The Cottam power stations were a pair of power stations on over of mainly arable land situated at the eastern edge of Nottinghamshire on the west bank of the River Trent at Cottam near Retford. The larger coal-fired station was decommissioned by EDF Energy in 2019 in line with the UK's goal to meet its zero-coal power generation by 2025. The smaller in-use station is Cottam Development Centre, a combined cycle gas turbine plant commissioned in 1999, with a generating capacity of 440 MW. This plant is owned by Uniper.
The site is one of a number of power stations located along the Trent valley and is one of the so-called Hinton Heavies. The West Burton power stations are downstream and Ratcliffe-on-Soar Power Station is upstream. The decommissioned High Marnham Power Station was upstream. Under the Central Electricity Generating Board in 1981/82 Cottam power station was awarded the Christopher Hinton trophy in recognition of good housekeeping; the award was presented by junior Energy Minister David Mellor. After electricity privatisation in 1990, ownership moved to Powergen. In October 2000, the plant was sold to London Energy, who are part of EDF Energy, for £398 million.
In January 2019, EDF Energy announced that the coal station was due to cease generation in September 2019 after more than 50 years of operation. The station closed as planned on 30 September 2019. Demolition of Cottam power station began in 2021, with Brown and Mason carrying out the works.
Construction Work was begun in April 1964 on the site of Mickleholme Farm by the Central Electricity Generating Board Midlands Project Group from Bournville. Mickleholme Farm laid between the precipitators and the cooling towers. The modernist architects for the buildings on site were the Nottingham practice of Yorke Rosenberg Mardall. Extensive use was made of 'Cottam Amber' coloured cladding around the boiler and turbine house, 'emphasising its functional grandeur at the heart of the complex'. The English architectural critic Reyner Banham dubbed the office block as 'over-wrought and made gratuitously rhetorical'.
The main contractor for the construction of the 2,000 MW power station was Balfour Beatty. The coal plant was supplied by the New Conveyor Company of Smethwick. John Thompson boilers supply steam to English Electric 500 MW steam turbines. The maximum continuous rating of each boiler is 2,400 lb/sq.in and 568 °C at the superheater. The power station opened in 1968 when owned by the Central Electricity Generating Board.
The ground level before construction varied between 3.35 m and 5.18 m (11 and 17 ft) ordnance datum (O.D.) In order to provide adequate protection against flooding, the area in which the main building is constructed was raised to 7.92m (26 ft) ordnance datum by filling from borrow pits on site, but the coal store and cooling tower area remain at the original level of 4.87m (16 ft) ordnance datum. The nature of the sub-soil was investigated by trial bores and found to be good load bearing marl at depths between 4.26m and 12.19m (14 and 40 ft) below the existing ground level and overlain by sand and gravel strata on top of which lay clay or silt and top soil.
The main building was 209.39 m (687 ft) long by 124.35 m (408 ft) wide and housed four 500 MW boiler-turbine units. The height of the boiler house was 65.22 m (214 ft) and turbine house 34.44 m (113 ft). The building was of steel construction with blockwork up to 10.66m (35 ft), above which there was a light-weight corrugated sheet cladding and windows.
By completing the pile caps on units 1 and 2, the steel erection work was able to progress, while pile caps and flooring were completed on units 3 and 4. This enabled the steel work to be erected on units 3 and 4 from finished floor level while the flooring was being completed on units 1 and 2. This reduced the time taken to construct the main building.
Within the boiler house and between boilers 2 and 3, an escalator was erected which in several stages extended to the boiler drum level to assist with the movement of men and materials.
To the north of the main building was the precipitator bay and chimney. The four flues from the boiler were contained within a single chimney which stood 190.5 m (625 ft) above ground level. In order to improve plume dispersal, the outer chimney casing was terminated 7.62 m (25 ft) short of the four flues which stood at a height of 198.12 m (650 ft).
To the east of the site of the main building are eight cooling towers which are 114.3 m (375 ft) in height and have a base diameter of 94.48 m (310 ft) overall. Beyond this are the coal plant and the coal stocking area. The 400 kV switching station is to the south of the site from which feeders join the National Grid system by way of other substations in the area. To the west are the station workshops and administration block of offices, which were connected to the turbine house by an enclosed overhead walkway. Other associated buildings such as the control block, water treatment plant house, oil storage compound etc., are disposed around and adjacent to the site of the main building.
The cladding of the main building was painted in "Cottam Amber" colour, designed to blend with the brickwork of houses and farms in the vicinity. Extensive grassing and tree planting was carried out on land around the site when construction work had finished. A 15 m high tree-clad ridge was constructed to designs by Kenneth and Patricia Booth to shield Cottam village from the visual mass and noise of the station.
Boilers The four 500 MW boilers at Cottam power station were manufactured by John Thompson Water Tube Boilers Limited, in conjunction with Clarke Chapman & Co. Ltd. Each had an evaporation rate at M.C.R. of 1.542 tonne/hour (3,400 lb/hr). The boiler plant was designed for short time overload operation. By bypassing two of the H.P. feed heaters and increasing the firing rate by 8% an increase of 5% electrical output could be obtained.
Coal was fed from the bunker to the fuel pulverising mills by variable speed drag-link feeders. The four barrel-type mills rotated at 15 rev/min and are swept by hot air which carried the pulverised fuel (P.F.) mixture to eight classifiers that rejected any unground pieces of coal back to the mill. Eight exhausters passed the P.F. to 32 turbulent P.F. burners arranged in four rows of eight burners on the boiler front. Each P.F. burner had an integral oil burner which was used for lighting up purposes and low load operation when instability with P.F. firing would be experienced. Combustion air was fed to the burners by two forced draught fans which passed warm air ducted from the top of the boiler house through two rotary regenerative air heaters to the secondary or combustion air registers around each burner. The air heaters could be bypassed on the gas and air side to facilitate optimum operating conditions.
The boiler feed water passed through the economiser before entering the drum and was then circulated around the combustion chamber water wall tubes by any three of the four boiler water circulating pumps. Steam from the drum was passed to the H.P. turbine through a horizontal primary superheater bank, pendant superheater platens, and pendant final superheater bank. The superheater platens – which were situated directly above the combustion chamber – differ from other heaters in that the heat would be imparted to the steam by radiation as well as convection. The other heaters were later in the gas duct and relied mainly on convection for heat transfer. Steam temperature control was achieved by two stages of attemperation, one of which is between the primary super heater and the superheater platens and the other, which controlled the final steam temperature, was immediately before the final superheater inlet. Exhaust steam from the H.P. turbine would be returned to the boiler for reheating at a constant pressure before being returned to the I.P. turbine. This was achieved by a horizontal primary and a pendant final reheater situated in the gas duct. Steam temperature control was achieved by non-contact type attemperators.
The boiler was kept clean by 42 gun type soot blowers in the combustion chamber and 42 long retractable blowers which cleaned the pendant and convection surfaces, all operating under automatic control from the control room.
The hot gasses from the combustion chamber were drawn through both the super heater and re-heater banks, and the air heater and precipitators by induced draught fans which expelled the gasses through the F.G.D. to the chimney. The fans would maintain a slight vacuum within the combustion chamber in order to prevent combustion gasses leaking into the boiler house. The precipitators which were entirely of steel construction collected the dust by electrostatic means, meaning there were no mechanical collectors.
Turbo-alternators Each of the four turbines was an English Electric Company multi-cylinder impulse reaction machine which would operate on a single reheat cycle with terminal steam connections of 158.6 bar (2,300 lbf/in²), 566 degrees Celsius (1051 degrees Fahrenheit) and would exhaust at a back pressure of 1.5 mmHg. Steam from the boiler passed through four strainers and two pairs of combined stop and emergency valves, each pair being associated with two throttle valves which regulated admission of steam to the H.P. cylinder inlet belt. The H.P. cylinder was composed of eight stages in total. The steam would expand through the first five stages towards the governor end and then reverse its direction and flow between the inner and outer case to the last three stages. Reversing the steam flow within the H.P. cylinder helped to balance the thrust, thus relieving the load on the single thrust bearing. From the H.P. cylinder, the steam was fed to the boiler reheater and returned to the I.P. cylinder through two strainers and two pairs of I.P. emergency valves, each pair of which was associated with a pair of interceptor valves which were attached to the cylinder. The I.P. section of the turbine was double flow with seven stages to each flow.
The exhaust steam from the I.P. cylinder would be passed to the three L.P. cylinders by cross-over pipes reducing cross sections, which distributed the flow of steam equally to each L.P. cylinder through which it expanded to the condenser. Each cylinder was double flow with five stages to each flow. A special feature of the Cottam machines was the radial condenser in which the tube nests were disposed right round the turbine L.P. shafts in a common casing. This reduced the steam velocity in the exhaust space, which together with the reduced losses in the exhaust duct improved the efficiency of the condenser. The weight of the whole structure was some hundreds of tons less than earlier structures, and the foundation block was also greatly simplified, since only a rudimentary structure above basement floor level was necessary under the L.P. turbine.
Feed water system Following condensation of the low pressure exhaust steam in the condenser, the feed water would be passed to a condensate pump mounted under the condenser. From this receiver the condensate was drawn by one or two extraction pumps and passed through a discharge strainer. The low pressure feed heating system consisted of five direct contact heaters with one high level deaerator to provide a high feed pump suction head. The direct contact L.P. heaters were arranged in two banks, comprising three and two heaters respectively. Within each bank the heaters were stacked above each other so that the condensate could drain from the lower pressure heater by gravity. The heights of the heaters were approximately inversely proportional to the bled steam pressures.