Publications

For safety issues related to the storage of hydrogen under high pressure it is necessary to determine how the gas is released in the case of failure. In particular there exist limited quantitative information on the near-field properties of the gas jets which are important for establishing proper decay laws in the far-field. This paper reports recent CFD results for air and helium obtained in the near-field of the highly under-expanded jets. The gas jets are released from a 30-bar tank with the same opening (orifice). The Reynolds number based on the diameter of the orifice and corresponding gas conditions at the exit was well beyond 106 . The 3D Compressible Multi-Component Navier-Stokes equations were solved directly without relying on the compressibility-corrected turbulence models. The numerical model was initially tested on a one-component (air-air) case where a few aerospace-driven data sets are available for validation. The shock geometry is characterized through the Mach disk position and diameter. These are compared to the results known from the literature and to the scaling laws developed based on the dimensional analysis. In the second two-component (helium-air) jet scenario the density field was validated and examined together with other fields in the attempt to suggest potential initial conditions for the forthcoming far-field simulations.

The lack of experimental data on hydrogen dispersion led to the experimental project DRIVE (Experimental Data for Hydrogen Automotive Risks Assessment for the validation of numerical tools and for the Edition of guidelines) that involves the CEA (French Atomic Energy Commission) the National Institute of Industrial Environment and Risks (INERIS) the French car manufacturer PSA PEUGEOT CITROËN and the Research Institute on Out of Equilibrium Phenomena (IRPHE). The CEA has developed an experimental setup named GARAGE in order to analyze the condition of formation of an explosive atmosphere in an enclosure. This is a full scale facility in which a real car can be parked. Hydrogen releases were simulated with helium which volume fraction was measured with mini-katharometers. These thermal conductivity probes allow spatial and time volume fraction variations measurements. We present experimental results on the dispersion of helium in the enclosure due to releases in a typical car. The tested parameters are the location of the source (engine bottom of the car storage) and the flow rate. Emphasis is put on the influence of these parameters on the time evolution of the volume fraction in the enclosure as well as on the vertical distribution of helium.

In the context of hydrogen production from biomass or organic waste with dark fermentation this study analysed 55 studies (339 experiments) in the literature looking for the effect of operating parameters on the process performance of dark fermentation. The effect of substrate concentration pH temperature and residence time on hydrogen yield productivity and content in the biogas was analysed. In addition a linear regression model was developed to also account for the effect of nature and pretreatment of the substrate inhibition of methanogenesis and continuous or batch operating mode. The analysis showed that the hydrogen yield was mainly affected by pH and residence time with the highest yields obtained for low pH and short residence time. High hydrogen productivity was favoured by high feed concentration short residence time and low pH. More modest was the effect on the hydrogen content. The mean values of hydrogen yield productivity and content were respectively 6.49% COD COD−1 135 mg L−1 d −1 51% v/v while 10% of the considered experiments obtained yield productivity and content of or higher than 15.55% COD COD−1 305.16 mg L−1 d −1 64% v/v. Overall this study provides insight into how to select the optimum operating conditions to obtain the desired hydrogen production.

Experimental data from vented explosion tests using lean hydrogen–air mixtures with concentrations from 12 to 19% vol. are presented. A 63.7-m3 chamber was used for the tests with a vent size of either 2.7 or 5.4 m2. The tests were focused on the effect of hydrogen concentration ignition location vent size and obstacles on the pressure development of a propagating flame in a vented enclosure. The dependence of the maximum pressure generated on the experimental parameters was analyzed. It was confirmed that the pressure maxima are caused by pressure transients controlled by the interplay of the maximum flame area the burning velocity and the overpressure generated outside of the chamber by an external explosion. A model proposed earlier to estimate the maximum pressure for each of the main pressure transients was evaluated for the various hydrogen concentrations. The effect of the Lewis number on the vented explosion overpressure is discussed.

Any technical installation need appropriate safety barriers installed to prevent or mitigate any adverse effects concerning people property and environment. In this context a safety barrier is a series of elements each consisting of a technical system or human action that implement a planned barrier function to prevent control or mitigate the propagation of a condition or event into an undesired condition or event. This is also important for new technologies as hydrogen refuelling stations being operated at very high pressures up to 900bar. In order to establish the needed barriers a hazard identification of the installation has to be carried out to identify the possible hazardous events. In this study this identification was done using the generic layout of a future large hydrogen refuelling station that has been developed by the EU NoE HySafe. This was based on experiences with smaller scale refuelling stations that has been in operation for several years e.g. being used in the former CUTE and ECTOS projects. Using this approach the object of the study is to support activities to further improve the safety performance of future larger refuelling stations. This will again help to inform the authorities and the public to achieve a proper public awareness and to support building up a realistic risk and safety perception of the safety on such future refuelling stations. In the second step the hazardous events that may take place and the barriers installed to stop hazards and their escalation are analysed also using in-house developed software to model the barriers and to quantify their performance. The paper will present an overview and discuss the state-of-the-art of the barriers established in the generic refuelling station.

In this paper the deflagration region and characteristics of the hydrogen flow which was generated by high-pressure hydrogen discharge from storage vessels were studied. A 3-D analytic model is established based on the species transfer model and the SST k −ω turbulence model. The established model is applied to the research of the flow characteristics of the hydrogen under-expanded jet under different filling pressures of 30 MPa 35 MPa and 40 MPa respectively. The evolution process of hydrogen combustible cloud is analyzed under the filling pressure of 30 MPa. It is revealed that a supersonic jet is formed after the high-pressure hydrogen discharge outlet In the vicinity of the Mach disk the hydrogen jet velocity and temperature reach the maximum values and the variation of filling pressure has little effect on the peak values of the hydrogen jet flow velocity and temperature during the considered pressure range. In the rear of the Mach disk the variation rates of the hydrogen flow velocity and temperature are in inversely proportional to the hydrogen filling pressure. At the preliminary stage the discharged hydrogen is apple-shaped which expands along the radial and then the axial growth rate of the hydrogen cloud increases with the passage of time.

To avoid failures due to hydrogen embrittlement it is important to know the amount of hydrogen absorbed by certain steel grades under service conditions. When a critical hydrogen content is reached the material properties begin to deteriorate. The hydrogen uptake and embrittlement of three different carbon steels (API 5CT L80 Type 1 P110 and 42CrMo4) was investigated in autoclave tests with hydrogen gas (H₂) at elevated pressure and in ambient pressure tests with hydrogen sulfide (H₂S). H₂ gas with a pressure of up to 100 bar resulted in an overall low but still detectable hydrogen absorption which did not cause any substantial hydrogen embrittlement in specimens under a constant load of 90% of the specified minimum yield strength (SMYS). The amount of hydrogen absorbed under conditions with H₂S was approximately one order of magnitude larger than under conditions with H₂ gas. The high hydrogen content led to failures of the 42CrMo4 and P110 specimens.

An efficient production of hydrogen from a mixture of methanol and water is possible in a spark discharge. In this discharge there is a synergistic effect of high-energy electrons and high temperature interactions which enables an efficient course of endothermic processes such as the production of hydrogen from methanol. The water to methanol molar ratio of 1:1 was kept constant during the study. While the discharge power and feed flow rate were varied from 15 to 55 W and from 0.25 to 2 mol/h respectively which corresponded to the residence time of the reactants in the plasma zone from 58 to 7 ms. The cooled gas mixture contained 56 to 60% of H2. Other gaseous products of the process were CO CO2 and a small amount of CH4. The maximum energy yield was 16.2 mol(H2)/kWh which represents 20% of the theoretical energy yield when the substrates are in a liquid phase.

The use of hydrogen as an energy carrier is a real perspective for Europe since a number of breakthroughs now enable to envision a deployment at the industrial scale. However some safety issues need to be further addressed but experimental data are still lacking especially about the explosion dynamics in realistic dimensions. A set of hydrogen-air vented explosions were thus performed in two medium scale chambers (1 m3 and 10 m3). Homogeneous mixtures were used (10% to 30% vol.). The explosion overpressure was measured inside the chamber and outside on the axis of the discharge from the vent. The incidence of the external explosion is clearly seen. All the results in this paper and the predictions from the standards differ greatly meaning that a significant effort is still required. It is the purpose of the French project DIMITRHY to help progressing.

This paper describes a series of numerical simulations with release and ignition of hydrogen. The objective of this work was to re-investigate the accidental explosion in an ammonia plant which happened in Norway in 1985 with modern CFD tools. The severe hydrogen-air explosion led to two fatalities and complete destruction of the factory building where the explosion occurred. A case history of the accident was presented at the 1.st ICHS in Pisa 2005.<br/>The numerical simulations have been performed with FLACS a commercial CFD simulation tool for gas dispersion and gas explosions. The code has in the recent years been validated in the area of hydrogen dispersion and explosions.<br/>The factory building was 100 m long 10 m wide and 7 m high. A blown-out gasket in a water pump led to release of hydrogen from a large reservoir storing gaseous hydrogen at 3.0 MPa. The accident report estimated a total mass of released hydrogen between 10 and 20 kg. The location of the faulty gasket is known but the direction of the accidental release is not well known and has been one of the topics of our investigations. Several simulations have been performed to investigate the mixing process of hydrogen-air clouds and the development of a flammable gas cloud inside the factory building resulting in a simulation matrix with dispersions in all axis directions. Simulations of ignition of the different gas clouds were carried out and resulting pressure examined. These results have been compared with the damages observed during the accident investigation.<br/>We have also performed FLACS simulations to study the effect of natural venting and level of congestion. The height of the longitudinal walls has been varied leading to different vent openings at floor level at the ceiling and a combination of the two. This was done to investigate the effects of congestion with regards to gas cloud formation.<br/>The base case simulation appears to be in good accordance to the observed damages from the accident. The simulations also show that the build up of the gas cloud strongly depends on the direction of the jet and degree of ventilation. The CFD study has given new insights to the accident and the results are a clear reminder of the importance of natural venting in hydrogen safety.