Note: originally was published on E.N.I’s Ecos 1n 1998.
The powerful station of El Haouaria, at Cape Bon, might be compared to a father who gives an energetic but carefully controlled push to the child sitting on a swing.
It is a marvel of technology; no other gas pipeline station in the West can compare with it: it has an installed capacity of 216 MW and its job is to give the natural gas from the Tunisian stations of Feriana and Sbikha, the impulse it needs to cross the Mediterranean.
On average, 2,350,000 cubic meters of gas transit through Cape Bon every hour. Without slowing it down, the plant treats, cleans and compresses it, and dispatches it to Mazara del Vallo.
The incoming gas has a pressure of 60 bars; as it goes through the station it receives a boost that raises the pressure to approximately 130-140 bars on average, and in particular situations to 220 bars.
To make the methane move with the flow and pressure conditions required for the two gaslines that link the Tunisian-Algerian border (Saf-Saf) with Cape Bon, says Giuseppe Peluso, who is the technical manager of Sergas (the company in charge of the gasline's operation and maintenance) and Scogat (the company established to build the trans-Tunisian gasline), it is necessary to give it a certain amount of energy. To this end, three compression stations have been installed along the Tunisian stretch of the Transmed, at Feriana, Sbikha and Cape Bon.
But to cross from Cape Bon to Mazara del Vallo, the methane needs a strong thrust: it has traveled from Algeria to Cape Bon in two pipes, each with a diameter of 48 inches (about 121 centimeters), but before the transport lines descend into the Sicilian Channel, the two pipes become five: three 20-inch and two 26-inch.
So the gas has to be given the power to go into a narrower pipe section. Moreover, in the Sicilian Channel the gasline follows the profile of the seabed, descending to 640 meters, and at that depth the temperature is considerably cooler. Hence the need to give a thrust that will substantially raise not only the pressure but the temperature of the gas.
The Cape Bon station is special because it has to ensure the arrival at Mazara del Vallo of the natural gas to put into the Italian network. So it must never stop working. It was designed to carry on despite breakdowns and black-outs. All the mechanical, electrical and electronic parts are "redundant" as the technicians say, meaning that there is a surplus of them.
"For a start, everything is arranged to ensure a constant supply of electricity", says Mr. Peluso. Even if Steg's Tunisian electricity grid were blocked, the machines of the Cape Bon station would still be able to pump the gas to Italy.
"We have a first turbo-generator, then a second, and if they were both out of action, the power generator groups would immediately come into operation." And in any case, a series of batteries for privileged users would provide power for the safety plant, even in poor operating conditions. Nuovo Pignone's nine turbo-compressors are self-sustaining, even in the event of a power cut.
It is imperative to convey the gas to Italy, precisely observing all the conditions imposed by Snam. Mr. Peluso says that the programming of the transport and the optimization of the operations are done directly by the huge dispatching room at San Donato, the brilliant elder sister of the highly efficient dispatch room which is located at the Cape Bon station and remotely controls the whole Tunisian stretch of the TransMed gasline.
San Donato decides the amount of gas to be delivered to Mazara del Vallo, the hourly flow-rate, pressure and temperature. It also indicates how many, and which, machines should be used, in order to convey the gas along the route, at each of the three Tunisian stations: the entry station at Feriana, which stands 720 meters above sea level, on the plateau straddling the Algerian-Tunisian frontier; the intermediate station at Sbikha, 120 meters above sea level; and the exit station of El Haouaria, at Cape Bon.
The Cape Bon booster station is in harmony with the landscape and with the environment, because its plants work without producing the slightest polluting emission. First, the turbo-compressors run on methane. Secondly, after compression, the gas is cooled by air, not water.
Thirdly, the oil used for the turbines and compressors is collected, down to the last drop, in a collector and sent to the cisterns of the local company that regenerates it. Sixty people - 58 Tunisians and 2 Italians - live and work at the El Haouaria station.
Relations with the local population are excellent. Maintenance work is done by local technicians and workers. The cordiality existing between the station staff and the community is expressed on many occasions, such as the festival of the trees and the falconry festival, which are ancient customs.
© 2000 Mena Report (www.menareport.com)