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Introduction To Hydrogen ApplicationHydrogen applications, or end-use technologies, can be grouped by sectors:
Transport applications, especially cars and buses, seem to be of highest priority but due to stringent performance and cost targtes, significant market penetration is not likely to occur before two decades. Stationary applications are not believed to play a relevant role for the hydrogen energy consumption in Europe before 2020 neither. However there could be significant development of niche markets in transport, stationary, and portable applications, which would positively contribute to further technological progress and public acceptance, despite their marginal impact on the total energy use. Hydrogen can be used to power vehicles my means of internal combustion engines (ICEs), fuel cells (FC) or gas turbines. FCs have a higher useful energy conversion efficiency than simple ICEs and they are therefore often used in automotive applications. ICEs are, however, well established technology that is relatively easy to convert from conventional liquid fuels to hydrogen, so some car manufacturers are also working on ICEs specifically for hydrogen. Gas turbines are today much too large to be used in road vehicles, but there are R&D development in countries including Germany and the USA aiming at developing smaller units, which when used with other energy conversion technologies in hybrid cycles, might improve the effectiveness (RisoEnergyReport:3:2004). Like any vehicle the driving range of a hydrogen vehicle depends on the amount of fuel, in this case hydrogen, that it can carry. Hydrogen has a lower volumetric energy content, especially in the gas phase, than conventional fuels such as gasoline, and storage of hydrogen on the vehicle is therefore a challenge. The storage system itself also includes a considerable weight and volume – thick walled vessels needed for gaseous high pressure storage (pressure 250 – 700 bar) or insulation and a boil-off management system for storage of liquefied hydrogen at cryogenic temperatures, see also figure 1. Several large R&D projects are in progress to solve these challenges and to address alternative solid storage techniques, e.g. metal hydrides. The low volumetric energy content and the limited infrastructure for hydrogen refuelling has also encouraged vehicle manufacturers to study the use of more conventional liquid fuels (e.g gasoline and methanol) that can be converted to hydrogen-rich gas mixtures by a “fuel processor” in the vehicle. However, it seems as if most vehicle manufacturers today focus on direct use of hydrogen for propulsion, and for most projects gaseous hydrogen is used instead of liquid hydrogen. Fuel processing may have a more significant role to play as auxiliary power units (APU) in, for example trucks. For on-board reforming in Fuel cell vehicles, methanol has been considered because it operates at lower temperatures and is more tolerant to intermittent demand. Gasoline or LPG reforming would even be more practical, since this infrastructure is already existing and could allow the introduction of respective vehicles even at a lower number. R&D activity on on-board reforming for passenger vehicles has significantly diminished in consideration of the intrinsic complexity and cost compared to the limited impact on CO2 emissions compared to direct use of hydrogen. Still on laboratory scale, but highly promising is the OTM (Oxygen Transport Memebrane) technology. References: Riso National Laboratory (2004) Riso Energy Report 3. {\tt http://www.risoe.dk/rispubl/energy\_report3/ris\-r\-1469.pdf}.(BibTeX) |