What is CNG?

Compressed Natural Gas, or CNG, is quite simply gas that has been compressed (typically between 1500 and 4000 psi) such that it can be transported in pressure vessels rather than by pipeline or LNG as is the traditional method.

While interest in CNG technology and transport has grown in recent years, it is by no means a new idea. In many countries outside North America, CNG is the primary fuel source for vehicles, displacing gasoline. Within North America, CNG is generally used to fuel transit and fleet vehicles in large cities, as well as in a limited number of personal Natural Gas Vehicles (NGVs).

The current swell of interest in CNG is along a different line than the vehicle fuel applications described above. As much as 4,500 trillion cubic feet (tcf) of gas can be defined as stranded world-wide (Zeus Development Corp., 2003); with North American production of conventional natural gas reaching a plateau, there is growing interest in monetizing these reserves, previously regarded as too remote or expensive to bring to market. In cases where stranded reserves are located relatively close to a market, CNG technology can be a viable method for transporting this otherwise stranded gas to market. Currently there is a great deal of interest in the marine transport of CNG from offshore reserves to the mainland, precluding the need for an expensive, or technically impossible, undersea pipeline or LNG developments.

The first attempt to transport CNG commercially by sea was in the 1960s, when Columbia Gas Company converted a troop transport ship into a CNG carrier. Limited by the technology of the time, the carrier required steel pressure vessels with very thick, heavy walls, in order to contain the high-pressure gas. The result of the heavy containers was that, in the end, shipping costs per unit of gas delivered were simply too high to sustain the project (Roche, 2003). While not a commercial success, the Columbia experiment proved that natural gas could be safely transported by sea in pressure vessels.

Today, with the development of modern, high-strength steels and composite technologies, as well as novel design solutions, the CNG proponents have solved the weight problem that scuttled the Columbia project.

CNG is now coming to be seen as a viable method of monetizing stranded gas reserves or bringing gas into stranded markets.