Cockenzie power station

Cockenzie power station
Cockenzie Power Station Viewed from the south in March 2003
Location of Cockenzie power station in UK Scotland
Country	Scotland
Location	Cockenzie
Coordinates	55°58′06″N 2°58′18″W / 55.96833°N 2.97167°W / 55.96833; -2.97167Coordinates: 55°58′06″N 2°58′18″W / 55.96833°N 2.97167°W / 55.96833; -2.97167
Status	Closed
Commission date	1967
Decommission date	15 March 2013
Operator(s)	South of Scotland Electricity Board (1967–1991) Scottish Power (1991–2013)
Thermal power station
Primary fuel	Coal
Power generation
Nameplate capacity	1,200 MW
grid reference NT394754

Cockenzie power station is a closed coal-fired power station in East Lothian, Scotland. It is situated on the south shore of the Firth of Forth, near the town of Cockenzie and Port Seton, 8 mi (13 km) east of the Scottish capital of Edinburgh.^[1] The station has dominated the local coastline with its distinctive twin chimneys, since it opened in 1967. Initially operated by the nationalised South of Scotland Electricity Board, it has been operated by Scottish Power since the privatisation of the industry in 1991. In 2005 a WWF report named Cockenzie as the UK's least carbon-efficient power station, in terms of carbon dioxide released per unit of energy generated.^[2] The 1,200 megawatt power station ceased generating energy on 15 March 2013 around 8.30am.^[3][4] As of May 2014 the main station is being dismantled by Brown and Mason Ltd, a UK-based demolition company. There are plans to replace the station with a Combined Cycle Gas Turbine (CCGT) power station.

History

Under a design by the firm of celebrated architect Sir Robert Matthew, construction of Cockenzie power station began in 1959 on the site of the former Preston Links Colliery. The site is also thought to have been the hiding place of General John Cope after the defeat of his army at the Battle of Prestonpans on 21 September 1745.^[1] Much of the electrical equipment for the station was manufactured by Bruce Peebles & Co., Edinburgh. The station began generating electricity in 1968 for the then South of Scotland Electricity Board (SSEB). In 2000-01, Cockenzie generated a record load factor, supplying 3,563 GWh of electricity and burning 1,500,000 tonnes of coal.^[1]

Specification

The power station occupies a 24 hectare site. It generated electricity at a frequency of 50 hertz using four identical 300 megawatt (MW) generating units, for a peak supply of 1200 MW.^[1]

Cockenzie Power Station was the largest coal-fired power station in Great Britain when it opened in 1967.

Operations

Coal deliveries

Coal was originally supplied to the station directly from the deep mines of the neighbouring Midlothian Coalfield, but these have since been exhausted or closed. Subsequently coal was supplied from open cast mines in the Lothians, Fife, Ayrshire and Lanarkshire. Russian coal was used latterly as it has a low sulphur content which helped reduce sulphur oxide (SOx) emissions to the atmosphere. The power station was the first to use the "merry-go-round" system of coal deliveries by rail.^[5] This system uses hopper wagons which carry around 914 tonnes of coal per train. Coal was also delivered by lorries and is known as 'road borne' coal.

Coal handling plant

Coal was delivered to the station's coal plant, which has the capacity to hold up to 900,000 tonnes of coal on a storage bing.^[1] The coal plant and storage bing are situated on the opposite side of B1348 road between Prestonpans and Cockenzie and Port Seton, and the main station. The coal, known as 'raw coal' at this stage was weighed, sampled and screened for metal and stones before being transported to the main station and stored in bunkers. Coal was transported from the coal plant to storage bunkers in the main station by a conveyor belt.

Milling plant

There are 6 pulverising mills per unit which ground down the raw coal until it had the consistency of sand. The ground coal is called 'pulverised fuel' (PF). PF burns more efficiently than large lumps of coal, which reduces waste. The PF was then blown into the furnace along with preheated air by 6 large mechanical fans called Primary Air (PA) Fans.^[1] At full load each unit burned around 100 tonnes of coal per hour.

Draught plant

Each unit has 2 large Forced Draught (FD) Fans. For efficiency these fans drew warm air from an intake at the top of the station. This combustion air was passed through the Air Heater which increased its temperature. Dampers were used to control the quantity of air admitted to the furnace and direct some of the air to the Primary Air (PA) Fans. There are also 2 large Induced Air (ID) Fans on each unit. These drew the hot gases from the Boiler, through the Air Heater where the heat is transferred to the incoming combustion air. The gases are then exhausted up the chimney. The exhaust flow of these fans was also controlled by dampers in the ducting. Working in tandem the Draught plant ensured the boiler was always under a slight vacuum. This created a draw of combustion air into the boiler and an exhaust to the chimney. The exhaust gases could not be allowed to cool below a certain temperature, as there was a risk of the sulphur and nitrogen oxides in the flue gases condensing and forming acids which could have damaged the ID Fans.

Water use

The water used in the station's boilers was taken from the local water supply, known as 'towns water'. This is the same as the drinking water used to supply households. This water was used as it had already been screened and purified by Scottish Water.

Demineralisation plant

The station's water treatment plant further demineralised the towns water and removed any impurities. Although safe to drink water still contains dissolved silica (sand) and sodium (salt). Silica particles leave scale deposits on the boiler pipes which acts as an insulator, reducing heat transfer from the furnace to the water inside. This reduces the efficiency of the station and leads to increased running costs. Sodium encourages rust which weakens the walls of the boiler pipes and can cause them to fracture and burst, known as a boiler tube leak. A serious tube leak can lead to reduced generation or loss of the unit until repairs are carried out.

Hydrazine is added and used as a reducing agent to remove excess oxygen from the water. Free oxygen atoms in the water also encourage rust to form inside the boiler pipes. Caustic is also added to 'scour' the inside of the boiler tubes and remove any silica particles.

The demineralised water was then stored in large tanks inside the main station, ready to be used in the boilers.

Feedheating plant

Before the feedwater was introduced to the boiler it was heated up in stages. There are 7 feedwater heaters on each unit which gradually increase the pressure and temperature of the water, until it reached a final feed temperature of around 210 °C. A steam driven Main Boiler Feed Pump (MBFP) pumped the water through the boiler Economiser and into the boiler Drum.

Boiler

The boiler Drum is a pressurised high tensile steel chamber where the water boiled into steam. The water here was pressurised to 170 bar and heated further to 360 °C. On the bottom of each Drum are 6 large bore pipes known as Downcomers. These directed the water into the boiler water pipes where it was heated by the furnace. The water was then directed back into the Drum where it flashed off into saturated steam. The steam was then further heated by passing through Primary and Secondary Superheaters until it reached 565 °C. The superheated steam was then piped to the unit turbine.

Turbine

There was 1 turbine and alternator per unit. The turbine had 1 High Pressure (HP) stage, 1 Intermediate Pressure (IP) stage and 2 Low Pressure (LP) stages all connected in tandem to the same shaft. The superheated steam entered the HP turbine at a temperature of 566 °C and a pressure of 162 bar. The exhaust steam from the HP turbine travelled back through the boiler Reheater and entered the IP turbine at the same temperature but at a lower pressure of 43.5 bar. The exhaust steam from the IP turbine then entered the LP turbines. The steam was used to drive the turbines, causing the shaft to rotate at 3,000 rpm. This speed drove the Alternator and gave a frequency of 50 cycles per second (Hz) and allowed connection to the National Grid. Electricity was generated at 17 kilovolts (kV).

Condenser

After use, the steam was condensed back into water, by passing it through the Condenser. Seawater from the Firth of Forth was used as a cooling medium. Over 500,000 litres per minute of water were used for cooling. The seawater was then discharged back into the Firth of Forth.^[1] Controls ensured the discharged seawater was kept close to the temperature of the sea, to avoid creating a 'tropical' environment and upsetting the local ecosystem.

Ash removal and use

The ash dump at Musselburgh

The burning of coal in power stations generates ash and dust. The station's electrostatic precipitators captured fly ash from the flue gases, preventing it from entering the atmosphere. Bottom ash was also produced by the station. Ash from the station is sold through the ScotAsh company, a joint venture between Scottish Power and Blue Circle. It is used in the construction industry and in products such as grout and cement. Any remaining ash was piped to the large lagoons in the nearby town of Musselburgh, where it was capped and planted, and used as a nature reserve.^[1]

Electricity distribution

The electricity was initially generated at 17 kV. This was stepped up via a transformer to 275 kV for distribution on the National Grid. The electricity was distributed to Scotland, and England too, which it is connected to via a double circuit overhead line, operating at 275 kV and 400 kV, to Stella near Newcastle upon Tyne.^[1]

Post-privatisation and future

From 1991 to 2013, the station was operated by the privatised Scottish Power utility group. It surpassed its originally intended lifespan. It was run as a 'marginal station', guaranteeing seasonal and peak supply and covering non-availability of other power stations. For this reason considerable investment was made to improve start-up times to maximise generating opportunities in the deregulated electricity generation market. From 2001, the station exported electricity to Northern Ireland via an undersea power link.^[1]

CCGT replacement

The coal-fired power station was forced to close due to the Large Combustion Plant Directive (LCPD). This is an EU directive that aims to reduce acidification, ground level ozone and particulates by controlling the emissions of sulphur dioxide, oxides of nitrogen and dust from large combustion plants. To reduce emissions a Boosted Over Fire Air plant was fitted to reduce the concentration of oxides of nitrogen in the flue gas. The station closed on 15 March 2013, earlier than expected.^[4]

Scottish Power are currently considering replacing it with a Combined Cycle Gas Turbine (CCGT) power station. Natural gas is a much more efficient fuel than coal and will more than halve carbon and nitrogen dioxide emissions compared to the existing power station. If the station is built, it will require a 17 km (11 mi) gas pipeline from East Fortune, to supply it with fuel.^[6]

In 2011 planning permission to replace the coal-fired power station was approved by the Scottish Government. The new 1,000 megawatt (MW) CCGT power station will create up to 1,000 jobs in demolition and construction and 50 full-time positions when completed. The approval is in line with the recommendations of the report of the public inquiry. Conditions imposed on the consent will minimise disturbance in the area during construction and minimise impacts on the environment and on protected species. The development will be carbon capture ready and will be required to fit full carbon capture and storage technology once it is commercially and technically proven. A separate application for a 17 km (11 mi) pipeline from the existing gas network at East Fortune to the new power station has also been approved.

In the 1990s, leading maritime expert Professor Alf Baird was hired by ScottishPower to investigate the case for a £30 million marine terminal to replace Cockenzie Power Station that would bring the world’s biggest cruise ship companies to the East Lothian community. Cockenzie is said to be the “optimal” site for a port because it has little tidal movement, strong rail links and room for expansion. While ships can already dock at Leith, Rosyth and Hound Point, these locations are thought to lack the necessary infrastructure to cater for large cruise liners. As of 19 June 2013, Scottish Power is considering the cruise project.^[7]

References

External links

Wikimedia Commons has media related to Cockenzie power station.

• YouTube - Lighting of the Chimneys during the Three Harbour Arts Festival
• YouTube - Steeplejacks on the station's chimneys in July 1997