Concern for potential global climate change will become greater within the next decade, forcing society to move toward energies that will minimize the emission of greenhouse gases. Hydrogen energy is considered to present a potential effective option for minimizing the release of greenhouse gases. The Japanese Government promoted the WE-NET (World Energy Network) Project (Phase I: 1993-1998, Phase II: 1999-2002), which envisions: (1) construction of a global energy network for the effective supply, transport, storage and utilization of renewable energies and (2) promotion of hydrogen energy entry into the market in the near and /or mid- future, even before the construction of a WE-NET system. In this paper, the results of the Phase I research and development are summarized and the Phase II program is described, placing an emphasis on the research and development of small-scale and distributed hydrogen utilization technologies such as fuel-cell vehicle related technologies.
The Japan hydrogen project, WE-NET (World Energy Network), has shown that high-density LH2 (liquid hydrogen) is the most promising medium for transporting and storing large-mass hydrogen efficiently and economically. In the future, large-mass liquid hydrogen storage technology for ground tanks and ocean tankers will be needed, and the commercial scale may be the same as existing LNG storage systems, which have a storage capacity of several hundreds of thousands of cubic meters. The conceptual designs of 200,000 m3 LH2 tankers and 50,000 m3 LH2 ground tanks were studied in WE-NET Phase I (1993-1998). This study has concluded that the optimized thermal insulation structure for a large storage tank should be developed. Therefore, in Phase II of WE-NET (1999-2002), we tested the thermal conductance and cryogenic compressive strengths of insulation materials in order to develop various insulation structures. Their conceptual designs were reviewed by analyzing experimental results. To realize the government target of introducing 50,000 fuel-cell vehicles by 2010 and 5 million vehicles by 2020, a hydrogen supply infrastructure must be constructed. Since LH2 is applicable for the hydrogen infrastructure, we have developed a high-performance LH2 container, a key component of the system. This paper describes the conceptual designs of LH2 tankers and LH2 ground tanks, elementary tests of various insulations, and also the LH2 infrastructure for fuel-cell vehicles.
Air Liquide Japan has studied the hydrogen liquefaction process, focusing on the supply of liquid hydrogen to the stations for fuel-cell vehicles in Phase II-Task 9 of the WE-NET Project. A survey of state-of-the-art hydrogen liquefaction technology has led to determination of the best process: Proven technology reveals the feasibility of utilizing a cold source of LNG to reduce the power of hydrogen liquefaction. A feasibility study was further detailed through the cooperation of IHI, in which the cryogenic reciprocating compressor applied to HP-stages of hydrogen recycle compression at the production capacity of 3t/d was reviewed. It was found that this process gives a cost-effective solution in terms of the power of liquefaction and investment required. The cost for liquid hydrogen production was also estimated and evaluated. This is a promising process that could lead to further advantages in large- capacity production.
The major activities of the Cryogenic Materials Working Group (Task 10) in the WE-NET Program are introduced, placing an emphasis on the mechanical properties of the structural materials to be used for liquid hydrogen vessels. Mechanical tests were conducted mainly using newly designed and installed liquid hydrogen facilities. In stainless steels, the fracture toughness of the weld at cryogenic temperatures is greatly increased by employing high-energy-density welding such as laser or electron-beam welding. In aluminum alloys, the properties of the welds at low temperatures are drastically improved by applying friction-stir welding. In addition, some properties of titanium and its alloy, which are considered as candidate materials for liquid hydrogen pumps, were also examined. Other activities related to the materials for liquid hydrogen vessels, including mechanical tests in gaseous hydrogen, assessment of local fracture toughness in welds and formulation of the database, are also briefly introduced.