Evaporative Cooling Tower

Efficient gas cooling with excellent process control

The Metso Evaporative Cooling Tower is a dry gas cleaning solution designed to cool hot off-gases by means of evaporation to a desired temperature.

Controllable outlet temperature coupled with advanced model-based automatic control for start-up and varying process conditions

The even temperature profile reduces the risk of condensation, protecting the tower and downstream equipment from corrosion

Two media nozzles which produce small droplets that are evaporated quickly. Guiding vanes and nozzles for even gas distribution and cooling

A large turn-down ratio and lower air consumption can be achieved in the tower design through the selection of nozzles and number of headers

The Evaporative Cooling Tower is typically manufactured from stainless steel to withstand both the temperature and the gas content. The gas cooling effect comes from evaporation of water sprayed into the tower through nozzles, where the water is atomized to tiny droplets with compressed air. The Evaporative Cooling Tower operates dry, meaning that all droplets are evaporated before they reach the bottom of the tower. The spray water flow is controlled in relation to the gas temperature at the cooling tower outlet.

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Operating principle

The hot process gas enters the tower from the top. The gas is evenly distributed by means of guiding vanes placed in the inlet. The top of the tower, separating the cross-section area from the incoming gas duct to the evaporative zone, is specifically designed not to disturb the gas profile downstream of the guiding vanes.

Special two-media nozzles are placed at the inlet part of the tower, in which the water is atomized to small droplets with compressed air. The nozzles are placed to create a uniform spray pattern that covers the entire cross-section area of the tower, which minimizes the risk for partial cooling of the gas. The small droplets evaporate quickly using the heat from the hot gas, reducing the temperature in the process. The small droplets provide a large surface area, reducing the retention time and length of the evaporative zone needed to ensure complete evaporation.

The amount of water injected into the tower is determined by a control loop based on the outlet temperature. As the temperature increases, more water is sent through the nozzles and vice versa. The control circuit of the water injection ensures that the gas leaving the cooling tower will have a steady temperature around the set-point suitable for the downstream equipment (e.g., bag filter or Hot ESP). To handle varying flow conditions, e.g. during a start-up, the temperature control is supplemented by an advanced model-based automatic control which ensures that the water injection adapts quickly to even large fluctuations in the heat load, keeping the operation steady and reducing the risk for over or under cooling. Dust settling at the bottom of the tower is continuously removed by a scraper conveyor and a rotary feeder.