Germany

Spontaneous ignition processes due to the high-pressure hydrogen releases into air were investigated both experimentally and theoretically. Such processes reproduce accident scenarios of sudden expansion of pressurized hydrogen into the ambient atmosphere in cases of tube or valve rupture. High-pressure hydrogen releases in the range of initial pressures from 20 to 275 bar and with nozzle diameters of 0.5 – 4 mm have been investigated. Glass tubes and high-speed CCD camera were used for experimental study of self-ignition process. The problem was theoretically considered in terms of contact discontinuity for the case when spontaneous ignition of pressurized hydrogen due to the contact with hot pressurized air occurs. The effects of boundary layer and material properties are discussed in order to explain the minimum initial pressure of 25 bar leading to the self-ignition of hydrogen with air.

Hydrogen as a carbon-free fuel is commonly expected to play a major role in future energy supply e.g. as an admixture gas in natural gas grids. Which impacts on residential and commercial gas appliances can be expected due to the significantly different physical and chemical properties of hydrogen-enriched natural gas? This paper analyses and discusses blends of hydrogen and natural gas from the perspective of combustion science. The admixture of hydrogen into natural gas changes the properties of the fuel gas. Depending on the combustion system burner design and other boundary conditions these changes may cause higher combustion temperatures and laminar combustion velocities while changing flame positions and shapes are also to be expected. For appliances that are designed for natural gas these effects may cause risk of flashback reduced operational safety material deterioration higher nitrogen oxides emissions (NOx) and efficiency losses. Theoretical considerations and first measurements indicate that the effects of hydrogen admixture on combustion temperatures and the laminar combustion velocities are often largely mitigated by a shift towards higher air excess ratios in the absence of combustion control systems but also that common combustion control technologies may be unable to react properly to the presence of hydrogen in the fuel.

Numerous studies have shown that a full electrification of passenger cars is needed to stay within the 1.5° C temperature rise. This article deals with the question of how the required shares of alternative vehicles can be achieved by the year 2050. In literature the preferred technology are battery electric vehicles as these are more energy efficient than hydrogen vehicles. To be able to demonstrate how alternative vehicles diffuse into the German market the passenger car investment behavior of private persons was investigated. For this purpose a discrete choice experiment (DCE) with 1921 participants was carried out empirically. The results of the DCE show that the investment costs in particular are important when choosing a vehicle. This is followed by the driving range fuel costs and vehicle type. Less important are the charging infrastructure and CO₂ emissions of the vehicle. A CO₂ tax is of least importance. The utility values of the DCE were used to simulate future market shares. For this purpose the open-source software Invest was developed and different scenarios were defined and calculated. This paper shows that conservative assumptions on attribute development leave a large gap until full electrification as conventional vehicles still account for around 62% of market shares in 2050. In order to achieve full electrification extreme efforts must be made targeting the technical and economic characteristics of the vehicles but also addressing person-related characteristics such as level of information the subjective norm or the technological risk attitude. A ban on new registrations of combustion engines from 2030 could also lead to a full electrification by 2050. An average annual increase in the market share of alternative vehicles of 2.4 percentage points is needed to achieve full electrification. Other important factors are measures that address the modal shift to other modes of transport (rail public transport car-sharing).

Metal hydrides are known as a potential efficient low-risk option for high-density hydrogen storage since the late 1970s. In this paper the present status and the future perspectives of the use of metal hydrides for hydrogen storage are discussed. Since the early 1990s interstitial metal hydrides are known as base materials for Ni – metal hydride rechargeable batteries. For hydrogen storage metal hydride systems have been developed in the 2010s [1] for use in emergency or backup power units i. e. for stationary applications.<br/>With the development and completion of the first submarines of the U212 A series by HDW (now Thyssen Krupp Marine Systems) in 2003 and its export class U214 in 2004 the use of metal hydrides for hydrogen storage in mobile applications has been established with new application fields coming into focus.<br/>In the last decades a huge number of new intermetallic and partially covalent hydrogen absorbing compounds has been identified and partly more partly less extensively characterized.<br/>In addition based on the thermodynamic properties of metal hydrides this class of materials gives the opportunity to develop a new hydrogen compression technology. They allow the direct conversion from thermal energy into the compression of hydrogen gas without the need of any moving parts. Such compressors have been developed and are nowadays commercially available for pressures up to 200 bar. Metal hydride based compressors for higher pressures are under development. Moreover storage systems consisting of the combination of metal hydrides and high-pressure vessels have been proposed as a realistic solution for on-board hydrogen storage on fuel cell vehicles.<br/>In the frame of the “Hydrogen Storage Systems for Mobile and Stationary Applications” Group in the International Energy Agency (IEA) Hydrogen Task 32 “Hydrogen-based energy storage” different compounds have been and will be scaled-up in the near future and tested in the range of 500 g to several hundred kg for use in hydrogen storage applications.

As a part of a German nuclear safety project on the combustion behaviour of hydrogen-carbon monoxide-air mixtures small scale experiments were performed to determine the lower flammability limit and the laminar burning velocity of such mixtures. The experiments were performed in a spherical explosion bomb with a free volume of 8.2 litre. The experimental set-up is equipped with a central spark ignition and quartz glass windows for optical access. Further instrumentation included pressure and temperature sensors as well as high-speed shadow-videography. A wide concentration range for both fuel gases was investigated in numerous experiments from the lower flammability limits up to the stoichiometric composition of hydrogen carbon monoxide and air (H2-CO-air) mixtures. The laminar burning velocities were determined from the initial pressure increase after the ignition and by using high-speed videos taken during the experiments.

This paper summarises the results from a blind-prediction study for models developed for estimating the consequences of vented hydrogen deflagrations. The work is part of the project Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations (HySEA). The scenarios selected for the blind-prediction entailed vented explosions with homogeneous hydrogen-air mixtures in a 20-foot ISO container. The test program included two configurations and six experiments i.e. three repeated tests for each scenario. The comparison between experimental results and model predictions reveals reasonable agreement for some of the models and significant discrepancies for others. It is foreseen that the first blind-prediction study in the HySEA project will motivate developers to improve their models and to update guidelines for users of the models.

Core of the Power-to-Gas (PtG) concept is the utilization of renewable electricity to produce hydrogen via water electrolysis. This hydrogen can be used directly as final energy carrier or can be converted to e.g. methane synthesis gas liquid fuels electricity or chemicals. To integrate PtG into energy systems technical demonstration and systems integration is of mayor importance. In total 128 PtG research and demonstration projects are realized or already finished in Europe to analyze these issues by May 2018. Key of the review is the identification and assessment of relevant projects regarding their field of application applied processes and technologies for electrolysis type of methanation capacity location and year of commissioning. So far main application for PtX is the injection of hydrogen or methane into the natural gas grid for storing electricity from variable renewable energy sources. Producing fuels for transport is another important application of PtX. In future PtX gets more important for refineries to lower the carbon food print of the products.

Introduction and commercialisation of hydrogen as an energy carrier of the future make great demands on all aspects of safety. Safety is a critical issue for innovations as it influences the economic attractiveness and public acceptance of any new idea or product. However research and safety expertise related to hydrogen is quite fragmented in Europe. The vision of a significant increased use of hydrogen as an energy carrier in Europe could not go ahead without strengthening and merging this expertise. This was the reason for the European Commission to support the launch on the first of March 2004 of a so-called Network of Excellence (NoE) on hydrogen safety: HySafe.

Hydrogen technology requires efficient and safe hydrogen storage systems. For this purpose storage in solid materials such as high capacity complex hydrides is studied intensely. Independent from the actual material to be used eventually any tank design will combine nanoscale powders of highly reactive material with pressurized hydrogen gas and so far little is known about the behaviour of these mixtures in case of incidents. For a first evaluation of a complex hydride in case of a tank failure NaAlH4 (doped with Ti) was investigated in a small scale tank failure tests. 80-100 ml of the material were filled into a heat exchanger tube and sealed under argon atmosphere with a burst disk. Subsequently the NaAlH4 was partially desorbed by heating. When the powder temperature reached 130 °C and the burst disk ruptured at 9 bar hydrogen overpressure the behaviour of the expelled powder was monitored using a high speed camera an IR camera as well as sound level meters. Expulsion of the hydrogen storage material into (dry) ambient atmosphere yields a dust cloud of finely dispersed powder which does not ignite spontaneously. Similar experiments including an external source of ignition (spark / water reacting with NaAlH4) yield a flame of reacting powder. The intensity will be compared to the reaction of an equivalent amount of pure hydrogen.

The different CFD tools used by the NoE HySafe partners are applied to a series of integral complex Standard Benchmark Exercise Problems (SBEPs). All benchmarks cover complementarily physical phenomena addressing application relevant scenarios and refer to associated experiments with an explicit usage of hydrogen. After the blind benchmark SBEPV1 and SBEPV3 with subsonic vertical release in a large vessel and in a garage like facility SBEPV4 with a horizontal under-expanded jet release through a small nozzle SBEPV5 covers the scenario of a subsonic horizontal jet release in a multi-compartment room.<br/>As the associated dispersion experiments conducted by GEXCON Norsk Hydro and STATOIL were disclosed to the participants the whole benchmark was conducted openly. For the purpose of validation only the low momentum test D27 had to be simulated.<br/>The experimental rig consists of a 1.20 m x 0.20 m x 0.90 m (Z vertical) vessel divided into 12 compartments partially even physically by four baffle plates. In each compartment a hydrogen concentration sensor is mounted. There is one vent opening at the wall opposite the release location centrally located about 1 cm above floor with dimensions 0.10 m (Y) times 0.20 m (Z). The first upper baffle plate close to the release point is on a sensitive location as it lies nearly perfectly in the centre of the buoyant jet and thus separates the flow into the two compartments. The actual release was a nominally constant flow of 1.15 norm liters for 60 seconds. With a 12mm nozzle diameter this corresponds to an average exit velocity of 10.17 m/s.<br/>6 CFD packages have been applied by 7 HySafe partners to simulate this experiment: ADREAHF by NCSRD FLACS by GexCon and DNV KFX by DNV FLUENT by UPM and UU CFX by HSE/HSL and GASFLOW by FZK. The results of the different participants are compared against the experimental data. Sensitivity studies were conducted by FZK using GASFLOW and by DNV applying KFX.<br/>Conclusions based on the comparisons and the sensitivity studies related to the performance of the applied turbulence models and discretisation schemes in the release and diffusion phase are proposed. These are compared to the findings of the previous benchmark exercises.