Quantitative risk assessment using a Japanese hydrogen refueling station model

Although hydrogen refueling stations (HRSs) are becoming widespread across Japan and are essential for the operation of fuel cell vehicles, they present potential hazards. A large number of accidents such as explosions or fires have been reported, rendering it necessary to conduct a number of qualitative and quantitative risk assessments for HRSs. Current safety codes and technical standards related to Japanese HRSs have been established based on the results of a qualitative risk assessment and quantitative effectiveness validation of safety measures over ten years ago. In the last decade, there has been much development in the technologies of the components or facilities used in domestic HRSs and much operational experience as well as knowledge to use hydrogen in HRSs safely have been gained through years of commercial operation. The purpose of the present study is to conduct a quantitative risk assessment (QRA) of the latest HRS model representing Japanese HRSs with the most current information and to identify the most significant scenarios that pose the greatest risks to the physical surroundings in the HRS model. The results of the QRA show that the risk contours of 10^?3 and 10^?4 per year were confined within the HRS boundaries, whereas the risk contours of 10^?5 and 10^?6 per year are still present outside the HRS. Comparing the breakdown of the individual risks (IRs) at the risk ranking points, we conclude that the risk of jet fire demonstrates the highest contribution to the risks at all of the risk ranking points and outside the station. To reduce these risks and confine the risk contour of 10^?6 per year within the HRS boundaries, it is necessary to consider risk mitigation measures for jet fires.     

Quantitative risk assessment on 2010 Expo hydrogen station

This paper presents a QRA study on a gaseous hydrogen refueling station of 2010 World Expo. Risks to station personnel, to refueling customers and to third parties are evaluated respectively. Uncertainties that intervene in the risk analysis are also discussed. The results show that the leaks from compressors and dispensers are the main risk contributors to first party and second party risks of the Expo station, indicating that risk mitigation measures should in the first place be implemented on compressors and dispensers. For the sake of the safety of station personnel, customers, and people outside the Expo station, additional safety barrier systems must be implemented on compressors and dispensers to prevent continuous release of hydrogen from happening. With appropriate mitigation measures on compressors and dispensers, risks to all three parties of the Expo station can be reduced to the value lower than the risk acceptance criteria.     

Development of uniform harm criteria for use in quantitative risk analysis of the hydrogen infrastructure

This paper discusses the preliminary results of the Risk Management subtask efforts within the International Energy Agency (IEA) Hydrogen Implementing Agreement (HIA) Task 19 on Hydrogen Safety to develop uniform harm criteria for use in the Quantitative Risk Assessments (QRAs) of hydrogen facilities. The IEA HIA Task 19 efforts are focused on developing guidelines and criteria for performing QRAs of hydrogen facilities. The performance of QRAs requires that the level of harm that is represented in the risk evaluation be established using deterministic models. The level of harm is a function of the type and level of hazard. The principle hazard associated with hydrogen facilities is uncontrolled accumulation of hydrogen in (semi) confined spaces and consecutive ignition. Another significant hazard is combustion of accidentally released hydrogen gas or liquid, which may or may not happen instantaneously. The primary consequences from fire hazards consist of personnel injuries or fatalities, or facility and equipment damage due to high air temperatures, radiant heat fluxes, or direct contact with hydrogen flames. The possible consequences of explosions on humans and structures or equipment include blast wave overpressure effects, impact from fragments generated by the explosion, the collapse of buildings, and the heat effects from subsequent fire balls. A harm criterion is used to translate the consequences of an accident, evaluated from deterministic models, to a probability of harm to people, structures, or components. Different methods can be used to establish harm criteria including the use of threshold consequence levels and continuous functions that relate the level of a hazard to a probability of damage. This paper presents a survey of harm criteria that can be utilized in QRAs and makes recommendations on the criteria that should be utilized for hydrogen-related hazards.     

Thermodynamic modeling of hydrogen refueling for heavy-duty fuel cell buses and comparison with aggregated real data

The foreseen uptake of hydrogen mobility is a fundamental step towards the decarbonization of the transport sector. Under such premises, both refueling infrastructure and vehicles should be deployed together with improved refueling protocols. Several studies focus on refueling the light-duty vehicles with 10 kg_H2 up to 700 bar, however less known effort is reported for refueling heavy-duty vehicles with 30–40 kg_H2 at 350 bar. The present study illustrates the application of a lumped model to a fuel cell bus tank-to-tank refueling event, tailored upon the real data acquired in the 3Emotion Project. The evolution of the main refueling quantities, such as pressure, temperature, and mass flow, are predicted dynamically throughout the refueling process, as a function of the operating parameters, within the safety limits imposed by SAE J2601/2 technical standard. The results show to refuel the vehicle tank from half to full capacity with an Average Pressure Ramp Rate (APRR) equal to 0.03 MPa/s are needed about 10 min. Furthermore, it is found that the effect of varying the initial vehicle tank pressure is more significant than changing the ambient temperature on the refueling performances. In conclusion, the analysis of the effect of different APRR, from 0.03 to 0.1 MPa/s, indicate that is possible to safely reduce the duration of half-to-full refueling by 62% increasing the APRR value from 0.03 to 0.08 MPa/s.     

Design proposal for hydrogen refueling infrastructure deployment in the Northeastern United States

Fuel cell vehicles (FCVs) are expected to be commercially available on the world market in 2015, therefore, introducing hydrogen-refueling stations is an urgent issue to be addressed. This paper proposes deployment plan of hydrogen infrastructure for the success of their market penetration in the Northeastern United States. The plan consists of three-timeline stages from 2013 to 2025 and divides the designated region into urban area, suburban area and area adjacent to expressway, so that easy to access to hydrogen stations can be realized. Station is chosen from four types of stations: off-site station, urban-type on-site station, suburban-type on-site station and portable station, associated with growing demand. In addition, on-site station is used as hydrogen production factory for off-site station to save total investment. This deployment plan shows that 83% of urban residents can reach station within 10 min in 2025, and that more than 90% people especially in four major cities: Boston, New York City, Philadelphia, and Washington, D.C. can get to station within 10 min by Geographic Information System (GIS) calculation.     

A quantitative risk assessment of a domestic property connected to a hydrogen distribution network

The increased reliance on natural gas for heating worldwide makes the search for carbon-free alternatives imperative, especially if international decarbonisation targets are to be met. Hydrogen does not release carbon dioxide (CO₂) at the point of use which makes it an appealing candidate to decarbonise domestic heating. Hydrogen can be produced from either 1) the electrolysis of water with no associated carbon emissions, or 2) from methane reformation (using steam) which produces CO₂, but which is easily captured and storable during production. Hydrogen could be transported to the end-user via gas distribution networks similar to, and adapted from, those in use today. This would reduce both installation costs and end-user disruption. However, before hydrogen can provide domestic heat, it is necessary to assess the ‘risk’ associated with its distribution in direct comparison to natural gas. Here we develop a comprehensive and multi-faceted quantitative risk assessment tool to assess the difference in ‘risk’ between current natural gas distribution networks, and the potential conversion to a hydrogen based system. The approach uses novel experimental and modelling work, scientific literature, and findings from historic large scale testing programmes. As a case study, the risk assessment tool is applied to the newly proposed H100 demonstration (100% hydrogen network) project. The assessment includes the comparative risk of gas releases both upstream and downstream of the domestic gas meter. This research finds that the risk associated with the proposed H100 network (based on its current design) is lower than that of the existing natural gas network by a factor 0.88.     

Quantitative risk assessment on a gaseous hydrogen refueling station in Shanghai

The potential risk exposure of people for hydrogen refueling stations is often a critical factor to gain authority approval and public acceptance. Quantitative risk assessment (QRA) is often used to quantify the risk around hydrogen facilities and support the communication with authorities during the permitting process. This paper shows a case study on a gaseous hydrogen refueling station using QRA methodology. Risks to station personnel, to refueling customers and to third parties are evaluated respectively. Both individual risk measure and societal risk measure are used in risk assessment. Results show that the compressor leak is the main contributor to risks of all three parties. Elevating compressors can be considered as an effective mitigation measure to reduce occupational risks while setting enclosure around compressors cannot. Both measures are effective to reduce risks to customers. As for third parties, societal risks can be reduced to ALARP region by either elevating compressors or setting enclosure around compressors. External safety distance of compressors cannot be considerably reduced by elevation of compressors, but can significantly be reduced by setting compressor enclosure. However, safety distances of the station are not very sensitive to both mitigation measures.     

Research on sealing performance and self-acting valve reliability in high-pressure oil-free hydrogen compressors for hydrogen refueling stations

Piston ring sealing and valve design play an important role in high-pressure oil-free reciprocating compressors for hydrogen refueling stations. The severe non-uniformity of the pressure distribution was suggested to be the root cause of the premature failure of the sealing rings, and therefore a mathematical model was established to simulate the unsteady flow within the gaps of piston rings, based on which the pressure distribution was obtained and the mechanism of the non-uniform abrasion of the rings was disclosed. The method to equalize the pressure difference through each ring was proposed by re-distributing the cut size of each ring, and it was validated experimentally. Aiming at the problem that the self-acting valves in hydrogen compressors could be easily destroyed by severe impact, this paper investigated the motion and impact of valves theoretically and experimentally, based on which the methodology was explored to design the parameters of valves for hydrogen compressors.     

Development of Ti1.02Cr2-x-yFexMny (0.6≤x≤0.75, y=0.25, 0.3) alloys for high hydrogen pressure metal hydride system

To save compressor investment and promote operation efficiency of hydrogen refueling station, the hydrogen storage alloys for high-pressure hydrogen metal hydride tank is developed. Ti_1.02Cr_2-x-yFe_xMn_y (0.6 ≤ x ≤ 0.75, y = 0.25, 0.3) alloys with main structure of C14 type Laves phase and low dehydrogenation enthalpy were prepared by plasma arc melting and heat treatment. Pressure-composition-temperature measurements show that hydrogen desorption plateau pressures increase with Cr substituted by Fe increasing. The maximum and reversible hydrogen storage capacities are more than 1.85 and 1.65 wt% at 201 K respectively. The hydrogen desorption plateau slopes are all less than 0.5. The symmetry weakening of 2a sites may deteriorate the plateau slop characteristic. Ti_1.02Cr_0.95Fe_0.75Mn_0.3 and Ti_1.02Cr_1.0Fe_0.75Mn_0.25 alloys are suitable for high pressure hybrid tank which can supply the effective hydrogen (more than 70 MPa) about 40.0, 44.2, 46.9 kg/m³ with 45, 70, 90 MPa compressor, respectively.     

Evaluating uncertainty in accident rate estimation at hydrogen refueling station using time correlation model

Hydrogen, as a future energy carrier, is receiving a significant amount of attention in Japan. From the viewpoint of safety, risk evaluation is required in order to increase the number of hydrogen refueling stations (HRSs) implemented in Japan. Collecting data about accidents in the past will provide a hint to understand the trend in the possibility of accidents occurrence by identifying its operation time However, in new technology; accident rate estimation can have a high degree of uncertainty due to absence of major accident direct data in the late operational period. The uncertainty in the estimation is proportional to the data unavailability, which increases over long operation period due to decrease in number of stations. In this paper, a suitable time correlation model is adopted in the estimation to reflect lack (due to the limited operation period of HRS) or abundance of accident data, which is not well supported by conventional approaches. The model adopted in this paper shows that the uncertainty in the estimation increases when the operation time is long owing to the decreasing data.     

Dynamic simulation for optimal hydrogen refueling method to Fuel Cell Vehicle tanks

A dynamic simulation approach to investigate an optimal hydrogen refueling method is proposed. The proposed approach simulates a transient temperature, pressure and mass flow rate of hydrogen flowing inside filling equipment in an actual station during the refueling process to an Fuel Cell Vehicle (FCV) tank. The simulation model is the same as in an actual hydrogen refueling station (HRS), and consists of a Break-Away, a hose, a nozzle, pipes and an FCV tank. Therefore, we can set actual configurations and thermal properties to the simulation model, and then simulate the temperature, pressure and mass flow rate of hydrogen passing through each position based on the supply conditions (temperature and pressure) at the Break-Away. In this study, the simulated temperature, pressure and mass flow rate are compared with the corresponding experimental data. Therefore, we show that the dynamic simulation approach can accurately obtain those values at each position during the refueling process and is an effective step in proposing the optimal refueling method.