Compressed natural gas (CNG) is an alternative fuel made from natural gas. It is formed by compressing natural gas to less than 1 % of its volume at standard atmospheric pressure. CNG is used to transport natural gas by sea for intermediate distances, especially to places where gas pipeline infrastructure is not in place. “CNG is also a viable option to transport natural gas from global reserves that are classified as stranded. Such gas sources are too small to justify large investments on pipeline infrastructure and liquefaction and regasification plants,” notes Spartaco Angelini, manager of the EU-funded GASVESSEL project. On top of that, CNG could reduce the amount of gas being flared that is associated with oil extraction. “Stranded and flared gas represent about five times the volume of the natural gas currently used in Europe. To monetise both stranded and oil reserves, economic ways of transporting natural gas must be found,” adds Angelini.
Liquefied natural gas carriers: a financially viable option?
Traditional pressure vessels normally used to transport liquified natural gas (LNG) by ship cannot be used to transport CNG. The relevant thickness of the ship walls required to maintain the operating pressure of 300 bar would add significant weight to the vessels, reducing their loading capacity. Natural gas is stored in a liquid state mostly for transport over large distances or when pipelines for natural gas are not available. For distances up to 2 500 km and annual production of 7 billion m3, CNG is a more cost-effective option. Against this backdrop, the GASVESSEL project unveiled an integrated solution based on lightweight vessels that can operate at high pressures and lower costs than the reference systems on the international market. “Our new class of vessels could help the EU wean itself off of a single gas supplier and unlock and monetise energy resources (stranded, associated and flared gas) whose exploitation is currently not economically viable,” remarks Angelini.
Breakthrough CNG carrier design
“The main strength of our CNG technology is that it does not require investment in expensive liquefaction and regasification plants. Our innovative transport concept also relies on simpler and less expensive cargo loading/unloading logistics and plant engineering. The simplicity of the plant design ensures high safety levels and lower running and maintenance costs,” explains Angelini. The new lightweight pressure cylinders enable new ship designs with much higher payloads and dramatically lower transportation costs per gas volume. They were produced using filament winding, which involves the use of several layers of fibre-reinforced composite materials wrapped around a thin internal metal liner. The ship was designed and built according to the highest safety standards. A systematic examination of the operation of the compressed gas containment and handling system was also carried out. Safety levels are higher compared to those foreseen for LNG carriers. Three logistic gas exploitation scenarios were analysed to establish where and how the GASVESSEL concept provides added value. The economic viability of the CNG technologies developed in GASVESSEL was confirmed by extensive cost-benefit analysis conducted by project partners. “GASVESSEL outcomes will positively affect waterborne and multimodal transport, helping optimise gas supply within the EU by providing different sources of energy supply. We are confident that our CNG carriers will be prominent contenders for natural gas transport in the near future,” concludes Angelini.
GASVESSEL, transport, vessel, compressed natural gas, storage, CNG carrier, liquified natural gas, LNG