Advances in Dry Cooling Deployed at South African Power Stations

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1 Advances in Dry Cooling Deployed at South African Power Stations Steve Lennon Divisional Executive Eskom 2011 Summer Seminar August 1, 2011

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3 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 3

4 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 4

5 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 m 2 5

6 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 6

7 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 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 7

8 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 m 2 Finned-tube design similar to Matimba 8

9 MW l/kwh Eskom Specific Water Consumption Trend Coal-fired power stations 2010 specific water consumption value = 1.38 l/kwh generated Total installed dry cooled capacity Specific water consumption, l/kwh Year 0 9

10 Design Efficiency of Eskom Power Stations 42% 40% 38% 36% 34% 32% 30% Dry Cooled Wet Cooled Dry and Wet Cooled 10

11 litres/mwh Specific Water Consumption at Power Stations Dry Cooled Wet Cooled Dry and Wet Cooled 11

12 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 12

13 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 m 2 13

14 Medupi Progress Boiler 6 and Boiler 5 14

15 Medupi Air-Cooled Condensers Under Construction 15

16 Kusile Power Station (6 x 800 MW) Average back pressure kpa (at 9 m/s wind) LP turbine protection: 75 kpa Average steam velocity approximately 83 m/s at 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 m Approximately 58 m air inlet opening 12.4 MW auxiliary power consumption Total platform footprint m 2 16

17 Temperature, Pressure, % Amp Operational Experience: Majuba Unit 1 Trip During Unsteady Wind Period Boiler 3 Boiler 2 Boiler 1 Turbine Air Cooled Condenser 100 Wind direction during trip Majuba Unit 1 vacuum trip 13 November Generator Output, % ACC Pressure, kpa (abs) Steam temperature, ºC Air Inlet Temperature, ºC Fan motor current, Amp /11/13 14: /11/13 14: /11/13 15: /11/13 15: /11/13 15: /11/13 15: /11/13 15: /11/13 15:40 0 Time 17

18 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 18

19 Together Shaping the Future of Electricity Thank You 19