Rethinking “BLEVE explosion” after liquid hydrogen storage tank rupture in a fire

The underlying physical mechanisms leading to the generation of blast waves after liquid hydrogen (LH2) storage tank rupture in a fire are not yet fully understood. This makes it difficult to develop predictive models and validate them against a very limited number of experiments. This study aims at the development of a CFD model able to predict maximum pressure in the blast wave after the LH2 storage tank rupture in a fire. The performed critical review of previous works and the thorough numerical analysis of BMW experiments (LH2 storage pressure in the range 2.0–11.3 bar abs) allowed us to conclude that the maximum pressure in the blast wave is generated by gaseous phase starting shock enhanced by combustion reaction of hydrogen at the contact surface with heated by the shock air. The boiling liquid expanding vapour explosion (BLEVE) pressure peak follows the gaseous phase blast and is smaller in amplitude. The CFD model validated recently against high-pressure hydrogen storage tank rupture in fire experiments is essentially updated in this study to account for cryogenic conditions of LH2 storage. The simulation results provided insight into the blast wave and combustion dynamics, demonstrating that combustion at the contact surface contributes significantly to the generated blast wave, increasing the overpressure at 3 m from the tank up to 5 times. The developed CFD model can be used as a contemporary tool for hydrogen safety engineering, e.g. for assessment of hazard distances from LH2 storage.     

Liquid hydrogen releases show dense gas behavior

The number of maritime initiatives with hydrogen as alternative fuel is increasing. While most of the early projects aim at using compressed hydrogen the use of liquid hydrogen (LH2) is more practical and is expected to become more attractive for implementation on larger vessels due to more efficient storage, bunkering and handling of the fuel. In the industry there seems to be some confusion regarding the behavior of LH2 releases, in particular whether a release into air will behave like a dense gas or a buoyant gas. The understanding of this aspect is critical to optimize design with regard to safety. This article will explain the expected behavior of LH2 releases and discuss expected hazard distances from LH2 releases relative to gaseous hydrogen releases and LNG. Some other safety concerns of LH2, like indoor releases, releases from vent masts, potential BLEVEs and RPTs are also discussed. The article explains why a higher safety standard may be required when designing hydrogen fueled vessels than for existing LNG fueled vessels.     

CFD computations of liquid hydrogen releases

Hydrogen is widely recognized as an attractive energy carrier due to its low-level air pollution and its high mass-related energy density. However, its wide flammability range and high burning velocity present a potentially significant hazard. A significant fraction of hydrogen is stored and transported as a cryogenic liquid (liquid hydrogen, or LH₂) as it requires much less volume compared to gaseous hydrogen. In order to exist as a liquid, H₂ must be cooled to a very low temperature, 20.28 K. LH₂ is a common liquid fuel for rocket applications. It can also be used as the fuel storage in an internal combustion engine or fuel cell for transport applications. Models for handling liquid releases, both two-phase flashing jets and pool spills, have been developed in the CFD-model FLACS. The very low normal boiling point of hydrogen (20 K) leads to particular challenges as this is significantly lower than the boiling points of oxygen (90 K) and nitrogen (77 K). Therefore, a release of LH₂ in the atmosphere may induce partial condensation or even freezing of the oxygen and nitrogen present in the air. A pool model within the CFD software FLACS is used to compute the spreading and vaporization of the liquid hydrogen depositing on the ground where the partial condensation or freezing of the oxygen and nitrogen is also taken into account. In our computations of two-phase jets the dispersed and continuous phases are assumed to be in thermodynamic and kinematic equilibrium. Simulations with the new models are compared against selected experiments performed at the Health and Safety Laboratory (HSL).     

Numerical investigation of the leakage and explosion scenarios in China's first liquid hydrogen refueling station

Promoting fuel cells has been one of China's ambitious hydrogen policies in the past few years. Currently, several hydrogen fueling stations (HRSs) are under construction in China to fuel hydrogen-driven vehicles. In this regard, it is necessary to assess the risks of hydrogen leakage in HRSs. Aiming at conducting a comprehensive consequence assessment of liquid hydrogen (LH2) leakage on China's first liquid hydrogen refueling station (LHRS) in Pinghu, a pseudo-source model is established in the present study to simulate the LH2 leakage using a commercial CFD tool, FLACS. The effects of the layout of the LHRS, leakage parameters, and local meteorological conditions on the LH2 leakage consequence has been assessed from the perspectives of low-temperature hazards and explosion hazards. The obtained results reveal that considering the prevailing southeast wind in Pinghu city, the farthest low-temperature hazard distance and lower flammable limit (LFL) -distance occurs in the leakage scenario along the north direction. It is found that the trailer parking location in the current layout of the LHRS will worsen the explosion consequences of the LH2 leakage. Moreover, the explosion will completely destroy the control room and endanger people on the adjacent road when the leakage equivalent diameter is 25.4 mm. The performed analyses reveal that as the wind speed increases, the explosion hazard decreases.     

Validation strategy for CFD models describing safety-relevant scenarios including LH2/GH2 release and the use of passive auto-catalytic recombiners

The ability to simulate the whole chain of physical phenomena that may occur following an accidental hydrogen release is mandatory for future safety studies on an industrial or urban scale. In cooperation with the RWTH Aachen University, Forschungszentrum Jülich develops numerical methods to predict safety incidents connected with the release of either liquid hydrogen (LH₂) or gaseous hydrogen (GH₂), using the commercial computational fluid dynamics (CFD) code ANSYS CFX. The full sequence from the release, distribution or accumulation of accidentally released hydrogen, until the mitigation of accident consequences by safety devices is considered. The paper describes the current development status, gives examples of the validation and concludes with future work to provide the full range of hydrogen release and recombination simulation.     

Study on the harm effects of releases from liquid hydrogen tank by consequence modeling

The accidental releases of hydrogen from liquid storage and the subsequent consequences are studied from a harm perspective rather than a standpoint of risk. The cold, thermal and overpressure effects from hydrogen cold cloud, fireball, jet fire, flash fire, and vapor cloud explosion are evaluated in terms of two kinds of effect distances based on lethal and harmful criteria. Results show that for instantaneous release, the sequence of effect distances is vapor cloud explosion > flash fire > cold cloud > fireball, and for continuous release, the sequence is vapor cloud explosion > flash fire > jet fire > cold cloud. An overall comparison between instantaneous and continuous release reveals that the catastrophic rupture, rather than leakages, is the dominant event. Besides, the effect distances of liquid hydrogen tank are compared with those of 70 MPa gaseous storage with equivalent mass. Compared with 70 MPa gaseous storage, the liquid hydrogen storage may be safer under leak scenarios but more dangerous under catastrophic rupture scenario.     

Simulation on a proposed large-scale liquid hydrogen plant using a multi-component refrigerant refrigeration system

A proposed liquid hydrogen plant using a multi-component refrigerant (MR) refrigeration system is explained in this paper. A cycle that is capable of producing 100 tons of liquid hydrogen per day is simulated. The MR system can be used to cool feed normal hydrogen gas from 25 °C to the equilibrium temperature of −193 °C with a high efficiency. In addition, for the transition from the equilibrium temperature of the hydrogen gas from −193 °C to −253 °C, the new proposed four H₂ Joule–Brayton cascade refrigeration system is recommended. The overall power consumption of the proposed plant is 5.35 kWh/kg_LH2, with an ideal minimum of 2.89 kWh/kg_LH2. The current plant in Ingolstadt is used as a reference, which has an energy consumption of 13.58 kWh/kg_LH2 and an efficiency of 21.28%: the efficiency of the proposed system is 54.02% or more, where this depends on the assumed efficiency values for the compressors and expanders. Moreover, the proposed system has some smaller-size heat exchangers, much smaller compressor motors, and smaller crankcase compressors. Thus, it could represent a plant with the lowest construction cost with respect to the amount of liquid hydrogen produced in comparison to today’s plants, e.g., in Ingolstadt and Leuna. Therefore, the proposed system has many improvements that serve as an example for future hydrogen liquefaction plants.     

Ignition and heat radiation of cryogenic hydrogen jets

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.     

Solid air hydrogen liquefaction,the missing link of the hydrogen economy

The most challenging aspect of developing a green hydrogen economy is long-distance oceanic transportation. Hydrogen liquefaction is a transportation alternative. However, the cost and energy consumption for liquefaction is currently prohibitively high, creating a major barrier to hydrogen supply chains. This paper proposes using solid nitrogen or oxygen as a medium for recycling cold energy across the hydrogen liquefaction supply chain. When a liquid hydrogen (LH2) carrier reaches its destination, the regasification process of the hydrogen produces solid nitrogen or oxygen. The solid nitrogen or oxygen is then transported in the LH2 carrier back to the hydrogen liquefaction facility and used to reduce the energy consumption cooling gaseous hydrogen. As a result, the energy required to liquefy hydrogen can be reduced by 25.4% using N₂ and 27.3% using O₂. Solid air hydrogen liquefaction (SAHL) can be the missing link for implementing a global hydrogen economy.     

Optimization experimental design of stable production life and estimated ultimate recovery in gaseous compound of hydrogen and carbon from shale reservoir

In this study, a mixed numerical model is established to simulate the production performance of gaseous compound of hydrogen and carbon in shale reservoir. Estimated ultimate recovery (EUR) and stable production life (SPL) of gaseous compound of hydrogen and carbon are affected by reservoir parameters and production control parameters, such as Langmuir pressure, Langmuir volume, critical desorption pressure, fracture half length, permeability in stimulated reservoir volume (SRV) area, bottom hole flow pressure and production of gaseous compound of hydrogen and carbon. Therefore, in the later research, in order to reduce the number of numerical experiments, the orthogonal experimental method is used to optimize the influence of hydrocarbon ERU and SPL, and analyze the main control factors affecting these two indices at the same time. The purpose of this paper is to optimize the production of hydrocarbons by orthogonal experimental method and find the main controlling factors affecting the production of compound of hydrogen and carbon. Two groups of orthogonal experiments were designed to find the best scheme in the process of compound of hydrogen and carbon development. The calculative results show that the output of hydrogen and carbon compounds has a highly significant impact on SPL, Langmuir volume and capability in SRV have a significant impact, and Langmuir pressure Critical destruction pressure and hydraulic fracture half-length had no significant effects.     

CFD simulation of heat transfer and phase change characteristics of the cryogenic liquid hydrogen tank under microgravity conditions

The heat transfer and phase change processes of cryogenic liquid hydrogen (LH₂) in the tank have an important influence on the working performance of the liquid hydrogen-liquid oxygen storage and supply system of rockets and spacecrafts. In this study, we use the RANS method coupled with Lee model and VOF (volume of fraction) method to solve Navier-stokes equations. The Lee model is adopted to describe the phase change process of liquid hydrogen, and the VOF method is utilized to calculate free surface by solving the advection equation of volume fraction. The model is used to simulate the heat transfer and phase change processes of the cryogenic liquid hydrogen in the storage tank with the different gravitational accelerations, initial temperature, and liquid fill ratios of liquid hydrogen. Numerical results indicate greater gravitational acceleration enhances buoyancy and convection, enhancing convective heat transfer and evaporation processes in the tank. When the acceleration of gravity increases from 10^?2 g0 to 10^?5 g0, gaseous hydrogen mass increases from 0.0157 kg to 0.0244 kg at 200s. With the increase of initial liquid hydrogen temperature, the heat required to raise the liquid hydrogen to saturation temperature decreases and causes more liquid hydrogen to evaporate and cools the gas hydrogen temperature. More cryogenic liquid hydrogen (i.e., larger the fill ratio) makes the average fluid temperature in the tank lower. A 12.5% reduction in the fill ratio resulted in a decrease in fluid temperature from 20.35 K to 20.15 K (a reduction of about 0.1%, at 200s).     

Numerical modelling of release of subsonic and sonic hydrogen jets

For the general public to use hydrogen as a vehicle fuel, they must be able to handle hydrogen with the same degree of confidence as conventional liquid and gaseous fuels. For refuelling hydrogen cars, hydrogen is stored at high pressures up to 700 bar. The hazards associated with jet releases from accidental leaks of such highly pressurized storage must be considered since a jet release and dispersion can result in a fire or explosion. Therefore, it is essential to understand the dispersion characteristics of hydrogen to determine the extent of the flammable cloud when released from a high-pressure source. These parameters are very important in the establishment of the safety distances and sizes of hazardous zones. This paper describes the work done by us in modelling of dispersion of accidental releases of hydrogen, using the FRED (Fire Explosion Release Dispersion) software. The dispersion module in FRED is validated against experimental data available in the open literature for steady release and dispersion of cold and ambient hydrogen gas. The validation is performed for a wide range of hole sizes (0.5–4 mm), pressure (1.7–400 bar) and temperature (50–298 K).The model predictions of hydrogen gas jet velocity, concentration decay as a function of distance as well as radial concentration distribution are in good agreement with experiments. Overall, it is concluded that FRED can accurately model accidental release and dispersion of hydrogen in unconfined and open configurations.     

Hydrogen wide area monitoring of LH2 releases

The characterization of liquid hydrogen (LH2) releases has been identified as an international research priority to expand the safe use of hydrogen as an energy carrier. The elucidation of LH2 release behavior will require the development of dispersion and other models, guided and validated by empirical field measurements such as those afforded by Hydrogen Wide Area Monitoring (HyWAM). HyWAM can be defined as the quantitative spatial and temporal three-dimensional monitoring of planned or unintentional hydrogen releases. With support provided through the FCH JU Prenormative Research for the Safe Use of Liquid Hydrogen (PRESLHY) program, HSE performed a series of LH2 releases to characterize the dispersion and pooling behavior of cold hydrogen releases. The NREL Sensor Laboratory developed a HyWAM system based upon a distributed array of point sensors that is amenable for profiling cold hydrogen plumes. The NREL Sensor Laboratory and HSE formally committed to collaborate on profiling the LH2 releases. This collaboration included the integration of the NREL HyWAM into the HSE LH2 release hardware. This was achieved through a deployment plan jointly developed by the NREL and HSE personnel. Under this plan, the NREL Sensor Laboratory provided multiple HyWAM modules that accommodated 32 sampling points for near-field hydrogen profiling during the HSE PRESLHY LH2 releases. The NREL HyWAM would be utilized throughout the LH2 release study performed under PRESLHY by HSE, including Work Package 3 (WP3—Release and Mixing--Rainout) and subsequent work packages (WP4—Ignition and WP5—Combustion). Under the auspices of the PRESLHY WP6 (Implementation), data and findings from the HSE LH2 Releases are to be made available to stakeholders in the hydrogen community. Comprehensive data analysis and dissemination is ongoing, but the integration of the NREL HyWAM into the HSE LH2 Release Apparatus and its performance as well as some key outcomes of the LH2 releases in WP3 are presented.     

Hydrogen supply chain and challenges in large-scale LH2 storage and transportation

Hydrogen is considered to be one of the fuels of future and liquid hydrogen (LH2) technology has great potential to become energy commodity beyond LNG. However, for commercial widespread use and feasibility of hydrogen technology, it is of utmost importance to develop cost-effective and safe technologies for storage and transportation of LH2 for use in stationary applications as well as offshore transportation. This paper reviews various aspects of global hydrogen supply chain starting from several ways of production to storage and delivery to utilization. While each these aspects contribute to the overall success and efficiency of the global supply chain, storage and delivery/transport are the key enablers for establishing global hydrogen technology, especially while current infrastructure and technology are being under development. In addition, while all storage options have their own advantages/disadvantages, the LH2 storage has unique advantages due to the familiarity with well-established LNG technology and existing hydrogen technology in space programs. However, because of extremely low temperature constraints, commercialization of LH2 technology for large-scale storage and transportation faces many challenges, which are discussed in this paper along with the current status and key gaps in the existing technology.     

全球加氢站产业、技术及标准进展综述

以美国、欧洲、日本、中国的加氢站作为考察对象,就产业投资运营、主要设备商、相关标准进行梳理,结果表明：在加氢站投资及运营管理方面,美国、欧洲、日本具有较为成熟的经验;在氢增压、储存、加注等技术方面,德国、日本保持领先地位。在诸多氢气和液氢的技术领域,美国保持领先地位;在一些细分技术领域,英国、法国、挪威、俄罗斯具有优势;在加氢站标准方面,美国、日本具有较为完善的标准体系。中国已解决70 MPa氢气增压、加注、储存等领域的部分技术难题,但与其他国家相比,离子液式氢压缩机、液氢泵、液氢储罐、液氢加氢枪等产品的研发仍需持续推进。     

Economic analysis of near-term California hydrogen infrastructure

A detailed economics model of hydrogen infrastructure in California has been developed and applied to assess several potential fuel cell vehicle deployment rate and hydrogen station technology scenarios. The model accounts for all of the costs in the hydrogen supply chain and specifically examines a network of 68 planned and existing hydrogen stations in terms of economic viability and dispensed hydrogen cost. Results show that (1) current high-pressure gaseous delivery and liquid delivery station technologies can eventually be profitable with relatively low vehicle deployment rates, and (2) the cost per mile for operating fuel cell vehicles can be lower than equivalent gasoline vehicles in both the near and long term.     

Screen channel LAD bubble point tests in liquid hydrogen

This paper presents experimental results for the liquid hydrogen bubble point tests for liquid acquisition devices (LADs) operating in low gravity cryogenic propulsion systems. The purpose of the test was to investigate parameters that affect screen channel LAD performance in a low pressure liquid hydrogen (LH₂) propellant tank and to demonstrate several ways to increase the LH₂ bubble point pressure. Three fine mesh screen channel LAD samples were tested in LH₂ over the range of 16.7 K < T < 21.1 K and 31.5 kPa < P < 155 kPa using gaseous helium and hydrogen as pressurant gases. Results show that bubble point pressure is affected by screen mesh type, liquid temperature and pressure, and type of pressurization gas. Higher bubble points are achieved by using a finer mesh screen and pressurizing and subcooling the liquid with gaseous helium. In addition, there is evidence that the screen pore is itself temperature dependent.     

Effect of heat transfer through the release pipe on simulations of cryogenic hydrogen jet fires and hazard distances

Jet flames originated by cryo-compressed ignited hydrogen releases can cause life-threatening conditions in their surroundings. Validated models are needed to accurately predict thermal hazards from a jet fire. Numerical simulations of cryogenic hydrogen flow in the release pipe are performed to assess the effect of heat transfer through the pipe walls on jet parameters. Notional nozzle exit diameter is calculated based on the simulated real nozzle parameters and used in CFD simulations as a boundary condition to model jet fires. The CFD model was previously validated against experiments with vertical cryogenic hydrogen jet fires with release pressures up to 0.5 MPa (abs), release diameter 1.25 mm and temperatures as low as 50 K. This study validates the CFD model in a wider domain of experimental release conditions - horizontal cryogenic jets at exhaust pipe temperature 80 K, pressure up to 2 MPa ab and release diameters up to 4 mm. Simulation results are compared against such experimentally measured parameters as hydrogen mass flow rate, flame length and radiative heat flux at different locations from the jet fire. The CFD model reproduces experiments with reasonable for engineering applications accuracy. Jet fire hazard distances established using three different criteria - temperature, thermal radiation and thermal dose - are compared and discussed based on CFD simulation results.     

Ignited releases of liquid hydrogen: Safety considerations of thermal and overpressure effects

If the 'Hydrogen Economy' is to progress, more hydrogen fuelling stations are required. In the short term and in the absence of a hydrogen distribution network, these fuelling stations will have to be supplied by liquid hydrogen (LH2) road tankers. Such a development will increase the number of tanker offloading operations significantly and these may need to be performed in close proximity to the general public.The aim of this work was to determine the hazards and severity of a realistic ignited spill of LH2 focussing on; flammability limits of an LH2 vapour cloud, flame speeds through an LH2 vapour cloud and subsequent radiative heat levels after ignition. The experimental findings presented are split into three phenomena; jet-fires in high and low wind conditions, 'burn-back' of ignited clouds and secondary explosions7 post 'burn-back'. An attempt was made to estimate the magnitude of an explosion that occurred during one of the releases. The resulting data were used to propose safety distances for LH2 offloading facilities which will help to update and develop guidance for codes and standards.     

Validation of CFD modelling of LH2 spread and evaporation against large-scale spill experiments

Hydrogen is widely recognized as an attractive energy carrier due to its low-level air pollution and its high mass-related energy density. However, the safety characteristics of hydrogen are a concern, primarily due to its wide flammability range and high burning velocity. A significant fraction of hydrogen is stored and transported as a cryogenic liquid. Therefore, loss of hydrogen containments may lead to the formation of a pool on the ground. In general, very large spills will give a pool, whereas moderate sized spills may evaporate immediately. Accurate hazard assessments of storage systems require a proper prediction of the liquid hydrogen pool evaporation and spreading when conditions are conducive to the formation of a pool.A pool model handling the spread and the evaporation of liquid spills on different surfaces has recently been implemented in the 3D-Computational Fluid Dynamics (CFD) tool FLACS [1], [2], [3] and [4]. As the influence of geometry on the liquid spread is taken into account in the pool model, realistic industrial scenarios can be investigated. The model has been extensively validated for Liquefied Natural Gas (LNG) spills [5] and [6]. The model has previously been tested for LH₂ release in the framework of the EU-sponsored Network of Excellence HySafe where experiments carried out by BAM were modelled. In the large-scale BAM experiments [7], 280 kg of liquid hydrogen was spilled in 6 tests adjacent to buildings. In these tests, the pool spreading, the evaporation, and the cloud formation were investigated. Simulations of these tests are found to compare reasonably well with the experimental results.In the present work, the liquid hydrogen spill experiments carried out by NASA are simulated with the pool model. The large-scale NASA experiments [8] and [9] consisted of 7 releases of liquefied hydrogen at White Sand, New Mexico. The release test 6 is used. During these experiments, cloud concentrations were measured at several distances downwind of the spill point. With the new pool model feature, the FLACS tool is shown to be an efficient and accurate tool for the investigation of complex and realistic accidental release scenarios of cryogenic liquids.