Safety

The paper describes CFD modelling of lean hydrogen mixture deflagrations. Large eddy simulation (LES) premixed combustion model developed at the University of Ulster to account phenomena related to large-scale deflagrations was adjusted specifically for lean hydrogen-air flames. Experiments by Kumar (2006) on lean hydrogen-air mixture deflagrations in a 120 m3  vessel at initially quiescent conditions were simulated. 10% by volume hydrogen-air mixture was chosen for simulation to provide stable downward flame propagation; experiments with the smallest vent area 0.55 m2  were used as having the least apparent flame instabilities affecting the pressure dynamics. Deflagrations with igniter located centrally near vent and at far from the vent wall were simulated. Analysis of simulation results and experimental pressure dynamics demonstrated that flame instabilities developing after vent opening made the significant contribution to maximum overpressure in the considered experiments. Potential causes of flame instabilities are discussed and their comparative role for different igniter locations is demonstrated.

During the synthesis of hydrogen by methane steam reforming mixtures composed of H2 CH4 CO and CO2 are produced in the process. In this work the explosion reactivity of these mixtures on the basis of detonation cell size and laminar flame speed is calculated using a reactant assimilation simplification and a kinetic approach. The detonation cells width are calculated using the Cell_CH Kurchatov institute method and the laminar flame velocities are calculated with Chemkin Premix using different detailed chemical kinetic mechanisms. These calculations are used to define if these mixtures could be considered having a medium or a high reactivity for risk assessment in case of leak in the hydrogen plants.

A numerical approach is developed to simulate detonation propagation attenuation failure and re-initiation in hydrogen–air mixture. The aim is to study the condition under which detonations may fail or re-initiate in bifurcated tubes which is important for risk assessment in industrial accidents. A code is developed to solve compressible multidimensional transient reactive Navier–Stokes equations. An Implicit Large Eddy Simulation approach is used to model the turbulence. The code is developed and tested to ensure both deflagrations (when detonation fails) and detonations are simulated correctly. The code can correctly predict the flame properties as well as detonation dynamic parameters. The detonation propagation predictions in bifurcated tubes are validated against the experimental work of Wang et al. [12] and found to be in good agreement with experimental observations.

The detonation propensity of hydrogen-air mixtures with addition of methane ethane or propane in wide range of compositions is analyzed. The analysis concerned the detonation cell width ignition delay time RSB and parameters. Results are presented as a function of hydrogen molar fraction. Computations were performed with the use of three Cantera 2.1.1. scripts in the Matlab R2010b environment. The validated mechanisms of chemical reactions based on data available in the literature were used. Six mechanisms were assessed: GRI-Mech 3.0 LLNL SanDiego Wang POLIMI and AramcoMech. In conclusion the relation between detonation propensity parameters 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 study a solution for a liquid pool spreading model with a continuous spill is compared with that for a liquid pool spreading model with an instantaneous spill under the same total release volume. As reducing spill time in completely releasing liquid from a tank it is evaluated whether the solution for a continuous spill approaches to that for an instantaneous spill or not. Also effects of the viscous term in the liquid pool spreading model with continuous and instantaneous spills on the liquid pool spreading behaviour are investigated.

Hydrogen energy applications can be used outdoor and thus exposed to environmental varying conditions like wind. In several applications natural ventilation is the first mitigation means studied to limit hydrogen build-up inside a confined area. This study aims at observing and understanding the influence of wind on light gas build-up in addition. Experiments were performed with helium as releasing gas in a 1-m 3 enclosure equipped with ventilation openings varying wind conditions openings location release flow rate; obstructions in front of the openings to limit effects of wind were studied as well. Experimental results were compared together and with the available analytical models.

In the present work the capabilities of the computational fluid dynamics (CFD) code ADREA-HF to predict deflagration in homogenous near stoichiometric hydrogen-air mixture in a model of a tunnel were tested. The tunnel is 78.5 m long. Hydrogen-air mixture is located in a 10 m long region in the middle of the tunnel. Two cases are studied: one with a complete empty tunnel and one with the presence of four vehicles near the center of the tunnel. The combustion model is based on the turbulent flame speed concept. The turbulent flame speed is a modification of Yakhot's equation in order to account for additional physical mechanisms. A sensitivity analysis for the  parameter of the combustion model and for the mesh resolution was made for the empty tunnel case. The agreement between experimental and computational results concerning the value of the maximum pressure and the time it appears is satisfactory in both cases. The sensitivity analysis for the parameter of the combustion model showed that even small changes in it can have impact on the simulating results whereas the sensitivity analysis of the mesh resolution did not reveal any significant differences.

The course is an introduction to the procedures for safe handling of hydrogen flammable and toxic gases by small users working in the field of hydrogen and fuel cells. Theoretical and practical aspects are emphasized aiming at identifying the main hazards and reduce the risks associated with the use of these gases. Topics: 1. Market hydrogen production fuel cells and energy storage; 2. International System of Units Comparison between the ideal gas and real gases; 3. Safety of gases and hydrogen; 4. Cylinders fittings and valves for gases and hydrogen; 5. Purge of gases; 6. Infrastructure for gases and hydrogen; 7. Accidents with hydrogen.

This paper is devoted to a benchmarking exercise of the EUROPLEXUS code against several large scale deflagration and detonation experimental data sets in order to improve its hydrogen combustion modeling capabilities in industrial settings. The code employs an algorithm for the propagation of reactive interfaces RDEM which includes a combustion wave as an integrable part of the Reactive Riemann problem propagating with a fundamental flame speed (being a function of initial mixture properties as well as gas dynamics parameters). An improvement of the combustion model is searched in a direction of transient interaction of flames with regions of elevated vorticity/shear in obstacle-laden channels and vented enclosures.