Working Principle of a Closed-Circuit Evaporative Cooler

A closed-circuit evaporative cooler is a spray-type direct cooling device. It sprays water directly into the high-temperature flue gas, allowing the evaporation of the water mist to absorb heat.

This reduces the temperature of the hot converter flue gas from 800-10,000°C to a range of 150-200°C before it enters the electrostatic precipitator. Evaporative coolers are simple, require little investment, consume little water and power, and can improve the resistivity of the flue gas. However, they can increase flue gas volume, moisture content, corrosiveness, and gas cohesion.

In a spray cooling tower, an evaporative cooler sprays water droplets directly onto the high-temperature flue gas flowing through the tower. The water absorbs heat from the flue gas through the sensible heat of rising temperatures and the latent heat of evaporation, thereby cooling the flue gas. Utilizing the latent heat of vaporization of water offers excellent cooling effects, requires minimal water, and minimally increases the flue gas volume due to water evaporation. However, direct cooling is not suitable for flue gas initial temperatures below 150°C. 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 flue gas temperature after cooling through the evaporative cooler must be maintained above 150°C, generally 20-30°C higher than this, resulting in a flue gas outlet temperature of approximately 170°C.

The cross-sectional flow rate of hot flue gas within the evaporative cooler should generally be no greater than 1.5-2.0 m/s. This is primarily to ensure that the evaporation time required for water droplets is shorter than the residence time of the flue gas within the evaporative cooler, ensuring sufficient cooling. Therefore, the evaporative cooler must have a certain height, which is determined by the time it takes for the water droplets to completely evaporate within the cooler. This evaporation time, in turn, is related to the droplet size and the flue gas inlet and outlet temperatures. Consequently, the required water pressure is relatively high, reaching 4-6 MPa. Therefore, when designing and selecting an evaporative cooler, a heat balance calculation is required to determine the matching relationship between the water volume and the flue gas volume, and the heat balance calculation results are used to ultimately determine the structural dimensions of the equipment.