Evaporative coolers are a type of direct spray cooling equipment. They work by directly spraying water into high-temperature flue gas. The evaporation of the water mist absorbs heat, thus reducing the temperature of the converter's hot flue gas from 800–10000°C to 150–200°C before it enters the electrostatic precipitator. Evaporative coolers are simple, require low investment, and consume little water and power. They can also improve the resistivity of flue gas dust; however, they increase the volume, moisture content, corrosiveness, and adhesion of the flue gas.
Evaporative coolers spray water droplets directly into the high-temperature flue gas flowing through the spray cooling tower. The sensible heat of the water during heating and the latent heat during evaporation absorb heat from the flue gas, thus cooling it. Utilizing the latent heat of vaporization of water provides excellent cooling with minimal water consumption and minimal increase in flue gas volume due to water evaporation. However, direct cooling is unsuitable for flue gas with an initial temperature below 150℃. Furthermore, the cooling temperature must not fall below the flue gas's saturation temperature (dew point) to prevent condensation, which can lead to equipment corrosion and pipe blockage. Therefore, the temperature of the flue gas after passing through the evaporative cooler should be maintained above 150℃, typically 20-30℃ higher. Consequently, the flue gas outlet temperature should be around 170℃.
The cross-sectional velocity of the hot flue gas within the evaporative cooler should generally not exceed 1.5-2.0 m/s. This is primarily to ensure that the evaporation time required for water droplets is less than the residence time of the flue gas within the cooler, ensuring sufficient cooling. Therefore, the evaporative cooler must have a certain height, determined by the complete evaporation time of the water droplets. This evaporation time, in turn, depends on the droplet size and the inlet and outlet temperatures of the flue gas. Consequently, a relatively high water pressure of 4-6 MPa is required.
Therefore, when designing and selecting an evaporative cooler, it is necessary to perform heat balance calculations to determine the matching relationship between water volume and flue gas volume, and use the results of the heat balance calculations to finally determine the structural dimensions of the equipment.