen storage tank should exceed 84 min. The FRR increase to this level reduces the societal risk to an acceptable level. The increase in the FRR to 91 min reduces the risk in terms of the cost of the incident to GBP 300 following the threshold cost of minor injury published by the UK Health and Safety Executive. The Frequency–Number (F–N) of the fatalities curve is developed to demonstrate the effect of mitigation measures on the risk reduction to socially acceptable levels. The performed sensitivity study confirms that with the broad range of input parameters including the fire brigade response time the risk of rupture of standard hydrogen tank-TPRD systems inside the road tunnel is unacceptable. One of the solutions enabling an inherently safer use of hydrogen-powered vehicles in tunnels is the implementation of breakthrough safety technology—the explosion free in a fire self-venting (TPRD-less) tanks.
Hydrogen Safety Challenges: A Comprehensive Review on Production, Storage, Transport, Utilization, and CFD-Based Consequence and Risk Assessment
Mar 2024
Publication
This review examines the central role of hydrogen particularly green hydrogen from renewable sources in the global search for energy solutions that are sustainable and safe by design. Using the hydrogen square safety measures across the hydrogen value chain—production storage transport and utilisation—are discussed thereby highlighting the need for a balanced approach to ensure a sustainable and efficient hydrogen economy. The review also underlines the challenges in safety assessments points to past incidents and argues for a comprehensive risk assessment that uses empirical modelling simulation-based computational fluid dynamics (CFDs) for hydrogen dispersion and quantitative risk assessments. It also highlights the activities carried out by our research group SaRAH (Safety Risk Analysis and Hydrogen) relative to a more rigorous risk assessment of hydrogenrelated systems through the use of a combined approach of CFD simulations and the appropriate risk assessment tools. Our research activities are currently focused on underground hydrogen storage and hydrogen transport as hythane.
Tactical Depressurization of Hydrogen and CNG Tanks Using Rifles and Other Projectiles
Sep 2021
Publication
After a tank has been exposed to crash violence or an external fire it might in some situations be judged dangerous to move the vessel due to the risk of a sudden tank rupture. Therefore Swedish rescue services have a long history of using rifles to penetrate and therefore depressurize the vessels. In this paper some first steps on providing guidance on the selection of ammunition and required stand back distance are presented. The results indicate that a stand back distance on the order of 100 m is required and that the standard 7.62 Ball should only be used for composite CNG-tanks while stronger ammunitions are needed for steel and composite hydrogen tanks. However more research is required to provide a more solid scientific underpinning of the tactic guidance.
A CFD Analysis of Liquefied Gas Vessel Explosions
Dec 2021
Publication
Hydrogen is one of the most suitable candidates in replacing fossil fuels. However storage issues due to its very low density under ambient conditions are encountered in many applications. The liquefaction process can overcome such issues by increasing hydrogen’s density and thus enhancing its storage capacity. A boiling liquid expanding vapour explosion (BLEVE) is a phenomenon in liquefied gas storage systems. It is a physical explosion that might occur after the catastrophic rupture of a vessel containing a liquid with a temperature above its boiling point at atmospheric pressure. Even though it is an atypical accident scenario (low probability) it should be always considered due to its high yield consequences. For all the above-mentioned reasons the BLEVE phenomenon for liquid hydrogen (LH2) vessels was studied using the CFD methodology. Firstly the CFD model was validated against a well-documented CO2 BLEVE experiment. Secondly hydrogen BLEVE cases were simulated based on tests that were conducted in the 1990s on LH2 tanks designed for automotive purposes. The parametric CFD analysis examined different filling degrees initial pressures and temperatures of the tank content with the aim of comprehending to what extent the initial conditions influence the blast wave. Good agreement was shown between the simulation outcomes and the LH2 bursting scenario tests results.
Controlling the Pressure of Hydrogen-natural Gas Mixture in an Inclined Pipeline
Feb 2020
Publication
This paper discusses the optimal control of pressure using the zero-gradient control (ZGC) approach. It is applied for the first time in the study to control the optimal pressure of hydrogen natural gas mixture in an inclined pipeline. The solution to the flow problem is first validated with existing results using the Taylor series approximation regression analysis and the Runge-Kutta method combined. The optimal pressure is then determined using ZGC where the optimal set points are calculated without having to solve the non-linear system of equations associated with the standard optimization problem. It is shown that the mass ratio is the more effective parameter compared to the initial pressure in controlling the maximum variation of pressure in a gas pipeline.
A Comparative Study of CFD-Modelling for Lean Premixed Hydrogen Deflagrations in Large-scale Vented Vessels
Sep 2021
Publication
Hydrogen combustion inside a post-accident nuclear reactor containment may pose a challenge to the containment integrity which could alter the fission-product release source term to the public. Combustion-generated overpressures may be relieved by venting to adjacent compartments through relief panels or existing openings. Thus an improved understanding of the propagation of lean hydrogen deflagrations in inter-connected compartments is essential for the development of appropriate management strategies. GOTHIC is a general purpose lumped parameter thermal-hydraulic code for solving multi-phase compressible flows which is accepted as an industry-standard code for containment safety analyses. Following the Fukushima accident the application of three-dimensional computational fluid dynamics methods to high-fidelity detailed analysis of hydrogen combustion processes has become more widespread. In this study a recently developed large-eddy-simulation (LES) capability is applied to the prediction of lean premixed hydrogen deflagrations in large-scale vented vessels of various configurations. The LES predictions are compared with GOTHIC predictions and experimental data obtained from the large-scale vented combustion test facility at the Canadian Nuclear Laboratories. The LES methodology makes use of a flamelet- or a progress-variable-based combustion model. An empirical burning velocity model is combined with an advanced finite-volume framework and a mesh-independent subfilter-scale model. Descriptions of the LES and GOTHIC modelling approaches used to simulate the hydrogen reactive flows in the vented vessels along with the experimental data sets are given. The potential and limitations of the lumped parameter and LES approaches for accurately describing lean premixed hydrogen deflagrations in vented vessels are discussed.
Worst Case Scenario for Delayed Explosion of Hydrogen Jets at a High Pressure: Ignition Position
Sep 2021
Publication
Delayed explosion of free field hydrogen releases at a high pressure is subject of multiple investigation performed by various authors in the past years. These studied considered various parameters such as pressures flow rates etc. and their influence on the resulting overpressure. However the influence of the ignition position on the maximum overpressure was not fully explored. Current investigation addressed by computational fluid dynamics (CFD) simulations and experimental measurement fills this gap. This work demonstrates that the ignition positions corresponding to 55%-65% of H2/air mixture give the maximum overpressure. This observation initially observed numerically and afterword confirmed experimentally. A simple model is also suggested.
Studies on the Impact of Hydrogen on the Results of THT Measurement Devices
Dec 2021
Publication
An essential prerequisite for safe transport and use of natural gas is their appropriate odorization. This enables the detection of uncontrolled gas leaks. Proper and systematic odorization inspection ensures both safe use of gas and continuity of the process itself. In practice it is conducted through among others measuring odorant concentrations in gas. Control devices for rapid gas odorization measurements that are currently used on a large scale in the gas industry are equipped with electrochemical detectors selective for sulfur compounds like tetrahydrothiophene (THT). Because the selectivity of electrochemical detector response to one compound (e.g. THT) the available declarations of manufacturers show that detector sensitivity (indirectly also the quality of the measurement result) is influenced by the presence of increased e.g. sulfur or hydrogen compound content in the gas. Because of the lack of sufficient source literature data in this field it was necessary to experimentally verify this impact. The results of studies on experimental verification of suspected influence of increased amounts of hydrogen in gas on the response of electrochemical detector was carried out at the Oil and Gas Institute—National Research Institute (INiG—PIB). They are presented in this article. The data gathered in the course of researching the dependence between THT concentration measurement result quality and hydrogen content in gas composition enabled a preliminary assessment of the threat to the safety of end users of gaseous fuels caused by the introduction of this gas into the distribution network. Noticing the scope of necessary changes in the area of odorization is necessary to guarantee this safety.
Nanotechnology Enabled Hydrogen Gas Sensing
Sep 2019
Publication
An important contribution to industry standards and to effective installation of hybrid renewable energy systems is evaluation of hydrogen (H2) monitoring techniques under pilot-scale and/or real-world conditions. We have designed a hybrid system to integrate solar power electrolysis and hydrogen fuel cell components in a DC micro-grid with capacity to evaluate novel nanomaterials for enhanced H2 gas sensing performance. In general enhanced hydrogen sensing performance is evaluated by high sensitivity selectivity and stability as well as low power consumption. Unique properties such as high surface area to volume ratio a large number of surface active sites high specific surface area and reactivity are key attributes of nanomaterials used for gas sensing. These attributes enable sensors to be embedded in Internet-of-Things applications or in mobile systems. With rapid development of hydrogen-based technologies for clean energy applications there remains a requirement for faster accurate and selective H2 sensors with low cost and low power consumption. Operating principles for these sensors include catalytic thermal conductivity electrochemical resistance based optical and acoustic methods. In this paper we review performance of H2 gas sensors based on conductometric devices operating at room temperature up to 200 °C. The focus of this work includes nanostructured metal oxides graphene materials and transition metal dichalcogenides employed as sensing materials.
Modelling of Ventilated Hydrogen Dispersion in Presence of Co-flow and Counter-flow
Sep 2021
Publication
In the framework of the EU-funded project HyTunnel-CS an inter-comparison among partners CFD simulations has been carried out. The simulations are based on experiments conducted within the project by Pro-Science and involve hydrogen release inside a safety vessel testing different ventilation configurations. The different ventilation configurations that were tested are co-flow counter-flow and cross-flow. In the current study co-flow and counter-flow tests along with the no ventilation test (m' = S g/s d = 4 mm ) are simulated with the aim to validate available and well-known CFD codes against such applications and to provide recommendations on modeling strategies. Special focus is given on modeling the velocity field produced by the fan during the experiments. The computational results are compared with the experimental results and a discussion follows regarding the efficiency of each ventilation configuration.
On the Evaluation of ALD TiO 2 , ZrO 2 and HfO 2 Coatings on Corrosion and Cytotoxicity Performances
May 2021
Publication
Magnesium alloys have been widely studied as materials for temporary implants but their use has been limited by their corrosion rate. Recently coatings have been proven to provide an effective barrier. Though only little explored in the field Atomic Layer Deposition (ALD) stands out as a coating technology due to the outstanding film conformality and density achievable. Here we provide first insights into the corrosion behavior and the induced biological response of 100 nm thick ALD TiO2 HfO2 and ZrO2 coatings on AZ31 alloy by means of potentiodynamic polarization curves electrochemical impedance spectroscopy (EIS) hydrogen evolution and MTS colorimetric assay with L929 cells. All three coatings improve the corrosion behavior and cytotoxicity of the alloy. Particularly HfO2 coatings were characterized by the highest corrosion resistance and cell viability slightly higher than those of ZrO2 coatings. TiO2 was characterized by the lowest corrosion improvements and though generally considered a biocompatible coating was found to not meet the demands for cellular applications (it was characterized by grade 3 cytotoxicity after 5 days of culture). These results reveal a strong link between biocompatibility and corrosion resistance and entail the need of taking the latter into consideration in the choice of a biocompatible coating to protect degradable Mg-based alloys.
Australians’ Considerations for Use of Hydrogen in the Transport Sector
Sep 2019
Publication
Hydrogen fuel cells power a range of vehicles including cars buses trucks forklifts and even trains. As fuel cell electric vehicles emit no carbon emissions and only produce water vapor as a by-product they present an attractive option for countries who are experiencing high pollution from transport. This paper presents the findings of ten focus groups and a subset of a national survey which focused specifically on use of hydrogen in the transport sector (N=948). When discussing hydrogen transport options Australian focus group participants felt that rolling out hydrogen fuel cell buses as a first step for fuel cell electric vehicle deployment would be a good way to increase familiarity with the technology. Deploying hydrogen public transport vehicles before personal vehicles was thought to be a positive way to demonstrate the safe use of hydrogen and build confidence in the technology. At the same time it was felt it would allow any issues to be ironed out before the roll out of large-scale infrastructure on a to support domestic use. Long haul trucks were also perceived to be a good idea however safety issues were raised in the focus groups when discussing these vehicles. Survey respondents also expressed positive support for the use of hydrogen fuel cell buses and long-haul trucks. They reported being happy to be a passenger in a fuel cell bus. Safety and environmental benefits remained paramount with cost considerations being the third most important issue. Respondents supportive of hydrogen technologies were most likely to report purchasing a hydrogen vehicle over other options
The Challenges of Hydrogen Storage on a Large Scale
Sep 2021
Publication
With the growing success of green hydrogen the general trend is for increased hydrogen production and large quantities of storage. Engie’s projects have grown from a few kilos of hydrogen to the quest for large scale production and associated storage – e.g. several tons or tens of tons. Although a positive sign for Engie’s projects it does inevitably result in challenges in new storage methods and in risks management related to such facilities; particularly with hydrogen facilities being increasingly placed in the vicinity of general public sites. For example a leak on hydrogen storage can generate significant thermal and overpressure effects on surrounding people/facilities in the event of ignition. Firewalls can be installed to protect individuals / infrastructure from thermal effects but the adverse result is that this solution can increase the violence of an explosion in case of delayed ignition or confinement. The manner of emergency intervention on a pool fire of hydrogen is also totally different from intervention on compressed gaseous hydrogen. The first part of this presentation will explain different means to store hydrogen in large quantities. The second part will present for each storage the specific risks generated. The third and final part will explain how these risks can be addressed on a technical point of view by safety devices or by other solutions (separation distance passive/active means …).
A Flammability Limit Model for Hydrogen-air-diluent Mixtures Based on Heat Transfer Characteristics in Flame Propagation
May 2019
Publication
Predicting lower flammability limits (LFL) of hydrogen has become an ever-important task for safety of nuclear industry. While numerous experimental studies have been conducted LFL results applicable for the harsh environment are still lack of information. Our aim is to develop a calculated non-adiabatic flame temperature (CNAFT) model to better predict LFL of hydrogen mixtures in nuclear power plant. The developed model is unique for incorporating radiative heat loss during flame propagation using the CNAFT coefficient derived through previous studies of flame propagation. Our new model is more consistent with the experimental results for various mixtures compared to the previous model which relied on calculated adiabatic flame temperature (CAFT) to predict the LFL without any consideration of heat loss. Limitation of the previous model could be explained clearly based on the CNAFT coefficient magnitude. The prediction accuracy for hydrogen mixtures at elevated initial temperatures and high helium content was improved substantially. The model reliability was confirmed for H2-air mixtures up to 300 C and H2-air-He mixtures up to 50 vol % helium concentration. Therefore the CNAFT model developed based on radiation heat loss is expected as the practical method for predicting LFL in hydrogen risk analysis.
CFD Simulations of Large Scale LH2 Dispersion in Open Environment
Sep 2021
Publication
An inter-comparison among partners’ CFD simulations has been carried out within the EU-funded project PRESLHY to investigate the dispersion of the mixture cloud formed from large scale liquid hydrogen release. Rainout experiments performed by Health and Safety Executive (HSE) have been chosen for the work. From the HSE experimental series trial-11 was selected forsimulation due to its conditions where only liquid flow at the nozzle was achieved. During trial-11 liquid hydrogen is spilled horizontally 0.5 m above a concrete pad from a 5 barg tank pressure through a 12 mm (1/2 inch) nozzle. The dispersion takes place outdoors and thus it is imposed to variant wind conditions. Comparison of the CFD results with the measurements at several sensors is presented and useful conclusions are drawn.
Flammability Reduction in a Pressurised Water Electrolyser Based on a Thin Polymer Electrolyte Membrane through a Pt-alloy Catalytic Approach
Jan 2019
Publication
Various Pt-based materials (unsupported Pt PtRu PtCo) were investigated as catalysts for recombining hydrogen and oxygen back into water. The recombination performance correlated well with the surface Pt metallic state. Alloying cobalt to platinum was observed to produce an electron transfer favouring the occurrence of a large fraction of the Pt metallic state on the catalyst surface. Unsupported PtCo showed both excellent recombination performance and dynamic behaviour. In a packed bed catalytic reactor when hydrogen was fed at 4% vol. in the oxygen stream (flammability limit) 99.5% of the total H2 content was immediately converted to water in the presence of PtCo thus avoiding safety issues. The PtCo catalyst was thus integrated in the anode of the membrane-electrode assembly of a polymer electrolyte membrane electrolysis cell. This catalyst showed good capability to reduce the concentration of hydrogen in the oxygen stream under differential pressure operation (1–20 bar) in the presence of a thin (90 μm) Aquivion® membrane. The modified system showed lower hydrogen concentration in the oxygen flow than electrolysis cells based on state-of-the-art thick polymer electrolyte membranes and allowed to expand the minimum current density load down to 0.15 A cm−2 . This was mainly due to the electrochemical oxidation of permeated H2 to protons that were transported back to the cathode. The electrolysis cell equipped with a dual layer PtCo/IrRuOx oxidation catalyst achieved a high operating current density (3 A cm−2 ) as requested to decrease the system capital costs under high efficiency conditions (about 77% efficiency at 55 °C and 20 bar). Moreover the electrolysis system showed reduced probability to reach the flammability limit under both high differential pressure (20 bar) and partial load operation (5%) as needed to properly address grid-balancing service
Large-eddy Simulation of Tri-fuel Combustion: Diesel Spray Assisted Ignition of Methanol-hydrogen Blends
May 2021
Publication
Development of marine engines could largely benefit from the broader usage of methanol and hydrogen which are both potential energy carriers. Here numerical results are presented on tri-fuel (TF) ignition using large-eddy simulation (LES) and finite-rate chemistry. Zero-dimensional (0D) and three-dimensional (3D) simulations for n-dodecane spray ignition of methanol/hydrogen blends are performed. 0D results reveal the beneficial role of hydrogen addition in facilitating methanol ignition. Based on LES the following findings are reported: 1) Hydrogen promotes TF ignition significantly for molar blending ratios βX = [H2]/([H2]+[CH3OH]) ≥0.8. 2) For βX = 0 unfavorable heat generation in ambient methanol is noted. We provide evidence that excessive hydrogen enrichment (βX ≥ 0.94) potentially avoids this behavior consistent with 0D results. 3) Ignition delay time is advanced by 23–26% with shorter spray vapor penetrations (10–15%) through hydrogen mass blending ratios 0.25/0.5/1.0. 4) Last adding hydrogen increases shares of lower and higher temperature chemistry modes to total heat release.
Combustion Characteristics of Premixed Hydrogen/Air in an Undulate Microchannel
Jan 2022
Publication
This work reports a numerical investigation of microcombustion in an undulate microchannel using premixed hydrogen and air to understand the effect of the burner design on the flame in order to obtain stability of the flame. The simulations were performed for a fixed equivalence ratio and a hyperbolic temperature profile imposed at the microchannel walls in order to mimic the heat external losses occurred in experimental setups. Due to the complexity of the flow dynamics combined with the combustion behavior the present study focuses on understanding the effect of the fuel inlet rate on the flame characteristics keeping other parameters constant. The results presented stable flame structure regardless of the inlet velocity for this type of design meaning that a significant reduction in the heat flux losses through the walls occurred allowing the design of new simpler systems. The increase in inlet velocity increased the flame extension with the flame being stretched along the microchannel. For higher velocities flame separation was observed with two detected different combustion zones and the temperature profiles along the burner centerline presented a non-monotonic decrease due to the dynamics of the vortices observed in the convex regions of the undulated geometry walls. The geometry effects on the flame structure flow field thermal evolution and species distribution for different inlet velocities are reported and discussed.
Hydrogen Jet Structure in Presence of Forced Co-, Counter- and Cross-flow Ventilation
Sep 2021
Publication
This paper presents results of experimental investigations on unignited horizontal hydrogen jets in air in presence of co- cross- and counter-flow. Hydrogen concentration distributions are obtained as functions of distance to the hydrogen release nozzle. The H2-jet variables are two nozzle diameters 1 mm and 4 mm and two H2-jet mass flow rates 1 g/s up to 5 g/s. A propeller fan is used to provide forced ventilation compared to the case with no ventilation three different airflow velocities up to 5 m/s were studied systematically. It was found that any forced ventilation in co- cross- and counter-flow direction reduces the size of the burnable mixture cloud of the H2-jet compared to a free jet in quiescent air.
CFD Model Based Ann Prediction of Flammable Vapor Colour Formed by Liquid Hydrogen Spill
Sep 2021
Publication
Unintended releases can occur during the production storage transportation and filling of liquid hydrogen which may cause devastating consequences. In the present work liquid hydrogen leak is modeled in ANSYS Fluent with the numerical model validated using the liquid hydrogen spill test data. A three-layer artificial neural network (ANN) model is built in which the wind speed ground temperature leakage time and leakage rate are taken as the inputs the horizontal diffusion distance and vertical diffusion distance of combustible gas as the outputs of the ANN. The representative sample data derived from the detailed calculation results of the numerical model are selected via the orthogonal experiment method to train and verify the back propagation (BP) neural network. Comparing the calculation results of the formula fitting with the sample data the results show that the established ANN model can quickly and accurately predict the horizontal and vertical diffusion distance of flammable vapor cloud relatively. The influences of four parameters on the horizontal hazard distance as well as vertical hazard height are predicted and analyzed in the case of continuous overflow of liquid hydrogen using the ANN model.
Hydrogen Dispersion and Ventilation Effects in Enclosures under Different Release Conditions
Apr 2021
Publication
Hydrogen is an explosive gas which could create extremely hazardous conditions when released into an enclosure. Full-scale experiments of hydrogen release and dispersion in the confined space were conducted. The experiments were performed for hydrogen release outflow of 63 × 10−3 m3/s through a single nozzle and multi-point release way optionally. It was found that the hydrogen dispersion in an enclosure strongly depends on the gas release way. Significantly higher hydrogen stratification is observed in a single nozzle release than in the case of the multi-point release when the gas concentration becomes more uniform in the entire enclosure volume. The experimental results were confirmed on the basis of Froud number analysis. The CFD simulations realized with the FDS code by NIST allowed visualization of the experimental hydrogen dispersion phenomenon and confirmed that the varied distribution of hydrogen did not affect the effectiveness of the accidental mechanical ventilation system applied in the tested room.
Experimental Study of the Explosion Severity of Vented Methane/Hydrogen Deflagrations
Sep 2021
Publication
Adding hydrogen to mains natural gas has been identified as one of the main strategies to reduce CO2 emissions in the United Kingdom. This work aims to characterise the explosion severity of 80:20 v./v. methane/hydrogen blends (‘a blend’) and methane vented deflagrations. The explosion severity of homogenous mixtures was measured in a 15 m3 cubic steel chamber in which the relief area was provided by four windows and a door covered with polypropylene sheet. The pressure increase over time was characterised using piezo-resistive pressure transducers and the flame speed was estimated using ionisation probes installed in the walls of the enclosure. The explosion severity of both mixtures was determined for different equivalence ratios from lean to rich mixtures. The pressure over time presented very similar behaviour for both mixtures comprising multiple peaks divided into three main stages: a first stage related to a spherical confined explosion until the opening of the vent a second stage generated by increased combustion during venting and an oscillatory peak generated by acoustic disturbances with the enclosure. A slight increase in the first stage overpressure was observed for the blend in comparison with methane regardless of the equivalence ratio but no general trend in pressure was observed for other stages of the propagation. The effect of the blockage ratio on explosion severity was studied by adding metallic elements representing furniture in a room.
Behavior of Barrier Wall under Hydrogen Storage Tank Explosion with Simulation and TNT Equivalent Weight Method
Mar 2023
Publication
Hydrogen gas storage place has been increasing daily because of its consumption. Hydrogen gas is a dream fuel of the future with many social economic and environmental benefits to its credit. However many hydrogen storage tanks exploded accidentally and significantly lost the economy infrastructure and living beings. In this study a protection wall under a worst-case scenario explosion of a hydrogen gas tank was analyzed with commercial software LS-DYNA. TNT equivalent method was used to calculate the weight of TNT for Hydrogen. Reinforced concrete and composite protection wall under TNT explosion was analyzed with a different distance of TNT. The initial dimension of the reinforced concrete protection wall was taken from the Korea gas safety code book (KGS FP217) and studied the various condition. H-beam was used to make the composite protection wall. Arbitrary-Lagrangian-Eulerian (ALE) simulation from LS-DYNA and ConWep pressure had a good agreement. Used of the composite structure had a minimum displacement than a normal reinforced concrete protection wall. During the worst-case scenario explosion of a hydrogen gas 300 kg storage tank the minimum distance between the hydrogen gas tank storage and protection wall should be 3.6 m.
Spherically Expanding Flame Simulations in Cantera Using a Lagrangian Formulation
Sep 2021
Publication
A Lagrangian-based one-dimensional approach has been developed using Cantera to study the dynamics of spherically expanding flames. The detailed reaction model USC-Mech II has been employed to examine flame propagating in hydrogen-air mixtures. In the first part our approach has been validated against laminar flame speed and Markstein number data from the literature. It was shown that the laminar flame speed was predicted within 5% on average but that discrepancies were observed for the Markstein number especially for rich mixtures. In the second part a detailed analysis of the thermo-chemical dynamics along the path of Lagrangian particles propagating in stretched flames was performed. For mixtures with negative Markstein lengths it was found that at high stretch rates the mixture entering the reaction-dominated period is less lean with respect to the initial mixture than at low stretch rate. This induces a faster rate of chemical heat release and of active radical production which results in a higher flame propagation speed. Opposite effects were observed for mixtures with positive Markstein lengths for which slower flame propagation was observed at high stretch rates compared to low stretch rates."
H-Mat Hydrogen Compatibility of NBR Elastomers
Sep 2021
Publication
The H2@Scale program of the U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office (HFTO) is supporting work on the hydrogen compatibility of polymers to improve the durability and reliability of materials for hydrogen infrastructure. The hydrogen compatibility program (H-Mat) seeks “to address the challenges of hydrogen degradation by elucidating the mechanisms of hydrogen-materials interactions with the goal of providing science-based strategies to design materials (micro)structures and morphology with improved resistance to hydrogen degradation.” Previous work on ethylene propylene diene indicated hydrogen interaction with plasticizer increased its migration to the surface and coalescing within the elastomer compound. New research on nitrile butadiene (NBR) has found hydrogen and pressure interactions with a series model rubber-material compounds to behave similarly in some compounds and improved in other compounds that is demonstrated through volume change and compression-set differences in the materials. Further studies were conducted using a helium-ion microscope (HeIM) which revealed significant morphological changes in the plasticizer-incorporating compounds after static exposure and pressure cycling as evidenced by time-of-flight secondary ion mass spectrometry. Additional studies using x-ray chromatography revealed that more micro-voids/-cracks developed after gas decompression in unfilled materials than in filled materials; transmission electron microscopy (TEM) probed at the nano-meter level showing change in filler distribution and morphology around Zinc-based particles.
Computational Fluid Dynamics Simulations of Hydrogen Releases and Vented Deflagrations in Large Enclosures
Nov 2019
Publication
This paper presents model predictions obtained with the CFD tool FLACS for hydrogen releases and vented deflagrations in containers and larger enclosures. The paper consists of two parts. The first part compares experimental results and model predictions for two test cases: experiments performed by Gexcon in 20-foot ISO containers (volume 33 m3 ) as part of the HySEA project and experiments conducted by SRI International and Sandia National Laboratories in a scaled warehouse geometry (volume 45.4 m3 ). The second part explores the use of the model system validated in the first part to accidental releases of hydrogen from forklift trucks inside a full-scale warehouse geometry (32 400 m3 ). The results demonstrate the importance of using realistic and reasonably accurate geometry models of the systems under consideration when performing CFD-based risk assessment studies. The discussion highlights the significant inherent uncertainty associated with quantitative risk assessments for vented hydrogen deflagrations in complex geometries. The suggestions for further work include a pragmatic approach for developing empirical correlations for pressure loads from vented hydrogen deflagrations in industrial warehouses with hydrogen-powered forklift trucks.
Knowledge and Technology Transfer via Publications, Patents, Standards: Exploring the Hydrogen Technological Innovation System
Nov 2022
Publication
Clean technologies play a crucial role in reducing greenhouse gas emissions and protecting the climate. Hydrogen is a promising energy carrier and fuel that can be used in many applications. We explore the global hydrogen technological innovation system (TIS) by analyzing the three knowledge and technology transfer channels of publications patents and standards. Since the adoption of hydrogen technologies requires trust in their safety this study specifically also focuses on hydrogen safety. Our results show that general and hydrogen safety research has increased significantly while patenting experienced stagnation. An analysis of the non-patent literature in safety patents shows little recognition of scientific publications. Similarly publications are under-represented in the analyzed 75 international hydrogen and fuel cell standards. This limited transfer of knowledge from published research to standards points to the necessity for greater involvement of researchers in standardization. We further derive implications for the hydrogen TIS and recommendations for a better and more impactful alignment of the three transfer channels.
Risk Assessment of a Hydrogen Refueling Station in an Urban Area
May 2023
Publication
After the Paris Agreement was signed in 2015 many countries worldwide focused on the hydrogen economy aiming for eco-friendly and renewable energy by moving away from the existing carbon economy which has been the primary source of global warming. Hydrogen is the most common element on Earth. As a light substance hydrogen can diffuse quickly; however it also has a small risk of explosion. Representative explosion accidents have included the Muskingum River Power Plant Vapor Cloud Explosion accident in 2007 and the Silver Eagle Refinery Vapor Cloud Explosion accident in 2009. In addition there was an explosion in a hydrogen tank in Gangneung Korea in May 2019 and a hydrogen refueling station (HRS) in Norway exploded in 2018. Despite this risk Korea is promoting the establishment of HRSs in major urban centers including downtown areas and public buildings by using the Regulatory Sandbox to install HRSs. This paper employed the Hydrogen Risk Assessment Model (HyRAM) of Sandia National Laboratories (SNL) a quantitative risk assessment (QRA) program specialized in hydrogen energy for HRSs installed in major urban hubs. A feasibility evaluation of the site conditions of an HRS was conducted using the French land use planning method based on the results obtained through evaluation using the HyRAM and the overpressure results of PHAST 8.0. After a risk assessment we confirmed that an HRS would be considered safe even if it was installed in the city center within a radius of influence of jet fires and overpressure.
Numerical Investigation on the Flame Structure and CO/NO Formations of the Laminar Premixed Biogas–Hydrogen Impinging Flame in the Wall Vicinity
Nov 2021
Publication
The near-wall flame structure and pollutant emissions of the laminar premixed biogashydrogen impinging flame were simulated with a detailed chemical mechanism. The spatial distributions of the temperature critical species and pollutant emissions near the wall of the laminar premixed biogas–hydrogen impinging flame were obtained and investigated quantitatively. The results show that the cold wall can influence the premixed combustion process in the flame front which is close to the wall but does not touch the wall and results in the obviously declined concentrations of OH H and O radicals in the premixed combustion zone. After flame quenching a high CO concentration can be observed near the wall at equivalence ratios (ϕ) of both 0.8 and 1.2. Compared with that at ϕ = 1.0 more unburned fuel is allowed to pass through the quenching zone and generate CO after flame quenching near the wall thanks to the suppressed fuel consumption rate near the wall and the excess fuel in the unburned gases at ϕ = 0.8 and 1.2 respectively. By isolating the formation routes of NO production it is found that the fast-rising trend of NO concentration near the wall in the post flame region at ϕ = 0.8 is attributed to the NO transportation from the NNH route primarily while the prompt NO production accounts for more than 90% of NO generation in the wall vicinity at ϕ = 1.2. It is thus known that thanks to the effectively increased surface-to-volume ratio the premixed combustion process in the downsized chamber will be affected more easily by the amplified cooling effects of the cold wall which will contribute to the declined combustion efficiency increased CO emission and improved prompt NO production.
Brief Review on High-Temperature Electrochemical Hydrogen Sensors
Dec 2022
Publication
Hydrogen sensors especially those operating at high temperatures are essential tools for the emerging hydrogen economy. Monitoring hydrogen under process conditions to control the reactions for detecting confined species is crucial to the safe widespread use and public acceptance of hydrogen as fuel. Hydrogen sensors must have a sensitivity ranging from traces of hydrogen (parts per million (ppm)) up to levels near the lower explosive limit (LEL = 4% H2 in the air) for safety reasons. Furthermore they need to operate in cryogenic ambient and high-temperature environments. Herein emphasis is given to hydrogen sensors based on solid oxide electrolytes (operating at high temperatures) in particular oxygen ion and proton conductors. The review is devoted to potentiometric amperometric and combined amperometric-potentiometric hydrogen sensors. Experimental results already reported in the international literature are presented and analyzed to reveal the configuration principle of operation and the applied solid electrolytes and electrodes of the high-temperature hydrogen sensors. Additionally an amperometric sensor able to detect hydrogen and steam in atmospheric air through a two-stage procedure is presented and thoroughly discussed. The discussion reveals that high-temperature hydrogen sensors face different challenges in terms of the electrodes and solid electrolytes to be used depending on the operating principle of each sensor type.
Analysis to Support Revised Distances between Bulk Liquid Hydrogen Systems and Exposures
Sep 2021
Publication
The minimum distances between exposures and bulk liquid hydrogen listed in the National Fire Protection Agency’s Hydrogen Technology Code NFPA 2 are based on historical consensus without a documented scientific analysis. This work follows a similar analysis as the scientific justification provided in NFPA 2 for exposure distances from bulk gaseous hydrogen storage systems but for liquid hydrogen. Validated physical models from Sandia’s HyRAM software are used to calculate distances to a flammable concentration for an unignited release the distance to critical heat flux values and the visible flame length for an ignited release and the overpressure that would occur for a delayed ignition of a liquid hydrogen leak. Revised exposure distances for bulk liquid hydrogen systems are calculated. These distances are related to the maximum allowable working pressure of the tank and the line size as compared to the current exposure distances which are based on system volume. For most systems the exposure distances calculated are smaller than the current distances for Group 1 they are similar for Group 2 while they increase for some Group 3 exposures. These distances could enable smaller footprints for infrastructure that includes bulk liquid hydrogen storage tanks especially when using firewalls to mitigate Group 3 hazards and exposure distances. This analysis is being refined as additional information on leak frequencies is incorporated and changes have been proposed to the 2023 edition of NFPA 2.
The NREL Sensor Laboratory: Status and Future Directions for Hydrogen Detection
Sep 2021
Publication
The NREL Hydrogen Sensor Laboratory was commissioned in 2010 as a resource for the national and international hydrogen community to ensure the availability and proper use of hydrogen sensors. Since then the Sensor Laboratory has provided unbiased verification of hydrogen sensor performance for sensor developers end-users and regulatory agencies and has also provided active support for numerous code and standards development organizations. Although sensor performance assessment remains a core capability the mission of the NREL Sensor Laboratory has expanded toward a more holistic approach regarding the role of hydrogen detection and its implementation strategy for both assurance of facility safety and for process control applications. Active monitoring for detection of unintended releases has been identified as a viable approach for improving facility safety and lowering setbacks. The current research program for the Sensor Laboratory addresses both conventional and advanced developing detection strategies in response to the emerging large-scale hydrogen markets such as those envisioned by H2@Scale. These emerging hydrogen applications may require alternative detection strategies that supplement and may ultimately supplant the use of traditional sensors for monitoring hydrogen releases. Research focus areas for the NREL Sensor Laboratory now encompass the characterization of released hydrogen behavior to optimize detection strategies for both indoor and outdoor applications assess advanced methods of hydrogen leak detection such as hydrogen wide area monitoring for large scale applications implement active monitoring as a risk reduction strategy to improve safety at hydrogen facilities and to provide continuing support of hydrogen safety codes and standards. In addition to assurance of safety detection will be critical for process control applications such as hydrogen fuel quality verification for fuel cell vehicle applications and for monitoring and controlling of hydrogen-natural gas blend composition.
Application of Pipeline QRA Methodologies to Hydrogen Pipelines in Support of the Transition to a Decarbonised Future
Sep 2021
Publication
Hydrogen is expected to play a key role in the decarbonised future of energy. For hydrogen distribution pipelines are seen as the main method for mass transport of hydrogen gas. To support the evaluation of risk related to hydrogen pipelines a revised QRA methodology is presented based on currently available and industry accepted guidance related to natural gas. The QRA approach is primarily taken from HSE UK’s MISHAP methodology [1]. The base methodology is reviewed and modifications suggested to adapt it for use with hydrogen gas transport. Compared to natural gas it was found that the escape distances for hydrogen (based on the degree of heat flux) were lower. However as for the overall risk for both individual and societal the case with hydrogen was more severe close to the pipeline. This was driven by the increased ignition probability of hydrogen. The approach may be used as part of the review and appraisal process of hydrogen projects
Hydrogen Blowdown Release Experiments at Different Temperatures in the Discha-facility
Sep 2021
Publication
In this work experiments on horizontal hydrogen jet releases from a 2.815 dm³ volume tank to the ambience are described. For the main experimental series tank valve and release line were cooled down to a temperature of approx. 80 K in a bath of liquid nitrogen. As a reference similar experiments were also performed with the uncooled tank at ambient temperature. The releases were carried out through four nozzles with different circular orifice diameters from 0.5 to 4 mm and started from initial tank pressures from 0.5 to 20 MPa (rel.). During the releases pressures and temperatures inside the vessel as well as inside the release line were measured. Outside the nozzle further temperature and hydrogen concentration measurements were performed along and besides the jet axis. The electrostatic field builtup in the jet was monitored using two field meters in different distances from the release nozzle and optical observation via photo and video-cameras was performed for the visualization of the H2-jet via the BOS-method. The experiments were performed in the frame of the EU-funded project PRESHLY in which several tests of this program were selected for a comparative computational study the results of which will also be presented at this conference. So on the one hand the paper gives a comprehensive description of the facility on the other hands it also describes the experimental procedure and the main findings.
Shock Tube Experiments on Flame Propagation Regimes and Critical Conditions for Flame Acceleration and Detonation Transition for Hydrogen-air Mixtures at Cryogenic Temperatures
Sep 2021
Publication
A series of more than 100 experiments with hydrogen-air mixtures at cryogenic temperatures have been performed in a shock tube in the frame of the PRESLHY project. A wide range of hydrogen concentrations from 8 to 60%H2 in the shock tube of the length of 5 m and 50 mm id was tested at cryogenic temperatures from 80 to 130K at ambient pressure. Flame propagation regimes were investigated for all hydrogen compositions in the shock tube at three different blockage ratios (BR) 0 0.3 and 0.6 as a function of initial temperature. Pressure sensors and InGaAs-photodiodes have been applied to monitor the flame and shock propagation velocity of the process. The experiments at ambient pressure and temperature were conducted as the reference data for cryogenic experiments. A critical expansion ratio for an effective flame acceleration to the speed of sound was experimentally found at cryogenic temperatures. The detonability criterion for smooth and obstructed channels was used to evaluate the detonation cell sizes at cryogenic temperatures as well. The main peculiarities of cryogenic combustion with respect to the safety assessment were that the maximum combustion pressure was several times higher compared to ambient temperature and the run-up-distance to detonation was several times shorter independent of lower chemical reactivity at cryogenic conditions.
Heat Transfer Models for Refueling Safety of Hydrogen Vehicle
Sep 2021
Publication
Due to the simple structure and quick refueling process of the compressed hydrogen storage tank it is widely used in fuel cell vehicles at present. However temperature rise may lead to a safety problem during charging of a compressed hydrogen storage tank. To ensure the refueling safety the thermal effects need to be studied carefully during hydrogen refueling process. In this paper based on the mass and energy balance equations a general heat transfer model for refueling process of compressed hydrogen storage tank is established. According to the geometric model of the tank wall structure we have built three lumped parameter models: single-zone (hydrogen) dual-zone (hydrogen and tank wall) and triple-zone (hydrogen tank wall liner and shell) model. These three lumped parameter models are compared with U.S. Naval gas charging model and SAE MC method based refueling model. Under adiabatic and diathermic conditions four models are built in Matlab/Simulink software to simulate the hydrogen refueling process under corresponding conditions. These four models are: single-zone singletemperature (hydrogen) dual-zone single-temperature (hydrogen) dual-zone dual-temperature (hydrogen and tank wall temperatures) and triple-zone triple-temperature (hydrogen tank wall liner and tank wall shell temperatures). By comparing the analytical solution and numerical solution the temperature rise of the compressed hydrogen storage tank can be described. The analytical and numerical solutions on the heat transfer during hydrogen refueling process will provide theoretical guidance at actual refueling station so as to improve the refueling efficiency and to enhance the refueling safety.
Safety and Other Considerations in the Development of a Hydrogen Fueling Protocol for Heavy-duty Vehicles
Sep 2021
Publication
Several manufacturers are developing heavy duty (HD) hydrogen stations and vehicles as zeroemissions alternatives to diesel and gasoline. In order to meet customer demands the new technology must be comparable to conventional approaches including safety reliability fueling times and final fill levels. For a large HD vehicle with a storage rated to 70 MPa nominal working pressure the goal to meet liquid fuel parity means providing 100 kg of hydrogen in 10 minutes. This paper summarizes the results to date of the PRHYDE project efforts to define the concepts of HD fueling which thereby lays the groundwork for the development of the safe and effective approach to filling these large vehicles. The project starts by evaluating the impact of several different assumptions such as the availability of static vehicle data (e.g. vehicle tank type and volume) and station data (e.g. expected station precooling capability) but also considers using real time dynamic data (e.g. vehicle tank gas temperature and pressure station gas temperature etc.) for optimisation to achieve safety and efficiency improvements. With this information the vehicle or station can develop multiple maps of fill time versus the hydrogen delivery temperature which are used to determine the speed of fueling. This will also allow the station or vehicle to adjust the rate of fueling as the station pre-cooling levels and other conditions change. The project also examines different steps for future protocol development such as communication of data between the vehicle and station and if the vehicle or station is controlling the fueling.
Performance of Hydrogen Storage Tanks of Type IV in a Fire: Effect of the State of Charge
Sep 2021
Publication
The use of hydrogen storage tanks at 100% of nominal working pressure (NWP) is expected only after refuelling. Driving between refuellings is characterised by the state of charge SoC <100%. There is experimental evidence that Type IV tanks tested in a fire at initial pressures below 1/3 NWP leaked without rupture. This paper aims at understanding this phenomenon. The numerical research has demonstrated that the heat transfer from fire through the composite overwrap at storage pressures below NWP/3 is sufficient to melt the polymer liner. This melting initiates hydrogen microleaks through the composite before it loses the load-bearing ability. The fire-resistance rating (FRR) is defined as the time to rupture in a fire of a tank without or with blocked thermally activated pressure relief device. The dependence of a FRR on the SoC is demonstrated for the tanks with defined material properties and volumes in the range of 36–244 L. A composite wall thickness variation is shown to cause a safety issue by reducing the tank’s FRR and is suggested to be addressed by tank manufacturers and OEMs. The effect of a tank’s burst pressure ratio on the FRR is investigated. Thermal parameters of the composite wall i.e. decomposition heat and temperatures are shown in simulations of a tank failure in a fire to play an important role in its FRR.
A Brief History of Process Safety Management
Sep 2021
Publication
Common root causes are often to be found in many if not most process safety incidents. Whilst largescale events are relatively rare such events can have devastating consequences. The subsequent investigations often uncover that the risks are rarely visible the direct causes are often hidden and that a ‘normalization of deviation’ is a common human characteristic. Process Safety Management (PSM) builds on the valuable lessons learned from past incidents to help prevent future recurrences. An understanding of how PSM originated and has evolved as a discipline over the past 200 years can be instructive when considering the safety implications of emerging technologies. An example is hydrogen production where risks must be effectively identified mitigated and addressed to provide safe production transportation storage and use .
Hydrogen Wide Area Monitoring of LH2 Releases at HSE for the PRESLHY Project
Sep 2021
Publication
The characterization of liquid hydrogen (LH2) releases has been identified as an international research priority to facilitate the safe use of hydrogen as an energy carrier. Empirical field measurements such as those afforded by Hydrogen Wide Area Monitoring can elucidate the behavior of LH2 releases which can then be used to support and validate dispersion models. Hydrogen Wide Area Monitoring can be defined as the quantitative three-dimensional spatial and temporal profiling of planned or unintentional hydrogen releases. The NREL Sensor Laboratory developed a Hydrogen Wide Area Monitor (HyWAM) based upon a distributed array of hydrogen sensors. The NREL Sensor Laboratory and the Health and Safety Executive (HSE) formally committed to collaborate on profiling GH2 and LH2 releases which allowed for the integration of the NREL HyWAM into the HSE LH2 release behavior investigation supported by the FCH JU Prenormative Research for the Safe Use of Liquid Hydrogen (PRESLHY) program. A HyWAM system was deployed consisting of 32 hydrogen measurement points and co-located temperature sensors distributed downstream of the LH2 release apparatus developed by HSE. In addition the HyWAM deployment was supported by proximal wind and weather monitors. In a separate presentation at this conference “HSE Experimental Summary for the Characterisation Dispersion and Electrostatic Hazards of LH2 for the PRESLHY Project” HSE researchers summarize the experimental apparatus and protocols utilized in the HSE LH2 releases that were performed under the auspices of PRESLHY. As a supplement to the HSE presentation this presentation will focus on the spatial and temporal behavior LH2 releases as measured by the NREL HyWAM. Correlations to ambient conditions such as wind speed and direction plume temperature and hydrogen concentrations will be discussed in addition to the design and performance of the NREL HyWAM and its potential for improving hydrogen facility safety.
Approaches and Methods to Demonstrate Repurposing of the UK's Local Transmission System (LTS) Pipelines for Transportation of Hydrogen
Sep 2021
Publication
Hydrogen has the potential as an energy solution to contribute to decarbonisation targets as it has the capability to deliver low-carbon energy at the scale required. For this to be realised the suitability of the existing natural gas pipeline networks for transporting hydrogen must be established. The current paper describes a feasibility study that was undertaken to assess the potential for repurposing the UK’s Local Transmission System (LTS) natural gas pipelines for hydrogen service. The analysis focused on SGN’s network which includes 3000 km of LTS pipelines in Scotland and the south of England. The characteristics of the LTS pipelines in terms of materials of construction and operation were first evaluated. This analysis showed that a significant percentage of SGN’s LTS network consists of lower strength grades of steel pipeline that operate at low stresses which are factors conducive to a pipeline’s suitability for hydrogen service. An assessment was also made of where existing approaches in pipeline operation may require modifications for hydrogen. The effects of changes in mechanical properties of steel pipelines on integrity and lifetime as a result of potential hydrogen degradation were demonstrated using fitness-for-purpose analysis. A review of pipeline risk assessment and Land-Use Planning (LUP) zone calculations for hydrogen was undertaken to identify any required changes. Case studies on selected sections of the LTS pipeline were then carried out to illustrate the potential changes to LUP zones. The work concluded with a summary of identified gaps that require addressing to ensure safe pipeline repurposing for hydrogen which cover materials performance inspection risk assessment land use planning and procedures.
Condensed Phase Explosions Involving Liquid Hydrogen
Sep 2021
Publication
Liquid hydrogen may have an important role in the storage and transportation of hydrogen energy. It may also provide the best option for some users of hydrogen energy notably the aviation sector. In the 1960’s liquid hydrogen spillages in open uncongested conditions sometimes produced violent condensed phase explosions as well as the familiar gas phase flash and sustained pool fire. Testing showed that burning mixtures of LH2 and solid oxygen/nitrogen readily transitioned to detonation for oxygen concentrations in the solid phase at or above 50%. Such explosive events have been observed in more recent research work on LH2 spillage and the pressure effects could be significant in some accident scenarios. There is a need to understand how solids are produced following spillage and what factors determine the level of oxygen enrichment. This paper describes the physical processes involved in the accumulation of solids during a horizontal discharge at ground level based on observations made in a recent HSE test that led to a condensed phase explosion. Areas where solids accumulated but remained in intimate contact with LH2 are identified. The paper also includes a thermodynamic and fluid mechanical analysis of the condensation process that includes the calculation of densities of mixtures of LH2 and air in different proportions. When the difference in flow speed between air and underlying LH2 is low a stable condensation layer can develop above the liquid where the temperature is just under the initial condensation point of air allowing sustained oxygen enrichment of condensate.
Observation of the Hydrogen Dispersion by Using Raman Scattering Measurement and Increase of Measurable Distance
Sep 2017
Publication
Preparing for the arrival of the hydrogen society it is necessary to develop suitable sensors to use hydrogen safely. There are many methods to know the hydrogen concentration by using conventional sensors but it is difficult to know the behavior of hydrogen gas from long distance. This study measured hydrogen dispersion by using Raman scattering light. Generally some delays occur when using conventional sensors but there are almost no delays by using the new Raman sensor. In the experiments 6mm & 1mm diameter holes are used as a spout nozzle to change initial velocities. To ensure the result a special sheets are used which turns transparent when it detected hydrogen and visualized the hydrogen behaviour. As a result the behaviour of the hydrogen gas in the small container was observed. In addition measurable distance is increased by the improvement of the device.
Effect of Wind on Cryogenic Hydrogen Dispersion from Vent Stacks
Sep 2021
Publication
Liquid hydrogen vent stacks often release hydrogen for example due to pressure relief from an underutilized tank boiling off hydrogen or after hydrogen delivery and transfer (trucks often depressurize through the tank vent stack to meet pressure regulations for on-road transport).<br/>A rapid release of cryogenic hydrogen through a vent stack will condense moisture from the entrained air forming a visible cloud. It is often assumed that the extent of the cold hydrogen is concurrent with the cloud. In this work a laser-based Raman scattering diagnostic was used to map out the hydrogen location during a series of vent stack release experiments. A description of the diagnostic instrument is given followed by a comparison of hydrogen signals to the visible cloud for releases through a liquid hydrogen vent stack. A liquid hydrogen pump was used to vary the flowrate of hydrogen through the vent stack and tests were performed under low and high wind conditions as well as low and high humidity conditions. The hydrogen was observed only where the condensed moisture was located regardless of the humidity level or wind. These measurements are being used to validate models such as those included in Sanda’s HyRAM toolkit and inform safety codes and standards.
Investigation of Hydrogen Leaks from Double Ferrule Fittings
Sep 2021
Publication
The use of hydrogen is expected to increase rapidly in the future. Leakage of hydrogen pipework are the main forms of safety problems in hydrogen utilization. In this paper a numerical model of hydrogen leakage and diffusion in pipe joints was established. The Schlieren + high-speed camera is used in experiments to observe the leakage of hydrogen in the pipe joints. In addition the shape and size of the scratches in the tube were statistically analyzed. Finally the leakage characteristics of double ferrule joints with scratches are experimentally analyzed. For the two scratch sizes the critical pressure values for the vortex transition are 0.2 MPa and 0.03 MPa. Through our experimental process some practical experience and suggestions are given.
Evidence Base Utilised to Justify a Hydrogen Blend Gas Network Safety Case
Sep 2021
Publication
Blending hydrogen with natural gas up to 20 % mol/mol has been identified as a key enabler of hydrogen deployment within the UK gas network. This work outlines the evidence base generated to form the basis of safety submitted to the Health and Safety Executive (HSE) to justify a demonstration of hydrogen blending on a live public gas network within the UK supplying a hydrogen blend to 668homes over the course of 10 months. An evidence base to demonstrate that gas users are not prejudiced by the addition of hydrogen is required by the Gas Safety (Management) Regulations [1] to allow hydrogen distribution above the 0.1 mol% limit specified within the regulations. The technical evidence generated to support the safety case presented to the HSE concerned the implications of introducing a hydrogen blend on appliance operation materials gas characteristics and operational procedures. The outputs of the technical evidence workstreams provided input data to a Quantitative Risk Assessment (QRA) of the GB gas distribution network. The QRA was developed in support of the safety case to allow a causal understanding of public risk to be understood where harm due to gas usage was defined as risk to life caused either by carbon monoxide poisoning or as a result of fires/explosions. Public records were used to calibrate and validate the base risk model to understand the dynamics of public risk due to natural gas usage. The experimental and analytical results of the technical workstreams were then used to derive risk model inputs relating to a hydrogen blend. This allowed a quantified comparison of risk to be understood to demonstrate parity of safety between natural gas and a hydrogen blend. This demonstration of risk parity is a condition precedent of allowing the distribution and utilisation of hydrogen blends within the GB gas network.
Research Efforts for the Resolution of Hydrogen Risk
Jan 2015
Publication
During the past 10 years the Korea Atomic Energy Research Institute (KAERI) has performed a study to control hydrogen gas in the containment of the nuclear power plants. Before the Fukushima accident analytical activities for gas distribution analysis in experiments and plants were primarily conducted using a multidimensional code: the GASFLOW. After the Fukushima accident the COM3D code which can simulate a multi-dimensional hydrogen explosion was introduced in 2013 to complete the multidimensional hydrogen analysis system. The code validation efforts of the multidimensional codes of the GASFLOW and the COM3D have continued to increase confidence in the use of codes using several international experimental data. The OpenFOAM has been preliminarily evaluated for APR1400 containment based on experience from coded validation and the analysis of hydrogen distribution and explosion using the multidimensional codes the GASFLOW and the COM3D. Hydrogen safety in nuclear power has become a much more important issue after the Fukushima event in which hydrogen explosions occurred. The KAERI is preparing a large-scale test that can be used to validate the performance of domestic passive autocatalytic recombiners (PARs) and can provide data for the validation of the severe accident code being developed in Korea
Gas Turbine Enclosures: Determining Ventilation Safety Criteria using Hydrogen Explosion Modelling
Sep 2021
Publication
Dilution ventilation is the current basis of safety following a flammable gas leak within a gas turbine enclosure and compliance requirements are defined for methane fuels in ISO 21789. These requirements currently define a safety criteria of a maximum flammable gas cloud size within an enclosure. The requirements are based on methane explosion tests conducted during a HSE Joint Industry Project which identified typical pressures associated with a range of gas cloud sizes. The industry standard approach is to assess the ventilation performance of specific enclosure designs against these requirements using CFD modelling. Gas turbine manufacturers are increasingly considering introducing hydrogen/methane fuel mixtures and looking towards operating with hydrogen alone. It is therefore important to review the applicability of current safety standards for these new fuels as the pressure resulting from a hydrogen explosion is expected to be significantly higher than that from a methane explosion. In this paper we replicate the previous methane explosion tests for hydrogen and hydrogen/methane fuel mixtures using the explosion modelling tool FLACS CFD. The results are used to propose updated limiting safety criteria for hydrogen fuels to support ventilation CFD analysis for specific enclosure designs. It is found that significantly smaller gas cloud sizes are likely to be acceptable for gas turbines fueled by hydrogen however significantly more hydrogen than methane is required per unit volume to generate a stoichiometric cloud (as hydrogen has a lower stoichiometric air fuel ratio than methane). This effect results in the total quantity of gas in the enclosure (and as such detectability of the gas) being broadly similar when operating gas turbines on hydrogen when compared to methane.
Numerical Simulations of Suppression Effect of Water Mist on Hydrogen Deflagration in Confined Spaces
Sep 2021
Publication
Hydrogen safety issues attract focuses increasingly as more and more hydrogen powered vehicles are going to be operated in traffic infrastructures of different kinds like tunnels. Due to the confinement feature of traffic tunnels hydrogen deflagration may pose a risk when a hydrogen leak event occurs in a tunnel e.g. failure of the hydrogen storage system caused by a car accident in a tunnel. A water injection system can be designed in tunnels as a mitigation measure to suppress the pressure and thermal loads of hydrogen combustion in accident scenarios. The COM3D is a fully verified three-dimensional finite-difference turbulent flow combustion code which models gas mixing hydrogen combustion and detonation in nuclear containment with mitigation device or other confined facilities like vacuum vessel of fusion and semi-confined hydrogen facilities in industry such as traffic tunnels hydrogen refueling station etc. Therefore by supporting of the European HyTunnel-CS project the COM3D is applied to simulate numerically the hydrogen deflagration accident in a tunnel model being suppressed by water mist injection. The suppression effect of water mist and the suppression mechanism is elaborated and discussed in the study.
Investigation on Cooling Effect of Water Sprays on Tunnel Fires of Hydrogen
Sep 2021
Publication
As one of the most promising renewable green energies hydrogen power is a popularly accepted option to drive automobiles. Commercial application of fuel cell vehicles has been started since 2015. More and more hydrogen safety concerns have been considered for years. Tunnels are an important part of traffic infrastructure with a mostly confined feature. Hydrogen leak followed possibly by a hydrogen fire is a potential accident scenario which can be triggered trivially by a car accident while hydrogen powered vehicles operate in a tunnel. Water spray is recommended traditionally as a mitigation measure against tunnel fires. The interaction between water spray and hydrogen fire is studied in a way of numerical simulations. By using the computer program of Fire Dynamics Simulator (FDS) tunnel fires of released hydrogen in different scales are simulated coupled with water droplet injections featured in different droplet sizes or varying mass flow rates. The cooling effect of spray on hot gases of hydrogen fires is apparently observed in the simulations. However in some circumstance the turbulence intensified by the water injection can prompt hydrogen combustion which is a negative side-effect of the spray.
Development of Risk Mitigation Guidance for Sensor Placement Inside Mechanically Ventilated Enclosures – Phase 1
Sep 2019
Publication
Guidance on Sensor Placement was identified as the top research priority for hydrogen sensors at the 2018 HySafe Research Priority Workshop on hydrogen safety in the category Mitigation Sensors Hazard Prevention and Risk Reduction. This paper discusses the initial steps (Phase 1) to develop such guidance for mechanically ventilated enclosures. This work was initiated as an international collaborative effort to respond to emerging market needs related to the design and deployment equipment for hydrogen infrastructure that is often installed in individual equipment cabinets or ventilated enclosures. The ultimate objective of this effort is to develop guidance for an optimal sensor placement such that when integrated into a facility design and operation will allow earlier detection at lower levels of incipient leaks leading to significant hazard reduction. Reliable and consistent early warning of hydrogen leaks will allow for the risk mitigation by reducing or even eliminating the probability of escalation of small leaks into large and uncontrolled events. To address this issue a study of a real-world mechanically ventilated enclosure containing GH2 equipment was conducted where CFD modelling of the hydrogen dispersion (performed by AVT and UQTR and independently by the JRC) was validated by the NREL Sensor laboratory using a Hydrogen Wide Area Monitor (HyWAM) consisting of a 10-point gas and temperature measurement analyzer. In the release test helium was used as a hydrogen surrogate. Expansion of indoor releases to other larger facilities (including parking structures vehicle maintenance facilities and potentially tunnels) and incorporation into QRA tools such as HyRAM is planned for Phase 2. It is anticipated that results of this work will be used to inform national and international standards such as NFPA 2 Hydrogen Technologies Code Canadian Hydrogen Installation Code (CHIC) and relevant ISO/TC 197 and CEN documents.
Towards the Efficient and Time-accurate Simulations of Early Stages of Industrial Explosions
Sep 2021
Publication
Combustion during a nuclear reactor accident can result in pressure loads that are potentially fatal for the structural integrity of the reactor containment or its safety equipment. Enabling efficient modelling of such safety-critical scenarios is the goal of ongoing work. In this paper attention is given to capturing early phases of flame propagation. Transient simulations that are not prohibitively expensive for use at industrial scale are required given that a typical flame propagation study takes a large number of simulation time steps to complete. An improved numerical method used in this work is based on explicit time integration by means of Strong Stability Preserving (SSP) Runge-Kutta schemes. These allow an increased time step size for a given level of accuracy—reducing the overall computational effort. Furthermore a wide range of flow conditions is encountered in analysis of accelerating flames: from incompressible to potentially supersonic. In contrast numerical schemes for spatial discretization would often prove lacking in either stability or accuracy outside the intended flow regime—with density-based schemes being traditionally designed and applied to compressible (Ma>0.3) flows. In the present work a formulation of an all-speed density-based numerical flux scheme is used for simulation of slow flames starting from ignition. Validation was carried out using experiments with spherical lean hydrogen flames at laboratory scale. Turbulence conditions in the experiments correspond to those that can arise in a nuclear reactor containment during an accident. Results show that the new numerical method has the potential to predict flame speed and pressure rise at a reduced computational effort.
Effect of Flow Speed on Ignition Characteristics of Hydrogen/air Mixtures
Sep 2021
Publication
A fuel cell vehicle has a purging system for exhausting contaminated hydrogen gas. Notwithstanding the allowable hydrogen emissions levels in the purging system are regulated by the GTR a further research on the safety requirement of emissions concentrations is therefore needed for the vehicle design into a more rational system. In the present study the effects of flow speed concentration humidity on ignition characteristics of hydrogen/air mixtures were experimentally investigated. The results demonstrate that the value of Lower Flammable Limit increased with an increase in the velocity of hydrogen/air mixtures and slightly increased with a decrease in oxygen concentration.
Quantitive Risk Assessment of the Model Representing Latest Japanese Hydrogen Refuelling Stations
Sep 2021
Publication
Current safety codes and technical standards related to Japanese hydrogen refueling stations (HRSs) have been established based on qualitative risk assessment and quantitative effectiveness validation of safety measures for more than ten years. In the last decade there has been significant development in the technologies and significant increment in operational experience related to HRSs. We performed a quantitative risk assessment (QRA) of the HRS model representing Japanese HRSs with the latest information in the previous study. The QRA results were obtained by summing risk contours derived from each process unit. They showed that the risk contours of 10-3 and 10-4 per year were confined within the HRS boundaries whereas those of 10-5 and 10-6 per year are still present outside the HRS boundaries. Therefore we analyzed the summation of risk contours derived from each unit and identified the largest risk scenarios outside the station. The HRS model in the previous study did not consider fire and blast protection walls which could reduce the risks outside the station. Therefore we conducted a detailed risk analysis of the identified scenarios using 3D structure modeling. The heat radiation and temperature rise of jet fire scenarios that pose the greatest risk to the physical surroundings in the HRS model were estimated in detail based on computational fluid dynamics with 3D structures including fire protection walls. Results show that the risks spreading outside the north- west- and east-side station boundaries are expected to be acceptable by incorporating the fire protection wall into the Japanese HRS model.
An Experimental Study of Propagating Spherical Flames in Unconfined Hydrogen-oxygen Explosions
Sep 2021
Publication
The study to understand the flame propagation behaviors of hydrogen-oxygen explosions is required to make a precise risk assessment. Moreover although research has investigated the propagating spherical flames in unconfined hydrogen-air explosions no study to date has examined the hydrogen-oxygen explosions. The spherical flame propagation in unconfined hydrogen-oxygen explosions have been investigated using a soap bubble method. In the present experiments hydrogen-oxygen mixtures were filled in a 10 cm diameter soap bubble and ignited by an electric spark at the center. The flame propagation behaviors were measured by a high-speed Schlieren photography. The laminar burning velocities and critical flame radii for the onset of flame acceleration in unconfined hydrogen-oxygen explosions were estimated. Results demonstrated that the laminar burning velocities of hydrogenoxygen mixtures were much faster than those of hydrogen-air mixtures. In addition the shift value of maximum laminar burning velocity for hydrogen-oxygen mixtures towards a leaner equivalence ratio is observed. The experimental flame speeds for all experiments were increased owing to diffusionalthermal and Darrieus-Landau instabilities although the measured flame radii were small. The critical flame radius corresponding to the onset of flame acceleration decreased with the decrease in equivalence ratio.
Numerical Study of Hydrogen Addition Effects on Aluminum Particle Combustion
Sep 2021
Publication
In this study the combustion of submicron-sized Al particles in air was studied numerically with a particular focus on the effect of hydrogen addition. Oxidation of the Al particles and the interaction with hydrogen-related intermediates were considered by regarding them as liquid-phase molecules initially. Zero- and One-dimensional numerical simulations were then carried out to investigate the effect of the hydrogen addition on fundamental combustion characteristics of the Al flame by calculating properties such as ignition delay time and flame speed. Our attention was paid to how the hydrogen chemistry is coupled with the Al oxidation process. Numerical results show that the hydrogen addition generally reduces the reactivity of Al such that the flame speed and temperature decrease while it can greatly shorten ignition delay times of the Al flame depending on initial temperatures.
Safety Planning and Management in EU Hydrogen and Fuel Cells Projects - Guidance Document
Sep 2021
Publication
The document provides information on safety planning implementation and reporting for projects involving hydrogen and/or fuel cell technologies. It does not intend to replace or contradict existing regulations which prevail under all circumstances. Neither is it meant to conflict with relevant international or national standards or to replace existing company safety policies codes and procedures. Instead this guidance document aims to assist projects and project partners in identifying hazards and associated risks in prevention and/or mitigation of them through a proper safety plan in implementing the safety plan and reporting safety related events. This shall help in safely delivering the project and ultimately producing inherently safer systems processes and infrastructure.
The Effect of Hydrogen Containing Fuel Blends Upon Flashback in Swirl Burners
Feb 2011
Publication
Lean premixed swirl combustion is widely used in gas turbines and many other combustion Processes due to the benefits of good flame stability and blow off limits coupled with low NOx emissions. Although flashback is not generally a problem with natural gas combustion there are some reports of flashback damage with existing gas turbines whilst hydrogen enriched fuel blends especially those derived from gasification of coal and/or biomass/industrial processes such as steel making cause concerns in this area. Thus this paper describes a practical experimental approach to study and reduce the effect of flashback in a compact design of generic swirl burner representative of many systems. A range of different fuel blends are investigated for flashback and blow off limits; these fuel mixes include methane methane/hydrogen blends pure hydrogen and coke oven gas. Swirl number effects are investigated by varying the number of inlets or the configuration of the inlets. The well known Lewis and von Elbe critical boundary velocity gradient expression is used to characterise flashback and enable comparison to be made with other available data. Two flashback phenomena are encountered here. The first one at lower swirl numbers involves flashback through the outer wall boundary layer where the crucial parameter is the critical boundary velocity gradient Gf. Values of Gf are of similar magnitude to those reported by Lewis and von Elbe for laminar flow conditions and it is recognised that under the turbulent flow conditions pertaining here actual gradients in the thin swirl flow boundary layer are much higher than occur under laminar flow conditions. At higher swirl numbers the central recirculation zone (CRZ) becomes enlarged and extends backwards over the fuel injector to the burner baseplate and causes flashback to occur earlier at higher velocities. This extension of the CRZ is complex being governed by swirl number equivalence ratio and Reynolds Number. Under these conditions flashback occurs when the cylindrical flame front surrounding the CRZ rapidly accelerates outwards to the tangential inlets and beyond especially with hydrogen containing fuel mixes. Conversely at lower swirl numbers with a modified exhaust geometry hence restricted CRZ flashback occurs through the outer thin boundary layer at much lower flow rates when the hydrogen content of the fuel mix does not exceed 30%. The work demonstrates that it is possible to run premixed swirl burners with a wide range of hydrogen fuel blends so as to substantially minimise flashback behaviour thus permitting wider used of the technology to reduce NOx emissions.
Numerical Evaluation of Terrain Landscape Influence on Hydrogen Explosion Consequences
Sep 2021
Publication
The aim of this study is to assess numerically the influence of terrain landscape on the distribution of probable harmful consequences to personnel of hydrogen fueling station caused by an accidentally released and exploded hydrogen. In order to extract damaging factors of the hydrogen explosion wave (maximum overpressure and impulse of pressure phase) a three-dimensional mathematical model of gas mixture dynamics with chemical interaction is used. It allows controlling current pressure in every local point of actual space taking into account complex terrain. This information is used locally in every computational cell to evaluate the conditional probability of such consequences on human beings as ear-drum rupture and lethal ones on the basis of probit analysis. In order to use this technique automatically during the computational process the tabular dependence ""probit-functionimpact probability"" is replaced by a piecewise cubic spline. To evaluate the influence of the landscape profile on the non-stationary three-dimensional overpressure distribution above the earth surface near an epicenter of accidental hydrogen explosion a series of computational experiments with different variants of the terrain is carried out. Each variant differs in the level of mutual arrangement of the explosion epicenter and the places of possible location of personnel. Two control points with different distances from the explosion epicenter are considered. Diagrams of lethal and ear-drum rupture conditional probabilities are build to compare different variants of landscape profile. It is found that the increase or decrease in the level of the location of the control points relative to the level of the epicenter of the explosion significantly changes the scale of the consequences in the actual zone around the working places and should be taken into account by the risk managing experts at the stage of deciding on the level of safety at hydrogen fueling stations.
Building Hydrogen Competence, a Technology Aligned Skills and Knowledge Approach
Sep 2021
Publication
There is a pressing need for a framework and strategic approach to be taken to workforce safety training requirements of new hydrogen projects. It is apparent that organisations embarking on projects utilizing or producing green hydrogen need to implement a program of training for their workforce in order to ensure that all personnel within their organisation understand not only the environmental benefits of green hydrogen but also the safety considerations that come with either producing or using hydrogen as a fuel. Energy Transition must be safe to be successful. If such an approach is taken by industry and stakeholders it is also possible to use the high level content as a vehicle and basis to offer public audiences which also require a basic level of understanding in order to fully accept the transition to using hydrogen more widely as a fuel. This will be crucial to the success of national hydrogen strategies. Coeus Energy has developed an innovative framework of training following engagement with operators keen to ensure their duty of care responsibilities have been met. Whilst having highly skilled personnel already employed within their organisations specific hydrogen content is still required for workforce competence. This is where the framework need arises as the knowledge is required at all levels of an organisation.
Evaluation of Selectivity and Resistance to Poisons of Commercial Hydrogen Sensors
Sep 2013
Publication
The development of reliable hydrogen sensors is crucial for the safe use of hydrogen. One of the main concerns of end-users is sensor reliability in the presence of species other than the target gas which can lead to false alarms or undetected harmful situations. In order to assess the selectivity of commercial of the shelf (COTS) hydrogen sensors a number of sensors of different technology types were exposed to various interferent gas species. Cross-sensitivity tests were performed in accordance to the recommendations of ISO 26142:2010 using the hydrogen sensor testing facilities of NREL and JRC-IET. The results and conclusions arising from this study are presented.
Explosive Phase Transition in LH2
Sep 2021
Publication
This paper describes two models for analysing and simulating the physical effects of explosive phase transition of liquid hydrogen (LH2) also known as cold BLEVE. The present work is based on theoretical and experimental work for liquefied CO2. A Rankine Hugoniot analysis for evaporation waves that was previously developed for CO2 is now extended to LH2. A CFD-method for simulating two-phase flow with mass transfer between the phases is presented and compared with the Rankine Hugoniot analysis results. The Rankine Hugoniot method uses real fluid equations of state suited for LH2 while the CFD method uses linear equations of state suited for shock capturing methods. The results show that there will be a blast from a catastrophic rupture of an LH2 vessel and that the blast waves will experience a slow decay due to the large positive pressure phase.
Hydrogen Component Leak Rate Quantification for System Risk and Reliability Assessment through QRA and PHM Frameworks
Sep 2021
Publication
The National Renewable Energy Laboratory’s (NREL) Hydrogen Safety Research and Development (HSR&D) program in collaboration with the University of Maryland’s Systems Risk and Reliability Analysis Laboratory (SyRRA) are working to improve reliability and reduce risk in hydrogen systems. This approach strives to use quantitative data on component leaks and failures together with Prognosis and Health Management (PHM) and Quantitative Risk Assessment (QRA) to identify atrisk components reduce component failures and downtime and predict when components require maintenance. Hydrogen component failures increase facility maintenance cost facility downtime and reduce public acceptance of hydrogen technologies ultimately increasing facility size and cost because of conservative design requirements. Leaks are a predominant failure mode for hydrogen components. However uncertainties in the amount of hydrogen emitted from leaking components and the frequency of those failure events limit the understanding of the risks that they present under real-world operational conditions. NREL has deployed a test fixture the Leak Rate Quantification Apparatus (LRQA) to quantify the mass flow rate of leaking gases from medium and high-pressure components that have failed while in service. Quantitative hydrogen leak rate data from this system could ultimately be used to better inform risk assessment and Regulation Codes and Standards (RCS). Parallel activity explores the use of PHM and QRA techniques to assess and reduce risk thereby improving safety and reliability of hydrogen systems. The results of QRAs could further provide a systematic and science-based foundation for the design and implementation of RCS as in the latest versions of the NFPA 2 code for gaseous hydrogen stations. Alternatively data-driven techniques of PHM could provide new damage diagnosis and health-state prognosis tools. This research will help end users station owners and operators and regulatory bodies move towards risk-informed preventative maintenance versus emergency corrective maintenance reducing cost and improving reliability. Predictive modelling of failures could improve safety and affect RCS requirements such as setback distances at liquid hydrogen fueling sites. The combination of leak rate quantification research PHM and QRA can lead to better informed models enabling data-based decision to be made for hydrogen system safety improvements.
Measurement and Modeling on Hydrogen Jet and Combustion from a Pressurize Vessel
Sep 2021
Publication
Hydrogen safety is an important topic for hydrogen energy application. Unintended hydrogen releases and combustions are potential accident scenarios which are of great interest for developing and updating the safety codes and standards. In this paper hydrogen releases and delayed ignitions were studied.
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