Cooling towers are used to cool water by evaporating a portion of the water. This is accomplished by pumping water to the top of the cooling tower and allowing it to cascade down to a collection basin.
While the water cascades down to the basin, there is air flow over the water, which evaporates a portion of the liquid, resulting in cooling. The design and size of the cooling tower ranges significantly and is primarily dependent on the heating load and water volume required to cool it. Therefore, the number, size and type of pumps will also vary.
Cooling water pumps are used to pump the water from the cooling tower basin to the plant for cooling, after which it is returned to the top of the cooling tower where it cascades back down to the basin. Within power plants, there can be large cooling towers that are sized for the plant cooling requirements and the cooling of the condenser. The condenser load is generally much greater than the plant cooling load, so there are different pumps for each service. Pumps used to circulate water for plant cooling are often referred to as cooling water pumps, and pumps used to circulate water through a condenser in a power plant are often referred to as circulating water pumps.
Water within a cooling tower does have some special considerations. The water is aerated, containing dissolved gases, and is typically treated with chemicals. Additionally, the liquid level in the basin, flow and head requirements are important application considerations for pump selection. Common pumps for cooling towers are either horizontal or vertical rotodynamic pumps (Image 1 for examples).
For more information on cooling tower pump application, refer to HI guidebook, Power Plant Pumps: Guideline for Application and Operation at pumps.org.