Above is a container ship having a box-shaped pressure vessel as a fuel tank, and below is one with traditional cylindrical fuel tanks. Click to enlarge.

Pressure vessels are normally designed in the form of a cylindrical or spherical tank. These shapes are, in principle, highly efficient in withstanding internal pressure, but rather inefficient in terms of space utilization. The tanks fit very poorly within a typically prismatic-shaped room. They cannot be packed closely together, so they do not efficiently utilize the overall space.

Moreover, cylindrical or spherical tanks are not easily scalable to very large sizes because the wall thickness of the tank must increase proportionally to its overall radius. Therefore, a large pressure vessel unavoidably will have very thick walls, which are difficult and expensive to manufacture, requiring a great amount of thick-walled steel to be rolled, forged, and welded together.

The box-shaped pressure vessel has an internal, load-carrying lattice-type structure. The lattice pattern is modular in all three spatial directions, thereby effectively anchoring and balancing pressure forces on the external walls of the vessel. The modular lattice can easily be adapted to prescribed pressure levels as the overall volumetric dimensions are directly linked to the number of repetitive modules.

Image shows a lattice pattern that is lined inside a prismatic pressure tank.

A giant prismatic pressure vessel with a size of 20,000 m³ and a design pressure of 10 atmospheres (10 bar_g) can be built simply by scaling up a smaller pressure vessel. The thickness of steel walls remains unchanged and that the weight of steel per unit storage volume goes down as the vessel size increases.

If we use cylindrical pressure vessels to supply LNG fuel for a large container ship, for example, many fuel tanks will be needed. Those tanks will take up large and valuable space onboard because the cylinders have to be lined up. In our case, however, much less space is needed. The operation of a ship becomes simpler with one fuel tank rather than with many.

Furthermore, our box-type pressure vessel can be designed with dimensions that precisely fit a ship. For a container ship, there may be room for a substantially higher number of containers to be loaded than when using cylindrical vessels. In a case study on a 13,000 TEU container ship, the value of the increased transport capacity tuned out $8.4 million for one year of operation for one ship.

—Professor Chang

The manufacturing cost of a pressure vessel would be reduced as well. Several types of special steel for cryogenic applications have been investigated in design and analysis studies, and this includes a new type of high-manganese steel that is being developed by POSCO. Regardless of materials, in any instance of large pressure vessels, the new lattice tank technology can offer significant savings of combined capital and operational costs.

Our box-type pressure vessel represents ground-breaking research. This innovative technology will dramatically change the rules of the game for industry concerning production, transportation, and storage of fluids under high pressure and at low temperatures.

—Professor Bergan

KAIST’s prismatic pressure vessel is being presented at Gastech 2014, the largest global conference and exhibition in the natural gas, LNG, and hydrocarbons industry. This event is taking place 24-27 March at KINTEX in Ilsan, Republic of Korea.

The showcased prismatic pressure vessel was a scale-down model with a volume size of 80 m³ and design pressure of 10 atmospheres. The vessel complies with the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC), the international standard for the appropriateness of design, fabrication, and inspection of boilers and pressure vessels. It passed the 15 pressure testing in January 2014 and received an accreditation from the ASME BPVC (ASME U2 Stamp).

Resources

• Prismatic pressure tank having lattice structure WO 2012148154 A2