Development of Korean hydrogen fueling station codes through risk analysis

When hydrogen fueling stations were constructed first time in Korea in 2006, there were no standards for hydrogen fueling stations. Hence the CNG (Compressed Natural Gas) station codes were temporarily adopted. In last three years, from 2006 to 2009, the studies for the development of hydrogen fueling station standards were carried out, with the support of the Korean government. In this study, three research groups cooperated to develop optimized hydrogen fueling station codes through risk analysis of hydrogen production and filling systems. Its results were integrated to develop the codes. In the first step to develop the codes, the standards for CNG stations and hydrogen fueling station were compared with each other and analyzed. By referring to foreign hydrogen fueling station standards, we investigated the potential problems in developing hydrogen fueling station codes based on the CNG station standards. In the second, the results of the high-pressure hydrogen leakage experiment were analyzed, and a numerical analysis was performed to establish the safety distance from the main facilities of a hydrogen fueling station to the protection facilities. In the third, HAZOP (Hazard and Operability) and FTA (Fault Tree Analysis) safety assessments were carried out for the on-site and off-site hydrogen fueling stations—currently being operated in Korea— to analyze the risks in existing hydrogen fueling stations. Based on the study results of the above three groups, we developed one codes for off-site type hydrogen fueling stations and another codes for on-site type hydrogen fueling stations. These were applied from September 2010.     

Safety investigation of hydrogen charging platform package with CFD simulation

Hydrogen has been expected as one of the most promising green energy sources, especially in transportation section. Despite its great potential as a new source of energy, it is reluctant to build hydrogen charging stations for the fear of accidents such as hydrogen leakage, fire, and following explosion. To reduce those problems and promote the acceptance of hydrogen charging station, this study focuses on the hydrogen charging platform package (HCPP) which is a new type of the mobile hydrogen station. Hydrogen leakage cases are investigated using CFD (computational fluid dynamics) simulation. The simulation is performed with the whole configuration of the HCPP including main components, storage, compressor, and dispenser. Based on the risk assessment, hydrogen leak scenarios with high possibilities of accidents are simulated. The simulation results show the leak length of hydrogen gas, its dispersion, and the various ranges of volume ratios of leaked hydrogen gas. Based on the simulation results, it is clearly confirmed that the leaked hydrogen gas with high concentration stays inside the HCPP. Therefore, the effects of ventilation to reduce the possibility of the explosion are continuously considered to investigate the safety of the HCPP in the case of the leakage accident.     

A study of hydrogen leak and explosion in different regions of a hydrogen refueling station

The consequences of hydrogen leaks and explosions are predicted for the sake of the safety in hydrogen refueling stations. In this paper, the effect of wind speed on hydrogen leak and diffusion is analyzed in different regions of a hydrogen refueling station, and the influence of delayed ignition time on hydrogen explosion after an accidental hydrogen leak is further studied by numerical simulation. Results show that the effect of wind speed on the probability of hydrogen fires is distinctive in different regions of hydrogen refueling station. The size of combustible clouds in the trailer front region and the outer region increases in the low wind speed case, and the front of combustible clouds is formed in a spherical shape in the outer region, which can greatly increase the probability of hydrogen explosion. However, the high wind speed may cause an increase of the risk of accidents in the near ground region. Moreover, a non-linear correlation is shown between the rate of combustible cloud dissipation and wind speed after the hydrogen stops leaking. In addition, it is found that an increase in delayed ignition time may lead to an increase in explosion intensity, which is related with the larger high temperature area and stronger explosion overpressure. Two flame fronts and the reverse propagation of the explosion overpressure can be observed, when the delayed ignition time is larger.     

Security risk analysis of a hydrogen fueling station with an on-site hydrogen production system involving methylcyclohexane

Although many studies have looked at safety issues relating to hydrogen fueling stations, few studies have analyzed the security risks, such as deliberate attack of the station by threats such as terrorists and disgruntled employees. The purpose of this study is to analyze security risks for a hydrogen fueling station with an on-site production of hydrogen from methylcyclohexane. We qualitatively conducted a security risk analysis using American Petroleum Institute Standard 780 as a reference for the analysis. The analysis identified 93 scenarios, including pool fires. We quantitatively simulated a pool fire scenario unique to the station to analyze attack consequences. Based on the analysis and the simulation, we recommend countermeasures to prevent and mitigate deliberate attacks.     

Development of a web-based 3D virtual reality program for hydrogen station

The hydrogen fueling station is an infrastructure of supplying fuel cell vehicles. It is necessary to guarantee the safety of hydrogen station equipment and operating procedure for decreasing intangible awareness of danger of hydrogen. Among many methods of securing the safety of the hydrogen stations, the virtual experience by dynamic simulation of operating the facilities and equipment is important. Thus, we have developed a virtual reality operator education system, and an interactive hydrogen safety training system. This paper focuses on the development of a virtual reality operator education of the hydrogen fueling station based on simulations of accident scenarios and hypothetical operating experience. The risks to equipment and personnel, associated with the manual operation of hydrogen fueling station demand rigorous personnel instruction. Trainees can practice how to use all necessary equipments and can experience twenty possible accident scenarios. This program also illustrates Emergency Response Plan and Standard Operating Procedure for both emergency and normal operations.     

The public's acceptance toward building a hydrogen fueling station near their residences: The case of South Korea

South Korea is pushing for advancing the emergence of the hydrogen economy in order to reduce greenhouse gas emissions and promote economic growth. In this regard, a significant expansion of hydrogen charging stations is scheduled, but one of the biggest obstacles to this is the public acceptance of building a hydrogen fueling station near their residences. This article collected the data on the public acceptance toward building a hydrogen fueling station on a nine-point scale from a survey of 1000 people across the country, and analyzed the factors affecting public acceptance employing the ordered probit model. The respondents' approval rate for building a hydrogen fueling station near their residences (48.0%) was slightly higher than twice the opposition rate (23.0%). However, the sum of opposition (23.0%) and neutrality or indifference (29.0%) exceeded half of the total respondents, suggesting that the government's additional efforts were needed to improve acceptance. While some factors positively influenced the public acceptance, others affected it negatively. The various implications that can be obtained from these findings for building hydrogen fueling stations are discussed.     

Opportunities and data requirements for data-driven prognostics and health management in liquid hydrogen storage systems

During the past decade, Prognostics and Health Management (PHM) has become an important set of tools in various areas of industry and academic reliability engineering. PHM consists of a variety of mathematical and computational methods used to support data-driven decision-making to increase the safety, availability, and reliability of complex engineering systems. In particular, PHM can provide crucial insight into reliability and safety design improvements for developing technologies where historical performance and failure data are limited. This is the case of hydrogen fueling and storage technologies. This work presents a high-level approach for designing data-driven PHM applications for bulk liquid hydrogen (LH₂) storage systems for hydrogen fueling stations. This paper addresses core aspects of the design, development, and implementation of data-driven PHM applications that can improve the reliability assessment of hydrogen components. The analysis focuses on the relationship between data availability and diagnostic/prognostic capabilities; potential challenges; and integration schemes for current risk mitigation measures. We identify potential condition-monitoring data sources for key components in an LH₂ storage system, including storage tanks, piping, and pumps. We determine that the short-term goals for the implementation of data-driven models in PHM frameworks in hydrogen systems should focus on developing adequate data collection and analysis strategies, as well as exploring the effect on reliability, safety, and regulations for hydrogen systems.     

Optimization of the overall energy consumption in cascade fueling stations for hydrogen vehicles

Hydrogen fueling stations are emerging around and in larger cities in Europe and United States together with a number of hydrogen vehicles. The most stations comply with the refueling protocol made by society of automotive engineers and they use a cascade fueling system on-site for filling the vehicles. The cascade system at the station has to be refueled as the tank sizes are limited by the high pressures. The process of filling a vehicle and afterward bringing the tanks in refueling station back to same pressures, are called a complete refueling cycle. This study analyzes power consumption of refueling stations as a function of number of tanks, volume of the tanks and the pressure in the tanks. This is done for a complete refueling cycle. It is found that the energy consumption decreases with the number of tanks approaching an exponential function. The compressor accounts for app. 50% of the energy consumption. Going from one tank to three tanks gives an energy saving of app. 30%. Adding more than four tanks the energy saving per extra added tank is less than 4%. The optimal numbers of tanks in the cascade system are three or four.     

Mixing and warming of cryogenic hydrogen releases

Laboratory measurements were made on the concentration and temperature fields of cryogenic hydrogen jets. Images of spontaneous Raman scattering from a pulsed planar laser sheet were used to measure the concentration and temperature fields from varied releases. Jets with up to 5 bar pressure, with near-liquid temperatures at the release point, were characterized in this work. This data is relevant for characterizing unintended leaks from piping connected to cryogenic hydrogen storage tanks, such as might be encountered at a hydrogen fuel cell vehicle fueling station. The average centerline mass fraction was observed to decay at a rate similar to room temperature hydrogen jets, while the half-width of the Gaussian profiles of mass fraction were observed to spread more slowly than for room temperature hydrogen. This suggests that the mixing and models for cryogenic hydrogen may be different than for room temperature hydrogen. Results from this work were also compared to a one-dimensional (streamwise) model. Good agreement was seen in terms of temperature and mass fraction. In subsequent work, a validated version of this model will be exercised to quantitatively assess the risk at hydrogen fueling stations with cryogenic hydrogen on-site.     

Design of a hydrogen community

This paper discusses the conceptual design of a scalable and reproducible hydrogen fueling station at Santa Monica, California. Hydrogen production using renewable energy sources such as biogas, which accounts for 100% of the total production, has been discussed. The fueling station consists of a direct fuel cell (DFC) 300 fuel cell for on-site generation of 136 kg/day of hydrogen and 300 kW of electric power, five hydrogen storage tanks (storage capacity of 198 kg of H₂ at 350 and 700 bar), four compressors which assist in dispensing 400 kg of hydrogen in 14 h, two hydrogen dispensers operating at 350 bar and 700 bar independently and a SAE J2600 compliant hydrogen nozzle. Potential early market customers for hydrogen fuel cells and their daily fuel requirements have been computed. The safety codes, potential failure modes and the methods to mitigate risks have been explained. A well-to-wheel analysis is performed to compare the emissions and the total energy requirements of conventional gasoline and fuel cell vehicles.     

Development of efficient hydrogen refueling station by process optimization and control

Development of efficient hydrogen refueling station (HRS) is highly desirable to reduce the hydrogen cost and hence the life cycle expense of fuel cell vehicles (FCVs), which is hindering the large scale application of hydrogen mobility. In this work, we demonstrate the optimization of gaseous HRS process and control method to perform fast and efficient refueling, with reduced energy consumption and increased daily fueling capacity. The HRS was modeled with thermodynamics using a numerical integration method and the accuracy for hydrogen refueling simulation was confirmed by experimental data, showing only 2 °C of temperature rise deviation. The refueling protocols for heavy duty FCVs were first optimized, demonstrating an average fueling rate of 2 kg/min and pre-cooling demand of less than 7 kW for 35 MPa type III tanks. Fast refueling of type IV tanks results in more significant temperature rise, and the required pre-cooling temperature is lowered by 20 K to achieve comparable fueling rate. The station process was also optimized to improve the daily fueling capacity. It is revealed that the hydrogen storage amount is cost-effective to be 25–30% that of the nominal daily refueling capacity, to enhance the refueling performance at peak time and minimize the start and stop cycles of compressor. A novel control method for cascade replenishment was developed by switching among the three banks in the order of decreased pressure, and results show that the daily refueling capacity of HRS is increased by 5%. Therefore, the refueling and station process optimization is effective to promote the efficiency of gaseous HRS.     

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.     

Energetic evaluation of hydrogen refueling stations with liquid or gaseous stored hydrogen

The future success of fuel cell electric vehicles requires a corresponding infrastructure. In this study, two different refueling station concepts for fuel cell passenger cars with 70 MPa technology were evaluated energetically. In the first option, the input of the refueling station is gaseous hydrogen which is compressed to final pressure, remaining in gaseous state. In the second option, the input is liquid hydrogen which is cryo-compressed directly from the liquid phase to the target pressure. In the first case, the target temperature of −33 °C to −40 °C [1] is achieved by cooling down. In the second option, gaseous deep-cold hydrogen coming from the pump is heated up to target temperature. A dynamic simulation model considering real gas behavior to evaluate both types of fueling stations from an energetic perspective was created. The dynamic model allows the simulation of boil-off losses (liquid stations) and standby energy losses caused by the precooling system (gaseous station) dependent on fueling profiles. The functionality of the model was demonstrated with a sequence of three refueling processes within a short time period (high station utilization). The liquid station consumed 0.37 kWh/kg compared to 2.43 kWh/kg of the gaseous station. Rough estimations indicated that the energy consumption of the entire pathway is higher for liquid hydrogen. The analysis showed the high influence of the high-pressure storage system design on the energy consumption of the station. For future research work the refueling station model can be applied to analyze the energy consumption dependent on factors like utilization, component sizing and ambient temperature.     

The simulation and analysis of leakage and explosion at a renewable hydrogen refuelling station

The number of hydrogen refuelling stations (HRSs) is steadily growing worldwide. In China, the first renewable hydrogen refuelling station has been built in Dalian for nearly 3 years. FLACS software based on computational fluid dynamics approach is used in this paper for simulation and analysis on the leakage and explosion of hydrogen storage system in this renewable hydrogen refuelling station. The effects of wind speed, leakage direction and wind direction on the consequences of the accident are analyzed. The harmful area, lethal area, the farthest harmful distance and the longest lethal distance in explosion accident of different accident scenarios are calculated. Harmful areas after explosion of different equipments in hydrogen storage system are compared. The results show that leakage accident of the 90 MPa hydrogen storage tank cause the greatest harm in hydrogen explosion. The farthest harmful distance caused by explosion is 35.7 m and the farthest lethal distance is 18.8 m in case of the same direction of wind and leakage. Moreover, it is recommended that the hydrogen tube trailer should not be parked in the hydrogen refuelling station when the amount of hydrogen is sufficient.     

Dynamic simulation of the effect of vehicle-side pressure loss of hydrogen fueling process

This study explains the fundamental mathematical equations used for the main component models that are implemented in freely available library for hydrogen fueling station. The paper provides a background to the model formulation and theory, useful for the further investigations of hydrogen fueling stations. The model was verified against a specific manufacturer model, and it was validated by using test data from an actual fueling station. The study works as documentation and validation of the model formulation. The simulation library is used to make a model for investigating how the pressure loss in the vehicle affects the fueling process. Keeping the temperature out of the station constant and fueling to 80 MPa in the compressed hydrogen storage system, the pressure loss in the compressed hydrogen storage system directly correlates to the final temperature. The final temperature increases with increasing pressure losses. It is also shown that with no pressure loss in the vehicle the fueling has no limit in fueling speed as the heat of compression depends on the mass filled and the enthalpy of the mass, and not the filling time.     

Recommended pre-operation cleanup procedures for hydrogen fueling station

The stainless steel (SS) tubing and in-line filters are found to be sources of particulates in hydrogen fuel from new hydrogen stations. The internal coating of fueling nozzle can be delaminated during fueling as another particulate source. Organic residues, acetone, heptanes, and C₄Cl₄F₆ isomers are found in new SS tubing, which also emits hydrogen sulfide and carbonyl sulfide. Nitrogen contained in new storage tanks, if not properly removed, can elevate the nitrogen concentration in hydrogen fuel. We find that high pressure hydrogen flow can remove particulates, sulfur compounds and residual organic compounds from SS tubing. However, in-line filters should be cleaned by sonication and nitrogen contained in new storage tank pumped away. It is recommended that internal coating of fueling nozzle or SS tubing should not contain oxygen in chemical composition.     

Estimation of consequence and damage caused by an organic hydride hydrogen refueling station

Organic hydride hydrogen refueling stations are currently being developed in Japan. For these stations, we estimate the consequence and damage caused by explosions and heat radiation after a hydrogen leak, and the acute toxicity caused by the leakage and dispersion of methylcyclohexane and toluene energy carriers. First, the organic hydride hydrogen refueling station is defined, and an accident scenario for four leak sizes of hydrogen and chemical leak accidents is set. Next, simulations of the blast wave pressure and heat radiation after the hydrogen leak and of atmospheric dispersion for the evaporation after liquid methylcyclohexane and toluene leaks are performed. Probit functions or threshold values are created for each type of effects caused by the explosion, heat and the inhalation effect on humans of toluene acute toxicity. Population data for the area surrounding the station are created in a 10-m mesh. The consequence and damage are estimated for each leak size. The results show that although the explosion and chemical leak affects the area around the refueling station, the effects are small in all of the accident scenarios. In contrast, although the area of the heat effect is limited to inside the refueling station, the burn damage is large, and there is a need for conducting quantitative risk assessment.     

Experimental study on hydrogen explosions in a full-scale hydrogen filling station model

In order for fuel cell vehicles to develop a widespread role in society, it is essential that hydrogen refuelling stations become established. For this to happen, there is a need to demonstrate the safety of the refuelling stations. The work described in this paper was carried out to provide experimental information on hydrogen outflow, dispersion and explosion behaviour. In the first phase, homogeneous hydrogen–air mixtures of a known concentration were introduced into an explosion chamber and the resulting flame speed and overpressures were measured. Hydrogen concentration was the dominant factor influencing the flame speed and overpressure. Secondly, high-pressure hydrogen releases were initiated in a storage room to study the accumulation of hydrogen. For a steady release with a constant driving pressure, the hydrogen concentration varied as the inlet airflow changed, depending on the ventilation area of the room, the external wind conditions and also the buoyancy induced flows generated by the accumulating hydrogen. Having obtained this basic data, the realistic dispersion and explosion experiments were executed at full-scale in the hydrogen station model. High-pressure hydrogen was released from 0.8 to 8.0 mm nozzle at the dispenser position and inside the storage room in the full-scale model of the refuelling station. Also the hydrogen releases were ignited to study the overpressures that can be generated by such releases. The results showed that overpressures that were generated following releases at the dispenser location had a clear correlation with the time of ignition, distance from ignition point.     

Analysis of a hydrogen station roll-out strategy to introduce hydrogen vehicles in Andalusia

The issue of the distribution of a sufficient infrastructure of hydrogen fueling stations to enable meeting of the initial demand and to satisfy the different roll-out scenarios has been addressed by different authors, in different geographies, and with different methods and approaches. In this paper, we use a spatial approach to study the prospect of a sequential roll-out strategy from the present time to 2030 for Andalusia, a region in southern Spain. In every stage, we identify main nodes and clusters by examining in which areas of this region the roll-out of fueling stations should start. Finally, we estimate the number and size of fueling stations for every stage, as well as the investment required for this infrastructure roll-out based on the estimated costs for each type of hydrogen fueling station over the aforesaid time.     

Analysis of customer queuing at hydrogen stations

An analysis is presented of service rates at nineteen retail hydrogen stations in a heavily-used California network to gain insight into station capacity impacts on customer wait times. Each station has only one fueling position resulting from just one, one-sided dispenser. Collected data of each refueling step for 1000's of hydrogen refuelings in California provides insight into station and network capacity for both California and emerging infrastructure elsewhere. The analysis herein concludes that customers would be exponentially better served with a network of larger, multi-position stations instead of smaller, one position stations.