Germany
Guidelines and Recommendations for Indoor Use of Fuel Cells and Hydrogen Systems
Oct 2015
Publication
Deborah Houssin-Agbomson,
Simon Jallais,
Elena Vyazmina,
Guy Dang-Nhu,
Gilles Bernard-Michel,
Mike Kuznetsov,
Vladimir V. Molkov,
Boris Chernyavsky,
Volodymyr V. Shentsov,
Dmitry Makarov,
Randy Dey,
Philip Hooker,
Daniele Baraldi,
Evelyn Weidner,
Daniele Melideo,
Valerio Palmisano,
Alexandros G. Venetsanos,
Jan Der Kinderen and
Béatrice L’Hostis
Hydrogen energy applications often require that systems are used indoors (e.g. industrial trucks for materials handling in a warehouse facility fuel cells located in a room or hydrogen stored and distributed from a gas cabinet). It may also be necessary or desirable to locate some hydrogen system components/equipment inside indoor or outdoor enclosures for security or safety reasons to isolate them from the end-user and the public or from weather conditions.<br/>Using of hydrogen in confined environments requires detailed assessments of hazards and associated risks including potential risk prevention and mitigation features. The release of hydrogen can potentially lead to the accumulation of hydrogen and the formation of a flammable hydrogen-air mixture or can result in jet-fires. Within Hyindoor European Project carried out for the EU Fuel Cells and Hydrogen Joint Undertaking safety design guidelines and engineering tools have been developed to prevent and mitigate hazardous consequences of hydrogen release in confined environments. Three main areas are considered: Hydrogen release conditions and accumulation vented deflagrations jet fires and including under-ventilated flame regimes (e.g. extinguishment or oscillating flames and steady burns). Potential RCS recommendations are also identified.
The Role of Trust and Familiarity in Risk Communication
Sep 2009
Publication
In socio-economics it is well known that the success of an innovation process not only depends upon the technological innovation itself or the improvement of economic and institutional system boundaries but also on the public acceptance of the innovation. The public acceptance can as seen with genetic engineering for agriculture be an obstacle for the development and introduction of a new and innovative idea. In respect to hydrogen technologies this means that the investigation compilation and communication of scientific risk assessments are not sufficient to enhance or generate public acceptance. Moreover psychological social and cultural aspects of risk perception have to be considered when introducing new technologies. Especially trust and familiarity play an important role for risk perception and thus public acceptance of new technologies.
Hydrogen Safety- New Challenges Based on BMW Hydrogen 7
Sep 2007
Publication
The BMW Hydrogen 7 is the world’s first premium sedan with a bi-fuelled internal combustion engine concept that has undergone the series development process. This car also displays the BMW typical driving pleasure. During development the features of the hydrogen energy source were emphasized. Engine tank system and vehicle electronics were especially developed as integral parts of the vehicle for use with hydrogen. The safety-oriented development process established additional strict hydrogen-specific standards for the Hydrogen 7. The fulfilment of these standards were demonstrated in a comprehensive experimentation and testing program which included all required tests and a large number of additional hydrogen-specific crash tests such as side impacts to the tank coupling system or rear impacts. Furthermore the behaviour of the hydrogen tank was tested under extreme conditions for instance in flames and after strong degradation of the insulation. Testing included over 1.7 million km of driving; and all tests were passed successfully proving the intrinsic safety of the vehicle and also confirming the success of the safety-oriented development process which is to be continued during future vehicle development. A safety concept for future hydrogen vehicles poses new challenges for vehicles and infrastructure. One goal is to develop a car fuelled by hydrogen only while simultaneously optimizing the safety concept. Another important goal is removal of (self-imposed) restrictions for parking in enclosed spaces such as garages. We present a vision of safety standards requirements and a program for fulfilling them.
Real-gas Equations-of-State for the GASFLOW CFD Code
Sep 2011
Publication
GASFLOW is a finite-volume computer code that solves the time-dependent two-phase homogeneous equilibrium model compressible Navier–Stokes equations for multiple gas species with turbulence. The fluid-dynamics algorithm is coupled with conjugate heat and mass transfer models to represent walls floors ceilings and other internal structures to describe complex geometries such as those found in nuclear containments and facilities. Recent applications involve simulations of cryogenic hydrogen tanks at elevated pressures. These applications which often have thermodynamic conditions near the critical point require more accurate real-gas Equations-of-State (EoS) and transport properties than the standard ideal gas EoS and classical kinetic-theory transport properties. This paper describes the rigorous implementation of the generalized real-gas EoS into the GASFLOW CFD code as well as the specific implementation of respective real-gas models (Leachman's NIST hydrogen EoS a modified van der Waals EoS and a modified Nobel-Abel EoS); it also includes a logical testing procedure based upon a numerically exact benchmark problem. An example of GASFLOW simulations is presented for an ideal cryo-compressed hydrogen tank of the type utilized in fuel cell vehicles.
Evaluation of Optical and Spectroscopic Experiments of Hydrogen Jet Fires
Sep 2009
Publication
This paper reports results of evaluating joint experiments under the work programme of Hysafe occurring at HSL who provided the test facilities and basic measurements to generate jet fires whereas Fraunhofer ICT applied their equipment to visualise the jet fires by fast video techniques IR-cameras and fast scanning spectroscopy in the NIR/IR spectral region. Another paper describes the experimental set up and main findings of flame structures and propagation resolved in time. The spatial distribution of species and temperate as well as their time history and fluctuations give a basis of the evaluation of effects caused by such jet fires. Fraunhofer ICT applied their comprehensive evaluation codes to model the radiation emission from 3-atomic species in the flame especially H2O in the Infrared spectral range. The temperatures of the hydrogen flame were about 2000 K as found by least squares fit of the measured molecular bands by the codes. In comparison with video and thermo camera frames these might enable to estimate on a qualitative level species distribution and air entrainment and temperatures to identify hot and reactive zones. The risk analysis could use this information to estimate heat transfer and the areas of risk to direct inflammation from the jet fires by semi-empirical approaches.
Energy Storage as Part of a Secure Energy Supply
Mar 2017
Publication
Florian Ausfelder,
Christian Beilmann,
Martin Bertau,
Sigmar Bräuninger,
Angelika Heinzel,
Renate Hoer,
Wolfram Koch,
Falko Mahlendorf,
Anja Metzelthin,
Marcell Peuckert,
Ludolf Plass,
Konstantin Räuchle,
Martin Reuter,
Georg Schaub,
Sebastian Schiebahn,
Ekkehard Schwab,
Ferdi Schüth,
Detlef Stolten,
Gisa Teßmer,
Kurt Wagemann and
Karl-Friedrich Ziegahn
The current energy system is subject to a fundamental transformation: A system that is oriented towards a constant energy supply by means of fossil fuels is now expected to integrate increasing amounts of renewable energy to achieve overall a more sustainable energy supply. The challenges arising from this paradigm shift are currently most obvious in the area of electric power supply. However it affects all areas of the energy system albeit with different results. Within the energy system various independent grids fulfill the function of transporting and spatially distributing energy or energy carriers and the demand-oriented supply ensures that energy demands are met at all times. However renewable energy sources generally supply their energy independently from any specific energy demand. Their contribution to the overall energy system is expected to increase significantly.<br/>Energy storage technologies are one option for temporal matching of energy supply and demand. Energy storage systems have the ability to take up a certain amount of energy store it in a storage medium for a suitable period of time and release it in a controlled manner after a certain time delay. Energy storage systems can also be constructed as process chains by combining unit operations each of which cover different aspects of these functions. Large-scale mechanical storage of electric power is currently almost exclusively achieved by pumped-storage hydroelectric power stations.<br/>These systems may be supplemented in the future by compressed-air energy storage and possibly air separation plants. In the area of electrochemical storage various technologies are currently in various stages of research development and demonstration of their suitability for large-scale electrical energy storage. Thermal energy storage technologies are based on the storage of sensible heat exploitation of phase transitions adsorption/desorption processes and chemical reactions. The latter offer the possibility of permanent and loss-free storage of heat. The storage of energy in chemical bonds involves compounds that can act as energy carriers or as chemical feedstocks. Thus they are in direct economic competition with established (fossil fuel) supply routes. The key technology here – now and for the foreseeable future – is the electrolysis of water to produce hydrogen and oxygen.<br/>Hydrogen can be transformed by various processes into other energy carriers which can be exploited in different sectors of the energy system and/or as raw materials for energy-intensive industrial processes. Some functions of energy storage systems can be taken over by industrial processes. Within the overall energy system chemical energy storage technologies open up opportunities to link and interweave the various energy streams and sectors. Chemical energy storage not only offers means for greater integration of renewable energy outside the electric power sector it also creates new opportunities for increased flexibility novel synergies and additional optimization.<br/>Several examples of specific energy utilization are discussed and evaluated with respect to energy storage applications. The article describes various technologies for energy storage and their potential applications in the context of Germany’s Energiewende i.e. the transition towards a more sustainable energy system. Therefore the existing legal framework defines some of the discussions and findings within the article specifically the compensation for renewable electricity providers defined by the German Renewable Energy Sources Act which is under constant reformation. While the article is written from a German perspective the authors hope this article will be of general interest for anyone working in the areas of energy systems or energy technology.
Simulation of the Efficiency of Hydrogen Recombiners as Safety Devices
Sep 2011
Publication
Passive auto-catalytic recombiners (PARs) are used as safety devices in the containments of nuclear power plants (NPPs) for the removal of hydrogen that may be generated during specific reactor accident scenarios. In the presented study it was investigated whether a PAR designed for hydrogen removal inside a NPP containment would perform principally inside a typical surrounding of hydrogen or fuel cell applications. For this purpose a hydrogen release scenario inside a garage – based on experiments performed by CEA in the GARAGE facility (France) – has been simulated with and without PAR installation. For modelling the operational behaviour of the PAR the in-house code REKO-DIREKT was implemented in the CFD code ANSYS-CFX. The study was performed in three steps: First a helium release scenario was simulated and validated against experimental data. Second helium was replaced by hydrogen in the simulation. This step served as a reference case for the unmitigated scenario. Finally the numerical garage setup was enhanced with a commercial PAR model. The study shows that the PAR works efficiently by removing hydrogen and promoting mixing inside the garage. The hot exhaust plume promotes the formation of a thermal stratification that pushes the initial hydrogen rich gas downwards and in direction of the PAR inlet. The paper describes the code implementation and simulation results.
Analysis of Transient Hydrogen Release, Dispersion and Explosion in a Tunnel with Fuel Cell Vehicles using All-Speed CFD Code
Sep 2019
Publication
Hydrogen energy is expanding world wide in recent years while hydrogen safety issues have drawn considerable attention. It is widely accepted that accidental hydrogen release in an open air environment will disperse quickly hence not causing significant hydrogen hazards. A hydrogen hazard is more likely to occur when hydrogen is accidentally released in a confined place i.e. parking garages and tunnels. Prediction the consequences of hydrogen detonation is important for hydrogen safety assessment and for ensuring the safety of installations during accidents. Hence an accident scenario of hydrogen release nd detonation in a tunnel is analysed with GASFLOW-MPI in this paper. GASFLOW-MPI is a well validated parallel CFD code focusing on hydrogen transport combustion and detonation. GASFLOWMPI solves compressible Navier-Stokes equations with a powerful all-speed Arbitrary-Lagrangian-Eulerian (ALE) method hence it can cover both the non-compressible flow during the hydrogen relesase and dispersion phases and the compressible flow during combustion and detonation. A 3D model of a tunnel including eight cars is modelled. Firstly the hydrogen dispersion in the tunnel is calculated. Then the detonation in the tunnel is calculated by manually igniting the hydrogen at the top of the tunnel when the λ criterion is maximum. The pressure loads are calculated to evaluate the consequence of the hazard.
Application of the Validated 3D Multiphase-multicomponent CFD Model to an Accidental Liquid Hydrogen Release Scenario in a Liquefication Plant
Sep 2017
Publication
Hydrogen-air mixtures are flammable in a wide range of compositions and have a low ignition energy compared to gaseous hydrocarbons. Due to its low density high buoyancy and diffusivity the mixing is strongly enhanced which supports distribution into large volumes if accidentally released. Economically valuable discontinuous transportation over large distances is only expected using liquid hydrogen (LH2). Releases of LH2 at its low temperature (20.3 K at 0.1 MPa) have additional hazards besides the combustible character of gaseous hydrogen (GH2). Hazard assessment requires simulation tools capable of calculating the pool spreading as well as the gas distribution for safety assessments of existing the future liquid hydrogen facilities. Evaluating possible risks the following process steps are useful:
- Possible accident release scenarios need to be identified for a given plant layout.
- Environmental boundary conditions such as wind conditions and humidity need to be identified and worst case scenarios have to be identified.
- A model approach based on this information which is capable of simulating LH2 releases vaporization rates and atmospheric dispersion of the gaseous hydrogen.
- Evaluate and verify safety distances identify new risks and/or extract certain design rules.
Trends in Gas Sensor Development for Hydrogen Safety
Sep 2013
Publication
Gas sensors are applied for facilitating the safe use of hydrogen in for example fuel cell and hydrogen fuelled vehicles. New sensor developments aimed at meeting the increasingly stringent performance requirements in emerging applications are presented based on in-house technical developments and a literature study. The strategy of combining different detection principles i.e. sensors based on electrochemical cells semiconductors or field effects in combination with thermal conductivity sensor or catalytic combustion elements in one new measuring system is reported. This extends the dynamic measuring range of the sensor while improving sensor reliability to achieve higher safety integrity through diverse redundancy. The application of new nanoscaled materials nano wires carbon tubes and graphene as well as the improvements in electronic components of field-effect resistive-type and optical systems are evaluated in view of key operating parameters such as sensor response time low energy consumption and low working temperature.
Interaction of Hydrogen Jets with Hot Surfaces
Sep 2017
Publication
The formation of hydrogen jets from pressurized sources and its ignition when hitting hot devices has been studied by many projects. The transient jets evolve with high turbulence depending on the configuration of the nozzle and especially the pressure in the hydrogen reservoir. In addition the length of the jets and the flames generated by ignition at a hot surface varies. Parameters to be varied were initial pressure of the source (2.5 10 20 and 40 MPa) distance between the nozzle and the hot surface (3 5 and 7 m) and temperature of the hot surface (between 400 and 1000 K). The interaction of the hydrogen jets is visualized by high-speed cinematography techniques which allow analysing the jet characteristics. By combination of various methods of image processing the visibility of the phenomena on the videos taken at 15 000 fps was improved. In addition high-speed NIR spectroscopy was used to obtain temperature profiles of the expanding deflagrations. The jets ignite already above 450 K for conditions mainly from the tubular source at 40 MPa. In addition the propagation of the flame front depends on all three varied parameters: temperature of the hot surface pressure in the reservoir and distance between nozzle and hot surface. In most cases also upstream propagation occurs. A high turbulence seems to lead to the strong deflagrations. At high temperatures of the ignition sources the interaction leads to fast deflagration and speeds up- and downstream of the jet. The deflagration velocity is close to velocity of sound and emission of pressure waves occurs.
Ignition and Heat Radiation of Cryogenic Hydrogen Jets
Sep 2011
Publication
In the present work release and ignition experiments with horizontal cryogenic hydrogen jets at temperatures of 35–65 K and pressures from 0.7 to 3.5 MPa were performed in the ICESAFE facility at KIT. This facility is specially designed for experiments under steady-state sonic release conditions with constant temperature and pressure in the hydrogen reservoir. In distribution experiments the temperature velocity turbulence and concentration distribution of hydrogen with different circular nozzle diameters and reservoir conditions was investigated for releases into stagnant ambient air. Subsequent combustion experiments of hydrogen jets included investigations on the stability of the flame and its propagation behaviour as function of the ignition position. Furthermore combustion pressures and heat radiation from the sonic jet flame during the combustion process were measured. Safety distances were evaluated and an extrapolation model to other jet conditions was proposed. The results of this work provide novel data on cryogenic sonic hydrogen jets and give information on the hazard potential arising from leaks in liquid hydrogen reservoirs.
Regulations and Research on RC&S for Hydrogen Storage Relevant To Transport and Vehicle Issues with Special Focus on Composite Containments
Sep 2011
Publication
Developers interested in high pressure storage of hydrogen for mobile use increasingly rely on composite cylinders for onboard storage or transport of dangerous goods. Thus composite materials and systems deserve special consideration. History gives interesting background information important to the understanding of the current situation as to regulations codes and standards.<br/>Based on this review origins of different regulations for the storage of hydrogen as dangerous good and as propellant for vehicles will be examined. Both categories started out using steel and sometimes aluminium as cylinder material. With composite materials becoming more common a new problem emerged: vital input for regulations on composite pressure systems was initially derived from decades of experience with steel cylinders. As a result both regulatory fields suffer somewhat from this common basis. Only recent developments regarding requirements for composite cylinders have begun to go more and more separate ways. Thus these differences lead to some shortcomings in regulation with respect to composite storage systems.<br/>In principle in spite of separate development these deficits are in both applications very much the same: there are uncertainties in the prediction of safe service life in retesting procedures of composite cylinders and in their intervals. Hence different aspects of uncertainties and relevant approaches to solutions will be explained.
Hydrogen Detection- Visualisation of Hydrogen Using Non Invasive Optical Schlieren Technique BOS
Sep 2005
Publication
The detection of hydrogen after its accidental release is not only important for research purposes but will be much more important under safety aspects for future applications when hydrogen should be a standard energy resource. At Fraunhofer ICT two principally different approaches were made: first the new optical background-oriented schlieren method (BOS) is used for the visualization of hydrogen distribution and mixing processes at a rate of up to 1000 frames per second. The results from experiments with small scale injection of hydrogen/air–mixtures into air flows and free jets of hydrogen and hydrogen/air–mixtures emerging from 1” hoses simulating exhaust pipes will be discussed and interpreted with support from selected high speed videos. Finally mixing zones and safety distances can be determined by this powerful method.
Optimal Development of Alternative Fuel Station Networks Considering Node Capacity Restrictions
Jan 2020
Publication
A potential solution to reduce greenhouse gas (GHG) emissions in the transport sector is the use of alternative fuel vehicles (AFV). As global GHG emission standards have been in place for passenger cars for several years infrastructure modelling for new AFV is an established topic. However as the regulatory focus shifts towards heavy-duty vehicles (HDV) the market diffusion of AFV-HDV will increase as will planning the relevant AFV infrastructure for HDV. Existing modelling approaches need to be adapted because the energy demand per individual refill increases significantly for HDV and there are regulatory as well as technical limitations for alternative fuel station (AFS) capacities at the same time. While the current research takes capacity restrictions for single stations into account capacity limits for locations (i.e. nodes) – the places where refuelling stations are built such as highway entries exits or intersections – are not yet considered. We extend existing models in this respect and introduce an optimal development for AFS considering (station) location capacity restrictions. The proposed method is applied to a case study of a potential fuel cell heavy-duty vehicle AFS network. We find that the location capacity limit has a major impact on the number of stations required station utilization and station portfolio variety.
Design of Catalytic Recombiners for Safe Removal of Hydrogen from Flammable Gas Mixtures
Sep 2007
Publication
Several today’s and future applications in energy technology bear the risk of the formation of flammable hydrogen/air mixtures either due to the direct use of hydrogen or due to hydrogen appearing as a by-product. If there’s the possibility of hydrogen being released accidentally into closed areas countermeasures have to be implemented in order to mitigate the threat of an explosion. In the field of nuclear safety passive auto-catalytic recombiners (PAR) are well-known devices for reducing the risk of a hydrogen detonation in a nuclear power plant in the course of a severe accident. Hydrogen and oxygen react on catalyst materials like platinum or palladium already far below conventional flammability limits. The most important concern with regard to the utilization of hydrogen recombiners is the adequate removal of the reaction heat. Already low hydrogen concentrations may increase the system temperature beyond the self-ignition limit of hydrogen/air mixtures and may lead to an unintended ignition on hot parts of the PAR.<br/>Starting from the nuclear application since several years IEF-6 and LRST perform joint research in the field of passive auto-catalytic recombiners including experimental studies modelling and development of new design concepts. Recently approaches on specifically designed catalysts and on passive cooling devices have been successfully tested. In a design study both approaches are combined in order to provide means for efficient and safe removal of hydrogen. The paper summarizes results achieved so far and possible designs for future applications.
Effects of Oxidants on Hydrogen Spontaneous Ignition: Experiments and Modelling
Sep 2017
Publication
Experiments were performed on the influence of oxidants (air pure oxygen O2 and pure nitrous oxide N2O at atmospheric pressure) in the straight expansion tube after the burst disk on the hydrogen spontaneous ignition. The lowest pressure at which the spontaneous ignition is observed has been researched for a 4 mm diameter tube with a length of 10 cm for the two oxidant gases. The ignition phenomenon is observed with a high speed camera and the external overpressures are measured. Numerical simulations have also been conducted with the high resolution CFD approach detailed chemistry formerly developed by Wen and co-workers. Comparison is made between the predictions and the experimental data.
Experimental Study of Ignited Unsteady Hydrogen Releases from a High Pressure Reservoir
Sep 2011
Publication
In order to simulate an accidental hydrogen release from the high pressure pipe system of a hydrogen facility a systematic study on the nature of transient hydrogen jets into air and their combustion behavior was performed at the KIT hydrogen test site HYKA. Horizontal unsteady hydrogen jets from a reservoir of 0.37 dm3 with initial pressures of up to 200 bar have been investigated. The hydrogen jets released via round nozzles 3 4 and 10 mm were ignited with different ignition times and positions. The experiments provide new experimental data on pressure loads and heat releases resulting from the deflagration of hydrogen–air clouds formed by unsteady turbulent hydrogen jets released into a free environment. It is shown that the maximum pressure loads occur for ignition in a narrow position and time window. The possible hazard potential arising from an ignited free transient hydrogen jet is described.
Validation of Cryo-Compressed Hydrogen Storage (CCH2) – A Probabilistic Approach
Sep 2011
Publication
Due to its promising potential to overcome the challenge of thermal endurance of liquid hydrogen storage systems cryo-compressed hydrogen storage (CcH2) is regarded as a verypromising physical storage solution in particular for use in larger passenger vehicles with high energy and long range requirements. A probabilistic approach for validation of safe operation of CcH2 storage systems under automotive requirements and experimental results on life-cycle testing is presented. The operational regime of BMW's CcH2 storage covers pressures of up to 35 MPa and temperatures from +65 C down to -240 C applying high loads on composite and metallic materials of the cryogenic pressure vesselcompared to ambient carbon fiber reinforced pressure vessels. Thus the proof of fatigue strength under combined pressure and deep temperature cyclic loads remains a challenging exercise. Furthermore it will be shown that the typical automotive safety and life-cycle requirements can be fulfilled by the CcH2 vehicle storage system and moreover that the CcH2 storage system can even feature safety advantages over a CGH2 storage system mainly due to the advantageous thermodynamic properties of cryogenic hydrogen the lower storage pressure and due to the intrinsic protection against intrusion through the double-shell design.
Flame Propagation Near the Limiting Conditions in a Thin Layer Geometry
Sep 2019
Publication
A series of experiments on hydrogen flame propagation in a thin layer geometry is presented. Premixed hydrogen-air compositions in the range from 6 to 15%(vol.) H2 are tested. Semi-open vertical combustion chamber consists of two transparent Plexiglas side walls with main dimensions of 90x20 cm with a gap from 1 to 10 mm in between. Test mixtures are ignited at the open end of the chamber so that the flame propagates towards the closed end. Ignition position changes from top to bottom in order to take into account an effect of gravity on flame propagation regimes. High-speed shadow imaging is used to visualize and record the combustion process. Thermal-diffusion and Darrieus-Landau instabilities are governing the general flame behaviour. Heat losses to side walls and viscous friction in a thin layer may fully suppress the flame propagation with local or global extinction. The sensitivity to heat losses can be characterized using a Peclet number as a ratio of layer thickness to laminar flame thickness. Approaching to critical Peclet number Pec = 42 the planar or wrinkled flame surface degradants to one-or two-heads "finger" flame propagating straight (for two-heads flame) or chaotic (for one-head "finger" flame). Such a "fingering" of the flame is found for the first time for gaseous systems and very similar to that reported for smouldering or filtering combustion of solid materials and also under micro-gravity conditions. The distance between "fingers" may depend on deficit of limiting component. The processes investigated can be very important from academic and practical points of view with respect to safety of hydrogen fuel cells.
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