Sea NG Prepares for Launch Party

The world's first commercial compressed natural gas (CNG) scheme is in line to go ahead by the end of the year, according to its proponent Sea NG.

David Stenning, the chief executive of Calgary-based Sea NG, said that given the hoped-for completion of a contract for a project in the Caribbean or Mediterranean, the company fully expects to award construction of three Coselle CNG carriers in the next three months.

Last week's full design approval for construction of Sea NG's Coselle ship concept leaves the way clear for such an order.

The approval for this class of vessel has been issued by the American Bureau of Shipping. The same organisation issued an earlier approval in principle for the design as long ago as 1997.

Now, several incarnations of the company later, Sea NG becomes the first organisation to gain full design approval from a marine classification society for construction of a CNG ship and its gas containment system.

"We can now launch our first project with this new class of ship," said Stenning. He gave no further details about the prospective schemes in the Caribbean or Mediterranean beyond saying there are some "very serious projects in the late stages of negotiation with serious customers".

The 120 metre-long vessels to be ordered will have capacity to carry a cargo of 1.4 million cubic metres of gas, which is stored in dense phase at a pressure of 3200-psi inside coils of small diameter high strength steel pipeline.

"The steel we use is basically high-quality linepipe," said Stenning. "It is not an unusual spec in any way, and is easily obtained within three months of ordering."

The market Sea NG is aiming for is to carry moderate volumes of gas over medium distances of 200 to 2000 kilometres.

"We fit into a middle-distance gap between submarine pipelines and liquefied natural gas, which both require relatively large threshold volumes," said Stenning.

The Coselle system reduces the volume of gas by a factor of 300 compared with atmospheric pressure.

Full liquefaction reduces gas volume by a factor of 600, but also brings in the need for major facilies at each end compared with CNG's minimal requirements for loading and offloading. The Sea NG approach is one of the simplest of the proposals from the various groups working on CNG.

"We are not nearly as efficient on the sea as LNG, but we avoid the huge costs of a liquefaction plant at one end and regasification facilities at the other," said Stenning.

All valves are sited in an above-deck manifold system. The 16 Coselles in the vessels currently planned are arranged in four stacks of four, contained in an inert atmosphere in the hold. The small diameter of the pipe also provides safety advantages.