Qtn.: What is the need of Cooling Towers?
Ans.: The hot water-a by product of all the process, power, metal work and sugar plants, as well as many of other industries needs to be cooled before it can be reused or even discharged back in to the atmosphere. The cooling tower with its simple mechanism transfers the heat from the water in to the air does just that! A vast assortment of cooling towers is available to suit the specific cooling requirements of various industries.
Qtn.: What is a Cooling Tower ?
Ans.: Cooling towers is a heat rejection device that cools and process water using the evaporative cooling principal in whom it extracts waste heat to the atmosphere through the cooling of a water stream to a lower temperature. This process allows a small portion of the water being cooled to evaporate in to a moving air stream to provide significant cooling to the rest of that water stream. The heat from the water stream transferred to the air stream raises the air temperature and its relative humidity to 100%, and this air is discharged to the atmosphere.
Qtn.: How does a Cooling Tower work ?
Ans.: They act as giant air washers. Finely misted water is sprayed in to a column of moving air. In the cooling tower, this mist is intended to increase the surface area of the water so that heat can be transferred from the water to the air more effectively. These giant towers are intrinsic to almost every industry, especially the process plants, as they represent a relatively inexpensive and dependable means of removing low-grade heat from cooling tower.
In a process plant cooling towers are used to cool the process water coming from heat exchanger. The make up water source is used to replenish the water lost to the evaporation. Hot water from heat exchanger is sent to the cooling towers. The water exits the cooling tower and sent back to the heat exchangers or to the other units for further cooling as this process cools the water to the ambient temperature only.
Qtn.: How many type of Cooling Towers?
Ans.: Cooling towers can be categorized in to two main types:
Qtn.: What are the open circuit & close circuit Cooling Towers?
Open Circuit Cooling Towers
A direct or open circuit cooling tower is an enclosed structure with internal means to distribute the warm water fed to it over a packing or ‘fill area’ The fill area provides a vastly expanded air water interface for heating of the air and evaporation to take place. The water cooled as it descends through the fill by gravity while in direct contact with air that passes over it. The cooled water is than collected in a cold water basin below the fill from which it is pumped back to the process to absorb more heat. The heated and moisture laden air leaving the fill area is discharged to the atmosphere at a point remote enough from the air inlets to prevent its being drawn back in to the cooling tower.
Close Circuit Cooling Towers
An indirect or closed circuit cooling tower involves no direct contact of the air and the fluid, usually water or a glycol mixture, being cooled. Unlike the open cooling tower, the closed circuit cooling tower has two separate fluid circuits. One is an external circuit in which water is re-circulated on the outside of the second circuit, which is tube bundles (closed coils) which are connected to the process for the hot fluid being cooled and returned in a closed circuit. Air is drawn through the re-circulating water cascading over the outside of the hot tubes, providing evaporative cooling similar to an open cooling tower. In operation heat flows from the internal fluid circuit, through the tube walls of the coil, to the external circuit and then by the heating of the air and evaporation of some of the water, to the atmosphere. Operation of the closed circuit cooling towers is therefore very similar to the open cooling tower with one exception. The process fluid being cooled is contained in a “closed” circuit and is not directly exposed to the atmosphere or the re-circulated external water.
Qtn.: What are package & field erected Cooling Towers?
Ans.: Most heating and cooling application require cooling towers below 10,000 gal/min. Towers of this type, called package cooling towers, usually are mass produced in factories with FRP structure & casing. This type of cooling tower is manufactured so it can be transported easily to the job site.
The towers requiring a thermal duty, beyond the capabilities of a package cooling towers are larger, requiring them to be manufactured, shipped & assembled at site. These are field-erected towers and generally used in most industrial and utility applications. Field erected mechanical draught towers can handle flow rates from 10,000 to 3,50,000 gal/min.
Qtn.: What are the fouling agents of the Cooling Towers?
Ans.: The performance of a cooling tower is directly proportional to the efficiency of the heat transfer. There are some of the common causes that reduces the heat transfer co-efficient as
Qtn.: What is scale menace?
Ans.: When water evaporates from the cooling tower, it leaves scale deposits on the surface of the fill from the minerals that were dissolved in the water. Scale build up acts as a barrier to heat transfer from the water to the air. Excessive scale build up is telltale sign of water treatment problems.