Comparative risk assessment of liquefied and gaseous hydrogen refueling stations

Several countries are incentivizing the use of hydrogen (H₂) fuel cell vehicles, thereby increasing the number of H₂ refueling stations (HRSs), particularly in urban areas with high population density and heavy traffic. Therefore, it is necessary to assess the risks of gaseous H₂ refueling stations (GHRSs) and liquefied H₂ refueling stations (LHRSs). This study aimed to perform a quantitative risk assessment (QRA) of GHRSs and LHRSs. A comparative study is performed to enhance the decision-making of engineers in setting safety goals and defining design options. A systematic QRA approach is proposed to estimate the likelihood and consequences of hazardous events occurring at HRSs. Consequence analysis results indicate that catastrophic ruptures of tube trailer and liquid hydrogen storage tanks are the worst accidents, as they cause fires and explosions. An assessment of individual and societal risks indicates that LHRSs present a lower hazard risk than GHRSs. However, both station types require additional safety barrier devices for risk reduction, such as detachable couplings, hydrogen detection sensors, and automatic and manual emergency shutdown systems, which are required for risk acceptance.     

Trade-off study between risk and benefit in safety devices for hydrogen refueling stations using a dynamic physical model

As hydrogen refueling stations become increasingly common, it is clear that a high level of economic efficiency and safety is crucial to promoting their use. One way to reduce costs is to use a simple orifice instead of an excess flow valve, which Japanese safety regulations have identified as a safety device. However, there is concern about its effect on refueling time and on risk due to hydrogen leakage. To clarify the effect, we did a study of model-based refueling time evaluation and quantitative risk assessment for a typical refueling station. This study showed that an orifice is an effective alternative safety device. The increase in refueling time was less than 10%, based on simulations using a dynamic physical model of the station. Neither was there a significant difference in the risk between a configuration with excess flow valves and one with an orifice.     

Quantitative risk assessment of an urban hydrogen refueling station

Hydrogen is one of important energy source in the next generation of renewable energy. It has powerful strength such as no emission from CO2 for fuel, Nevertheless, many countries have difficulties to expand hydrogen infra due to high risky from hydrogen. Especially, the hydrogen refueling station which is located in urban area has congested structure and high population around, it has higher risk than conventional refueling station. This paper presents a quantitative risk assessment (QRA) of a high pressure hydrogen refueling station in an urban area with a large population and high congestion between the instruments and equipment. The results show that leaks from the tube-trailer and dispenser as well as potential explosion of the tube-trailer are the main risks. For the safety of the station operator, customers and people surrounding the refueling station, additional mitigation plans such as adding additional safety barrier system have to be implemented on the compressor and dispenser in order to prevent continuous release of hydrogen from an accident.     

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.     

Risk assessment for liquid hydrogen fueling stations

In recent years, consumers calling for the protection of the environment on a regional and global scale are demanding the use of vehicles that do not emit harmful exhaust. It is anticipated that one response to this demand is the widespread use of fuel cell vehicles (FCVs). In order to achieve this, it is necessary to provide hydrogen fueling stations where FCVs can refuel.     

Liquid pump-enabled hydrogen refueling system for heavy duty fuel cell vehicles: Fuel cell bus refueling demonstration at Stark Area Regional Transit Authority (SARTA)

We have demonstrated a hydrogen (H₂) refueling solution capable of delivering precooled, compressed gaseous hydrogen for heavy duty vehicle (HDV) refueling applications by refueling transit buses over a three-month period under real-world conditions. The system uses a submerged pump to deliver pressurized liquid H₂ from a cryogenic storage tank to a dispensing control loop that vaporizes the liquid and adjusts the pressure and temperature of the resulting gas to enable refueling at 35 MPa and temperatures as low as −40 °C, consistent with the SAE J2601 standard. Using our full-scale mobile refueler, we completed 118 individual bus filling events using 13 different vehicles, involving a total of 3,700 kg of H₂ dispensed. We report filling statistics from the entire campaign, details on individual fills (including fill times, final state of charge, benefits of pre-cooled fills, and back-to-back filling capabilities), and discuss transit agency feedback on technology performance. In our final test, the system successfully completed an endurance test using a single dispenser involving 52 consecutive individual fills over an 11.5-h period, dispensing 1,322 kg of H₂ with an average fill rate of 3.4 kg/min and peak rate of 7.1 kg/min, and reaching an average SOC of 97.6% across all fills.     

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.     

Improved safety by crossanalyzing quantitative risk assessment of hydrogen refueling stations

With the goal of building 310 hydrogen refueling stations (HRSs) in Korea by 2022, restrictions, such as location restrictions and separation distances, are being eased, so developing ways to improve technology and safety. As HRSs contain major facilities such as compressors, storage tanks, dispenser, and priority control panels, and a leakage could result in a large fire or explosion caused by an ignition source. To perform quantitative risk assessment, programs, namely, Hy-KoRAM and Phast/Safeti were used in this study. It could determine the damage range and effect on radiant heat and flame length, as well as personal and societal risks, using these programs. The crossanalysis of the two programs also improves the facility's safety and the reliability of the results.     

Development of a cross-contamination-free hydrogen sampling methodology and analysis of contaminants for hydrogen refueling stations

Hydrogen used in proton exchange membrane-based fuel cell applications is subject to very high quality requirements. While the influences of contaminations in hydrogen on long-term stability have been intensively studied, the purity of hydrogen for mobile applications provided at hydrogen refueling stations (HRS) is rarely analyzed. Hence, in this study, we present sampling of hydrogen at HRS with a specially designed mobile tank for up to 70 MPa. These samples are precisely analyzed with a sophisticated ion molecule reaction mass spectrometer (IMR-MS), able to determine concentrations of contaminants down to the ppb-level. Sampling and analysis of hydrogen at an HRS supplied by electrolysis revealed a high purity, but likewise considerable contaminations above the threshold of the international standard ISO 14687:2019. In this study, a state-of-the-art analysis coupled with a developed methodology for fuel cell electric vehicle-independent sampling of hydrogen with a mobile tank system is demonstrated and applied for comprehensive studies of hydrogen purity.     

Techno-economic optimization of wind energy based hydrogen refueling station case study Salalah city Oman

Clean energy resources will be used more for sustainability improvement and durable development. Efficient technologies of energy production, storage, and usage results in reduction of gas emissions and improvement of the world economy. Despite 30% of electricity being produced from wind energy, the connection of wind farms to medium and large-scale grid power systems is still leading to instability and intermittency problems. Therefore, the conversion of electrical energy generated from wind parks into green hydrogen consists of an exciting solution for advancing the development of green hydrogen production, and the clean transportation sector. This paper presents a techno-economic optimization of hydrogen production for refueling fuel cell vehicles, using wind energy resources. The paper analyses three configurations, standalone Wind-Park Hydrogen Refueling Station (WP-HRS) with backup batteries, WP-HRS with backup fuel cells, and grid-connected WP-HRS. The analysis of different configurations is based on the wind potential at the site, costs of different equipment, and hydrogen load. Therefore, the study aims to find the optimized capacity of wind turbines, electrolyzers, power converters, and storage tanks. The optimization results show that the WP-HRS connected to the grid has the lowest Present Worth Cost (PWC) of 6,500,000 €. Moreover, the Levelized Hydrogen Cost (LHC) of this solution was found to be 6.24 €/kg. This renewable energy system produces 80,000 kg of green hydrogen yearly.     

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.     

Quantitative risk assessment of a hydrogen refueling station by using a dynamic physical model based on multi-physics system-level modeling

Numerous accidents in HRSs have been reported worldwide in accident databases; therefore, many researchers have performed quantitative risk assessments (QRAs) of HRSs to enable risk-informed decision making in determining the safety distances or risk mitigation measures. The HRSs, located in urban areas such as Tokyo in Japan, are situated in congested areas with tall buildings and high population density; thus, they have relatively narrow station areas. However, the QRAs are generally suitable for large plants such as nuclear power plants or chemical plants; therefore, relatively small plants or installations, such as HRSs, have not yet been considered as QRA objects. Hence, it is necessary to conduct detailed QRAs with risk analyses and reduce the applied uncertainties for relatively small plants or installations. We applied a model-based approach of risk assessment to model the HRS process using multi-physics system-level modeling and simulated a target system using Modelica—an equation-based, object-oriented modeling language that allows acausal modeling of complex cyber-physical systems The primary aim of this study was to conduct a QRA of an HRS based on multi-physics system-level modeling. First, we modeled the HRS components and physical relationships between the components using basic physical equations. Then, we elucidate a QRA based on the constructed model. The difference in the leakage rates due to the leak positions and dynamic behavior of the model parameters were calculated using the constructed model. Finally, we estimated the individual risks of all the scenarios and compared the resulting risk contours based on the constructed model that includes the hydrogen-fuel dynamic behavior with those based on the traditional model. These results indicate that it is possible to assess whether the risks around the station boundary are acceptable based on the scenario information obtained by evaluating the risks near the station.     

Liquid pump-enabled hydrogen refueling system for heavy duty fuel cell vehicles: Pump performance and J2601-compliant fills with precooling

We have developed a hydrogen (H₂) refueling solution capable of delivering precooled, compressed gaseous hydrogen for heavy duty vehicle (HDV) refueling applications. The system uses a submerged pump to deliver pressurized liquid H₂ from a cryogenic storage tank to a dispensing control loop that vaporizes the liquid and adjusts the pressure and temperature of the resulting gas to enable refueling at 35 MPa and temperatures as low as ?40 °C. A full-scale mobile refueler was fabricated and tested over a 6-month campaign to validate its performance. We report results from tests involving a total of 9000 kg of liquid H₂ pumped and 1350 filling cycles over a range of conditions. Notably, the system was able to repeatably complete multiple, back-to-back 30 kg filling cycles in under 6 min each, in full compliance with the SAE J2601-2 standard, demonstrating its potential for rapid-throughput HDV refueling applications.     

An index-based risk assessment model for hydrogen infrastructure

This study focuses on the development of a risk assessment model associated with the safety of a hydrogen infrastructure system. The safety of hydrogen infrastructure is one of the crucial pre-requisites for a sustainable economy and accordingly, its design should be made based upon the performance to investigate and evaluate the risks from or out of the required infrastructure. In order to support strategic decision-making for safe hydrogen infrastructure, this study proposes an appropriate index-based risk assessment model. The model evaluates the hydrogen infrastructure using the relative risk ranking of the hydrogen activities such as hydrogen production, storage and transportation, and the relative impact levels of regions. The relative risk rankings of the hydrogen activities are rated a quantitative risk analysis, whereas the relative impact level of regions is rated based on the regional characteristics such as population density. With consideration of regional characteristics, the proposed model makes it possible not only to assess the risks of processes and technologies associated with hydrogen but also to compare the relative safety levels of the hydrogen infrastructures made up with various hydrogen activities. In order to show the features and capabilities of the model, four future hydrogen infrastructure scenarios in Korea are examined in the study. The result shows that distributed production, and mass storage and transportation via liquefied hydrogen facility are relatively safer than centralized production, and compressed-gaseous hydrogen storage and transportation, respectively.     

Quantitative risk assessment of the interior of a hydrogen refueling station considering safety barrier systems

A quantitative risk assessment of human life during the operation of a hydrogen refueling station (HRS) is conducted. We calculate the risks for three accident scenarios: a hydrogen leak from the external piping surrounding a dispenser, a hydrogen leak from an accumulator connection piping and a hydrogen leak from a compressor/connection piping in the HRS. We first calculate the probability of accident by multiplying the estimated leak frequency with the incident occurrence probability considering the ignition probability and failure probability of the safety barrier systems obtained through event tree analysis for each scenario. We next simulate the blast and flame effects of the ignition of concentration fields formed by hydrogen leakage. We then use existing probit functions to estimate the consequences of eardrum rupture, fatalities due to displacement by the blast wave, fatalities due to head injuries, first-degree burns, second-degree burns, and fatal burn injuries by accident scenario, leak size, and incident event, and we estimate the risk distribution in 1-m cells. We finally assess the risk reduction effects of barrier placement and the distance to the dispenser and quantify the risk level that HRSs can achieve under existing law. Quantitative risk assessment reveals that the risk for a leak near the dispenser is less than 10⁻⁶ per year outside a distance of 6 m to the dispenser. The risk for a leak near the accumulators and compressors exceeds 10⁻⁴ per year within a distance of 10 m from the ignition point. A separation of 6 m to the dispenser and a barrier height of 3 m keep the fatal risk from burns to the workers, consumers and residents and passersby below the acceptable level of risk. Our results therefore show that current laws sufficiently mitigate the risks posed by HRSs and open up the possibility for a regulatory review.     

Optimal siting and sizing of hydrogen refueling stations considering distributed hydrogen production and cost reduction for regional consumers

Hydrogen fuel cell vehicles are currently facing two difficulties in achieving their general use: the lack of hydrogen refueling stations and high hydrogen prices. Hydrogen refueling stations are the middle stage for delivering hydrogen from its sources to consumers, and their location could be affected by the distributed locations of hydrogen sources and consumers. The reasonable siting and sizing of hydrogen refueling stations could both improve the hydrogen infrastructure and reduce regional consumers' cost of using hydrogen. By considering the hydrogen life cycle cost and using a commercial volume forecasting model, this paper creates a relatively thorough and comprehensive model for hydrogen station siting and sizing with the objective of achieving the optimal costs for consumers using hydrogen. The cost‐based model includes the selection of the hydrogen sources, transportation methods, and storage methods, and thus, the hydrogen supply chain can also be optimized. A numerical example is established in Section 4 with the solution algorithm and results.     

An optimized control method for a high utilization ratio and fast filling speed in hydrogen refueling stations

A well-designed control system with a high utilization ratio of hydrogen and a fast filling speed are two critical objectives to ensure the reduction of cost and time required in the refueling process. In this paper, the popular three-stage refueling process is modeled with the aim to address both objectives. Using the real gas law of hydrogen, the utilization ratio of hydrogen filling is analyzed and the filling flowrate and time of each stage are evaluated. A multi-objective iterative optimization model is established and an optimization algorithm for the filling process is proposed to achieve both fast refueling and high utilization. Numerical results can be applied to the optimization of an actual hydrogen filling process. Besides, the tests show that an optimized control method can significantly improve the utilization ratio and allow refueling in a widely acceptable time.     

Development and CFD analysis for determining the optimal operating conditions of 250 kg/day hydrogen generation for an on-site hydrogen refueling station (HRS) using steam methane reforming

The objective of this study to develop and undertake a comprehensive CFD analysis of an effective state-of-the-art 250 kg/day hydrogen generation unit for an on-site hydrogen refueling station (HRS), an essential part of the infrastructure required for fuel cell vehicles and various aspects of hydrogen mobility. This design consists of twelve reforming tubes and one newly designed metal fiber burner to ensure superior emission standards and performance. Experimental and computational modeling steps are conducted to investigate the effects of various operating conditions, the excess air ratio (EAR) at the burner, the gas hourly space velocity (GHSV), the process gas inlet temperature, and the operating pressure on the hydrogen production rate and thermal efficiency. The results indicate that the performance of the steam methane reforming reactor increased significantly by improving the combustion characteristics and preventing local peak temperatures along the reforming tube. It is shown that EAR should be chosen appropriately to maximize the hydrogen production rate and lifetime operation of the reformer tube. It is found that high inlet process gas temperatures and low operating pressure are beneficial, but these parameters have to be chosen carefully to ensure proper efficiency. Also, a high GHSV shortens the residence time and provides unfavorable heat transfer in the bed, leading to decreased conversion efficiency. Thus, a moderate GHSV should be used. It is shown that heat transfer is an essential factor for obtaining increased hydrogen production. This study addresses the pressing need for the HRS to adopt such a compact system, whose processes can ensure greater hydrogen production rates as well as better durability, reliability, and convenience.     

Experiment of cryo-compressed (90-MPa) hydrogen leakage diffusion

To improve safety regulations for fuel cell vehicles and hydrogen infrastructures, experiments on cryo-compressed hydrogen leakage diffusion were conducted. The experimental apparatus can supply 90 MPa hydrogen at various temperature conditions (50 K–300 K) at a maximum flow rate of 100 kg/h. The hydrogen leakage flow rate was measured using pinhole nozzles with different outlet diameters (0.2 mm, 0.4 mm, 0.7 mm, and 1 mm). It was confirmed that the hydrogen leakage flow rate increases as the supply temperature decreases. To evaluate the hydrogen flow rate including the cryogenic condition, the orifice equation for liquid was found to be appropriate. The orifice flow coefficient converged to a constant value of 0.6 on the high-density condition side. The hydrogen concentration distribution was measured by injecting high-pressure hydrogen from the 0.2-mm pinhole for 10 min under a constant pressure/temperature condition. The axial hydrogen concentration distribution obtained by the ambient temperature (～300 K) hydrogen injection test well agreed with the experimental formula based on previous research studies. In addition, as the hydrogen injection temperature decreased, it was found that the hydrogen concentration increased, and an empirical formula of the 1% concentration distance for the cryogenic hydrogen system was newly presented. Additional tests were conducted using pinholes of different diameters, and a 1% concentration distance was confirmed to be proportional to the hydrogen leakage flow rate to the 0.5th power.