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Experiments and Simulations of Large Scale Hydrogen-Nitrogen-Air Gas Explosions for Nuclear and Hydrogen Safety Applications
Sep 2023
Publication
Hydrogen safety is a general concern because of the high reactivity compared to hydrocarbon-based fuels. The strength of knowledge in risk assessments related to the physical phenomena and the ability of models to predict the consequence of accidental releases is a key aspect for the safe implementation of new technologies. Nuclear safety considers the possibility of accidental leakages of hydrogen gas and subsequent explosion events in risk analysis. In many configurations the considered gaseous streams involve a large fraction of nitrogen gas mixed with hydrogen. This work presents the results of a large scale explosion experimental campaign for hydrogen-nitrogen-air mixtures. The experiments were performed in a 50 m3 vessel at Gexcon’s test site in Bergen Norway. The nitrogen fraction the equivalence ratio and the congestion level were investigated. The experiments are simulated in the FLACS-CFD software to inform about the current level of conservatism of the predictions for engineering application purposes. The study shows the reduced overpressure with nitrogen added to hydrogen mixtures and supports the use of FLACS-CFD-based risk analysis for hydrogen-nitrogen scenarios.
Safe Design for Large Scale H2 Production Facilities
Sep 2023
Publication
To contribute to a more diverse and efficient energy infrastructure large quantities of hydrogen are requested for industries (e.g. mining refining fertilizers…). These applications need large scale facilities such as dozens of electrolyzer stacks from atmospheric pressure to 30 bar with a total capacity ranging from 100 up to 400 MW and associated hydrogen storage from a few to 50 tons.
Local use can be fed by electrolyzer in 20 feet container and stored in bundles with small volumes. Nevertheless industrial applications can request much bigger capacity of production which are generally located in buildings. The different technologies available for the production of hydrogen at large scale are alkaline or PEM electrolyzer with for example 100 MW capacity in a building of 20000 m3 and hydrogen stored in tube trailers or other fixed hydrogen storage solution with large volumes.
These applications led to the use of hydrogen inside large but confined spaces with the risk of fire and explosion in case of loss of containment followed by ignition. This can lead to severe consequences on asset workers and public due to the large inventories of hydrogen handled.
This article aims to provide an overview of the strategy to safely design large scale hydrogen production facilities in buildings through benchmarks based on projects and literature reviews best practices & standards regulations. It is completed by a risk assessment taking into consideration hydrogen behavior and influence of different parameters in dispersion and explosion in large buildings.
This article provides recommendations for hydrogen project stakeholders to perform informed-based decisions for designing large scale production buildings. It includes safety measures as reducing hydrogen inventories inside building allocating clearance around electrolyzer stacks implementing early detection and isolation devices and building geometry to avoid hydrogen accumulation.
Local use can be fed by electrolyzer in 20 feet container and stored in bundles with small volumes. Nevertheless industrial applications can request much bigger capacity of production which are generally located in buildings. The different technologies available for the production of hydrogen at large scale are alkaline or PEM electrolyzer with for example 100 MW capacity in a building of 20000 m3 and hydrogen stored in tube trailers or other fixed hydrogen storage solution with large volumes.
These applications led to the use of hydrogen inside large but confined spaces with the risk of fire and explosion in case of loss of containment followed by ignition. This can lead to severe consequences on asset workers and public due to the large inventories of hydrogen handled.
This article aims to provide an overview of the strategy to safely design large scale hydrogen production facilities in buildings through benchmarks based on projects and literature reviews best practices & standards regulations. It is completed by a risk assessment taking into consideration hydrogen behavior and influence of different parameters in dispersion and explosion in large buildings.
This article provides recommendations for hydrogen project stakeholders to perform informed-based decisions for designing large scale production buildings. It includes safety measures as reducing hydrogen inventories inside building allocating clearance around electrolyzer stacks implementing early detection and isolation devices and building geometry to avoid hydrogen accumulation.
Public Perception of Hydrogen: Response to an Open-ended Questions
Sep 2023
Publication
Widespread use of hydrogen and hydrogen-based fuels as energy carriers in society may enable the gradual replacement of fossil fuels by renewable energy sources. Although the development and deployment of the associated technologies and infrastructures represent a considerable bottleneck it is generally acknowledged that neither the technical feasibility nor the economic viability alone will determine the extent of the future use of hydrogen as an energy carrier. Public perception beliefs awareness and knowledge about hydrogen will play a significant role in the further development of the hydrogen economy. To this end the present study examines public perception and awareness of hydrogen in Norway. The approach adopted entailed an open-ended question examining spontaneous associations with the term ‘hydrogen’. The question was fielded to 2276 participants in Wave 25 of the Norwegian Citizen Panel (NCP) an on-line panel that derives random samples from the general population registry. The analysis focused on classifying the responses into negative associations (i.e. barriers towards widespread implementation of hydrogen in society) neutral associations (e.g. basic facts) and positive associations (i.e. drivers towards widespread implementation of hydrogen in society). Each of the 2194 responses were individually assessed by five researchers. The majority of the responses highlighted neutral associations using words such as ‘gas’ ‘water’ and ‘element’. When considering barriers vs. drivers the overall responses tend towards positive associations. Many respondents perceive hydrogen as a clean and environmentally friendly fuel and hydrogen technologies are often associated with the future. The negative sentiments were typically associated with words such as ‘explosive’ ‘hazardous’ and ‘expensive’. Despite an increase in the mentioning of safety-related properties relative to a previous study in the same region the frequency of such references was rather low (4%). The responses also reveal various misconceptions such as hydrogen as a prospective ‘source’ of clean energy.
Purging Hydrogen Distribution Pipelines: Literature Review, Description of Recent Experiments and Proposed Future Work
Sep 2023
Publication
The aim of the H21 project is to undertake measurements analysis and field trials to support the safe repurposing of Great Britain’s natural gas distribution network for hydrogen. As part of this project work has been ongoing to identify aspects of existing natural gas procedures that will need to be modified for hydrogen and to support the development of new procedures. This has included a review of the scientific basis of current displacement purging practices analysis of the potential implications of switching from natural gas to hydrogen and experimental support work. The reduced density and viscosity of hydrogen means that minimum purging velocities should (in principle) be higher for hydrogen to avoid stratification and ensure adequate removal of the purged gas during pipeline purging operations. A complicating factor is the high molecular diffusivity of hydrogen (roughly three times that of natural gas) which causes hydrogen to mix over short distances more rapidly than natural gas. Current models for pipeline purging do not take into account the mixing effect related to molecular diffusion. The wider flammable limits lower ignition energy and greater potential for combustion to transition from deflagration to detonation with hydrogen means that indirect purging with nitrogen is currently being investigated for distribution pipelines. This paper reviews the ongoing analysis of hydrogen pipeline purging and discusses a potential future scientific programme of work aimed at developing a new pipeline purging model that accounts for molecular diffusion effects.
Hydrogen Recombiners for Non-nuclear Hydrogen Safety Applications
Sep 2023
Publication
Hydrogen recombiners are catalyst-based hydrogen mitigation systems that have been successfully implemented in the nuclear industry but have not yet received serious interest from the hydrogen industry. Recombiners have been installed in the containment buildings of many nuclear power plants to prevent the accumulation of hydrogen in potential accidents. The attractiveness of hydrogen recombiners for the nuclear industry is due to the confined state of the containment building where hydrogen cannot be vented easily and its passive design where no power or actions are needed for the unit to operate. Alternatively in the hydrogen industry most applications utilize ventilation to mitigate potential hydrogen accumulation in confined areas and passive safety is not essential. However many applications in the hydrogen industry may utilize hydrogen recombiners from a different approach. For instance recombiners could be utilized in emerging hydrogen areas to minimize the costs of ventilation upgrades or built into hydrogen appliances to avoid vent connections. The potential applications for recombiners in the hydrogen industry have different atmospheric conditions than the nuclear industry which may impact the catalyst in the units and render them less effective. Thus experiments have been performed to investigate the limits of the recombiner catalyst and if modifications to the catalyst can extend their use to the hydrogen industry. This paper will present and discuss the applications of interest conditions that may affect the catalyst and results from experiments investigating the catalyst behaviour at temperatures less than 0 °C and carbon monoxide concentrations up to 1000 ppm.
Public Facing Safety and Education for Hydrogen Fueling Infrastructure
Sep 2023
Publication
Building safe and convenient fuelling stations is key to deploying the arrival of commercial/public-use fuel cell electric vehicles (FCEVs). As the most public-facing hydrogen applications second only to the FCEVs hydrogen stations are an efficient tool to educate the public about hydrogen safety and normalize its use to fill up our vehicles. However as an emerging technology it is the industry’s responsibility to ensure that fuelling infrastructures are designed and maintained in accordance with established safety standards and thus that the fuelling process is inherently safe for all users. On the other end it is essential that consumers have all the necessary information at reach to help them feel safe while fuelling their zero-emission vehicles.<br/>This paper will provide a snapshot of the safety systems used to help protect members of the public using hydrogen fueling stations as well as the information used to educate people using this equipment. This will cover the different processes involved in hydrogen fueling stations the dangers that are present to customers and members of the public at these sites and the engineering design choices and equipment used to mitigate these dangers or prevent them from happening. Finally this paper will discuss the crucial role of understanding the dangers of hydrogen at a public level and showing the importance of educating the public about hydrogen infrastructure so that people will feel comfortable using it in their everyday lives.
Buoyant Jet Model to Predict a Vertical Thermal Stratification During Refueling of Gaseous Hydrogen Tanks in Horizontal Position with Axial Injection
Sep 2023
Publication
Thermodynamic modeling of hydrogen tank refueling i.e. 0 dimension (0D) model considers the gas in the tank as a single homogeneous volume. Based on thermodynamic considerations i.e. mass and energy balance equations the gas temperature and pressure predicted at each time step are volume-averaged. These models cannot detect the onset of the thermal stratification nor the maximum local temperature of the gas inside the tank.<br/>For safety reasons the temperature must be maintained below 85 °C in the composite tank. When thermal stratification occurs the volume-averaged gas temperature predicted by 0D models can be below 85 °C while local temperature may significantly exceed 85 °C. Then thermally stratified scenarios must be predicted to still employ 0D models safely.<br/>Up to now only computational fluid dynamics (CFD) approaches can predict the onset of the thermal stratification and estimate the amplitude of thermal gradients. However CFD approaches require much larger computational resources and CPU time than 0D models. This makes it difficult to use CFD for parametric studies or a live-stream temperature prediction for embedded applications. Previous CFD studies revealed the phenomenon of jet deflection during horizontal refueling of hydrogen tanks. The cold hydrogen injected into the warm gas bulk forms a round jet sinking down towards the lower part of the tank due to buoyancy forces. The jet breaks the horizontal symmetry and dumps the cold gas towards the lower part of the tank.<br/>The jet behavior is a key factor for the onset of the thermal stratification for horizontally filled tanks. Free round jets released in a homogeneous environment with a different density than the jet density were extensively investigated in the literature. A buoyant round jet modeling can be applied to predict the jet deflection in the tank. It requires initial conditions that can be provided by 0D refueling models. Therefore 0D models coupled with a buoyant round jet modeling can be used to predict the onset of the thermal stratification without CFD simulation. This approach clarifies the validity domain of 0D models and thus improves the safety of engineering applications
Gas Leak Detection Using Acoustics and Artificial Intelligence
Sep 2023
Publication
Gas leak detection on a production site is a major challenge for the safety and health of workers for environmental considerations and from an economic point of view. In addition flammable gas leaks are a safety risk because if ignited they can cause serious fires or explosions. For these reasons Acoem Metravib in collaboration with TotalEnergies One Tech R&D Safety has developed for the past four years a system called AGLED for the early detection localization and classification of such leaks exploiting acoustics and artificial intelligence driven by physics. Numerous tests have been conducted on a theater representative of gas production facilities created by TotalEnergies in Lacq (France) to build a robust learning database of leaks varying in flowrates exhaust diameters and also types (hole nozzle flange...). Moreover to limit the number of false alarms a relearning strategy has been implemented to handle unexpected disturbances (wildlife human activities meteorological events...). The presented paper describes the global architecture of the system from noise acquisition to the gas leak probability and coordinates. It gives a more in-depth look at the relearning algorithm and its performance in various environments. Finally thanks to a complementary collaboration with Air Liquide an example of test campaign in a real industrial environment is presented with an emphasis on the improvement obtained through relearning.
Design for Reliability and Safety: Challenges and Opportunities in Hydrogen Mobility Assets
Sep 2023
Publication
Safety and reliability are important performance attributes of any engineered system where humanmachine interactions are present. However they are usually approached as afterthoughts or in some cases unintended consequences of the system design and development process that must be addressed and verified in subsequent design stages. In plain words safety and reliability are often seen as constraints that add layers of complexity and extra costs to the minimum functional system of interest. No longer. Shell Hydrogen is embedding the Design for Reliability and Safety approach to engineer our products and assets in such a way that safety and reliability are at the core of a concurrent engineering process throughout the system lifecycle. This has been achieved in practice by leveraging systems reliability and safety engineering methods along with the experience and expertise of Shell Hydrogen original equipment manufacturers and system integrators in designing building and operating hydrogen assets for mobility applications.<br/>The challenges in implementing this approach are many ranging from access to historical data on equipment and component safety and reliability performance to lack of standardization in the industry when dealing with hydrogen related hazards. In this paper we will describe the approach in more detail some of our early successes and failures during deployment and the continual improvement journey that lies ahead.
Design of Long-Life Wireless Near-Field Hydrogen Gas Sensor
Sep 2023
Publication
A wireless near-field hydrogen gas sensor is proposed which detects the leaking hydrogen near its source to achieve fast response and high reliability. The proposed sensor can detect leaking hydrogen in 100ms with nearly no delay due to hydrogen diffusion in space. The overall response time is shortened by orders of magnitude compared to conventional sensors according to simulation results. Over 1 year of maintenance interval is empowered by wireless design based on Bluetooth low energy protocol.
Very Low-cost Wireless Hydrogen Leak Detection for Hydrogen Infrastructure
Sep 2023
Publication
A unique hydrogen leak detection strategy is the use of powerless indicator wraps for fittings and other pneumatic elements within a hydrogen facility. One transduction mechanism of such indicators is a color change that is induced by a reaction between a pigment and released hydrogen. This is an effective way to detect hydrogen leaks and to identify their source before they become a safety event however this technology requires visual (manual) inspection to identify a color change or leak. One improvement in this strategy would be to improve the communication of the visual response to an end-user. Element One (E1) has previously developed and introduced DetecTape® a self-fusing silicone non-reversible hydrogen leak detecting tape for application to potential leak sites in hydrogen piping valves and fittings and it has been successfully commercialized with excellent feedback. Element One’s sensors can be fabricated using either pigments or thin films which both change color and conductivity. Neither change requires an external power source. The conductivity change may be communicated as a wireless transmission such as passive radio frequency identification devices (RFID) to an appropriate receiving system where it may be remotely monitored to achieve higher levels of safety and reliability at low cost. Element One will report on its recent progress in the commercial development of remotely monitored hydrogen leak detection using several wireless protocols including passive RFID.
Hydrogen Dispersion Following Blowdown Releases into a Tunnel
Sep 2023
Publication
This paper presents work undertaken by the HSE as part of the Hytunnel-CS project a consortium investigating safety considerations for fuel cell hydrogen (FCH) vehicles in tunnels and similar confined spaces. The test programme investigating hydrogen dispersion in tunnels involved simulating releases analogous to Thermally activated Pressure Relief Devices (TPRDs) typically found on hydrogen vehicles into the HSE Tunnel facility. The releases were scaled and based upon four scenarios: cars buses and two different train designs. The basis for this scaling was the size of the tunnel and the expected initial mass flow rates of the releases scenarios. The results of the 12 tests completed have been analysed in two ways: the initial mass flow rates of the tests were calculated based upon facility measurements and the Able-Noble equations of state for comparison to the intended initial flow rate; and observations of the hydrogen dispersion in the tunnel were made based on 15 hydrogen sensors arrayed along the tunnel. The calculated mass flow rates showed reasonable agreement with the intended initial conditions showing that the scaling methodology can be used to interpret the data based on the full-scale tunnel of interest. Observations of the hydrogen dispersion show an initial turbulent mixing followed by a movement of the mixed hydrogen/air cloud down the tunnel. No vertical stratification of the cloud was observed but this effect could be possible in longer tunnels or tunnels with larger diameters. Higher ventilation rates in the tunnel resulted in a reduction of the residence time of the hydrogen and a slight increase in the dilution.
Deflagration-to-detonation Transition Due to a Pressurised Release of a Hydrogen Jet. First Results of the Ongoing TAU_NRCN-CEA Project
Sep 2023
Publication
A sudden release of compressed gases and the formation of a jet flow can occur in nature and various engineering applications. In particular high-pressure hydrogen jets can spontaneously ignite when released into an environment that contains oxygen. For some scenarios these high-pressure hydrogen jets can be released into a mixture containing hydrogen and oxygen. This scenario can possibly lead to a wide range of combustion regimes such as jet flames slow or fast deflagrations or even hazardous detonations. Each combustion regime is characterized by typical pressures and temperatures however fast transition between regimes is also possible.<br/>A common project between Tel Aviv University (TAU) Nuclear Research Center Negev (NRCN) and Commissariat à l’Energie Atomique et aux énergies alternatives (CEA) has been recently launched in order to understand these phenomena from experimental modelling and numerical points of view. The main goal is to investigate the dynamics and combustion regimes that arise once a pressurized hydrogen jet is released into a reactive environment that contains inhomogeneous concentrations of hydrogen steam and air.<br/>In this paper we present the first numerical results describing high-pressure hydrogen release obtained using a massively parallel compressible structured-grid flow solver. The experimental arrangements devoted to this phenomenon will also be described.
Sudden Releases of Hydrogen into a Tunnel
Sep 2023
Publication
This paper presents work undertaken by the HSE as part of the Hytunnel-CS project a consortium investigating safety considerations for fuel cell hydrogen (FCH) vehicles in tunnels and similar confined spaces. The sudden failure of a pressurised hydrogen vessel was identified as a scenario of concern due to the severity of the consequences associated with such an event. In order to investigate this scenario experimentally HSE designed a bespoke and reusable ‘sudden release’ vessel. This paper presents an overview of the vessel and the results of a series of 13 tests whereby hydrogen was released from the bespoke vessel into a tunnel at pressures up to 65 MPa. The starting pressure and the volume of hydrogen in the vessel were altered throughout the campaign. Four of the tests also included congestion in the tunnel. The tests reliably autoignited. Overpressure measurements and flame arrival times measured with exposed-tip thermocouples enabled analysis of the severity of the events. A high-pressure fast-acting pressure transducer in the body of the vessel showed the pressure decay in the vessel which shows that 90% of the hydrogen was evacuated in between 1.8 and 3.2 ms (depending on the hydrogen inventory). Schlieren flow imagery was also used at the release point of the hydrogen showing the progression of the shock front following initiation of the tests. An assessment of the footage shows an estimated initial velocity of Mach 3.9 at 0.4 m from the release point. Based on this an ignition mechanism is proposed based upon the temperature behind the initial shock front.
Pressure Evolution from Head-on Reflection of High-speed Deflagration in Hydrogen Mixtures
Sep 2023
Publication
Our previous reported experiments revealed that the reflection of high-speed deflagrations in hydrogenair and hydrogen-oxygen mixtures produces higher mechanical loading and reflected pressures than reflecting detonations. This surprising result was shown to correlate with the onset of detonation in the gases behind the reflected shock. We revisit these experiments with the aim of developing a closed-form model for the pressure evolution due to the shock-induced ignition and rapid transition to detonation. We find that the reflection condition of fast deflagrations corresponds to the chain-branching crossover regime of hydrogen ignition in which the reduced activation energy is very large and the reaction characteristic time is very short compared to the induction time. We formulate a closed-form model in the limit of fast reaction times as compared to the induction time which is used to predict a square wave pressure profile generated by self-similar propagation of internal Chapman-Jouguet detonation waves followed by Taylor expansion waves. The model predictions are compared with Navier-Stokes numerical simulations with full chemistry as well as simple Euler calculations using calibrated one-step or twostep chain-branching models. Both simplified numerical models were found to be in good agreement with the full chemistry model. We thus demonstrate that the end pressure evolution due to the reflection of high-speed deflagrations can be well predicted analytically and numerically using relatively simple models in this ignition regime of main interest for safety analysis and explosion mitigations. The slight departures from the square wave model are investigated based on the physical wave processes occurring in the shocked gases controlling the shock-to-detonation transition. Using the two-step model we study how the variations of the rate of energy release control the pressure evolution in the end gas extending the analysis of Sharpe to very large rates of energy release.
Modeling of Tube Deformation and Failure under Conditions of Hydrogen Detonation
Sep 2023
Publication
In case of accidental conditions involving high-speed hydrogen combustion the considerable pressure and thermal loads could result in substantial deformation and/or destruction of the industrial appliances. Accounting of such effects in the safety analysis with CFD tools can provide critical information on the design and construction of the sensitive appliances’ elements. The current paper presents the development and the implementation of a new 3D-technique which makes possible to perform simulations of the gas-dynamic processes simultaneously with adaptation of the geometry of complex configurations. Using the data obtained in the experiments on the flame acceleration and DDT in the tubes of industrial arrangements performed in MPA and KIT the authors performed a series of the combustion simulations corresponding to the experimental conditions. The combustion gas-dynamics was simulated using COM3D code and the tube wall material behavior was modelled using finite-element code ABAQUS - © Dassault Systèmes with real-time data exchange between the codes. Obtained numerical results demonstrated good agreement with the observed experimental data on both pressure dynamics and tube deformation history.
SSEXHY Experimental Results on Pressure Dynamics from Head-on Reflections of Hydrogen Flames
Sep 2023
Publication
In the past few years CEA has been fully involved at both experimental and modeling levels in projects related to hydrogen safety in nuclear and chemical industries and has carried out a test program using the experimental bench SSEXHY (Structure Submitted to an EXplosion of HYdrogen) in order to build a database of the deformations of simple structures following an internal hydrogen explosion. Different propagation regimes of explosions were studied varying from detonations to slow deflagrations.<br/>During the experimental campaign it was found that high-speed deflagrations corresponding to relatively poor hydrogen-air mixtures resulted in higher specimen deformation compared to those related to detonations of nearly stoichiometric mixtures. This paper explains this counter-intuitive result from qualitative and quantitative points of view. It is shown that the overpressure and impulse from head-on reflections of hydrogen flames corresponding to poor mixtures of specific concentrations could have very high values at the tube end.
Fuel Cell Vehicle Hydrogen Emissions Testing
Sep 2023
Publication
The NREL Hydrogen Sensor Laboratory is comprised of researchers dedicated to furthering hydrogen sensor technology and detection methodology. NREL has teamed up with researchers at Environment and Climate Change Canada (ECCC) and Transport Canada (TC) to conduct research to quantify hydrogen emissions from Fuel Cell Electric Vehicles (FCEV). Test protocols will have a large effect on monitoring and regulating the hydrogen emissions from FCEVs. How emissions are tested will play an important role when understanding the safety and environmental implications of using FCEVs. NREL Sensor Laboratory personnel have partnered with other entities to conduct multiple variations of emissions testing for FCEVs. This experimentation includes testing different models of FCEVs under various driving conditions while monitoring the hydrogen concentration of the exhaust using several different test methods and apparatus. Researchers look to support regulatory bodies by providing useful data that can support more consistent and relevant safety and environmental standards. We plan to present on the current test methods and results from recent emissions measurements at ECCC.
Effect of Methane Addition on Transition to Detonation in Hydrogen-Air Mixtures Due to Shock Wave Focussing in a 90 - Degree Corner
Sep 2023
Publication
The main purpose of this work is to investigate the influence of methane addition in methane-hydrogen-air mixture (φ = 0.8 – 1.6) on the critical conditions for transition to detonation in a 90-deg wedge corner. Similar to hydrogen-air mixtures investigated previously [1] methane-hydrogen-air mixtures results showed three ignition modes weak ignition followed by deflagration with ignition delay time higher than 1 μs strong ignition with instantaneous transition to detonation and third with deflagrative ignition and delayed transition to detonation. Methane addition caused an increase in the range of 3.25 – 5.03% in the critical shock wave velocity necessary for transition to detonation for all mixtures considered. For example in stoichiometric mixture with 5% methane in fuel (95% hydrogen in fuel) in air the transition to detonation velocity was approx. 752 m/s (an increase of 37 m/s from hydrogen-air) corresponding to M = 1.89 (an increase of 0.14 from hydrogen-air) and 75.7% (an increase of 4.7% from hydrogen-air) of speed of sound in products. Also similar to hydrogen-air mixture the transition to detonation velocity increased for leaner and richer mixture. Moreover it was observed that methane addition in general increased the pressure limit at the corner necessary for transition to detonation.
X-ray Absorpton Spectroscopy Study on Hydrogen Recombination Catalysts of Palladium Nanoparticles on Titanium Oxide under Wet Condition
Sep 2023
Publication
Hydrogen recombination catalyst is useful tool for reducing hydrogen in closed area. The catalyst is known to be poisoned under wet condition in long time use. The study is focused on the behavior of pre-oxidized Pd nanoparticle as the hard-used catalyst in high humidity environment by comparison of alumina and titanium oxide supports using in situ X-ray absorption spectroscopy technique. The reduction of surface oxide layer of Pd/TiO2 was promoted by water during hydrogen recombination although the reduction reaction of Pd/Al2O3 was inhibited by water.
Field Test Series for Development of Mitigation Barriers and its Designs Against Hydrogen Explosion
Sep 2023
Publication
A field test series where a composite pressure vessel for hydrogen is exploded by fire 1) to provide the facts and the data for the safety distance based on overpressure; 2) to validate the current status of mitigation barrier per KGS FP216 and further designs for developments of the codes and standards relating to hydrogen refueling stations. A pair of barriers to be tested are installed approximately 4 m apart standing face to face. The explosion source is a type-4 composite vessel of 175 L filled with compressed hydrogen up to 70 MPa. The vessel is in the middle of the barriers and the body part is heated with an LPG burner until it blows out. The incident overpressures from the blast are measured with 40 high-speed pressure sensors which are respectively installed 2 to 32 m away from the explosion. In the tests with the barrier constructed per the current status of KGS FP216 the explosion of the vessel resulted in partial destruction of the reinforced concrete barrier and made the steel plate barrier dissociated from the foundation then flew away approximately 25 m. The peak overpressure was 14.65 kPa at 32 m. The test data will be further analyzed to select the barriers for the subsequent tests and to develop the codes and standards for hydrogen refueling stations.
Enhancing Safety of Liquid and Vaporised Hydrogen Transfer Technologies in Public Areas for Mobile Applications
Sep 2023
Publication
Federico Ustolin,
Donatella Cirrone,
Vladimir V. Molkov,
Dmitry Makarov,
Alexandros G. Venetsanos,
Stella G. Giannissi,
Giordano Emrys Scarponi,
Alessandro Tugnoli,
Ernesto Salzano,
Valerio Cozzani,
Daniela Lindner,
Birgit Gobereit,
Bernhard Linseisen,
Stuart J. Hawksworth,
Thomas Jordan,
Mike Kuznetsov,
Simon Jallais and
Olga Aneziris
International standards related to cryogenic hydrogen transferring technologies for mobile applications (filling of trucks ships stationary tanks) are missing and there is lack of experience. The European project ELVHYS (Enhancing safety of liquid and vaporized hydrogen transfer technologies in public areas for mobile applications) aims to provide indications on inherently safer and efficient cryogenic hydrogen technologies and protocols in mobile applications by proposing innovative safety strategies which are the results of a detailed risk analysis. This is carried out by applying an inter-disciplinary approach to study both the cryogenic hydrogen transferring procedures and the phenomena that may arise from the loss of containment of a piece of equipment containing hydrogen. ELVHYS will provide critical inputs for the development of international standards by creating inherently safer and optimized procedures and guidelines for cryogenic hydrogen transferring technologies thus increasing their safety level and efficiency. The aim of this paper is twofold: present the state of the art of liquid hydrogen transfer technologies by focusing on previous research projects such as PRESLHY and introduce the objectives and methods planned in the new EU project ELVHYS.
A Model for Assessing the Risk of Liquid Hydrogen Transport through Road Tunnels
Sep 2023
Publication
Among the new energy carriers aimed at reducing greenhouse gas emissions the use of hydrogen is expected to grow significantly in various applications and sectors (i.e. industrial commercial transportation etc.) due to its high energy content by weight and zero carbon emissions. The increasingly widespread use of hydrogen will require massive distribution from production sites to final consumers and the delivery by means of liquid hydrogen road tankers may be a suitable cost-effective option for market penetration in the short-medium term. Liquid hydrogen (LH2) presents different hazards compared to gaseous hydrogen and an accidental release in confined spaces such as road tunnels might lead to the formation of a flammable hydrogen cloud that might deflagrate or even detonate. Nevertheless the potential negative effects on users in the event of accidental leakage of liquid hydrogen from a tanker in road tunnels so far have not been sufficiently investigated. Therefore a 3D Computational Fluid Dynamics model for the release of LH2 and its dispersion within a road tunnel was developed in this study. The proposed model was validated by a comparison with certain experimental and numerical studies found in the literature. Such modeling is demanding for long tunnels. Therefore the results of the simulations (e.g. the amount of hydrogen contained within the cloud) were combined with established simplified consequence methods to estimate the overpressures generated from a potential hydrogen deflagration. This was then used to evaluate the effects on users while evacuating from the tunnel. The findings showed that the worst scenario is when the release is in the middle of the tunnel length and the ignition occurs 90 s after the leakage.
Safety Challenges Related to the Use of Hydrogen-Natural Gas Blends in Gas Turbines
Sep 2023
Publication
In a context of the decarbonization of the power sector the gas turbine manufacturers are expected tohandle and burn hydrogen or hydrogen/natural gas mixtures. This evolution is conceptually simple in order to displace CO2 emissions by H2O in the combustion exhaust but raises potential engineering andsafety related questions. Concerning the safety aspect the flammability domain is wider and the laminar flame speed is higher for hydrogen than for natural gas. As a result handling fuels with increased hydrogen concentration should a priori lead to an increased the risk of flammable cloud formation with air and also increase the potential explosion violence.<br/>A central topic for the gas turbine manufacturer is the quantification of the hydrogen fuel content from which the explosion risk increases significantly when compared with the use of natural gas. This work will be focused on a risk study of the fuel supply piping of a gas turbine in a scenario where mixing between fuel and air would occur. The pipes are a few dozens of meters long and show singularities: elbows connections with other lines … They are operated at high temperature and atmospheric or high pressure.<br/>The paper will first highlight through CFD modelling the impact of increasing hydrogen content in the fuel on the explosion risk based on a geometry representative of a realistic system. Second the quantification of the explosion effects will be addressed. Some elements of the bibliography relative to flame propagation in pipes will be recalled and put in sight of the characteristics of the industrial case. Finally a CFD model proposed recently for accounting for methane or hydrogen flames propagating in long open steel tubes was used to assess a hydrogen fuel content from which the flame can strongly accelerate and generate significative pressure effects for a flammable mixture initially at atmospheric conditions.
CFD Modelling of Startup Fuelling Phase Accounting for All Hydrogen Refuelling Station Components
Sep 2023
Publication
Further development of hydrogen-fuelled transport and associated infrastructure requires fundamentally based validated and publicly accepted models for fuelling protocol development particularly for heavy-duty transport applications where protocols are not available yet. This study aims to use computational fluid dynamics (CFD) for modelling the entire hydrogen refuelling station (HRS) including all its components starting from high-pressure (HP) tanks a mass flow meter pressure control valve (PCV) a heat exchanger (HE) nozzle hose breakaway and up to 3 separate onboard tanks. The paper focuses on the initial phase of the refuelling procedure in which the main purpose is to check for leaks in the fuelling line and determine if it is safe to start fuelling. The simulation results are validated against the only publicly available data on hydrogen fuelling by Kuroki and co-authors (2021) from the NREL hydrogen fuelling station experiment. The simulation results – mass flow rate dynamics as well as pressure and temperature at different station locations - show good agreement with the measured experimental data. The development of such models is crucial for the further advancement of hydrogen-fuelled transport and infrastructure and this study presents a step towards this goal.
Improvement of MC Method in SAE J2601 Hydrogen Refuelling Protocol Using Dual-zone Dual-Temperature Model
Sep 2023
Publication
The MC method refuelling protocol in SAE J2601 has been published by the Society of Automotive Engineers (SAE) in order to safely and quickly refuel hydrogen vehicles. For the calculation method of the pressure target to control the refuelling stop we introduced a dual-zone dual-temperature model that distinguishes the hydrogen temperature in the tank from the wall temperature to replace the dual-zone single-temperature model of the original MC method. The total amount of heat transferred by convection between hydrogen and the inner tank wall during the filling process was expressed as an equation of final hydrogen temperature final wall temperature final refuelling time tank inner surface area and the correction factor. The correction factor equations were determined by fitting simulation data from the 0D1D model where hydrogen inside the tank is lumped parameter model (0D) and the tank wall is a one-dimensional model (1D). For the correction factor of the linear equation its first-order coefficient and constant term have a linear relationship with the initial pressure of the storage tank and their R2 values obtained from the fitting are greater than 0.99. Finally we derived a new equation to calculate the final hydrogen temperature which can be combined with the 100% SOC inside the vehicle tank to determine the pressure target. The simulation results show that the final SOC obtained are all greater than 96% using the modified pressure target and the correction factor of the linear equation.
Risk Management in a Containerized Metal Hydride Storage System
Sep 2023
Publication
HyCARE project supported by the Clean Hydrogen Partnership of the European Union deals with a prototype of hydrogen storage tank using a solid-state hydrogen carrier. Up to 40 kilograms of hydrogen are stored in twelve tanks at less than 50 barg and less than 100 °C. The innovative design is based on a standard twenty-foot container including twelve TiFe-based metal hydride (MH) hydrogen storage tanks coupled with a thermal energy storage in phase change materials (PCM). This article aims at showing the main risks related to hydrogen storage in a MH system and the safety barriers considered based on HyCARE’s specific risk analysis.<br/>Regarding the TiFe MH material used to store hydrogen experimental tests showed that the exposure of the MH to air or water did not cause spontaneous ignition. Furthermore an explosion within the solid MH cannot propagate due to internal pore size. Additionally in case of leakage the speed of hydrogen desorption from the MH is self-limited which is an important safety characteristic since it reduces the potential consequences from the hydrogen release scenario.<br/>Regarding the integrated system the critical scenarios identified during the risk analysis were: explosion due to release of hydrogen inside or outside the container internal explosion inside MH tanks due to accidental mix of hydrogen and air and asphyxiation due to inert gas accumulation in the container. This identification phase of the risk analysis allowed to pinpoint the most relevant safety barriers already in place and recommend additional ones if needed to further reduce the risk that were later implemented.<br/>The main safety barriers identified were: material and component selection (including the MH selected) safety interlocks safety valves ventilation gas detection and safety distances.<br/>The risk management process based on risk identification and assessment contributed to coherently integrate inherently safe design features and safety barriers.
Study on the Inherent Safety of On-board Methanol Reforming Hydrogen Production Fuel Cell System
Sep 2023
Publication
Methanol as a liquid phase hydrogen storage carrier has broad prospects. Although the on-board methanol reforming hydrogen fuel cell system (MRFC) has long been proposed to replace the traditional hydrogen fuel cell vehicle the inherent safety of the system itself has rarely been studied. This paper adopted the improved method of Inherently Safer Process Piping (ISPP) to evaluate the pipeline inherent safety of MRFC. The process data such as temperature pressure viscosity and density were obtained by simulating the MRFC in ASPEN HYSYS. The Process Stream Characteristic Index (PSCI) and risk assessment of jet fire and vapor cloud explosion was carried out for the key streams with those simulated data. The results showed the risk ranks of different pipelines in the MRFC and the countermeasures were given according to different risk ranks. Through the in-depth study of the evaluation results this paper demonstrates the risk degree of the system in more detail and reduces the fuzziness of risk rating. By applying ISPP to the small integrated system of MRFC this paper realizes the leap of inherent safety assessment method in the object and provides a reference for the inherent safety assessment of relevant objects in the future.
Engineering Models for Refueling Protocol Development: Validation and Recommendations
Sep 2023
Publication
Fouad Ammouri,
Nicola Benvenuti,
Elena Vyazmina,
Vincent Ren,
Guillaume Lodier,
Quentin Nouvelot,
Thomas Guewouo,
Dorine Crouslé,
Rony Tawk,
Nicholas Hart,
Steve Mathison,
Taichi Kuroki,
Spencer Quong,
Antonio Ruiz,
Alexander Grab,
Alexander Kvasnicka,
Benoit Poulet,
Christopher Kutz and
Martin Zerta
The PRHYDE project (PRotocol for heavy duty HYDrogEn refueling) funded by the Clean Hydrogen partnership aims at developing recommendations for heavy-duty refueling protocols used for future standardization activities for trucks and other heavy duty transport systems applying hydrogen technologies. Development of a protocol requires a validated approach. Due to the limited time and budget the experimental data cannot cover the whole possible ranges of protocol parameters such as initial vehicle pressure and temperature ambient and precooling temperatures pressure ramp refueling time hardware specifications etc. Hence a validated numerical tool is essential for a safe and efficient protocol development. For this purpose engineering tools are used. They give good results in a very reasonable computation time of several seconds or minutes. These tools provide the heat parameters estimation in the gas (volume average temperature) and 1D temperature distribution in the tank wall. The following models were used SOFIL (Air Liquide tool) HyFill (by ENGIE) and H2Fills (open access code by NREL). The comparison of modelling results and experimental data demonstrated a good capability of codes to predict the evolution of average gas temperature in function of time. Some recommendations on model validation for the future protocol development are given.
An Improved Passive Scalar Model for Hazardous H2-Air Ignition Prediction
Sep 2023
Publication
As hydrogen becomes an increasingly popular alternative fuel for transportation the need for tools to predict ignition events has grown. Recently a cost-effective passive scalar formulation has been developed to address this need [1]. This approach employs a self-reacting scalar to model the hydrogenair chain-branched explosion (due to reactions of the type Reactant + Radical → Radical + Radical). The scalar branching rate is derived analytically from the kinetic Jacobian matrix [2]. The method accurately reproduces ignition delays obtained by detailed chemistry for temperatures above crossover where branching is the dominant process. However for temperatures below the crossover temperature where other phenomena like thermal runaway are more significant the scalar approach fails to predict ignition events correctly. Therefore modifications to the scalar framework have been made to extend its validity across the entire temperature range. Additionally a simple technique for approximating the molecular diffusion of the scalar has been developed using the eigenvector of the Jacobian which accounts for differences in the radical pool’s composition and non-unity Lewis number effects. The complete modified framework is presented and its capability is evaluated in canonical scenarios and a more challenging double mixing layer.
Calculating the Fundamental Parameters to Assess the Explosion Risk Due to Crossover in Electrolysers
Sep 2023
Publication
With the predicted high demand of hydrogen projected to support the neutral carbon society transition in the coming years the production of hydrogen is set to increase alongside the demand. As electrolysis is set to be amongst the main solutions for green hydrogen production ensuring the safety of electrolysers during operation will become a central concern. This is mainly due to the crossover risk (hydrogen into oxygen or the other way around) in the separators as throughout the years several cases of incidents have been reported. This study aims to evaluate the methodologies for calculating H2/O2 detonation cell size and laminar flame velocity using detailed kinetic mechanisms at the operating conditions of electrolysers (up to 35 bar and 360 K). Therefore the modeling of H2/O2 and H2/Air shock tube delay times and laminar flame speeds at initial different pressures and temperature based on the GRI mech 3.0 [1] Mevel et al.[2] Li et al.[3] Lutz et al. [4] and Burke et al. [5] kinetic mechanisms were performed and compared with the available experimental data in the literature. In each case a best candidate mechanism was then chosen to build a database for the detonation cell size then for the laminar flame speeds up to the operating conditions of electrolysers (293-360K and 1-35 bar).
Impact on Canadian Residential End Use Appliances with the Introduction of Hydrogen into the Natural Gas Stream - An Application
Sep 2023
Publication
Canada’s commitment to be net-zero by 2050 combined with ATCO’s own Environmental Social and Governance goals has led ATCO to pursue hydrogen blending within the existing natural gas system to reduce CO2 emissions while continuing to provide safe reliable energy service to customers. Utilization of hydrogen in the distribution system is the least-cost alternative for decarbonizing the heating loads in jurisdictions like Alberta where harsh winter climates are encountered and low-carbon hydrogen production can be abundant. ATCO’s own Fort Saskatchewan Hydrogen Blending Project began blending 5% hydrogen by volume to over 2100 customers in the Fall of 2022 and plans to increase the blend rates to 20% hydrogen in 2023. Prior to blending ATCO worked together with DNV to examine the impact of hydrogen blended natural gas to twelve Canadian appliances: range/stove oven garage heater high and medium efficiency furnaces conventional and on demand hot water heaters barbeque clothes dryer radiant heater and two gas fireplaces. The tests were performed not only within the planned blend rates of 0-20% hydrogen but also to higher percentages to determine how much hydrogen can be blended into a system before appliance retrofits would be required. The testing was designed to get insights on safety-related combustion issues such as flash-back burner overheating flame detection and other performance parameters such as emissions and burner power. The experimental results indicate that the radiant heater is the most sensitive appliance for flashback observed at 30 vol% hydrogen in natural gas. At 50% hydrogen the range and the radiant burner of the barbeque tested were found to be sensitive to flashback. All other 9 appliances were found to be robust for flashback with no other short-term issues observed. This paper will detail the findings of ATCO and DNV’s appliance testing program including results on failure mechanisms and sensitivities for each appliance.
Explosion Replication Test of FCEV Hydrogen Tank
Sep 2023
Publication
Due to the increased interest in alternative energy sources hydrogen device safety has become paramount. In this study we induced the explosion of a hydrogen tank from a fuel cell electric vehicle (FCEV) by igniting a fire beneath it and disabling the built-in temperature pressure relief device. Three Type 4 tanks were injected gaseous hydrogen at pressures of 700 350 and 10 bar respectively. The incident pressure generated by the tank explosion was measured by pressure transducers positioned at various points around the tank. A protective barrier was installed to examine its effect on the resulting damage and the reflected pressure was measured along the barrier. The internal pressure and external temperature of the tanks were measured in multiple locations. The 700- and 350-bar hydrogen tanks exploded approximately 10 and 16 min after burner ignition respectively. The 10-bar hydrogen tank did not explode but ruptured approximately 29 min after burner ignition The explosions generated blast waves fireballs and fragments. The impact on the surrounding area was evaluated and we verified that the blast pressure fireballs and fragments were almost completely blocked by the protective barrier. The results of this study are expected to improve safety on an FCEV accident scene.
Experimental Characterization of the Operational Behavior of a Catalytic Recombiner for Hydrogen Mitigation
Sep 2023
Publication
One of the significant safety concerns in large-scale storage and transportation of liquefied (cryogenic) hydrogen (LH2) is the formation of flammable hydrogen/air mixtures after leakages during storage or transportation. Especially in maritime transportation hydrogen accumulations could occur within large and congested geometries. The installation of passive auto-catalytic recombiners (PARs) is a suitable mitigation measure for local areas where venting is insufficient or even impossible. Numerical models describing the operational behavior of PARs are required to allow for optimizing the location and assessing the efficiency of the mitigation measure. In the present study the operational behavior of a PAR with a compact design has been experimentally investigated. In order to obtain data for model validation an experimental program has been performed in the REKO-4 facility a 5.5 m³ vessel. The test procedure includes two phases steady-state and dynamic. The results provide insights into the hydrogen recombination rates and catalyst temperatures under different boundary conditions.
UK HSE Hydrogen for Heating Evidence Review Process
Sep 2023
Publication
As part of the UK Government’s Net Zero targets to tackle Climate Change the Health and Safety Executive (HSE) aims to reach an authoritative view on the safety of using 100% hydrogen for heating across the UK to feed into Government policy decisions by the mid-2020s. This paper describes the background and process of a programme of work led by HSE in support of the Department for Energy Security and Net Zero (formerly BEIS) that will inform strategic policy decisions by 2026. The strategic framework of HSE’s programme of work was defined between BEIS and HSE. HSE’s programme of work follows on from a previous project which engaged with HSE policy regulatory and scientific colleagues working with industry stakeholders identifying knowledge gaps for the safe distribution storage and use of hydrogen gas in domestic industrial and commercial premises. These knowledge gaps were subsequently used in discussions with stakeholders to prioritise research projects and evidence gathering exercises. To review this scientific evidence HSE developed a review framework and convened Evidence Review Groups (ERGs) to cover all evidence areas encompassing topics such as quantified risk assessment material compatibility and operational procedures. These ERGs include representation from relevant divisions across HSE (policy regulation and science). The paper explains the structure of HSE’s input into the hydrogen for heating programme the ERG process and timelines along with the proposed outputs. Additional activities have been undertaken by HSE within the programme to highlight specific issues in support of the review process which will also be discussed.
Computational Fluid Dynamic (CFD) Analysis of a Cold-adsorbed Hydrogen Tank During Refilling
Sep 2023
Publication
Hydrogen has the potential to be an important source of clean energy but the development of efficient and cost-effective methods for storing hydrogen is a key challenge that needs to be addressed in order to make widespread use of hydrogen as a possible energy sourc. There are different methods for storing hydrogen (i.e. compressed it at high pressures liquefied by cooling the hydrogen to a temperature of -253°C and stored with a chemical compound) each with its own advantages and disadvantages.<br/>MAST3RBoost (Maturing the Production Standards of Ultraporous Structures for High Density Hydrogen Storage Bank Operating on Swinging Temperatures and Low Compression) is a European project which aims to provide a solid benchmark of cold-adsorbed H2 storage (CAH2) at low compression (100 bar or below) by maturation of a new generation of ultraporous materials for mobility applications i.e. H2-powered vehicles including road and railway air-borne and waterborne transportation. Based on a new generation of Machine Learning-improved ultraporous materials – such as Activated Carbons (ACs) and high-density MOFs (Metal-organic Frameworks) – MAST3RBoost project will enable a disruptive path to meet the industry goals by developing the first worldwide adsorption-based demonstrator at the kg-scale.<br/>The design of the tank is supported by numerical investigation by mean of the use of Computational Fluid Dynamic (CFD) commercial code. In this a paper a preliminary analysis of the refilling of tank is presented focused on the effect of different tank configurations on the hydrogen temperature and on the hydrogen adsorption.
Safety Aspects Related to the Underground Hydrogen Storage
Sep 2023
Publication
The transition from fossil fuels to the renewable energies (wind solar) is a key factor to face climate change and build a sustainable reliable and secure energy system. To balance the intermittent energy demand and supply affecting the renewable sources the surplus of electrical energy may be converted in hydrogen and then storage in geological formations. While the risks associated to the natural gas storage in the sub-surface are well known from decades those associated with hydrogen underground storage (UHS) are relatively underexplored. This paper presents an inventory of risks related to large H2-storage in depleted gas and oil fields salt caverns and aquifers. Different issues such as integrity and durability of materials H2 leakages and interaction with the reservoir H2 uncontrolled outflow from the wellhead with potential combustion of air-hydrogen mixture (fire and explosion) soil subsidence and induced seismicity are analyzed.
Numerical Simulations of the Critical Diameter and Flame Stability for the Hydrogen Jet Flames
Sep 2023
Publication
This study focuses on development of a CFD model able to simulate the experimentally observed critical nozzle diameter for hydrogen non-premixed flames. The critical diameter represents the minimum nozzle size through which a free jet flame will remain stable at all driving pressures. Hydrogen non-premixed flames will not blow-out at diameters equal to or greater than the critical diameter. Accurate simulation of this parameter is important for assessment of thermally activated pressure relief device (TPRD) performance during hydrogen blowdown from a storage tank. At TPRD diameters below the critical value there is potential for a hydrogen jet flame to blow-out as the storage tank vents potentially leading to hydrogen accumulation in an indoor release scenario. Previous experimental studies have indicated that the critical diameter for hydrogen is approximately 1 mm. In this study flame stability is considered across a range of diameters and overpressures from 0.1 mm to 2 mm and from 0.2 MPa to 20 MPa respectively. The impact of turbulent Schmidt number Sct which is the ratio of momentum diffusivity (kinematic viscosity) and mass diffusivity on the hydrogen concentration profile in the region near the nozzle exit and subsequent influence on critical diameter was investigated and discussed. For lower Sct values the enhanced mass mixing resulted in smaller predicted critical diameters. The use of value Sct=0.61 in the model demonstrated the best agreement with experimental values of the critical diameter. The model reproduced the critical diameter of 1 mm and then was applied to predict flame stability for under-expanded hydrogen jets.
CO2 Effect on the Fatigue Crack Growth of X80 Pipeline Steel in Hydrogen-Enriched Natural Gas: Experiment vs Density Functional Theory Calculation
Sep 2023
Publication
The influence of hydrogen-enriched natural gas (HENG) and CO2 on the mechanical property of X80 pipeline steel were investigated via fatigue crack growth rate (FCGR) tests and density functional theory (DFT) calculations. The results show that the FCGR in H2 was slightly faster than that in HENG while it was slower than that in the N2/CO2/H2 mixtures. The enhanced FCGR by CO2 further increased with the increasing CO2 content. DFT calculation results show that the adsorbed CO2 on the iron surface significantly increased the migration rate of H atoms from surface to subsurface. This promotes the entry of hydrogen into the steel.
Ignition and Flow Stopping Considerations for the Transmission of Hydrogen in the Existing Natural Gas Network
Sep 2023
Publication
This work formed part of the H21 programme whose objective is to reach the point whereby it is feasible to convert the existing natural gas (NG) distribution network to 100% hydrogen (H2) and provide a contribution to decarbonising the UK’s heat and power sectors with the focus on decarbonised fuel at point of use. Hydrogen has an ATEX Gas Group of IIC compared to IIA for natural gas which means further precautions are necessary to prevent the ignition of hydrogen during network operations. Both electrostatic and friction ignition risks were considered. Network operations considered include electrostatic precautions for polyethylene (PE) pipe and cutting and drilling of metallic pipes. As a result of the updated basis of safety from ignition considerations existing flow stopping methods were reviewed to see if they were compatible. Commonly used flow stopping methods were tested under laboratory conditions with hydrogen following the methodologies specified in the Gas Industry Standards (GIS). A new basis of safety for flow stopping has been proposed that looks at the flow past the secondary stop as double isolations are recommended for use with hydrogen.
Investigation of the Suitability of Viper: Blast CFD Software for Hydrogen and Vapor Cloud Explosions
Sep 2023
Publication
Many simplified methods for estimating blast loads from a hydrogen or vapor cloud explosion are unable to take into account the accurate geometry of confining spaces obstacles or landscape that may significantly interact with the blast wave and influence the strength of blast loads. Computation fluid dynamics (CFD) software Viper::Blast which was originally developed for the simulation of the detonation of high explosives is able to quickly and easily model geometry for blast analyses however its use for vapor cloud explosions and deflagrations is not well established. This paper describes the results of an investigation into the suitability of Viper::Blast for use in modeling hydrogen deflagration and detonation events from various experiments in literature. Detonation events have been captured with a high degree of detail and relatively little uncertainty in inputs while deflagration events are significantly more complex. An approach is proposed that may allow for a reasonable bounding of uncertainty potentially leading to an approach to CFD-based Monte Carlo analyses that are able to address a problem’s true geometry while remaining reasonably pragmatic in terms of run-time and computational investment. This will allow further exploration of practical CFD application to inform hydrogen safety in the engineering design assessment and management of energy mobility and transport systems infrastructure and operations.
CFD Simulation and ANN Prediction of Hydrogen Leakage and Diffusion Behavior in a Hydrogen Refuelling Station
Sep 2023
Publication
Hydrogen refuelling stations are an important part of the infrastructure for promoting the hydrogen economy. Since hydrogen is a flammable and explosive gas hydrogen released from high-pressure hydrogen storage equipment in hydrogen refuelling stations will likely cause combustion or explosion accidents. Studying high-pressure hydrogen leakage in hydrogen refuelling stations is a prerequisite for promoting hydrogen fuel cell vehicles and hydrogen refuelling stations. In this work an actual-size hydrogen refuelling station model was established on the ANSYS FLUENT software platform. The computational fluid dynamics (CFD) models for hydrogen leakage simulation were validated by comparing the simulation results with experimental data in the literature. The effects of ambient wind speed wind direction leakage rate and leakage direction on the diffusion behaviors of the released hydrogen were investigated. The spreading distances of the flammable hydrogen cloud were predicted using an artificial neural network for horizontal leakage. The results show that the leak direction strongly affected the flammable cloud flow. The ambient wind speed has complicated effects on spreading the flammable cloud. The wind makes the flammable cloud move in certain directions and the higher wind speed accelerates the diffusion of the flammable gas in the air. The results of the study can be used as a reference for the study of high-pressure hydrogen leakage in hydrogen refuelling stations.
A New Dimensionless Number for Type IV Composite Pressure Vessel Designer to Increase Efficiency and Reduce Cost
Sep 2023
Publication
A new dimensionless number (DN) is proposed in order to evaluate the performance of a high-pressure vessel composite structure. It shows that very few composite part is used at its maximum loading potential during bursting. Today for 70 MPa on-board type IV composite tanks DN values close to 20%. The suggested DN will be a useful indicator for an industrial application. By maximizing the DN at the design phase it is possible to minimize the mass of the composite structure of a CPV to reduce the manufacturing time and cost. To increase the DN as close as possible to 100% it is necessary to succeed in increasing the overall loading of the composite structure to have better oriented fibre. For this it seems necessary to find new processes which make it possible to better orient the fibre.
Experimental Study on the Effect of the Ignition Location on Vented Deflagration of Hydrogen-air Mixtures in Enclosure
Sep 2023
Publication
No countermeasures exist for accidents that might occur in hydrogen-based facilities (leaks fires explosions etc.). In South Korea discussions are underway regarding measures to ensure safety from such accidents such as the construction of underground hydrogen storage tank facilities. However explosion vents with a minimum ventilation area are required in such facilities to minimize damage to buildings and other structures due to accidental explosions. These explosion vents allow the generated overpressure and flames to be safely dispersed outside; however a safe separation distance must be secured to minimize damage to humans. This study aimed to determine the safe separation distance to minimize human damage after analyzing the dispersed overpressure and flame behavior following a vent explosion. Explosion experiments were conducted to investigate the influence of the ignition source location on internal and external overpressure and external flame behavior using a cuboid concrete structure with a volume of 20.33 m3 filled with a hydrogen-air mixture (29.0 vol.%). The impact on overpressure and flame was increased with the increasing distance of the ignition source from the vent. Importantly depending on the ignition location the incident pressure was up to 24.4 times higher while the reflected pressure was 8.7 times higher. Additionally a maximum external overpressure of 30.01 kPa was measured at a distance of 2.4 m from the vent predicting damage to humans at the “Injury” level (1 % fatality probability). Whereas no significant damage would occur at a distance of 7.4 m or more from the vent.
Modelling of Hydrogen Dispersion with Effects
Sep 2023
Publication
The paper shows the latest developments of Gexcon’s consequence modelling software EFFECTS with validation based on hydrogen experimental data for different storage conditions and scenarios including liquid hydrogen two-phase jet releases. The effect of atmospheric turbulence on the dispersion and potential worst-case scenarios of hydrogen which are very different from heavy gas releases are discussed. Beside validation for gaseous hydrogen releases a validation study for pressurised liquid hydrogen jet releases including a sensitivity analysis is performed and the results are compared with experimental data.
GT Enclosure Dispersion Analysis with Different CFD Tools
Sep 2023
Publication
A gas turbine is usually installed inside an acoustic enclosure where the fuel gas supply system is also placed. It is common practice using CFD analysis to simulate the accidental fuel gas release inside the enclosure and the consequent dispersion. These numerical studies are used to properly design the gas detection system according to specific safety criteria which are well defined when the fuel gas is a conventional natural gas. Package design is done to prevent that any sparking items and hot surfaces higher than auto-ignition temperature could be a source of ignition in case of leak. Nevertheless it is not possible to exclude that a leakage from a theoretical point of view could be ignited and for this reason a robust design requires that the enclosure structure is able to withstand the overpressure generated by a gas cloud ignition. Moving to hydrogen as fuel gas makes this design constraint much more relevant for its known characteristics of reactiveness large range of flammability maximum burning velocity etc. In such context gas leak and dispersion analysis become even more crucial because a correct prediction of these scenarios can guide the design to a safe configuration. The present work shows a comparison of the dispersion of different leakages inside a gas turbine enclosure carried out with two different CFD tools Ansys CFX and FLACS. This verification is considered essential since dispersion analysis results are used as initial conditions for gas cloud ignition simulations strictly necessary to predict the consequence in term of overpressure without doing experimental tests.
A SWOT Analysis of the Green Hydrogen Market
Jun 2024
Publication
Since the Industrial Revolution humanity has heavily depended on fossil fuels. Recognizing the negative environmental impacts of the unmoderated consumption of fossil fuels including global warming and consequent climate change new plans and initiatives have been established to implement renewable and sustainable energy sources worldwide. This has led to a rapid increase in the installed solar and wind energy capacity. However considering the fluctuating nature of these renewable energy sources green hydrogen has been proposed as a suitable energy carrier to improve the efficiency of energy production and storage. Thus green hydrogen produced by water electrolysis using renewable electricity is a promising solution for the future energy market. Moreover it has the potential to be used for the decarbonization of the heavy industry and transportation sectors. Research and development (R&D) on green hydrogen has grown considerably over the past few decades aiming to maximize production and expand its market share. The present work uses a SWOT (strengths weaknesses opportunities and threats) analysis to evaluate the current status of the green hydrogen market. The external and internal factors that affect its market position are assessed. The results show that green hydrogen is on the right track to becoming a competitive alternative to fossil fuels soon. Supported by environmental benefits government incentives and carbon taxes roadmaps to position green hydrogen on the energy map have been outlined. Nevertheless increased investments are required for further R&D as costs must be reduced and policies enforced. These measures will gradually decrease global dependency on fossil fuels and ensure that roadmaps are followed through.
Techno‐Economic Analysis of Hydrogen as a Storage Solution in an Integrated Energy System for an Industrial Area in China
Jun 2024
Publication
This study proposes four kinds of hybrid source–grid–storage systems consisting of pho‐ tovoltaic and wind energy and a power grid including different batteries and hydrogen storage systems for Sanjiao town. HOMER‐PRO was applied for the optimal design and techno‐economic analysis of each case aiming to explore reproducible energy supply solutions for China’s industrial clusters. The results show that the proposed system is a fully feasible and reliable solution for in‐ dustry‐based towns like Sanjiao in their pursuit of carbon neutrality. In addition the source‐side price sensitivity analysis found that the hydrogen storage solution was cost‐competitive only when the capital costs on the storage and source sides were reduced by about 70%. However the hydro‐ gen storage system had the lowest carbon emissions about 14% lower than the battery ones. It was also found that power generation cost reduction had a more prominent effect on the whole system’s NPC and LCOE reduction. This suggests that policy support needs to continue to push for genera‐ tion‐side innovation and scaling up while research on different energy storage types should be en‐ couraged to serve the needs of different source–grid–load–storage systems.
A Novel Hydrogen Supply Chain Optimization Model - Case Study of Texas and Louisiana
Jun 2024
Publication
The increasing political momentum advocating for decarbonization efforts has led many governments around the world to unveil national hydrogen strategies. Hydrogen is viewed as a potential enabler of deep decarbonization notably in hard-to-abate sectors such as the industry. A multi-modal hourly resolved linear programming model was developed to assess the infrastructure requirements of a low-carbon supply chain over a large region. It optimizes the deployment of infrastructure from 2025 up to 2050 by assessing four years: 2025 2030 2040 and 2050 and is location agnostic. The considered infrastructure encompasses several technologies for production transmission and storage. Model results illustrate supply chain requirements in Texas and Louisiana. Edge cases considering 100% electrolytic production were analyzed. Results show that by 2050 with an assumed industrial demand of 276 TWh/year Texas and Louisiana would require 62 GW of electrolyzers 102 GW of onshore wind and 32 GW of solar panels. The resulting levelized cost of hydrogen totaled $5.6–6.3/kgH2 in 2025 decreasing to $3.2–3.5/ kgH2 in 2050. Most of the electricity production occurs in Northwest Texas thanks to high capacity factors for both renewable technologies. Hydrogen is produced locally and transmitted through pipelines to demand centers around the Gulf Coast instead of electricity being transmitted for electrolytic production co-located with demand. Large-scale hydrogen storage is highly beneficial in the system to provide buffer between varying electrolytic hydrogen production and constant industrial demand requirements. In a system without low-cost storage liquid and compressed tanks are deployed and there is a significant renewable capacity overbuild to ensure greater electrolyzer capacity factors resulting in higher electricity curtailment. A system under carbon constraint sees the deployment of natural gas-derived hydrogen production. Lax carbon constraint target result in an important reliance on this production method due to its low cost while stricter targets enforce a great share of electrolytic production.
A Study on the Promoting Role of Renewable Hydrogen in the Transformation of Petroleum Refining Pathways
Jun 2024
Publication
The refining industry is shifting from decarbonization to hydrogenation for processing heavy fractions to reduce pollution and improve efficiency. However the carbon footprint of hydrogen production presents significant environmental challenges. This study couples refinery linear programming models with life cycle assessment to evaluate from a long-term perspective the role of low-carbon hydrogen in promoting sustainable and profitable hydrogenation refining practices. Eight hydrogen-production pathways were examined including those based on fossil fuels and renewable energy providing hydrogen for three representative refineries adopting hydrogenation decarbonization and co-processing routes. Learning curves were used to predict future hydrogen cost trends. Currently hydrogenation refineries using fossil fuels benefit from significant cost advantages in hydrogen production demonstrating optimal economic performance. However in the long term with increasing carbon taxes hydrogenation routes will be affected by the high carbon emissions associated with fossil-based hydrogen losing economic advantages compared to decarbonization pathways. With increasing installed capacity and technological advancements low-carbon hydrogen is anticipated to reach cost parity with fossil-based hydrogen before 2060. Coupling renewable hydrogen is expected to yield the most significant economic advantages for hydrogenation refineries in the long term. Renewable hydrogen drives the transition of refining processing routes from a decarbonization-oriented approach to a hydrogenation-oriented paradigm resulting in cleaner refining processes and enhanced competitiveness under emission-reduction pressures.
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