Numerical simulation of hydrogen discharge in a partially enclosed space (original) (raw)
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Numerical modelling of hydrogen release and dispersion
MATEC Web of Conferences, 2021
Hydrogen is the most abundant element on earth, being a low polluting and high efficiency fuel that can be used for various applications, such as power generation, heating or transportation. As a reaction to climate change, authorities are working for determining the most promising applications for hydrogen, one of the best examples of crossborder initiative being the IPCEI (Important Project of Common European Interest) on Hydrogen, under development at EU level. Given the large interest for future uses of hydrogen, special safety measures have to be implemented for avoiding potential accidents. If hydrogen is stored and used under pressure, accidental leaks from pressure vessels may result in fires or explosions. Worldwide, researchers are investigating possible accidents generated by hydrogen leaks. Special attention is granted to the atmospheric dispersion after the release, so that to avoid fires or explosions. The use of consequence modelling software within safety and risk studies has shown its' utility worldwide. In this paper, there are modelled the consequences of the accidental release and atmospheric dispersion of hydrogen from a pressure tank, using state-of-the-art QRA software. The simulation methodology used in this paper uses the "leak" model for carrying out discharge calculations. This model calculates the release rate and state of the gas after its expansion to atmospheric pressure. Accidental release of hydrogen is modelled by taking into account the process and meteorological conditions and the properties of the release point. Simulation results can be used further for land use planning, or may be used for establishing proper protection measures for surrounding facilities. In this work, we analysed two possible accident scenarios which may occur at an imaginary hydrogen refuelling station, accidents caused by the leaks of the pressure vessel, with diameters of 10 and 20 mm, for a pressure tank filled with hydrogen at 35 MPa / 70 MPa. Process Hazard Analysis Software Tool 8.4 has been used for assessing the effects of the scenarios and for evaluating the hazardous extent around the analysed installation. Accident simulation results have shown that the leak size has an important effect on the flammable/explosive ranges. Also, the jet fire's influence distance is strongly influenced by the pressure and actual size of the accidental release.
CFD Simulation of Hydrogen Release, Dispersion and Auto-Ignition in Enclosures
2011
CFD simulations of auto-ignition of hot hydrogen flowing into a cylindrical enclosure where ambient air prevails were conducted. One-step global reaction was incorporated into ANSYS® software to simulate the chemical reaction between hydrogen and oxygen. Auto ignition was obtained for different inflow temperatures, agreeing with classical results of h2-o2 explosion limits, referred to as the "peninsula". Temperature range of the reaction zone lies below the value of the adiabatic flame temperature of a constant pressure process. This is due to the fact that although the enclosure is of constant volume, ignition takes place in a negligible fraction of the total volume; therefore the absolute pressure remains unchanged. Ignition delay decreases with the increase of the hydrogen inflow temperature. Moreover, their values are similar theoretical predictions.
International Journal of Hydrogen Energy, 2009
During an accidental release, hydrogen disperses very quickly in air due to a relatively high density difference. A comprehensive understanding of the transient behavior of hydrogen mixing and the associated flammability limits in air is essential to support the fire safety and prevention guidelines. In this study, a buoyancy diffusion computational model is developed to simultaneously solve for the complete set of equations governing the unsteady flow of hydrogen. A simple vertical cylinder is considered to investigate the transient behavior of hydrogen mixing, especially at relatively short times, for different release scenarios: (i) the sudden release of hydrogen at the cylinder bottom into air with open, partially open, and closed tops, and (ii) small hydrogen jet leaks at the bottom into a closed geometry. Other cases involving the hydrogen releases/leaks at the cylinder top are also explored to quantify the relative roles of buoyancy and diffusion in the mixing process. The numerical simulations display the spatial and temporal distributions of hydrogen for all the configurations studied. The complex flow patterns demonstrate the fast formation of flammable zones with implications in the safe and efficient use of hydrogen in various applications.
Hydrogen Dispersion and Ventilation Effects in Enclosures under Different Release Conditions
Energies
Hydrogen is an explosive gas, which could create extremely hazardous conditions when released into an enclosure. Full-scale experiments of hydrogen release and dispersion in the confined space were conducted. The experiments were performed for hydrogen release outflow of 63 × 10−3 m3/s through a single nozzle and multi-point release way optionally. It was found that the hydrogen dispersion in an enclosure strongly depends on the gas release way. Significantly higher hydrogen stratification is observed in a single nozzle release than in the case of the multi-point release when the gas concentration becomes more uniform in the entire enclosure volume. The experimental results were confirmed on the basis of Froud number analysis. The CFD simulations realized with the FDS code by NIST allowed visualization of the experimental hydrogen dispersion phenomenon and confirmed that the varied distribution of hydrogen did not affect the effectiveness of the accidental mechanical ventilation sys...
CFD modelling of hydrogen release, dispersion and combustion for automotive scenarios
Journal of Loss Prevention in the Process Industries, 2008
The paper describes the analysis of the potential effects of releases from compressed gaseous hydrogen systems on commercial vehicles in urban and tunnel environments using computational fluid dynamics (CFD). Comparative releases from compressed natural gas systems are also included in the analysis. This study is restricted to typical non-articulated single deck city buses. Hydrogen releases are considered from storage systems with nominal working pressures of 20, 35 and 70 MPa, and a comparative natural gas release (20 MPa). The cases investigated are based on the assumptions that either fire causes a release via a thermally activated pressure relief device(s) (PRD) and that the released gas vents without immediately igniting, or that a PRD fails. Various release strategies were taken into account. For each configuration some worstcase scenarios are considered. By far the most critical case investigated in the urban environment, is a rapid release of the entire hydrogen or natural gas storage system such as the simultaneous opening of all PRDs. If ignition occurs, the effects could be expected to be similar to the 1983 Stockholm hydrogen accident [Venetsanos, A. G., Huld, T., Adams, P., & Bartzis, J. G. (2003). Source, dispersion and combustion modelling of an accidental release of hydrogen in an urban environment. Journal of Hazardous Materials, A105, 1-25]. In the cases where the hydrogen release is restricted, for example, by venting through a single PRD, the effects are relatively minor and localised close to the area of the flammable cloud. With increasing hydrogen storage pressure, the maximum energy available in a flammable cloud after a release increases, as do the predicted overpressures resulting from combustion. Even in the relatively confined environment considered, the effects on the combustion regime are closer to what would be expected in a more open environment, i.e. a slow deflagration should be expected. Among the cases studied the most severe one was a rapid release of the entire hydrogen (40 kg) or natural gas (168 kg) storage system within the confines of a tunnel. In this case there was minimal difference between a release from a 20 MPa natural gas system or a 20 MPa hydrogen system, however, a similar release from a 35 MPa hydrogen system was significantly more severe and particularly in terms of predicted overpressures. The present study has also highlighted that the ignition point significantly affects the combustion regime in confined environments. The results have indicated that critical cases in tunnels may tend towards a fast deflagration, or where there are turbulence generating features, e.g. multiple obstacles, there is the possibility that the combustion regime could progress to a detonation. When comparing the urban and tunnel environments, a similar release of hydrogen is significantly more severe in a tunnel, and the energy available in the flammable cloud is greater and remains for a longer period in tunnels. When comparing hydrogen and natural gas releases, for the cases and environments investigated and within the limits of the assumptions, it appears that hydrogen requires different mitigation measures in order that the potential effects are similar to those of natural gas in case of an accident. With respect to a PRD
Development of a Realistic Hydrogen Flammable Atmosphere Inside a 4M 3 Enclosure
2017
To define a strategy of mitigation for containerized hydrogen systems (fuel cells for example) against explosion, the main characteristics of flammable atmosphere (size, concentration, turbulence...) shall be well-known. This article presents an experimental study on accidental hydrogen releases and dispersion into an enclosure of 4 m (2 m x 2 m x 1 m). Different release points are studied: two circular releases of 1 and 3 mm and a system to create ring-shaped releases. The releases are operated with a pressure between 10 and 40 bars in order to be close to the process conditions. Different positions of the release inside the enclosure i.e. centred on the floor or along a wall are also studied. A specific effort is made to characterize the turbulence in the enclosure during the releases. The objectives of the experimental study are to understand and quantify the mechanisms of formation of the explosive atmosphere taking into account the geometry and position of the release point and...
Dispersion and catalytic ignition of hydrogen leaks within enclosed spaces
An experimental investigation is conducted into the nature of catalytic ignition of leaked hydrogen gas within an enclosure, and the nature of hydrogen dispersion under varied venting conditions. Using a 1/16th linear scale two-car garage as a model, and a platinum foil as a catalytic surface, it is found that for all conditions tested, catalytic ignition is observed after the leaked hydrogen comes in contact with the catalytic surface, which is initially at or near room temperature. After ignition, these surface reactions lead to steady-state surface temperatures in the range of 600–800 K, dependent on inlet conditions in terms of mixture composition and flow rate. In addition, varying the venting opportunities from the garage walls suggests that not only total area, but also the number and position of vents may impact the nature of hydrogen accumulation within an enclosed structure.► We conduct an experimental study of hydrogen leaks within enclosures. ► Catalytic ignition and hydrogen accumulation is considered. ► Catalytic ignition is observed from room temperature tested for all conditions tested. ► Varied vent position may impact the total accumulated hydrogen.
International Journal of Hydrogen Energy, 2011
The use of stationary H 2 and fuel cell systems is expected to increase rapidly in the future. In order to facilitate the safe introduction of this new technology, the HyPer project, funded by the EC, developed a public harmonized Installation Permitting Guidance (IPG) document for the installation of small stationary H 2 and fuel cell systems for use in various environments. The present contribution focuses on the safety assessment of a facility, inside which a small H 2 fuel cell system (4.8 kW e) is installed and operated. Dispersion experiments were designed and performed by partner UNIPI. The scenarios considered cover releases occurring inside the fuel cell at the valve of the inlet gas pipeline just before the pressure regulator, which controls the H 2 flow to the fuel cell system. H 2 was expected to leak out of the fuel cell into the facility and then outdoors through the ventilation system. The initial leakage diameter was chosen based on the Italian technical guidelines for the enforcement of the ATEX European directive. Several natural ventilation configurations were examined. The performed tests were simulated by NCSRD using the ADREA-HF code. The numerical analysis took into account the full interior of the fuel cell, in order to investigate for any potential accumulation effects. Comparisons between predicted and experimental H 2 concentrations at 4 sensor locations inside the facility are reported. Finally, an overall assessment of the ventilation efficiency was made based on the simulations and experiments.
CFD Modeling of Hydrogen Releases and Dispersion in Hydrogen Energy Station
This paper presents the results of computational fluid dynamics (CFD) modeling of hydrogen releases and dispersion in simple geometries and a real industrial environment. The PHOENICS CFD software package was used to solve the continuity, momentum and concentration equations with the appropriate boundary conditions, buoyancy model and turbulence models. Numerical results for simple geometries were compared with the published data on hydrogen dispersion. The similarity study of helium and hydrogen releases has been conducted. Numerical results on hydrogen concentration predictions were obtained in the real industrial environment, which is a hydrogen energy station (HES) produced by Stuart Energy Systems Corporation. The CFD modeling was then applied to the risk assessment under hypothetical failure hydrogen leak scenarios in the HES. CFD modeling has proven to be a reliable, effective and relatively inexpensive tool to evaluate the effects of hydroge n leaks in the HES.
NUMERICAL SIMULATION OF HYDROGEN DISPERSION INSIDE A COMPARTMENT USING HYDRAGON CODE
During severe accident in the nuclear power plant, a considerable amount of hydrogen can be generated by an active reaction of the fuel-cladding with steam within the pressure vessel which may be released into the containment of nuclear power plant. Hydrogen combustion may occur where there is sufficient oxygen, and the hydrogen release rates exceed 10% of the containment. During hydrogen combustion, detonation force and short term pressure may be produced. The production of these gas species can be detrimental to the structural integrity of the safety systems of the reactor and the containment. In 1979, the Three Mile Island (1979) accident occurred. This accident compelled experts and researchers to focus on the study of distribution of hydrogen inside the containment of nuclear power plant. However after the Fukushima Dai-ichi nuclear power plant accident (2011), the modeling of the gas behavior became important topic for scientists. For the stable and normal operation of the containment, it is essential to understand the behavior of hydrogen inside the containment of nuclear power plant in order to mitigate the occurrence of these types of accidents in the future. For this purpose, it is important to identify how burnable hydrogen clouds are produced in the containment of nuclear power plant. The combustion of hydrogen may occur in different modes based on geometrical complexity and gas composition. Reliable turbulence models must be used in order to obtain an accurate estimation of the concentration distribution as a function of time and other physical phenomena of the gas mixture. In this study, a small turbulence model are in reasonable agreement as compared to the benchmark experimental data.