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.

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.

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.

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

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).

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).

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.

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

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
Through put 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 – 32.8r/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 O₂	90-150
Oil	Not detectable µg/l
CO₂	Not detectable µg/l
SiO₂	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 O₂	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 SO₂ 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