United Kingdom

The Hydrogen and Fuel Cell (H2FC) European research infrastructure cyber-laboratory is a software suite containing ‘modelling’ and ‘engineering’ tools encompassing a wide range of H2FC processes and systems. One of the core aims of the H2FC Cyber-laboratory has been the creation of a state-of-the-art hydrogen CFD modelling toolbox. This paper describes the implementation and validation of this new CFD modelling toolbox in conjunction with a selection of the available ‘Safety’ engineering tools to analyse a high pressure hydrogen release and dispersion scenario. The experimental work used for this validation was undertaken by Shell and the Health and Safety Laboratory (UK). The overall goal of this work is to provide and make readily available a Cyber-laboratory that will be worth maintaining after the end of the H2FC project for the benefit of both the FCH scientific community and industry. This paper therefore highlights how the H2FC Cyber-laboratory which is offered as an open access platform can be used to replicate and analyse real-world scenarios using both numerical engineering tools and through the implementation of CFD modelling techniques.

Correct use of Computational Fluid Dynamics (CFD) tools is essential in order to have confidence in the results. A comprehensive set of Best Practice Guidelines (BPG) in numerical simulations for Fuel Cells and Hydrogen applications has been one of the main outputs of the SUSANA project. These BPG focus on the practical needs of engineers in consultancies and industry undertaking CFD simulations or evaluating CFD simulation results in support of hazard/risk assessments of hydrogen facilities as well as on the needs of regulatory authorities. This contribution presents a summary of the BPG document. All crucial aspects of numerical simulations are addressed such as selection of the physical models domain design meshing boundary conditions and selection of numerical parameters. BPG cover all hydrogen safety relative phenomena i.e. release and dispersion ignition jet fire deflagration and detonation. A series of CFD benchmarking exercises are also presented serving as examples of appropriate modelling strategies.

Commercial use of hydrogen on-board fuel cell vehicles necessitates the compression of hydrogen gas up to 700 bar raising unique safety challenges. Potential hazards to be addressed include jet fires from high-pressure hydrogen on-board storage. Previous studies investigated effects of jet fires that occur when pressure relief devices (PRDs) on hydrogen fuel cell vehicles activate. This investigation examines plane jets’ axis switching and flame length accounting for compressibility effects and turbulent combustion near the point of release. Comparison with experimental data and previous plane jet simulation results reveal that combustion process does not affect flow dynamics in compressible region of jet flow. Furthermore a theoretical design of a variable aperture pressure relief device is examined which would enable the blow-down time to be minimized while reducing deterministic separation distances is examined using Computational Fluid Dynamics (CFD) techniques. Design recommendations are suggested for a novel PRD design.

The introduction of hydrogen into the UK natural gas main has been reviewed in terms of how materials within the gas distribution network may be affected by contact with up to 80% Natural Gas : 20 mol% hydrogen blend at up to 2 barg. A range of metallic polymeric and elastomeric materials in the gas distribution network (GDN) were assessed via a combination of literature review and targeted practical test programmes.

The work considered:

• The effect of hydrogen on metallic materials identified in the network
• The effect of hydrogen on polymeric materials identified in the network
• The effect of hydrogen exposure on polyethylene pipeline techniques (squeeze off and collar electrofusion)

The trials concluded that the majority of metallic materials showed no significant deterioration in mechanical (tensile) properties when stored in hydrogen environments compared to those stored in analogous methane or blended gas atmospheres up to 2barg. Polymeric materials showed no deterioration to efficiency of squeeze-off nor collar electrofusion in socket or shoulder orientations following soaking in hydrogen methane or hydrogen blends.

The characterization of liquid hydrogen (LH2) releases has been identified as an international research priority to expand the safe use of hydrogen as an energy carrier. The elucidation of LH2 release behavior will require the development of dispersion and other models guided and validated by empirical field measurements such as those afforded by Hydrogen Wide Area Monitoring (HyWAM). HyWAM can be defined as the quantitative spatial and temporal three-dimensional monitoring of planned or unintentional hydrogen releases. With support provided through the FCH JU Prenormative Research for the Safe Use of Liquid Hydrogen (PRESLHY) program HSE performed a series of LH2 releases to characterize the dispersion and pooling behavior of cold hydrogen releases. The NREL Sensor Laboratory developed a HyWAM system based upon a distributed array of point sensors that is amenable for profiling cold hydrogen plumes. The NREL Sensor Laboratory and HSE formally committed to collaborate on profiling the LH2 releases. This collaboration included the integration of the NREL HyWAM into the HSE LH2 release hardware. This was achieved through a deployment plan jointly developed by the NREL and HSE personnel. Under this plan the NREL Sensor Laboratory provided multiple HyWAM modules that accommodated 32 sampling points for near-field hydrogen profiling during the HSE PRESLHY LH2 releases. The NREL HyWAM would be utilized throughout the LH2 release study performed under PRESLHY by HSE including Work Package 3 (WP3—Release and Mixing--Rainout) and subsequent work packages (WP4—Ignition and WP5—Combustion). Under the auspices of the PRESLHY WP6 (Implementation) data and findings from the HSE LH2 Releases are to be made available to stakeholders in the hydrogen community. Comprehensive data analysis and dissemination is ongoing but the integration of the NREL HyWAM into the HSE LH2 Release Apparatus and its performance as well as some key outcomes of the LH2 releases in WP3 are presented.

This paper describes a CFD study of a scenario involving the vertical downward release of hydrogen from a thermally-activated pressure relief device (TPRD) under a fuel cell car. The volumetric source model is applied to simulate hydrogen release dynamics during the tank blowdown process. Simulations are conducted for both unignited and ignited releases from onboard storage at 35 MPa and 70 MPa with TPRD orifice 4.2 mm. Results show that after TPRD opening the hazards associated with the release of hydrogen lasts less than two minutes and the most hazardous timeframe occurs within ten seconds of the initiation of the release. The deterministic separation distances for unignited releases are longer than those for ignited releases indicating that the separation distances are dominated by delayed ignition events rather than immediate ignition events. The deterministic separation distances for both unignited and ignited hydrogen downward releases under the car are significantly shorter than those of free jets. To ensure the safety of people a deterministic separation distance of at least 10 m for 35 MPa releases is required. This distance should be increased to 12 m for the 70 MPa release case. To ensure that the concentration of hydrogen is always less than 4% at the location of the air intake of buildings the deterministic separation distance should be at least 11 m for 35 MPa releases and 13 m for 70 MPa releases.

In recent years new-found interest in the hydrogen economy from both industry and academia has helped to shed light on its potential. Hydrogen can enable an energy revolution by providing much needed flexibility in renewable energy systems. As a clean energy carrier hydrogen offers a range of benefits for simultaneously decarbonizing the transport residential commercial and industrial sectors. Hydrogen is shown here to have synergies with other low-carbon alternatives and can enable a more cost-effective transition to de-carbonized and cleaner energy systems. This paper presents the opportunities for the use of hydrogen in key sectors of the economy and identifies the benefits and challenges within the hydrogen supply chain for power-to-gas power-to-power and gas-to-gas supply pathways. While industry players have already started the market introduction of hydrogen fuel cell systems including fuel cell electric vehicles and micro-combined heat and power devices the use of hydrogen at grid scale requires the challenges of clean hydrogen production bulk storage and distribution to be resolved. Ultimately greater government support in partnership with industry and academia is still needed to realize hydrogen's potential across all economic sectors.

Link to document download on Royal Society Website

Numerical investigations have been conducted on the effect of the internal geometry of a local contraction on the spontaneous ignition of pressurized hydrogen release through a length of tube using a 5th-order WENO scheme. A mixture-averaged multi-component approach was used for accurate calculation of molecular transport. The auto-ignition and combustion chemistry were accounted for using a 21-step kinetic scheme. It is found that a local contraction can significantly facilitate the occurrence of spontaneous ignition by producing elevated flammable mixture and enhancing turbulent mixing from shock formation reflection and interaction. The first ignition kernel is observed upstream the contraction. It then quickly propagates along the contact interface and transits to a partially premixed flame due to the enhanced turbulent mixing. The partially premixed flames are highly distorted and overlapped with each other. Flame thickening is observed which is due to the merge of thin flames. The numerical predictions suggested that sustained flames could develop for release pressure as low as 25 bar. For the release pressure of 18 bar spontaneous ignition was predicted but the flame was soon quenched. To some extent this finding is consistent with Dryer et al.'s experimental observation in that the minimum release pressure required to induce a spontaneous ignition for the release through a tube with internal geometries is only 20.4 bar.

Previous studies have demonstrated that while blowdown pressure is reproduced well by both adiabatic and isothermal analytical models the dynamics of temperature cannot be predicted well by either model. The reason for the last is heat transfer to cooling during expansion gas from the vessel wall. Moreover when exposed to an external fire the temperature inside the vessel increases i.e. when a thermally activated pressure relief device (TPRD) is still closed with subsequent pressure increase that may lead to a catastrophic rupture of the vessel. The choice of a TPRD exit orifice size and design strategy are challenges: to provide sufficient internal pressure drop in a fire when the orifice size is too small; to avoid flame blow off expected with the decrease of pressure during the blowdown; to decrease flame length of subsequent jet fire as much as possible by the decrease of the orifice size under condition of sufficient fire resistance provisions to avoid pressure peaking phenomenon etc. The adiabatic model of blowdown [1] was developed using the Abel-Nobel equation of state and the original theory of underexpanded jet [2]. According to experimental observations e.g. [3] heat transfer plays a significant role during the blowdown. Thus this study aims to modify the adiabatic blowdown model to include the heat transfer to non-ideal gas. The model accounts for a change of gas temperature inside the vessel due to two “competing” processes: the decrease of temperature due to gas expansion and the increase of temperature due to heat transfer from the surroundings e.g. ambience or fire through the vessel wall. This is taken into account in the system of equations of adiabatic blowdown model through the change of energy conservation equation that accounts for heat from outside. There is a need to know the convective heat transfer coefficient between the vessel wall and the surroundings and wall size and properties to define heat flux to the gas inside the vessel. The non-adiabatic model is validated against available experimental data. The model can be applied as a new engineering tool for the inherently safer design of hydrogen tank-TPRD system.

Having a robust evidence base enables us to tackle real issues causing pain and suffering in the workplace. Critically it enables us to better understand developing issues and ways of working to ensure that we support innovation rather than stifle it through lack of knowledge. For example the work on the use of 3D printers in schools demonstrates HSE’s bility to engage and understand the risks to encourage safe innovation in a developing area (see p47).<br/>Other examples in this report show just a selection of the excellent work carried out by our staff often collaborating with others which contributes to improving how we regulate health and safety risks proportionately and effectively.<br/>One of HSEs key priorities is to prevent future cases of occupational lung disease by improving the management and control of hazardous substances. The case study on measuring Respirable Crystalline Silica exposure contributes to this and to recognise developing and future issues such as the work on diacetyl in the coffee industry (see p24 and p39). This type of scientific investigation gives our regulators good trusted information enabling critical decisions on the actions needed to protect workers.<br/>The case study on publishing new guidance on the use of Metalworking Fluids (MWF) demonstrates the important contribution of collaborative science to improving regulation. If used inappropriately exposure to MWF mist can cause serious long-term lung disease and it was recognised that users needed help to control this risk. HSE scientists and regulators worked with industry stakeholders to produce new free guidance which reflects changes in scientific understanding in a practical easy to use guide. As well as enabling users to better manage the risks and as a bonus likely save money it has assisted regulation by providing clear benchmarks for all to judge control against. An excellent example of science contributing to controlling serious health risks (see p22).<br/>These case studies are excellent examples of how science contributes to reducing risk. Hopefully they will inspire you to think about how risk in your workplace could be improved and where further work might be needed.