Advances in Dry Cooling Deployed at South African Power...

Steve LennonDivisional ExecutiveEskom

2011 Summer SeminarAugust 1, 2011

Advances in Dry Cooling Deployed at South African Power Stations

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Eskom’s Move to Dry-Cooling

• Eskom historically utilized wet-cooled power stations

• In 1966 it was decided to extend Grootvlei Power Station –3 factors had to be considered:

– Growing demand for electrical power

– Opportunity to exploit coal fields

– Obligation to optimize the utilization of water

• Eskom strategy:

– Add generation capacity without increase in water consumption

– Gain experience in dry-cooling

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Eskom’s Pioneer: Grootvlei PS

• Grootvlei Unit 5 and 6 added – dry-cooled

• Unit 5: Indirect system with spray condenser and dry cooling tower

• Unit 6: Indirect system with surface condenser and dry cooling tower

Largest dry-cooling units in the world at the time

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Matimba Power Station (6 x 665 MW)

• Design: Known turbine characteristics, energy output was maximized over given ambient temperature range

• Average back pressure: 18.6 kPa

• LP turbine protection: 65 kPa

• Average steam velocity 80 m/s at 18.6 kPa

• Station orientated with prevailing wind direction towards boiler

• 2 x 5 m exhaust ducts

• ACC details per unit

– 48 fans, 10 m diameter

– 8 streets with 6 fans per street

– Street length 70.8 m

– 12 MW auxiliary power consumption

• Total platform footprint 35 700 m2

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Matimba Power Station Finned-Tubes

• Oval tube and rectangular fin design

• 2.5 and 4mm fin pitch in 2-row staggered bundles

• Carbon steel tubes with carbon steel punched fins, then hot dip galvanized

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Kendal Power Station (6 x 686 MW)

• Surface condenser with SS tubes

• Circulating water flow: 16.8 m3/s

• Galvanised heat exchanger tubes

– 11 sectors which can be individually isolated

– Total of 1 980 km of finned tube/tower

– Horizontal, radial arrangement

• Tower dimensions

– Diameter at tower base 144 m

– Total height 165 m

• Thermal design

– Known turbine characteristics, energy output was maximized over given ambient temperature range

• 3.4 MW auxiliary power consumption/unit

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Majuba Power Station (3 x 657 MW)

• Average back pressure: 16.6 kPa

• LP turbine protection: 70 kP

• Station orientated with prevailing wind direction towards boiler

• 2 x 5.5 m exhaust ducts

• ACC details per unit

– 48 fans, 10 m diameter

– 8 streets with 6 fans per street

– 45 m air inlet opening

– 8.2 MW auxiliary power consumption

• Total platform footprint 20995 m2

• Finned-tube design similar to Matimba

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Eskom Specific Water Consumption Trend

0

2000

4000

6000

8000

10000

12000

1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Year

MW

0

0.5

1

1.5

2

2.5

l/k

Wh

Total installed dry cooled capacity

Specific water consumption, l/kWh

• Coal-fired power stations

• 2010 specific water consumption value = 1.38 l/kWh generated

10© 2011 Electric Power Research Institute, Inc. All rights reserved.

Design Efficiency of Eskom Power Stations

30%

32%

34%

36%

38%

40%

42%

Dry Cooled Wet Cooled Dry and Wet Cooled

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Specific Water Consumption at Power Stations

0

500

1000

1500

2000

2500

litre

s/M

Wh

Dry Cooled Wet Cooled Dry and Wet Cooled

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Cost of Dry vs. Wet Cooling

• Cooling system choice to be based on life cycle costing including capital, O&M, plant output and cost of water

• Relative costs for wet and dry indirect cooling systems in 1996:

– Capital cost of dry system was approximately 170% of wet system cost (surface condenser)

– More than 1% reduction in average unit output for dry system

• Footprint of dry natural draft cooling towers is typically 300% of that of a wet cooling tower of comparable size

• Challenge for retrofitting dry cooling systems is capital costs

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Medupi Power Station (6 x 794 MW)

• Average back pressure: 14.1 kPa (at 9m/s wind)

• LP turbine protection: 75 kPa (a)

• Average steam velocity approximately 78 m/s at 14.1 kPa (a)

• Station orientated with prevailing wind direction towards boiler

• 2 x 6.2 m exhaust ducts

• ACC details per unit

– 64 fans, 11m diameter

– 8 streets with 8 fans per street

– Street length 108 m

– Approximately 52 m air inlet opening

– 12.4 MW auxiliary power consumption

• Total platform footprint 72252 m2

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Medupi Progress Boiler 6 and Boiler 5

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Medupi Air-Cooled Condensers Under Construction

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Kusile Power Station (6 x 800 MW)

• Average back pressure 11.55 kPa (at 9 m/s wind)

• LP turbine protection: 75 kPa

• Average steam velocity approximately 83 m/s at 11.55 kPa

• Station orientated with prevailing wind direction towards boiler

• 2 x 6 m exhaust ducts

• ACC details per unit

– 64 fans, 11 m diameter

– 8 streets with 8 fans per street

– Street length 100.1 m

– Approximately 58 m air inlet opening

– 12.4 MW auxiliary power consumption

• Total platform footprint 66052 m2

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Operational Experience: Majuba Unit 1 Trip During Unsteady Wind Period

Majuba Unit 1 vacuum trip

13 November 2004

0

10

20

30

40

50

60

70

80

90

100

2004/11/13

14:49

2004/11/13

14:57

2004/11/13

15:04

2004/11/13

15:11

2004/11/13

15:18

2004/11/13

15:25

2004/11/13

15:33

2004/11/13

15:40

Time

Te

mp

era

ture

, P

ress

ure

, %

0

50

100

150

200

250

Am

p

Generator Output, %

ACC Pressure, kPa (abs)

Steam temperature, ºC

Air Inlet Temperature, ºC

Fan motor current, Amp

Air Cooled Condenser

Turbine

Boiler

2

Boiler

3

Boiler

1

Wind

direction

during trip

2

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Future Role of Dry Cooling

• Key technology in South Africa’s climate change impact adaptation strategy

• All future coal plants will be dry cooled

• Application to other technologies being evaluated –especially solar thermal

18

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Together…Shaping the Future of Electricity

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