Power Stations and Water Demand
POWER STATIONS WATER DEMAND General In the UK, about 50% of all water use is for cooling power stations i . There is little or no information on this very important climate change, environmental and social issue in the UK. However, other countries such as the USA and Australia have carried out detailed studies on the very significant water demand of power stations and its impact on water resources, the environment and competing water demands of other sectors such as domestic, commercial, agricultural and industrial use. Thermal electric generating plant (fossil fuel and nuclear power stations) generate electricity by converting water into high pressure steam that drives turbines. Once water has gone through this cycle, it is cooled and condensed back to water and then reheated to drive the turbines again. The process of condensation requires a separate cooling water resource to absorb the heat of the steam. Cooling Technologies There are two principal cooling technologies in use today:•
Closed-cycle systems discharge heat through evaporation in cooling towers and recycle water within the power station. This system requires less water than once-through systems since the water required is limited to the amount lost through the evaporative process (1,136 to 2,271 litres/MWh water withdrawal and 1,136 to 1,817 litres/MWh water consumption) ii . However, close-cycle systems consume about the same amount of water as oncethrough systems. Since closed-cycle cooling systems are expensive, oncethrough cooling systems are far more common.
•
Once-through systems require the intake of a continual flow of cooling water. The water demand for the once-through cooling system is 30 to 50 times that of a closed-cycle system (75,708 to 189,270 litres/MWh water withdrawal and 1,136 litres/MWh water consumption).
The amount of water used for power station cooling varies by each specific power station’s electricity generating technology and size. For example, nuclear power stations require the most water for cooling, followed by baseload fossil fuel power stations. Water Use and Consumption In the USA thermal electric generating power stations draw in more than 200 billion gallons (750 billion litres) per day, whilst most decentralised energy technologies require little or no water cooling iii .
POWER STATIONS WATER DEMAND
1
Water use is the amount of water that is withdrawn from an adjacent water body (lakes, streams, rivers, estuaries, etc) that passes through the various stages of a power station and then ultimately discharged back into the original water body. Environmental concerns surrounding water use centre round any chemical or physical alteration of the water body and any impacts these changes may have on the plants, fish and animals who reside in the ecosystem. For example, the power stations using once-through cooling on the USA Great Lakes kill in excess of 40 million fish a year due to impingement. Water consumption is the amount of water consumed in power station operations that is lost, typically through power station cooling towers. Freshwater consumption may appear low (3%) compared with water withdrawal but even at 3%, over 3 billion gallons (over 11 billion litres) of freshwater a day is consumed, which is equivalent to consuming the volume of more than 4,500 Olympic sized swimming pools each day (US Department of Energy). It is important to understand that whether water is extracted from the mains (potable water) or from non potable water resources or from the environment (lakes, streams, rivers, estuaries, etc) it is all water resources which is competing with water demands for other sectors such as domestic, commercial, agricultural and industrial use for what are declining water resources brought about by climate change, particularly in the Western USA, Australia and the South East of England. In the USA iv current and future water-related environmental regulations and requirements challenge the operation of existing power stations and the permitting of new thermal electric generating power stations. For example, a 500MW power station that employs once-through cooling uses over 12 million gallons (45 million litres) per hour for cooling and other process requirements. Typical wet recirculating cooling water system flow rates for a 500MW coal fired power station are shown in Figure 1.
Figure 1 - Process Flow Schematic for Wet Recirculating Cooling Water System
gpm – gallons per minute (3.784 litres per minute)
Source: US Department of Energy, 2006
POWER STATIONS WATER DEMAND
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The US Geological Survey v estimates that US thermal electric generating power stations accounts for 136,000 million gallons (515,000 litres) per day of freshwater withdrawals (39% of US freshwater consumption), ranking only slightly behind agricultural irrigation (40% of US freshwater consumption) as the largest source of freshwater withdrawals in the USA. In Europe, E.ON’s vi process water consumption for their power stations increased from 82.5 million m3 (82.5 billion litres) in 2005 to 105.6 million m3 (105.6 billion litres) in 2006. Of this, E.ON’s power stations in the UK process water consumption accounted for 23.1 million m3 (23.1 billion litres) in 2006 with the increase in process water consumption primarily due to increased use of coal.
Allan Jones MBE Chief Development Officer, Energy and Climate Change 17 August 2010 i
South East England Development Agency – Taking Stock Fact Sheet 4: Energy and Water.
ii
Parliament of Australia: Department of Parliamentary Services – Water Requirements of Power Stations 2006. http://www.aph.gov.au/Library/Pubs/rn/2006‐07/07rn12.pdf
iii
Power Scorecard – Water Quality Issues of Electricity Production: Consumption of Water Resources. http://powerscorecard.org/issue_detail.cfm?issue_id=5
iv
US Department of Energy – Fossil Power Plant‐Water Related R&D Program – original paper http://www.netl.doe.gov/technologies/coalpower/ewr/pubs/Power%20Gen%202006_Water%20R& D.pdf and 2006 Update http://www.netl.doe.gov/technologies/coalpower/ewr/pubs/IEP%20Power%20Plant%20Water%20R &D%20Updated%200406.pdf v
United States Geological Survey (USGS) – Estimated Use of Water in the United States in 2000, USGS Circular 1268: March 2004. http://pubs.usgs.gov/circ/2004/circ1268/pdf/circular1268.pdf
vi
E.ON – Power and Gas – Responsibility – Environment – Operational Environmental Protection: Water Consumption http://www.eon.com/en/unternehmen/8543.jsp and Key Figures http://www.eon.com/en/unternehmen/8532.jsp
POWER STATIONS WATER DEMAND
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Closed-cycle systems discharge heat through evaporation in cooling towers and recycle water within the power station. This system requires less water than once-through systems since the water required is limited to the amount lost through the evaporative process (1,136 to 2,271 litres/MWh water withdrawal and 1,136 to 1,817 litres/MWh water consumption) ii . However, close-cycle systems consume about the same amount of water as oncethrough systems. Since closed-cycle cooling systems are expensive, oncethrough cooling systems are far more common.
•
Once-through systems require the intake of a continual flow of cooling water. The water demand for the once-through cooling system is 30 to 50 times that of a closed-cycle system (75,708 to 189,270 litres/MWh water withdrawal and 1,136 litres/MWh water consumption).
The amount of water used for power station cooling varies by each specific power station’s electricity generating technology and size. For example, nuclear power stations require the most water for cooling, followed by baseload fossil fuel power stations. Water Use and Consumption In the USA thermal electric generating power stations draw in more than 200 billion gallons (750 billion litres) per day, whilst most decentralised energy technologies require little or no water cooling iii .
POWER STATIONS WATER DEMAND
1
Water use is the amount of water that is withdrawn from an adjacent water body (lakes, streams, rivers, estuaries, etc) that passes through the various stages of a power station and then ultimately discharged back into the original water body. Environmental concerns surrounding water use centre round any chemical or physical alteration of the water body and any impacts these changes may have on the plants, fish and animals who reside in the ecosystem. For example, the power stations using once-through cooling on the USA Great Lakes kill in excess of 40 million fish a year due to impingement. Water consumption is the amount of water consumed in power station operations that is lost, typically through power station cooling towers. Freshwater consumption may appear low (3%) compared with water withdrawal but even at 3%, over 3 billion gallons (over 11 billion litres) of freshwater a day is consumed, which is equivalent to consuming the volume of more than 4,500 Olympic sized swimming pools each day (US Department of Energy). It is important to understand that whether water is extracted from the mains (potable water) or from non potable water resources or from the environment (lakes, streams, rivers, estuaries, etc) it is all water resources which is competing with water demands for other sectors such as domestic, commercial, agricultural and industrial use for what are declining water resources brought about by climate change, particularly in the Western USA, Australia and the South East of England. In the USA iv current and future water-related environmental regulations and requirements challenge the operation of existing power stations and the permitting of new thermal electric generating power stations. For example, a 500MW power station that employs once-through cooling uses over 12 million gallons (45 million litres) per hour for cooling and other process requirements. Typical wet recirculating cooling water system flow rates for a 500MW coal fired power station are shown in Figure 1.
Figure 1 - Process Flow Schematic for Wet Recirculating Cooling Water System
gpm – gallons per minute (3.784 litres per minute)
Source: US Department of Energy, 2006
POWER STATIONS WATER DEMAND
2
The US Geological Survey v estimates that US thermal electric generating power stations accounts for 136,000 million gallons (515,000 litres) per day of freshwater withdrawals (39% of US freshwater consumption), ranking only slightly behind agricultural irrigation (40% of US freshwater consumption) as the largest source of freshwater withdrawals in the USA. In Europe, E.ON’s vi process water consumption for their power stations increased from 82.5 million m3 (82.5 billion litres) in 2005 to 105.6 million m3 (105.6 billion litres) in 2006. Of this, E.ON’s power stations in the UK process water consumption accounted for 23.1 million m3 (23.1 billion litres) in 2006 with the increase in process water consumption primarily due to increased use of coal.
Allan Jones MBE Chief Development Officer, Energy and Climate Change 17 August 2010 i
South East England Development Agency – Taking Stock Fact Sheet 4: Energy and Water.
ii
Parliament of Australia: Department of Parliamentary Services – Water Requirements of Power Stations 2006. http://www.aph.gov.au/Library/Pubs/rn/2006‐07/07rn12.pdf
iii
Power Scorecard – Water Quality Issues of Electricity Production: Consumption of Water Resources. http://powerscorecard.org/issue_detail.cfm?issue_id=5
iv
US Department of Energy – Fossil Power Plant‐Water Related R&D Program – original paper http://www.netl.doe.gov/technologies/coalpower/ewr/pubs/Power%20Gen%202006_Water%20R& D.pdf and 2006 Update http://www.netl.doe.gov/technologies/coalpower/ewr/pubs/IEP%20Power%20Plant%20Water%20R &D%20Updated%200406.pdf v
United States Geological Survey (USGS) – Estimated Use of Water in the United States in 2000, USGS Circular 1268: March 2004. http://pubs.usgs.gov/circ/2004/circ1268/pdf/circular1268.pdf
vi
E.ON – Power and Gas – Responsibility – Environment – Operational Environmental Protection: Water Consumption http://www.eon.com/en/unternehmen/8543.jsp and Key Figures http://www.eon.com/en/unternehmen/8532.jsp
POWER STATIONS WATER DEMAND
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