Didcot power stations
Didcot power station is an active natural gas and power plant that supplies the National Grid. A combined coal and oil power plant, Didcot A, was the first station on the site and opened in 1968 and was demolished between 2014 and 2020. The power station is situated in Sutton Courtenay, near Didcot in Oxfordshire, England. Additionally Didcot OCGT is a gas-oil power plant, originally part of Didcot A and now independent that continues to provide emergency backup power for the National Grid.
A large section of the boiler house at Didcot A Power Station collapsed on 23 February 2016 while the building was being prepared for demolition. Four men were killed in the collapse. The combined power stations featured a chimney, demolished in 2020, which was one of the tallest structures in the UK, and could be seen from much of the surrounding landscape. It had previously had six hyperbolic cooling towers, three of which were demolished in 2014 and the remaining three in 2019. RWE Npower applied for a certificate of immunity from English Heritage, to stop the towers being listed to allow their destruction. In February 2020, the final chimney of Didcot A was demolished.
Didcot A
History
Didcot A Power Station was a coal and gas-fired power station designed by architect Frederick Gibberd. Construction of the 2,000 MWe power station for the Central Electricity Generating Board began during 1964, and was completed in 1968 at a cost of £104m, with up to 2,400 workers being employed at peak times. It was located on a site, formerly part of the Ministry of Defence Central Ordnance Depot. A vote was held in Didcot and surrounding villages on whether the power station should be built. There was strong opposition from Sutton Courtenay but the yes vote was carried, due to the number of jobs that would be created in the area.The main chimney was tall with the six cooling towers each. The cooling towers were arranged in two groups of three; these were located to the north west and to the south of the main building. The original design was for eight cooling towers but the consultant architect Frederick Gibberd proposed that the number be reduced to six to mitigate the visual impact of the station. The consequent limitation in cooling capability reduced the overall thermal efficiency of the power station.
English Heritage declined to give listed building status to Didcot A Power Station in 2013. Though it recognised there were some interesting features, for example the "carefully designed" setting and Gibberd's detailing, there were better examples elsewhere. The station ceased operation on 22 March 2013.
Operation
The station used four 500 MWe generating units. In 2003 Didcot A burnt 3.7Mt of coal. The station burned mostly pulverised coal, but also co-fired with natural gas. Didcot was the first large power station to be converted to have this function. In addition, a small amount of biomass, such as sawdust, was burned at the plant. This was introduced to try to depend more on renewable sources following the introduction of the Kyoto Protocol and, in April 2002, the Renewables Obligation. It was hoped that biomass could replace 2% of coal burnt. In 1996 and 1997, Thales UK was awarded contracts by Innogy to implement the APMS supervisory and control system on all of the four units, then enabling optimised emissions monitoring and reporting. Between 2005 and 2007 Didcot installed overfire air systems on the four boilers to reduce emissions of nitrous oxide. This ensured compliance with the Large Combustion Plant Directive.Some ash from Didcot A was used to manufacture building blocks at a factory on the adjacent Milton Park and transported to Thatcham for the manufacture of Thermalite aerated breeze blocks using both decarbonized fly and raw ash, but most was mixed with water and pumped via a pipeline to former quarries in Radley.
Environmental protests
On the morning of Thursday 2 November 2006, 30 Greenpeace trespassers invaded the power station. One group chained themselves to a broken coal-carrying conveyor belt. A second group scaled the 650 ft high chimney, and set up a 'climate camp'. They proceeded to paint "Blair's Legacy" on the side of the chimney overlooking the town. Greenpeace asserted that Didcot Power Station was the second most polluting in Britain after Drax in North Yorkshire, whilst Friends of the Earth describe it as the ninth worst in the UK.A similar protest occurred early on 26 October 2009, when nine climate change protesters climbed the chimney, and eleven chained themselves to the coal delivery conveyors; the latter group were cut free by police after five hours, but the former waited until 28 October before coming down again — all twenty were arrested, and power supplies continued uninterrupted. The power station was installing improved security fencing at the time.
2013 closure
Didcot A opted out of the Large Combustion Plant Directive which meant it was only allowed to run for up to 20,000 hours after 1 January 2008 and had to close by 31 December 2015 at the latest. The decision was made not to install flue gas desulphurisation equipment which would have allowed continued generation.Studies did continue into whether there was a possibility that Didcot A might be modernised with new super-clean coal burning capabilities; with RWE partly involved in the study, however in September 2012 RWE Npower announced that Didcot A using its current coal burning capabilities would close at the end of March 2013. On 22 March 2013, Didcot A closed and the de-commissioning process began.
In 2007, Didcot was identified as a possible site for a new nuclear power station but, as at August 2019, nothing further had been heard of the proposal.
Demolition
The three southern cooling towers of Didcot A were demolished by explosives on Sunday 27 July 2014 at 05:01 BST. The contractors had insisted that the demolition would take place between 3 am and 5 am; the towers were demolished at 5.01am.There had been a campaign to move the time of the demolition to 6 a.m. or later to enable local people to watch the demolition more conveniently, but RWE refused. Despite the early morning demolition, many thousands of people turned out to watch from vantage points, as well as those who watched the towers come down via a live Internet stream and the event trended on Twitter with the hashtag #DidcotDemolition.
The three remaining cooling towers were demolished by explosion early on 18 August 2019. The chimney was demolished at 07:30 GMT on 9 February 2020.
2016 collapse
On 23 February 2016, a large section of the former boiler house at Didcot A power station collapsed while the building was being prepared for demolition. One person was killed outright and three people were listed as missing presumed dead. Four or five people were injured, three seriously. Additionally, around 50 people were treated for dust inhalation. The rubble from the collapse was high and unstable, which along with the instability of the remaining half of the building hampered search efforts.The collapse occurred at around 16:00 GMT, and Thames Valley Police declared a "major incident" shortly thereafter. Initial reports of an explosion were ruled out by police after being reported in the media for several hours following the incident.
The boiler house was a steel framed building with the boilers suspended from the superstructure and above ground level to allow for their expansion. At the time of the collapse it was being prepared for explosive demolition on 5 March, a process which involved cutting the structure to weaken it.
On 17 July 2016, what remained of the structure was demolished in a controlled explosion. The bodies of the three missing men were still in the remains at that time. A spokesman said that due to the instability of the structure, they had been unable to recover the bodies. Robots were used to place the explosive charges due to the danger and the site was demolished just after 6 o'clock in the morning. The families said that they wanted their dead relatives back in one piece, not hundreds of pieces but the demolition company highlighted the inherent danger of rescue operations citing that "legally you could not justify humans going back in."
The search for the missing men continued the day after the controlled demolition. On 31 August 2016, it was confirmed that a body had been found in the rubble and the search had been paused to allow specialist teams to recover the body. On 3 September the body was identified as Christopher Huxtable from Swansea.
On 8 September 2016 police confirmed they had found the body of one of the remaining two missing men. On 9 September, the body was formally identified as that of missing workman Ken Cresswell.
The last missing worker was found on 9 September. He was identified as John Shaw from Rotherham.
Rail services
Like many power stations built at the time, Didcot was served by a rail loop which is a branch from the Great Western Main Line. This allowed weekly coal and oil trains to service the Power Station. Rail facilities included a west-facing inlet connection and an east-facing station outlet connection to the GWML, hopper lines No. 1 and No. 2, and injectors for fly ash on a dust and ash disposal loop. The loop has not been used since the station's closure in 2013 and the track has been partially lifted for construction of a new warehouse on the site of the old coal pits. Initially the coal was supplied from the Nottingham coalfields then latterly from South Wales or Avonmouth when the Northern coal pits were closed. The service from South Wales was usually operated by one Class 66 locomotive pulling 25 EWS Coal Cars. The service ran from Avonmouth in Bristol, down the main line, reversing at Didcot Parkway and into the power station. The connections to the main line were severed in mid-2018 in association with the Oxford area remodelling.Technical specifications
The technical specifications below were correct as at time of commissioning; later modifications may have changed these.Turbine
Manufacturer: C.A. Parsons & Co, LtdH.P. cylinder steam:
Inlet 158.6 bar at 565 deg. C
Exhaust 42.0 bar at 365 deg. C
I.P. cylinder steam:
39.0 bar at 565 deg. C
Condenser Vacuum:
-965 mbar
Generator
Manufacturer: C.A. Parsons & Co, LtdMaximum continuous rating: 500 MW at 23,500 volts
Phase current: Three phases at 14,450 amps each
Efficiency: 98.63%
Stator cooling: Demineralised water
Rotor cooling: Hydrogen
Boiler
Manufacturer: Babcock & Wilcox LtdMaximum continuous rating: 422 kg/s
Efficiency: 90.76%
Steam at superheater: 165.5 bars at 568 deg. C.
Steam at reheater outlet: 40.3 bars at 568 deg. C.
Feed water temperature: 256 deg. C.
Type of firing: Front face, 48 burners
Dimensions of furnace:
29.6 m wide
9.1 m deep
45.7 m high
Circulating water system
Number of cooling towers: 6Cooling tower capacity: 11.4 cubic meters per second each
Cooling tower dimensions:
Height: 114 m
Diameter: base 91 m, top 54 m
Thickness: 0.6m tapering to 0.2m
Total evaporation in six towers: 59 x 103 cubic meters/day
Water temperature fall in tower: 10 deg. C
Condenser water flow: 17.0 cubic meters per second
Water temperature rise in condenser: 10 deg. C
Circulating water pump capacity: 18.2 cubic meters per second
Make-up water taken from the River Thames : 45m gal/day
Water returned to the River Thames: 32m gal/day
Coal plant
Manufacturer: Babcock-Moxey Ltd.Train capacity: 1,016 tonnes, 32.5 tonnes per wagon
Quantity of coal used per day : 18,289 tonnes
Main chimney
Dimensions: highBase Diameter:
Number of flues: 4
Gas at exit: 97 km/h at 100 deg. C.
Motor powers
Induced draught fan motor: 1,710 kWForced draught fan motor: 1,200 kW
Circulating water pump motor: 6,150 kW
Feed pump motor: 6,410 kW
Didcot B
History
Didcot B is the newer sibling initially owned by National Power, constructed from 1994-7 by Siemens and National Power's in house project team, and uses a gas turbine type power plant to generate up to 1,440 MWe of electricity. It opened in July 1997.Specification
It consists of two 680 MWe modules, each with two 230 MW Siemens gas turbines and two heat recovery steam generators, built by International Combustion, and a steam turbine.2014 fire
On 19 October 2014, the cooling towers serving one of the steam turbines at Didcot B caught fire. Two of the fifteen fan-assisted cooling towers in the row were completely destroyed, one was seriously damaged, and one suffered light damage. The cause was probably an electrical fault in one of the cooling fans.Didcot OCGT
History
Didcot OCGT is an Open Cycle Gas Turbine that was originally part of Didcot A built in 1968 that uses four open-cycle gas turbines which are each powered by a pair of Rolls-Royce Avon engines to generate 100MW of electricity.The site was made separate from the Didcot A station as part of the decommissioning process being retained to provide a strategic emergency backup for the National Grid providing a fast-responding source of additional electricity in periods of high demand.