Advances in Dry Cooling Deployed at South African Power Stations

Steve Lennon Divisional Executive Eskom

2011 Summer Seminar August 1, 2011

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

• 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

• 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

• 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

• 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

• 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

• Coal-fired power stations • 2010 specific water consumption value = 1.38 l/kWh generated 12000 2.5

10000 2

8000

Total installed dry cooled capacity 1.5 Specific water consumption, l/kWh

6000

MW l/kWh

1 4000

0.5 2000

0 0 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Year

42%

40%

38%

36%

34%

32%

30%

Dry Cooled Wet Cooled Dry and Wet Cooled

2500

2000

1500

litres/MWh 1000

500

Dry Cooled Wet Cooled Dry and Wet Cooled

• 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

• 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

• 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

Boiler Boiler Boiler 3 2 1 Turbine Majuba Unit 1 vacuum trip Wind 13 November 2004 Air Cooled Condenser 100 direction 250 during trip 90

80 200

60 150 Generator Output, %

ACC Pressure, kPa (abs) Amp

40 Steam temperature, ºC 100 Temperature, Pressure, % Pressure, Temperature, 30 Air Inlet Temperature, ºC

Fan motor current, Amp 20 50

0 0 2004/11/13 2004/11/13 2004/11/13 2004/11/13 2004/11/13 2004/11/13 2004/11/13 2004/11/13 14:49 14:57 15:04 15:11 15:18 15:25 15:33 15:40 Time

• 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

Thank You