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Transport Using PipelinesEven though hydrogen distributed in pipelines demands better/more tightness for the pipe material itself and for seals and fittings and rises specific materials compatibility issues, the procedure is well known and has been safely in use for many years in industrial areas (IskovH:2000) for local distribution, which mean lengths of more than 2000 km. However, this is still modest as compared to a complete national or even international network delivering energy for fuelling stations, house warming, and industrial needs, especially related to a financial comparison with the current electrical, natural gas or propane system. Hydrogen’s growing importance and the requirement of serving mass will lead to a hydrogen network of pipelines in order to connect new large scale production sites with end users and applications. In the long run hydrogen will be directly delivered via pipelines to filling centres, fuelling stations, to fuel cells used in small-scale distributed power generation etc. Prior to this situation, decentralized hydrogen production will take advantage of the existing natural gas infrastructure. The pipeline grid will possibly make use of the existing natural gas infrastructure which will be adapted to hydrogen. It must be pointed out that piping hydrogen is problematic due to the energy required for pumping and the low volumetric energy density of hydrogen, demanding higher flow rates which in turn lead to greater flow resistance. Consequently about 4.6 times more energy is required to move hydrogen through a pipeline than for natural gas and 10% of the energy is lost every 1000Km (SylvesterBradleyO:2003). The capacity of a given pipeline configuration to carry energy is somewhat lower when it carries hydrogen than when it carries natural gas. In a pipe of a given size and pressure, hydrogen flows about three times faster, but since it also contains about three times less energy per cubic foot, a comparable amount of energy gets through the pipe. The fact that hydrogen may not be compatible with the current piping infrastructure due to brittleness of material, seals and the incompatibility of pump lubrication poses further problems. If the use of hydrogen pipelines were to be expanded, possible embrittlement problems would have to be considered. Pipes and fittings can become brittle and crack as hydrogen diffuses into the metal of which they are made. The severity of this problem depends on the type of steel and weld used and the pressure in the pipeline. The technology is available to prevent embrittlement, but depending on the configuration being considered, distribution costs may be affected. Smaller piping can be used for hydrogen than those used for natural gas, due to the higher pressure requirements, smaller molecule etc. For example, the 3/8” tube that is appropriate for fuelling a bus with hydrogen would only be big enough to fuel a car with natural gas, not a natural gas bus (CampbellK:2002). However, if considering utilizing a single design for both hydrogen and natural gas, natural gas provides the limiting diameter, but the pressures and material compatibility for hydrogen must be met. Compressors would generally have to be refitted with new seals and valves. References: Campbell K. and Cohen J. (2002) Why hydrogen vehicle fueling is different than natural gas. Presented at the World NGV 2002: 8th International and 20th National Conference and Exhibition, Washington, D.C..(BibTeX) |