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Hendrina Power Station

Hendrina power station is located approximately 40km south of Middelburg at the town of Hendrina in Mpumalanga.  At the time it was built it was the largest station to be designed by ESCOM (Electricity Supply Commission), with an ultimate generating capacity of 2 000MW, consisting of ten 200 MW machines.  In November 1965 the first four machines were placed on order for commissioning in 1970, to supply the bulk of the increase in generation capacity required at that stage.

The first unit went into operation in 1970 and the last in 1976.  The station’s power is fed into the 400 kV network.

 

 PS hendr 43831.jpg
Aerial view of Hendrina Power Station

 In the same year, 1965, a contract to supply the coal requirements of the power station was awarded to Trans-Natal Coal Corporation Ltd.  This led to the establishment of Optimum as an underground mine.  Optimum Colliery is situated on the Witbank coalfield, which is the main coal-producing area of South Africa.  Because of the shallowness of the coal seams in some areas, provision was made in the late 1960s to sue opencast mining methods, together with underground operations. The mine is currently producing approximately 12 million tons of raw coal per annum, using draglines.  Optimum Colliery will continue to supply Hendrina power station for its full life expectancy of 50 years.

Between 1995 and 1997, five of Hendrina’s ten units were refurbished.  They now boast some of the most advanced system control technology in the world. The station’s 5-in-1 control room was the first in the Southern Hemisphere. From 2001 to 2005 the remainder of Hendrina’s ten units was refurbished, however not to the same extent as the previous units’ refurbishments.  Hendrina received a gold award from the National Productivity Institute.

 Basic Cycle

Fuel and combustion

Coal is obtained for the Optimum Colliery and transported by a duplicate overland conveyor system, with a route length of 2 290m, to four coal staiths and an emergency stockpile.  In addition, emergency facilities are provided to accept coal delivered by rail.   From the staithes the coal is fed into boiler bunkers, of which there are six per boiler, each providing a storage capacity of 24 hour’s operation at full load.  From the bunker a variable coal feeder feeds the coal into a vertical spindle mill, of which there are two types: the ball-and-ring type found in Units 1 to 7 and the roller type in Units 8 to 10.  Here the coal is ground into a very fine powder.  Forced-draught fans draw warm air from the top of the boiler house and the air is preheated by means of air heaters.  The heated air divides into secondary air and a remaining portion, which is boosted by the primary air fan to become primary air.  The primary air transports the pulverised coal from the mill to the pulverised-fuel burners.  Secondary air is then added to the burners to aid  the combustion process in the furnace. On initial lighting up of the boiler, burners supplied with fuel oil are inserted into the boiler and electrically ignited.  Once the unit load reaches 80MW, the first mill supplying pulverised coal is placed on load. The second and third mills are then progressively placed on load, and once the furnace protection as armed the oil burners are retracted.

Hend23.jpg
Exterior view of Hendrina Power Station

The boilers have a burn rate of about 105 tons per hour; producing coarse ash and fly ash at a ratio of 1:6.  The coarse ash falls to the bottom of the boiler, where it is cooled by quenching spray nozzles and collected in water-filled hoppers.  Then it is pumped to the ash disposal dams.

The fly ash is carried in the flue gases to the precipitators or fabric filter plant where 99.5% to 99.8% of it is removed and collected I the dust hoppers.  The fly ash is ten extracted from the hoppers by hydro vac units, which in effect water ejectors are creating an ash-water mixture.  This is discharged into the ash pit via sluice ways.  Ash pumps then pump the ash-water mixture to the ash disposal dams.  Before the flue gases enter the precipitators, on Units 2 and 4, SO³ is injected into them to decrease the resistivity of the ash, thereby enhancing the efficiency of the electrostatic precipitators or fabric filer plants, to be discharged into the atmosphere via the two 155 m high smokestacks.

HENDRINA333.jpg

HENDRINA222.jpg

Steam circuit

 Heat produced by the burning coal is absorbed by the demineralized water contained in the boiler furnace wall tubing.  From the boiler drum, which separates the water and steam, additional heat via the various super heaters produces superheated steam at a final steam temperature of 543ºC and 11,0 MPa (gauge).  The super- heated steam gives each boiler a maximum continuous rating at the turbine stop valve of 214 kg/s.

 The superheated steam leaves the final super heater and is fed into the high-pressure turbine where it expands, releasing part of it energy and rotating the turbine at 300 r/min (5) Hz).  After exhausting from the high-pressure turbine, the steam, now at 125ºC and 0.2 MPa, is fed into the low-pressure turbine at a rate of 150 kg/s.  Coupled to the shaft of the two in-line turbines is a generator, where the turbine’s energy is converted into electrical energy at a rated 220 MVA.  The generator’s output voltage of 16.5 kV is stepped up by the generator transformer to a transmission voltage of 400 kV.  This is then distributed to the national grid.

 Cooling and recirculation

 Exhaust steam from the low-pressure turbine is condensed in a two-pass surface condenser with a vertically divided water box, containing 16 440 tubes each having a diameter of 23 mm, through which cooling water passes.  The condensate is collected I the hot well below the condenser and withdrawn y extraction pumps.  From here it is pumped back to the oiler through a feed-heating system and de-aerator.

 Fuel Handling

 Coal is obtained from the opencast Optimum Colliery and delivered directly by a duplicate overland conveyor system to four coal staithes behind the station (east side) or, alternatively, to an emergency stockpile.  The crushed coal, smaller than 50 mm, is transported to the plant at a rate of 480 000 tons a month.  The four staithes have capacities of 25 000 tons each, while the capacity of the emergency stockpile is about 100 000 tons.  Two systems of incline conveyors, north and south, deliver the coal reclaimed from their respective staithes to the boiler bunkers, of which there are six per boiler.  Each bunker has a capacity of 478 tons, giving sufficient storage capacity at the boilers for 24 hours operation at full load.

 Mill Feeders

 From the boiler bunkers the coal is fed to the corresponding mills via coal feeders.  On Units 1 to 5 the Mitchell feeders regulate the coal flow by means of a variable-speed rotary table and a fixed plough.  On Units 6 to 10 the newly installed SPIRAC feeders employ a variable-speed shaft-less screw system for coal flow control.  The feeders are controlled in direct proportion to the primary airflow.  The two induced-draught fans, driven by 6.6 kV motors, draw combustion gases from the furnace over the surfaces of the steam super-heaters, economiser and air preheaters through electrostatic precipitators or fabric filter bags and into the smokestack.  The induced-draught fan motors have an output rating of 1 585 kW, 1 129kW and 1 750 kW at 746 r/min for Units 1 and 6 to 10. Units 2 and 4, and Units 3 and 5, giving a design capacity for the fans of about 222 kg/s each.  The precipitators or fabric filter bags collect between 99.5% and 99.8% of the dust or fly ash from the flue gases.

 Turbines

 There are 10 Kraftwerk Union (KWU/AEG) impulse-type high pressure and reaction-type low-pressure, double-casing condensing turbines, with and economical continuous rating of 200 MW.  Each turbine consists of a high-pressure (HP) and a low-pressure (LP) cylinder.  The HP cylinder has an inner and outer casing.  A double-casing arrangement is employed to allow a more rapid war-up rate and reduce the probability of high differential temperatures bring experienced.  The LP section consists of an inner and an outer casing of welded construction.

 The LP end walls are of a double-shell construction, which provides high rigidity and low weight.  The steam is exhausted into the main condenser below the LP cylinders.  Live steam heated to a of 540ºC and a pressure of 10.5 MPa is admitted into the HP section of the turbine through two hydraulically operated emergency stop valves and four governor valves.  The steam from governor valves 1 and 3 flows from above into the fully admitting nozzle segments arranged in the inner casing while the steam from governor valve 4 flows directly into stage 1 from below without the interposition of nozzles.  The steam is expanded into the seven following stages and after redirection into a further none fully admitting impulse stages.  Heat energy from the steam is released as the steam passes through the HP turbine and flows into the LP double-flow cylinder at a temperature of 125ºC and a pressure of 0.29 MPa.  The steam flows through moving and stationary blades on each side of the LP rotor into the condenser.  Steam is exhausted from the LP cylinder at 36.6ºC and 7.0 kPa.

             henhen.jpg

 Condensers

 The plant is equipped with two-ass regenerative type surface condensers, one per turbine.  Air entering the condenser as well as that entrained in the exhaust steam is removed by steam air ejectors as an air vapour mixture and released to the atmosphere, maintaining the vacuum conditions created by the reduction of the volume of the steam as the steam cools down.  Condensation takes place over tube bundles composed of 16 440 tubes with a cooling surface area of 11 700m².  The condensate is then extracted from the condenser by extraction pumps.

 Extraction pumps

 Each unit has two centrifugal three-stage condensate extraction pumps.  The purpose of the extraction pumps is to extract the condensed steam from the condenser hot-well.  The pumps are rated at 100% duty and therefore only one pump is operational under normal operating conditions.  The pumps are designed to operate with a suction head ranging from atmospheric pressure to near perfect vacuum conditions.  To overcome the resistance of the KP condensate train and the head of pipework to the d-aerator as well as the de-aerator pressure, the pump has a discharge pressure of 1.25 MPa.

 Feed-heating plant

 The two LP heaters are of the tube-shell type.  The condensate passes through a U-shaped tube nest while bled steam from the low-pressure turbine extractions passes through the heater’s shell.  The condensate entering LP heater no 1 has an inlet temperature of about 41.8º and its outlet temperature at LP heater o 2 is about 80.8º.

 De-aerator

 There are two de-aerators per unit, mounted adjacent to the storage tank.  The de-aerator supplies a suction head for the boiler feed pumps and removes oxygen and condensable gases from the feed-water.  This is achieved by breaking the feed-water into find droplets and subjecting it to bled steam, which boils the water to release entrained gases.  De-aeration increases the feed-water temperature 127ºC.

henfan.jpg

 Boiler feed pumps

 Each unit has three feed pumps, of which two are 50% electrically driven duty pumps and the third a 100% steam-turbine driven duty pump.  The 100% duty feed pump, manufactured by Sulzer, is a multistage centrifugal type supplied with feed-water from a booster pump driven via a gearbox from the main pump shaft.  The booster pump is supplied with feed-water from the de-aerator.  The delivery rate is controlled by the three-element control of the boiler, namely the team flow, the feed flow and the drum level controller.  The steam feed pump delivers water at a rate of 227 kg/s and a pressure of about 14.0 MPa at maximum continuous rating.  The turbine speed is variable between 4 220 r/min and 5 200 r/min depending on a unit output of between 100 MW and 200 MW.  The electric feed pumps, manufactured by KSB Pumps, are multistage centrifugal pumps driven by electric motor with a rated power output of 2 355 kW and a speed of 2 985 r/min.  The delivery pressure per pump is about 14.5 MPa with a rated capacity of 113.6 kg/s.

 High pressure feed heaters

 There are two parallel banks of HP heaters with three heaters in each bank.  The heaters are of the tube-shell conductive type.  The feed-water enters the U-shaped tube nest and is heated by bled steam entering the heater’s shell.  The inlet temperature of the feed-water entering the HP heater bank is 128ºC and the outlet temperature 221ºC.  From here the water enters the economiser section of the boiler.

 Circulating water system (CW)

 Hendrina power station is equipped with two separate cooling water plants, one located at each end of the station.  Each plant consists of a pump house equipped with six CW pumps and cooling towers (four North and three South).  Each pump feeds its own unit condenser directly, or the pumps can be interconnected to feed to feed the condensers in a common mode.  Units 5 and 6 can be cooled by either the north or the south CW plant.  Included in the CW system are tap-offs for auxiliary cooling, such a lubricating oil coolers and seal oil coolers.  The delivery rate of each of these pumps is 6.6³/s with a delivery head of 19.5 m.  The pumps are driven by 6.6 kV induction motors with a rated power output of 1 570 kW.

 Cooling Towers

 Hendrina’s seven cooling towers are of the natural-draught wet-cooling type.  The four north cooling towers serviced Units 1 to 5 while the three south towers service Units 6 to 10.  At each unit approximately 100 litres of CW evaporates per second at full load.  This loss is replaced by raw water supplied from the terminal reservoirs.  Each of the cooling tower ponds has a capacity of 8 172 000 litres.  The tower has an overall height of 116 m, with a base diameter of 80 m.  The temperature drop in the towers is about 11ºC.

 Water treatment plant

 Raw water is supplied to Hendrina power station at a rate of about 70 Ml per day.  The water is received from either the Komati or the Isutu water scheme, with the use of three pumping stations at Vygeboom, Bosloop and Nooitgedacht supplying the water via Arnot power station.  Hendrina power station can also be fed from the Vaal River.  Depending on the number of generator in serviced, about 62 ML is used for cooling water make-up ad about 8 ML is fed to the water purification plant.  Raw water is first treated for domestic use and then subjected to further treatment for use as boiler feed- water.  Domestic or potable water is water that has been chemically treated (clarified and bactericide-eliminated), with pH value of between 8.2 and 8.5 in line with SABS Standard 241-1984.

 Boiler feed-water is demineralised treated water with a conductivity of ˂0.10µS/cm.  The demineralisation plant is fed from the water purification plant’s sand filters.  The water passes through exchange units, degassing towers, anion exchange units and mixed-bed exchange units, thereby producing demineralised water that is fed into the two demin storage tanks.  The amount of potable water and demineralised was produced per day is, on average 2.8 MI and 3 MI respectively, depending on demand.

 Generators

 Each generator is rated at 222 MVA and able to generate 200 MW at 0.9 lagging power factor or 222 MW at unity power factor.  However, due to limited turbine output power the output of the generator is limited to 200 MEE.  The sent-out power is 190 MW because the remaining 10 W is being used to run the unit auxiliary plant.  The generated voltage is 16.5 kV which is stepped up to 420 kV by the generator transformer before it is fed into the national grid.  The output voltage may vary depending on demand by the system.  The generated voltage is also stepped down from 16.5 kV to 6.6 kV by means of the unit transformer, which supplies all the unit auxiliary plant.

 At the turbine end the rotor is coupled to the turbine, while the slip-rings and brush-gear are arranged at the exciter end.  The generator is filled with hydrogen at a pressure of 310 kPa.  The shaft is sealed at both ends by means of seal collars and an axial shaft seal arrangement.  Fans mounted at each end of the rotor circulate the hydrogen within the generator.

 Generator cooling is achieved by means of hydrogen gas and de-mineralised water.  Hydrogen gas is used to cool the stator and rotor while de-mineralised water is used to cool the stator windings, phase connections and main bushings.  The hydrogen is cooled by surface-type water coolers and the demineralised water is cooled by the primary water coolers.

 The rotor field current is supplied from the exciter set through the slip-ring brush-hear.  The rotor is coupled to the exciter through a speed-reduction gearbox that drives the exciter at a speed of 1 000 r/min.  The exciter is rated at 850 kW, 280V and 3 050 A.  The normal excitation current at full load and unity power factor is about 2 000A.

 Between 1994 and 2002 the original Automatic Voltage Regulator (AVR) and pilot exciter system was replaced with microprocessor-based AVR make, type Unitrol D, which has an automatic and manual channel.  The operator is able to rate or lower the generator voltage set point, and the AVR will automatically control the output voltage.

 Previously the generator protection relays were of the electro-mechanical type.  These were replaced between 1994 and 2002 with modern numerical-type relays that protect the generator, generator transformer and unit transformer.

Hend21.jpg

 Sulphur injection plant

 

 The sulphur injection plant was installed to reduce the amount of fly ash emitted into the atmosphere.  The purpose of the sulphur injection plant is to decrease the resistivity of the ash, thereby enhancing the efficiency of the electrostatic precipitators, as the precipitators were originally designed to handle fly ash from coal with sulphur content greater than 1.2%.  The sulphur plant on the south side has been decommissioned due to the retrofitting of the electrostatic precipitators with fabric filter plants, and at present the sulphur plant on the north side only serves boilers 2 and 4.  The fabric filter plants were installed to comply with the increasingly stringent permissible dust emission rates imposed at the Chief Air Pollution Control Officer.

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 Technical Data 

Generating capacity 1 985 MW​
Fuel
​Mining company ​Ingwe
​Calorific value ​±24.0 MJ/kg (dry basis)
​Ash Content ​±25.5% (dry basis)
​Sulphur content ​±0.9% (dry basis)
​Coal consumed at full load ​± 1 000 tons per hour
​Total annual consumption ​±6 500 000 tons
​Coal staithe capacity 100 000 tons (four staithes with 25 00 tons capacity each)
​Stockpile capacity ​100 000 tons
​Boiler bunker capacity ​2 868 tons per unit (six bunkers per unit with 478 tons capacity each)
​Fuel oil type ​FO6
​Consumption per boiler
Boilers 1-5 Cold Start

Boilers 6-10 Cold Start

21 tonnes Hot start 5 tonnes

47.4 tonnes Hot start 18 tonne

Mills
​Manufacturer
​Type
​Units 1-7 ​Babcock & Wilcox 8.SE
​Units 8-10 ​PHI MPS 140
​Number ​6 per unit
​Rotational speed
​Babcock & Wilcox 8.SE ​40.0 r/min
​MPS 140: ​40.7 r/min
​Rated output
​Babcock & Wilcox 8.SE ​24 tons per hour
​MPS 140: ​21.3 tons per hour
​Mill motors:
​Manufacturer ​FEC
​Output ​216 kW
​Speed ​980 r/min​
Mill Feeders: Units 1-5
​Make and type ​Mitchell MEB No 60
​Number ​6 per unit
​Minimum coal throughput ​10 tons per hour
​Maximum coal throughput ​30 tons per hour
​Throughput control ​Variable-speed rotary table with fixed plough
Mill Feeders: Units 6-10
​Make and type ​Spirotech 420 – Variable shaftless screw
​Number ​6 per unit
​Minimum coal throughput ​10 tons per hour
​Maximum coal throughput ​30 tons per hour
Induced-draught Fan Motors
​Manufacturer
​Units 1,3 and 5-10 ​Alsthom
​Units 2 and 4 ​AEI
​Motor output
​Units 1 and 6-10 ​1 585 kW at 746 r/min
​Units 2 and 4 ​1 129 kW at 744 r/min
​Units 3 and 5 ​1 750 kW at 746 r/min
Smokestack
​Number ​2
​Height ​155 m
​Diameter (base) ​20.8 m
​Diameter (top) ​11.7 m
​Foundation ​69 piles at a depth of 19.1 m
Turbines
​Manufacturer ​Kraftwerk Union (KWU/AEG)
​Type​ ​Multi cylinder impulse reaction
​Rating (generator output) ​222.2 MVA at unity power factor
​Speed ​3 000 r/min
​Steam flow to HP cylinder (at 200 MW) ​202 kg/s
​Steam flow to LP cylinder ​154 kg/s
​Steam flow at no load ​5.6 k/s
​Working pressure before ESV’s ​10.5 MPa
​Working temperature before ESV’s ​538ºC
​Pressure on LP cylinder ​290.3 kPa
​Temperature to LP cylinder ​132.5º
​Heat used per kg of steam ​2 506.3 kj/kWh
​Heat consumption ​8 884.6 kj/kWh
​Cycle efficiency ​32%​
Condenser
​Type ​Two-pass re-generative type surface condenser
​Cooling principle ​Conduction
​Number of tubes ​16 440
​Tube material ​50 MS 71 Fj8 and stainless steel in the flash box area
​Total tube surface area ​11 700 m²
​Condenser  pressure (design) ​7.12 kPa
​Condenser steam pressure ​36ºC
​Condenser steam flow (design) ​142.2 kg/s
​Extraction pumps
​Motor manufacturer ​AEG
​Supply ​6.6 kV/3-phase/50 Hz
​Power ​400 kW
​Pump manufacturer ​AEG
​Type ​Centrifugal, 3 stage 100% duty
​Number per condenser ​2
​Delivery flow ​664 m³/h
​Delivery head ​125m WG
 




 

Condensate at 25ºC

 

 

PH

9.1 to 9.3

 

Dissolved O

˂0.0020 ppm

 

SiO

˂0.010 ppm

 

Fe

˂0.010 ppm

 

Oil

nil

 

K(HI)

˂0.20µS/cm

 

Low pressure Feed Heaters

 

 

Bled steam temperature to LP heater

 

 

No 1

63.2ºC

 

No 2

83.8ºC

 

Condensate inlet temperature

 

 

No 1

41.8ºC

 

Condensate outlet temperature

 

 

No 1

60.2ºC

 

No 2

81.0ºC

 

De-aerator

 

 

Bled-steam temperature

130ºC

 

Bled-steam pressure

300 kPa

 

Condensate outlet temperature

127ºC

 

Feed water after de-aerator dissolved O

0.01 m³/l

 

Boiler Feed Pumps (electric)

 

 

Manufacturer

KSB Pumps

 

Number

2 per unit 50% duty pumps

 

Type

Multistage (6) centrifugal

 

Discharge capacity

101.0 kg/s

 

Discharge pressure

±14.5 MPa

 

Suction pressure

400 kPa

 

Pump speed

 2 985 r/min

 

Flow-rate control

Regulating valve/leak-off valve

 

Feed pump motor

 

 

Manufacturer:

 

 

Unit 1

Mitsubishi

 

Units 2-10

ASI and GEC

 

Motor power output

2 355 kW

 

Units 1-10

 

 

Motor speed

2 985 r/min

 

Boiler feed pumps (turbine driven)

 

 

Pump manufacturer​

Sulzer

Number

1 per unit

Type

Multistage

Discharge capacity (maximum)

227.0 kg/s

Discharge pressure

±14.0 MPa

Suction head required

61.3 m

Turbine manufacturer

AEG Kanis

Steam pressure before ESV

±2.24 MPa

Steam temperature before ESV

340ºC

Exhaust pressure

±250 kPa

Turbine speed

4 750 – 5 200 r/min

Main pump speed

Turbine speed

Flow rate control

Turbine speed / feed water control valves

High-pressure feed heaters

 

Number

6 sets of 3 running parallel

Bled steam temperature

 

No 1A – 1B

213ºC

No 2A – 2B

276ºC

No 3A – 3B

336ºC

Bled Steam pressure

 

No 1A -1B

760 Pa

No 2A -2B

1.4 MPa

No 3A -3B

2.4 MPa

Water inlet temperature

 

No 1A -1B

168.6ºC

No 2A -2B

194ºC

No 3A-3B

221ºC

Primary-air fans

 

Manufacturer

Howden SA Fan Co

Number

6 per unit

Type

Single inlet, centrifugal

Flow control

 

Units 1-4

Fluid drive

Units 6-10

Horizontal multi-blade damper

Motor

6.6 kV induction

Motor rated output

 

Units 1-5

272 kW

Units 6 and 7

350 kW

Units 8-10

153 kW

Motor speed

 

Units 1 and 8-10

1 485 r/min

Units 2-5

1 480 r/min

Units 6 and 7

1 475 r/min

Fan delivery temperature

240ºC

Fan delivery pressure

 

Units 1-5

9.03 kPa

Units 6-10

6.55 kPa

Capacity

 

Units 1-5

95 m³/s

Units 6-10

76 m³/s

Pulverised fuel burners

 

Number

24 per unit

Fuel oil burners

 

Number

24 per unit

Delivery capacity EACH

 

Boiler 1-5

B &W

Unit 1Stack

 

Units 2-5

El-Paso

Unit 1-5 / tower number

5

Max continuous rating

200 kg/s

Final steam pressure

11.0 MPa

Final steam temperature

540ºC

Height (roof to hopper)

49.5 m

Width at burner level

15.95 m

Depth at burner level

11.07 m

Furnace volume

4 004 995 m³

Unit 6-10 / tower number

5

Max continuous rating

214.2 kg/s

Final steam pressure

11.0 MPa

Final steam temperature

543ºC

Height (roof to hopper)

56 m

Width at burner level

14.77 m

Depth at burner level

14.75 m

Furnace volume

4 100 m³

Air preheaters – Units 1-5

 

Manufacturer

Davidson

Type

Regenerative – 2 per boiler

Total heating surface

10 346 m³

Rotational speed

±1.7 r/min

Motor power

5.6 kW

Air preheaters – Units 6-10

 

Manufacturer

Howden

Type

Regenerative – 2 per boiler

Total heating surface

10 580 m³

Rotational speed

±0.79 r/min

Motor power

11 kW

Precipitators

 

Manufacturer

 

Unit 2

Lurgi

Unit 4

Brandt

Type

Electrostatic

Construction

Concrete with concrete hopper

Number per boiler

2

Number of fields

3

Overall collecting efficiency

98%

Fabric filter plant – Units 1,3 &5 & 6-10

 

Type

Pulse jet fabric filer

Casings

2 per unit

Cells

2 per casing

Pulsing

Random pulse by means of rotating manifold

Bag type

Polyacrylonitrile

Bag length

8 m

Quantity of bags

 

Unit 1,3 & 5

8 120

Units 6-10

7 884

Temperature control

Attemperation

Pulse air supply

Roots-type blowers

Overall collecting efficiency

99%

Forced draught fans

 

Manufacturer

Howden

Type

Double inlet centrifugal

Number

2 per boiler

Volume flow per boiler

 

Units 1-5

257 m³/s

Units 6-10

247.7 m³/s 

Mass flow per boiler

 

Units 1-5

244 kg/s

Units 6-10

247.6 kg/s

Motor output rotary

 

Units 1-5

637 kW

Units 6-10

1 057 kW

Motor speed

990 r/min

Fan control

Radial van control

Cooling water system

 

Motor manufacturer

 

North side

Bruce Peebles

South side

GEC

Type

Vertical 6.6 kV squirrel-cage induction

Pump manufacturer

 

North side

Allen Gwynnes

South side

Sulzer

Discharge capacity

6.6 m³/s

Speed

247.5 r/min

Delivery head

19.5 m

Cooling towers

 

Number

7

Type

Hyperbolic concrete packed with multi-deck plastic

North side

3 CR 12x-grit

South side

Natural-draught wet cooling

Height

116 m

Diameter at base of shell

80 m

Diameter at throat

51.3 m

Diameter at top

57 m

Capacity (each)

11 m³/s, max 14 m³/s

Temperature drop

±11ºC

Generator – Units 1-10

 

Manufacturer

Kraftwerk Union Siemens

Rated capacity

222.2 MVA

Terminal voltage

16.5 kV

Current

7 780 A

Power factor

0.9 (lagging)

Speed

3 000 r/min (50 Hz)

Cooling medium

 

Stator

Demin water and hydroen

Rotor

Hydrogen at 310 kPa

Generator transformers

 

Manufacturer

 

Unit 1

Industrie Elettriche di Legnano

Unit 2

Oerlikonn

Units 4,6,8,10

Alsthom

Units 3,5,7,9

Brrruce Peebles

Rated Capacity

220 MVA

Rated voltage

 

LV

16.5 kV

HV

420 kV

Unit transformers

Stepdown from 16.5 kV to 6.6 kV

Rating

20 MVA

Manufacturer

 

Units 1 and  6-10

ASEA

Units 2-5

ASGEN

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