United States

The objective of this work was to enable the safe design of hydrogen pressure vessels by measuring the fatigue crack growth rates of ASME code-qualified steels in high-pressure hydrogen gas. While a design framework has recently been established for high-pressure hydrogen vessels a material property database does not exist to support the design calculations. This study addresses such voids in the database by measuring the fatigue crack growth rates of three different heats of ASME SA-372 Grade J steel in 100 MPa hydrogen gas. Results showed that the fatigue crack growth rates were similar for all three steel heats although the highest-strength steel appeared to exhibit the highest growth rates. Hydrogen accelerated the fatigue crack growth rates of the steels by as much as two orders of magnitude relative to anticipated crack growth rates in inert environments. Despite such dramatic effects of hydrogen on the fatigue crack growth rates measurement of these properties enables reliable definition of the design life of steel hydrogen containment vessels.

The ignition limits of hydrogen/air mixtures in turbulent jets are necessary to establish safety distances based on ignitable hydrogen location for safety codes and standards development. Studies in turbulent natural gas jets have shown that the mean fuel concentration is insufficient to determine the flammable boundaries of the jet. Instead integration of probability density functions (PDFs) of local fuel concentration within the quiescent flammability limits termed the flammability factor (FF) was shown to provide a better representation of ignition probability (PI). Recent studies in turbulent hydrogen jets showed that the envelope of ignitable gas composition (based on the mean hydrogen concentration) did not correspond to the known flammability limits for quiescent hydrogen/air mixtures. The objective of this investigation is to validate the FF approach to the prediction of ignition in hydrogen leak scenarios. The PI within a turbulent hydrogen jet was determined using a pulsed Nd:YAG laser as the ignition source. Laser Rayleigh scattering was used to characterize the fuel concentration throughout the jet. Measurements in methane and hydrogen jets exhibit similar trends in the ignition contour which broadens radially until an axial location is reached after which the contour moves inward to the centerline. Measurements of the mean and fluctuating hydrogen concentration are used to characterize the local composition statistics conditional on whether the laser spark results in a local ignition event or complete light-up of a stable jet flame. The FF is obtained through direct integration of local PDFs. A model was developed to predict the FF using a presumed PDF with parameters obtained from experimental data and computer simulations. Intermittency effects that are important in the shear layer are incorporated in a composite PDF. By comparing the computed FF with the measured PI we have validated the flammability factor approach for application to ignition of hydrogen jets.

Hydrogen is a notoriously difficult substance to store yet has endless energy applications. Thus the study of long-term hydrogen storage and high-pressure bulk hydrogen storage have been the subject of much research in the last several years. To create a research path forward it is important to know what research has already been done and what is already known about hydrogen storage. In this review several approaches to hydrogen storage are addressed including high-pressure storage cryogenic liquid hydrogen storage and metal hydride absorption. Challenges and advantages are offered based on reported research findings. Since the project looks closely at advanced manufacturing techniques for the same are outlined as well. There are seven main categories into which most rapid prototyping styles fall. Each is briefly explained and illustrated as well as some generally accepted advantages and drawbacks to each style. An overview of hydrogen adsorption on metal hydrides carbon fibers and carbon nanotubes are presented. The hydrogen storage capacities of these materials are discussed as well as the differing conditions in which the adsorption was performed under. Concepts regarding storage shape and materials accompanied by smaller-scale advanced manufacturing options for hydrogen storage are also presented.

For hydrogen fuelled vehicles to attain significant market penetration it is essential that any potential risks be controlled within acceptable levels. To achieve this goal on-board vehicle hydrogen storage systems should undergo risk analyses during early concept development and design phases. By so doing the process of eliminating safety-critical failure modes will help guide storage system development and be more efficient to implement than if undertaken after the design-freeze stage. The focus of this paper is the development of quantitative risk analyses of storage systems which use onboard reversible materials such as conventional AB5 metal hydrides the complex hydride NaAlH4 or other material candidates currently being researched. Collision of a vehicle having such a hydrogen storage system was selected as a dominant accident initiator and a probabilistic event tree model has been developed for this initiator. The event tree model contains a set of comprehensive mutually exclusive accident sequences. The event tree represents chronological ordering of key events that are postulated to occur sequentially in time during the accident progression. Each event may represent occurrence of a phenomenon (e.g. hydride chemical reaction and dust cloud explosion) or a hardware failure (e.g. hydride storage vessel rupture). Event tree branch probabilities can be quantified using fault tree models or basic events with probability distributions. A fault tree model for hydride dust cloud explosion is provided as an example. Failure probabilities assigned to the basic events in the fault tree can be estimated from test results published data or expert opinion elicitation. To account for variabilities in the probabilities assigned to fault tree basic events and hence to propagate uncertainties in event tree sequences Monte Carlo sampling and Latin Hypercube sampling were employed and the statistics of the results from both techniques were compared.

We have analyzed vacuum insulation failure in an automotive cryogenic pressure vessel (also known as cryo-compressed vessel) storing hydrogen (H2). Vacuum insulation failure increases heat transfer into cryogenic vessels by about a factor of 100 potentially leading to rapid pressurization and venting to avoid exceeding maximum allowable working pressure (MAWP). H2 release to the environment may be dangerous if the vehicle is located in a closed space (e.g. a garage or tunnel) at the moment of insulation failure. We therefore consider utilization of the hydrogen in the vehicle fuel cell and electricity dissipation through operation of vehicle accessories or battery charging as an alternative to releasing hydrogen to the environment. We consider two strategies: initiating hydrogen extraction immediately after vacuum insulation failure or waiting until MAWP is reached before extraction. The results indicate that cryogenic pressure vessels have thermodynamic advantages that enable slowing down hydrogen release to moderate levels that can be consumed in the fuel cell and dissipated onboard the vehicle even in the worst case when the vacuum fails with a vessel storing hydrogen at maximum refuel density (70 g/L at 300 bar). The two proposed strategies are therefore feasible and the best alternative can be chosen based on economic and/or implementation constraints.

Hydrogen sensors are recognized as an important technology for facilitating the safe implementation of hydrogen as an alternative fuel and there are numerous reports of a sensor alarm successfully preventing a potentially serious event. However gaps in sensor metrological specifications as well as in their performance for some applications exist. The U.S. Department of Energy (DOE) Fuel Cell Technologies Office published a short list of critical gaps in the 2007 and 2012 Multiyear Project Plans; more detailed gap analyses were independently performed by the Joint Research Centre (JRC) and the National Renewable Energy Laboratory (NREL). There have been however some significant advances in sensor technologies since these assessments including the commercial availability of hydrogen sensors with fast response times (t90 < 1 s which had been an elusive DOE target since 2007) improved robustness to chemical poisons improved selectivity and improved lifetime and stability. These improvements however have not been universal and typically pertain to select platforms or models. Moreover as hydrogen markets grow and new applications are being explored more demands will be imposed on sensor performance. The hydrogen sensor laboratories at NREL and the JRC are currently updating the hydrogen safety sensor gap analysis through direct interaction with international stakeholders in the hydrogen community especially end users. NREL and the JRC are currently organizing a series of workshops (in Europe and the United States) with sensor developers end-users and other stakeholders in 2017 to identify technology gaps and to develop a path forward to address them. One workshop was held on May 10 in Brussels Belgium at the Headquarters of the Fuel Cell and Hydrogen Joint Undertaking. A second workshop is planned at NREL in Golden CO USA. This paper reviews improvements in sensor technologies in the past 5 to 10 years identifies gaps in sensor performance and use requirements and identifies potential research strategies to address the gaps. The outcomes of the Hydrogen Sensors Workshops are also summarized.

Hydrogen has the potential to be used by many countries as part of decarbonising the future energy system. Hydrogen can be used as a fuel ‘vector’ to store and transport energy produced in low-carbon ways. This could be particularly important in applications such as heating and transport where other solutions for low and zero carbon emission are difficult. To enable the safe uptake of hydrogen technologies it is important to develop the international scientific evidence base on the potential risks to safety and how to control them effectively. The International Association for Hydrogen Safety (known as IA HySAFE) is leading global efforts to ensure this. HSE hosted the 2018 IA HySAFE Biennial Research Priorities Workshop. A panel of international experts presented during nine key topic sessions: (1) Industrial and National Programmes; (2) Applications; (3) Storage; (4) Accident Physics – Gas Phase; (5) Accident Physics – Liquid/ Cryogenic Behaviour; (6) Materials; (7) Mitigation Sensors Hazard Prevention and Risk Reduction; (8) Integrated Tools for Hazard and Risk Assessment; (9) General Aspects of Safety.<br/>This report gives an overview of each topic made by the session chairperson. It also gives further analysis of the totality of the evidence presented. The workshop outputs are shaping international activities on hydrogen safety. They are helping key stakeholders to identify gaps in knowledge and expertise and to understand and plan for potential safety challenges associated with the global expansion of hydrogen in the energy system.

In conjunction with John Zink Co. LLC the Chevron Energy Technology Company conducted a three part study evaluating potential issues with switching refinery process heaters from fuel gas to hydrogen fuel for the purpose of greenhouse gas emissions reduction via CO2 capture and storage.

The focus was on the following areas:

• Heater performance
• Burner performance and robustness
• Fuel gas system retrofit requirements

This paper will summarize the findings of the study.

Various studies and market trends show that the number of hydrogen fuelling stations will increase to the thousands in the US by 2050. NFPA 2 Hydrogen Technologies Code (NFPA2) the nationally adopted primary code governing hydrogen safety is relatively new and hydrogen vehicle technology is a relatively new and rapidly developing technology. In order to effectively aid and accelerate the deployment of standardized retail hydrogen fuelling facilities the permitting of hydrogen fuelling stations employing outdoor bulk liquid storage in the state of California.

In an effort to better understand how the applicants consultants and more importantly the Authorities Having Jurisdiction (AHJ)s are interpreting and applying the NFPA 2 especially for complex applications the newest hydrogen stations with the largest amount of bulk hydrogen storage in urban environment settings were identified and the permit applications and permit approval outcomes of the said stations were analysed. Utilizing the pubic record request process LH2 station permit applications were reviewed along with the approval outcomes directly from the municipalities that issued the permits. AHJs with H2 station permitting experience were interviewed. Case studies of permit hydrogen fuelling station permit applications were then complied to document both the perspectives of the applicant and the AHJ and the often iterative and collaborative nature of permitting.

The current permitting time for Liquid Hydrogen (LH2) stations can range from 9 to 18 months in the California. Five out of the six LH2 stations applications required Alternative Means & Methods (AM&Ms) proposals and deviations from the prescriptive requirements of the Code were granted. Furthermore AHJs often requested additional documents and studies specific to application parameters in addition to NFPA 2 requirements.

Reliable methods are needed to predict ignition boundaries that result from compressed hydrogen bulk storage leaks without complex modelling. To support the development of these methods a new high-pressure stagnation chamber has been integrated into Sandia National Laboratories’ Turbulent Combustion Laboratory so that relevant compressed gas release scenarios can be replicated. For the present study a jet with a 10:1 pressure ratio issuing from a small 0.75 mm radius nozzle has been examined. Jet exit shock structure was imaged by Schlieren photography while quantitative Planar Laser Rayleigh Scatter imaging was used to measure instantaneous hydrogen mole fractions downstream of the Mach disk. Measured concentration statistics and ignitable boundary predictions compared favorably to analytic reconstructions of downstream jet dispersion behaviour. Model results were produced from subsonic jet dispersion models and by invoking self-similarity jet scaling arguments with length scaling by experimentally measured effective source radii. Similar far field reconstructions that relied on various notional nozzle models to account for complex jet exit shock phenomena failed to satisfactorily predict the experimental findings. These results indicate further notional nozzle refinement is needed to improve the prediction fidelity. Moreover further investigation is required to understand the effect of different pressure ratios on measured virtual origins used in the jet dispersion model.