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Kriel Power Station
 
Kriel power station was the first of the new giants.  The station is situated 150 kilometres east of Johannesburg.  Generating 3 000 MW, was the forerunner of the new generation of giant coal-fired power stations developed to generate the increasing supply of electricity demanded by South Africa’s constant growth.  When it was completed in 1979.  Kriel was the largest coal-fired power station in the Southern Hemisphere. Though its primacy has since been surpassed by Eskom’s newer plant, generating 3 600 MW and more, Kriel was instrumental in breaking ground for these stations.  Many of the technological, operational and structural problems encountered in the 3 600 MW giants were first solved at Kriel.

1kriel.jpg
Mr I D van der Walt, Dr Straszacker and Mr Jan H Smith looking at the 
​plan for Kriel power station


       2kriel.jpg
       A general view of the site where Kriel power station was constructed between Ogies and Bethal




 Kriel consists of six 500 MW units, giving it an installed capacity of 3 000 MW. The station was completed in 1979, after almost 10 years of construction.  Kriel was one of the first coal-fired power stations to receive its coal from a fully mechanised coal mine.
 
Coal is transported via overland conveyors belts from Amcoal’sKriel colliery to coal staithes with a capacity of 120 620 tons.  From the staithes, the coal is fed onto underground conveyors which in turn feed incline conveyors that deliver the coal to seven boiler bunkers situated 37 metres above ground level in the boiler house.

Kriel is unique in that each turbine generator set is separate.  In Eskom’s other power stations all the turbines are housed in a single turbine hall and placed along the same axis.  Kriel’s power is fed into the 400 kV network. 
  
The EDR (Electrodialysis Reversal Plant) installed at Kriel is the largest of its kind in the Southern Hemisphere.  In 1983 Kriel started using Vaal River water which contains four times more dissolved salts that the normally used Usutu water.  The existing demineralising water plant could not cope with the high salt concentration, so the Vaal river water had to be retreated before being admitted to the demineralising plant.  It took the contractors only 12 weeks to erect the EDR plant.

Kriel power station was the first of the new giants generating 3 000 MW, was the forerunner of the new generation of giant coal-fired power stations built to generate the increasing supply of electricity demanded by South Africa’s constant growth.  When it was completed in 1979, Kriel was the largest coal-fired power station in the Southern Hemisphere.  Though its primacy has since been surpassed by Eskom’s newer plants, each generating 3 600 MW and more, Kriel was instrumental in breaking ground for these stations. Many of the technological, operational and structural problems encountered in the 3 600 MW giants were first solved at Kriel.  The station is unique in that each turbine-generator set is separate, whereas in Eskom’s other stations all the turbines are housed in a single turbine hall, all placed along the same axis.

Water Management

Kriel is operated as a zero liquid effluent discharge site all water used being kept in a closed circuit on the site to prevent pollution.  Local watercourses are closely monitored to ensure that pollution control measures are effective.

Waste Management

Kriel generates various types of solid waste such as coal ash and domestic waste.  All ash is disposed of in an ash dam.  Annually the dry sides of the dam are covered with topsoil and re-vegetated to create useful land, improve the visual quality and suppress wind-blown dust.  Domestic waste is disposed of on the registered local municipal waste dump.
kriel4.jpg 
 
 
Land and Estate Management

Re-vegetation of the ash dump and rehabilitation of the ash-filled soils resulting from the opencast mining operations restore the agricultural potential of the land.



The Basic Cycle

Coal is transported via overland conveyor belts from Amcoal’s Kriel Colliery to coal staithes with a capacity of 120 620 tons.  From the staithes the coal is fed onto underground conveyors , which in turn feed incline conveyors that deliver the coal to seven boiler bunkers situated 37 metres above ground level in the boiler house.  Variable-speed volumetric feeders convey the coal to the pulverised-fuel mills, where it sis ground to a find powder by hollow-core steel balls running in a circular track.  The pulverised coal is then dried and transported to the boiler burners by a stream of hot air, ignited and blown into the furnace, where it burns at a temperature of about 1 275°C.  The ash fusion temperature is in the region of 1 300ºC.  Fly ash coarse, ash are produced as a result of combustion in a ratio of about 10.1. Electrostatic precipitators separate about 99.6%of the fly ash from the flue gases, which then pass through the chimney into the atmosphere 213m above ground level.  Coarse ash falls to the bottom of the boiler, where it is collected in water-filled hoppers and pumped to the ash dams.  The fly ash in the precipitators is removed by a pneumatic system, dampened with 18% water and carried by a conveyor system to the ash dams. The boiler walls consist of tubing that contains the boiler feed water.  This water absorbs the heat from the coal burning in the furnace.  It is converted into steam inside the tubes themselves, as the Kriel boiler was designed without a steam drum.  The steam is passed though super heaters, where the steam temperature is increased at a very high pressure and then conveyed in pipes to the high pressure (HP) turbine.  As the velocity of the steam increases in the turbine, it caused the turbine rotor to spin. Exhaust steam from the HP turbine is returned to the re-heater section of the boiler, where the steam temperature is again increased, but at a lower pressure.  From the re-heaters the steam is conveyed in pipes to the intermediate-pressure (UP) turbine and from there the exhaust steam is passed to the two low-pressure (LP) turbines.  The spent steam is exhausted into the condenser, where it is condensed under vacuum conditions, and the condensate is pumped via the LP feed heaters to the de-aerator, which serves as a storage tank for the boiler feed water.  The boiler feed pumps pump the condensate back to the economiser section of the boiler via two banks of HP heaters (at a temperature of 240ºC) 240ºC) to repeat the cycle.  The condenser consists of an airtight casing and small diameter tubes through which cold water from the cooling towers is constantly pumped.  The cooling water circulated through the condenser is sprayed into the lower levels of a cooling tower, where evaporation removes the unwanted heat.  The up draught of air in the cooling tower, which facilitates cooling of water, id due entirely to convection. The cooled water is reused for cooling. Coupled with the shift of four in-line cylinders is the generator rotor, a cylindrical electromagnet enclosed in a gastight housing containing the generator stator windings.  Electricity generated by the rotation of the rotor with its electromagnetic field passes from the generator stator windings to a transformer that raises the voltage from 18 kV to the transmission voltage of 400 kV. 

Unit Control

Each of Kriel’s six boiler-turbine sets is run as a separate entity with its own controls and instrumentation incorporated in its own control desks and panels.  There are three control rooms, each serving a pair of sets.  Operators monitor and control the sequence functions associated with start-up, normal operation, shutdown and emergency operation.  The operators are, via the station control room, in permanent contact with the national and regional control centres that make up the integrated generation and transmission system. The control equipment of a boiler-turbine unit consists of an integrated system for analogue, binary and subgroup control, as well as alarm and supervisory functions.  Control facilities ensure safe and efficient operation at all times by a minimum number of skilled operators and plant attendants.  All operations for normal, cold, warm or hot start-up loading and d-loading and normal shutdown of the power plant are conducted from the unit control room in manual, or partially or fully automatic, modes as required for each functional group. The analogue control system provides fully automatic load control of the whole unit and facilities for set point of subgroups as well as manual control of each drive.  Similarly, binary control provides fully automatic run-up of the major plant groups plus a facility for individual drive control.  In the event of the failure of running auxiliaries standby plant is automatically switched on.  If main plant groups fail, the unit automatically runs back to the highest possible safe state.  Data-logging computers continuously monitor the main operating and alarm systems and provide a constant flow of information on video screens and printers.

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Fuel Handling

Kriel Colliery uses both conventional underground mining methods and opencast mining Boilers 1 to 3 are designed to use coal from the underground workings, which is of a higher quality than that from the opencast mine used of boilers 4 to 6.  In practice, due to supply constraints, boilers 1 to 3 use a mixture of under-ground and opencast coals.  A duplicate overland conveyor system is used to transport coal crushed to about 25 mm to the power station.  Coal is fed directly to the power station coal staithes or diverted to the emergency stockpile at rates of up to 1 600 tons per hour.  The storage capacity of the emergency stockpile is 1 700 000 tons.
From the coal staithes the coal is conveyed to seven boiler bunkers with a capacity of eight hours full-load coal supply to each of the mills served by that bunker.  The six boilers are each served by two boiler bunkers with capacities of 9 950 tons.

Volumetric Coal-Feeder

From the boiler bunkers the coal is fed to the mills via coal feeders, which regulate the coal flow by means of a variable-speed control and a profile plate.  The feeder speed is controlled in direct relation to the primary airflow at between 45% and 95%.  This ensures a delivery capacity of between 22.5   and  50,76 tons of coal per hour on units 1 and 3 and of 27.9 to 57,07 tons of coal per hour on units 4 to 6.  Each mill is provided with coal from a separate feeder.

Pulversing Coal Mills

The mills at Kriel are of the medium-speed, vertical, pressure type manufactured by Babcock and Wilcox.  There are two varieties in use.  Units 1 to 3 are fitted with 10,8E mills with a maximum grinding capacity of 47.8 tons/h.  The grinding elements consist of a stationary upper grinding ring fitted with hydraulic tension rams, and 240ºC) to repeat the cycle .a lower rotating grinding ring fitted with hydraulic tension rams, and a lower rotating grinding ring spun at 32,8 r/min by a 3,3 kV GEC electrical motor through a reduction gearbox.  The 11 coal grinding balls run in tracks between the upper and lower grinding rings.  They are hollow spheres made from a special wear-resistant steel and have a diameter of 768 mm. The grinding elements of the 12.0E mills are constructed in the same way.  However, they have only 10 grinding balls with a diameter of 930 mm, a rotation speed of 26.8  r/min and a maximum grinding capacity of 60 t/h.  The pulverised coal is transported from the mill by means of primary air. r/min, and that of units 4 to 6 is 650 kW at 1 485 r/min.
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Primary Air Fans

The primary air (PA) fans are manufactured by Howden and driven by 3.3 kV squirrel-cage induction motors.  The output of units 1 to 3 is 465 kW at 1 486 r/min, and that of units 4 to 6 is 650 kW at 1 485 r/min. The PA fan impeller is of a single-inlet.  It handles hot, dirty air at an inlet air temperature of between 150ºC and 250ºC and a delivery air pressure of between 5 and 10 kPa.  The pulverised coal is heated and transported to the boiler burners by the primary air via pipes at a velocity of 18 m/s. Each boiler is fitted with 36 PF burners arranged in the four rows on the from and rear walls of the furnace, There is a fuel oil burner to each PF burner.  Fuel oil is used at start-up or during unstable furnace conditions to ignite or stabilise the coal flame.  The fuel oil is stored in four storage tanks with a combined capacity of 1 350 tons.

Boilers

The six Steinmüller-Benson (once-through) boilers include circulating pumps in a combined circulation design.  This allows the flow through the evaporator section to be boosted if the boiler load falls below 37%.  Below 37% load the water/steam passes from the evaporating tubes into a separating vessel where the steam and ware are separated.  The water drains naturally off the bottom of the vessel to a collecting vessel where the water level is controlled as in a boiler drum.  The circulating pump recirculates the water by pumping it from the collecting vessel to the economiser inlet line.  At loads above 37%, the boiler feed water flows in a continuous circuit through the boiler where it is converted into steam.  This steam is superheated to 516ºC at a pressure of 17,2 MPa and fed into the HP turbine where the heat energy is converted to mechanical energy.  Exhaust steam is returned to the reheated section of the boiler at a temperature of 298ºC and a pressure of 3,5 Mpa, and reheated to a temperature of 516ºC at 3,2 MPa before being fed to the IP turbine.  Steam exhausting from the LP turbine is condensed and pumped to the boiler as feed water at 240ºC and 21,8 Mpa at a maximum rate of 424 kg/s.   A pair of forced-fraught fans driven by 3,3 kV squirrel-cage induced draught fans driven by 3,3 kV motors draw combustion gases from the furnace over the surfaces of the steam super heaters, re heaters, economiser and iar preheaters, through electrostatic precipitators and into the chimney.  Each boiler has a capacity of 440 kg/s of steam.  The total mass of each boiler’s cold water content in the circulating circuit is 168 300 kg.  The furnace volume is approximately 10 856 m³ and the surface of the heat exchange tubing totals 67 639 m²
 
Turbines

The turbines installed at Kriel were manufactured by Brown-Boveri and are of the reaction impulse blading type.  Each of the six turbine units has a high-pressure single-flow double casing cylinder, an intermediate-pressure double-flow double-casing cylinder and twin low-pressure double-flow single-casing cylinders.  The internal and external casings of the high-pressure and intermediate-pressure cylinders allow for fast start-up and rapid load variation.  Live steam heated to a temperature of 510ºC and a pressure of 16,1 MPa (abs) enters the HP turbine via the emergency stop valves and governor valves.  The heat energy of the steam is released as it passes through 20 rows of fixed and 20 rows of moving blades.  The fixed blades form part of the casing, whereas the moving blades are fitted to the turbine shaft.  The volume of the steam increases with the drop in pressure as it passes through the blades, transferring heat energy to the blades.  Steam exhausts from the HP cylinder at 298ºC and 3,5 MPa (abs).

KRIEL TURBINE SET.jpg
Turbine Set
 
 
The exhaust steam is returned to the re heater part of the boiler, where its temperature is raised to 516ºC at a pressure of about 3,2 MPa (abs).  It enters the IP cylinder via the interceptor and throttle valves at 510º and 3,16 MPa (abs).  Entering at the centre of the IP cylinder, the steam flows outwards and horizontally to the shaft in both directions, through 15 fixed and 15 moving blades.  The IP turbine exhausts steam now enters the two LP double-flow cylinders at a pressure of 431 kPa (abs) and a temperature of 245ºC.  The steam flows through 12 moving and 12 stationary blades on each side of the Alp rotor into the condenser.  Steam exhausts from the LP cylinder at 40ºC and 7,7 kPa (abs).
KRIEL HIGH PRESSURE TURBINE.jpg 
 High pressure turbine
 
Condensers

He LP turbine exhaust steam is condensed in the condenser, which consists of an airtight casing.  This maintains the vacuum conditions created by the reduction of the volume of the steam as it cools down.  Condensation takes place over tube bundles composed of 26 000 admiralty brass tubes with a cooling surface area of 23 520m².  The condensate is then extracted from the condenser by extraction pumps.

Extraction Pumps (multistage)

Only one of the two pumps is in service at any one , with the second acting as backup.  The first stage of pump operation extracts water from the condenser and pumps it via two of the three available 50% condensate polishers.  The water then returns to the second stage of the extraction pump, and from here it is pumped via the condenser level controller to the first of four low-pressure feed water heaters.

Condensate polishing plant

Three 50% Ammonex deep-bed polishers remove soluble impurities by an ion exchange process, also acting as a very efficient high-speed filter to remove insoluble crud.

Feed-heating plant

LP heaters 1,2,3 and 4 are of the tube-shell type.  As the feed water passes through the tubes, it is heated by steam flowing over the outside of the tubes.  The feed water inlet temperature at LP heater 1 is ±40ºC, and the outlet temperature at LP heater 4 is ±150C.

De-aerator

The de-aerator and heater are mounted on top of a storage tank.  It supplies a suction head for boiler feed pumps and removes oxygen from the water when the units are operating in all-volatile water treatment (AVT) mode.  The de-aerator also heats the water from 150ºC to ±176ºC.  The normal mode of unit operation has been changed to combined-oxygen water treatment (XOT) in which case the gas extraction function of the de-aerator is disabled.

Boiler Feed Pumps

Two of the three Sulzer feed pumps are electrically driven 50% duty pumps, and the third is a 100% duty steam turbine driven pump.  The pumps consisting of a booster pump and a multi stage main pump,  are supplied with condensate from the de aerator storage tanks.  The delivery rate of the steam-driven feed pump is controlled by the turbine speed.  At maximum continuous rating (MCR) the steam feed pump delivers water at a rate of 415 kg/s at a pressure of 21,3 MPa.  The electric feed pumps are driven by electric motors with a power output of 10 000 kW and a speed of 1 492 r/min.  The main pump is driven by a step-up gearbox that speeds the main pump up to 6 826 r/min.  Delivery pressure is 26,8 MPa at up to 241 kg/s per pump.  The delivery rate is controlled by means of regulating valves.

High-Pressure Feed Heaters

There are two banks of two heaters each.  The HP heater inlet temperature is ±176ºC and the outlet temperature 240ºC.  The heaters are of the header type.  Form here the water enters the economiser section of the boiler.

Circulating Water System (CW)

Raw water is used to cool the condenser and lubricating oil coolers, etc.  The water is circulated through the system by 12 CW pumps situated in two pump houses between the cooling tower ponds.  The delivery rate of each of these pumps is 5,65 m³/s at a 22,4 m head.  These pumps are driven by electric motors at 328  r/min.

Cooling Towers

Kriel’s four cooling towers are of the natural-draught type and service six turbine sets.  Cooling water supplied to the turbine sets is conditioned to prevent fouling of the cooling plant tubes.  The pH of the water is controlled at 8,4.  Maximum allowable solids are limited to 100 NTU.  The cooling towers ponds each have a capacity of 12 176 m³ of water.  Each cooling tower has a wetted surface packing area of 6 250 m² and an effective cooling volume of 11 375 m³.  The air inlet area of the towers is 2 317 m³.  The temperature drop in the towers is ±15,8ºC.

Water Treatment Plant

Raw water is supplied to Kriel at a rate of 5,91 M/day from the Usutu water scheme.  Raw water is first filtered, and then either treated for domestic use or subjected to further treatment for use as boiler water.  The domestic or potable water is bacteria-free, while the boiler water is demineralised water with a conductivity of 0,0056 Scm.  Raw water flows first through a mixing tank where polyelectrolyte and Superfloc are added, and then through clarifloculators.  It then passes through sand filters, cation and anion units and mixed bed units into the demineralised storage tanks before being supplied to the station.  Demineralised water loss amounts to between 5 000 and 9 000 l/h per unit (boiler/turbine set) under full load conditions.
PS 9407.jpg 
 
 

Generators

Kriel’s six generators have total engineering capacity of 3 000 MW, each being able to generate 500 MW at a lagging power factor of 0,9.  The generating voltage is 18 000 volts.  Each generator sends out 475 MW at a rated output of 550 MVA, the remaining 25 MW being used to run the unit’s auxiliary plant.  The generation voltage is stepped up from 18 kV to 400 kV by generator transformers before it is fed into the national grid.

Special Features
Sulphur Injection Plant

Installed on all units, this plant reduces the amount of fly ash emitted into the atmosphere.

The SO injection helps to extract a range of fly ash particles which would otherwise escape the electrostatic precipitators because of their small size and because the precipitators were designed to handle fly ash from coal with a sulphur content of 1% plus.  At this stage the sulphur content is much lower.  The SO injection raises the sulphur content on the fly ash, thus increasing precipitator efficiency.

Kriel Circuit Diagram

KRIEL CIRCUIT DIAGRAM.JPG 
 kriel list 1.JPG                                            kriel list 2.JPG



TECHNICAL DATA​

Generating capacity

6 x 500 MW – 3000 MW

Fuel

 

Mining company

Amcoal

Calorific value

 

(underground coal)

23.4 MJ/kg (dry basis)

(opencast coal)

18.2-20.4 MJ/kg (dry basis)

Ash content

 

(underground coal)

23.4% (dry basis)

Sulphur content

 

(underground coal)

±1% (dry basis)

(opencast coal)

±1% (dry basis)

Coal consumed at full load

±1 400 tons/h

Total annual consumption

±8-9 million tons

Coal staithe capacity

120 620 tons

Staithe 1

72 000 tons

Staithe 2

48 620 tons

Stockpile capacity

1,7 million tons

Boiler bunker capacity

19 900 tons per unit

Fuel oil

Waxy

Storage capacity

1 350 tons

Annual consumption (total)

±4 000 kl

Mills

 

Manufacturer

Babcock & Wilcox (SA)

Type

Medium-speed, vertical-spindle

Number

6 per unit

Model

10.8E – Unit 1-3

12.0E – 4-6

Rotational speed

10.8E – 32.8 r/min

12.0E – 26.8 r/min

Rated output

10.8E – 47.8 tons/h

12.9E – 60 tons/h

Feeders

 

Manufacturer

Stock Equipment

Number

6 per unit

Minimum coal throughput

22.5 tons/h Units 1-3

27.9 tons/h Units 4-6

Maximum coal throughput

50.76 tons/h Units 1-3

57.07 tons/h Units 4-6

Throughput control

Variable-speed 380V DC motors

Induced-draught Fans

 

Manufacturer

Davidson & Co Ltd

Type

Bab 141A double-inlet impreller

Number

2 per boiler

Volume flow per boiler

(design)

1 030 m³/s /Units 1-3

10162 m³/s/Units 4-6

Mass flow per boiler (design)

 


Generating capacity

6 x 500 MW – 3000 MW

Fuel

 

Mining company

Amcoal

Calorific value

 

(underground coal)

23.4 MJ/kg (dry basis)

(opencast coal)

18.2-20.4 MJ/kg (dry basis)

Ash content

 

(underground coal)

23.4% (dry basis)

Sulphur content

 

(underground coal)

±1% (dry basis)

(opencast coal)

±1% (dry basis)

Coal consumed at full load

±1 400 tons/h

Total annual consumption

±8-9 million tons

Coal staithe capacity

120 620 tons

Staithe 1

72 000 tons

Staithe 2

48 620 tons

Stockpile capacity

1,7 million tons

Boiler bunker capacity

19 900 tons per unit

Fuel oil

Waxy

Storage capacity

1 350 tons

Annual consumption (total)

±4 000 kl

Mills

 

Manufacturer

Babcock & Wilcox (SA)

Type

Medium-speed, vertical-spindle

Number

6 per unit

Model

10.8E – Unit 1-3

12.0E – 4-6

Rotational speed

10.8E – 32.8 r/min

12.0E – 26.8 r/min

Rated output

10.8E – 47.8 tons/h

12.9E – 60 tons/h

Feeders

 

Manufacturer

Stock Equipment

Number

6 per unit

Minimum coal throughput

22.5 tons/h Units 1-3

27.9 tons/h Units 4-6

Maximum coal throughput

50.76 tons/h Units 1-3

57.07 tons/h Units 4-6

Throughput control

Variable-speed 380V DC motors

Induced-draught Fans

 

Manufacturer

Davidson & Co Ltd

Type

Bab 141A double-inlet impreller

Number

2 per boiler

Volume flow per boiler

(design)

1 030 m³/s /Units 1-3

10162 m³/s/Units 4-6

Mass flow per boiler (design)

745 kg/s Units 1-3

778 kg/s Units 4-6

Impeller shaft coupling

Bibby

Motor output

2 360 kW Units 1-3

2 500 kW Units 4-6

Motor speed

596 r/min

Air control method

CS-vane

Chimneys

 

Number

2

Height

213 m

Diameter (base)

23.8 m

Diameter (top) ID

13.8 m

Foundation

93 piles of 1 220 mm diameter

Turbines

 

Manufacturer

Brown Boveri/CEM

Type

Multi-cylinder impulse reaction

Rating (generator output)

550 MVA

Speed

3 000 r/min

Steam flow to HP turbine

415.7 kg/s at MCR

HP exhaust steam flow to RH

381.3 kg/s

Work rate of HP cylinder

33.85% or 146.2 MW

HP cylinder blading efficiency

90.9%

Steam flow to IP turbine

394.6 kg/s at MCR

Work rate of IP cylinder

37.64% or 192.4 MW

IP cylinder blading efficiency

92.2%

Steam flow to LP 1

162.5 kg/s

Steam flow to LP 2

159.8 kg/s

Work rate of LP 1 & 2

28.51% or 174.7 MW

LP cylinder efficiency

86.69%

Total work of turbine train

513.1 MW

Total efficiency

98.15%

Condenser

 

Type

Dual-pressure surface

Cooling principle

Conduction

Type and number of tubes

26 000 admiralty brass

Total tube surface area

23 520 m²

Condenser pressure

7.7 kPa (abs)

Condenser steam pressure

40ºC

Condenser steam flow

280.7 kg/s

Extraction pumps

 

Motor manufacturer

GEC

Type

3.3 kV induction

Power output

1 500 kW

Speed

1 488 r/min

Pump manufacturer

Sulzer

Type

Multistage

First stage

Single impeller

Delivery pressure

650 kPa

Second stage

4 impellers

Delivery pressure

650 kPa

Second stage

4 impellers

Delivery pressure

3 800 kPa

Condensate at 25ºC

 

pH

8.5-9

Dissolved O

90-150

Oil

Not detectable µg/l

CO

Not detectable µg/l

SiO

5 µg/max

Fe

3 µ/l max

Low pressure Feed Heaters

 

Bled steam temperature

No 1, 68ºC

No 2, 86ºC

No 3, 157ºC

No 4, 245ºC

Water inlet temperature

No 1, 40ºC

 

Water outlet temperature

No 1, 66ºC

No 2, 84ºC

No 3, 112ºC

No 4, 141ºC

Steam safety valve

No 3, 686 kPa

No 4, 686 kPa

Water safety valves

No 1- 4, 4 000 kPa

De-aerator

 

Steam pressure

800 kPa

Safety valve

1 100 kPa

Water temperature

176ºC

Feed-water After De-aerator

 

Dissolved O

90-150 µg/1max

Boiler Feed Pumps (electric)

 

Manufacturer

Sulzer

Number

2 per unit

Type

Multistage

Discharge capacity

241 kg/s

Discharge pressure

26.8 MPa (abs)        

Motor power output

10 000 kW

Motor speed

1 492 r/min

Main pump speed

6 826 r/min

Flow rate control

Regulating valve

PA Fans

 

Manufacturer

Howden SA Fan Co

Number

6 per unit

Fabricated from

Boiler quality steel

Assembly       

Welded to impeller shaft

Type

Single inlet type

Coupling

Wellman Bibby

Motor

3.3 kV squirrel cage induction

 

 

Motor output

465 kW Units 1-3

650 kW Units 4-6

Motor speed

1 486 r/min Units 1-3

1 485 r/min Units 4-6

Fan delivery temperature

150-250ºC

Fan delivery pressure

5-10 kPa

Pulverised-Fuel Burners

 

Number

36 per unit

Fuel oil Burners

 

Number

36 per unit

Delivery capacity (each

305 kg/h

 

 

 

 

Boilers

 

Manufacturer

 

Steinmuller (Africa) (Pty) Ltd

Type

6

Number Maximum continuous rating

440 kg/s

Final steam pressure

17.2 MPa

Final steam temperature

516ºC

Re heater steam pressure

3.42 MPa

Re heater steam temperature

 

516ºC

Height (roof to hopper)

71.3 m

Width at burner level

23.5 m

Depth at burner level

14.17 m

Boiler expansion (downwards)

300 mm

Boiler water content cold

168 300 kg

Furnace volume

±10 856 m³

Total heating surface area

67 639 m²

Boiler Circulation Pump

 

Manaufacturer

KSB

Number

1 per boiler

Type

Wet winding motor, glandless pump

Rated capacity

200 kg/s

Power

850 kW

Speed

2 950 r/min

Voltage

3.3 kV

Re Heaters

 

Type

7 245 m², Re heater 1

3 645 m², Re heater 2

Heat absorption

13.64 kJ/m²/s Re heater 1

26.72 kJ/m²/s Re heater 2

Protection

4 safety valves

Total discharge capacity

498 kg/s

Super heaters

 

Number

3 per boiler

Type

Convective

Heating surfaces

4 330 m². Super heater 1

3 545 m² Super heater 2

2 700 m² Super heater 3

Heat absorption

28.3 kJ/m²/s

Protection

4 safety valves

Total discharge capacity

440 kg/s

Economiser

 

Type

Gilled tube

Heating surface

37 994 m²

Heat absorption

4.6 kJ/m²s

Air Pre heaters

 

Type

Davidson regenerative

Number

2 per boiler

Total heating surface

65 840 m²

Rotation speed

±25 r/min

Motor power

18.5 kW

Total heat absorption

1.85 kJ/m²s

Precipitators

 

Manufacturer

Brandt Engineering

Type

Electrostatic, ((with SO pre-treatment)

Number

2 per boiler

Number of passes

4

Number of fields

3 – Units 1-3

4 – Units 4-6

Flue gas dust concentration at inlet

12.27 g/Am³ - Units 1-3

14.28 g/Am³ - Units 4-6

Flue gas dust concentration at outlet

41.54 mg/Am³ - Units  1-3

17.00 mg/Am3 - Units  4-6

Overall collecting efficiency

99.65% - Units 1-3

99.88% - Units 4-6

Forced Draught Fans

 

Manufacturer

Davidson & Co Ltd

Type

Bab 92 A double-inlet impeller

Number

2 per boiler

Volume flow per boiler (design)

714 m³/s – Units 1-3

745 m³/s – Units 4-6

Mass flow per boiler (design)

667 kg/s – Units 1-3

696 kg/s – Units 4-6

Motor speed

745 r/min

Air control method

Vane inlet control system

Boiler  Feed Pumps (turbine driven)

 

Manufacturer

Sulzer

Type

Multistage

Number

1 per unit

Discharge capacity

482 kg/s

Discharge pressure

25.8 MPs (abs)

Turbine speed

4 500 r/min at full load

Main pump speed

Turbine speed

Flow rate control

Turbine speed

High pressure Feed Heaters

 

6A & 6B steam safety valve

2.5 MPa

Water inlet temperature

178ºC

Water outlet temperature

207ºC

Bled steam temperature

±431ºC

Bled steam pressure

±1.8 MPa

7A & 7B steam safety valve

5.0 MPa

Water outlet temperature

240ºC

Steam inlet temperature

297ºC

Steam inlet pressure

3.4 MPa

Water safety pressure for all HP heaters

25 Mpa

Cold-water System

 

Motor manufacturer

Mitsubishi

Type

3.3 kV squirrel-cage screen protected

Rated Power

1 491 kW

Motor poles

18

Pump

Vertical mixed flow, centrifugal, concrete volute

Discharge capacity

5.65 m³s

Speed

328 r/min

Pump power consumption

1 400 kW

Suction branch bore at impeller

1 150 mm

Discharge branch bore at impeller

1 500 mm

Impeller

Stainless steel BS 3100

Cooling Towers

 

Number

4

Type

Concrete construction natural draught

Height

136 m

Diameter at base ring beam

91.38 m

Pond diameter

100 m

Depth of pond

1.8 m

Capacity of tower pond

12 176 m³

Throat diameter

58.3 m

Diameter at the top

63.47 m

Air inlet area

2 317 m²

Number of vertical piles supporting shell

36

Height of vertical piles

1.9 m

Quantity of air at specified barometric passing through tower when cooling 9.32m³ water/s under following conditions:

 

Circulating flow rate

12.3 kg/s

Cooling range

16,719 m³/s 15.8ºC

Re cooled water temperature

24ºC

Atmospheric dry bulb temperature

15.45ºC

Atmospheric wet bulb temperature

11.05ºC

Relative humidity

61.4%

Mean atmospheric pressure

84.7 kPa

Circulating Water

 

pH

8.4

Total alkalinity

120 mg/l (max)

Hardness

400 mg/l

Generators

 

Manufacturer

CEM/BBC

Rated capacity

555 MVA

Terminal voltage

18 kV (50 Hz)

Power factor

0.9 (lagging)

Cooling medium rotor

Hydrogen at 400 kPa

Cooling medium stator

De mineralised water

Total efficiency of generators

98.15%

Water and Effluent

 

Total raw water consumption

150 Ml/day

Cooling water

90 Ml/day

Potable water production

9 Ml/day

De mineralised water production

8.6 Ml/day

Main Contractors

 

Boilers

L&C Steinmuller (Africa) (Pty) Ltd

Precipitators

Brandt Engineering

Turbines

Brown Boveri/CIE, Electro Mecanique (CEM)

Generator transformers

ASEA Electric (SA) Ltd

Cooling towers

Monohan & Frost

Cooling water pumps and boiler feed pumps

Sulzer Bros (SA) Ltd

Chimneys

Monohan & Frost

Cabling and switchgear

Hubert Davies Construction (Pty) Ltd

Instrumentation and control

Siemens AG c/o Siemens Ltd

Process computers

Leeds & Northrup

Low pressure services

Stewarts & Lloyds Ltd

Fire control system

Mather & Platt (SA) (Pty) Ltd

Coal and ash conveyors

Spencer (Melksham) SA (Pty) Ltd

Water treatment plant

D H Harris Ltd

Coal silos and civil works

CMGM Glybeton & Monasiebou

 


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