|<Connah's Quay Power Station is located north of the A548 between Connah's Quay and Flint|
The Central Electricity Generating Board
Central Electricity Generating
Board is responsible for the generation and bulk supply of electricity in
England and Wales. It operates the largest
control anywhere in the world. This system is controlled by a
central headquarters in London and five regions, who are charged with the
operation of the power stations and transmission lines within their areas.
Connah's Quay Power Station is under the control of the North Western
Region which, with its headquarters in Manchester, stretches from
Aberystwyth to Buxton and then to Carlisle.
power generated in the CEGB's power stations is supplied at different
high-duty voltages over the grid or supergrid transmission networks. Power
is then tapped off at distribution points in order to supply local Area
Boards who provide individual supplies to houses, factories and offices.
grid and supergrid lines enable generating plant at power stations to be
pooled so as to give both security of electricity supply and economy of
operation. A Grid Control System ensures that power 15 available to meet
fluctuations in demand as and when they occur. At the same time, the
control system ensures that the most efficient stations meet the bulk of
demand, with the older and less efficient stations used for standby duty.
The costs of supplying the consumer are thus kept as low as is possible.
CEGB also has two specialist construction and design divisions. One is
concerned with new power stations and the other with transmission lines.
Quay power station in Clwyd is on the south shore of the Dee estuary. It
is 15 kilometres from the City of Chester and 6 kilometres from the
ancient town of Flint. It has a staff of about 250.
of the 80 hectare site began on 22 March 1950 and was completed in 1958.
The station and cooling towers are, in the main, supported on precast
concrete piles, 90 centimetres square, of which over 5000 were driven into
station's six boilers and turbo-alternators have a total generating
capacity of 192 000 kilowatts. This capacity is equal to the average
demand for electricity from a city the size of Cardiff. This means that
over 400 000 tonnes of coal are burnt annually in the station and most of
this is North Wales coal from the Flint and Wrexham areas.
main building is 119m long, 72m wide and 40m high. The station's three
cooling towers are
Fuel Ash (PFA) - a by-product from the coal-burning process - has been
used to reclaim 242 hectares of saltings and derelict land close to the
station. The ash is either pumped into lagoons for settlement or passed
through a pneumatic disposal system to provide moisture-controlled PFA for
the construction industry.
The building of a power station on the Dee estuary was originally intended by Chester City Council in order to replace their existing station at Queensferry. Following the establishment of the British Electricity Authority in 1948, the project was reviewed. It was decided that a large-scale station was required to meet the increasing electrical demand in the North Wales area.
Connah's Quay Power Station
|< Aerial view of Connah's Quay Power Station|
comprehensive aerial and ground survey of the district was undertaken.
From the data obtained it
clear that the present site was the most practicable.
area mainly consisted of tidal saltings, which were totally covered at
Spring tides with the exception of a small rock outcrop at the entrance to
Reclamation on a major scale was necessary. It was undertaken by dredging and pumping sand from a suction dredger anchored in an inland lagoon on the opposite side of the river from the station site. From the pumps on this dredger a sand and water mixture was discharged through a pipe at a rate of 34 045 cubic metres an hour. The sand from the mixture settled and the water was drained away through pipes provided. A total of about 812 000 tonnes of sand were pumped in nine weeks. After the deposition of the sand the top soil was relaid. The result was a general site level of 6.7m above Ordnance Datum; the depth of the pumped sand being approximately 2.4m. The whole of the work was completed by 1 August 1950.
|< Site plan of the station|
One of six boilers in operation at Connah's Quay
Quay is a coal-fired station which works in accordance with the principles
outlined in the preceding section How electricity is made. In the
following pages details are given of the various parts of the station.
station is installed with six ICL water tube
complete steam raising unit, including the economiser and air heater, is
supported on structural steelwork. This rests upon the basement level and
is independent from the building structure.
boiler is of tri-drum type, each drum being of hollow forged steel
construction. All boiler and furnace tubes are 82.Smm outside diameter.
The finned tube construction consists of two 25.4mm wide fins welded
diametrically opposite each other.
boiler is provided with two forced and two induced draught fans. These
respectively handle air for combustion and withdraw gases from the boiler
the boiler the flue gases pass to an electrostatic precipitator. This is
arranged in two independent sections so that one half of the plant can be
shut down at a time for maintenance. Each precipitator is equipped with
its own high tension house and rectifying
equipment. From the
precipitator the gases pass to the induced draught fans and are then
discharged to the main flue and chimney.
overleaf shows a cross-section of the power station in order to illustrate
its operating cycle. From the coal store, fuel is carried along a conveyor
system (1) and discharged by means of coal tippers (2)
into the bunker (3). It then falls through
weighers(4) into the coal pulverising mill (5) where it is ground to a
powder as fine as flour. The mill consists of a round metal table on which
large steel rollers or balls are positioned. The table revolves, forcing
the coal under the rollers or balls which crush it.
is drawn from the top of the boiler house (6) by the forced draught fan (7)
and passed through air pre-heaters (8) to the hot air duct
(9) From here some of the air passes directly to the burners and
the remainder is taken to the pulverising mill, where it is mixed with the
powdered coal, blowing it along pipes to the burners (10)
of the furnace (11)
Here it mixes with the rest of the air and
burns with great heat.
boiler consists of a large number of tubes (12) extending almost the full
height of the structure and the heat produced raises the temperature of
the water circulating in them to create steam which passes to the steam
drum (13) at very high pressure. The steam is then heated further in the
superheater (14) and fed through the outlet valve
to the steam turbine (16)
the turbine the steam passes into a condenser (17), to
flue gases leaving the boiler are used to reheat the condensate in the
and pass through the air pre-heaters (8) to
the electro-static precipitator (20). Finally they are drawn by the
induced draught fan (21) into the main flue (22) and to the chimney (23).
electro-static precipitator consists of metal plates which are
electrically charged. Dust and grit in the flue gases are attracted on to
these plates, so
ash is either sold for use in road and building constructions or piped as
a slurry of ash and water to a settling lagoon, where the water drains
off. Once this lagoon has been filled, it can be returned to agricultural
use, or the ash removed for other purposes.
Oil-fired power stations have boilers that are very similar although there is no coal handling or pulverising plant
One of two induced draught fans associated with each precipitator.
|< The turbine hall. Each of the six turbo-generators has a rating of 24,000 kilowatts|
Coal handling plant
turbine plant consists of six 32 000 kilowatt turbo-generators with an
economic rating of 26 000 kilowatts. The turbines are twin-cylinder
machines with a duplex exhaust and are reaction type running at 3000
revolutions per minute. The operating steam conditions are 41.4 bars
pressure and a temperature of 412.8 C at the turbine stop valve.
high pressure rotor has 48 rows of blades and each low pressure rotor has
twelve rows of blades (six rows of moving blades in each section). From
the last stages of the low pressure cylinder the steam is exhausted to a
three-pass-surface type condenser capable of maintaining a vacuum of 971
millibars of mercury when the turbine is operating at its economic
continuous rating; the cooling water inlet temperature being 18 C and the
outlet temperature being 28 C.
three-phase totally-enclosed ventilated type and is connected
directly to the rotor of the turbine through a multiclaw semi-flexing
coupling. It is excited by its own exciter, directly driven from the
alternator shaft. The alternator is cooled by means of a closed-air
system, the air being circulated by two motor-driven fans. These are each
capable of providing the quantity of air necessary when the machine is
operating at 60 per cent of its maximum continuous rating.
10 000 tonnes of coal are consumed at Connah's Quay each week. Sidings
deal with supplies that are delivered by rail wagons and they accommodate
road borne coal also.
are two sidings, each 1000m long for the reception of coal wagons from the
British Rail main lines. The reception sidings feed a system of exchange
sidings which join with two major tracks that lead to the two coal wagon
tippler plants. Each of the wagon tipplers discharges at an average rate
of 254 tonnes per hour when handling 20.3
coal from the hopper is discharged onto a short feeder conveyor which, in
turn, feeds a main belt conveyor designed to deliver coal at the rate of
254 tonnes per hour to the coal junction house; there it can be fed either
to the boiler house bunkers or to the coal storage area.
the junction house coal can be conveyed by means of two belts into the
boiler house. The belts are each capable of handling coal at the rate of
127 tonnes per hour as a continuous normal operation. Each
belts is capable of working independently of the other in case it
should be necessary to close one down for repair.
|One of several pulverised fuel mills which grind the coal to a consistency of face powder.|
the boiler house, coal is discharged into small hoppers, which feed two
shuttle conveyors capable of serving the three hoppers of each boiler
bunker. From the bunker outlets coal is fed through chutes down to the
coal grinding mills of which there are three for each boiler. During the
course of grinding the raw coal is dried by means of hot air which is also
used as primary air to the burners. Each mill is provided with its own
exhauster fan designed to deliver the coal laden alr to each of the
burners via a system of fuel piping.
ash from the pulverised coal fired boilers is in two forms. One form is
the heavy 'bottom ash', or clinker, deposited in an ash hopper, which is
an integral part of the boiler. This ash is then ejected by manual
intervention into a sluiceway and conveyed in a stream of water, via ash
pumps and an overhead launder into a lagoon.
second form of ash is Pulverised Fuel Ash (PFA). This is carried away by
the flue gases and is then removed from the gas stream by means of the
electrostatic precipitators. The two precipitators per boiler have PFA
hoppers into which the ash falls by means of gravity. The ash is then fed,
intermittently, into a pressure vessel situated beneath and connected to
the precipitator hopper. Assisted by a stream of air the PFA is then piped
to one of two ash storage silos. Each silo can hold 100 tonnes of ash.
From the silo the PFA can be discharged in a dry state into road tankers
or, if it is required in a moist condition, then it can be discharged via
a conditioner where a controlled amount of water is added according to the
To condense the exhaust steam from the turbines each turbo-alternator required 88 725 litres of water per minute to pass through its condenser. The minimum flow of the River Dee is insufficient to meet the requirements of six machines, so it is necessary to have a cooling tower system.
Pulverised fuel mill
Ash and PFA handling plant
Circulating water system
|< The coal handling plant. Approximately 10,000 tonnes of coal are burned at the station each week.|
|< The three cooling towers have become a familiar landmark along the Dee estuary|
Make up water pump house
Water treatment plant
is drawn from the cooling tower ponds via twin open rectangular culverts,
which connect to the circulating water pump house. There are six pumps,
each having a capacity of 95 500 litres per minute which discharge to twin
ducts running underneath the whole length of the turbine house. Each
condenser has an inlet connection from each of the ducts and an outlet
connection into each of the two discharge ducts, which return the water to
the cooling towers.
are three reinforced concrete cooling towers each capable of cooling 11.4
million litres of water per hour from 29.0 C to 21.0 C dependent upon the
prevailing weather conditions. They stand upon a common pond which can be
divided to enable operation of one half of any tower.
towers are 76m high, 72m in diameter at the bottom and 34m diameter at the
rim. The cooling tower pond, 2m in depth, holds about 38 million litres of
water. The towers are fitted with spray eliminators and de-icing
equipment. Each tower weighs approximately 4217 tonnes.
of make-up water for the cooling towers and for the ash and dust sluice
water are drawn from the River Dee. A piled dolphin 11m from the bank of
the river carries two 508mm pipes, through which water is drawn to make-up
water pumps in the pump house on the river bank. The make-up water is
drawn at periods of low ebb tides when the salt content of the main
channel is at a minimum. This compensates for losses from the system and
replaces water drawn from the ponds for sluicing purposes and returned to
the river. The pump house contains three vertical pumps each having a
capacity of 18 084 litres per minute.
water to feed the boilers must be of a high degree of purity in order to
prevent corrosion and the formation of scale and other matter. The station
has a complete water treatment plant installed which receives water from
the local authority town main. The treatment is carried out in a mixed bed
|Auxiliary switchgear house|
|Part of the 132,000 volt switchgear compound||
compressors and air receivers are installed,
generators are connected to the 132kV system through 36 MVA 11.8/132kv
generator transformers, which are situated in the 132kV switchgear
compound. The transformers are of the oil immersed type with tan assisted
cooling. Each transformer is fitted with 'on load' tap changing equipment.
main 132kV switchgear is of the bulk oil type and has a breaking capacity
rating of 3500 MVA. There are six generator units, two station transformer
units and eight feeder units as well as busbar coupler and bus-section
switch units. Six feeders, all of the overhead line type, are installed.
station is connected to the 132kV switchgear compound by a cable tunnel.
This conveys all maln and multicore cables running between the station and
the administration block two adjacent rooms house the control panels and
the panels mounting the station protective relays. A laylight and roof
lighting provides normal lighting for the control room. Cold cathode
lighting mounted above the laylight provides illumination during hours of
was assumed at one time that nothing would grow on PF ash, so topsoil,
sometimes as much as 0.90m deep was spread on the surface where ash had
been lald. The cost of such an operation on large areas was enormous.
CEGB initiated research at both Birmingham and Leeds Universities to study
every aspect of the >>
Control and relay rooms
Pulverised fuel ash
< Operation of the station can be continuously monitored from the control room
|< Harvesting wheat on PFA at Connah's Quay Power Station|
growth of plants in ash. This
research, together with practical field trials, showed that ash, without
any soil covering whatever, can support the growth of certain crops. For
satisfactory results the ash is lagooned, since it has been found that
weathering improves it still further. When feasible, the incorporation
with the ash surface of as little as 76mm of soil, subsoil or shale is
beneficial. The lack of plant nutrients is serious though and has to be
made good by the application of fertilizer.
of 242 hectares of salt marsh land at Connah's Quay began in 1954, soon
after the station was commissioned. The cultivation of reclaimed land
started during 1956. The area reclaimed continued to increase as did the
equivalent area under cultivation.
cultivation experiments were carried out by members of Birmingham
University, working in conjunction with the CEGB. The area involved
amounts to approximately 65 hectares and something in excess of 500 000
tonnes of PFA Were used. No topsoil has been used; the PFA surface has had
essential fertilizers and trace elements added according to the crop being
crops that have been sown include cereals such as wheat, oats and barley;
various root crops like potatoes, beetroot and carrots and a selection of
various grasses, (some
producing characteristics), cabbages and cauliflowers. The results
obtained could be described as varying from good to excellent.
of the reclaimed areas is now restricted to grass. Consideration is being
given to a long term experiment concerning the rearing of cattle,
sustained solely on the grazing and produce from the
The experiment would continue into the third and fourth generation
|Potatoes and mangelwurzels grown on PFA on reclaimed salt marshes adjacent to the station|
|Produced by Reprographic Services CEGB (North Western Region) 825 Wilmslow Road, Manchester M20 8RU|