STATE OF THE ART AND RESEARCH PRIORITIES IN HYDROGEN SAFETY

Wide spread deployment and use of hydrogen and fuel cell technologies can occur only if hydrogen safety issues have been addressed in order to ensure that hydrogen fuel presents the same or lower level of hazards and associated risk compared to conventional fuel technologies. To achieve this goal, hydrogen safety research should be directed to address the remaining knowledge gaps using risk-informed approaches to develop engineering solutions and Regulation Codes and Standards (RCS) requirements that meet individual and societal risk acceptance criteria, yet are cost-effective and market-competitive. IA HySafe and JRC IET partnered to organize a Research Priorities Workshop in Berlin on October 16-17, 2012 hosted by BAM (on behalf of IA HySafe) to address knowledge gaps in CFD modelling of hydrogen safety issues. The findings of the workshop are described in the report. The document aims to become a reference document for researchers/scientists and technical (including industry) experts working in the area worldwide. It is also a welcomed contribution for the Fuel Cell and Hydrogen Joint Undertaking (FCH JU) and for other funding bodies/organizations that must make decisions on research programmes and during the selection/choice of projects to be financially supported pursuing the safe use of hydrogen within Horizon 2020 framework.JRC.F.2-Energy Conversion and Storage Technologie

Gap Analysis of CFD Modelling of Accidental Hydrogen Release and Combustion

The report describes the findings of a workshop that was held at the Institute for Energy (JRC) in Petten Netherlands, on the topic "Gap analysis of CFD modelling of hydrogen release and combustion". The main topic was divided in 6 sub-topics: release and dispersion, auto-ignition, fires, deflagrations, detonations and DDT, and accident consequences. For each sub-topic, the main gaps in CFD modelling were identified and prioritised.JRC.DDG.F.2-Cleaner energ

Prioritisation of Research and Development for modelling the safe production, storage, delivery and use of hydrogen.

Hydrogen is expected to play an important role in the energy mix of a future low carbon society, (the European Strategic Energy Technology Plan of the European Commission (COM 2007 - 723) and in the Hydrogen, Fuel Cells & Infrastructure Technologies Program-Multi-Year Research, Development, and Demonstration Plan of the USA Department of Energy (DoE 2007). Hydrogen safety issues must be addressed in order to ensure that the wide spread deployment and use of hydrogen and fuel cell technologies can occur with the same or lower level of hazards and associated risk compared to the conventional fossil fuel technologies. Hydrogen safety is a EU Policy relevant issue as it is stated in the priority 3 Action 2 (Continuous improvement in safety and security) of the EU “Energy 2020 A strategy for competitive, sustainable and secure energy”: “The same security and safety considerations will also be upheld in the development and deployment of new energy technologies (hydrogen safety, safety of CO2 transportation network, CO2 storage, etc…)” Computational Fluid Dynamics (CFD) is one of the tools to investigate safety issues related to the production, storage, delivery and use of hydrogen. CFD techniques can provide a wealthy amount of information on the dynamics of hypothetical hydrogen accident and its consequences. The CFD-based consequence analysis is then used in risk assessments. This report describes the output of a workshop organised at the Institute for Energy and Transport (JRC) in Petten, Netherlands to identify the gaps and issues in CFD modelling of hydrogen release and combustion. A hydrogen accident usually follows a typical sequence of events: an unintended release, the mixing of hydrogen with air to form a flammable mixture, the ignition of the flammable cloud and depending on the conditions, and a fire or an explosion (deflagration or/and detonation). For each stage of the accident, the critical CFD issues have been identified and prioritised. Beyond the specific issues of CFD modelling that are described for each accident stage in the report, some general modelling issues can be found in all stages: • lack of an extensive validation of CFD codes/models that covers all the relevant range of conditions that can be found in hypothetical accident scenarios e.g. in terms of geometrical lay-out, leak flow rates. • lack of a CFD validation protocol for hydrogen like it exists for Liquefied Natural Gas (LNG): the Model Evaluation Protocols (MEP) for assessment of models for accident consequences, with guidance on evaluating models in terms of scientific assessment, verification and validation. • lack of a database of experiments for validation of hydrogen models. • in some cases, lack of complete and accurate experimental data for the CFD validation. The goals of this work were to perform a state of the art review in CFD modelling of hypothetical accidents scenarios related to hydrogen technologies and identify and prioritise the gaps in the field. The report is based on a dedicated workshop organised in Petten with the participation of external experts an extensive literature review performed by experts in the field and the direct expertise and experience of the experts. The experts were carefully selected according to their experience/expertise, number of scientific publications and participations to International Conferences, seminars, workshops and to international and/or European co-funded projects such as HySafe (Hydrogen Safety), HyApproval (Approval of Hydrogen Re-fuelling Stations), European Integrated Hydrogen Projects. By performing a state of the art review of CFD modelling for hydrogen safety issues, a consensus was reached among the scientific experts as to the main gaps in the field and on the priority of the research needs.JRC.F.2-Cleaner energ

STATE-OF-THE-ART AND RESEARCH PRIORITIES IN HYDROGEN SAFETY

On October 16-17, 2012, the International Association for Hydrogen Safety (HySafe) in cooperation with the Institute for Energy and Transport of the Joint Research Centre of the European Commission (JRC IET Petten) held a two-day workshop dedicated to Hydrogen Safety Research Priorities. The workshop was hosted by Federal Institute for Materials Research and Testing (BAM) in Berlin, Germany. The main idea of the Workshop was to bring together stakeholders who can address the existing knowledge gaps in the area of the hydrogen safety, including identification and prioritization of such gaps from the standpoint of scientific knowledge, both experimental and theoretical including numerical. The experience highlighting these gaps which was obtained during both practical applications (industry) and risk assessment should serve as reference point for further analysis. The program included two sections: knowledge gaps as they are addressed by industry and knowledge gaps and state-of-the-art by research. In the current work the main results of the workshop are summarized and analysed.JRC.F.2-Cleaner energ

An Intercomparisation of CFD Models to Predict Lean and Non-Uniform Hydrogen Mixture Explosions

The paper describes an exercise on comparison of Computational Fluid Dynamics (CFD) models to predict deflagrations of a lean uniform hydrogen-air mixture and a mixture with hydrogen concentration gradient. The exercise was conducted within the work-package "Standard Benchmark Exercise Problem" of the EC funded Network of Excellence "Hydrogen Safety as an Energy Carrier", which seeks to provide necessary accuracy in the area of applied hydrogen safety simulations. The experiments on hydrogen-air mixture deflagrations in a closed 1.5 m in diameter and 5.7 m high cylindrical vessel were chosen as a benchmark problem to validate CFD codes and combustion models used for prediction of hazards in safety engineering. Simulations of two particular experiments with approximately the same amount of hydrogen were conducted: deflagration of a uniform 12.8% vol. hydrogen mixture and deflagration of a non-uniform hydrogen mixture, corresponding to an average12.6% vol. hydrogen concentration (27% at the top of the vessel, 2.5% at the bottom of the vessel) with ignition at the top of the vessel in both cases. The comparison of the simulation results for pressure and flame dynamics against the experimental data is reported.JRC.F.2-Cleaner energ

Modelling of Lean Uniform and Non-Uniform Hydrogen-Air Mixture Explosions in a Large-Scale Closed Vessel

Simulation of hydrogen-air mixture explosions in a closed large-scale vessel with uniform and non-uniform mixture compositions was performed by the group of partners within the EC funded project ¿Hydrogen Safety as an Energy Carrier¿ (HySafe). Several experiments were conducted previously by Whitehouse et al. in a 10.7 m3 vertically oriented (5.7-m high) cylindrical facility with different hydrogen-air mixture compositions. Two particular experiments were selected for simulation and comparison as a Standard Benchmark Exercise (SBEP) problem: combustion of uniform 12.8% (vol.) hydrogen-air mixture and combustion of non-uniform hydrogen-air mixture with average 12.6% (vol.) hydrogen concentration across the vessel (vertical stratification, 27% vol. hydrogen at the top of the vessel, 2.5% vol. hydrogen at the bottom of the vessel); both mixtures were ignited at the top of the vessel. The paper presents modelling approaches used by the partners, comparison of simulation results against the experiment data and conclusions regarding the non-uniform mixture combustion modelling in real-life applications.JRC.F.2-Cleaner energ

An Inter-Comparison Exercise on CFD Model Capabilities to Simulate Hydrogen Deflagrations with Pressure Relief Vents

The comparison between experimental data and simulation results of hydrogen explosions in a vented vessel is described in the paper. The validation exercise was performed in the frame of the European Commission co-funded Network of Excellence HySafe (Hydrogen Safety as an Energy Carrier) that has the objective to facilitate the safe introduction of hydrogen technologies. The mitigation effect of vents on the strength of hydrogen explosions is a relevant issue in hydrogen safety. Experiments on stoichiometric hydrogen deflagrations in a 0.95 m3 vessel with vents of different size (0.2 m2 and 0.3 m2) have been selected in the available scientific literature in order to assess the accuracy of computational tools and models in reproducing experimental data in vented explosions. Five organizations with experience in numerical modelling of gas explosions have participated to the code benchmarking activities with four CFD codes (COM3D, REACFLOW, b0b and FLUENT) and one code based on a mathematical two-zone model (VEX). The numerical features of the different codes and the simulations results are described and compared with the experimental measurements. The agreement between simulations and experiments can be considered satisfactory for the maximum overpressure while correctly capturing some relevant parameters related to the dynamics of the phenomena such as the pressure rise rate and its maximum has been shown to be still an open issue.JRC.F.2-Cleaner energ