The plant's feedstock is ethane which arrives at the plant after a series of processes. First, natural gas liquids from offshore oil and gas fields are piped to the Shell/Esso gas processing plant at St Fergus. Here the methane is removed and the remaining gas liquids are sent via a 138-mile underground pipeline to the Shell/Esso Natural Gas Liquids plant which is adjacent to the ExxonMobil Chemical’s ethylene plant at Mossmorran. The ethane is separated and purified and sent to the ethylene plant.
The ethane is heated in a steam mix, a process which breaks down or 'cracks' the ethane into ethylene, hydrogen and other byproducts. Sudden cooling then stops the reaction and the subsequent mixture of gases is compressed, chilled and separated in a series of distillation towers.
Uncracked ethane is recycled and all other by-product gases are further processed and shipped to Europe for chemical production, or used as fuel in the plant’s furnaces and gas turbine.