Natural draft cooling towers, also commonly called hyperbolic or hyperboloid towers are commonly used in industrial facilities where the total heat extraction rate is at the level of several hundred MW.
Water evaporation accounts for 70% – 80% of the water consumed in cooling towers.
The actual amount of water evaporated is determined by the wet-bulb temperature and by the cooling demand of the system.
Upon evaporation, the water leaves behind salts, carbonates and other solids, that are added to those contained in the water remaining in the circuit, gradually increasing their concentration.
To control the concentration of salts and carbonates and other dissolved solids, it is required to purge water from the basin. This water blow-down represents approximately 20-30% of the water consumed in the towers.
The cooling tower also acts as a mighty air cleaner, absorving dirt and bacteria suspended in the air which accumulate at the basin of the cooling tower.