Decarbonising St Fergus Gas Terminal

Delivering a Greenhouse Gas emission saving of more than 450 te CO2e per year at St Fergus Gas Terminal

450 te CO2e per year Annual Greenhouse Gas Emission saving 20% Processing over 20% of the UK’s gas supply <6 months Payback Period

px delivered a Greenhouse Gas (GHG) emission saving of >450 te CO2e through the substitution of a fuel gas purge with nitrogen on a safety critical flare system.

What We Did

LP Flare System

The LP flare system provides a safe means of disposing of gas in emergency scenarios via a flare gas header, which is subsequently fed to a flare riser and eventually relieved to the atmosphere via a flare tip. To avoid air ingress into the flare header, the system is provided with a continuous purge which as per the original design of the flare system consists of hydrocarbon gas. The purge rate is determined to maintain a specified superficial velocity in the flare header.

Nitrogen Substitution

As part of px’s drive for continuous environmental improvement, optimisation work was undertaken to minimise the hydrocarbon purge rate to the minimum technical limit. This initially provided a 20% reduction in flare emissions. Further work was then undertaken to test the practicality of substitution of the purge gas with nitrogen. Two elements had to be satisfied, the use of nitrogen had to be demonstrated to be safe and to demonstrate that the operation was Best Available Technology (BAT).

A test program was developed and undertaken by the asset team. The tests were successful, and the modification was made permanent through the px Management of Change process. The modification included regular sampling of the flare emissions to confirm that the nitrogen purge is still BAT.


  • 450 te CO2 e Greenhouse Gas (GHG) emission saving per annum
  • Project payback with 6 months