Necessity of Cooling Towers in thermal power station

 

Necessity of Cooling Towers in thermal power station

The demand for electric power has increased to such an extent that it is now no longer justifiable to site the large power station near river sides. The present trend is to locate the power station near the load Centre with an use of large and highly efficient cooling towers at the places where the power stations are located away from the river areas.

A cooling tower is a semi enclosed device for evaporative cooling of water by contact with air. It is a wooden, steel or concrete structure and corrugated surfaces or troughs or baffles or perforated trays are provided inside the tower for uniform distribution and better atomization of the cooling tower on the top and allowed to tickle in from of thin sheets or drops. The air flows from bottom of the tower or perpendicular to the direction of water flow and then exhausts to the atmosphere after effective cooling. To prevent the escape of water particles with air, draft eliminators are provided at the top of the tower.

Factors affecting the cooling water in a cooling tower:

1.      Temperature of air.

2.      Humidity of air.

3.      Temperature of hot water.

4.      Size and height of tower

5.      Velocity of air entering the tower

6.      Accessibility of air to all parts of the cooling water.

7.      Degree of uniformity in descending.

Types of cooling Towers

The cooling towers are mainly classified into following types :

1.      Atmospheric cooling tower.

2.      Natural draught cooling tower.

3.      Forced or induced draught cooling tower

Atmospheric cooling tower

In this cooling tower hot water is allowed to fall over louvers. The air flowing across in transverse direction cools the cools the falling water. These towers are used for small capacity power plants such as diesel power plants.

Natural draught cooling tower

The natural draft towers are closely built structures which are quite tall and have the top portion working as stack. The cooling depends upon the tower height and temperature of air, and so these towers have their limitation when large cooling capacity is required. 

 (a)

                    (b) Hyperbolic cooling Tower

Forced or induced draught cooling towers

In the tower draught 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 slots and the rising air cools the waters. A forced draught cooling tower