According to a recent release from the Energy Information Administration (EIA), many power plants have switched to dry cooling systems, and have cut water use by 95 percent as a result. These facilities typically rely on rivers or lakes to offset the heat being generated and produce steam for driving turbine generators. The trade-off with a dry cooling system's ability to conserve water is that these systems are expensive and require energy to operate.
Nuclear plants, plants that burn biomass or coal, as well as some natural gas plants, and even some solar facilities use steam generation. In a dry cooling environment, once the steam has passed through the turbine, it must be cooled to reform as a liquid, which can be sent back to the boiler or steam generator.
According to the U.S. Geological Survey, electric power generation accounts for about 40 percent of water withdrawals in the United States. This figure includes the more than 61 percent of thermoelectric generating capacity that relies on recirculating cooling systems. These systems keep water in closed-loop piping so that it can be used repeatedly.
Plants that use once-through cooling systems withdraw large amounts of water from nearby sources, and then they discharge it back to the original source at higher temperatures. Dry cooling systems are classified as either direct and indirect. In the case of direct dry cooling systems, no water is consumed, with steam condensed using ambient air. In the case of indirect dry cooling systems, steam is condensed in conventional condensers that are cooled by water, but this water is retained in a closed system. As a result, no water is lost to evaporation, which means very little water is used.
Hybrid cooling systems are a mix between dry and wet cooling, and they can use both water and air to condense steam. These systems are typically designed to be operated as dry cooling systems during the cooler seasons and as wet cooling systems during the hotter seasons.
Due to their typical locations, dry cooling can also be an attractive option for solar power systems. In areas such as Arizona and California, solar resources are relatively high, and water resources are relatively low. This fact is why many new concentrated solar plants utilize dry cooling, which has helped fuel its growth.
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