Cooling Tower Section 1 API

8/20/2019 Cooling Tower Section 1 API

1/44

COOLING TOW RS

SECTION

OPERATION ND CONSTRUCTION

There a e exhibits placed

in

the center of

Ihe

book that

will be

referred

to later in the program. The J should

be

removed

and

set aside now

so

Ihal they

will be

handy

when needed.

1.

A refinery uses

as much as

25 barrels of

water

for every

barrel

of crude processed.

A 200,OOO·bal l ei-a-day refinery

mi

g

ht

use as much as

barrels of water.

. 2. Of all

the water

used

by

a refinery, 80

to

90 is used

as

cool-

•

ant to absorb energy.

3. Look

at

tn15

heat

exchanger.

HOT

COOL

~ L I Q U I D

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

liquid is exchanged or transferred

to

the _ _

4. eat always travels from areas of higher

te

mperature

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/ d ocreases).

6. After a

while,

the temperature

of

water

becomes so hillh

that

it

can no

longer absorb from

the hot

liquid .

7.

The

water in

this

h

eat

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.

1

•

5,000,000

heat

water

lower

decreases

heat

cooler

coo1


2/44

9. 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

cooling water can he and reused

or further cooling.

he amount o water needed for cooling in a large refinery is

in

the

range of tho.usands/millions) of barrels per day.

of barrels

o

water per

day from

the water

supply would

be

extremely

The amount

of

water needed

is

so large

th t

many water sup-

plies would /would not) be able

to

provide enough.

A refinery

must

be careful about the qu lity 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 liest way to handle hot water

is

to discharge it / cool and

reuse

it .

. Hot water is cooled for reuse in special cooling

OF HE T

TR NSFER

Suppose

a

steel

rod

is heated

t

one end.

c

The entire rod heats up evenly./Section gets

hot

first.)

19.

AJ

s ~ t o n

A becomes hot,

it

acquires thermal, or

energy.

•

20. Thermal, or heat, energy always travels from higher

to

temperature regions.

2

replacE'(t

cooled

millions

c o ~ t l y or expE'nsive

would not

pollution

reuse

cool and reuse it

tower :::

,

Section gets hot first.

he t

lower


3/44

21

s

one seetion

of

the steel rod beeomes hot,

the

rod (conducts/

does not

conduct) the

heat

to the colder sections.

22 In this example, the heat

tran

sfer from section A to C (occurs/

does not occur) by conduction.

3 . Conduction occurs when heat or thermal energy flows

through a

substance

from a

to a

temperature region.

24 Suppose a hot baT of steel is placed in contact with a cold one.

COLO

BAR

HOT BAR

B

POINT OF CONTACT

A

The. heat energy from baT A (will transfer/will not transfer)

to

baT B

25 The cold bar becomes hot first

at

the point

of

_ _

26

. Then,

the heat

is transferred through the bar by

27 Another method

of heat

transfer is convection.

WATER

rn BURNER

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

the

bottom only).

28

. 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.

29

s

the

water

at

the

bottom of the vessel gets hot,

it

will

(float

to the top/

stay at

the bottom).

30 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

fioat to the top

physical movement


4/44

31. Convection

is

the transfer of thermal or heat energy by actual

within a 5ubstance.

3

.

Heat

transfer also occurs in another way.

f you bring your hand

near any

hot object you

f l

/

do

not

feel) the heat from it.

33. Usually solids liquids

or

gases have a high enough tempera-

ture

to

emit

radiate

energy.

34. This method of heat transfer or flow

is

called convection /

radiation).

Review

35. There are three methods of heat transfer:

r d

iation conduc-

tion and

36. Heat flowing within a substa:lce

from

a higher temperature

region

to

a lower temperature region is heing transferred

by

37. This shows a flame heating the bottom opening

of

, duct.

~

OLD

AIR

Ai;

it enters

the

cold air absorbs thermal ener

gy

and

e c o m ~

88. As the air becomes hot

it

rises and leaves

th

e duct taking

its

energy with it.

39. The method of heat traMler

by

physical movement is calleu

4

physical movement

feel

hent

or

thennal

radiati on

.

.

convection

conduction

hot

heat, or thennal

convection

•


5/44

HOW COOLING

TOWERS

COOL W TER

Result,

f

Evaporation

•

;-. 40. S o r r ~ Conn of energy is required for any movement or change

in matter.

o boil water) a source of _______ energy is needed.

41.

The

molecules in any body

of

water move

due to

the

heat

_______ in them.

42.

The

speed of the molecules depends upon the

amount

of

heat

energy in them.

The

more heat, the the

molecules

move

.

43.

In

any body of wat

er

some molecules move faster than others.

/

/

The

molecules which move faster have (more/ less) heat

energy.

44. Some molecules

moYe

fa st 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.

45.

As

the

molecules leave the body of water,

_______

energy with them.

they take their

46. The

,

olecules that remain have a lower level of heat energy.

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

faster

.

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

moving molecules have to in speed.

48. Adding heat energy

to

the molecules will cause them to move

?nce moving fast enough, the molecules will es;ap:. ·;hi;

IS

evaporahon

_

. ._- . _

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

same).

5O I ;Cooling towers are designed to expose hot water to the air.

This

(a

llows/ does not allow) partial evaporation of the wate r.

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

hat Affects Evaporation

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

to

be in contact with air.

53. The larger the surface in contact

wi

th air, the (more/1ess)

molecul

es

can leave a body of water at a given time.

5

•

heat

energy

•

faster

more

higher

heat

slower

increase

faster

is cooler

allows

cools

needs

more


6/44

\ :

54. The

more

water molecules that leave a body

or

water at a

given time, the (faster/ slowe, ) the rate of evaporation.

55. These two basins contain the same amount of \vater.

A

8

The rate of evapOl ation is faster from basin A / B).

56.

The

faste, the

rate

of evaporation from a body of water, the

(fasteri slower) the body of water will cool.

57. Cooling towe S are designed to provide the

hot

water with a

_ surlaceato-air contact.

58 .

The hotter

the water, the more (fast / slow) -moving molecul.s

in it.

59. Hot water will evaporate than cold

lVater.

.

Atmospheric pressure exerts /does not exert) pressure

on

a

body of water.

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.

f

it

becomes water saturated it will no longer

water molecules.

/ 65 .

The

higher the humidity of th e air in

contact

with the water,

the the rate or evaporation.

eview

•

66. Hot

water evaporates

at

a (higher/ lower)

rat

e than cold water.

/ 67 . Which

of

the following affect the

rate

of water evaporation:

a) humidity of the air

b) surface

of

contact

e t w e ~ n

water and

air

c) the temperature of the water

6

faster

B

faster

large

fast

faster

exerts

resist '

low

rises, or increases

slower

higher

n;b;c

·t· . : ,:

: '

'

' , .

.

;. ,


7/44

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 discarded when hot.

/

When a plant was located near a river or stream, the cool water

was taken into the plant upstream and released

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

surface and cooled by surface exposure to the

70. The open pond

coo

ling system was eventually modified.

HEAT EXCHANGER

COOL

WATER

SPRAY POND COO LING SYSTEM

In this system, hot cooling water is over the

pond surface.

71.

By spraying

the

hot water, more water-to-

surface contact is reached.

72. With a larger water-te-air surface contact. the rate of evapora

tion increases/ decreases).

~ 7 3 .

However, wind could blow away the sprayed water, resulting

in water and damage to

nearqy

structures.

,

.

74.

The

spray pond . ystem was also modified.

,

FENCE

•

o reduce water loss due to drift, and to prevent property

damage. this system includes _ around the pond.

7

'

.'

downstriam

' . '

.

• 1

·

. '

.. ,,:

'. ,

. .

--,. .

:.; , .,

,

.'

I

,

air

or·itmosph r

; . ~ ~ .

.,. .

:

,

,.

:;.;..,

.

'.

. ' ; .:; ; .6

.'

sprayed

air

. .

Increases

.,.

.


8/44

75

he

air contacting both of these ponds

is

at the same humidity

level.

O

WINO

" ' U ~ l u A I R

WINO

B

As e v p o r t i o ~ occurs, the air in conlact wilh th water

becomes (morelless) saturated.

76. As the ail becomes m Te saturated, the rate of evaporation

77 . he air over pond B never becomes saturated because it is

constantly being with new air.

78.

he

rate of evaporation is mnre constant

in

pond (A/ B).

79.

he

rate

of evaporation in the open pond, t

he

spray pond,

and the spray type cooler

is

greatly affected by the prevailing

80.

he

rate of evaporation

is

also aflected by the .

of

the

air.

Atmospheric Cooling Towers

81. Exhibit 1 shows an atmosphen c cooling

tower

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

_ : _ .

_ velocity and the relative _

_

of the air.

82. Some of the wind entering the tower is carried upward,

but

most of the wind blows straight the tower.

83

.

he

wind flow through the tower is interrupted and changed

by the and bars

84. he louvers help direct wind and also

prevent

water

/

85.

he

hot air and water vapors leaving the top of the tow

have to pass through

the

.

86. Some atmospheric cooling towers have adjustable sections of

and drift to aid

in

the

control of air flow .

87 ':The splash bars slow down the raU of water and break it up

into small

8

more

decreases

replaced

B

wind

humidity

wind; humi dity

through

louvers ; splash

loss

drift eliminators

.

. . .

louvers

; e

liminators

.

drops

. .

.

.

l , ,


9/44

, ,

, ,

Cooling T W ~

i

, "

, , .'

EXHI IT

OOKLEY

, "' j

" ( " ' j ':

.

. :

::::

"".':

'

,

"

,: .. .

:;

':

:

.

,

, , ,

-,

.' , .

:

.

.

,

" . ,

'

;.

'.

I .

:. " . · r ·

,

It

, -

:.

.

:

'. .' .

"

, ,

.

"

. .

, ,


10/44

=::>

COOLED

WOTl :

BASIN

ATMOSPHERIC COOLING

TOVIER

j'

:\

,

..

_ _ _?HOT AIR

ANO

WATER VAPO j

.

/

FROM HO

'

WATER

I

,

•

I·

,

,

" '".oC l

. I

i

J

;

,

•

,

j

-

1 1 r b ~ ~ ~ ~ ~ ~

MAKE

-

WATE

CO

OL

WATER

,

, ,

- : ,

. ' , .

: j l

. . ...,

-,

. • I ~

I .


11/44

I

.

l . ,,

;,

NATURAL - DRAFT COO LING TOWER

HOT

AIR AND W

ATER

VAPOR

•

I - -CHIMNEY

. HOT W4-r


12/44

FORCEO ORAFT

COOLING TOWER

HOT AIR

DRIFT

M N AT OR

HOT WATER N

SPLASH BARS

SO

LID

SIDES

S

~ O O L E D

WATER BASIN

COOL WATER


13/44

. .I .

WAT. Q B SIN

INDUCED-DRAFT COOLING TOWER (CROSS-FLOW)

HOT l ND

V POR

ROSS FLOW

IR

M KEUP W TER

COOL W TER


14/44

INDUCED DRAFT COOLING TOWERS

A.

COUNTERFLOW

I R ~

AIR

B. CROSSFLOW

...... -

LOUVERED

SIDES


15/44

88. The longer contact

of

water with air causes quicker·

and faster than in a spray pond.

89. Due to evaporation and drift, there is

some

\vater

which has to be replaced with makeup

90.

s

the

quantity

of air passing up and through the cooling tower

changes, water loss due to evaporation and drift

91. The longer air remains

in

a cooling tower, the (more / less)

moisture

it

absorbs.

92. he

more moisture the al contains, the :faster/ slower)

it

ac(:.epts more moisture.

93. In order to

get

maximum evaporation in a cooling tower, the

air should pass through (quickly/ slowly).

94. Look at this drawing.

D

IRECTIO

N OF

PREV ILING

WIND

-

A

B

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

95. For best operational results, atmospheric cooling towers

should be placed

so

that the prevailing wind blows through

the (shortest / longest) dimension

of

the tower.

/96 :

In

an

atmo

spheric cooling tower, a lO-mile-per-hour wind

wi l

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

97. Without wind, an atmospheric cooling towe l operates (more

efficiently/ less efficiently).

9

. Atmospheric cooling towers are designed

to

operate

best

under

the

normal prevailing wind conditions at each site.

f wind velocity is much higher tha n normal , there will be ...

higher than normal loss

of

water due to (drift/ evaporation).

99. High winds

will

cause water to be blown (rom atmospheric

cooling towers. Such towers are placed so that water blown

from them will not cause to surrounding

buildings or equipment.

9

.

evaporation

cooling

loss

water

changes

more

slower

quickly

A

shortest

more

less efficiently

drift

damage


16/44

100.

Whenever watel is cooled by evaporation,

1

here

IS

always

some water

_

101 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 ga;lon(s) of water

due

to

102 Drift loss is usually about 0.

2 of the

water

flow

or about

gallon s) per 100 gallons.

'

103 . Makeup water is used to replace water loss due 10

or leaks.

104. If there are no leaks and a cooling tower cool s 100 gallons of

water 10°F, there

will

be gallon s)

of

water

loss due

t

evaporation

and

, alIon(s) due

t

drift.

eview

105.

An atmospheric cooling tower depends upon wi

nd C _

and

the

relative of

the

air for effe


17/44

. he splash bars break the falling wa

ter

into fine drops in order

to provide better air-to- contact.

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

heats uP. it beeomes (lighter/heavier).

When it

is

light enough. the air

in

the chimney.

; J.l1e heateu air is replaced with co ld air that

e n t e ~ s

the tower

through

the

Beeause of its design. a natural-draft tower (does/ does not)

depend as much on the wind direction as the atmospheric

tower.

rature of th e air inside the chimney is always

_

than the atmospheric temperature.

. This difference in temperature causes a constant _

to exist.

he natural-draft cooling tower (needs/ does not need) drift

eliminators.

Makeup water is needed to replace water loss due to leaks

and

. Louvers or baffles

at

times are installed around the air inlet

of the natural-draft tower.

9p.ch louvers or baffles can / cannot) control the amount of

aIr

entering the tower.

.

y

regulating the amount of air entering the tower, the

amount of cooling due to can be regulated.

Cooling Towers

Atmospheric cooling towers depend upon the natural

flow

of

up and across the falling wate

r.

Natural-draft cooling towers create an upward

flow

of

h r o u ~

the falling water.

3 shows a forced-draft cooling tower. he air flow

through the falli ng water is produced by •

ernal construction of a forced-draft cooling tower is

c;imilar to an atmQspheric tower, but the sides are ,_

Motor...{ riven fans force air into the tower through openings

near the of the tower.

11

water

lighter

rises

air inlet

.-

\

\

.,

J

does not

_.

....

.

.

·

, ,

>

.

- -

'.

hi

gher, or warmer .

· .. . f

draft, 01

flow,

or

movemen

does not need

evaporation

can

evaporation

. aIr

au

fans ·

closed. or solid

bottom, or base

.

',

· . , .

, / :: \ '

. ',

,

.

I

, 'I ; 1

,

..


18/44

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

amount and D air passing throug

h

uSed

in forced-dra

ft

cooling towers should produce a

large of air with a low velocity.

2. Both mechanical-draft and atmospheric towers

are

provided

with

_ _

to prevent water

loss

due to air velocity:·

. f one

01

more of the fans is shut down, the cnoling 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 flow.

In a forced-draft cooling towel , the fans (push pull)

the

air

through the towe,

Look at Exhib

it

4. In the induced-draft cooling tower, the fan

is located at the of the tower.

7 s the fan ro

tate

s, it (pulls/ pushes) the air through the tower.

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

can be carried away easily

by the

_ _ _

. his reduces th e

po

ss ibility 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 ype.

In the counterflow type, the largest

part

of the tower has

ides.

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

time

in

the same

direction

as

/ an

opposite direction from)

the

falling water, •

Both towers

have. movable

s ide louvers to regulate the

- -

ntake.

.

In

both towers. the air volume flowing through the tower is

controlled by the of

the f n

and the

amount

of opening of t

he

side

12

humidity

volume. or amount

drift eliminators .

less; air

ans; air

push

top

pulls

wind

.,

i

cooling tower,

01

air intake

.

cro

ss

now

enclosed , or solid

•

an

opposite direction from

speed

louvers


19/44

-Cell Cooling Towers

Large eooHng towers are usually constructed in

ells

or sections

which can be operated independently.

The cooling capacity of a multi-eell cooling tower

c n be

de

creased

y

taking one

or

more out of service

. This

is

:lower side view of an atmospheric cooling tower.

The drawing indicates that the tower has cells

47 f

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

entire tower has to be

48 Any cell can be operated independently. f one cell in a multi

cell tower must

be

shut down, the entire tower (must also bel

need not be)

shut

down.

Review

149

An atmospheric cooling tower depends greatly upon

the

natural

velocity

for

effective operation.

150 The

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

causes its own

, 151 Mechanical draft

towers

depend

upon motor driven

o force the air through them.

152 The induced·draft tower (pushes/ pulls)

air

through

the

tower.

,153. A tower with fans

at

the bottom is (an induced / a forced)

-draft tower.

154 All cooling towers cool water primarily by the process of

155 The

rate

'of evaporation of water depends upon

the

water

surface-to-air contact and on the relative

of the air.

13

sections,

or

cells

three

shut down

need not be

wind

draft

.fans

pulls

a forced

•

.

evaporation

humidity


20/44

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

the rate of evapol·ation.

The greater

the

water-to·air contact, the more

__

_ _ _

is accomplished.

.

The .plash bars in cooling towers break up the spray

of

water

into smaller droplets as

well

as prolonging

the

water-to

___ --_

contact.

f the air passing th; ough a cooling tower is water·saturated

to the maximum, there

will

'

will

not) be

any

cooling due to

evaporation.

. f

there is no e aporation taking place,

but

the air

is

cooler

than the watel , there

will

be (no/ some) cooling du

' to on·

duetion, convection, and radiation.

In a cooling tower there is always some cooling

o

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 a

re

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 produc

ed

by drift,

ll? aks,

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 all'

passing through them, as well as the

__

_

o

evaporation of the water.

14

(aster,

or

greater

cooling,

or

evaporation

will

not

some

radiation

evaporation

loss

are not

makeup

ans

controls

mechanical·draft

can

humidity

'

•

ir

rate,

or

amount


21/44

nstruction aterials

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

it

4. In

a cooling tower, practically all

parts

are exposed

to

____________

and

__________

__

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

cooling tower construction because

they

corrode or

rust

(rapidlyIslowly),

76.

The

best grades of California redwood are used because they

resist cOT "osion caused by and ____ -_

77

.

laetals

WhlCh resist corrosion are used in certain

parts

of red-

wood towers. Copper-coated nails resist ______

78. Cast-iron is used in anchoring members

that

hold

the

tower

on its concrete basin, but

it

does corrode and has to be

_ _ _ _ _ _ _ _ _

occasionally,

179.

Brass boltS, washers, and

nuts

are used because they also

_______ corrosion and rust.

180. 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) .

181.

Although some wood resists corrosion and rot and has rela

tively little expansion due

to

heat, wood sw lls when

it

absorbs

water

and when

it

dries.

182. Expansion and contraction from either temperature change

or water content change

can _____

he tower structure.

188. Treating the tower wood with creosote increases its resistance

to 1.t0th

water-logging and moisture ________

__

184.

Synthetic materials are (more/ less) damaged by corrOS Ion,

water-log and,

rot

than

wood.

186. Regardless of the material used in construction, cooling towers,

like other refinery units, should be peri-

odically for structural soundness,

Cooling Tower Mechanical Equipment

186. The

fans on forced- and induced-draft towers are driven

QY

electric

____________

187.

The

pressure necessary

to

circulate

the

cooling water through •

the plant cooling water system is provided

by

direct-acting

steam

or

motor-driven

_ _

_____

188.

All mechanical equipment with rotating or moving

parts

must

be lubricated on a definite schedule

to prevent

exceSSIve

15

.

corrodes, or rusts

.,

water; air

rapidly

water;

ail'

corrosion

replaced

resist

well

'.

'I ' . , '

,

' ' J ' q

, i

contracts, or shrinks ;i

,

weaken

rot, or

damage

less

,

,

. ,

'

:

..,

,

.

.

•

. ;

.

¥

. :

./;

.

inspected, or checked

;'

.J" · . t

il

motors

pumps

wear

..

,

,

,

.

'.

. ,

. ' ,


22/44

The operator must lubricate equipment regularl y and

all equipment daily for other co nditions

which require repair or replacement.

AFFECTING

COOLING TOWER PERFORMANCE

. The most important factor in

any

kind of cooling tow. r

is

how

fast

the water

any

condition which prevents

water

from evapo-

rating

.'.

the

efficiency of the cooling tower.

Air contains moisture or water vapor.

On a

damp day,

the

air holds (a

lot of

/ very little) water.

f 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

On damp,

humid

days, a cooling tower works (be

ter

than

/

not as well as) it does on dry days.

that affects the rate of evaporation

is

t

he

amount

of in

the

air in

contact

with

the

\vater.

and

Relative Humidity

. Air becomes denser as

the

temperature decrea., s.

Air

is densest

when

temperatures

are

very hot

/ very cold ).

. More moisture can

be

contained

in

air if

it

is less dense.

Very cold air

can

contain (more/ less) moisture

than

hot air.

Temperature

(is / is not) an

important

factor in measuring

humidity.

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) .

Pound is

an

expression of a specific

quantity.

1

pound

and 10

pounds are (relative/ absolute) expressions

of

quantity

.

per quantity is (relative/

absolute) humidity.

Temperature is not considered in measurements

of

absolute

humidity.

~ t > s o l u t e

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.

6

check. or j n s p

evaporates

reduces

a lot

of

dry

o.

not as well as

humidity. or moisture

very cold

less

is

weight

per

given volume

a0so1ute

absolute

do not


23/44

. order tc know how much evaporation can take place, it is

_sary

to know how much more

the

air

absorb.

ipposewe have a humidity reading that says air at 85

0

holds

of the maximum it could hold

at that

temperature.

~ ~ \ ~ ~ ~ I ; ~ S expressed as degree of

saturation

/ weight per

humidity reading s given a

p ~ r c e n t a g e

of maximwn

Humidity erprE:S.Sed as a

f J f : ' T ~ n t a g e ot

maximum humidity at

a given t a n ~ t U e s rtlative / e;bso\utE: / humidity .

206. A r e I a t i . . - ~

humidity

reading doc do.,; not) give

an

indica·

tion of how much more wa ter air can absorb.

207.

f

air bolds all the water vapor it can hold at

any

temperature,

it

is

aaid

to

be

.208. The

relative humidity

o

air

at the point of saturation

lS

0 0

209.

AJ.

relative humidity increases, evaporation

210.

T h ~ \ . p e r f o r m a n c e of a cooling tower increases/ decreases) as

the

relative

humidity increases.

211.

Relative humidity is the least/ most) important variable

af·

fecting

the

performance of cooling towers.

Dry.and Wet-Bulb

Temperatures

212. This combination of thermometers and wick is a hygrometer.

'

THERMOMETER

The thermometers are identical except

that

one bulb s covered

bya

17

water .

degree of saturatio_n

relative

doos

saturated

100

decreases

decreases

most

'

•

wick


24/44

:213. Beeause the wick is saturated with water, the thermometer

I it covers is called a ·bulb thermometer.

214.

Evaporation has a cooling effect.

I

I

I f

the water in the wick

of

the wet-bulb thermometer is

evaporating, t

wiJ

show a (warmer/cooler) temperature than

the other thermometer. .

215. The

faster evaporation occurs,

the

(greater/ less) difference

there will be in flte readings.

216.

Evaporation will occur faster If the air surrounding the wick

is (moisUdry)

.

217.

In

dry air, the wet-bulb reading is always (lower/ higher) than

the dry-bulb reading.

218.

Suppose the dry bulb reads 90°F and the wet bulb reads 75°F.

100

90

80 %

90

/ b

/ .

f0

7

-.e

50 / · 0

0:

80

f-

w

~

70

:E

a:

W

:

./

V;

t =

/

/

V

0 V

/ .

V

V

v

V

y

V

0

'

:n

m

,

:.-

20 1

<

m

10

0

•

I

:x:

f-

ro

60

--'

=>

ro

f-

50

w

;0:

,,:

V V / V

t:

V V

./

V

/ V /

/

V

V

C

3:

>2

i

-<

40

;:::::

v::

V

:/

50

60

70

80

90

100

II: DRY UL TEMPERATURE

The

chart shows that the relative humidity is_____ .

ZI9. I f the dry bulb reads 60°F and the wet bulb reads GO°F, the

relative humidity is

.

l20. The greater the difference between readings, the (higher

lower) tbe relative humidity.

18

wet

cooler

greater

dry

lower

50

100

lower


25/44

, .

A sling psychrometer also measures relative humidity.

GAUZE

WICK

. .. .

.

. .

.. _- .

DRY

BULB

The operator whirls the sling psychrometer n the outside

atmosphere after saturating the wick with --'_

22.

f

the atmosphere

is

not

satura

ted , there will be _ _ _

readings on the two thermometers.

:23.

When the wet bulb reads lower t

han

the dry bulb, it

is

because

water

has

from

th

e wick.

124

Evaporation causes

25. Cooling tower performance is (highest / low est) when wet- 'and

, dry-bulb temperatures are equal.

Even when the air is saturated in the tower, some cooling

occurs

y

convection and conduction.

1Zl

Therefore

,

cooling

t owers do not depend entirely on

_ to accomplish cooling.

When the outside air

is

cooler than

the

water being cooled,

some cooling occurs due

to

radiation, and

even though none occurs due to evaporation.

228

)ve'\thoullh no evaporation occurs,

i

the air is cooler than

the

, water; heat IS transferred from

the

water

to the

.

.

229 . The heated air

then

carries the

heat

with

it

out of the tower

by

_ _ _

230

Cooling towers are never 100 efficient.

f

the

wet-bulb temperature is 65°F, that would be the n -

mum a pproach

temper ture of the water.

The

lowest possible water temperature after cooling with the

above condition would be

(6

0 F

above

65'F).

23I

The

efficiency of cooling towers, regardless of

type

increases

as the difference between wet-bulb and dry-bulb temperature

19

•

water

different

evaporated

cooling

lowest

evaporation

conveetion

conduction

convection

above

65 F

increases


26/44

Operation

The degree

or

cooling in cooling

towers in part

depends

on

the

amount of air flowing through the

In

addition il the air is hot and humid the degree 01 cooling

is (more/less) than when the air is cold and dry.

air temperature may result in too much

_

Water freezesat

3Z0F

In winter, air temperatw e well below 32°F may cause cooling

water to

on

parts of the coo

lin

g tower.

6. Because of more co ld air contact, water broken up into small

droplets freezes (faster/slower) than

if

it was in a solid stream.

(onnations may

~

_

the passages between

splash bars.

The

operator has to watch (or fannation of ice around the fan.

I ice builds up around the Ian too much it

may

shut

off

the

How

01

In cold weather moisture-filled air is

li

kely

to

form _

on

the

fan blades and other moving parts.

This may cause overloading 01 the fan motor and costly

The operator needs to know how to prevent _

. formation in the tower and

on

moving parts.

One way to control

fr

eezing

is to

limit the quantity of

cold

entering the tower.

In

atmospheric towers, adjustable louvers can

limit the

intake

01

44

To

limit the intake

of

air

in

induced-and forc

ed

-

draft

towers

the can be slowed

or

shut down .

245

Decreasing the pitch

of

the Ian blades will also reduce the

ntake.

246

f ice has formed

in

the fill deck it can be melted by reducing

the

amount of co

ld

entering the tower.

247. The incoming water will melt the ice because the water is

248 ans which do not have variable-pitch blades are usually

equipped so

that

the direction of rotation can be

Now tum the page,

2

turn the boo t over, and go on .

•

tower

less

cooling

freeze

laster

block

Ice

damage, or repairs

ice

alf

f ns

air

hot,

or

warm

changed. or reversed

•


27/44

On a forced-draft towel', the fan pushes the aIr into the

(top bottom)

of

the tower.

R ,d sing the pitch

of

the fan blades causes air to be (pushed

into

/ ;

ucked out of) the tower. .

Since

the ail

in

the

tower is hot, reversing

the

fan

can/cannot)

melt an ice buildup.

: -

The quantity

of

ail' flowing through the forced- or induced

draft towel' can be controlled:

by shutting off one or more _ ;

by

changing the pitch 01' direction of rotation of

and

by

changing the

of

fan motors.

and Summary

Cooling towers are needed

in

modern refineries

to

reduce

the

temperature of cooling water. Cooling water needs cooling

so

that

it can again

be

used

in

exchangers

to:

condense petroleum

cool products enough so that they do not go off

in storage due to heat; and to products

to

pressure- or fire-safe storage temperature.

Cooling towers depend mostly on the (conduction

of

heat

from water to air/ partial evaporation of water .

Evaporation depends on water-to-

contact.

The most important condition affecting the rate of evapora

tion: is the (temperature/ relative humidity) of the air.

: .

Atmospheric cooling towers depend primarily upon the pre-

f. vailing

for

performance.

The natural-draft tower is designed in such a manner

that

the

heat of hot water causes a through it.

f-

In fo""ed- and induced-draft cooling towers, the draft is

caused by motor-driven

The draft in forced- and

(eaaier/harder)

to

control

towers:

induced-draft cooling towers is

than

the

draft

in atmospheric

Redwood

and

fir

is used in

the

construction of cooling towers

because it resists wet

21

•

bottom

.

sucked out

of

, ,

can ::t ,,'

fans

fan

blades

-.'

: ; :(:1

:

.•

,

.

.

'. .

..

" .

. . .

.

:

,r- ,

.

.

..

.,.. t

·t

I

::

'

..

'.

,

peed

. ' :'

..

vapors

specification

cool

.

.

,;

partial evaporation

of

watt

air

relative humidity

.

...

wind

-;-

.'.

.

•

.

. t

,.

draft

.'

,

.'.

,.

:-

ans

': 1>

..

¥

i'

.

I

,

. , .1

I'

,

',.

easIer

t

.

' : .

ot

,.

':i

.


28/44

Ideally, metal

parts

of the towers should be highly

to con-osian .

. Metal

parts are

coated with special

to

in·

crease their corrosion

resi

stance.

The operator should keep

alert

to evidence 1 excessIve

and wet

Cooling towers perlorm best when th air passing through

them-

is

cool .and (dry jwet).

.are instruments used in

determining

the _ 1

the air.

f there

is

no difference

in

the temperature reading of a dry. and

w e t b u l b thermometer the relative humidity is .

.

At

100

relative humidity, there

will

be (some/

no

) cooling

due

to evaporation.

Even though there m

ight

not be any cooling due

to

evapora·

tion, a cooling tower

will

still cool water slig

htly

due to

radiation,

and

.

In cold climates, where temperatures get belol. Ireezing, the

- operator must guard against the (ormation 1 _

in

the tower as wen as the fans.

A natural·dralt tower (needs /does

not need

drift eliminators.

All

other towers have

to

reduce loss of water due to wind .

73

. Makeup water is needed in cooling towers to replace water

loss aue to leaks, and _

CONDITIONING

ND CHEMICAL PROPERTIES OF WATER

1

H20 is a chemical symbol (or water. It shows that a water

molecule is a compound made up

o

two atom s of hydrogen

and one atom of

2

wnen hydrogen and oxygen combine to (orm water, the

process

is

a (chemical/physical) change.

22

• J

:

r e s l s t n

coating or paint

corrosion. or rust: rot

dry

relative humidit} «

100

•

no

conduction; convection

ice

does not need

drirt eliminators

evaporation; drift

•

oxygen

chemical


29/44

3. The drawings show different changes that water can undergo.

E J

t ~ ~

(

I

. .

, ,) ,,)

(

-' r ))

I

-

l

ICE (SOLID) WATER (L IQUID)

BELOW

32

F

32 F

TO

212 F

STEAM (GAS)

ABOVE

212 F

These

changes are (chemical / physical).

4. Whether water is a solid liquid

or

vapor its molecule are

. still composed of two atoms and one

atom.

~ e a t i n g or

cooling water causes

it

to change state from one

form

to

another

. Changing·

the

state

of

water is only a change.

. .

6.

A ·ehemical change occurs only when atoms

or

molecules

change from one substance into an entirely

substance.

: ·7 .Water does

not

undergo chemical change easily.

. Chemically,

it

is relatively (stable/ unstable).

il 8:'

Water also has a good heat capacity. That means that

it

has

,

.

i

.a good capacIty

to

absorb .

9. BTU stands for British Thermal Unit. It is a measurement of

quantity of

energy.

10 pteiji£ al is the number of BTU's required to raise the tem

perature of pound of any substance ° . For water this

takes 1 BTU.

To raise 2 pounds

of

water by 1OF for example requires

BTU's.

,

.

11.

Here

is

a table of specific heat values for different substances.

,

\r "

toY;'

,.

l '.'

t'

Substanee

t

b*_

Air

.

..

. :

Alcohol

r ' ··Aluminum

" . Brass

...

.... Copper

fj

>;; ·Earth (dry soil)

• c-

Glass

'. :

,

..

Gold

;

J

,

ce

Iron

(steel)

;; "

. (

. ..

Specific Heats

Sp.

Ht

.

Substance

Sp.Ht.

0.24

Kerosine 0.50

0.

60

Lead

0.03

0.22

Lube Oil 0.45

0.091

Mercury 0.033

. 0.093

Steam

0.48

0.20

Stone

0.192

0.21

Tin

0.055

0.032

Water 1.00

0.51

Wood (avg.)

'0.42

0.115

Zinc

0.093

.' Kerosine has a specific heat value of

23

, .

•

physical

hydrogen

oxygen

physical

different

stable

heat

heat

2

0.50

,-


30/44

12. To raise the temperature of 2 pounds of kerosine by 1°F

,requires BTU.

3 . When any 1iquid or fluid is used as a coolant, it absorbs heat

energy from the material being _ _

. As a coolant absorbs heat energy, its temperalllre'

5. Raising the temperature of 1 gallon of

ker

osine a certain

amount requires (more/ less) heat than raising a gallon of

water the s me amount.

16. A substance with a high specific heat can absorb (more/

less

)

heat per degree of temperature change than a substance with

a low specific heat.

17. A substance with a high specific heat should make a good /

poor) coolant.

18 . Water can disso1ve

m l.n

y things. Water

is

norrnally a (good /

poor) solvent.

19. Many tiny, i n s o ~ u b l e particles, such as grains of sand, rust,

and calcium carbonate, become suspen e

in

water .

Water can contain two kinds

of

solids : (1) dissolved solids

and

2)

solids.

20 . Water

is

made up of two and one

atom.

21. Chemically speaking, water is (stable/ unstable ' .

22. Water makes a good coolant because it has a _

specific heat.

23.

Because

of

its

properties. water can

carry various solids.

_ . and

24. The two types of solids th t can be found

n water are

and solids.

OF TOT L SOLIDS

O

COOLING

25

. The makeup water used in refineries comes from natural

sources such as rivers, lakes, and wells.

Such waters are likely to contain both and

solids even though they may appear per-

fectly clear.

24

•

1

cooled

rIse

s

less

.

more

good

good

suspended,

or

undissolve

hydrogen

oxygen

stable

high

dissolve

dissolved; suspended

dissolved

suspendod

..


31/44

26.

Because the water circulates many times through pipes, ex

changers" rooling towers, and basins, it picks up (more/ less)

solids.

27. ,The total solids increase because the water

. i·

a little

bit

of

the substances it contacts.

,i8'.'When water evaporates,

it

(takes/does not take) the solids

with it.

,

~ R

.'

-

29. Mter

partial evaporation,

the

solids tend to concentrate in

v l

the remaining water. Ccx.>led

water leaving a cooling tower

} ~ has (mOl'e:

1ess

) total sohds per gallon

than

the hot water

i

.

entering the tower.

. \ ~ t

.I .

..

'

80. The circulating water

in

a cooling system has (more/less)

'total solids than the fresh makeup water.

. ·ji} : . •

:

sl

f,

So,

the

discarding

of

some

cooling water and the addition

of

ll

'

~

m a k e u p water tends to keep the total volume of solids

)J

.(up/down).

r '

Suspended solids tend to settle out in sections o(

the

cooling

.system where

the

vel

oc

ity o(

the

water is (slowed/increased).

C'

1

f

3S

. 'Some diasolved solids are less soluble in hot water than in cold

i;l¥"i .a

ter

. When the water becomes hot, these dissolved solids

. , . ,

Decome

solids

. ; ...

,

.

34. Calcium and magnesium carbonate are less soluble in hot

", ,:: water than in cold water. When cooling water goes through

0" •

t .: heat exchanger, calcium and magnesium carbonate become

, . . solids.

, ' j

':'1- i

1 : ~

,.>

~ e ~

~ t e r containing calcium and magnesium carbonate

,_ .'

. , \8

>otled

n a vessel, form on the sides and

~ bottom of the vessel.

t-f f > : ,

.

l-

....

'

.oj.

36

. The aame thing happens when

the

water

pa

sses

through a

'. '

heat '

"","

... .. .....

.}1 " " , )

3 i : D e p o s i t s

or scales (ormed in the tubing o( heat exchangers

'- ,will {increase/decrease} heat transfer.

...... r··

>1 :1/ ,:

S 8 . ,The 'buildup of deposits in an exchanger, regardless of

the

t . . 'cause or

source of the deposit, is called fouling. Fouling makes

~ i l t P e r i o d i c necessary. ' .

¥

A

~ o a r s e , suspended solids also cause wear in narrow passages

..

;or turns in the flow. This

kind

of wear is (erosion/ corrosion).

'

~

4 0 . ri. oo much buildup of solids is permitted in a cooling tower,

. . . it, too, has to be periodically.

,

25

more

•

dissolves

,,

does not take "

, "

more

{

more

down

exchanger

.

decrease

::.:

cleaning

,

••

-

\

erosion

cleaned


32/44

41. Tiny, microscopic plants sometimes thrive in cooling water

systems.

These tiny growths, often green in

col

or, r

eq

ui

re ligh

t in order

to grow. They

start

growing on the wa

ll

s of

clo

sed/open)

parts

of

the system.

42

Parts

of the

growth break away from the

wa

lls and

start

floating in the water. They become part of the

solids. .

43. They Cfl n

plug narrow passages

in

the system

and

damage

woodinthe

. These are biological, or living, substances.

To

control or stop

their growth they have to be _ _

45

. The biological growths are algae and slime. There are a number

of varieties; all cause to cooling systems.

46. Cooling water,

in

addition to dissolved so

li

ds and suspended

solids, contains some dissolved oxygen and carbon dioxide

which

are

solids/gases).

47

. It

is

not the water in the system that causes cor ro sion, erosion,

and fouling.

It is the disSolved suspended

so li

ds, and

dissolved

KEEPING COOLING WATER IN CONDITION

48. Waters from different water sources are likely to contain

kinds and quantities of solids and gases.

49

. The chemical analyses and the physical tests made on the

different waters are likely to be _ _ _

50

The chemist prescribes what the operator must

do

to keep

the

cooling water in good

51

The operator may

be

required to make a

few si

mple tests and

change his

of

the water as the te

st ma

y indicate.

52. Because each cooling system is different and t he natural make·

up water is different, methods of treatment are

CONTROLLING

SUSPENDED

ND DISSOLVED

SOLIDS

,63 . If it is necessary or the operator

to

make certain

te

sts on

cooling water, his supervisor will arrange f

or

the necessary

instructions and for the test .

.

5

.

Chemists use two measures to express the quantity of various

f .

impurities in water: grains per gallon gr

. /

ga

l

) and parts per

: million PPM).

One

grain per gallon equals

17

parts per millio

n

f the

total

solids in cooling water is 10 gr./ gal., the

PPM

is

26

open

suspended

cooling towers

killed, or poisoned

dama

ge

or

fouling

gases

solids

gases

different,

or

various

different

condition

l:

eatrnent; r eonditi

different

equipment, or tools

170


33/44

:55: Cooling water analyses usually are reported in

PPM. 50

PPM

. total solids means that in one million pounds of water there

; ". are pounds of suspended and dissolved solids.

. t

.•

~

56.;rhere are both suspended and dissolved solids in the natural

makeup water. These

solidc; in

crease in the cooling tower water

~ ~ b e c ~

of and because

of

the treating

. chemIcals that are added.

. ','

, ,

,

,

. 57.

Some small increase of both kinds of solids also comes from

:t he basins, pipes, and wood

in

the cooling system .

.

. : r h e total

of

solids in cooling waters varies from one PPM in

;,j;lt relatively clear water to 50,000 PPM in muddy river water

~ " .

Muddy rive,' water probably has (more / less) suspended solids

. : : :

~

than dissolved solids.

~ . ~ : . ,

' . . ,

,' •.;,·,(-

.t

... - .4 . , •

.

,:.\i.i"

- ~ . . : . ~ . "

sedimentation Ba$in$

-',

,

'1


34/44

Mechanical and hemical Clarifiers

68

. Mechanical clarifiers take up less space than sedimentation

basins.

V RI BLE

SPEED DRI

OUTLET L A I U ~ ~ ~ ~ r

.

HARD

WATER

INLET

CHEMICA,L FEED

INLET

~ ~ ~ ~ J i S L U D G E OUTLET

Here, turbid water and coagulating chemicals are

fed

in

through (the same inlet /different inlets),

69 The design

of

the clarifier causes the chemicals to be thor-

oughly with the raw, turbid ,vater.

70.

Aluminum compounds such as aluminum sulfate, sodium

aluminate, and iron compounds, such as ferrous sulCate and

ferric chloride. are coagulants.

When added to turbid water with other chemicals, they speed

up

71 . Coagulants with other chemicals form a spongy floc which

settles rapidly, taking with it sediments, algae particles, and

other suspended

72 The chemicals coagulate the suspended solids so th t they

become heavy enough to settle quickly to the

of the clarifier tank.

73 The solids pile up as sludge on the bottom of the clarifier tank.

A rotating scraper moves the sludge toward the center where

it

can

enter the sludge

•

.

74 Because the chemicals speed up the settling, these clarifiers

require more/less) space than a sedimentation basin.

75

Because

of

the coagulating action

of the

chemicals, water from

these clarifiers is

th n

water from sedimenta-

tion basins.

8

L

.

different in

ts

mixed

.-

sedimentation,

or purification

solids, or matter

bottom

outlet

.

less

clearer

or

deaner


35/44

Filtration

76

. Suspended s

oli

ds can be removed fr

om

water by filtering the

solids out. Filte,'s

wo

rk by

ei

ther gravity

01'

pressure.

OPEN TO ATMOSPHERE

SAND

GRAVEL

WATER INLET

' , '

: . . : 7 -

_

-

'

BACKWASH OUTLET

l2::==

FILTERED

WATER

:= f t t=OUTLET

~ = = = = ~ ~ ~ ~ H I N L E T

This is a filter,

77, Note that the tank

[o

r this filter is completely enclosed.

•

BACKWASHING FILTER

BACKWASH OUTLET

'I·

,'

,, , This is a ilter.

78.

'Both gravity and '

pr

essure filters can produce

backwash.

:,i: Water can be forced back in the _

_ direction

~ normal flow

•

.

79.

,

The solids trapped in and on the filt er bed

r

e backwashed or

I(

ftusbed

into the disposal system.

.

Filters

are usually installed in batteries of two or more so

th t

. '< the flow of filtered water c n continue through t least one

o ,filter while the other is being

2

gravity

pressure

;

,:: - ' .',

,

:

:',

- ',

: .

.

.?,

, ',0,

: ~ :

'.

.

1 i,

; f

.

iI

. -i ,

I

' i

:.'

,,':

, ,

.f

:. '

t ' .

. r

,

opposite, or .e.·en

.

waste.

backwashed,


36/44

Hard water is water which contains dissolved

Distilled water does not contain either dissolved solids and

gases

or suspended solids and gases.

t

is ther

ef

ore soft/ hard).

Rain water

is not entirely so t because

it

picks up some hard-

ness from the solids and gases in the

Natural water from wells, lakes, and streams is often quite

hard.

When

the

water is heated, some

of

the dissolved solids in the

water fann

insoluble in the equipment.

85.

The hardness itself does not cause

corr

osion

in

the system

but the deposits create a condition favorable to _ _

by other impurities in the water.

86.

Cooling water conditioning is necessary to prevent

or

minimize

.. .corrosion fouling and formation in heat

.exchanger equipment.

87. The dissolved solids which cause calcium and magnesium

hardness also cause scale formation

if

the cooling water be

comes hotter/ colder).

88. Calcium and magnesium scale on heat exchanger tubes

significantly reduces

the

transfer

of

_

hrough

the tube walls.

89. Scale also reduces

the

flow

of

fluid through the heat exchanger

shell, completely plugging some or all

of

t

he

exchanger

if

it

is not removed .

90 . The formation of scale makes the equipmen t less efficient

, . and makes costly necessary.

•

91.

There are three widely used methods for conditioning water

against scaling.

One method is

to

soften

the

water by making

the

soluble

compounds insoluble so

that they

can be remoyed

by

settling

T

30

•

solid.

soft

air or atmosphere

deposits, or solids, or

50

corrosion

scale

hotter

heat

tub es or passages .e

cleaning

or repair

filtration


37/44

, '.

92.

This is a cold-process softener.

: ;

,

•...

CHEMICAL

INLET

MECHANICAL

M I ~ E R

,.

,. .

. ,

,. '

,

....

The softening reaction is accomplished

by

feeding in chemicals

such as ·lime nd soda ash and mixing them with the water

'Jli

·

by means

; 98 This softener uses heat as well as chemicals .

1I1J

_1

'- li;-.,'

, HARD WATER

.

INLET = = ; e : : ~

W

;;;.;;;

' : ¥ . ~ :

. I '

#

..

,: ..

CHEMICAL

INLET

it::I'

r , = . ~ - - - S,'EAM IN

~ E = = T R E A T E D

WATER

TO F I L T E R ~

SLUDGE

BLOW QFF

~ y

U H e r e

the raw water and the chemicals are heated y

~ ~ ~

.

~ ~

L

i

94;;

,There is / is no) mechanical mixing.

~

H e a t speeds up the softening reaction.

~ r B e c a u s e the reaction is speeded up in a given amount of time

i ~

hot-process softener can soften (more/ less) water.

i.,. ,

'.

••

31

.

,

...

'

.,

,.

,

mechanical

.:-

.

1 ~ ,

.,

steam

IS

no

more

,


38/44

96. f the processing rate for

bot.h

hot·

an

d coJd·process

unit ; i5

the same, the size of the hot / cold ) unii can be smaller.

97. eat makes the softening reaction mor£' complete.

For a given amount of processing time, the water from :

hot/cold)

unit

is likely

to

be softer.

98. Because its reaction is faster and more complete. chemical

costs for

th

hot-process unit are usually higher/ lower) than

th cqsts for the cold unit.

99 The amount

of

chemicals used depends, however, on th

hardness

of

the raw

100. Generally, the higher

th

hardness

of

th

raw water, the

higherflower) the chemical costs to soften the water.

101.

Zeolites, chemicals that produce ion

exc

hange, are

also

used

. to soften water.

.

.

HARD

WATER

INLET

ZEOLITE

SOFT

WATER

T

LET

==o; \lV

ION EXCHANGE

UNIT

REGENERANT

TANK

(SODIUM CHLORIDE BRINE)

In this kind of softener, the water intimately mixes with /

passes through) th zeolite.

102. An ion is an

atom

that

either

has

extra

electrons or is m j ~ i n

some electrons.

An ion exchange involves one substance collecting ions from,

or giving up ions to, another substance.

Passing

th

water through

th

zeolite makes possible/

prevents) ion exchange.

32

hot

hot

lower

water

higher

.

passes through

makes possible


39/44

Usually, the zeolite has sodium ions attached to it.

When hard water passes through the zeolite, the sodium ions

of the zeolite exchange with calcium

or

magnesium ions

of

the raw

calcium 01 gnes Um removed, the

water

is now

than it was.

When all the sodi

um

attached to the zeolite has been removed,

the zeolite

can

st

ill

.

can

no

longer) exchange ions.

Suppose a sodium chloride brine

is

flushed through the

saturated zeolite.

There (

now

can be still can t be) an ion exchange.

The zeolite now exchanges or

ions with the brine.

The brine gives up ions to

the

zeolite.

sodium once more attached to it, the zeolite

is

re

activated.

. It can (once again/ still no longer) soften water passed through

to

.

The zeolite can only be reac tivated a certain number

of

times.

..

.

,

Eventually, the zeolite mu st be

Zeolite softeners yield much softer water than is usually

needed

in

a .cooling system.

Their use

is

generaJly limited to providing very soft boiler

feed water and some

of

the water in the

I

ooling

system

.

112.

Sulphuric acid also can be used in water to control scale.

Sulphuric acid is highly

113. Therefore, the quantity

of

acid added to the water has to be

carefully

114. The

sulphuriC acid acts on scale-forming substances

to

keep

tbem dissolved in the water.

Tbis means tbat adding sulphuric acid to the water makes

seale-forming substances (morelless) soluble .

115.

So long as these substances remain soluble,

it

is (easy/ difficult)

for them to settle out and form scale.

•

116. Retarding the rate at which scale-forming substances settle

out

(speeds up/slows down)

the

formation of scale.

117 ~ o t h r way to control the formation of scale is to blow down

or discard some cooling water continuously,

This lost water is then replaced with (hard / soft) makeup water.

33

water

·:.;, :;l

,

•

.

'.

"

.'

s o f t ~ .

..

can no longer

..

now can

calcium;

sodiwri ·

; , .

once again

makeup ,

,

corrosive

more

slows

soft

.


40/44

ROSION CONTROL

Cooling water corrodes by destroying the metal which it

Perfectly pure water is not corrosive.

Cooling water corrodes because there are dissolved

and gases in it. '

Dissolved solids in the natural makeup water become can·

centrated because of _ which takes place in

the cooling tower.

.Gases such as oxygen and carbon dioxide are picked up trom

the

in

the cooling tower.

Carbon dioxide causes the water to become acidic. Acidic

water is corrosive/non--corrosive).

Oxygen in contact

with iron

causes oxidation

or

hese fonns of corrosion are in part eliminated by using

corrosion-resisting

in

construction of parts

which come in contact with cooling water.

But, using expensive metals entirely is more costly than

the water to lessen its tendency to corrode

metal.

i. One way

to

treat the water

to

prevent corrosion

is

to

inhibit

or stabilize the water chemically so that it will not attack

, . Another approach is to treat the water

so that it

deposits a

tbin, protective film on the of the metal.

lhoclic

Protection

1.

he tarnishing of polished metal is a fonn

of

.

Oxidation of the metal occurs in dry air. Water is not involved

in

the

corrosion This kind of corrosion

is

called dry

•

). Because water is involved, the kind of corrosion which occurs

in cooling systems

is

(wet/dry) corrosion.

1

During

wet

corrosion,

two

reactions occur at the same time.

Metal passes into the water and hydrogen p:\SSes

out

of

the

nto the metal.

34

,

,

contacts

solids

.

,

I

evaporation

\

aJr

corrosive

rust, or corrosion

metals, or matei

ials .

.

.

conditioning, or softenins

metal

surface

wet

water

.

, . .:

.

.

,

. ,

.. .


41/44

1 ~ 2 .

When this occurs, there is a tiny

flow

of electricity between

• the water and the

133 The metal is the anode and the water is

thecathode

GALVANOMETER

CATHODE

.;;. ::-\- HYDROGEN

IRON CONDENSER BOX

The a l v a n ; ~ e t e r indicates a small flow of

, .;

34 Iron is going into solution from the metal walls (anode) and

hydrogen is l

eav

ing the water at the

135. Suppose a strong direct current

is

applied in the opposite

direction.

ELECTRICAL

SOURCE

+

In this situation, hydrogen leaves the water

and is taken from the rod.

136

The anode, which may be scrap iron, corrodes,

metal from the iron condenser box is

.

137 This arrangement provides cathodic protection metal

in the cooling water system.

To keep the current flowing in the right direction at tbe right

magnitude, the operator may be required

to

make adiust-

ments of the outside source.

138

.

The amount of current that must be applied from the outside

source

(depends/dOes not depend) on the corrosiveness

of

the

water and on stray c\PTtnt trom nearby electrical equipment.

,

1·;

, . .

metal

,

, .

current,

or

electricity;

:a

.- ,

:.

cathode ·1

metal

Prevented .

.,

,

.'

,

''',:

,

. ..

current o r ' e l ; o C t ; C i t y

'.

depends :.

.,,


42/44

TESTING FOR ACIDITY ND ALKALINITY

139. Water from any source is either

ac

id

ic

alkaline

or

neutral.

Litmus

paper

and phenolphthalein and methyl-orange solu

tions are indicators that

do

not show neutral water but can

indicate either acidic

ir

water.

140

. I f blue litmus paper

is

dipped in acidic water, it turns red.

I f

then dipped in alkaline water, the paper turns

once more.

141.

Phenolphthalein solution is colorless and stays colorless

In

ae:idic

water.

I t turns

red when added to water.

142. A drop of methyl-orange solution is yellowish-orange. When

added

to

alkaline water it remains yellowish-orange, but turns

reddish-orange when added to water.

143.

Litmus paper, phenolphthalein and methyl-orange onl y

in

dicate whether a sample

of

water is acid or alkaline.

They do not indicate the degree of acidity or

144. The degree of acidity or alkalinity can be es tablished by

finding a

p

value for a given sample.

p SCALE

, 1 I I I I , , I I I

o

1 2 3 4 5 6 7 B 9 10

11

12 13 14

t - - I . - - - A C I O - - - - t- I - - A L K A L I N E --1

NEUTR L

A sample of water with a p value of 7

is

145. A sample of water with a p value of 5

is

146_

A sample of water with a

p

value of 9.5 ;s

147 . I f you want to increase the p value of the cooling water,

you would add (an acid/ an alkali) .

148.

Water with a high

p

value is (more/less) likely to form

:Sea e than to corrode metal.

149. Water with a pH value

of

9.0 causes red litmus paper to tum

•

150.

Water with a pH of 4.0 causes methyl-orange indicator

to

turn - orange.

151. A sample of water with a p value of 11.3 causes phenol-

:phthalein indicator

to turn

36

alkaline

hlue

alkaline

acidic

alkalinity

neutral

acidic

alkaline

an alkali

rnor

blue

reddish

,

.

red

•

'

.;.


43/44

152 Phenolphthalein in 4.0

pH

water is

_____

153

If

applied excessively,

the

chlorine and phenolic compounds

used as i n f e c t a n t s and algaecides are to

the wood

in

cooling towers.

154.

Excess alkalinity over a long period

of

time

is

damaging

to

cooling tower lumber. Water which is damaging to lumber is

likely to have a (high/low) pH value.

155.

Wood contains organic acids which act to protect

it

from

rotting.

These acids can be washed out by sub-

stances with high pH values.

156.

Excessive chlorine also destroys the natural preservatives in

cooling towel wood .

Excessive

and excessive

should be avoided,

REVIEW AND SUMMARY

157. Water for cooling is (readily available/ scarce) in most areas.

158 Water has the capacity to absorb (more/ less)

heat

than most

available coolants,

•

159.

Water

is (more/ less) costly than other possible coolants.

. Water from natural sources is/is not) corrosive to metals.

Water

has

/ does not have)

scale-forming

'and fouling

tendencies.

162 Water

is non-eombustible and therefore does not add

to

dangers from fire.

It

also responds readily to a large variety of

treatments.

153 Accumulation of suspended solids in cooling water may be

reduced

by

filtration, adding

soft

water,

sedimentation, and continuous from the

system.

164.

In

cloling W81.-.er

the main problem with

hard

water makeup

is that

it

(does not evaporate Quickly/increases scale.fonning

tendencies) ,

165

Lime-soda and zeolite processes are used to ,-

water.

37

. ,

colorless'

high

alkaline

,: .

. .

i i,..\

. .;.":

' ..

" \

. .

·

;

,

"

·

alkaline; < : h l o r i n e

' .

' .

,

,r

·

; j

.

..

' ,:.: "

-..

.

,

•

,,

1

r e a d i l y : a V a i l a b j ~

more

less

IS

has

r

-

s;

t.

"

.

chemical,

r

·fl.

,

f '

makeup

l o w d o w n

'

increases

soften


44/44

166. The

pH

value is

an

expression of (hardn., --softness/acidity

alkalinity) of the water.

167 . Water with a

pH va

lue

of

3.9 is _ _

Water with a pH value

of

7.9 is _

168.

Water with a

pH

value

of

7.0 is _ .

169.

Algae and

sli

me are (mineral / biological) m:-\ter.

170. Algae occurs mostly where water is expo od to (darkness/

sunlight).

171. Algae and slime cause heat exchanger _

172. Coagulation is a process which may be aid

.d

by the use

of

17 . -Coagulation aids (tiltration only

/s

edime, cation only/both

tiltration

and

sedimentation).

. 174. Gases, especially oxygen

and hydrog

. . , sulfide, cause

of metal parts.

175. A process for protecting metal equipmen against electro·

.

, .

chemical corrosion

is pro

t· ction

ITHE END I

•

,

-

acidity-alkalinity

cid

alkaline

nelltral

biological

sunlight

fouling, or cloggin;

chemicals

-

.

both tiltration

and

sedimentation

corrosion

cathodic

. ,

..

-,

_

Documents

Cooling Tower Section 1 API