Successful commercialization of shape-adjustable pressure tank

Professors Daejun Chang and Pål G. Bergan (who worked on the project from 2009 to 2015 and is now retired) of the KAIST mechanical engineering department developed a prismatic pressure tank technology that can control the shape freely and was successfully commercialized. The technology was applied to the LNG fuel tank (15 m3, 9 bare) of a port cleaning ship at Ulsan Port.

Article | Fall 2018

Professors Daejun Chang and Pål G. Bergan (who worked on the project from 2009 to 2015 and is now retired) of the KAIST mechanical engineering department developed a prismatic pressure tank technology that can control the shape freely and was successfully commercialized. The technology was applied to the LNG fuel tank (15 m3, 9 bar) of a port cleaning ship at Ulsan Port.

This technology, called the lattice pressure vessel, will overcome the limitations of conventional pressure vessel technology, which was only possible with cylindrical or spherical containers, in a pressure-resistant manner through an internal lattice structure and present a new standard of pressure vessel design.

 

The research team started to commercialize the technology in cooperation with POSCO in 2012 after KAIST’s filing of the original patent in 2011, and proved the applicability of technology by successfully producing and testing four proto-type test tanks as well as receiving design approval from seven international certification authorities.

The technology was transferred to LATTICE Technology Co., Ltd., a KAIST technology start-up company for commercial promotion and sales. Recently, LATTICE Technology confirmed that it secured the order of the first lattice pressure vessel for an LNG fuel tank of a port cleaning ship.

The team’s technology can be used in LNG and liquid hydrogen fuel storage for environmentally-friendly deepsea-going ships. Note that one large-sized ship emits an amount of pollutants comparable to that from 5,000 automobiles.

Unlike strong exhaust gas regulations for automobiles, there has been no strong regulation on exhaust gas from ships, and as a result, large-sized ships operating in the ocean have been releasing sulfur oxides, nitrogen oxides, fine dusts, and carbon dioxide in large quantities using low-quality heavy oil as fuel. The International Maritime Organization (IMO) under the UN is tightening regulations on the emissions of large ships every year. In particular, it has announced a regulation to reduce the sulfur content of ship fuel down to 0.1% by 2020.

In order to achieve this goal, ships must switch their fuels to LNG and liquid hydrogen. The technology of storing these fuels has been the biggest technical and economic obstacle. The lattice pressure vessel was recognized as an ideal pressure tank technology to eliminate such stumbling blocks and was finally commercialized successfully.

Conventional spherical or cylindrical pressure tanks have size limitations due to the simultaneously increase in the shell thickness. Moreover, small defects after fabrication may grow rapidly on the surface because the pressure load is endured only by the membrane stress similarly to a balloon.

Since the space around the cylinder is unusable, it has been difficult to solve the space efficiency problem in which the actual storage space is less than half when using multiple cylinders.

The team applied a lattice structure internally to develop a completely different design theory from the existing pressure vessels. The two opposing sides receiving the internal pressure were connected to the lattice structure and the surface of the container was made to withstand the pressure with the bending stress using a stiffener. In addition, as LEGGO blocks build up, the regular modular structures are repeatedly used to make a large tank.

This design structure has several advantages. Structural multiplicity can greatly increase safety and maintain the thickness of the structure, even when the tank is large, ensuring maximum space efficiency. In addition, the lattice structure limits the movement of the internal fluid, which greatly reduces the risk of sloshing (load due to fluid movement inside the tank) as well as the weight, which is the biggest challenge in LNG storage tanks for ships.

Professor Chang’s team and LATTICE Technology’s technical team conducted commercialization development research focusing on weight reduction and economic efficiency. If the inner grid structure is too dense, the tank becomes lighter, but it also becomes difficult to produce and less economical.

On the other hand, replacing multiple cylinders with a single lattice pressure vessel can reduce the cost and operational complexity of piping, electrical equipment, as well as the economics of the tank itself. The team developed a grid-type pressure tank that reduced weight and cost while replacing multiple cylinders with a single tank through structural and production optimization.

 

 

Professor Chang said, “Pressure vessels are the most common devices for storing materials and energy. They are widely used in various fields from home to industry. The application range of lattice pressure vessels is very wide. It will be applicable to land-based industrial facilities, railways and vehicles.”

The research was carried out with the support of the joint research by POSCO and the market-creating technology development project of the Small and Medium Business Administration.