What is Cooling Towers | Types Of Cooling Towers

What is Cooling towers

The place where acquisition of land is very expensive, we may use cooling tower for cooling purposes. A cooling tower requires smaller area than a spray pond. It is an artificial device used to cool the hot cooling water coming out of condenser effectively. The cooling tower is a semi – enclosed device made of steel or concrete structure and corrugated surfaces or trough or baffles are provided inside the tower for uniform distribution and better atomization of water in the tower. The hot water coming out from the condenser falls down in radial sprays from height and the atmospheric air enters from the base of the tower. The partial evaporation of water takes place which reduces the temperature of circulating water.

This cooled water is collected in the pond at the base of the tower and pumped into the condenser. Draft eliminators are provided at the top of the tower to prevent the escaping of water particles with air.

According to the method of air circulation, cooling towers are classified as:

1. Natural draught type cooling tower

2. Mechanical draught type cooling tower
a. Forced draught type
b. Induced draught type

3. Hyperbolic draught cooling tower

Natural draught type cooling tower

In this hot water from condenser is pumped at the top where water sprays through a series of spray nozzles. Then waterfalls over decks, the decks also increase the amount of wetted surface in the tower and breaks up the water into droplets.
The air flowing across in transverse direction cools the falling water. These towers are used for small capacity power plants such as diesel power plants.

Forced draught cooling tower

In this tower draught air fan is installed at the bottom of tower. The hot water from the condenser enters the nozzles. The water is sprayed over the tower filling slats and the rising air cools the water. The entrained water is removed by eliminators located at the top.

Induced draught cooling tower

The difference here is in the supply of air. The drought fans installed at the top of tower draw air thought the tower. The hot water is allowed to pass thought the tower bellow the eliminators. The air moving in the upward direction cools the down coming hot water particles issued from spray nozzles some percentage (1%) of total water goes into air in the form of water vapour.

Hyperbolic cooling tower

It is usually made of steel reinforced cement concrete to withstand high wind pressure. First type of this type was installed in US at big sandy station of kenvcky power Co. It is capable of handling 120×103 gpm and cools the water from 43oc to 30o C. It has minimum diameter of 39.5 m and maximum diameter of 74.5 m and 400 meters high.

The hot water from the condenser is supplied to the ring troughs. Which are placed at 8-10 m above the ground level? The nozzles are provided on the bottom side of troughs to break up water into sprays. The air enters the cooling tower just above the pond located at the bottom, from the air openings provided, rises upward and absorbs heat from the falling water spray. The cooled water is collected into the pond. Some makeup water is supplied to overcome the losses into the atmosphere along with air due to evaporation. It needs about 35% of makeup water for compensating. This type of cooling tower is generally used since it is very efficient.

Advantages:

(1) No air fans are required so power cost and auxiliary equipments are totally eliminated.
(2) Hyperbolic structure creates its own draught assuring efficient operation even when there is no wind.
(3) Operation and maintenance cost are reduced.
(4) Ground fogging is avoided in hyperbolic towers.

Major drawbacks

(1) Its initial cost inconsiderably very high.
(2) Its performance varies with the personal changes in DBT and RH of air.