Didcot power stations

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,[9] with up to 2,400 workers being employed at peak times. The station began generating power on 30 September 1970.[1] It was located on a 1.2 square kilometres (300 acres) 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 200 m (660 ft) tall[10] with the six cooling towers 114 m (374 ft)[11] 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.[12]

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.[13] The station ceased operation on 22 March 2013.[3][2]

The station used four 500 MWe generating units. In 2003 Didcot A burnt 3.7Mt of coal. The station burned mostly pulverised coal, but later 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 (now Npower) to implement the APMS supervisory and control system on all of the four units, then enabling optimised emissions monitoring and reporting.[14] 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 (near Newbury, Berkshire) 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.

2006 Greenpeace Protest

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,[15] whilst Friends of the Earth describe it as the ninth worst in the UK.[16]

A similar protest occurred early on 26 October 2009, when nine climate change protesters climbed the chimney,[10] 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.[17]

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,[18] however in September 2012 RWE Npower announced that Didcot A using its current coal burning capabilities would close at the end of March 2013.[6] On 22 March 2013, Didcot A closed and the de-commissioning process began.[2][3]

In 2007, Didcot was identified as a possible site for a new nuclear power station[19] but, as of August 2019, nothing further had been heard of the proposal.

The three southern cooling towers of Didcot A were demolished by explosives on Sunday 27 July 2014 at 05:01 BST.[20][21]

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,[22] 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.[23]

The three remaining cooling towers were demolished by explosion early on 18 August 2019.[24] The chimney was demolished at 07:30 GMT on 9 February 2020.[25]

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.[26][27] One person was killed outright and three people were listed as missing presumed dead.[28] Four or five people were injured,[26][27] three seriously.[28] Additionally, around 50 people were treated for dust inhalation.[26] The rubble from the collapse was 9 metres (30 ft) high and unstable, which along with the instability of the remaining half of the building hampered search efforts.[28]

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.[26][27]

The boiler house was a steel framed building with the boilers suspended from the superstructure and above ground level to allow for their expansion.[13] 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.[29]

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 (BST). 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."[30]

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.[31] On 3 September the body was identified as Christopher Huxtable from Swansea.[32]

On 8 September 2016 police confirmed they had found the body of one of the remaining two missing men.[33] On 9 September, the body was formally identified as that of missing workman Ken Cresswell.[34]

The last missing worker was found on 9 September.[35] He was identified as John Shaw from Rotherham.[36]

In 2018, Coleman and Company who were doing the demolition announced they were stepping down from the demolition, they were replaced by Brown and Mason.

During the demolition of the three remaining cooling towers on 18 August 2019, debris from one of the collapsing towers hit a nearby pylon, causing it to explode and catch fire. The substation was shut down to allow the fire to burn out without intervention. Several people received minor burns but did not require medical attention. Up to 40,000 homes lost electricity until power was restored two hours later.

Railways around Didcot
Great Western Main Line to Paddington Moreton Junction Main to relief line crossovers Didcot, Newbury & Southampton Railway Didcot East Junction Didcot Parkway Didcot Railway Centre Didcot West Junction Cherwell Valley line to Oxford Didcot North Junction Foxhall Junction Didcot Power Station Milton Park Great Western Main Line to Swindon

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.[37] 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.[38] 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.[39] The connections to the main line were severed in mid-2018 in association with the Oxford area remodelling.[40][41]

The technical specifications below were correct as at time of commissioning; later modifications may have changed these.

Manufacturer: C.A. Parsons & Co, Ltd

H.P. cylinder steam:
Inlet 158.6 bar (2,300 lb/sq.in.) at 565 deg. C
Exhaust 42.0 bar (610 lb/sq.in.) at 365 deg. C

I.P. cylinder steam:
39.0 bar (565 lb/sq.in) at 565 deg. C

Condenser Vacuum:
-965 mbar (28.5 Hg)

Manufacturer: C.A. Parsons & Co, Ltd
Maximum 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

Manufacturer: Babcock & Wilcox Ltd
Maximum continuous rating: 422 kg/s (3,350,000 lb/hr)
Efficiency: 90.76%
Steam at superheater: 165.5 bars (2,400 lb/sq.in.) at 568 deg. C.
Steam at reheater outlet: 40.3 bars (585 lb/sq.in.) at 568 deg. C.
Feed water temperature: 256 deg. C.
Type of firing: Front face, 48 burners
Dimensions of furnace:
29.6 m (97 ft) wide
9.1 m (30 ft) deep
45.7 m (150 ft) high

Number of cooling towers: 6
Cooling tower capacity: 11.4 cubic meters per second (150,000 gal/min.) each
Cooling tower dimensions:
Height: 114 m (375 ft)
Diameter: base 91 m (300 ft), top 54 m (176 ft)
Thickness: 0.6m (23 in.) tapering to 0.2m (7 in.)
Total evaporation in six towers: 59 x 103 cubic meters/day (13m gal/day)
Water temperature fall in tower: 10 deg. C
Condenser water flow: 17.0 cubic meters per second (225,000 gal/min)
Water temperature rise in condenser: 10 deg. C
Circulating water pump capacity: 18.2 cubic meters per second (240,000 gal/minute)
Make-up water taken from the River Thames (max): 45m gal/day
Water returned to the River Thames: 32m gal/day

Manufacturer: Babcock-Moxey Ltd.
Train capacity: 1,016 tonnes (1,000 tons), 32.5 tonnes (32 tons) per wagon
Quantity of coal used per day (max): 18,289 tonnes (18,000 tons)

Dimensions: 199 m (654 ft) high
Base Diameter: 23 m (75 ft)
Number of flues: 4
Gas at exit: 97 km/h (60 mph) at 100 deg. C.

Induced draught fan motor: 1,710 kW (2,290 h.p.)
Forced draught fan motor: 1,200 kW (1,600 h.p.)
Circulating water pump motor: 6,150 kW (8,250 h.p.)
Feed pump motor: 6,410 kW (8,600 h.p.)

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 (combined cycle) gas turbine type power plant to generate up to 1,440 MWe of electricity.[42] It opened in July 1997.

It consists of two 680 MWe modules, each with two 230 MW SGT5-4000F[43] (former V94.3A) Siemens gas turbines and two heat recovery steam generators, built by International Combustion (since 1997 known as ABB Combustion Services), and a steam turbine.

On 19 October 2014 just after 8pm, three of the mechanical wooden 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.[44] The cause was probably an electrical fault in one of the cooling fans.[45] RWE Npower managed to get half the plant back into operation on 20 October 2014 whilst the other half would remain out of action until the four damage cooling towers were repaired. The station returned to full operation in 2015.

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.[46]

The site was made separate from the Didcot A station as part of the decommissioning process[47] 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.[48]

Didcot OCGT uses four open cycle gas turbines which are gas-oil fired with combustion gases from all four units combined into a single 101m chimney that has a distinctive blue top.[49]