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Didcot Power Stations


									How to find us                                            Take the first exit across the bridge to the next
Didcot A and B power stations are just off the A4130      roundabout. For the B station, take the first exit left
on the outskirts of the town of Didcot in Oxfordshire.    and follow the signs for the B Station Security Gatehouse.
                                                          For the A station, take the second exit left and follow
From Oxford and the north                                 the signs for the A Station Security Gatehouse.
Take the A34 south bypassing Abingdon until the
junction with the A4130 is reached. Take the second       Visit to:
exit at the roundabout and travel to the next round-      • Find out more about our ‘Energy to live, energy to
about. Take the first exit across the bridge to the         learn’ education programme.
next roundabout. For the B station, take the first exit
left and follow the signs for the B Station Security
Gatehouse. For the A station, take the second exit
                                                          • Order online npower’s free educational Power Pack
                                                            resources for Key Stages 1–4, which focus on energy
                                                            and power.
                                                                                                                                                       Didcot Power Stations
left and follow the signs for the A Station Security      • Get helpful lesson ideas and activities from our
Gatehouse.                                                  Renewable Energy education web link.
From High Wycombe and the east via the M40
Leave the M40 at Junction 7 Take the A329 to
Wallingford. At Wallingford take the A4130 to Didcot.
At Didcot follow the relevant signs for both stations.
From London or the west via the M4 and Newbury
and the south
Leave the M4 at Junction 13 and follow the A34
northwards until the junction with the A4130. Take
the 4th exit at the roundabout and travel to the next

Didcot A and B Power Stations
Oxfordshire OX11 7HA
T (0)1235/51 22 91
F (0)1235/51 60 97

                                                                                                                       Design WPA Pinfold 0061/09/04
Flexible power from                                        RWE npower, part of the RWE Group, is a leading
                                                           integrated UK energy company. We are one of the UK’s
coal and gas                                               largest energy suppliers. We have over 8,000MW of
                                                           generation capacity in the UK from our diverse portfolio
                                                           of flexible, low-cost generation assets, sell our expertise
The npower site at Didcot is host to two power stations    in power generation in key markets and are market leaders
– the 2,000MW dual-fired A station and the 1,360MW         in renewable energy development.
combined cycle gas turbine B station.

Together the two power stations are capable of producing   npower, one of the UK’s leading energy   Our current operational wind farms
                                                           suppliers serves around 6 million        have a combined capacity of 267MW,
enough electricity to meet the needs of over 3 million     residential and business customers.      with many other projects at various
people – equivalent to the demand of three counties the    We are also commited to developing       stages of development. We have
                                                           innovative products which allow our      nine hydroelectric power stations in
size of Oxfordshire.                                       customers to make sustainable energy     Scotland and Wales, with a combined
                                                           choices, such as our domestic green      capacity of some 50MW.
                                                           energy product, npower Juice.

                                                           We are market leaders in both
                                                           onshore and offshore wind energy
                                                           developments and operation and
                                                           small-scale hydroelectric generation
                                                           in the UK.
01 Coal supply                           05 Generator                              08 Cooling towers
The coal is delivered to the station     The generator rotor is directly coupled   The warmed river water from the
by train and placed on the stockpile     to the turbine shaft and rotates          condensers passes to the six cooling
or taken by conveyor to the boiler       within the stator. As the turbine shaft   towers, where it is sprayed over
house.                                   spins, it rotates the generator rotor,    packing in the base of the tower,
                                         an electro-magnet weighing 74 tonnes.     and cooled by evaporation in the        Didcot A began commercial operation in 1970 as a
02 Pulverising mill                      The electromagnet is energised by         natural up-draught of air. Some of
The coal is ground as fine as face       direct current from the exciter,          the cooling water condenses into        coal-fired power station. It developed the capability to
powder in a pulverising mill, picked     a small generator situated at the         tiny floating droplets, like an early
up by a powerful stream of hot air       outboard end of the main generator.       morning mist. This creates the water    operate flexibly in response to the variation in demand
and blown into the boiler to burn                                                  vapour plume that can be seen
like a gas.                              Electricity is generated in the stator:   coming from the top of the towers.      for electricity.
                                         a series of hollow, insulated, copper     Lower winter temperatures increase
03 Boiler                                conductor bars that are cooled by         condensation making the plume
The heat produced converts               extremely pure water. Power is            larger.
extremely pure boiler feedwater          produced at 23,500 volts alternating                                              Didcot A is a dual-fired power station,   Because of changing market and
into steam in the 500 kilometres         current. Each of the four generators      09 Electrostatic precipitators
of tubing that form the boiler walls.    produces 500MW when running at            Before the boiler gases are             owned and operated by npower part         environmental factors, three of its
The steam leaves the boiler at           full capacity.                            discharged from the main chimney,       of RWE npower. Commercial operation       four 500MW generating units were
a temperature of 568°C and at                                                      some 99% of the fine dust,              began in 1970 and the station can         converted to dual-firing, in order
165.5 bar.                               06 Generator transformer                  produced by burning pulverised
                                         Electricity from the generator is         coal, is removed from the flue          generate 2,000MW of electricity –         that they can burn natural gas as an
For greater efficiency, the steam        produced at a voltage of 23,500           gases by electrostatic precipitators.   enough power to meet the needs            alternative to coal. Didcot A became
passes through the boiler twice.         volts. For transmission along the                                                 of some 2 million people, equivalent      the first large power station in the UK
                                         national grid system, the voltage         Coarse ash falls to the bottom
Three of Didcot A’s four boilers have    is increased to 400,000 volts in          of the boilers where it is sluiced      to twice the total population of          to have this facility.
been modified to burn gas as well as     the generator transformer.                out, crushed and carried by high        Oxfordshire.
coal. Special burners have been fitted                                             pressure water to settling pits.                                                  The station is at the forefront of
that reduce the amount of oxides of      07 Condenser
nitrogen in the boiler gases.            The spent steam from the turbine          The ash and dust is sold for use        Didcot A was originally designed as       technological innovation in the way
                                         exhaust goes to the condenser,            in civil engineering projects or for    a coal-fired power station operating      plant is controlled. The main control
04 Turbine                               where it is turned back into water by     the manufacture of building blocks.     at base load, and has subsequently        room has the latest computer-based
The steam passes through the             passing over tubes containing cold        Surplus pulverised fuel ash is
blades of the turbine’s high pressure    water drawn from the River Thames.        pumped to Radley to reclaim             developed a capability to operate         systems, to assist the operations staff
stage, turning the blades and            The condensate is pumped back             disused gravel pits.                    flexibly in response to variable power    to maximise plant performance and to
turbine shaft at 3000 revolutions        to the boiler for re-use.                                                         demands at lower load factors.            minimise costs.
per minute. The turbine shaft is
linked to the generator. The steam
returns to the boiler for reheating,
and then goes back to the turbine’s
intermediate pressure stage and
three low pressure stages.
The power process at Didcot A



                                05        04                  09

As part of the UK’s commitments to CO2 reductions under
the Kyoto Protocol, the government has set an indicative
target of 10% of electricity to be supplied by eligible
renewable sources by 2010. The Renewables Obligation
(RO), which came into effect in April 2002, is a key policy
instrument in the government’s strategy to achieve these
targets. Renewable targets can be met from a variety of
sources, including wind, hydro and biomass generation.

Following successful wood biomass       Co-firing of biomass in an existing
co-firing trials at Didcot A Power      power station provides a much more
Station to determine if there were      immediate source of renewable
any environmental and operations        generation and clearly has a role in
impacts, we received approval from      meeting both the electricity suppliers.
the Environment Agency (EA) for         It can also play an essential role in
commercial operation of wood            providing an initial market for biomass,
(as sawdust) co-firing. Since gaining   supporting both the forestry industry
EA approval we have constructed a       and sustainable agriculture through the
biomass/coal blending facility that     encouragement of energy crops.
could replace up to 2% of the coal
we burn with biomass (Didcot A burnt
3.7mt of coal in 2003).
Didcot B has two electricity                04 Generator                            09 Cooling towers
generating modules. Each module             Inside the generator, the rotor         Warmed river water from the
consists of two gas turbines (which         (an electro-magnet) turns inside the    condenser passes to 31 low-level
are similar in principle to a jet engine)   stator (made up of copper bars) and     cooling towers. The river water
and a steam turbine – each turbine          creates an electric current. Each gas   passes through side radiators,
has an associated generator. The            turbine generator has an output of      cascades through plastic packing,
exhaust gases from the gas turbines         225MW of electricity.                   and is cooled by a stream of cold
pass through special boilers, known                                                 air. The air is drawn in by low-noise
as heat recovery steam generators           05 Heat recovery steam                  fans, which are set in the top of the                            09
(HRSGs), where steam is raised to           generator (HRSG)                        cooling towers.
supply the steam turbines.                  On leaving the turbine, the exhaust
                                            gas (now at around 545°C) passes        The towers are specially designed
01 Filters                                  through the HRSG (which is a dense      to minimise the frequency of visible
The air needed by the gas turbine           matrix of finned tubes), where up to    plumes of water vapour, normally
is drawn in through an intake filter        320 tonnes of high pressure steam       associated with traditional cooling
and then compressed in the turbine          per hour is raised for the steam        towers, and they are plume free for
compressor.                                 turbine. Finally, the waste gas         most of the year.
                                            (now at a temperature of 93°C) is
02 Combustion chamber                       discharged to the atmosphere            10 Generator transformer
The compressed air enters the               through the chimney.                    Electricity from the three generators   05
combustion chamber at over 16                                                       on each module is produced at a
times atmospheric pressure. The air         06 Steam turbine                        voltage of 15,750 volts. This is
is mixed with natural gas and burned        Steam from the HRSG is fed to the       stepped up to 400,000 volts in the
in the combustion chamber.                  steam turbine where it turns the        generator transformer, before the                                                08
The burning air-gas mixture is at a         blades on the turbine shaft.            electricity is passed to the National                                 07
temperature of 1160°C – hot enough                                                  Grid Company’s substation on the             03             01
to melt glass.                              07 Steam turbine generator              Didcot A site for transmission
                                            The turbine shaft turns the             around the country.
03 Gas turbine                              generator rotor to produce 230MW                                                          02
The exhaust gas expands through             of electricity.
the blades of the gas turbine turning                                                                                                      04              10
the blades and turbine shaft at 3,000       08 Condenser
revolutions per minute. The turbine         The spent steam from the turbine
shaft is linked to the compressor and       exhaust goes to the condenser,
the generator.                              where it passes over tubes
                                            containing cold water drawn from
                                            the River Thames. The condensate
                                            is pumped to the feedwater storage
                                            tank and then back to the HRSGs
                                            and used again in a continuous cycle.
Great Crested Newt –
a protected species
carefully moved to a new
home on the Didcot site.

                           Caring for the community
                           and the environment
                           Didcot A and B power stations play     We offer guided tours of the site
                           a major role in the local community.   to interested parties, to foster a
                           Rather than downplay our presence,     greater understanding of the power
                           we aim to work in harmony with our     generation process and our care for
                           neighbours, and we meet regularly      the environment.
                           with representatives from Didcot and
                           surrounding villages to consider the   Didcot A has always been at the
                           views of local people.                 forefront in recognising the importance
                                                                  of environmental care. A Field Study
                           We have valued links with local        Centre and Nature Reserve were
                           authorities and educational            established on an area to the west of
                           establishments. We sponsor a number    the site. This natural habitat for wild
                           of local educational projects and      plants, birds and animals is visited by
                           environmental initiatives. We also     thousands of schoolchildren each year.
                           support a wide range of community
                           groups and charities through our       Conservation work is continuing by
                           charitable giving programme and        the protection of wild orchids that have
                           employee volunteer scheme.             a special place in the ecology of the
                                                                  Didcot site. A colony of the protected
                                                                  Great Crested Newt was relocated from
                                                                  the Didcot B site to the Nature Reserve
                                                                  prior to the construction of Didcot B.
                                                                                     Field study centre at
                                                                                     Sutton Courtenay.

Landscaping included the preservation      While Didcot A is less efficient than
of as many existing trees as possible.     Didcot B, it plays a vital part in
A substantial programme of planting        balancing demand for electricity
has been undertaken on both sites,         throughout the day.
with some 30,000 trees and shrubs
being planted to date at Didcot B.         Great care is taken to limit the
                                           environmental impact of both stations.
The high efficiency of Didcot B power      We endeavour to keep noise and
station, together with the composition     nuisance to a minimum. Extensive
of the natural gas fuel, results in the    monitoring is carried out of site noise
station having minimal environmental       levels, emissions to the atmosphere,
impact.                                    and discharges of cooling water into
                                           the River Thames.
Compared with an equivalent-sized,
coal-fired power station, Didcot B         Both A and B stations operate under
produces virtually no emissions of         licences granted by the Environment
sulphur dioxide, half the carbon dioxide   Agency and operating conditions
and less than a fifth of the amounts       agreed with the local authority. The
of oxides of nitrogen.                     environmental record of both stations
                                           is open to public scrutiny through the
At Didcot A, major improvements have       publication of independently-verified,
been made by the installation of low       annual Environmental Performance
NOx burners, the capability to burn gas    Reviews.
on three of the four generating units,
and a £20 million investment project in    Environmental management systems
dust capture efficiency.                   at Didcot A and B are certified to
                                           international standard ISO 14001.

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