Lennon Eskom Dry Cooling

Steve LennonDivisional ExecutiveEskom

2011 Summer SeminarAugust 1, 2011

Advances in Dry Cooling Deployed at South African Power Stations

3 2011 Electric Power Research Institute, Inc. All rights reserved.

Eskoms 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


Eskoms 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


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


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


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


Majuba Power Station (3 x 657 MW)

Average back pressure: 16.6 kPa

LP turbine protection: 70 kP


2 x 5.5 m exhaust ducts




45 m air inlet opening

8.2 MW auxiliary power consumption

Total platform footprint 20995 m2

Finned-tube design similar to Matimba


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/kW

h

Total installed dry cooled capacity

Specific water consumption, l/kWh

Coal-fired power stations

2010 specific water consumption value = 1.38 l/kWh generated


Design Efficiency of Eskom Power Stations

30%

32%

34%

36%

38%

40%

42%

Dry Cooled Wet Cooled Dry and Wet Cooled


Specific Water Consumption at Power Stations

0

500

1000

1500

2000

2500

litre

s/M

Wh

Dry Cooled Wet Cooled Dry and Wet Cooled


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


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)


2 x 6.2 m exhaust ducts


64 fans, 11m diameter


Street length 108 m

Approximately 52 m air inlet opening




Medupi Progress Boiler 6 and Boiler 5


Medupi Air-Cooled Condensers Under Construction


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


2 x 6 m exhaust ducts




Street length 100.1 m

Approximately 58 m air inlet opening




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, C

Air Inlet Temperature, C

Fan motor current, Amp

Air Cooled Condenser

Turbine

Boiler

2

Boiler

3

Boiler

1

Wind

direction

during trip

2


Future Role of Dry Cooling

Key technology in South Africas climate change impact adaptation strategy

All future coal plants will be dry cooled

Application to other technologies being evaluated especially solar thermal

18


TogetherShaping the Future of Electricity

Thank You

Lennon Eskom Dry Cooling

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