api - cooling tower

The amount of water needed for cooling in a large refinery is in the range of thousands/millions of barrels per day.. HOW COOLING TOWERS COOL WATER To boil water, a source of energy is

COOLING TOWERS

SECTION 1

OPERATION AND CONSTRUCTION

‘There are exhibits placed in the center of the book that will be referred

to later in the program They should be removed and set aside now so

that they will be handy when needed

5

1 Á reñnery uses as much as 25 barrels of water for every barrel

of crude processed

A 200,000-barrel-a-day refinery might use as much as

——_ — barreÌs oÍ water

Of all the water used by a refinery, 80 to 90% is used as cool-

ant to absorb — _—— _ energy :

3 Look at tnis heat exchanger

COOL WATER

CooL, LIQUID

As the liquid travels through the pipe, the heat from the

liquid is exchanged or transferred to the 7

4 Heat always travels from areas of higher temperature to areas

of (higher/lower) temperature

5, Water can absorb only so much heat

As water becomes hotter, its effectiveness as a coolant (in-

creases /decreases)

6 After a while, the temperature of the water becomes so high

that it can no longer absorb _ from the hot

liquid

7 The water in this heat exchanger works as a coolant only as

long as it is than the liquid being cooled

8 Maximum cooling is achieved by constantly replacing hot

water with — — water

In order to provide for further cooling, two things are possible

First, the hot cooling water can be discharged and

with fresh water

Or, the hot coolïng water can be and reused

for further cooling

The amount of water needed for cooling in a large refinery is

in the range of (thousands/millions) of barrels per day

Drawing millions of barrels of water per day from the water

supply would be extremely

The amount of water needed is so large that many water sup-

plies (would/would not) be able to provide enough

Arefinery must be careful about the quality of the water it

discharges

Discharging millions of barrels of hot water per day might

cause a — ——— — problem

Cooling the hot water enables the refinery to

water over and over again

The best way to handle hot water is to (discharge it/cool and

reuse it)

Hot water is cooled for reuse in special cooling

METHODS OF HEAT TRANSFER

18

19 As séction A becomes hot, it acquires thermal, or

Suppose a steel rod is heated at one end

21

22

23

As one section of the steel rod becomes hot, the rod (conducts/

does not conduct) the heat to the colder sections

In this example, the heat transfer from section A to C (occurs/

does not occur) by conduction

Conduction occurs when heat or thermal energy flows

through a substance from a._== toa

The cold bar becomes hot first at the point of

Then, the heat is transferred through the bar by

Another method of heat transfer is convection

WATER

The burner heats the water in the vessel (all at once/at the

bottom only)

As the water at the bottom of the container gets hot, it be-

comes less dense

A volume of hot water weighs (more/less) than the same

volume of cold water

As the water at the bottom of the vessel gets hot, it will (float

to the top/stay at the bottom)

In this case, heat is carried to other parts of the vessel by

(conduction/physical movement)

3

conducts occurs higher; lower

will transfer

contact conduction

at the bottom only

less

float to the top

À physical movement

31 Convection is the transfer of thermal or heat energy by actual

within a substance

82 Heat transfer also occurs in another way

If you bring your hand near any hot object you (feel/do not

feel) the heat from it

33 Usually, solids, liquids or gases have a high enough tempera-

ture to emit or yadiate_ energy

34 This method of heat transfer or flow is called (convection/

radiation)

Review

„ 85 There are three methods of heat transfer: radiation, conduc-

tion, and

86 Heat flowing within a substance from a higher temperature

region to a lower temperature region is being transferred by

As it enters, the cold air absorbs thermal energy and becomes

88 As the air becomes hot, it rises and leaves the duct, taking its

energy with it

39 The method of heat transfer by physical movement is called

physical movement

feel heat, or thermal radiation

convection

conduction

hot heat, or thermal convection

HOW COOLING TOWERS COOL WATER

To boil water, a source of energy is needed

The molecules in any body of water move due to the heat

in them

The speed of the molecules depends upon the amount of heat

energy in them The more heat, the the

In any body of water, some molecules move faster than others

The molecules which move faster have (more/less) heat

energy

Some molecules move fast enough to break away from the

body of water and mix with the air

The molecules that break away first have a (higher/lower)

amount of heat energy

As the molecules leave the body of water, they take their

energy with them

The molecules that remain have a lower level of heat energy

With a lower level of energy, these molecules move (slower/

faster)

In order for them to escape from the body of water, the slow-

moving molecules have to ïm speed

Adding heat energy to the molecules will cause them to move

Once moving fast enough, the molecules will escape This )

After partial evaporation, a body of water (is cooler/stays the

same)

Cooling towers are designed to expose hot water to the air

This (allows/ does not allow) partial evaporation of the water

This partial evaporation (cools/does not cool) the water

What Affects Evaporation

52

53

In order for water to evaporate, it (needs/does not need) to

be in contact with air

The ‘larger the surface in contact with air, the (more/less)

molecules can leave a body of water at a given time

needs

more

The more water molecules that leave a body of water at a

given time, the (faster/slower) the rate of evaporation

These two basins contain the same amount of water

The rate of evaporation is faster from basin (A/B)

The faster the rate of evaporation from a body of water, the

(faster/slower) the body of water will cool

Cooling towers are designed to provide the hot water with a _

surface-to-air contact

The hotter the water, the more (fast/slow) -moving molecules

in it

Hot water will evaporate —————— — _ than cold water

Atmospheric pressure (exerts/does not exert) pressure on a

body of water

7 61, Atmospheric pressure (resists/does not resist) the molecules

escaping from a body of water

- 62 It is easier for water molecules to leave a body of water at (high/low) atmospheric pressures

63 As air acquires moisture (water molecules), its humidity

64 Air can hold only a certain amount of water molecules If it

becomes water saturated, it will no longer

water molecules

⁄ 65 The higher the humidity of the air in contact with the water, the

the rate of evaporation

66 Hot water evaporates ata (higher/lower) rate than cold water

/ 87 Which of the following affect the rate of water evaporation:

/

a) humidity of the air

b) surface of contact between water and air

c) the temperature of the water

CONSTRUCTION OF COOLING TOWERS

68 In the early days of continuous processing, no attempt was

made to cool process water Water that was cool already was ®

taken into the plant from the outside, then disearded when hot,

Z When a plant was loeated near a river or stream, the cool water 8 3 was taken into the plant upstream and released _ downstream -; „

69 When a plant was not located near a river, the water was taken

from a pond Hot process water was returned to the pond từ, iN surface and cooled by surface exposure to the _ air, or atmosphere

70 The open pond cooling system was eventually modified

71 By spraying the hot water, more water-to- — air

surface contact is reached

72 With a larger water-to-air surface contact, the rate of evapora-

573 However, wind could blow away the sprayed water, resulting

é

74 The spray pond system was also modified

To reduce water loss due to drift, and to prevent property se

damage, this system includes around the pond 1 fences, orswal

As evaporation occurs, the air in contact with the water

becomes (more/less) saturated

As the air becomes more saturated, the rate of evaporation

The air over pond B never becomes saturated because it is

The rate of evaporation is more constant in pond (A/B)

The rate of evaporation in the open pond, the spray pond,

and the spray type cooler is greatly affected by the prevailing

The rate of evaporation is also affected by the

Exhibit 1 shows an atmospheric cooling tower

This cooling tower, like a pond system, depends on the

velocity and the relative _

of the air

Some of the wind entering the tower is carried upward, but

most of the wind blows straight the tower

The wind flow through the tower is interrupted and changed

The louvers help direct wind and also prevent water

The hot air and water vapors leaving the top of the tower

Some atmospheric cooling towers have adjustable sections of

control of air flow

878 The splash bars slow down the fall of water and break it up

Cooling Towers

EXHIBIT BOOKLET

NATURAL~ DRAFT COOLING TOWER

EXHIBIT 3

FORCED-—DRAFT COOLING TOWER

HOT AIR DRIFT ELIMINATOR

INDUCED-DRAFT COOLING TOWER (CROSS-FLOW)

INDUCED-DRAFT COOLING TOWERS

The longer contact of water with air causes quicker

and faster —_ — _ thanina spray pond

Due to evaporation and drift, there is some water a

which has to be replaced with makeup

As the quantity of air passing up and through the cooling tower

changes, water loss due to evaporation and drift

The longer air remains in a cooling tower, the (more/less)

moisture it absorbs

the more moisture the air contains, the ‘faster/slower) it

accepts more moisture

In order to get maximum evaporation in a cooling tower, the

air should pass through (quickly /slowly)

Look at this drawing

DIRECTION OF PREVAILING WIND

—

IRí ÿ

More evaporation will take place in tower (A/B)

For best operational results, atmospheric cooling towers

should be placed so that the prevailing wind blows through

the (shortest /longest) dimension of the tower

In an atmospheric cooling tower, a 10-mile-per-hour wind will

cause (more/less) cooling than a 1-mile-per-hour wind

Without wind, an atmospheric cooling tower operates (more

efficiently /less efficiently)

Atmospheric cooling towers are designed to operate best under

the normal prevailing wind conditions at each site

If wind velocity is much higher than normal, there will bea

higher than normal loss of water due to (drift /evaporation)

High winds will cause water to be blown from atmospheric

cooling towers Such towers are placed so that’ water blown

from them will not cause to surrounding

bee „ evaporation cooling loss water

When cooling water 10°F by evaporation, one percent of the

water is lost due to evaporation In cooling 100 gallons of

water 10°F, a tower loses gailon(s) of water

Drift loss is usually about 0.2% of the water flow or about

gallon(s) per 100 gallons

Makeup water is is used to replace water loss due to _,

, or leaks

If there are no leaks and a cooling tower cools 100 gallons of

water 10°F, there will be gallon(s) of water

loss due to evaporation and gallon(s) due to

An atmospheric cooling tower depends upon wind

and the relative of the air for effective operation

The spray of water falling down the tower is broken up into

Small droplets by _mmL._ bars,

In atmospheric cooling towers, evaporation and drift are

major causes of water

For best operational results, the atmospheric cooling towers

are placed so that the prevailing wind blows through the

(shortest /longest) dimension of the tower

Atmospheric cooling towers usually operate hest at (high/

moderate) wind velocities

The towers are located so that water blown from them will

not nearby buildings or equipment

Natural-Draft Cooling Towers

111

112

118

Heat in a furnace causes hot flue gases to flow

through the stack causing a draft

Exhibit 2 shows a natural-draft cooling tower The top part

0.2 evaporation drift

velocity humidity

bars

The splash bars break the falling water into fine drops in order

to provide better air-to- contact

Some of the heat in water transfers to the air As the air

heats up, it becomes (lighter /heavier)

‘When it is light enough, the air _ in the chimney

“ne heateu air is replaced with cold air that enters the tower

Because of its design, a natural-draft tower (does/does not)

depend as much on the wind direction as the atmospheric

tower

The temperature of the air inside the chimney is always

than the atmospheric temperature

Louvers or baffles at times are installed around the air inlet

of the natural-draft tower

nh louvers or baffles (can/cannot) control the amount of

air entering the tower

By regulating the amount of air entering the tower, the

amount of cooling due to can be regulated

Mechanical-Draft Cooling Towers

Atmospheric cooling towers depend upon the natural flow of

up and across the falling water

Natural-draft cooling towers create an upward flow of

through the falling water

Exhibit 8 shows a forced-draft cooling tower The air flow

through the falling water is produced by

The internal construction of a forced-draft cooling tower is

similar to an atmospheric tower, but the sides are-

Motor-driven fans force air into the tower through openings

near the_ —_—— ——— of the tower

11

water

“|

lighter \ » tel rises

SS air inlet does not

The cooling of the water in all towers depends mainly on the

amount and of air passing through

Fans used in forced-draft cooling towers should produce a

large of air with a low velocity

Both mechanical-draft and atmospheric towers are provided

due to air velocity -

If one or more of the fans is shut down, the cooling rate is

due to low -to-water contact

The degree of cooling can be adjusted by controlling one.or

more of the — and the rate of —_———— fiow

Induced-Draft Cooling Towers

In a forced-draft cooling tower, the fans (push ‘pull) the air

through the tower

Look at Exhibit 4 In the induced-draft cooling tower, the fan

is located at the of the tower

As the fan rotates, it (pulls/pushes) the air through the tower

The air is driven upward.from the top of the tower, where it

can be carried away easily by the

This reduces the possibility of wet air reentering the

at the bottom

Exhibit 5 shows two types of induced-draft cooling towers

The tower with its sides open is the — type

In the counterflow type, the largest part of the tower has

sides

In a tower with solid sides, the induced air travels most of the

time in (the same direction as/an opposite direction from) the

Both towers have movable side louvers to regulate the

intake

In both towers, the air volume flowing through the tower is

controlled by the of the fan and the amount

of opening of the side

i-Cell Cooling Towers

Large cooling towers are usually constructed in cells or sections

which can be operated independently

The cooling capacity of a multi-cell cooling tower can be de-

creased by taking one or more _-_— out of service sections, or cells This is g lower side view of an atmospheric cooling tower

CELLS

The drawing indicates that the tower has — _— cells three

47 If a tower with only one cell needs cleaning or repairs, the

48, Any cell can be operated independently If one cell in a multi-

cell tower must be shut down, the entire tower (must also be/

Review

149 An atmospheric cooling tower depends greatly upon the

150 The natural-draft tower is constructed in such a way that it

(151 Mechanical-draft towers depend upon motor-driven

159 The induced-draft tower (pushes /pulls) air through the tower pulls

158, A tower with fans at the bottom is (an induced /a forced) a forced

-draft tower

154 All cooling towers cool water primarily by the : process of * evaporation

155 The rate‘of evaporation of water depends upon the water

surface-to-air contact and on the relative —————————— humidity

of the air

13

The greater the water-to-air surface contact, the

the rate of evaporation

The greater the water-to-air contact, the more

is accomplished

- The splash bars in cooling towers break up the spray of water

into smaller droplets as well as prolonging the water-to-

+ contact

If the air passing through a cooling tower is water-saturated

to the maximum, there (will ‘wil] not) be any cooling due to

evaporation

If there is no evaporation taking place, but the air is cooler

than the water, there will be (no,some) cooling due to con-

duction, convection, and radiation

In a cooling tower there is always some cooling of water due

to conduction, convection, and

However, most of the cooling of water in a cooling tower is

accomplished by

In any other type of cooling tower, drift eliminators are needed

to minimize water because of the wind

However, in a natural-draft cooling tower, drift eliminators

_(are/are not) used

Any cooling tower is subject to water losses produced by drift,

leaks, and evaporation

These losses are compensated for by water

In mechanical-draft towers, the volume of air passing through

the tower can be adjusted by controlling one or more of the

Controlling the volume of air passing through the tower

(controls/does not control) the amount of cooling

It is easier to control the amount of cooling in a(n) (atmos-

pheric/mechanical-draft) cooling tower

Mechanical-draft towers (can/cannot) regulate or control the

amount of air passing through the tower

They cannot control the relative of the air

They cannot control the temperature of the

used for cooling

Mechanical-draft towers 'can control the amount of air

passing through them, as well as the _—— of

evaporation of the water

When iron is exposed to water and the oxygen in the air, it

- In a cooling tower, practically all parts are exposed to

and

Iron and carbon steel are used to a very limited extent in

cooling tower construction because they corrode or rust

(rapidly /slowly)

The best grades of California redwood are used because they

resist corrosion caused by _ and

Metals which resist corrosion are used in certain parts of red-

wood towers Copper-coated nails resist

Cast-iron is used in anchoring members that hold the tower

on its concrete basin, but it does corrode and has to be

occasionally

Brass bolts, washers, and nuts are used because they also

corrosion and rust

Fir wood is used as well as redwood because it resists rot due

to moisture Like fir, synthetic materials such as tensile, fiber-

glass, and other plastics resist moisture rot (poorly,’well)

Although some wood resists corrosion and rot and has rela-

tively little expansion due to heat, wood swells when it absorbs

water and when it dries

Expansion and contraction from either temperature change

or water content change can

Treating the tower wood with creosote increases its resistance

to oth water-logging and moisture

Synthetic materials are (more/less) damaged by corrosion,

water-log and rot than wood

Regardless of the material used in construction, cooling towers,

like other reñnery units, should be _ _ peri-

odically for structural soundness

Cooling Tower Mechanical Equipment

186 The fans on forced- and induced-draft towers are driven by

187

188,

electric

The pressure necessary to circulate the cooling water through

the plant cooling water system is provided by direct-acting

steam or motor-driven _-. -

All mechanical equipment with rotating or moving parts must

be lubricated on a definite schedule to prevent excessive

189 The operator must lubricate equipment regularly and

— _ all equipment daily for other conditions

which require repair or replacement

CONDITIONS AFFECTING COOLING TOWER PERFORMANCE

190 The most important factor in any kind of cooling tower is how

fast the water

191 Therefore, any condition which prevents water from evapo-

rating _mWms _ the efficiency of the cooling tower

192 Air contains moisture or water vapor

On a damp day, the air holds (a lot of /very little) water

198 If the air surrounding a cooling tower is very humid, the water

in the cooling tower does not evaporate as much as it would

if the air was

194 On damp, humid days, a cooling tower works (better than/

not as well as) it does on dry days

195 One factor that affects the rate of evaporation is the amount

of _ in the air in contact with the water

Absolute and Relative Humidity

196 Air becomes denser as the temperature decreases

Air is densest when temperatures are (very hot/very cold)

197 More moisture can be contained in air if it is less dense

Very cold air can contain (more/less) moisture than hot air

198 Temperature (is/is not) an important factor in measuring

humidity

199 Here is one way to express humidity measurements

Suppose we have a humidity measurement that reads 1 pound

of water in 10 pounds of air This reading is expressed as

(degree of saturation/weight per given volume)

200 Pound is an expression of a specific quantity

1 pound and 10 pounds are (relative/absolute; expressions

bsolute humidity readings tell how much water is in a given

quantity of air, but (do/do not) tell how much more water

the air can absorb