Sometimes
referred to as heat rejection devices, Cooling towers are systems that
provide cooling of water and other fluids through the removal of heat from
the fluid. Cooling towers are widely used in various industrial
applications. In most gas plants, a cooling tower is an essential component.
A cooling tower is an installation in which heat is separated from water. In
other words, Cooling towers are evaporative coolers which are used for
cooling water or other working medium to near-ambient temperature. They use
evaporation of water to reject heat from the system. Cooling towers vary in
size from small roof-top units to very large hyperbolic structures. The
smallest cooling towers are constructed for only a few gallons of water per
minute. The largest cooling towers can handle more than thousands of gallons
per minute. The pipes are obviously very large to accommodate this much
water in the larger towers and can range up to 12 inches in diameter.
Construction Materials of Cooling Towers
Construction materials of Cooling Towers should be non-corrosive, resistant
to chemicals, smooth, non-porous, opaque to sunlight and readily
disinfected. Materials used for construction shall not support the growth
and proliferation of microorganisms. We can categorize the construction
materials of cooling towers as follows:
- Fiberglass Reinforced Polyester (FRP)
- Metal
- Polyvinyl Chloride (PVC)
- Wood
- Concrete
Components of Cooling Towers
When we talk about the components of cooling towers, we find that most
cooling towers are made using the same basic components:
- A pump to bring the water to the top of the tower
- Spray nozzles to distribute the water over the fill.
- A fan to move outside air through the tower.
- The fill to expose the water surface to the air stream.
- A basin to capture and store the cooled water.
Accordingly we can categorize the components of cooling towers as
follows:
- Condenser pump & distribution systems
- Cooling Tower Basin
- Heat transfer media
- Cooling tower fan system
- Drift elliminators
How does a cooling tower works?
The working of a cooling tower is quite simple. The steps involved are as
follows:
- The water that needs to be cooled generally has a temperature between
40 and 60°C.
- It is pumped to the top of the cooling tower and flows down by way of
several wooden or plastics partitions inside the structure through which
the water stream is turned into droplets.
- When dropping, the water cools off under influence of an upwards
current of air and falls in a basin at the base of the cooling tower.
Thereafter, the water flows back to the production process in order to
serve as a coolant once more.
- In the cooling tower, the water cools down about 10 to 20°C.
Some cooling towers have one or more big fans, situated at the top and
these can be compared to ventilators.
- These fans draw the air upwards through the cooling tower, which
thereby extract heat from the plunging cooling water. This heat
extraction is partially due to the temperature difference, partially to
the conversion of part of the water into water vapour. This conversion
takes away a lot of heat.
- Huge cooling towers are so high that the 'chimney effect' develops so
much traction that sucking fans are not necessary.
There are various types of cooling towers which can be categorized as
follows:
- By Sizes and shapes: Cooling towers are available in all
kinds of shapes and sizes. The popular ones are the huge, somewhat
hourglass-shaped constructions, often found at power stations. Most
cooling towers are small the size depends more or less on the required
cooling capacity.
- By Material: The walls of the cooling towers are made of
concrete-both small and large models. Cooling towers are also
constructed wood, plastic, and metal. Concrete-wood-plastic combinations
are also possible.
- By One or more cells: Sometimes, cooling towers consist of
several cells, where each cell is able to operate independently. In such
cases, each cell has its own fan.
- By Construction: The cooling towers can be field-erected or
factory assembled.
- By method of heat transfer : Cooling Towers can be wet
cooling tower or dry cooling tower.
- By Air Flow: This can classify cooling towers into:
- Mechanical draft cooling tower
- Forced draft cooling tower
- Induced draft cooling tower
Applications of Cooling Towers
Cooling towers are beneficial in cooling fluids, particularly water, in a
large number of industrial applications. Useful applications for cooling
towers include:
- Air conditioning units
- Dry cleaning
- Water treatment
- Power generation
- Gas plants
Numerous industries in which cooling towers are used to reduce heat in
industrial facilities and systems are like:
- Water/wastewater
- Chemical
- Electric
- Pulp and paper
- Plastics industries
Buying Tips
When selecting a cooling tower, it is necessary to consider industrial
application, fluid type and volume, tower placement within the facility and
other environmental factors.
Cooling
Towers
