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 © 2011 Electric Power Research Institute, Inc. All rights reserved. 3 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 © 2011 Electric Power Research Institute, Inc. All rights reserved. 4 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 © 2011 Electric Power Research Institute, Inc. All rights reserved. 5 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 © 2011 Electric Power Research Institute, Inc. All rights reserved. 6 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 © 2011 Electric Power Research Institute, Inc. All rights reserved. 7 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 © 2011 Electric Power Research Institute, Inc. All rights reserved. 8 Eskom Specific Water Consumption Trend • 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 © 2011 Electric Power Research Institute, Inc. All rights reserved. 9 Design Efficiency of Eskom Power Stations 42% 40% 38% 36% 34% 32% 30% Dry Cooled Wet Cooled Dry and Wet Cooled © 2011 Electric Power Research Institute, Inc. All rights reserved. 10 Specific Water Consumption at Power Stations 2500 2000 1500 litres/MWh 1000 500 0 Dry Cooled Wet Cooled Dry and Wet Cooled © 2011 Electric Power Research Institute, Inc. All rights reserved. 11 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 © 2011 Electric Power Research Institute, Inc. All rights reserved. 12 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 © 2011 Electric Power Research Institute, Inc. All rights reserved. 13 Medupi Progress Boiler 6 and Boiler 5 © 2011 Electric Power Research Institute, Inc. All rights reserved. 14 Medupi Air-Cooled Condensers Under Construction © 2011 Electric Power Research Institute, Inc. All rights reserved. 15 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 © 2011 Electric Power Research Institute, Inc. All rights reserved. 16 Operational Experience: Majuba Unit 1 Trip During Unsteady Wind Period 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 70 60 150 Generator Output, % 50 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 10 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 © 2011 Electric Power Research Institute, Inc. All rights reserved. 17 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 © 2011 Electric Power Research Institute, Inc. All rights reserved. 18 18 Together…Shaping the Future of Electricity Thank You © 2011 Electric Power Research Institute, Inc. All rights reserved. 19.