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. A planning inquiry was completed in 1977. The Brent to St Fergus FLAGS pipeline was completed in 1980 and the Shell St Fergus terminal in 1981. Prior to this the associated gas from the Brent field had been flared offshore. Construction work started at Mossmorran in 1981. Shell Expro built the Fife Natural Gas Liquids (NGL) plant and the Braefoot Bay Marine Terminal, and Exxon Chemicals built the Fife Ethylene Plant adjacent to, and using feedstock from, the NGL plant, together with the ethylene jetty at Braefoot Bay. The plants were commissioned in 1985.

In addition to gas from the Brent field the FLAGS pipeline also carries gas from the Western Leg and Northern Leg Gas pipelines. The Fulmar gas line carries gas from the Central North Sea to St Fergus.

Exxon and Mobil merged to form ExxonMobil in 1999.

Structure

The Fife NGL plant is 3 km south-east of Cowdenbeath and covers an area of about 250 acres (100 ha). The plant comprises three parallel fractionation trains on the east side of the site. The ethylene plant is on the west side of the site and includes seven reaction furnaces with their associated chimneys, plus its own fractionation columns. The Mossmorran site overall includes about 11 product storage tanks.

The flare from the Mossmorran site is visible, day and night, from any high point in Edinburgh when significant flaring is taking place. The plants operate the following flaring equipment:

* three flares at Shell FNGL;
* one flare at ExxonMobil FEP;
* two ground flares which are operated by Shell FNGL but used by both sites as required.

The site is accessed east of the A909, off the south of the A92.

The Braefoot Bay site is 7 km south on the Firth of Forth. It includes six storage tanks and marine loading jetties.

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 pipeline to the Mossmorran site in Fife. 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. 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. 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.

The LNG 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.

Fife Ethylene Plant

At the Fife Ethylene Plant 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. 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. 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. A mixture called C5+ (compounds containing five or more carbon atoms) is removed from the bottom of the de-ethaniser and is used as a feedstock in the chemicals industry. From the acetylene converter the mixture passes to the third column, the ethylene splitter, unreacted ethane is recycled back to the furnaces and ethylene product is pumped to the ethylene pipeline or to Braefoot Bay. About half of the ethylene is routed to the 1,000 km UKOPA ethylene pipeline network, the remainder is pumped to the Braefoot Bay Terminal where it is stored at just below its boiling point of –103°C before loading at the ethylene jetty and shipping to Antwerp. The plant was originally designed to produce 500,000 tonnes of ethylene every year; it now produces 830,000 tonnes annually.

The products stored and exported at Mossmorran are:

Environmental concerns

Shell was fined £40,000 by the Scottish Environment Protection Agency

HOME


Content is Copyleft
Website design, code, and AI is Copyrighted (c) 2014-2017 by Stephen Payne


Consider donating to Wikimedia



As an Amazon Associate I earn from qualifying purchases