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Description of the transmission system
With more than 31,000 km of pipelines and 27 compressor stations, GRTgaz is one of the biggest transmission operators of natural gas in Europe.
1. Gas entry points in France
LNG terminals :
The natural gas is liquefied by cooling (at -160°C, its volume is reduced by a factor of 600) and transported by ship. On arrival at the LNG terminal, the natural gas is regasified and injected into the transmission system.
There are currently two LNG terminals in France: Fos-sur-Mer and Montoir-de-Bretagne. A second terminal will come into operation at Fos in 2008.
Border entry points :
GRTgaz’s transmission system is linked to the systems of other European transmission operators at three inland points. These are Loon-Plage, Taisnières and Obergailbach. On these sites, compressor stations process the natural gas, odorise it and inject it into GRTgaz’s system.
The Fos-sur-Mer and Montoir-en-Bretagne LNG terminals are also considered to be entry points.
2. Transmission
Pipelines :
Natural gas is carried underground via pipelines. These steel pipelines are buried in the ground at a depth of around 1 metre. Only small yellow marker posts reveal the presence of one of these pipelines.
The flow of natural gas is constantly monitored, and environmental protection is a major priority.
Compressor stations :
As it flows through the pipelines (at approximately 30 km/h), the natural gas slows down because of friction with the sides of the pipe. This process results in a drop in pressure at the end of the system. For this reason, compressor stations are located every 150 km or so, to offset the pressure drops. These stations are equipped with electrically-driven compressors or turbocompressors. They are automated and fitted with remote monitoring systems.
They are part of the 24/7 dispatching process on the system. Six of GRTgaz’s stations have ISO 14001 certification, and the aim is that they should all be certified by 2010.
Major engineering projects :
Click here for information on all of GRTgaz’s major engineering projects
3. Delivery
Public distribution :
On the outskirts of towns, the gas is taken over by the local distribution system. Delivery stations reduce the pressure of the gas to make it compatible with the distribution system, and meter the gas flow. The local distribution system, which has smaller pipes than on the transmission system, made of polyethylene (flexible black pipes with yellow stripes), then delivers the natural gas to the end customers (apartment buildings, offices, private houses, etc.).
Industrial customers :
Some industrial sites, which are big consumers of natural gas or located away from the local distribution systems, are connected directly to the transmission system.
Here, the natural gas is delivered to the industrial user at a “delivery station‿. This keeps the site permanently supplied, adapts the physical characteristics of the gas to the customer’s needs, and measures the quantities of gas delivered.
Storage :
Natural gas is delivered steadily, throughout the year, although consumption varies with the seasons. Stores of gas are maintained in natural underground reservoirs to ensure that supply is always sufficient to meet demand. So surplus gas received during the summer is stored ready for use in winter, when the weather is cold.
