Safety

This work programme was focused on identifying a suitable odorant for use in a 100% hydrogen gas grid (domestic use such as boilers and cookers). The research involved a review of existing odorants (used primarily for natural gas) and the selection of five suitable odorants based on available literature. One odorant was selected based on possible suitability with a Polymer Electrolyte Membrane (PEM) based fuel cell vehicle which could in future be a possible end-user of grid hydrogen. NPL prepared Primary Reference Materials containing the five odorants in hydrogen at the relevant amount fraction levels (as would be found in the grid) including ones provided by Robinson Brothers (the supplier of odorants for natural gas in the UK). These mixtures were used by NPL to perform tests to understand the effects of the mixtures on pipeline (metal and plastic) appliances (a hydrogen boiler provided by Worcester Bosch) and PEM fuel cells. HSE investigated the health and environmental impact of these odorants in hydrogen. Olfactory testing was performed by Air Spectrum to characterise the ‘smell’ of each odorant. Finally an economic analysis was performed by E4tech. The results confirm that Odorant NB would be a suitable odorant for use in a 100% hydrogen gas grid for combustion applications but further research would be required if the intention is to supply grid hydrogen to stationery fuel cells or fuel cell vehicles. In this case further testing would need to be performed to measure the extent of fuel cell degradation caused by the non-sulphur odorant obtained as part of this work programme and also other UK projects such as the Hydrogen Grid to Vehicle (HG2V) project would provide important information about whether a purification step would be required regardless of the odorant before the hydrogen purity would be suitable for a PEM fuel cell vehicle. If purification was required it would be fine to use Odorant NB as this would be removed during the purification step.

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We investigate an appropriate initial burst pressure of compressed hydrogen containers that correlates with a residual burst pressure requirement at the end of life (EOL) and report an influence of hydraulic sequential tests on residual burst pressure. Results indicate that a container damage caused by a drop  test during hydraulic sequential tests has a large influence on burst pressure. The container damage induced through hydraulic sequential tests is investigated using non-destructive evaluations to clarify a strength decreasing mechanism. An ultrasonic flaw detection analysis is conducted before and after the drop test and indicated that the damage occurred at the cylindrical and dome parts of the container after the drop test. An X-ray computed tomography imaging identifies a delamination inside laminated structure made of carbon fiber reinforced plastics (CFRP) layer with some degree of delamination reaching the end boss of the container. Results suggest that a load profile fluctuates in the CFRP layer at the dome part and that a burst strength of the dome part decreases. Therefore an observed decreasing in drop damage at the dome part can be used to prevent a degradation of EOL container burst strength.

Certification of hydrogen sensors to meet standards often prescribes using large-volume test chambers. However feedback from stakeholders such as sensor manufacturers and end-users indicates that chamber test methods are often viewed as too slow and expensive for routine assessment. Flow-through test methods are potentially an efficient and cost-effective alternative for sensor performance assessment. A large number of sensors can be simultaneously tested in series or in parallel with an appropriate flow-through test fixture. The recent development of sensors with response times of less than 1s mandates improvements in equipment and methodology to properly capture the performance of this new generation of fast sensors; flow methods are a viable approach for accurate response and recovery time determinations but there are potential drawbacks. According to ISO 26142 flow-through test methods may not properly simulate ambient applications. In chamber test methods gas transport to the sensor is dominated by diffusion which is viewed by some users as mimicking deployment in rooms and other confined spaces. Conversely in flow-through methods forced flow transports the gas to the sensing element. The advective flow dynamics may induce changes in the sensor behaviour relative to the quasi-quiescent condition that may prevail in chamber test methods. The aim of the current activity in the JRC and NREL sensor laboratories is to develop a validated flow-through apparatus and methods for hydrogen sensor performance testing. In addition to minimizing the impact on sensor behaviour induced by differences in flow dynamics challenges associated with flow-through methods include the ability to control environmental parameters (humidity pressure and temperature) during the test and changes in the test gas composition induced by chemical reactions with upstream sensors. Guidelines on flow-through test apparatus design and protocols for the evaluation of hydrogen sensor performance have been developed. Various commercial sensor platforms (e.g. thermal conductivity catalytic and metal semiconductor) were used to demonstrate the advantages and issues with the flow-through methodology.

The safe decommissioning as well as decontamination of the radioactive waste resulting from the nuclear accident in Fukushima Daiichi represents a huge task for the next decade. At present research and development on long-term safe storage containers has become an urgent task with international cooperation in Japan. One challenge is the generation of hydrogen and oxygen in significant amounts by means of radiolysis inside the containers as the nuclear waste contains a large portion of sea water. The generation of radiolysis gases may lead to a significant pressure build-up inside the containers and to the formation of flammable gases with the risk of ignition and the loss of integrity.

In the framework of the project “R&D on technology for reducing concentration of flammable gases generated in long-term waste storage containers” funded by the Japanese Ministry of Education Culture Sports Science and Technology of Japan (MEXT) the potential application of catalytic recombiner devices inside the storage containers is investigated. In this context a suitable catalyst based on the so-called intelligent automotive catalyst for use in a recombiner is under consideration. The catalyst is originally developed and mass-produced for automotive exhaust gas purification and is characterized by having a self-healing function of precious metals (Pd Pt and Rh) dissolved as a solid solution in the perovskite type oxides. The basic features of this catalyst have been tested in an experimental program. The test series in the REKO-4 facility has revealed the basic characteristics of the catalyst required for designing the recombiner system.

Vented deflagrations are one of the most challenging phenomenon to be replicated numerically in order to predict its resulting pressure time history. As a matter of fact a number of different phenomena can contribute to modify the burning velocity of a gas mixture undergoing a deflagration especially when the flame velocity is considerably lower than the speed of sound. In these conditions acceleration generated by both the flow field induced by the expanding flame and from discontinuities as the vent opening and the venting of the combustion products affect the burning velocity and the burning behaviour of the flame. In particular the phenomena affecting the pressure time history of a deflagration after the flame front reaches the vent area such as flame acoustic interaction and local pressure peaks seem to be closely related to a change in the burning behaviour induced by the venting process. Flame acoustic interaction and local pressure peaks arise as a consequence of the change in the burning behaviour of the flame. This paper analyses the video recording of the flame front produced during the TP experimental campaign performed by UNIPI in the project HySEA to analyse qualitatively the contribution of the generated flow field in a vented deflagration in its pressure-time history.

The possibility of flame acceleration (FA) and deflagration-to-detonation transition (DDT) when homogeneous hydrogen-carbon monoxide-air (H2-CO-air) mixtures are used rises the need for an efficient simulation approach for safety assessment. In this study a modelling approach for H2-CO-air flames incorporating deflagration and detonation within one framework is presented. It extends the previous work on H2-air mixtures. The deflagration is simulated by means of the turbulent flame speed closure model incorporating a quenching term. Since high flow velocities e.g. the characteristic speed of sound of the combustion products are reached during FA the flow passing obstacles generates turbulence at high enough levels to partially quench the flame. Partial flame quenching has the potential to stall the onset of detonation. An altered formulation for quenching is introduced to the modelling approach to better account for the combustion characteristics for accelerating lean H2-CO-air flames. The presented numerical approach is validated with experimental flame velocity data of the small-scale GraVent test rig [1] with homogeneous fuel contents of 22.5 and 25.0 vol-% and fuel compositions of 75/25 and 50/50 vol-% H2/CO respectively. The impact of the quenching term is further discussed on simulations of the FZK-7.2m test rig [2] whose obstacle spacing is smaller than the spacing in the GraVent test rig.

This paper examines the helium dispersion behaviour in a 16.6 m3 enclosure with a small opening in the floor and distributed leaks along the edges. Helium a simulant for hydrogen was injected near the center of the floor with an injection rate ranging from 2 to 50 standard liters per minute (Richardson number of 0.3–134) through an upward-facing nozzle. In a short-term transient the helium distribution predicted with the models of Baines & Turner (1969) and Worster & Huppert (1983) matched the measured distributions reasonably well. In a long-term transient the vertical helium profile always reached a steady state which consisted of a homogenous layer at the top overlaying a stratified layer at the bottom. The helium transients in the uniform layer predicted with the models of Lowesmith (2009) and Prasad & Yang (2010) assuming a vent was located in the ceiling were in good agreement with the measured transients.

This paper compares two approaches for predicting the consequences of vented hydrogen deflagrations: empirical engineering models (EMs) and computational fluid dynamics (CFD) simulations. The study is part of the project ‘Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations’ (HySEA) funded by the Fuel Cells and Hydrogen 2 Joint Undertaking (FCH JU) under grant agreement No 671461. The HySEA project focuses on vented hydrogen deflagrations in containers and smaller enclosures with internal congestion representative of industrial applications. Data from experiments conducted as part of the HySEA project are used to evaluate predictions from a selection of EMs and the CFD tool FLACS. The experiments involve various obstacle and venting configurations and initially quiescent homogeneous hydrogen-air mixtures with hydrogen concentrations in the range 15–24 vol%. There is a significant scatter in the maximum reduced overpressures predicted by the different EMs in the present study. For certain configurations there is an order of magnitude difference between the different EM predictions. Two versions of the CFD tool FLACS are used in the present study: i) the standard commercial release FLACS v10.7r2 and ii) an in-house development version termed FLACS-beta. The commercial release generally over-predicts the maximum overpressures measured in the experiments while the development version of FLACS gives improved results for several configurations.

In the context of the fatigue life design of components particularly those destined for use in hydrogen refuelling stations and fuel cell vehicles it is important to understand the hydrogen-induced fatigue crack growth (FCG) acceleration in steels. As such the mechanisms for acceleration and its influencing factors are reviewed and discussed in this paper with a special focus on the peculiar frequency dependence of the hydrogen-induced FCG acceleration. Further this frequency dependence is debated by introducing some potentially responsible elements along with new experimental data obtained by the authors.

This article is part of the themed issue ‘The challenges of hydrogen and metals’.

Link to document download on Royal Society Website

With downward trends in Australian equipment manufacturing there are increased numbers of overseas designed manufactured and certified hydrogen systems being introduced into Australia. In parallel there are also opportunities for hydrogen and its carriers to be exported to overseas. Certainty of reputable codes and standards is important to meet regulatory requirements and community safety expectations locally and overseas.

This paper is a progress report of Hydrogen Mobility Australia’s (HMA) Technical Committee on mapping the regulatory codes and standards (RCS) gaps in Australia and establishing a pathway together with Standards Australia and Commonwealth and State Governments. This paper will discuss the benefits of the pathway covering the areas of:

• Safety – Enable Australia to implement consensual rules to minimise avoidable risks to persons and goods to an acceptable level
• Environment – Ensure protection of the environment from unacceptable damage due to the operation and effects of products processes and services linked to hydrogen
• Elimination of barriers to trade – Provide consistency between international jurisdictions enabling streamlined entry of hydrogen related equipment from overseas
• Upskilling of Australian industry participants – Gain useful learnings from countries more advanced in their progress in implementing ISO standards and hydrogen sector development

This paper is jointly prepared by representatives of HMA Technical Committee and Department of Energy and Mining South Australian Government. The paper also highlights the initiatives of Commonwealth and State Governments to advance the hydrogen economy.