school energy&environment

The distribution

From the large pipes of the national distribution network, thousands of kilometres of smaller pipes are derived to convey natural gas to industrial plants and households. In the city networks managed by the distribution firms the gas pressure is maintained at lower levels than the large transport networks for technical and safety reasons. In 2016, 37,7% of the natural gas distributed in Italy is used in the civil sector, 21.8% in industry and about 31.1% in transport (Source: Bilancio Energetico Nazionale 2016 – Ministero dello Sviluppo Economico).
Before being conveyed to the distribution network, natural gas is added odour, i.e. it is mixed with a substance characterised by a strong smell called “mercaptans”. Therefore users immediately realise if there is a leak. In indoor environments, (e.g. a room), natural gas is mixed with the air and if an igniting factor is present (a flame or a spark caused by switching on the light), it explodes. Therefore, if we come back home or walk indoor and smell a strong odour, we need to avoid switching on the lights or starting any fire. Rather, we have to open doors and windows (natural gas is not toxic) and let it be dispersed outside. For those who cannot smell odours, ad hoc devices were created to signal any leak through visual or acoustic signals. Since natural gas is lighter than the air, such devices ought to be placed near the ceiling.
Environmental impacts associated with the transportation and distribution phases are of two kinds:

• Uncontrolled release of gas into the atmosphere as a result of leakage;
• Loss of water and gasoline deposited at the bottom of the pipeline.

In order to prevent gas leaks, gas pipelines are monitored constantly and the pressure along the entire distribution line is controlled so that leaks can be detected promptly. It has been estimated that over a distance of 4000 km, less than 1% of the gas transported by pipelines is lost. Generally, leakages are greater in the low-pressure urban distribution networks that carry gas to the residential areas, because often the pipes are old. The substitution of old distribution networks and the use of innovative materials is the best solution to drastically reduce leaks.