Japan

To make “Hydrogen vehicles and refuelling station systems” fit for public use research on hydrogen safety and designing mitigative measures are significant. For compact storage it is planned to store under high pressure (40MPa) at the refuelling stations so that the safety for the handling of high-pressurized hydrogen is essential. This paper describes the experimental investigation on the hypothetical dispersion and explosion of high-pressurized hydrogen gas which leaks through a large scale break in piping and blows down to atmosphere. At first we investigated time history of distribution of gas concentration in order to comprehend the behaviour of the dispersion of high-pressurized hydrogen gas before explosion experiments. The explosion experiments were carried out with changing the time of ignition after the start of dispersion. Hydrogen gas with the initial pressure of 40MPa was released through a nozzle of 10mm diameter. Through these experiments it was clarified that the explosion power depends not only on the concentration and volume of hydrogen/air pre-mixture but also on the turbulence characteristics before ignition. To clarify the explosion mechanism the numerical computer simulation about the same experimental conditions was performed. The initial conditions such as hydrogen distribution and turbulent characteristics were given by the results of the atmospheric diffusion simulation. By the verification of these experiments the results of CFD were fully improved.

A total of 12 ventilation experiments with various combinations of hydrogen release rates and ventilation speeds were performed in order to study how ventilation speed and release rate effect the hydrogen concentration in a closed system. The experiential facility was constructed out of steel plates and beams in the shape of a rectangular enclosure. The volume of the test facility was about 60m3. The front face of the enclosure was covered by a plastic film in order to allow visible and infrared cameras to capture images of the flame. The inlet and outlet vents were located on the lower front face and the upper backside panel respectively. Hydrogen gas was released toward the ceiling from the center of the floor. The hydrogen gas was released at constant rate in each test. The hydrogen release rate ranged from 0.002 m3/s to 0.02 m3/s. Ventilation speeds were 0.1 0.2 and 0.4 m3/s respectively. Ignition was attempted at the end of the hydrogen release by using multiple continuous spark ignition modules on the ceiling and next to the release point. Time evolution of hydrogen concentration was measured using evacuated sample bottles. Overpressure and impulse inside and outside the facility were also measured. The mixture was ignited by a spark ignition module mounted on the ceiling in eight of eleven tests. In the other three tests the mixture was ignited by spark ignition modules mounted next to the nozzle. Overpressures generated by the hydrogen deflagration in most of these tests were low and represented a small risk to people or property. The primary risk associated with the hydrogen deflagrations studied in these tests was from the fire. The maximum concentration is proportional to the ratio of the hydrogen release rate to the ventilation speed within the range of parameters tested. Therefore a required ventilation speed can be estimated from the assumed hydrogen leak rate within the experimental conditions described in this paper.

Storing a hydrogen fuel-cell vehicle in a garage poses a potential safety hazard because of the accidents that could arise from a hydrogen leak. A series of tests examined the risk involved with hydrogen releases and deflagrations in a structure built to simulate a one-car garage. The experiments involved igniting hydrogen gas that was released inside the structure and studying the effects of the deflagrations. The “garage” measured 2.72 m high 3.64 m wide and 6.10 m long internally and was constructed from steel using a reinforced design capable of withstanding a detonation. The front face of the garage was covered with a thin transparent plastic film. Experiments were performed to investigate extended-duration (20–40 min) hydrogen leaks. The effect that the presence of a vehicle in the garage has on the deflagration was also studied. The experiments examined the effectiveness of different ventilation techniques at reducing the hydrogen concentration in the enclosure. Ventilation techniques included natural upper and lower openings and mechanical ventilation systems. A system of evacuated sampling bottles was used to measure hydrogen concentration throughout the garage prior to ignition and at various times during the release. All experiments were documented with standard and infrared (IR) video. Flame front propagation was monitored with thermocouples. Pressures within the garage were measured by four pressure transducers mounted on the inside walls of the garage. Six free-field pressure transducers were used to measure the pressures outside the garage.

We have investigated hydrogen explosion risk and its mitigation focusing on compact hydrogen refuelling stations in urban areas. In this study numerical analyses were performed of hydrogen blast propagation and the structural behaviour of barrier walls. Parametric numerical simulations of explosions were carried out to discover effective shapes for blast-mitigating barrier walls. The explosive source was a prismatic 5.27 m3 volume that contained 30% hydrogen and 70% air. A reinforced concrete wall 2 m tall by 10 m wide and 0.15 m thick was set 2 or 4 m away from the front surface of the source. The source was ignited at the bottom centre by a spark for the deflagration case and 10 g of C-4 high explosive for two detonation cases. Each of the tests measured overpressures on the surfaces of the wall and on the ground displacements of the wall and strains of the rebar inside the wall. The blast simulations were carried out with an in-house CFD code based on the compressive Euler equation. The initial energy estimated from the volume of hydrogen was a time-dependent function for the deflagration and was released instantaneously for the detonations. The simulated overpressures were in good agreement with test results for all three test cases. DIANA a finite element analysis code released by TNO was used for the structural simulations of the barrier wall. The overpressures obtained by the blast simulations were used as external forces. The analyses simulated the displacements well but not the rebar strains. The many shrinkage cracks that were observed on the walls some of which penetrated the wall could make it difficult to simulate the local behaviour of a wall with high accuracy and could cause strain gages to provide low-accuracy data. A parametric study of the blast simulation was conducted with several cross-sectional shapes of barrier wall. A T-shape and a Y-shape were found to be more effective in mitigating the blast.

Ammonia is considered to be a potential medium for hydrogen storage facilitating CO2-free energy systems in the future. Its high volumetric hydrogen density low storage pressure and stability for long-term storage are among the beneficial characteristics of ammonia for hydrogen storage. Furthermore ammonia is also considered safe due to its high auto ignition temperature low condensation pressure and lower gas density than air. Ammonia can be produced from many different types of primary energy sources including renewables fossil fuels and surplus energy (especially surplus electricity from the grid). In the utilization site the energy from ammonia can be harvested directly as fuel or initially decomposed to hydrogen for many options of hydrogen utilization. This review describes several potential technologies in current conditions and in the future for ammonia production storage and utilization. Ammonia production includes the currently adopted Haber–Bosch electrochemical and thermochemical cycle processes. Furthermore in this study the utilization of ammonia is focused mainly on the possible direct utilization of ammonia due to its higher total energy efficiency covering the internal combustion engine combustion for gas turbines and the direct ammonia fuel cell. Ammonia decomposition is also described in order to give a glance at its progress and problems. Finally challenges and recommendations are also given toward the further development of the utilization of ammonia for hydrogen storage.

As policymakers and automotive stakeholders around the world seek to accelerate the electrification of road transport with hydrogen this study focuses on the experiences of Germany a world leader in fuel cell technology. Specifically it identifies and compares the drivers and barriers influencing the production and market penetration of privately-owned fuel cell electric passenger vehicles (FCEVs) and fuel cell electric buses (FCEBs) in public transit fleets. Using original data collected via a survey and 17 interviews we elicited the opinions of experts to examine opportunities and obstacles in Germany from four perspectives: (i) the supply of vehicles (ii) refuelling infrastructure (iii) demand for vehicles and (iv) cross-cutting institutional issues. Findings indicate that despite multiple drivers there are significant challenges hampering the growth of the hydrogen mobility market. Several are more pronounced in the passenger FCEV market. These include the supply and cost of production the lack of German automakers producing FCEVs the profitability and availability of refuelling stations and low demand for vehicles. In light of these findings we extract implications for international policymakers and future studies. This study provides a timely update on efforts to spur the deployment of hydrogen mobility in Germany and addresses the underrepresentation of studies examining both buses and passenger vehicles in tandem.

An integrated system to harvest efficiently the energy from the waste of pulp mill industry which is black liquor (BL) is proposed and evaluated. The proposed system consists of the supercritical water gasification (SCWG) of BL syngas chemical looping and power generation. To minimize the exergy loss throughout the system and to optimize the energy efficiency process design and integration is conducted by employing the principles of exergy recovery and process integration methods. Hydrogen is set as the main output while power is produced by utilizing the heat generated throughout the process. Process simulation is conducted using a steady state process simulator Aspen Plus. Energy efficiency is defined into three categories: hydrogen production efficiency power generation efficiency and total energy efficiency. From process simulation both of the integrated systems show very high total energy efficiency of about 73%.

Hydrogen may play a key role in a future sustainable energy system as a carrier of renewable energy to replace hydrocarbons. This review describes the fundamental physical and chemical properties of hydrogen and basic theories of hydrogen sorption reactions followed by the emphasis on state-of-the-art of the hydrogen storage properties of selected interstitial metallic hydrides and magnesium hydride especially for stationary energy storage related utilizations. Finally new perspectives for utilization of metal hydrides in other applications will be reviewed.

A method of risk identification is developed by comparing existing and advanced technologies from the viewpoint of comprehensive social risk. First to analyze these values from a multifaceted perspective we constructed a questionnaire based on 24 individual values and 26 infrastructural values determined in a previous study. Seven engineering experts and six social science experts were then asked to complete the questionnaire to compare and analyze a hydrogen energy system (HES) and a gasoline energy system (GES). Finally the responses were weighted using the analytic hierarchy process. Three important points were identified and focused upon: the distinct disadvantages of the HES compared to the GES judgments that were divided between experts in the engineering and social sciences fields and judgments that were divided among experts in the same field. These are important risks that should be evaluated when making decisions related to the implementation of advanced science and technology.

We investigate an appropriate initial burst pressure of compressed hydrogen containers that correlates with a residual burst pressure requirement at the end of life (EOL) and report an influence of hydraulic sequential tests on residual burst pressure. Results indicate that a container damage caused by a drop  test during hydraulic sequential tests has a large influence on burst pressure. The container damage induced through hydraulic sequential tests is investigated using non-destructive evaluations to clarify a strength decreasing mechanism. An ultrasonic flaw detection analysis is conducted before and after the drop test and indicated that the damage occurred at the cylindrical and dome parts of the container after the drop test. An X-ray computed tomography imaging identifies a delamination inside laminated structure made of carbon fiber reinforced plastics (CFRP) layer with some degree of delamination reaching the end boss of the container. Results suggest that a load profile fluctuates in the CFRP layer at the dome part and that a burst strength of the dome part decreases. Therefore an observed decreasing in drop damage at the dome part can be used to prevent a degradation of EOL container burst strength.