Demolition

Demolition at the site commenced in November 2018^[19] with the 'blow down' of the coal stock towers.^[20] The eastern boiler annexe was demolished on 11 April 2019.^[21] The boiler house, turbine hall and control room were all demolished on 4 February 2021.^[7]

On 9 December 2021, the chimney stack was demolished.^[22][23] Three days before this, Scottish Power had illuminated a slogan onto the chimney that read "Make Coal History".^[24] The explosives were triggered by the First Minister of Scotland, Nicola Sturgeon.^[8]

Electricity generation

The station consumed up to 4,500,000 tonnes (4,400,000 long tons; 5,000,000 short tons) of coal each year.^[11] Coal was delivered either by road or rail to the station's coal store, which had the capacity to hold up to 2,000,000 tonnes.^[3][11] It was then fed from the coal store to the boiler house by a conveyor belt capable of carrying 3,500 tonnes of coal per hour.^[11]

Each of the four boilers was serviced by eight pulverising units, each capable of processing 40 tonnes of coal an hour.^[11] The front-wall-fired Foster Wheeler boilers could each burn around 250 tonnes of coal an hour at full load.^[11] There were two forced draft and two induced draft fans on each boiler.^[11] Each boiler provided around 1,800 tonnes per hour of steam at a pressure of 168 bars (16,800 kPa) and a temperature of 568 °C (1,054 °F) to two 300 MW General Electric Company turbo generators.^[11][27] The thermal efficiency of the plant was around 37%.^[11]

Coal supply

Coal was originally supplied directly by conveyor belt from the neighbouring Longannet Colliery, until it closed in 2002 after a flood.^[25][28] Around half of the coal used was Scottish, and the rest had to be imported, the majority via the former British Steel plc ore loading facility at Hunterston Terminal in Ayrshire.^[3] Onward transport was by rail and the level of traffic required to supply Longannet's fuel demand caused congestion on the Scottish rail network.^[29] An alternative route, the Stirling-Alloa-Kincardine rail link, at the mouth of the river Forth was reopened in 2008, and was also used to deliver coal.^[30]

Cooling system

The chimney was 183 metres (600 ft) tall; the station did not have cooling towers, instead using water drawn from the Firth of Forth at a rate of 327,000 cubic metres (11,500,000 cu ft) per hour for the station's cooling condensers.^[11][27][31] The water was passed through coarse screens and then circulated by four electrically driven pumps.^[11] Once circulated through the station's condensers, the water was discharged into a mile long cooling channel, where heat was dissipated before the water reached a wide part of the Forth.^[11] Water used by the boilers was on a different cycle, and had to be deionised. Losses from this supply were made up by a plant capable of treating 218 cubic metres (7,700 cu ft) of water per hour.^[11]

Electrostatic precipitators and sulphur trioxide conditioning

The station was fitted with electrostatic precipitators (ESP) to reduce the station's particulate emissions. In the late 1980s, the station's units were fitted with sulphur trioxide (SO₃) conditioning equipment to lower the fly ash's electrical resistivity. This was to ensure the station maintained allowable particulate emissions. Between 1989 and 1994, the station's ESPs were given a major refurbishment. This meant that the SO₃ conditioning equipment did not need to be operated as frequently to maintain the allowed level of particulate emissions. This was beneficial as SO₃ is hazardous.^[11]

NOx reduction

In 1994, the station was awarded funding from the European Commission under the THERMIE Demonstration Programme. With this money, Unit 2 at the station was retrofitted with gas-reburn equipment. This was the largest scale application of this technology in the world. In this process, natural gas is injected into the boiler. This cut NOx emissions from Unit 2 by 50%, as well as giving a reduction in CO₂ and SO₂ emissions. In 1996, all the station's boilers were fitted with Low NOx burners. This reduced the station's NOx emissions by 40%.^[11]

The blend of coal fed to each unit was intended to minimise emissions of sulphur.^[3]

Carbon capture and storage

The UK's first carbon capture and storage (CCS) unit was commissioned at the station in 2009.^[13] It closed in 2011 after it became clear that it was not financially viable.^[32] Plans for a UK Government funded project to convert Longannet to CCS were abandoned in 2011 and no further plans for CCS at Longannet were announced.