Hydrogen, previously used as industrial gas, is expected to be used as a new energy resource. Hydrogen has low energy density per unit volume, so transporting and storing large amount of hydrogen gas is necessary. To improve efficiency of transportation and storage of hydrogen, Iwatani promotes a liquid hydrogen supplying system. Furthermore, we are working on a development of a cryo-pump system as the next generation of hydrogen refueling station. Iwatani has established the Research and Development Center in Amagasaki-city of Hyogo prefecture on April, 2013. This institute possesses a liquid hydrogen laboratory, which enables tests and evaluations of liquid hydrogen utilizations.
Hydrogen has been handled in high density such as 100 MPa and liquid in many places, where hydrogen thermal physical properties with high reliability are eagerly required. To answer the requirements, a book entitled “Hydrogen: Its Technology and Implications” published in 1975 by CRC Press Inc. has been introduced for the exact book to obtain thermal physical properties with high reliability.
The results of research and development and the latest trend on flow rate measurement technology for high-pressure hydrogen gas are introduced. Two kinds of test apparatuses, which were a gravimetric method and a master meter method, were developed for evaluating the metering performance of hydrogen dispenser in the hydrogen refueling station. These technologies were reflected to the industrial guideline and standard. The Japanese standard will be suggested to the international recommendation in near future. These actions and results are leading the world and will contribute to the realization of hydrogen society in Japan.
Accurate thermophysical properties of hydrogen are essential for the development of efficiently designed hydrogen-utilizing systems. Compressed hydrogen is supplied to fuel cell vehicles at hydrogen refueling stations, and the thermophysical properties at pressures up to 100 MPa are highly required. PVT property, speed-of-sound, viscosity, and thermal conductivity of high-pressure hydrogen have recently been measured, and the measurement techniques of them are presented. A database system compiling an equation of state and correlations based on the experimental data was developed, and an application of the database is also described.
This paper reviews current status and future directions of magnetic refrigeration system for hydrogen liquefaction. Hydrogen promises to be one of the most important energy sources in the near future. Liquid hydrogen can be utilized for infrastructure construction consisting of storage and transportation. Consuming energy of hydrogen liquefaction becomes comparable with the energy required for compressing hydrogen to 70 MPa, when high efficient liquefier is developed. Magnetic refrigeration that uses the magneto-caloric effect has potential to realize liquefaction efficiency higher than 50%, and also to be environmentally friendly and cost effective. Our hydrogen magnetic refrigeration system consists of Carnot cycle for liquefaction stage and active magnetic regenerator (AMR) cycle for precooling stages. Various magnetic materials were studied for candidate refrigerants. For the Carnot cycle, we developed a liquefaction stage with liquefaction efficiency higher than 80% using the heat pipe. For the AMR cycle, we studied two kinds of displacer systems and confirmed that the AMR effect expanded the cooling temperature span several times larger than adiabatic temperature change. From our simulation, FOM of 0.47 was estimated for the magnetic hydrogen liquefaction plant of 10 kg/day.
Hydrogen embrittlement (HE) of metallic materials, in particular hydrogen gas embrittlement (HGE) is reviewed to contribute the safety of hydrogen energy. Metal-hydrogen potential energy behavior on the metal surface and inside the metal is summarized by the current literatures and recent HE mechanism of hydrogen-enhanced strain-induced vacancy (HESIV) theory is described. Historical R&D of hydrogen technology is described from R&D of NASA space shuttle to that of high-pressure hydrogen storage of fuel cell vehicles (FCVs). Materials testing equipment in high-pressure hydrogen up to 230 MPa are developed. HGE of the engineering materials are examined in high-pressure hydrogen and summarized in the table of the AIST HGE evaluation of materials. Effects of hydrogen pressure up to 210 MPa, chemical composition by Ni equivalent and temperature from 77 to 773 K on HGE are discussed. Mechanical behavior of materials in liquid hydrogen and gaseous helium at 20 K is also discussed. Prevention of HGE using metallic structure control, surface coating on the surface and inhibitor gases added to hydrogen atmosphere is introduced.
Recent studies on hydrogen gas release and dispersion are overviewed in connection with safety of widespread utilization of hydrogen as an energy carrier. Full scale experiments on release of high pressure hydrogen gas under the supposition of accidental leakage in hydrogen fueling station were performed in the open field, in which the data of dispersion characteristics of flammable gas cloud were obtained. Computational studies on dispersion of hydrogen in a tunnel or an underpass on the assumption of accidental release from high pressure gas cylinders of fuel cell vehicle or bus were performed and showed the diffusion and decay of flammable gas cloud by effective ventilation. Regarding dispersion of hydrogen released in private garage or confined spaces, various types of experiments and analytical studies using different versatile CFD codes and different turbulence models were performed to analyze the flow of flammable gas and the effect of vent.