COOLING TOWER

 COOLING TOWER (CT):

         Purpose of cooling tower is to reduce temperature of circulating hot water to re-use this water again in boiler. This hot water is coming from the condenser.

        How cooling tower works? Hot water is coming at inlet of the tower and pumped up to the header. Header contains nozzles and sprinklers which is used to spray water and it will increase the surface area of water. After that, water comes to PVC filling, it used to reduce the speed of water. At top the CT, fan is used to circulate air from bottom to the top. Because of slow speed and more contact area of water, it makes a good connection between air and hot water. This will reduce the temperature of water by evaporation process and cooled water is collect at the bottom of the CT and used this cooled water again in the boiler.

Different parts of Cooling tower:

       1) Eliminator: It is not allowed to pass water. Eliminator is placed at top of tower, from which only hot air can pass.

       2) Spray nozzles and header: These parts are used to increase the rate of evaporation by increasing surface area of water.

        3) PVC falling: It reduce the falling speed of hot water and it similar as beehive.

       4) Mesh: When fan is ON, it used atmosphere air which contains some unwanted particles. Mesh is used to stop these particles and not allowed to enter in to CT.

        5) Float valve: It used to maintain level of water.

        6) Bleed valve: It used to control the concentration of minerals and salt.

        7) Body: Body or outer surface of CT is made up from FRP (fibre reinforced plastic), which protects the internal parts of CT.   

Cooling towers can be classified in two types:

     

       1)      Natural draught CT: In this type of CT, fan is not used for circulating air but here, by enclosing the heated air in the chimney and it will create pressure difference between heated air and surrounding air. Because of this pressure difference air is circulated in to the CT. it requires large hyperbolic tower, so capital cost is low but operating cost is low because of absence of fan. There are two types of natural draught CT; rectangular timber tower and reinforced concrete hyperbolic tower.

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         2)      Mechanical or Forced draught CT: In this type of CT, fan is used to circulate the air. When power plant is running on peak load, it requires a very high rate of cooling water. To rotate fan, it used motor with speed around 1000 rpm. Working principle is same as natural draught CT, only difference is fan is mounted on the base of CT. If fan is mounted on the top of the tower is called as induced draught CT which is most popular for very large capacity installation and require large capacity of fan. So, forced draught CT contains horizontal shaft for the fan and it placed at bottom of the tower and induced draught CT contains vertical shaft and it placed at top of the CT.