Mossmorran

The Mossmorran Natural Gas Liquids (NGL) plant is part of the northern North Sea Brent oil and gas field system and is located on the outskirts of Cowdenbeath, Scotland. The Mossmorran facilities comprise two plants: the Fife NGL Plant operated by Shell and the Fife Ethylene Plant operated by ExxonMobil. An associated sea-going tanker loading facility is located at Braefoot Bay, 4 miles (7 km) to the south.

History

With the commissioning of the Shell Brent Field in 1976, Shell Expro and Exxon Chemicals sought permission to build processing plants at Mossmorran to process the natural gas liquids from the St Fergus gas terminal.[1] A planning inquiry was completed in 1977.[2][1]

Operation

After gas and oil are separated on the offshore platforms, the gas is routed ashore via pipelines to the gas terminal at St Fergus. At the terminal methane is separated from the rest of the gas product. The methane is sent to a neighbouring National Grid plant which controls the gas flow into the National Transmission System. The remaining natural gas liquids are piped south via a 223 km pipeline to the Mossmorran site in Fife.[6] NGL from the other gas terminals at St Fergus can also be routed through the St Fergus - Mossmorran pipeline.

Fife NGL Plant

At the Fife NGL plant natural gas liquid is separated into its component parts by distillation in three sequential fractionation columns. These comprise a de-ethaniser, a de-propaniser and a de-butaniser, the constituent components and products from the plant are: ethane (C2H6), propane (C3H8), butane (C4H10) and pentane (C5H12) or natural gasoline.[5][7] The ethane is piped to an adjacent ethylene (ethene) cracker plant operated by ExxonMobil for processing and cracking. The propane and butane streams are chilled, liquefied and stored on Mossmorran site within double wall insulated, partly buried tanks; the gasoline is stored in floating-roof tanks. These liquids are then transported as required via pipeline to the marine terminal at Braefoot Bay on the Firth of Forth for loading onto ships for export.[7] Vapour return lines from Braefoot Bay are provided for the propane and butane facilities. Mossmorran has an adjacent road tanker terminal for road transportation of propane and butane.[7]

The NGL plant originally operated using two identical process modules (each with three columns) with a capacity of approximately 10,000 tonnes per day. This was later increased to 15,000 tonnes per day by the addition of a third process module and a few other upgrades in 1992 at a cost of roughly £100 million. The production capacity in 2014 was 12,500 tonnes/day.[5]

Fife Ethylene Plant

At the Fife Ethylene Plant[8] ethane feedstock from the NGL plant is treated to remove carbon dioxide (CO2). An amine based solution is used to 'wash' the feedstock to remove CO2.[9] Ethane is mixed with superheated steam and heated to 800-900°C in seven cracking furnaces to crack it into ethylene (ethene) (C2H4 or H2C=CH2). The ethylene mixture is then cooled to 25°C in a series of heat exchangers and finally routed to a quench tower where water cascades down through the gas to remove by-products such as tar. The gas is next compressed and enters a 'cold box' comprising a further series of heat exchangers which chill the gas until it is liquefied.[9] The liquid passes into a series of three tall fractionation towers and a reactor. In the first tower, the de-methaniser, hydrogen and methane are removed from the top and are used as fuel gas in the plant. The de-methanised product is taken from the bottom of the de-methaniser and passes to the second tower, the de-ethaniser. Ethylene, acetylene (C2H2) and any remaining ethane are taken from the top of the de-ethaniser and are routed to the acetylene converters where hydrogen is added to convert acetylene to ethylene in the presence of a catalyst.[9]

alternate names	Fife Ethylene Plant FEP Fife NGL
pushpin map	Scotland Fife
coordinates	56.097°N, -3.303°W
building type	Gas terminal
location	Mossmorran, Fife, Scotland
owner	ExxonMobil Chemical Limited (FEP), Shell (Fife NGL)
current tenants	ExxonMobil, Shell
completion date	1985
inauguration date	1985
floor area	133 acre

History

Structure

Operation

Fife NGL Plant

Fife Ethylene Plant

Environmental concerns

External links

References