Dry-Cooling Towers Help Cut Water Use in Power Stations

Ongoing operations to replace wet-cooling towers with dry-cooling systems are projected to reduce annual water consumption in thermal power plants by at least 13 million cubic meters, said a deputy manager at Iran's Thermal Power Plants Holding Company. “Iran has more than 130 thermal power stations, in which close to 130 mcm of water are used annually and converting wet towers into dry-cooling facilities will lessen water use by 10%,” Nasser Eskandari was also quoted as saying by the Energy Ministry’s news portal. The construction of dry-cooling towers has gained impetus in the aging Besat Power Plant in southern Tehran, Isfahan Power Plant in the eponymous central province and Shahid Mofatteh Power Plant in Hamedan Province, such that the last project has registered 70% progress and is expected to become operational in the current fiscal year (March 2023-24). “Wet-cooling towers account for 70% of total water consumption in power stations, that’s why replacing them with dry-cooling systems is on TPPHC’s agenda,” he said. Dry-cooling systems use air instead of water to cool the steam exiting a turbine. Such systems do not use water and can reduce total power plant water consumption by over 80%. The main purpose of large, industrial cooling towers is to remove the heat absorbed in the circulating cooling water systems of power plants, petroleum refineries, petrochemical plants and gas processing plants. While wet-cooling towers are designed to evaporate water into the air that flows through the tower, dry-cooling towers work differently in that they transfer heat from the power plant directly into the air. Dry cooling towers conduct heat transfer through air-cooled heat exchangers that separate the working fluid from the cooling air. Because there is no direct contact between the working fluid and the ambient air, there is no water loss in such systems. Thermal power plants in the country account for as little as 0.1% of total annual water consumption, Eskandari said. --- Farming Sector Iran's annual water consumption [extracted from ground and surface resources] tops a massive 100 billion cubic meters, of which less than 130 million cubic meters are used in power plants annually, which is insignificant compared to the farming sector that gobbles up 90 bcm of water per year, the official said.  Eskandari noted that of the total volume of water used in Iran, 2 bcm are used in industries, including petrochemical plants, steel mills and power stations, adding that as per the directive issued by the Energy Ministry in 2020, it is mandatory for all thermal power plants to use reclaimed wastewater (instead of potable water) in cooling towers. One dry cooling tower went on stream at Hamedan’s Shahid Mofatteh Thermal Power Plant in 2015, which reduced the power plant's water consumption from 3 mcm to 600,000 cubic meters. Ramin Thermal Power Plant in Ahvaz in southwest Khuzestan Province and Isfahan Power Plant will soon be supplied with treated wastewater for cooling towers. Drawing a parallel, the TPPHC official noted that the company’s annual water extraction from renewable water resources equals the amount of water used in Tehran in 33 days. Refuting the general belief that power industry is water-intensive, he said power plants have started tapping into unconventional resources as curbing water consumption is necessary, especially in Iran that has been grappling with disappearing underground water tables. The UNESCO 2017 World Water Development Report says treated wastewater could be invaluable in meeting the growing demand in farming and industrial sectors.  --- Recycled Water Environmentalists and experts say industries must use recycled water for heating and cooling instead of the scarce and costly potable water.  Power plants are gradually replacing costly water from wells, lakes and rivers with reclaimed wastewater.  “Iran’s 130 thermal power stations generated an estimated 332 billion kilowatt-hours of power in 2022, up 3% compared to a year ago,” the official said. “Of the total output, steam-powered plants, gas-powered stations and combined-cycle plants generated 83 billion kWh, 69 billion kWh and 181 billion kWh respectively in the nine-month period.” According to Eskandari, thermal power facilities account for 92% of Iran’s total power demand in the summer, but when demand falls, the figure declines to 80%. “Timely repair and maintenance of thermal facilities have helped them work at full capacity in the summer,” he said. The upgrading, repair and maintenance of thermal power plants have added 500 MW to the country’s electricity output.