Nitrogen oxide emissions

Nitrogen oxide (NOx) emissions, the only significant pollutant emissions from Snam’s activities, is mainly due to the combustion of natural gas in turbines installed in the compression systems (thrust and storage).

The use of natural gas as the main energy source allows sulphur oxides and particulate emissions to be minimised.

Total emissions of nitrogen oxides in 2018 amounted to 564 tonnes (+6.0% compared with 2017), while the indicator that parametrises emissions over the energy used remained unchanged.

The increase in NOx emissions is mainly due to the increase in the gas storage activity (+9%) and the need to use non-low emissions turbines (DLE- Dry Low Emissions) in the Minerbio storage plant. In 2019 the Minerbio storage plant will be equipped with DLE turbines only.

To contain emissions, a programme that calls for modifying certain turbines already in operation and the installation of new units with low emission combustion systems has been in the process of being implemented for years.

In 2018, 5 new DLE turbines came into service for transport operations in the Sergnano and Minerbio thrust plants. With these new turbines the average emissions ratings for the machinery installed capacity already low, were further reduced by 13.6% going from 4.4 to 3.8 ([mg/Nm3]/MW).

NOx emissions (t)

Total NOx emissions (t) (Bar chart)

NOx emissions/ energy use (kg/GJ)

NOx emissions/energy use (kg/GJ) (Line chart)

4 Emissions of NOx in the atmosphere were calculated based on direct measurements or, if not available, by means of emission factors present in the literature (EMEP/EEA “Air pollutant emission inventory guidebook” European Environment Agency).

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