In-depth | LNG IHI develops LNG tank
Te drive towards future green fuels such as LNG has kept the industry busy. Pushing the technology forward has seen Japanese shipbuilder IHI develop its self-supporting prismatic type B or SPB LNG fuel tank for mega container vessels
I
HI developed three concept future vessels last year, where they also carried out cost diagrams between the use of
HFO and LNG. Takenori Okazaki, manager of machinery system engineering group, IHI says: “Te disadvantage of LNG is that it has twice the fuel volume [as HFO], you would need to increase fuel tank space, which would then mean a reduction in cargo space that has complex fuel handling requirements, and as yet the infrastructure for supporting it is undeveloped.” However, even with the draw backs to
LNG as a fuel there is still interest in using the fuel in the future as Okazaki says: “If the infrastructure gets sorted out it will become more probable.” Today’s market for LNG fuel tanks has favoured the C-type pressurised tank such as the moss or spherical tanks. Te B-type IHI SPB tank allows more flexibility in the design of the tank and also can be constructed to a given space. Te ITC code outlines three different
tank types, the E-type for LPG, the C-type and the B-type. Where the C-type is the most popular tank type to be used at
not so much of a problem because of the fuel consumption. When you need to have large fuel tanks, especially in the case of smaller vessels, there isn’t the additional space. Te C-type which are spherical and so are more difficult to fit in,” he adds. Okazaki says that the SPB tank is strong,
IHI SPB LNG tank
present development of the B-type, such as the SPB tank, are starting to increase. Magnus Lindgren, principal surveyor
Tankers & Dry Cargo, DNV says that the advantage with the C-type tanks is that they can store LNG for a longer time without being used because of the pressure and temperature that the LNG is kept at. Tese tanks produce boil off, but this can then be recirculated back into the system. However, he also notes that SPB which does
not use high pressure utilises volume of space available better. “Te SPB tank does not take high pressure, so you would need to treat the boil-off gas differently from that of a C-type. Te handling of boil-off gas for larger vessels is
robust and best to fit a hull form. Te tank can be designed to fit the shape of the space available because of this it can take up less room and also has the advantage of being lighter in weight. IHI carried out 3D fine mesh FEM analysis, fatigue analysis, crack propagation analysis, evaluation of construction tolerance and quantitative tolerance control. Te tank in situ would be supported on
reinforced plywood, on chock constructions located at the top and bottom of the tank. Further insulation is provided by pre-fabricated PUF panels and cushion joints surrounding the tank. IHI have also highlighted that as the tank is not fitted directly to the hull and that should any damage to the inner hull occur that it can be easily accessed to be repaired. Due to the tank not being pressurised submerged pumps would be installed to feed the fuel.
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The Naval Architect September 2012
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