Safety

In the prospect of a safe use of hydrogen in our society one important task is to evaluate under which conditions the storage of hydrogen systems can reach a sufficient level of safety. One of the most important issues is the use of such system in closed area for example a private garage or an industrial facility. In the scope of this paper we are mainly interested in the following scenario: a relatively slow release of hydrogen (around 5Nl/min) in a closed and almost cubic box representing either a fuel cell at normal scale or a private garage at a smaller scale. For practical reasons helium was used instead of hydrogen in the experiments on which are based our comparisons. This kind of situation leads to the fundamental problem of the dispersion of hydrogen due to a simple vertical source in an enclosure. Many numerical and experimental studies have already been conducted on this problem showing the formation of either a stably stratified distribution of concentration or the formation of a homogeneous layer due to high enough convective flows at the top of the enclosure. Nevertheless most of them consider the cases of accidental situation in which the flow rate is relatively important (higher than 10Nl/min). Numerical simulations carried out with the CEA code Cast3M and a LES turbulence model confirm the differences of results already observed in experimental helium concentration measurements for a same injection flow rate and two different injection nozzle diameters contradicting simple physical models used in safety calculations.

Sandia National Laboratories has worked with stakeholders and original equipment manufacturers (OEMs) to develop scientific data that can be used to create risk-informed hydrogen codes and standards for the safe operation of indoor hydrogen fuel-cell forklifts. An important issue is the possibility of an accident inside a warehouse or other enclosed space where a release of hydrogen from the high-pressure gaseous storage tank could occur. For such scenarios computational fluid dynamics (CFD) simulations have been used to model the release and dispersion of gaseous hydrogen from the vehicle and to study the behavior of the ignitable hydrogen cloud inside the warehouse or enclosure. The overpressure arising as a result of ignition and subsequent deflagration of the hydrogen cloud within the warehouse has been studied for different ignition delay times and ignition locations. Both ventilated and unventilated warehouses have been considered in the analysis. Experiments have been performed in a scaled warehouse test facility and compared with simulations to validate the results of the computational analysis.

A prospective global market share of Electric vehicle (EV) Hybrid electric vehicle (HEV) and Hydrogen Fuel Cell Vehicle (HFCV) is expected to grow due to stringent emission regulation and oil depletion. However it is essential to secure protection against high-pressure hydrogen gas and high-voltage in fuel cell vehicles and thus needs to develop a technique for safety assessment of HFCV. In this experiment 8 research institutes including the Korea Automobile Testing and Research Institute Hyundai Motor Company took part in. This project was supported by the Ministry of Land Transportation and Maritime Affairs of the Republic of Korea.

Compressed natural gas (CNG) is being increasingly used as a clean transportation fuel. However for further reduction in emissions particularly NOx H-CNG mixture with ~ 20 % hydrogen is recommended. Presently most of the H-CNG mixture is produced by blending hydrogen with CNG. For hydrogen production Steam Methane Reforming (SMR) is a major process accounting for more than 90% of hydrogen production by various industries. In this process natural gas is first reformed to syn gas under severe operating conditions (Pressure 20-30 bar temperature 850-950 deg C) followed by conversion of CO to hydrogen in the shift reactor. Other method of hydrogen production such as electrolysis of water is more expensive. Further there are issues of safety with handling of hydrogen its storage and transportation for blending. In order to overcome these problems a single step compact process for the production of H-CNG gaseous mixture through low severity steam methane reforming of natural gas has been developed. It employs a catalyst containing nickel nickel oxide magnesium oxide and silica and has the capability of producing H-CNG mixture in the desired proportion containing 15-20 vol % hydrogen with nil CO production. The process is flexible and rugged allowing H-CNG production as per the demand. The gaseous H-CNG product mixture can directly be used as automobile fuel after compression. The process can help as important step in safe transition towards hydrogen economy. A demonstration unit is being set up at IOC R&D Centre.

We present an experimental investigation of the different concentration build-up regimes encountered during a release of helium/air mixture in an empty enclosure without ventilation. The release is a vertical jet issuing from a nozzle located near the floor. The nozzle diameter the flow rate and the composition of the injected mixture have been varied such that the injection Richardson number ranges from 6 × 10−6 to 190. The volume Richardson number which gives the ability of the release to mix the enclosure content ranges from 2 × 10−3 to 2 × 104. This wide range allowed reaching three distinct regimes: stratified stratified with a homogeneous upper layer and homogenous.

The project “Towards a Hydrogen Refuelling Infrastructure for Vehicles” (THRIVE) aimed at the determination of conditions to stimulate the building of a sustainable infrastructure for hydrogen as a car fuel in The Netherlands. Economic scenarios were constructed for the development of such an infrastructure for the next one to four decades. The eventual horizon will require the erection of a few hundred to more than a thousand hydrogen refuelling stations (HRS) in The Netherlands. The risk acceptability policy in The Netherlands implemented in the External Safety Establishments decree requires the assessment and management of safety risks imposed on the public by car fuelling stations. In the past a risk-informed policy has been developed for the large scale introduction of liquefied petroleum gas (LPG) as a car fuel and a similar policy will also be required if hydrogen is introduced in the public domain. A risk assessment methodology dedicated to cope with accident scenarios relevant for hydrogen applications is to be developed. Within the THRIVE project a demo risk assessment was conducted for the possible implementation of an HRS within an existing station for conventional fuels. The studied station is located in an urban area occupied with housing and commercial activities. The HRS is based on delivery and on-site storage of liquid hydrogen and dispensing of high pressure gaseous hydrogen into vehicles. The main challenges in the risk assessment were in the modelling of release and dispersion of liquid hydrogen. Definition of initial conditions for computational fluid dynamics (CFD) modelling to evaluate dispersion of a cold hydrogen air mixture appears rather complex and is not always fully understood. The modelling assumptions in the initial conditions determine to a large extent the likelihood and severity of potential explosion effects. The paper shows the results of the investigation and the sensitivity to the basic assumptions in the model input.

High-order perturbation solutions have been obtained for the simple physical model describing the LH2 spreading with a continuous spill and are shown to improve over the first-order perturbation solutions. The non-dimensional governing equations for the model are derived to obtain more general solutions. Non-dimensional parameters are sought as the governing parameters for the non-dimensional equations and the non-dimensional evaporation rate is used as the perturbation parameter. The results show that the second-order solutions exhibit an improvement over the first-order solutions with respect to the pool volume; however there is still a difference between numerical solutions and second-order solutions in the late stage of spread. Finally it is revealed that the third-order solutions almost agree with numerical solutions.

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.

Hydrogen fuelling in the US is unattended activity although this precedent is not without several challenges that have been addressed in the past decade. This paper provides the recent history and the generic safety case which has established this precedent for hydrogen. The paper also explores the longer history of unattended gasoline fuelling and attempts to help place hydrogen fuelling into the longer history of fuelling personal vehicles.

Various studies and market trends show that the number of hydrogen fuelling stations will increase to the thousands in the US by 2050. NFPA 2 Hydrogen Technologies Code (NFPA2) the nationally adopted primary code governing hydrogen safety is relatively new and hydrogen vehicle technology is a relatively new and rapidly developing technology. In order to effectively aid and accelerate the deployment of standardized retail hydrogen fuelling facilities the permitting of hydrogen fuelling stations employing outdoor bulk liquid storage in the state of California.

In an effort to better understand how the applicants consultants and more importantly the Authorities Having Jurisdiction (AHJ)s are interpreting and applying the NFPA 2 especially for complex applications the newest hydrogen stations with the largest amount of bulk hydrogen storage in urban environment settings were identified and the permit applications and permit approval outcomes of the said stations were analysed. Utilizing the pubic record request process LH2 station permit applications were reviewed along with the approval outcomes directly from the municipalities that issued the permits. AHJs with H2 station permitting experience were interviewed. Case studies of permit hydrogen fuelling station permit applications were then complied to document both the perspectives of the applicant and the AHJ and the often iterative and collaborative nature of permitting.

The current permitting time for Liquid Hydrogen (LH2) stations can range from 9 to 18 months in the California. Five out of the six LH2 stations applications required Alternative Means & Methods (AM&Ms) proposals and deviations from the prescriptive requirements of the Code were granted. Furthermore AHJs often requested additional documents and studies specific to application parameters in addition to NFPA 2 requirements.