Development of strategic hydrogen refueling station deployment plan for Korea

The Republic of Korea government has set yearly targets of hydrogen cars and buses and plans to install hydrogen refueling stations nationwide. This paper proposes a methodology for developing a strategic deployment plan with three mathematical models. For a given target, future refueling demand locations and amount from general road and expressway are systematically estimated. First, the required number of refueling stations to satisfy the target covering ratio of the total demand set by the government is determined by the Station number determination model. Next, the locations of the capacitated stations and the allocation of demand to the stations are determined by the second Max cover and the third p-median models. Since the max covering is more important than minimizing the travel time, the two models are used sequentially. The nationwide hydrogen station deployment plan for the years 2022–2040 obtained by the proposed methodology is reported.     

Accurate location planning for a wind-powered hydrogen refueling station: Fuzzy VIKOR method

This study seeks to enhance the site selection procedure for decision-makers to select the most effective wind-powered hydrogen refueling station via the aid of Fuzzy Multi-criteria Decision-making (FMCDM) approaches. To accomplish the purpose of the study, technical, economic, environmental, geographical, and social aspects constitute the influential criteria for prioritizing the eight aptest cities of Iran. Then, the Fuzzy Multi-criteria Optimization and Compromise Solution (FVIKOR) is employed to ascertain which alternative should be chosen as the most efficient one with respect to the criteria. In addition to several non-fuzzy MCDM techniques, the Fuzzy Technique for Order of Preference by Similarity to Ideal Solution (FTOPSIS) and a novel integrated method are applied for validation. Moreover, an FMCDM approach coupling FTOPSIS and FVIKOR has been introduced for the prioritization of different alternatives while many conflicting criteria exist. The simulation results of fuzzy and non-fuzzy approaches suggest that Manjil is the best option for the purpose of study. The numerical findings also imply utilizing a 100-kW turbine in Manjil generates 548,376 kWh of electricity, resulting in the prevention of 109,675 kg of CO₂ emissions and in the production of 8876 kg of hydrogen annually.     

Multi-hub hydrogen refueling station with on-site and centralized production

In recent decades, the consequences of climate changes due to greenhouse gas (GHG) emissions have become ever more impactful, forcing international authorities to find green solutions for sustainable economic development. In this regard, one of the global targets is the reduction of fossil fuels utilization in the transport sector to encourage the diffusion of more environmentally friendly alternatives. Among them, hydrogen is emerging as a viable candidate since it is a potentially emission-free fuel when produced by exploiting renewable energy sources (RES). Nevertheless, to allow widespread use of this gas in the transport sector, several technoeconomic barriers, including production cost, and lack of distribution and storage infrastructure, have to be overcome. Distributed hydrogen production via renewable energy-powered electrolysis could be an effective solution to reduce cost and lead to economies of scale. In this study a multi-hub configuration with on-site production from PV-powered electrolysis and centralized production from steam methane reforming (SMR) is proposed. In particular, an infrastructure network for a bus refueling station located in Lazio is considered as a case study. First, each hub, composed of PV panels, an electrolyzer, a compression system, high-pressure and low-pressure storages, and hydrogen dispensers with chiller, is modeled in a Matlab/Simulink environment. Then, a design perturbation analysis is carried out to determine the impact of the configuration on the refueling station performance in terms of carbon emissions levels and the Levelized Cost of hydrogen (LCOH). The results show a significant influence of the station size on the economic performance highlighting significant benefits (reduction up to 40% in the LCOH) for a 80 bus HUB with a saturating trend towards larger sizes. CO₂ emissions per unit mass of hydrogen are kept limited for all the stations thanks to the synergistic effects of SMR and Electrolyzer. Interconnecting more than one station each other further benefits can be achieved from the environmental perspective (savings up to 5 tons of CO₂ are demonstrated for a typical summer case study).     

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.     

Numerical simulation of hydrogen leakage diffusion in seaport hydrogen refueling station

Ningbo's seaport hydrogen refueling station was used as the research object. The effects of different leakage angles, wind direction, roof shape, leakage hole diameters, temperature, and humidity on the diffusion of hydrogen leakage were studied by numerical simulation. The influence of leakage angle on hydrogen leakage is mainly reflected in the presence or absence of obstacles. The volume of the flammable hydrogen cloud was reduced by 31.16%, and the volume of the hazardous hydrogen cloud was reduced by 63.22% when there was no obstacle. The wind direction can significantly impact hydrogen leakage, with downwind and sidewind accelerating hydrogen discharge and reducing the risk. At the same time, headwind significantly increases the volume of the flammable hydrogen cloud. Compared with no wind, the volume of the flammable hydrogen cloud increased by 71.73% when headwind, but the volume of the hazardous hydrogen cloud decreased by 24.00%. If hydrogen shows signs of accumulation under the roof, the sloping roof can effectively reduce the hydrogen concentration under the roof and accelerate the hydrogen discharge. When the leakage angle θ = 90°, the sloping roof reduced the volume of the flammable hydrogen cloud by 11.74%. The leakage process was similar for different leak hole diameters in the no wind condition. The inverse of the molar fraction of hydrogen on the jet centerline was linearly related to the dimensionless axial distance of the jet in different cases. Using a least squares fit, the decay rate was obtained as 0.0039. In contrast, temperature and humidity have almost no effect on hydrogen diffusion. Hydrogen tends to accumulate on the lower surface of the roof, near the roof pillars and the hydrogen dispenser. In this paper, a set of hydrogen detector layout schemes was developed, and the alarm success rate was verified to be 83.33%.     

Review on equipment configuration and operation process optimization of hydrogen refueling station

The construction of hydrogenation infrastructure is important to promote the large-scale development of hydrogen energy industry. The technical performance of hydrogen refueling station (HRS) largely determines the refueling efficiency and cost of hydrogen fuel cell vehicles. This paper systematically lists the hydrogen refueling process and the key equipment applicable in the HRS. It comprehensively reviews the key equipment configuration from the hydrogen supply, compression, storage and refueling of the HRS. On the basis of the parameter selection and quantity configuration method, the process optimization technology related to the equipment utilization efficiency and construction cost was quantitatively evaluated. Besides, the existing problems and prospects are put forward, which lays the foundation for further research on the technical economy of HRSs.     

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.     

A numerical study of hydrogen leakage and diffusion in a hydrogen refueling station

Studies focused on the behavior of the hydrogen leakage and diffusion are of great importance for facilitating the large scale application of the hydrogen energy. In this paper, the hydrogen leakage and diffusion in six scenarios which including comparison of different leakage position and different wind effect are analyzed numerically. The studied geometry is derived from the hydrogen refueling station in China. Due to the high pressure in hydrogen storage take, the hydrogen leakage is momentum dominated. The hydrogen volume concentration with the variation of the leakage time in different scenarios is plotted. More importantly, profiles of the flammable gas cloud at the end of the leakage are quantitatively studied. Results indicate that a more narrow space between the leakage hole and the obstacle and a smaller contact area with the obstacle make the profile of the flammable gas cloud more irregular and unpredictable. In addition, results highlight the wind effect on the hydrogen leakage and diffusion. Comparing with scenario which the wind direction consistent with the leakage direction, the opposite wind direction may result in a larger profile of the flammable gas cloud. With wind velocity increasing, the profile of the flammable gas cloud is confined in a smaller range. However, the presence of the wind facilitates the form of the recirculation zone near the obstacle. With an increase of the wind velocity, the recirculation zone moves downward along the obstacle. Thus, the hydrogen accumulation is more prominent near the obstacle.     

Experimental correlations and integration of gas boosters in a hydrogen refueling station

Air driven gas boosters are often deployed in small scale compression systems. Manufacturers specifications, reporting outlet flow for a fixed inlet pressure, do not reflect the batch operation from a limited source storage. Thus, the dynamic variation of critical process parameters such as efficiency, temperature and flow are not documented.Using a hydrogen refueling station demonstrator, the data from more than 20′000 compression cycles is compiled and analyzed. Experimentally derived correlations are determined for an air driven gas booster feeding a cascade storage. A specific analysis of the clearance volume and the working air pressure is introduced.An engineering tool was developed in MATLAB for performance forecasting. It allows the user to simulate the process trends with an accuracy of ±5%. In the context of a hydrogen refueling station, duration, temperature, compression cycles and air consumption data can be used for process management and maintenance planning.     

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.     

The cavity profile of a diaphragm compressor for a hydrogen refueling station

A low flow rate and short diaphragm life are the two disadvantages of diaphragm compressors when applied in hydrogen refueling stations. A new generatrix of the cavity profile of a diaphragm compressor was developed in this study to increase the cavity volume and decrease the diaphragm radial stress. A reduction in the diaphragm radial stress that resulted from the new design was validated by experiment and numerical simulation. The volumes of the cavities with different generatrices and the radial stress distribution of the diaphragm were investigated under various design conditions. The results indicated that the volume of the cavity with the new generatrix was approximately 10% larger than that with a traditional generatrix at the same allowable stress and cavity radius. At a similar cavity volume and radius, the radial stress values of the diaphragm in the cavity with the new generatrix were low. The decrease rate of the maximal radial stress of the diaphragm in the cavity with the new generatrix reached 13.8%. In the diaphragm centric region, where additional stress was induced by discharge holes, the maximal radial stress decrease rate reached 19.6%.     

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.     

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.     

Two-tier pressure consolidation operation method for hydrogen refueling station cost reduction

An operation strategy known as two-tier “pressure consolidation” of delivered tube-trailers (or equivalent supply storage) has been developed to maximize the throughput at gaseous hydrogen refueling stations (HRSs) for fuel cell electric vehicles (FCEVs). The high capital costs of HRSs and the consequent high investment risk are deterring growth of the infrastructure needed to promote the deployment of FCEVs. Stations supplied by gaseous hydrogen will be necessary for FCEV deployment in both the near and long term. The two-tier pressure consolidation method enhances gaseous HRSs in the following ways: (1) reduces the capital cost compared with conventional stations, as well as those operating according to the original pressure consolidation approach described by Elgowainy et al. (2014) [1], (2) minimizes pressure cycling of HRS supply storage relative to the original pressure consolidation approach; and (3) increases use of the station's supply storage (or delivered tube-trailers) while maintaining higher state-of-charge vehicle fills.     

Effect of wind condition on unintended hydrogen release in a hydrogen refueling station

Ambient condition, especially the wind condition, is an important factor to determine the behavior of hydrogen diffusion during hydrogen release. However, only few studies aim at the quantitative study of the hydrogen diffusion in a wind-exist condition. And very little researches aiming at the variable wind condition have been done. In this paper, the hydrogen diffusion in different wind condition which including the constant wind velocity and the variable wind velocity is investigated numerically. When considering the variable wind velocity, the UDF (user defined function) is compiled. Characteristics of the FGC (flammable gas cloud) and the HMF (hydrogen mass fraction) are analyzed in different wind condition and comparisons are made with the no-wind condition. Results indicate that the constant wind velocity and the variable wind velocity have totally different effect for the determination of hydrogen diffusion. Comparisons between the constant wind velocity and the variable wind velocity indicate that the variable wind velocity may cause a more dangerous situation since there has a larger FGC volume. More importantly, the wind condition has a non-negligible effect when considering the HMF along the radial direction. As the wind velocity increases, the distribution of the HMF along the radial direction is not Gaussian anymore when the distance between the release hole and the observation line exceeds to a critical value. This work can be a supplement of the research on the hydrogen release and diffusion and a valuable reference for the researchers.     

Impact of pipelines on cooling demand in the gaseous hydrogen refueling station

Hydrogen precooling is an effective method to realize safe, adequate, and fast filling for fuel cell vehicles. Estimating cooling demand is essential for the precooling unit configuration and energy analysis. Complex pipelines exist between the station's storage tanks and the vehicle cylinder. However, their impact on the cooling demand is often underestimated. In this paper, a thermodynamic model of the whole hydrogen refueling process was established to investigate the impact of pipelines in different positions. Accordingly, the influence of pipelines on the thermodynamic parameters was analyzed. Then the effects on the precooling performance were concluded. The results show that flow resistance before the breakaway increases total cooling demand by 9.9%. Meanwhile, heat dissipation through the pipe, located between the control valve and the heat exchanger, smoothens the cooling demand curve and reduces the total cooling demand by 5.7%. After the break-away, the flow resistance of pipelines significantly changes the mass flow rate curve and cooling demand. Heat absorption from the pipe wall slightly influences the cooling demand but jeopardizes refueling safety.     

Performance of a hydrogen refueling station in the early years of commercial fuel cell vehicle deployment

Since 2003, the National Fuel Cell Research Center at the University of California, Irvine (UCI) has operated the first U.S. publicly accessible hydrogen refueling station (HRS). During this period, the UCI HRS supported all manufacturers in the early, pre-commercialization years of the fuel cell electric vehicle (FCEV). This paper describes and analyzes the performance of the UCI HRS during the first five years of FCEV commercialization, over which time the station has dispensed the most hydrogen daily in the California network. The station performance is compared to aggregate data published by NREL for all U.S. HRSs. Using the Hydrogen Delivery Scenario Analysis Model, typical daily refueling profiles are analyzed to determine the effect on HRS design. The results show different daily refueling profiles could substantially affect HRS design and ultimately the cost of hydrogen. While technical issues have been reduced, the compressor, dispenser, and fueling rate are areas for improvement.     

Dynamic planning and energy management strategy of integrated charging and hydrogen refueling at highway energy supply stations considering on-site green hydrogen production

The layout of electric vehicles charging stations and hydrogen refueling stations (HRSs) is more and more necessary with the development of electric vehicles (EVs) and progress in hydrogen energy storage technology. Due to the high costs of HRSs and the low demand for hydrogen, it is difficult for independent HRSs to make a profit. This study focuses on the dynamic planning of energy supply stations on highways in the medium and long term, considering the growth of EV charging demand and the change in the proportion of hydrogen fuel cell vehicles (HFCVs). Based on the perspective of renewable energy generators (REGs), this study seeks the dynamic optimal configuration and comprehensive benefits of adding HRS and battery to existing EVCS considering the travel rules of new energy vehicles (NEVs). The results show that (1) It is profitable for REGs to invest in HRSs; (2) The economy of investment in batteries by REGs depends on the source-load matching. It is feasible only when the output of renewable energy is difficult to meet the demand. (3) The business model of REGs producing hydrogen on-site and supplying both electricity and hydrogen is feasible.     

Optimal operation of a photovoltaic generation-powered hydrogen production system at a hydrogen refueling station

As the popularity of fuel cell vehicles continues to rise in the global market, production and supply of low-carbon hydrogen are important to mitigate CO₂ emissions. We propose a design for a hydrogen refueling station with a proton exchange membrane electrolyzer (PEM-EL)-based electrolysis system (EL-System) and photovoltaic generation (PV) to supply low-carbon hydrogen. Hydrogen is produced by the EL-System using electricity from PV and the power grid. The system was formulated as a mixed integer linear programming (MILP) model to allow analysis of optimal operational strategies. Case studies with different objective functions, CO₂ emission targets, and capacity utilization of the EL-System were evaluated. Efficiency characteristics of the EL-System were obtained through measurements. The optimized operational strategies were evaluated with reference to three evaluation indices: CO₂ emissions, capacity utilization, and operational cost of the system. The results were as follows: 1) Regardless of the objective function, the EL-System generally operated in highest efficiency state, and optimal operation depended on the efficiency characteristics of the EL-System; 2) mitigation of CO₂ emissions and increase in capacity utilization of the EL-System required trade-offs; and 3) increased capacity utilization of the EL-System showed two opposing effects on hydrogen retail price.     

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.