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Drax Power Station
Drax, Selby, North Yorkshire, UK
associated engineer
Not known
date  1974, 1979 - 1986
era  Modern  |  category  Power Generation  |  reference  SE661271
ICE reference number  HEW 11
Drax is the UK’s largest and most efficient coal-fired power station, and it's currently (2009) the 48th largest power station of any kind in the world. Everything here is at a huge scale.
Drax Power Station has six generating units, each with a capacity of 660MW — enough to power around one million homes. Units 1-3 were completed in 1974 and units 4-6 in 1986. At full output, the station uses 36,000 tonnes of coal every day. The coal is delivered by rail and stockpiled.
The 259m high main chimney contains 44,000 tonnes of reinforced concrete, and is the tallest in the country. It is lined with titanium plate and has three elliptical flues, each serving two boilers.
Every generating unit has 10 pulverising mills. Inside each mill, 36 tonnes of coal per hour are ground to a powder by 10 hollow steel balls — each is 730mm in diameter and weighs 1.4 tonnes. A 9m diameter wheel with nine buckets scoops coal onto a conveyor, which feeds coal into the pulverising mill through a 450mm diameter pipe.
The powdered coal is blown into the combustion chamber of the boiler by an air stream. If the burner is not alight, propane and fuel oil are used to start the flame but the coal dust sustains the burning. The original burners were replaced in 2003, to reduce the quantity of oxides of nitrogen produced.
Each 4,000 tonne boiler is lined with 480km of water-filled steel tubing. The heat of combustion turns the water into superheated steam. This passes through a system of turbines — high pressure, intermediate, and three sets of low pressure turbines. Steam pushes the turbine blades and rotates the shaft. Blades increase in size as the steam pressure drops, to extract the maximum energy — the tips of the largest blades spin at 1.6 times the speed of sound.
Steam at 565 degrees Celsius and 15,600kN per sq m pressure enters the high pressure turbine. It is reheated to the same temperature but its pressure has dropped to 4,020kN per squ m in the intermediate pressure turbine. In the low pressure turbine the steam is at 306 degrees Celsius and 632kN per sq m pressure.
The turning shaft rotates an 86 tonne electromagnet at 3,000rpm inside the 305 tonne copper stator, generating a 23,500V alternating current. This is transformed to 400kV for transfer to the National Grid sub-station.
The exhaust steam from the turbines is condensed into water. It passes through a de-aerator to remove gases that could cause metal corrosion before it is pumped back into the tubes inside the boilers, at 568 litres per second.
Cooling water for the condenser is extracted from the River Ouse — 160 million litres of it every day. The water warms up after condensing the steam and is cooled by being dispersed into a fine spray inside the twelve 114m high cooling towers. Water drops into a 95m diameter pool at the bottom of each tower, where the sediment settles out before water is returned to the river.
Some 1.4 million tonnes of pulverised fuel ash is produced annually and collected by electrostatic precipitators in the boilers. This by-product is sold to Hargreaves CCP to make building blocks, cement products and grouts.
In 1988, Drax was the first power station to retrofit flue gas desulphurisation (FGD) equipment. The £680m scheme, comprising a dozen 4m diameter fans, became operational in 1995. The equipment was shut down for repairs in 1998, when cracks were discovered on all 12 fans. Without them, Drax emits more than 5,000 tonnes of sulphur dioxide gas per week.
The FGD equipment removes 90 percent of sulphur dioxide from the exhaust gas. This yields 1.5-1.75 million tonnes of gypsum annually as a by-product. It is sold to British Gypsum for use in plasterboard and other products. Ash and gypsum that are not of sufficient quality to be sold is disposed of on-site in a landscaped area (Barlow Mound).
In 2008, £100m of work began to install new turbines to cut carbon dioxide emissions by 5 percent. In 2010, Drax will have a £50m biomass processing facility. The 18,000 sq m site will receive, handle, store and process biomass for co-firing with coal. It is the largest such scheme in the world and will reduce carbon dioxide emissions by more than 15 percent.
A total of 1,179 vibro stone columns were fixed into the firm clay underlying the site in 2009, increasing the ground’s bearing capacity to up to 150kN. The columns are 450mm in diameter and penetrate 3.5m into the clay below 1m of made ground. However, in the area of the two new silos the columns are 6m deep.
The power station was built, owned and operated by the Central Electricity Generating Board. In 1990, ownership passed to National Power after the privatisation of the electricity industry. AES Corporation owned it from December 1999 until August 2003. On 15th December 2005, the Drax Group plc were floated on the London Stock Exchange.
Foundation design (1979-82): Tarmac National Construction
Flue gas de-sulphurisation fans (1995): Howdons Sirocco
Turbine supply (2008): Siemans Power Generation
Groundworks (2009): Pennine
Direct injection co-firing system (2009-10): Doosan Babcock Energy
Biomass processing plant (2009-10): Alstom
Biomass processing plant (2009-10): Topp & Holmes
Research: ECPK
reference sources   CEH North

Drax Power Station