- Cooling Tower Definition: A cooling tower is defined as a device that reduces the temperature of hot water from the condenser for reuse in the boiler.
- Working Principle: Hot water is sprayed, slowed down, and cooled by evaporation with the help of fans.
- Cooling Tower Parts: Key parts include eliminators, spray nozzles, PVC filling, mesh, float valve, and bleed valve.
- Natural Draught Cooling Tower: This type uses chimney effects for air circulation, leading to high capital costs but low operating costs.
- Mechanical Draught Cooling Tower: This type uses fans for air circulation, suitable for high-load conditions with either forced or induced draught systems.
The purpose of a cooling tower is to cool down hot water from the condenser so it can be reused in the boiler.
How Cooling Tower Works?
Hot water enters the tower and is pumped to the header, which has nozzles and sprinklers to spray the water, increasing its surface area. The water then passes through PVC filling to slow its speed. Fans at the top of the tower pull air from the bottom to the top.
The slow speed and increased contact area of the water enhance the interaction between air and water. This reduces the water’s temperature through evaporation. The cooled water is then collected at the bottom of the tower and reused in the boiler.
Different Parts of Cooling Tower
- Eliminator: It is not allowed to pass water. Eliminator is placed the at top of tower, from which only hot air can pass.
- Spray Nozzles and Header: These parts are used to increase the rate of evaporation by increasing surface area of water.
- PVC Falling: It reduces the falling speed of hot water and it is similar to beehive.
- Mesh: When the fan is ON, it uses atmosphere air which contains some unwanted dust particles. Mesh is used to stop these particles and do not allow to enter dust in to cooling tower.
- Float Valve: It is used to maintain level of water.
- Bleed Valve: It is used to control the concertation of minerals and salt.
- Body: Body or outer surface of cooling tower is often made up from FRP (fiber reinforced plastic), which protects the internal parts of cooling tower.
Types of Cooling Tower
Cooling towers can be classified in two types
1) Natural Draught Cooling Tower: In this type of cooling tower, fans are not used. Instead, enclosing the heated air in the chimney creates a pressure difference between the heated and surrounding air, causing air to enter the cooling tower. It requires large hyperbolic tower, so capital cost is high but operating cost is low because of absence of electrical fan. There are two types of natural draught cooling tower, rectangular timber tower and reinforced concrete hyperbolic tower.
2) Mechanical or Forced Draught Cooling Tower: In this type of cooling tower, fan is used to circulate the air. When power plant runs on peak load, it requires a very high rate of cooling water. To rotate fan, it uses motor with speed around 1000 rpm. Working principle is same as natural draught cooling tower, only difference is that here fan is mounted on the cooling tower. If fan is mounted on the top of the tower is called as induced draught cooling tower which is most popular for very large capacity installation and requires large capacity of fan. So, forced draught cooling tower contains horizontal shaft for the fan and it is placed at bottom of the tower and induced draught cooling tower contains vertical shaft and it is placed at top of the cooling tower.
