Chapter 5

Power Plant Engineering

Chapter 5 Condenser and Evaporative Cooling Towers

Chapter 5- 1

CHAPTER 5

CONDENSER AND EVAPORATIVE COOLING TOWER

5.1. Condenser .................................................................................................. 2

5.2. Evaporative Cooling Tower ..................................................................... 2

5.2.1. Major Components...............................................................................................3



5.1. Condenser Condenser is a shell-and-tube heat exchanger. Steam that comes from turbine goes to

the shell side of condenser while cooling water flows in the tubes. Steam transfer it energy to

the cooling water, and thus it condenses. The condensate is accumulated at the bottom of the

condenser, and then it goes to main feedwater pump as saturated liquid.

The temperature distribution of steam and cooling water is shown in Figure 6.1.

Tc,in

Th,in Th,out

Tc,out

LMTDITD

TTD

TR

Tsat Steam

Cooling Water

Figure 6.1. Temperature distribution of condenser.

In Figure 6.1, ITD = Initial Temperature Difference

TTD = Terminal Temperature Difference

TR = Temperature Rise in condenser

LMTD = Log Mean Temperature Difference

5.2. Evaporative Cooling Tower Cooling Towers have one function: Remove heat from the water discharged from the

condenser so that the water can be discharged to the river or recirculated and reused.

Some power plants, usually located on lakes or rivers, use cooling towers as a method of

cooling the circulating water (the third non-radioactive cycle) that has been heated in the

condenser. During colder months and fish non-spawning periods, the discharge from the

condenser may be directed to the river. Recirculation of the water back to the inlet to the

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Chapter 5- 3

condenser occurs during certain fish sensitive times of the year (e.g. spring, summer, fall) so

that only a limited amount of water from the plant condenser may be discharged to the lake or

river. It is important to note that the heat transferred in a condenser may heat the circulating

water as much as 40 degrees Fahrenheit (F). In some cases, power plants may have

restrictions that prevent discharging water to the river at more than 90 degrees F. In other

cases, they may have limits of no more than 5 degrees F difference between intake and

discharge (averaged over a 24 hour period). When Cooling Towers are used, plant efficiency

usually drops. One reason is that the Cooling Tower pumps (and fans, if used) consume a lot

of power.

5.2.1. Major Components

Cooling Tower (Supply) Basin

Water is supplied from the discharge of the Circulating Water System to a Distribution Basin,

from which the Cooling Tower Pumps take a suction.

Cooling Tower Pumps

These large pumps supply water at over 100,000 gallons per minute to one or more Cooling

Towers. Each pump is usually over 15 feet deep. The motor assembly may be 8 to 10 feet

high. The total electrical demand of all the Cooling Tower pumps may be as much as 5% of

the electrical output of the station.

Cooling Towers

There are 2 types of towers - mechanical draft and natural draft

Mechanical Draft Towers

Mechanical draft Cooling Towers have long piping runs that spray the water downward.

Large fans pull air across the dropping water to remove the heat. As the water drops

downward onto the "fill" or slats in the cooling tower, the drops break up into a finer spray.

On colder days, tall plumes of condensation can be seen. On warmer days, only small

condensation plumes will be seen



Natural Draft Towers

This photo shows a single natural draft cooling tower as used at a European plant. Natural

draft towers are typically about 400 ft (120 m) high, depending on the differential pressure

between the cold outside air and the hot humid air on the inside of the tower as the driving

force. No fans are used.

Whether the natural or mechanical draft towers are used depends on climatic and operating

requirement conditions.

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Simplified Diagrams

The diagrams below illustrate the arrangement of components within the system and the

major flow paths.

Forced - or Natural Draft Cooling Tower

The green flow paths show how the water is taken from a river (yellow) to an intake supply

basin (green) that the Circ Water Pumps take a suction from. The water is then pumped to the

Condenser where the water is heated.

The water is then sent to an exit distribution basin where the water then can be returned to the

river and/or pumped by the Cooling Tower Pumps to the Cooling Towers then the water

returned to the intake supply basin where the water can be reused.

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Natural Draft Cooling Tower

The green flow paths show how the warm water leaves the plant proper, is pumped to the

natural draft cooling tower and is distributed. The cooled water, including makeup from the

lake to account for evaporation losses to the atmosphere, is returned to the condenser.

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Chapter 5- 7

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