IMPROVING COOLING TOWER
OPERATION AND MAINTENANCE
ne of most conspicuous
process equipment is
the cooling tower. The
cooling tower is used to
cool hot process cooling
water streams, which is widely in use in
all process plants, so as to recycle it back
for use in various temperate units and
especially for steam regeneration. The
tower is located in the utility section and
is a large size humidification structure
consisting of draught fans at the top and
transfer pump at the bottom.
O
The process employed in cooling tower is
known as evaporative cooling. When one
cools his hot cup of tea by inter spraying
it between two cups in applying the
said process. Usually, water is cooled by
exposing its surface to available moving
air. Cooling of water on the surface of
a pond and spraying of water into slow
moving or forced air are other known
processes.
The cooling of water of varying degrees
involves heat transfer process in the
form of latent heat transfer as well as
sensitive heat due to the differences in the
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PECM Issue 30
temperature of the water and air. Cooling
by air depends on the moisture content
of air that is indicated by the wet bulb
temperature of the air in the surrounding.
The wet bulb temperature is the lowest
theoretical temperature of which the
water can be cooled. Theoretically,
enthalpy potential difference is the
driving force for the cooling tower heat
transfer process.
It is assumed that there is a film of air on
each particle of water. And the enthalpy
potential difference between the films
on each particle of water and the
surrounding provides the driving force for
the cooling process.
Cooling tower cools stream of water
by controlling the humidity of the air
passing through it. You will thereby
experience mist or carry over of moisture
around the tower. However, this should
be relatively very small because the
adequate engineering design will reduce
the mist level substantially. In the forced
draft tower the fan is mounted at the
base forcing air upwards whereas in the
induced draft towers the fan is at the top
polling the air below it. It has counter
flow and cross flow design depending
on the flow direction of water and air.
The air velocity, cross sections for air
passage as well as the length of the tower
play important roles in tower design.
Operational personnel can manipulate
the fan speed as well as the water rate to
achieve provisional temperature drop.
The cooling tower is therefore defined
as the equipment used to cool down the
temperature of process cooling water so
as to recycle it for reuse by controlling the
air humidity surrounding it.
I t has two main types ;
1. Mechanical draft towers; Forced and
Induced draft towers,
2. Natural draft or Hyperbolic type
towers; Atmospheric towers, Spray
ponds etc.
It can be assembled independently from
below grade where the water falls to
meters, and above grade where the water
is poured.