Natural Draft Cooling Towers
By: Nicholas Berkholz
ENG 3060 Section 003
What is a Natural Draft Cooling Tower
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What is a
Natural Draft
Cooling
Tower?
A Few
Important
Terms
Components
How it Works
Remarks
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A natural draft cooling tower is a means to remove waste
heat from a system and release it into the atmosphere.
Typically used at oil refineries, chemical plants and power
plants to remove heat absorbed from circulating cool water
systems.
A common shape is the hyperboloid (See Fig. 1)
Cooling towers have been around for over 100 years.
However, in their early for were only about 20 meters high.
Today, some can reach over 200 meters.
“As recently as 20 years ago, cooling towers were more the
exception than the rule in the industry because of their
severely high operating cost and the large amount of capital
required for construction. But with today's need for water
conservation and minimal environmental impact. industry is
turning more and more to recycling water.”(GC3)
Fig. 1
Important Terms
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Wht isisaa
What
Natural
Natural Draft
Draft
Cooling
Cooling
Tower?
Tower?
A Few
A
Few
Important
Important
Terms
Terms
Components
Components
How it Works
How it Works
Remarks
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Wet Bulb Air Temperature - the temperature a volume of
air would have if cooled adiabatically to saturation at
constant pressure by evaporation of water into it, all latent
heat being supplied by the volume of air(Wiki 1). Also
known as the dew point of ambient air.
Adiabatically - in meteorology, referred to also as adiabatic
cooling: when air cools or heats as it expands or contracts
with pressure change without losing or gaining heat energy
by radiation or to its surroundings. (Wiki 2)
Dry Bulb Air Temperature – The temperature at which a
thermometer reads freely in air but is shielded from
radiation and moisture.
Natural Draft or Stack Effect – When there is a large
pressure differential between the outside air and air within
a structure. Warm, moist air is less dense than dry air of the
same pressure thus causing the warm, moist air to rise.
Components
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What
Whatisisa a
Natural Draft
Natural
Draft
Cooling Tower?
Cooling
A Few
Important Terms
Tower?
Components
A Few
How it Works
Important
Remarks
Terms
Components
How it Works
Remarks
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Supply Basin
Tower Pumps
Cooling Towers
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Hot Water Inlet
Fill
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Vertical Ribs
Reinforced Concrete Shell
Internal Void
Diagonal Columns
Splash
Film
Hot Water Distribution System
Cold Water Collection
Drift Eliminators - Drift is water lost from cooling towers as liquid
droplets are entrained in the exhaust air. The drift loss is independent
of the water lost by evaporation. The drift loss may be expressed in
units of lb/hr or percentage of circulating water flow. Drift eliminators
are used to control this drift loss from the tower. (Mist)
Components
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What is a
Natural Draft
Cooling
Tower?
A Few
Important
Terms
Components
How it Works
Remarks
How it Works
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•
•
•
What is a
Natural Draft
Cooling
Tower?
A Few
Important
Terms
Components
How it Works
Remarks
•
Step 1 - As hot water enters the natural draft cooling
towers, through a series of pumps, to the warm water inlet
How it Works
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What is a
Natural Draft
Cooling
Tower?
A Few
Important
Terms
Components
How it Works
Remarks
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Step 2 - The warm water is then distributed into through a
packing or fill material inside the tower keeps the water
evenly distributed. This is plays a major role and contributes
heavily to the efficiency of the tower.
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(i.e. better the distribution allows for more contact time, and greater
surface area, which allows for more heat removal)
How it Works
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What is a
Natural Draft
Cooling
Tower?
A Few
Important
Terms
Components
How it Works
Remarks
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Step 3 - As the water is being distributed, the exposed
lower portion of the tower allows for air to pass over the
cold water basin. It’s this passing of the ambient air over
the cold water basin which actually creates the differential,
thus cause the natural draft or “Stack Effect.”
How it Works
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What is a
Natural Draft
Cooling
Tower?
A Few
Important
Terms
Components
How it Works
Remarks
•
Step 4 - As this differential is being produced the shape of
the tower itself, the hyperbolic shape, induces current
upwards.
Remarks
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What is a
Natural Draft
Cooling
Tower?
A Few
Important
Terms
Components
How it Works
Remarks
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This system is over all extremely efficient and typically
requires no fans or mechanical means to cool the water.
Very common practice now due to the structures strength
and minimum required materials to construct.
Efficiency of the tower depends on the ambient
temperature.