Offshore LNG 

Following on from the Snøhvit cooperation, StatoilHydro and Linde have built a test site at Munich to investigate whether the spiral-wound heat exchanger is rendered less effective when subject to motion onboard a floating LNG plant.

A recent cost-effective concept of an offshore LNG plant.

There are, however, other aspects that should be taken into account, for example:

• a floating plant has to be more compact than its onshore counterpartplant
• there are special challenges related to energy consumption
• safety aspects are crucial

To help meet these conditions, StatoilHydro is considering the possibility of combining a patented invention with its expertise in riser technology.

The patented invention concerns the use of carbon dioxide as a working medium for first stage (pre-) cooling, rather than propane as used in today’s plants.

Carbon dioxide has two advantages: first, it does not burn – a vital safety factor; second, it has a higher pressure than propane, which means that it is denser.

This higher density allows some of the equipment to be downsized. A drawback, however, is that energy consumption is greater. And this is where the second idea comes in.

By employing the riser technology, seawater can be drawn up from a depth of a 1 000 metres for general cooling purposes because its temperature rarely exceeds 6o C, even at the equator where the surface water temperature can be as high as 30o C.

By so doing, the difference in pre-cooler energy consumption between carbon dioxide and propane would be reduced to less than 5%.