Water use in thermoelectric power stations

Greater than direct domestic water usage

With all the concern about carbon dioxide emissions, it is easy forget that other major environmental issues exist in the electric power sector. One of them is the use of freshwater by thermoelectric power plants (coal, nuclear, oil, steam side of CCGT power plants). Water withdrawal by thermoelectric power plants is huge, averaging about 95 litres per kWh. Coal-fired power plants with once-through cooling systems withdraw 142 litres per kWh while nuclear power plants with once-through cooling systems require as much as 175 litres per kWh.

According to the US National Energy Technology Laboratory (NETL), thermoelectric power plants accounted for 39 per cent of all freshwater withdrawal in the U.S. in 2000. Domestic water usage through electricity consumption in the U.S. is approximately 1,100 litres per person per day, three times as high as direct domestic water use (about 378 litres per person per day).

Reducing water quantity

Fortunately, water withdrawal is not the main consideration when it comes to assessing environmental impact. What matters more is the influence on the freshwater quantity and quality.

Freshwater consumption by thermoelectric power plants occurs through evaporation. This figure is much lower than the withdrawal rate, about 0.35 to 6 litres per kWh. According to NETL, this is only 3 percent of the total freshwater consumption in the U.S. Given the global scarcity and the importance of freshwater however, this is still an important figure.
One solution is to employ alternative sources of water to supplement or replace the freshwater currently being used. Examples include surface and underground water from mine pools, water produced from geological carbon sequestration and coal-bed methane processes, and industrial and municipal wastewater.

Advanced cooling technologies and improved water reuse and recovery techniques can also reduce both water withdrawal and water consumption.

Improving water quality

The quality of the water returned to its source after use is another concern. Three main issues arise:

• Elevated temperatures of water released back into the environment can have a significant influence on the eco-system. This has been measured, monitored, and limited fairly well in recent years.
• Decontamination additives used to eliminate micro-organisms and prevent fouling. New, more environmentally sensitive additives are emerging on the market.
• The deposition into water systems of trace quantities of air pollutants removed from combustion flue gas (mercury, arsenic, selenium, ammonia, etc.). Research is currently being carried out to develop efficient technologies for detecting and removing these components.