HEAT EXCHANGERS

Instructions For Using Th is Manual

This is yo ur manual. You should write The following general procedure is recom- \
your name on the cover. Upon completion mended for using this manual:
you will find it helpful to keep it in an 1. Turn to Page 1. Read the material until
accessible place fo r future reference. you co me to the first problem or ques-
Problems may be included throughout the tion.
text. The solutions to the problems are given 2. Work the first problem or answer the
at the end of the book. The last page is a question, and enter the answer in the
validation s heet which has a number of proper space in ink. [f the problem or
questions and problems covering the entire question is shown in both English and
manuaL metric units of measurement, answer
The manual will be used in ~raining pro - only the part in units of measurement
grams all over the world. In some countries, that you use.
glish units of measurement such as feet, 3. Compare your answer with that shown
gallons, pounds , etc., are used. In other o n the reverse side of the Valida tion
countries, metric measurement units, such pages. Answers to problems in English
as meters, liters, kilograms, etc., are used. units of measurement are shown on the
In order for the manual to be of maximum back of the second Validation page ,
use, both metric and English units are shown. and answers in metric units are shown
The metric unit always appears first , and on the back of the first Validation page.
the English unit follows in brackets [ l. If your answer is correct, cont inue
Example: the temperature is 25 ' C [77' F]. reading until you come to the next
The metri c equivalent of the English unit problem and work it. If not, restudy
wili be rounded off to the nearest whole the manual until you understand the
number to s implify the text and examples. reason for your error. Rework the
A pressure of 150 psi may be shown as 10 problem if necessary. Leave your wrong
bars, when the exact equivalent is 10.34 bars. answer and note the correct one. This
If you are working in English units, you will keep you from making the same
may find it helpful to mark out the parts mistake later on.
that are in metric units, and vice versa. 4. Proceed ste pwise as shown above until
~ Some of the Figures have units of mea- you have completed the text.
surement. In such cases, two Figures are The above approach will require thought,
included . The first one uses metric units, making mistakes, and rethinking the s itua-
and the Figure number is followed by the tion. Concentrate on two things - the how
letter A (Example: Figure lA). The second and the why. Do not cheat yourself by tak-
Figure will be on the next page and will ing short-cuts or looking up the answers in
have English units. [t will be the same num- advance. It saves time and errors but pro-
ber as the first one, but it will be followed duces no real understanding. Your future
by the letter B (Figure lB). If you use metric depends on how efficiently you perform your
units, be sure to refer to Figures followed job and not on how rapidly you proceed
by the letter A; if you use English units, through this manual. Since this is your
refer to Figures followed by the letter B. manual, any erro rs you make are private.
 Training For Professional Performance

This manual is one of a series for your use It will also teach you how and whyequip-
in learning more about equipment that you ment functions.
work with in the oilfield. Its purpose is to In order for you to learn the contents of
assist in developing you r knowledge and the manual, you must dig out the pertinent
skills to the point that you can perform your facts and relate them to the subject. Simply
work in a mOTe professional manner. reading the material and answering the
The manual was prepared so that you can questions is not enough. The more effort you
"learn its contents on your own time, with· make to learn the material the more you
ou t the assistance of an instructor or class- will learn from the manuaL
room discussion. Educators refer to learning Teaching yourself requires self discipline
by self-study as Programmed Learning. It and hard work. In order to prepare yours~lf
is a method widely used in all industries as for the sacrifice you will have to make , you
a means of training employees to do their should set goals for yourself. Your ultimate
job properly and teach them how to perform goal is to perform your work in a professional
higher rated jobs. manner. Training is one step in reaching that
You can dem onstrate your desire to be a goal. Appli cation of what you learn is an-
professional by taking a positive attitude other. Seeking answers to questions is a third.
toward learning the contents of this manual Once you have established your final goal,
and others that are applicable to yo ur job. yo u must determine the means for reaching
A part of professional training is that of that goal. You may decide , for example, that
validating the trainee's knowledge of the you must complete a series of 10 or 15 man-
subject. Validation is for your benefit to uals to get the basic knowledge and skills
indicate that you have taught yourself the you need. After you decide whi ch training
material contained in the manuaL material is required, you should set a tim e
r The author of this manual has years of table for completin g each section of the
experience in operating petroleum equip- material.
ment. He also has the technical knowledge Achieving your final goal may take more
of how and why petroleum equipment func- than a year, and will require hours of hard
tions. The text was written for use by per- work on your part. You will know you have
sonnel with little or no previous experience achieved your goal when you understand
with petroleum equipment. Consequently, how and why to operate oilfield equipment
some of the rna terial may be familiar to you in order to obtain the maximum product at
if you have experience with oilfield equip- the lowest cost. Your sacrifice will have been
ment. From such experience, you have worth-while from the satisfaction of know-
observed the eft'ect of making operating ing that you can perform you r job in a
changes. The manual will help explain why methodical professional manner, instead of
the changes occurred that you observed. a trial-and-error-approach.
 ABBREVIATIONS & SYMBOLS USED IN THIS MANUAL

MEANING EXAMPLE
Temperature difference Temp diff is 10 0
Pressure difference Pres diff is 15 psi or ba~s

METRIC UNIT ABBREVIATIONS

ler liter 10 Itr : 10 liters

lcr/hr liCers per hour 20 Itr/hr: 20 liters per hour
m or mer meter 15 m: 15 meters
em cenCimecer 10 cm : 10 centimeters
km kilometer 5 km : 5 kilometers
m3 cubic meCers 10 m3 : 10 cubic meters
m3 /hr cubic me cers per hour 10 m3 /hr : 10 Cll mtr per hr
m3 /d cubic meCers per day 10 m 3 /d : 10 ell mtr per day
kcal kilocalories 20 kcal: 20 kilocalo r ies
kcal/hr kilocalories per hour 20 kcal/hr : 20 kilocalories per hr
kcal/m 3 kilocalo r ies per cubic 9500 kcal/m 3 : 9500 kilocalories
meCer of gas per cubic meter
kcal/kg kilocalories per kilogram. 10 000 kcal/kg: 10 000 kilocalories
per kilogram
gm gram 10 gm: 10 grams
kg kilogram. 25 kg: 25 kilograms
kg/ cm2 or bar kilograms per square cen - SO bars : SO kg per sq em
timeter of pressure
bars a kilograms per sq em of SO bars a : SO kg per sq cm absolute
absolute pressure
square meter 100 m2 : 100 square meters

ENGLISH UNIT ABBREVIATIONS

gal gallon 10 gal : 10 gallons

gpm gallons per minute 25 gpm : 25 gallons per minute
gph gallons per hour 25 gph: 25 gallons per hour
ef cubic feet 20 cf: 20 cub ic feet
cfm cubic feet per minute 50 cfm : 50 cubic feet per min
cfd cubic feet per day 50 cfd: 50 cubic feet per day
Mcfd thousand eu ft per day SO Mcf~ : ~')ur;'(fUu~ -eu"): c- vee" (fay
MMcfd million cu ft per day 50 MMcfd: 50;000,000 ell f e per day
BTU British Thermal Unit
BTU/hr British Thermal Units/hr 50 BTU/hr: so BTU per hour
MBTU/hr thousand BTU per hour 30 MBTU/hr: 30,000 BTU per hr
MMJ3TU/hr million BTU per hour 10 MMBTU/hr: 30,000.000 BTU per hr
BTU/cu ft BTU per cubic foot of gas 1000 BTU/Cll ft: 1000 BTU per ell ft
BTU/ l b BTU per pound 20,000 BTU/lb : 20 , 000 BTU per Ib
Ib pound 10 lb : 10 pounds
psi pounds per square inch of 750 psi : 750 Ib per sq in
pressure
psia pounds per square inch of 750 psia: 750 lb per sq in abs
absolute pressure
bbl barrel 20 bb l : 20 barrels
BPD barrels per day 100 BPD, 100 barrels per day
BOPD barrels of oil per day 100 BOPD: 100 bbl oil per day
BWPD barrels of ~ater per day 100 BWPD ": 100 bbl water per day
MEPD thousand barrels per day 10 HEPD: 10 , 000 bbl per day
sq ft square foot 25 sq ft: 25 square feet
 HEAT EXCHANGERS

INDEX

I. TYPES OF EXCHANGERS
A. Shell and Tube Exchangers . . . . . .• •.... . . • ••.... . . •. . . . . . 2
B. Hai r pin Exchange r s .... . . . .... .. . . . . .. .. •• • •• . ... • ... .. 11
C. Aerial Coolers . . .. . .. . . . ... . .. . . .. . .. . .• • . . .. . . • •. ... . 13
D. Hiscellaneous Types of Exchangers . .. . . . •• . .. . . .• •. .. . . 18

II . PRINCIPLES OF HEAT TRANSFER

A. General .• .... . .. ... .. . . . . .. ... • • ... . ..• •... . . .. •. .. . . 20
B. Temperature Difference . .. ... . . ••. . . . ..• •. ... . . .•.. ... 22
C. Resistance to Flow of Heat . . .. .•• •. . .• •• • •• ... •• .... . 31
D. Area . . ............. . ...•.••• . •• • • • •• • • •• • • •• •• • • •••• ,3 2

III . APPLICATION OF EXCHANGERS

A. Shell and Tube . ... . . . . .. . . . ••• .... .. • • . . ... . .• . . . .. . 38
B. Ha i rpin . .. . . . .. . ......... .. . . •.... . . • • . . . . ... • . ..... 39
C. Coils . .. . . .. .. . . .. ...• • .. . . . • . • . .. ... . • . •... .• •... . . 40
D. Ae r ial Coolers . . .. . . . .• . . . . . ••• .. . ... ••. .. . . . •• . . . .. 40

IV. OPERATION OF EXCHANGERS

A. Shell and Tube or Hairpin . .. .• • •. . . . . • • . . .. . . . • •.. .. . 41
B. Aerial Coolers . . .. ... .. . . . . . . •• • .... • •• . . . .. . • •... . . . 1.2

V. TROUBLESHOOTING EXCHANGERS
A. Shel l and Tube Exchangers .. .. . .... ... .••.. .. . .•• . ... . . 43
B. Aerial Coolers . . ... . . . . . .. . . . ... . . .. . •• •• ... ... • • ... . . 43

VI. GASOLINE PLANT EXCHANGER PROBLEMS

A. Gas-to- Gas Exchanger . . . . . . . . . . .... . ..• • . . . . . .. ••... . . 45
B. Gas Chiller . . . . ..... . .. . . . . .. . . . ... .•• • •••... . •. . . . . . 48

TABLE I, TYPICAL EXCHANGER COEFFICIENTS .. . . . .. • .... .. .. • ... . . . 55

TABLE II, EXTERNAL SURFACE AREA OF TUBES . . . .. • • • . •.. . •• ••.. . . . 56

VALIDATION - Metric Units ... ... .. .... . . ...... . .... • • .......•.. 59

SOLUTIONS TO PROBLEMS - Met r ic Units .... . • •. . . . . . .•• .. . . ..... . 60
VALIDATION - English Units .... ... .... .... .. ... .... ... .. .... ... 61
SOLUTIONS TO PROBLEMS - English Units . . .. •• .... . .. • . . .. . ... . . . 62

v
 ABBREVIATIONS & SYMBOLS USED IN THIS MANUAL

SYHBOL MEANING EXAMPLE

~ Temperature difference 6t ., 10 0 : Temp diff is 10°
ap Pressure difference 6P - IS: Pres diff is 15 psi or bars

METRIC UNIT ABBREVIATIONS

ltr liter 10 Itr: 10 liters

Itt'/hr liters per hour 20 Itr/hr: 20 liters per hour
m or mtr meter 15 m: 15 meters
em centimeter 10 em: 10 centimeters
km kilometer 5 km: 5 kilometers
m3 cubic meters 10 m3 : 10 cubic meters
m3 /hr cubic meters per hour 10 m3/hr: 10 cu mtr per hr
m3/d cubic meters per day 10 m3 /d: 10 Cll mtr per day
kcal kilocalories 20 keal : 20 kilocalories
kcal/hr kilocal ories per hour 20 kcal/hr; 20 kilocalories per hr
kcal/m 3 kilocalori es per cubic 9500 kcal/m 3 : 9500 kilocalories
meter of gas per cubic meter
keal/kg kilocalories per kilogram 10 000 keal/kg: 10 000 kilocalories
per kilogram
gm gram 10 gm: 10 grams
kg kilogram 25 kg: 25 kilograms
kg/cm 2 or bar kilograms per s quare cen- 50 bar s : 50 kg per sq em
timeter of pressure
bars a kilograms per sq em of 50 bars a: 50 kg per sq em absolut e
absolute pressure
squa re meter 100 m2 : 100 square meters

ENGLISH UNIT ABBREVIATIONS

gal gallon 10 gal: 10 gallons

gpm gallons per minute 25 gpm: 25 gallons per minute
gph gallons per hour 25 gph: 25 gallon s per hour
cf cubic feet 20 cf: 20 cubic feet
cfm c ubic feet per minu t e 50 cfm: 50 cubic feet per min
cfd cubic feet per day SO cfd: 50 cubic feet per day
Mefd thousand cu ft per day SO Mcfd: 50,000 cu ft per day
MMcfd million cu ft per day SO MMefd: 50,000,000 cu ft per day
BTU British Thermal Unit
BTU/hr British Thermal Units/hr 50 BTU/hr: 50 BTU per hour
MBTU/hr thousand BTU per hour 30 MBTU/hr: 30 ,000 BTU per hr
MMBTU/hr million BTU per hour 10 MMBTU/hr: 30 , 000,000 BTU per hr
BTU/eu ft BTU per cubic foot of gas 1000 BTU/eu ft: 1000 BTU per eu ft
BTU/lb BTU per pound 20,000 BTU/lb: 20,000 BTU per lb
lb pound 10 Ib: 10 pounds
psi pounds per squa re inch of 750 psi: 750 lb per sq in
pressure
psia pounds per square inch of 750 psi.: 750 lb per sq in abs
absolute pressure
bbl barrel 20 bbl: 20 barrels
BPO barrels per day 100 BPO: 100 barrels per day
BOPO barrels of oil per day 100 BOPO : 100 bbl oil per day
BWPO barrels of water per day 100 BWPO: 100 bbl water per day
MBPO thousand barrels per day 10 MBPO: 10,000 bb1 per day
sq it square foot 25 sq ft: 25 square feet

vi
 - 1-

HEAT EXCHANGERS

Heat exchangers are used to conserve heat and save fuel, or to supply
heat required by a process.

The simplest heat exchanger is a kitchen pan used to boil water.

Heat is transferred from the heating element on the stove to the water
in the pan. An ice tray in a refrigerator is another simple heat ex-
changer.

A heat exchanger can be thought of as any piece of equipment in

which heat is transferred from a warm material to a cool material through
a wall that separates the two materials.

HEAT EXCHANGERS IN A PROCESS PLANT

NOTE: This manual includes both metric and English units of

measurement. If you use English units, disregard the metric
units, and vice versa. Refer to the instruction page at the
front of the manual.
 -2-

I. TYPES OF EXCHANGERS

A. Shel l and Tube Exchangers

The most common type of heat exchangers used in process plants is
a form of shell and tube exchanger. Drawings of such equipment are
shown in Figures 1, 2, 3 and 4.

Shell and tube exchangers have two obvious major components:

1. A tube bundle, which may contain hundreds of tubes and

through which the tube side fluid flows; and

2. A shell that encases the tube bundle and through which

the shell side fluid flows.

For our purposes, a fluid is a liquid or gas or a mixture of the two.

The tube material is usually steel, bronze or aluminum, although

stainless steel or other alloys can be used in corrosive or severe tem-
perature services. The shell is almost always steel.

The inside of a tube usually can be cleaned fairly easily by push-

ing a rod through it, or using a high pressure jet on the end of the rod.
The outside surface of tubes in an exchanger tube bundle is more diffi-
cult to clean, as the surface of many of the tubes is inaccessible. Con-
sequently, the fluid that is the most likely to corrode usually flows in-
side the tubes. If special material, such as stainless steel, is re -
quired to prevent corrosion, only the tubes and channels have to be made
of the special material. If the corrosive fluid were to flow in the shell
side, the tubes and shell would have to be made of special metal.

When water is one of the fluids, the tubes are usually made of a
brass alloy called Admiralty, and water flows through the tubes.

If both fluids have similar corrosive properties, the stream with

the highest pressure usually flows through the tube side. This is be-
cause a tube will collapse from an external pressure about one-half the
internal pressure that is required to burst the tube. For example, a steel
 - 3-

FRONT END REAR END

SHEU TYPIS
STATIONARY HEAD TYP£5 HEAD TYPES

:JfL
A
E
~I
T
I~
L ~~IT FIXED TU8ESHEET
I LIKE "A" STATIONARY HEAD

~N~·
~b
ONE PASS SHELL

AND REMOVABlf COVER M

~ I-i--
FIXED TUBESHEET

I] LIKE "8" STATIONARY HEAD

e
F
m

,cCZti-:~n
- - - - -- - - -

B TWO PASS SHELL

WITH LONGITUDINAL BAFFLE N
FIXED TUBESHEEf
..... -~ LIKE He' STATIONARY HEAD

~I ------I----- I~
BONNET (INTEGRAL COVE'!)

.~ G
P ~IT
--
~

'1x r
SPliT flOW OUTSIDE PACKED FLOATING HEAD

=~=::fJt~:=;:"-==,~~,
C~~~l\~hg~~
~

~I --i- --i- I~
5
C H
m
FLOATING HEAD
WITH BACKING DEVICE

-- FF' ~~'::~}~ft~~
DOUBLE SPLIT FLOW

FIXII:O T
~
I
~I I
~ PUll THROUGH FLOATING HEAD

~-'C J I]
~ ~
CHANNEL INTEGRAL WlTt1 TUBE-
SHEET AND REMOVABLE COVER I
U

~
DIVIDED flOW
~ U_TUBE BUNDLE

~
"I,!.- - F' "'f-"f~

~
D
S':~ ·J._iJ
i.J K
W '~~~

PACKED flOATING TUBESHEE'f

SPECIAL HIGH PRESSURE CLOSURE KETTtE TYPE REBOltER WITH tANniN liNG

Cour tes y Tubular Ex changer Mfgrs . Assn.

FIGURE 1
TYPES OF SHELL AND TUBE EXCHANGERS
 -4-

1. Stationary Head-Channel 20. Slip·on Backing Flange

2. Stationary Head-Bonnet 21. Floating Head Cover-External
3. Stationary Head Flange-Channel or Bonnet 22. Floating Tubesheet Skirt
4. Channel Cover 23. Packing Box Flange
5. Stationary Head Nozzle 24. Packing
6. Stationary Tubesheet 25. Packing Follower Ring
7. Tubes 26. Lantern Ring
8. Shell 27. Tie Rods and Spacers
9. Shell Cover 28. Transverse Baffles or Support Plates
10. Shell Flange-Stationary Head End 29. Impingement Baffle
11. Shell Flange-Rear Head End 30. longitudinal Baffle
12. Shell Nozzle 31. Pass Partition
13. Shell Cover Flange 32. Vent Connection
14. Expansion Joint 33. Drain Connection
15. F~oating Tubesheet 34. Instrument Connection
16. Floating Head Cover 35. Support Saddle
17. Floating Head Flange 36. lifting Lug
18. Floating Head Backing Device 37. Support Bracket
19. Split Shear Ring 38. Weir
39. liquid Level Connection

courtes y Tubula r Exchanger Mfgr s . Assn.

l-PASS SHELL, 2-PASS TUBE EXCHANGER

FIGURE 2
HEAT EXCHANGER PARTS
 - 5-

I-PASS SHELL &TUBE

WITH ExpANSION JOINT
ON SHELL SIDE

lJ
"

courtesy Tubular Exchanger Mfgrs. Assn.

FIGURE 3
TYPES OF SHELL AND TUBE EXCHANGERS
 -6-

tube that will burst when its internal pressure reaches 186 bars
[2700 psi] will collapse when the pressure outside the tube reaches
83 bars [1200 psi]. It is less expensive to make an exchanger with the
higher pressure on the t ube side than to make i t wi th the higher pres-
sure on the shell side , providing no special metals are r equired .

As we will see later. the amount of heat transfer that occurs in

an exchanger depends upon the area of metal that separates the two
flui d s. In a shell and tube exchanger . the heat transfer area is the
external area of the tubes. The reason that shell and tube exchangers
are used commonly 1s that they are usually the least e xpensive means of
providing the area required for heat transfer to occur.

Most shell and tube exchangers are mounted in a horizontal position.

If either fluid is a liquid, it usually enters at the bottom of the ex-
changer - either shell or tube side - and flows out the top. With this
flow pattern the exchanger will stay full of liquid Rnd the entire tube
area will be utilized. If liquid flows in the top and out the bottom,
vapor pockets can form. and no heat transfer will take place in the tubes
that are within the vapor pocket.

Exchangers can be mounted vertically with no change in their effi -

ciency . but prevention of vapor pockets is just as important as in hori-
zontal mounting.

Shell and t ube exchangers have three common flow configurations :

1. Single pass

2. Two pass

3. Multipass

A fluid makes one pass when it flows from one end of the exchanger to
the other. The top exchanger on Figure 3 , is an example of a single pass
tube and single pass shell. Each fluid enters one end and leaves at the
other .
 - 7-

A fluid makes two passes when it enters one end, flows to the
other end~ and returns to the fi r st end . The lower exchanger on
Figure 3, has two passes on both the shell and tube sides .

A common arrangement is that shown in Figure 2 , which has two

passes on the tube side, and a single pass on the shell side .

Prob l em 1
Refe r to t he middle exchanger shown i n Fi gure 3.
a. How many passes does the t ube s i de flu i d make?
2 3

b. How many passes does t he she ll si de fl ui d ma ke?

1 2 3

An exchanger can have any number of passes. Each pass must be

sea l ed from the others so that the fluid does not by- pass the exc hanger .
Refer to Figure 2; the tube side fluid enters at the bottom on the left
and flows to the right in the lower half of tubes . When it reaches the
end, it turns 180 0 and flows to the left in the upper half of tubes. The
partition plate, Par t no. 31. seals t he lower inlet chamber on the t ube
side from the upper ou t let chamber. If the plate did not seal t he two
chambers. some inlet fluid would flow directly to the outlet end, and it
would receive no heat exchange.

The shell side of an exchanger is more difficult to seal, and conse-

quently more than two passes are se l dom used. The longitudinal baffle or
seal plate , item 30. shown on the 2- pass shell side exchanger in Figure 3 ,
has a packing groove along the entire length of the baffle that is filled
with asbestos or other packing to seal the top half of the shell from the
 -8 -

lower half . I f the baffle seal falls , some shell side f luid can flo w
in one nozzle and out the other without ever flowing th e length of the
exchanger .

The she ll s ide of s hell and tube e xc ha ngers has transver se ba ff l es ,

I tems 28 on Figures 2 and 3 , that serve two function s :

1. To keep the tubes from sagging or touching each ot her .

2. To direct the s hell side f luid t o f l ow in a s erp entine

manne r , that i s up and down , r ather than in a horizontal direct ion.
The maximum heat t ran sfer will take place whe n the s h e ll s id e fluid
flows at right angles to the tubes .

Another feat ur e of s hell and tube exchangers is that they can be

mad e so that the en tir e t ub e bundle can be removed. All of th e exchanger s
shown in Figures 2 , 3 and 4 except the top unit i n Figure 3 have r emovable
tube bundles . Replacing a fouled bundle can usually be done in a f raction
of the time required to cl ean it . In addition, the tube bundle can be
replaced , if necessa r y. f or much l ess than the cost of a new exchanger.

Where co rrosion or f ouling is not likely to occ ur in the exc hanger .

there is no reason to have a r emovab le tube bundle . A non r emovabl e or
fi xed tube sheet type of unit can be us ed. which is less cos tly than the
remova ble bundle . The top exchanger in Figu r e J i s an example of a f ix-
ed tube s hee t exchange r . Care must be taken in de signin g a fi xed tube
sheet eXChanger to al low for the differ ence in expan sio n or contra ction
of the s he ll and tubes so that the tubes don ' t pullout of the tube shee t
or buckle from compression .

For example , suppose hot oil at 3lSoC {600 D F1 is used on the s hel l
side to heat a stream of naphtha at J8 D c [lOO°Fl in a single pass fixed
~be sheet exc han ger . The average temper ature of the tubes will be
arou nd l 77 D C [ 350° F] . The s hel l or o ute r wall of the un i t will be a t
D
Jl5 C [60 0°Fl . At 3l5°C [600°F] temperatur e. the shell may "grow" in
length by 1 cm [1/2 in . l from expansion due to heat . whereas the tu bes
e l onga t e only 1/2 cm [1 /4 i n. ] from hea t. As the she ll expands, i t will
make the tubes stretch un t i l t hey pu l l out of the tub e s heet or b r eak in
two .
 -9-

KETTLE REBOILER

THERMOSIPHON REBOILER

courtesy Tubular Exchanger Mfgrs. Assn .

FIGURE 4
 -10-

This si tuation can 'be taken care of by installing an expansion

joint on the shell s ide (Top Exchanger of Figur e 3 . )

If the pressure on the she ll side is more than an expans i on joint

ca n take (usua l ly abo ut 17 ba rs [250 psi ] maximum) , a floating head or
V-tube bundle will probably be necessary to allow the tubes to expand
o r co ntract independent of the shell. Figur es 2, 3 and 4 indicate types
of const ruc tion which allow tube movement independent of the shell.

The up per illustration in Figure 4 is a type of shel l and tube

exchanger commonly called a rehoiler . It is actually a comb ination ex-
change r and gas -liquid separato r. I n this particular drawing , a heat-
i ng fluid s uch as s team or hot oil f l ows through the tubes. The shel l
side f lu id is a liq ui d which par tially vaporizes . It enters the bottom
of the shell in the nozzle at the lef t . As the fluid flows to the right,
some of it vaporizes and passes out the top nozzle in the cente r of t he
vessel .

The liquid that r emains flows over the weir , which is to the right
of the tube bundle, and drop s into the chamber on the right, where it is
withdrawn with a level controller or some othe r device. The height of
the weir is s ligh tly above the tube bundle so that liqu i d will always cover
the tubes in order that th e fu ll tube a r ea is availabl e for heat transfer .

The ill ust ration referr ed to is commonly called a ke ttle type r eboiler .
It would be used to provide the heat r eq uired in a stripper or fractiona-
tion towe r. Its design must provide for enough fre e space above the l evel
of l i quid over the tube bundle fo r vapors to separate from boiling liquid
in the shell .

The lower exchanger s hown in Figure 4 is ca lled a thermosiphon re-

boil er. The heating f luid makes a single pass through th e tube s id e . Li -
quid from a fractiona tion tower or stripper ente r s th e two bottom nozzles
on the shell side . Some of the liq uid vaporizes in the s hell side . The
combined shell side stream , which is liquid and vapor , passes out the top
and flows back to the tower from which it came .
 - 11-

Th e selection of a kettle o r thermo siphon type of r eboi ler i s made

by the designer of the tower to which the reboiler supplies heat. There
a re no hard Bnd fast rules for selection of one over the o the r .

The ke ttle type of r ebo i ler a l so is used in r ef r igeration plants

to chill a str eam of gas or absorp tion oil. In this application , the
refrigerant (usually propane or freon) flow s on the shel l s ide , and the
gas or absorption oil flows through the tubes. The r efrigerant is a co ld
liquid when it ent ers the exchanger . As it c ools the tube side s tream,
i t absorbs hea t and is vaporized . The vapors leave th e top of the unit
and flow to a compres sor . (See Manual P- IO. )

Shell and tube exchangers us ed in process plants a r e almos t always

designed and bu i lt for the spec ific appl ica tion in which they are used .
Their design a nd construction must be in accordance wi th r igid s pe ci fi ca-
tions by a heat exchange r assoc i at i on . Sin ce each exchanger is tailor-
made for one job, the re is li ttl e c hance that it could be effec t ively
used i n another application .

B. Ha irpin Exchangers
An ill ustration of a hairpin or U-tube type of exchange r i s s hown in
Figur e 5 . In most applications this is used as a single-pass, counter-
current flow exchanger . The t ube bundle can have several tubes , or a s ingl e
tube made of pipe. A s ingle t ube often has longitudinal fins on the outside
t o increase th e heat transfer area .

The tube bundle ca n be remo ved through the bac k end . A sealing de-
vice is l ocated on the f r on t end, which is easily disassembled to allow
removal of th e tubes.

The s hel l of the exchanger i s made of s t a nd ar d pipe.

Maker s of hairpin exc hanger s bu i ld them to standard sizes , using

standard materials fo r the shell and tubes.

When these exchanger s are used, the supp l ier determines whic h of the
standard uni ts , or a combination of stan dard units, will provide the re-
 - 12-

SINGLE TUBE WITH FINS

DE~AIL OF
DETAIL OF BEND.
FRONT TUBE SEAL

Cou:tcsy D=own Fin:uba Co .

MULTI-TUB( WITH FINS

DETAIL OF BEND
DETAIL OF
FRONT TUBE SE~L

FIGURE 5

HAIRPIN EXCHANGERS
 - 13-

quired heat transfer duty. The units are not tailor made to each appli-
cation as shell and tube units are.

The units are supplied with mounting brackets that enable them to
be stacked atop one another, or mounted side-by-side. Several units may
be required in a given service . They may be used in series or in paral-
lel.

One of the features of the hairpin exchangers is that additional

sections can be added to an existing installation at a reasonable cost .

C. Aerial Coolers
Aerial coolers are simply exchanger tubes exposed to a stream of
air moving across them. The tubes usually have aluminum fins pressed
onto the outer wall of the tubes to increase the heat transfer area.
Air is blown across the tubes with a f an driven with an elect ric motor
or engine. The exchangers are frequently called fin - fan units.

Drawings of typical aerial cool e r s are shown in Figure 6 .

The exchanger tubes usually have at least 2 passes, and frequently

have 6 or 8 passes. Air flow is single pass.

Each end of the exchanger has a header in which the tubes are rolled
or welded . Figure 7 shows a typical header. A plug is located in the
header opposite each tube to give access to the tubes for cleanout , to
replace, or to plug it if it is leaking.

Aerial coolers have 5 basic components ;

1. Tubes

2. Headers

3. Fan and driver

4. Plenum chamber

5. Support structure
 - 14-

- - - - -===-- -=: -=- =-= =-=-= - -

==-====--=; - - =.=

HE~AD~E~R1ll-~T:UB:E~S-@I ' ~~~~~~~J-l-nl HEADER

SUPPORT
FAN
DRIVER
D
FLUID
OUTLET

I NDUCED DRAFT

FLUID
INLET

TUBES v
~"~."
==== = = - - - - -
- - - - = - = = -=-= - --

~,C /
HEADER

U
FLUID
0 UTLET
CHAMBER "
FAN
SUPPORT
I

.-ll
FAN
DRIVER

- '-- FORCED DRAFT --

FIGURE 6
TYPES OF AERIAL COOLERS
 -15-
'i I

1-
11111~_

FIN DETAIL
TUBE SECTION

HOT
FLUID
TUBE INLET
INSPECTION
( PLUG U
~

I
\' HEADER AIR PAS /
FLOW PARTITION

COOL
FIGURE 7 ..FLUID
OUTLET
DETAIL OF HEADERS ON 4-PASS AERIAL COOLER
 -16-

Components are shown in Figure 6 . The fan can be mounted below the
tubes and blow air up~ which is a for ced draft arrangement ; or it can be
mounted above the tubes and suck air across the tubes, which is an induced
~ arrangement . The induced draft type is more expensive than the o ther.
However , it is often preferred on the basis that it is more efficient since
it offers less chance for hot exhaust air being s ucked back and drawn
through the tubes again.

During cold weather operation of aerial coolers, i t is often neces-

sary to restirct the flow of air across the tubes to prevent too much
cooling of the process fluid in the tubes . A common method fo r restricting
the air flow is to use louvers in the air stream. They are installed above
the tubes on forced draft units, and below th e tubes on induced draft types .
The louvers can be positioned by hand; or can be moved with an automatic
con troller.
In locations in which very low ambient temperatures occ ur, louvers
may not pr ovide enough restriction of air to prevent the fluid in the
tubes from freezing. A recirculating air system is provided for such
applications. In this type o f unit , air circulates through the blowe r,
acr oss the tubes, and back to the blower. Each time the air passes across
the tubes, its temperature ris es . The air t empe rature is controlled by
admitting some co ld air from outside the exchanger housing and discharging
an equal vol ume of circulating air to the atmosphere .

The blowers usuall y have 4 to 8 propeller type blades. The blades

are made of aluminum or plastic. The blades can be supplied with a vari-
able pitch to change the rate of air flow. Variable pitch blowers are us ed
selectively because of their cost and maintenance. The speed of the fan
can also be varied to contr ol air flow .

The tubes and headers in an aerial exchanger a r e usually made of

standard grades of s t eel . Special alloys can be used in corrosive serv-
ices. The structural portion is also made of stee l . It can be galvanized
for corro s ion pro tect ion .
Vibration switches are frequently mounted on ae rial coolers to shut
down the fan driver when excessive vibration occurs . Excessive vibration
is usually caused when one or more of the fan blades gets out of balance
 -17-

with the others. This can be caused by :

1. Accumulation of dirt or scale on the blade.

2. The blade turns 1n its housing, so that its pitch is

different from the others.

3. The blade cracks or breaks apart, or some material flies

off of the tip of the blade.

If corrective action is not taken immediately when a blade gets

out of balance. excessive vibration can cause the unit to fly apart and
damage or injure nearby equipment or personnel .

Worn bearings on the fan shaft can also cause excessive vibration.

MoSt aerial coolers used in process plants are tailormade for the
specific application in which they are used. Standard size units can
be used for engine radiators, air conditioning condensers, and other
similar services where the heat transfer duty is relatively constant.

One of the most commonly used aerial exchanger is that of a radiator

on an automobile. It is an induced draft type of aerial cooler. It
varies from a conventional cooler in that a core is used instead of tubes.
Since it operates at a low pressure, and a leak would not be hazardous,
a rugged co.nstruction is not required. The plates making up the core
are stamped to shape and soldered together in an assembly- line type of
construction that requires very little manual labor.
 -18-

AERIAL COOLER

D. Miscellaneous Types of Exchangers

Quite frequently the presence of an exchanger in process equipment
is not obvious. Pressure vessels, such as separators or contact or
towers, often have heating coils near the bottom of the vessel through
which a hot fluid circulates to prevent liquid in the vessel from freez -
ing. The coil is an exchanger tube and the vessel is the shell .

Pipe or tubing coils are frequently used in process equipment for

heat transfer. The length and size of the coil is determined in the
same manner as the design of a sophisticated shell and tube exchanger.

Another commonly used exchanger that is not obvious is that of a

pipe-in- a - pipe arrangement, where the fluid flowing inside the smaller
pipe 1s used to heat or cool the fluid in the outer pipe.
 -19-

(.
VESSEL
..
Heating
or
Coo ling
Coil
y----7
-
..l...-_
---
/
or
Heating

Cooling
_ _----L Fluid Inlet
PIPE-IN-PIPE EXCHANGER

COIL EXCHANGER IN VESS EL

Steam boilers and gas fi r ed heater s a re al so fo rms of heat ex-

c hanger s . They ar e no t i nc luded i n this manua l beca use they requir e
design and ope rating procedu res tha t a re not appli cable t o conve nt ional
heat exchanger s .

Problem 2
Match the items in the right column that most closely describe
those on the left.
1. Aerial cooler a . Single finned tube
2. Hairpin exchanger b. Kettle reboi1er
3. Shell & tube exchanger c. Radiator
 - 20 -

II. PRINCIPLES OF HEAT TRANSFER

A. General
The process that takes place in a heat exchanger is that of heat
transfer . For the sake of uniformity , we always consider heat movement
from the warm fluid to the cool fluid . In an aerial cooler , heat from
the fluid in the tubes transfers to air blowing across the tubes . In a
gas chille r , heat in the warm gas is tran sfer r ed to the cold refrigerant.

It is important that you visualize the movement of heat from the

warm fluid to the cold one in order to understand the principles of heat
transfer. You can think of heat transfer in an exchanger as though a
part of the warm fluid moved through the tube and mixed with the cool
fluid.

--- WAR.~
FLUID
-- -----..
COOL
FLUID
-
11 1 , 1 1 t t-!l
I
- - }
- -- --
HEAT
I I 1 1 1 I I .... \ \
\
-
-
--- -
- -- - --
-
HEAT TRANSFER
Heat flows from warm fluid to cool one.

Remember: heat transfer is the movement of heat from the warm fluid
to the cool one.

Anot her term you need to r emember is t hat of duty. The duty of an
exchanger is the amount of heat that is transferred . The duty is usua lly
expressed in kcal/hr [Bt u/hr] .
 - 21-

A keal is the amount of heat required to raise the temperature of

1 kg of water by lOCo A BTU is the amount of hea t required to raise
the temperature of 1 Ib o f water by 1°F.

Exampl es:

1. Calculate the heat required to raise the temperature of 4 . 5 kg

[10 Ib] of water from 38 to 48°C [100 to IlBOF}.

METRIC UNITS ENGLISH UNITS

Weight of water 4 . 5 kg 10 Ib
Temperature Change, ~T 48 - 38 118 - 100
Heat required 4.5 x 10 10 x 18
45 keal 180 BTU

2. When fuel gas burns, it gives off

3
9300 kcal/m [1000 BTU/ell ft . ]
A hot water heater holds 900 kg
[2000 Ib} of water at 32°C [9 0 °F . ]
what will the water temperature
900 kg of water 3
[200 Ib of wate r } be when 1 m [37 eu f t ] of fuel
gas is burned?

[lOB . 5°F]
 -22-

METRIC UNI'lS ENGLISH UNITS

3
Heat of combustion 9300 kcal/m 1000 BTU/cu ft
3
Volume of fuel 1 m 37 cu It
Hea t from fuel 9300 x 1 1000 x 37
9300 kcal 37 000 BTU

weight of water 900 kg 2000 Ib

9300 37 000
Wat er t emp rise 900 <= 10. Joe 2000 = lB . 5°F

Original water temp 3rc

Final water temp 42. Joe

Probl em 3
What volume of fuel would be required to raise the water temperature
in the exampl e to 52.6 oc [ 127°F]?
HETRIC 0.5 m3 m3 2 m
3
ENGLISH 17 cu ft 37 cu ft 74 cu ft

Heat transfer takes place in three steps:

1. Heat flows from the hot fluid to the tube wall.

2. It flows through the tube wall.

3. It flows into the cold fluid .

B. Temperature Difference
Suppose we have an insu l ated tank with 2 compartments. Water at
93°C [20Q oF ] is 1n one compartment, and oil at 38°C [100°F] 1s 1n the
othe r one . The heat in the hot water in contact with the partition will
flow into the wall, raising its temper atur e , and then flow into the cold
 - 23-

oil next to the wall, raising its temperature. A temperature profile

would look like this :

After a period of time, heat will flow from the water to the oil
so that the . temperature profile looks like this:

If the vessel stands indefinitely, the temperature in each compart-

ment will equalize, and no additional heat will flow.

Now let's take the same system and install agitators in each com-
partment to continually stir each liquid. The temperature profile at
the start looks like this :
 -24-

The temperature profile is much steeper in the agitated case. and

heat will flow at a much higher rate.

Look at t he temperature of each liquid next to the partition at

the start in each case . In the static cas e , the water and oil tempera-
tures next to the wall were each about 66°C [150°F.] In the agitated
case, the temperature of liquid close to the wall wa s the same as the
liquid in the vessel. In the static case, the temperature differen ce
between the hot and cold liquids at the partition was only a few degrees,
and heat flow was very slow. In the agitated case, the temperature
difference was almost 38°C [lOQ oF ) at the s tart. and heat flow was much
greater.

The temperature difference between fluids is the force that pushes

heat from the hot liquid to the cold one .

HMT

TEMPERATURE DIFFERENCE BETWEEN FLUIDS, 6T, IS FORCE THAT

DRIVES HEAT FROM WARM FLUID TO COOL FLUID
 - 25-

Now suppose that t he same oil and water are flowing through t he
shell and tube sides of an exchange r . If the flow of each liquid is
very slow, the t emperature difference will be ahout the same as that
in the static compartment case , and heat transfer will be slow . How-
ever, if we increase the velocity of the liquids 1n the exchan ger so
that the flow i s turbulent, as it was in the agitated compartme nt case ,
we will have the maximum t empe rature difference and the fastest flow
of he at .

The amount of turbulence that occur s depends upon the velocity of

the fluid . The greater the velocity , t he more turbulent the flow , and
more heat is transferred .

Exchangers are designed so that f l ow will be turbulent. You recall

in the study of shell and tube exchanger design that baffles are used
on the s hell side t o direct the flow of fluid . If ther e were no baffles ,
the shell side fluid would move slowly through the exchanger . The baffles
cause the fl uid to move up and down as it flows through the exc hange r.
thereby increasing the velocity . Enough ba ff les are included on the she ll
side to assure turbulent flow.

Turbulent flow of fluid in the t ubes is maintained by limiting the

number of tubes in an exchanger .

Example :

A stream of water flowing at a rate of 380 ltr/m {lOO gpmJ passes

through the tube side of an exchanger. The tubes will have turbu-
lent flow if the water rate through each of them is at lea st 8 ltr/m
{2 gpm .J How many tubes will be required ?

METRIC UNITS ENGLISH UNITS

Total water flow 380 ltr/m 100 gpm
Flow per tube 7.6 ltr/m 2 gpm
380 = 50 100
Number of tubes 2= 50
7.6
 -26-

The maximum number of tubes at 380 Itr/m {lOO gpm} flow is 50 in

order to maintain turbulent flo w.

Occasionally , the design is suc h that flow is not turbulent in the

tubes. In such cases , turbulence is induced by inserting a metal strip
in the tube that has been twisted in the shape of a spiral .

You can compare the flow of heat to that of water in a pipe. Suppose
you have a pressure tank at 3 bars [45 psi] full of water. You connect
a 1 em ll/2 in.] hose, and the flow rate will be about 75 Itr/m [20 gpm].
The pressure in the tank is t he driving force, and the size of hose is
the only thing that restricts the flow rate . In a heat exchanger, the
temperature difference is the driving force and the restriction to heat
flow will depend on the types of fluids . Heat moves slower through gas
than through liquid .

The temperature difference between fluids in an exchanger can vary

considerably from one end of the unit to the other . The average difference
throughout the exchanger is the driving force. Let ' s look at the tempera-
tures in an exchanger where water is used to cool a stream of oil. The
exchanger can be illustrated :

OIL

WATER

6< - 90 - 40 : 50'C
[6< - 194 - 104 : 90'FJ

Average u'T 50 + S • 29'C

----2-- 6< • 57 - 49 - S'C
[6< - 134 - 120 - 14'FJ
[Average 6T : 90 ; 14 • 520F]

CONCURRE~ FLOW IN EXCHANGER

 - Z7-

In this exchanger the fluids are flowing in the same di rection.

This is called concurrent flow. The temperature difference be tween
fluids varies from soaC [90°F ] at the inlet to aoc
[14°F] at the out-
let . 50 + 8 = 29
The average temperature difference would appear to be ----Z--- °c
[90; 14 _ SZOFj . However, if we were able to take temperature differ-
ences throughout the exchanger, we would find a pattern like this:

90"C [194"F]

SO°C [179"F] WATER TEMP

70 0 e [IS8"F]

60°C [140"F]
57°C [134"F]
AVG 6T - Z3"C [41"F]
sooe [IZZ"F] OIL 49°C [IZO"F]
TEMP
40°C [104"F]
INLET OUTLET
END END
TEMPERATURE OF WATER &OIL
AS THEY FLOW THROUGH EXCHANGER

The average temperature throughout the exchanger is 23°C [4 1°F]

instead of 29°C [52°F] as it first appeared.

Now , let's take the same exchanger and reverse the flow of water
so that it moves in the opposite direction to the gas. This is called
countercurrent flow . Flow will look like this:
 -28-

57°C
[134 'F]
WATER

6t 90 - 49 : 41'C
[6t 194 - 120 : 74'F] OIL
Average 6T ..
41 + 17
229°C
6t = 57 - 40 = 17'C
[6t = 134 - 104 = 30'F]
[Average 6T : 74 ; 30 = 520F]

COUNTERCURRENT FLOW IN EXCHANGER

The average temperature differ ence appears to be 41 + 17 • 290C

+ 30 0
2
2 a 52 Fl, which is the same as the arithmetic average in the con-
current flow case. However, a plot of the temperature difference between
the gas and water from one end of the exchanger to the othe r looks like
thi s :

90 G e [194'F]

WATER TEMP
BO°C [179'F]

70'C [158'F]

60'C [140'F] OIL

TEMP
57'C [134'F]
AVG T - 27'C [49'F]
50 0 e [122'F]

40°C [104 'F] I====:===~========:::=Jl 4o'c

WATER OIL
[104'F]

INLET INLET
END END
TEMPERATURE OF WATER &OIL
AS THE Y FLOW THROUGH EXCHANGER
 -29-

The aver age temperature di ffe r ence in this case is 27°C [49°F]
which approache s the arithmet ic average of 29°C [52°F].

The mean average temperatur e i n the count er c urrent flow was 27°C
[490F] ver s us 230C [4 1°F] for conc urrent flow. The concurrent exchange r
would have to be about 20% larger than the coun t e r curr en t one, fo r the
same dut y. Consequently, whenever possible, exchangers a r e designed for
countercurrent flow in ord er to get the maximum temperature difference
between the two f luids.

Here is another term to remember: TEMPERATIlRE APPROACH.. In the pre-

ceding coun t erc urr ent example , the fluid temperature difference on one end
was 41°C [74°F] and on the other end it was 17°C [30°F]. The ~ of the
two, in this case 17°C (30°F}, is the temperatur e approach.

Calculation of the average temperatur e difference involves the u se

of logarithms and is not necessary for yo u t o know the procedure . The
impo r tant thing fo r you to r emember is that the average temperature dif -
ference is somewhat less t han the arithmetic average. For our purposes ,
the a rithmetic average will be accurate eno ugh .

Example:

An amine exchanger has lean amine entering at l07°e [225°F} and

leaving at 79°C {175°F}; and foul amine e nte r s at 52°e {125°F} and
leaves at 79°e [175°F} . What is the average t emperature difference?

First , let ' s draw a picture of the exchanger :

l07°<i.
LEAN AMINE
6 t~107 - 79~28°C {225°F] {175°F] 6t=79 - 51=28°C
{~t=225 - 175sS00F} {~t;175 - 125=50°F]
0
• 51 e
RICH AMINE
[12S0F}

In this case, the temperature difference is 28°C {SO°F} on each end,

so the average temperature difference, 6T = 28°C {SOap} .
 -30-

Example :

An aerial cooler is used to cool gas from a compressor. The gas

inlet temperature is 12loC [250°F] and it will be cooled to 49°C
[120°F}. Air temperature rises from 32°C [90°F] to 60°C {140°Fj .
What is the average temperature difference?

A drawing of the exchanger looks like this:

~t-121 - 60=61 o C
121°C
{250°F]
.. GAS
49°C
{120°F]
.. b,t=49 - 32=:l7°C
{~t=250 - 140=110°F]
60°C
•[140°F] AIR

METRIC UNITS
- 32°G
[90°F}
{b,t=120 - 90=JOOFj

ENGLISH UNITS

61+17 78 = 390C
Average fiT =- 2-
=
2 = -110+30 140
- 2 - = 2""

Probl em 4
a. What is the average temperature difference in a radiator in
which water is cooled from 93°C (200° F] to 60°C (140°F] with air whose
temperat ure rises from 27°C (BOoF] to 49°C (120°F]?
METRI C 33°C 3B.50C 44°C
ENGLI SH 60°F 70°F BOoF
b. What i s the temperature approach?
METRIC 33°C 3B.50C 44°C
ENGLISH 60°F 70°F BOoF
 - 31-

C. Resistance to Flow of Heat

All materials have a natural resistance to the flow of heat through
them. Those with a high resistance are used for insulation .

The resistance to the flow of heat can be demonstrat ed by holding

a metal bar in a flame . The metal in contact with the fire may heat to

\ 1 / /

L -_ _ _ _ _ _ _ __ _ _ _ _ __ __ _ _ _ _ __ _ _ __ _ _ __ _ _ __ __ __ _ I~
~ ~

260°C [500°F] , but the other end of the bar can be held for several min-
utes before the heat from the fire travels the l ength of the bar. If
the bar is copper or aluminum. the open end will get hot much faster than
s t eel. If it is made of asbestos, little heat will flow from one end to
the other. Different fluids have different r esis t ances to heat flow.
Water has th e lowest resistanc e of common fluids. The resistance of
viscous fluids such as c rud e oil or glycol is higher than that of less
viscous gasoline or LPG. Gas has a greater resistance than liquids. In -
creasing the gas pressure will reduce the resistance to the flow of heat.

In an ideal exchanger, the resistance to the flow of heat is the same

for the shell fluid as that in the tubes. If both fluids are water, oil
or gas, resistance to heat flow in the hot stream will be about the same
as that of the cold one . Unfortunately, in most exchanger applications,
resi stance t o heat flow through the fluid s is quite different. A typical
 -32 -

example of such a case is an aerial cooler . Ai r has a high resistance

to heat flow. We compensate for its resistance by adding fins to the
exchanger tubes on the air side . The fins provide ext ra surface area
for heat to flow into the air .

The resistance to heat flow of an exchange r is c a lled i t s coefficient.

It is expressed as the heat transferr ed per unit surfa ce a r ea per degree
6T temperatur e d ifference per unit time . Total heat transferred equal s
the coefficient times surface area times AT.
physical properties of the fluids at flowing conditions , the flow rates
of the fl uids , the tube material and wall thickness. Calculation of the
coefficient is a specialty. Common values fo r coefficients for various
services are shown in Table I on page 55 at the end of the text material .

A low coefficient indicates a high resistance to flow, and vice versa.

Refer to Table 1: uudt!c the heading of "Miscellaneous" you see that a
gas-to-gas exchanger in which the pressure of each gas stream is 7 bars
[100 psi] has a coefficient of 195 kcal [40 BTU] ; whereas a unit operating
at 70 bars [1000 psil has a coefficient of 290 kcal [ 60 BTU]. More heat
transfer will take place at h i gher pressure because the resistance of
heat flow is less than at low pressur e. The higher the coefficient, the
lower t he resistance to heat flow , and the more heat transfer will take
place . What this means in practice is that an exchanger having a high
coefficient will require less area than one having a low coefficient.

D. Area
The final factor that affects the f l ow of heat is the area of the
exchanger . An exchanger with 10 tubes would obviously transfer twice as
much heat as one having 5 tubes. The area of an exchanger is the tota l
external area of the tubes in the unit.

Table II in the back of the book shows the external tube area per
lineal foot of tubes most commonly used in heat exchangers .
 -33-

Exampl e :

An exchanger has 300 tubes 20 mm dia [3/4 in . dia] and 6 m f20 ftJ
long . What is the total surface area?

Sol u tion :

METRIC UNITS ENGLISH UNITS

Number of tubes 300 300
Length of each tube 6 m 20 ft
Total length of tubing JOOx6 "'" 1800 m JOOx2 0 6000 ft
Si ze of tubes 20 mm 3/4 i n .
2
Area of tube (page 56) O. 0628m 1m 0.1963 sq ft/Et
TOtal area of tubes 1800 x 0 . 0628 6000 x 0.1963
2
113 m "" 1178 sq ft

Problem 5

An exchanger has 100 - 25 em [1 in. ] diameter tubes 6 m [20 ft] long.

What ; s the total surface area?
2 2 2
METRIC 23 m 47 m 94 m
ENGLISH 262 sq ft _ _ 524 sq ft __ 788 sq ft

To summarize . heat tran sfe r depends on ) fac tor s :

1. Tempera ture differenc e of the fluids .

2. Resistance to heat flow .

3. Area .

You re call we said t hat t he heat transfe r in an exchanger was ca l led

its duty . We can now derive t he fo rmul a for calculatin g the duty of a n
exchanger :
 - 34-

Duty - (Temp diff) x (Resistance to heat flow) x (Area)

We commonly use the following letters for each of the above factors :

Q • Duty, kcal/hr [BTU/hr)

U - Flow resistance (coefficient)
~T = Tempe r ature difference, DC or OF
The formula is: Q - U x A x 6T
When we a r e designi n g new exchan gers , we know t he duty . coeffic ient ,
and tempe r at ur e dif f e r e nce, and we want t o determine t he area . The for-
mula can be rearranged to ca l culate the area :

Area , A - ~
Now t hat we understand all the facto r s that affec t the duty of an
exchanger, let ' s work some more complicated problems .

Example:

An exchanger uses wate r to cool lean a ll . Water enters at 32 GC [90°F]

and leaves at 49 DC {120°F} . Lean oil en t e rs at B2°C [180 0 P] and
leaves at 38°e /lOO°FJ. The exchanger has 240 tubes 20 mm dia [3/4 in.
dial and 12 m [40 it} long . What is the duty of the exchanger?

LEAN OIL WATER

OUT

t
IT 240 - 20 mm [3/4 in.1 tube~ T
1 : r'\
-
I
~

:;
r'I

f1 I

1 / " -"
, I I I , I

I
I '
,
/1 "\./
: '-J I

LI -' H
t 32"C
[90"F]
WATER IN
12 m [ 40 ftl
t
82"C
[180"FI
LEAN OIL IN
 -35-

Solution :

We will use the formula Q U x A x !J.T

At=S2 - 49=33°C [lB00F] LEAN OIL I1t=38 - 32=6"C

(At=lBO - 120=60"F) IAt=lOO - 90=lO°F]
.. 49°C WATER
(l20°F]

Average I1T

[Average f::.T = 60+10 = 70 =. 350Pj

2 2

METRIC UNITS ENGLISH UNITS

Coefficient, u(page 55) 390 80

Calculate area:
Number of tubes 240 240

Length of tubes 12 m 40 ft
Total length of tubing 12x240 2880 m 40x240 9600 ft
Tube diameter 20 11IIi 3/4 in .
Unit area of tubes (page 56) 0.0628 0.1963
Total area of tubes 2880xO.0 628 9600x.01963
2
181 m 1884 sq ft
Heat transfer formula U x A x f::.T U x A x 6.T
Substitute in formula (390)x(1 81)x(19 . 5 (80) x (1884) x ( 35)

Duty 1 376 500 kcal/hr 5 275 200 BTU/hr

Example:

We have a gas chiller in which propane at - 40"C { - 40"P} is coolin g

from - loe to - 34"C [30°F to -30°F). If the duty of the cooler is
3000000 kcal/hr [12 . 0 MM BTU/hr], what is the area and how many
tubes 20 em dia by 12 m long [7/8 in . dia by 40 ft long) will be
required?
 - 36-

PROPANE
GAS
INLET (r VAPOR OUT
- 40"C
J L - l°C ~________~I LL-[_-4_0_0F_] __~
V [30"Pj
L
--
I I I
\} (r
GAS LIQUID PROPANE
OUTLET IN
GAS CHILLER

Solution :

Use the formula A =~ to find the area, and then determine

the number of tubes:

- lOC .. - 34° ~
[+30"Fj GAS [ - JO°F]
tJ.t=40 - L=39"C llt=40 - J4:6°C
[6t=30-(-40)=70°F]
.. - 40"C
[-40°F)
PROPANE
.. - 40"C
{ - 40"F}
[f1t=40 - 30=lO"Fj

Average !J.T = -39+6

2- 22.5"C

'T _ 70+10 _-
{Average u - 2 40"F]
 - 37-

METRIC UNITS ENGLISH UNITS

coefficient , U(Page 55) 460 90

6T
Duty, Q 3 000 000 kcallhr 12 000 000 BTUlhr
3 000 000 12 000 000
Substitute in formula
460x22.5 90x40
2
Area 290 m 3333 sq ft
Tube size 20 mm 718 in .
2
Unit tube area (page 56) 0 .0628 m 1m 0 .2291 sq ft/ft

Length of tubing ~ 3333

0.0628 0 . 2291
4618 m 14 550 ft
Length each tube 12 m 40 ft
4618 14 550
Number of tubes
12 40
=- 385 = 364

Problem 6
What will be the duty in an ami ne-to -water exchanger having a tube
area of 25 m2 [250 sq ftl and a temperature diffe rence of 33°C [60oFl?
METRIC 487 000 kca' / hr 561 000 kcal/hr , 100 000 kcal/hr
ENGLISH 1 .95 MM BTU/ hr 2.' MM BTU/hr 4.2 MM BTU/hr

TWO HAIRPIN EXCHANGERS CONNECTED IN SERIES

 -38-

Il l. APPLICATION OF EXCHANGERS

Heat exchangers ar e generally used for one of three reasons:

1. To tr ansf er heat i n order fo r a process t o occur.

2. To conserve he at .

3. To cool a hot s tream.

Some examples of each are :

1. Process exchangers
a. Reboilers
b. Condensers

2. Conserve heat
B. Gas-to- gas exchanger s .
h. Lean amine to foul amine excha ngers .
c. Lean oil to rich all exchangers
d. Fra c tionator preheaters

3. Coolers
a. Radiat ors
b. Compressor coolers
c. Product coolers

Selection of the t ype of exchanger to use in a partic ula r service

is us ua lly a matter of economics . However , se le c tion is of t en di c tated
by cir cumstances. For example if a process cooler was needed in a lo ca-
tion that had no wat er , an aerial cooler would be r equ ired.

A. Shell and Tube

The most widely used exchanger in pr ocess plants i s a shell and tube
exchange r. It can be designed in a vari e ty of confi gurations and t ailored
to do a specific job . Special materials for low temperature or corrosive
service can be used . They ca n be made long o r short, hori zon tal or ver -
tical . The advantage of shell and tube type exchangers over other t ypes
 -39-

is that since they are designed for a specific application, they are
more likely to perform satisfactorily than any other type.

The disadvantages of S & T units are that they are expensive, and
have a limited reuse value in another location.

TUBE BUNDLES FOR SHELL AND TUBE EXCHANGERS

B. Hairpin
Hairpin exchangers are usually used when the surface area require-
2
ment is less than 40 m [400 sq ft]. They are made in standard sizes.
Since standard size units must be selected to fit the particular heat
transfer service, the exchanger mayor may not perform as required by
the process. They are less expensive than S & T exchangers in smaller
sizes.

Probably the largest single use of hairpin exchangers is on packaged

process equipment. such as gas dehydrators, refrigerated hydrocarbon re-
covery plants, gas sweetening plants, etc.

The advantages of the hairpin exchangers are:

1. Low cost.

2. Ease of maintenance.

3. Ease of adding additional units.

4. Can easily be used in another application.

5. Good delivery.
 - 40-

The disadvantages of hairpin exchangers are:

1. May not pe~form to process requirements.
2. Limited selection of metals.
3. They ar e la r ger and take up more s pa ce .

C. Coils
Coil type exchangers are used when the s urfa ce area requirement is
low, and space is limited . They have a low coefficient , and are usually
us ed where a high temperature difference is available . Some common
applications are:

1. To heat fuel or instrument gas to prevent hydrate s from

forming.
2. For heating water in the bottom of vessels to prevent
freezing.
3. For small process exchangers in packaged equipment.

D. Aeria l Coolers
Aerial cool ers are used when no other process coolant (such as water)
is available. Some common applications of aerial coole rs a r e:

1. Engine radiators.

2. Process coole rs on packaged equipment and offshore platforms .

3. Fractionator con densers .

The main disadvantage of aerial coolers over S & T is that th e tem-

perature of fl uid out of the cooler is limited by ambient air temperature.
A temperature approach of lloC [20°F] is about the best that can be done.
This means that the outlet process fluid temp erature will be lloC {20°F]
above ambient air temperature. It is seldom economical to have a tempera-
ture approach of l ess than 16°C [JOoF]; many units use a 22°C [40°F] approach .

Aerial coolers must be carefully loca ted in a plant so that th ey do

not ci r culate air that has been warm~d f rom a heater or engine. They
should be on the upwind side of any heat source. They should be located
above walls or buildings that might divert the flow of air out of the ex -
changer back to the intake s id e of the fan.
 -41-

IV. OPERATION OF EXCHANGERS

A. Shell and Tube or Hairpin

In most cases, exchanger s are put in service by simply opening the
process fl uids through them . The cool fluid should be opened first.
If the hot fluid 1s 55°C [100°F] warmer than the cold one , the flow of
hot fluid should be opened gradually to prevent shocking the tubes with
a sudden surge of heat.

Shut down is the reverse , with the hot fluid closed first .

Prior to start UP. the outlet liquid side of exchangers should be

vented with the i nlet liquid line open until the liquid side 1s completely
full.
SHELL SIDE TUBE SIDE
FLUID OUTLET FLUID OUTLET
t Before star t - up, fill ex- t
Vents
Z changer with liquid by
venting air. Z1_ _ -<0<1)<] Vents

Z To start-up. open flow of·

coolest fluid first. Then
open warm fluid.
t
TUBE SIDE SHELL SIDE
FLUID INLET FLUID INLET

Routine operating checks are:

1. Observe fluid inlet and out l et temperatures and determine

the cause of a change from normal.
 - 42-

2. Observe the pressure drop on eac h s id e by reading press ure

gauges, and de t ermine the cause of a change from normal.

3. Reduce or increase the fluid flow as needed to obtain the

desired temperatures. For example, open the flow of water to
coolers in the summer , and close it in the winter .

Most reboilers have temperature controllers that con trol the temper-
ature of the shell side liquid by changing the flow of tube side fluid.
The temperature controller can be put in service when the shell side
liquid level is above the tubes, and the tubes have been warmed up by
slowly admitting the tube side fluid .

B. Aerjal Coolers
Aerial cooler s are started in the following sequence:

1. Start the fan. Check for vibration or unusual noises.

2. Open fluid through the tube s .

On shut down , fluid is blocked in, and then the fan is turned off.

Routine operating checks are :

1. Observe the cooler inlet and ou tlet temperatures and deter -

mine the cau se of a change.

2. Adjust the louvers or other air flow controls as necessary.

3. Check for leaks in the tubes or headers.

4. Check the fan fo r noise and vibration.

S. Check tube fins for damage or obstruction.

6. Periodically check the fan blades for speed, pitch, and

scale or dirt accumulation.
 -43-

v. TROUBLESHOOTI NG EXCHANGERS

A. Shell and Tube Exchan gers

A problem with an exchanger occurs when the hea t transfer duty
falls below design. It shows up when the fluid being cooled does not
get co ld enough. or the fluid being heated does not get hot enough.

TROUBLESHOOTING PROCEDURE

CAUSE OF LOSS OF DUTY PROCEDURE TO CORRECT

1. Low flow rat e of one or both Check flow rates . Raise to

fluids . design .

2. Inlet temperature of one or Check temperatures. Correct

both fluid s has changed . if necessary.

3. Vapor pocket 1n liquid s ide. Vent vapor on outl et end.

4. Tubes are corrod ed or plugged. a. Verify condition by

Condition can be on shell or measuring pressur e drop.
tube side, and will cause a b. Backwash un i t if possible.
high pressure drop. c. Clean tube s.

5. One or more tubes are leaking. a. Confirm leakage from pre ssure
The higher pressure fluid will observation or by analyzing low
flow into the low pressure pressure fluid for presence of
fluid . Pressure on the low high pressure fluid.
pressure side will ususally b. Shut down unit and plug
rise. leaking tubes.

B. Aeria l Coolers
Three types of problems occ ur on aerial coolers:

1. Mechanical difficulties with t he drive r, pulley, speed re-

ducer, shafL, etc . These are not exchanger problems, and will
not be discussed he re.
 -44-

2. Insufficient movement of air across the tubes. This is

an exchanger problem that is difficult to diagnose. The best solu-
tion to the problem is ·one of prevention. Pr oper air movement can
be maintained as follows:

a. Check the fan speed and replace belts or make other

repairs as needed.

b. Keep the fan blades c l ean and set at the right pitch.

c. Keep louvers clean and remove debris that may have

fallen on them .

d. Keep the tube fins clean.

e. Keep the area around the cooler c l ean and free of rags,
paper, debris, et~ that might lodge on the outside of the tubes .

f. Keep sources of heat, suc h as temporary heaters or

engines. away from the cooler s.

3. The final problem is one of insufficient heat transfer.

This shows up as a n increase in the fluid temperature out of the cooler.
He re is the pro cedure for finding the cause :

a. Check for an increase in the flow rate or temperature

of th e inlet flui d .

b. Check for proper air movement . See that lo uvers are

open, the fan is running at full speed , blades a r e clean and pitch
is prope r, and fins are clean and undamaged.

c. Check for tube leakage. A leak will usually show a stain

and will cause the out l et air to look smokey. Of course, a
severe liquid leak will drip to the gr ound and be obvious .

d. If the problem persists , internal corrosion or tube

plugging is indicated . It can usually be confirmed by checking
for an increase in pressure drop across the tubes . Aerial
coolers usually have 4 - 8 passes. The pressure drop of each
pass shou ld be checked t o see if one or more is higher than the
others.
 -45-

VI . GASOLINE PLANT EXCHANGER PROBLEMS

Heat transfer is one of the most critical processes in a refr iger a ted
gas processing plant. Recover y of product depends upon coo ling the gas
as low as possible. Consequently , heat exchangers must operate properly
in Qrd er to get the maximum production . In this section we will concern
our selves with the exchangers in the gas cooling system. Ope rat ion and
troubleshooting other process exchangers has been covered.

The two most important exc hangers in the gas stream are the gas-to- gas
exchanger. and the gas chiller. We will discuss each of them separately.
Refer to Figure 8 fo r a flow diagram .

A. Gas- to-Gas Exchanger

In the gas- t o-gas exchanger, some of the heat in the inlet gas s tream
is transferred to the cool gas from the absorber. These units a re us ually
designed for a 60 C [lOaF ] approach; that is, the temperature of the coo l
gas str eam out of the exchanger is 60 c [lOaF] below the temperature of
the inl et gas stream. This exchanger is critical beca use any heat that
remains in the inlet gas stream that should have been r emoved in the ex-
changer will have to be removed in the chiller. This will require addi -
tional refrigeration , which means more load on the r ef rige rat ion compre sso r,
and more compressor fuel costs.

A gas-to-gas exchanger is one of the most difficult to properly design.

It is not unusual for an exc hanger from one supplier to have 30% more area
than one from another when both are designing from the same data.

Design is difficult for two r easons :

1. Gas has a high resistance to heat flow . The velocity in

both the s hell Bnd tube sides is c ri tical in minimi zi ng the resistance.

2. Some condensation of the inlet stream us ua lly occurs which

has a s ignific ant effec t on the velo c ity and resistance to heat flow
(Li quid has a l ower resistance to the flow of heat. )
 - 46-

, r

r l ! ,; :':
,- T
~

L GAS -TO-GAS
~3aOC EXCHANGER
'1 ~lOOOFJ
INLET
GAS

Duty of gas-to-gas exchanger

is about the same as that of
chil l er. Loss of hea t tran s-
fer in gas -to- gas exc hanger
Lean will requ ire more cooling in
Absorption chiller, whi ch will take more
refrigeration compressor .
Oil

~L/ _23°C [-10°F]

ABSORBER 8 )
- laoC CHILLER
rOoF]

Ric h Oil

FIGURE a
GAS FLOW SYSTEM AT SUMMER OPERATING CONDITIONS
 -47-

It is important that the performance of a gas- to - gas exchanger in

a new plant be evaluated as soon as possible af ter start-up to es tablish
the actual performance of the unit to use as a basis for future com-
parison . For example, the unit shown in Figure 8 has a temperature
approach of SoC [IO° F] . Suppose in actual operation at design flow
rates, the approach was SoC [15°F]. In this case , the outlet gas tem-
perature on the shell side would be 29°C instead of 32°C [85°F instead
of gO°F]. You mayor may not be able to get the exchanger supplie.r to
correct the s ituation, but assuming that you do not, then your r eference
point for futu r e evaluation of the performance of the unit is a tempera -
ture approach of BOc [15°F]. Any time t he approach is more than 8°C
[15°F] at design flow rate the exchanger may not be performing properly
and you are probably wasting refrigeration in the chiller .

A common cause of loss of duty in the unit is that of excessive

glycol injection in the inlet gas stream. Glycol is injected to prevent
hydrates from forming in the unit. The quantity of glycol that is injected ,
and the manner in which it is injected, can have a significant effect on
the performance of the exchanger . Glycol has a high resistance to heat
flow , and an excessive flow will reduce the coefficient and thereby lower
the rate of heat transfer . The net effect will be to increase the tem-
perature approach.

The procedure for finding the ideal glycol rate is not an easy or
pleasant one. It is a matter of startin g with a high rate and slowly
cutting back until hydrates form , and then slightly increasing the rate.
The presence of hydrates is indicated in two ways :

1. The temperature app roach increases due to a loss of heat

transfer.

2. The pressure drop on the inlet stream (tube side on Figure

8) increases.

When hydrates form, they usually block the flow of gas through the
tube. Consequently, increasing the glycol injection rate will not help
 -48-

because no flow i s pa ssing through the pl ugged t ubes . Yo u wi ll have t o

mel t the hyd rat es by s huttin g down the re f r ige r a tion unit and let t he
exchanger heat up unt il the hydrat es melt.

The important thing to r emember about g lycol injec tion is that a

ce rtain quantity i s r eq uired at a ce rta in gas rat e to prevent hydrates
f rom fo rmin g , a nd the minimum s hould be he ld at all time s . The idea
that if a l itt l e does a l ot of good , a l ot will do even mo r e , does not
apply t o g l ycol injection . An excess of glyco l will re duce the amount
of heat transfer r ed in both the gas -c o- gas exchanger and t he ch ill er, and
will ultimately reduce the amount of cool ing and the r eby reduce t he re -
covery of LF-gas .

Since we are conce r ned at this point with heat transfer , and not
hydrate inhibition , we will not attempt to cover the detailed procedureE
for ope r ating the glycol i nj ection system . The important thing fo r you
to remember is that the glycol r a t e will affect the heat t ransfer r ate ,
and that it should be held as low as possible.

In the system shown on Figure 8 , the duty of the gas-to-gas exchan ge r

is about the same as that of the gas chiller . In other words , half of
the total gas cooling occurred i n the gas-to-gas exchange r. Had i t not
been used, the refrigeration l oad would be twice as much . The cost of
the. exchanger is about 20% that of the compressor . You can s ee r eadily
that the gas- t o-ga s exc hanger saves a s ignificant investment. You can
also s e e that the los s of a few degree s of cooling in the exc hange r can
add a significant l oad t o the chiller.

B. Gas Ch iller

The same principles that apply to glycol i njection are a ppl icable
to the chiller . In add ition, two other ope r atin g p roblems are often en-
coun t e r ed in it :

1. Low level of r ef rigerant in the shell s id e .

2. Accumulation of lube o il on the shell side .

 -49-

In order to get the maximum duty from a chiller, the level of re-
frigerant must be above the tube bundle. Very little heat transfer will
take place in tubes that are not immersed in liquid. However, deter -
mining the level of refrigerant in the exchanger is not an easy thing to
do. The refrigerant is boiling rather violently in the shell side, so
that it is almost a foam in the vessel.

You know that if you place a pan of water on your stove and heat it
until it boils violently, the level in the pan will rise, and will prob -
ably boil over onto the stove. The same situation occurs in the chiller.
If you have a gauge glass on the refrigerant side, the liquid in it is
not exposed to the same heat as the fluid inside the vessel. So, it is
not boiling, and will show a lower level than that in the vessel. Its
level will be that of the pan we set on the stove before we started boil-
ing water; whereas, the level inside the exchanger will be the level after
boiling started. Consequently, a gauge glass is not an accurate measure
of th e level of refrigerant in the chiller. It will indicate a change in
level inside the chiller, but will not show the actual level in the vessel.

GAS
INLET REFRIGERANT
VAPOR OUT
t Level of foam

Level indicated

GAS
t
LIQUID REFRIGERANT
in gauge glass

OUTLET
IN
 - 50-

The level in a gauge glass i ndic a tes t he pr oper level of liquid inside
an exchanger . The fluid inside a n exchanger is a mixt ure of liquid refrig-
erant and gas bubbles fo r med when the liquid boils . It 1s ligh t er than pure
l iq uid in t he gauge glass , so its level will be higher. The mixtu r e may cover
the floa t on t he level controller , mak ing it inoper ative . Th e level of mix-
tur e inside the vessel mus t be lowered until part of the float is exposed .
The level i n the ga uge glass wi l l be nea r e r to t he bottom of th e glass .

The s ame is true of a l eve l co n tr olle r on the ch iller. If the float

is lo cat ed inside the ve sse l, and you use the level in the gauge glass
to set the co ntroller, you may have such a high level in the vesse l that
the floa t on th e contr olle r is complet ely immersed in foam, in whic h ca se
the cont r oller will not functio n properly. It is impo ssibl e to adj ust a
level con trolle. r when the level of liquid is be l ow or above the float.
The float must be partially imme. r sed in liquid in order fo r it to fun c tion ,
and for you to change the level se ttin g .

You may set the control point on you r level cont r olle r when the float
is totally imme r sed in fluid , and it wil l appear to be operating satisfac -
torily. However , wh~n you r et urn a few minu tes l a t e r, the leve l may have
dropped out of the gauge gla ss . If the level co ntroller is an exte rn al
cDge type, the l evel in it i s more than likel y lower thDn t he level in the
c hil l er , unless it is picking up a lo t o f ambient heat and boilin g at a
greater rat e than the liquid In the chiller.

The location of the level controlle r and gau ge gla ss is important

in the ir pr oper use. The reft'igerant near th e end of an exc hanger is not
exposed to as much heat as that in the middle of the unit , so that i t is
in more of a liquid state than a foam . Conseq uent l y . a gauge gla ss or
level con tro l ler l ocat ed 0 11 the e nd of t he chi ll e r will sense a low l evel
of pure liquid , whereas it will se nse a higher level of foam nea r the cente r
of the vessel.

The situatio n is compo und ed by t he fact that th e lines that con nect
the level cont r oller t o the vessel a r e much large r than those connecting
the gauge glass . It is entirely possible for the gauge glass to show a
steady level of liquid, whereas the level controller is filled with foam
that is in t he vessel .
 - 51-

From the previous drawing , it would appea r tha t using the gauge glass
to set the level controller usually will r esult in the level inside the
chiller being higher than that indicated by t he gauge glass. The problem
does not lie 1n operating with a level higher than necessar y, but in
having a non-functioning level controller when the float is totally im-
mersed in liquid.

As far as the chiller is conce rned, the level of refrigerant should

be high enough so that all of the tubes are immersed . No additional
cooling will occur wh en the level rises above the tuhes . However , a
high liquid l evel will usually r es ult in liquid carryover out the top
of the unit, which may cause problems at the compressor.

The important th i ng to remember is that the level of refrige rant

indicated by a gauge glass is not necessarily the level of liquid in
the chiller or in the level controller. The level in the gauge glass
will genera lly be l ower than that in the chiller or l evel controller .
In some cases , you may have t o operate your chiller with the leve l in
the gauge gl ass near the bottom of the glass in order for the level con-
troller to f un ction . There have been instanc es wher e the l evel of boil-
ing refrigerant inside the exchanger was so much higher than the leve l
shown in the gauge glass that the gauge glass had to be lowered in order
to use it in setting the level controller .

The ideal level indication in a chil ler is a "bull s-eye " type of
gauge glass through which the interior of the vessel can be observed
from the outside . It is difficult to prevent ice from forming on these
gauges , which obst ructs your vision.

The re frigerant that flows to the chiller comes f rom a compresso r .

Most compressors require some lubrication in the compressor cylinders.
The l ube oil injected in the cyl ind ers will end up in the liquid refr ig-
erant. The lube oil will dissolve in the refrige rant at ambient tem-
perature ; however, it is less soluble at the temper ature in the chille~.

Consequently, it will separate from the refrigerant in the chiller.

 -52 -

If propane is the refrigerant, the l ube all will settle to the

bottom of the c hille r; i f freon is the refrigerant, the lube will collec t
on the top of the refrigerant in the chiller. However , in either case ,
the boiling that occurs in the c hill e r will agitate the fluid in the
vessel so that some of the lube oil will be dispe r sed throughout th e
vessel. Oil becomes viscous at low temperatures, and it will tend to
collect on the tube s , and act as an i n sulation to prevent the flow of
heat. The duty of the chil ler will decrease. an d the outlet gas temper -
ature will not be as low as it should be.

Severa l devices are available to remove l ube oil from refrigerant .

We will not attempt to describe them , but merely to point out that they
should be in operation at all times .

Even though you use some form of oil removal device , some lube oil
will usually find its way into th e chiller. The only way to remove it
is to drain it when the chiller is shut down . Consequently, each time
the unit i s down, you should drain oil that has accumulated . Oil s ho uld
be drained as soon as possible after shutdown while the r efrigerant is
still cold . As the refrigerant heats up , the oil will dissolve in it.

Draining the oil from a chiller usin g propane is no probl em because

the oil will se ttle to the bottom , and will flow out a drain line. How-
ever, draining oil from a unit using freon is more difficult . The oil
is lighter than liquid freon , and it will float to the top of the freon .
It will be necessary to adjust the level of freon in the chiller until
it is next to a drain connection on the vessel.

Corrosion in a chiller is rarely a problem. Water or oxygen must

be present for corrosion to occur, and neither are in the gas or refrig-
erant in sufficient concentrations for corrosion to occur . Consequently,
the likelihood of tube fai lure from corrosion is very remote . However ,
the possibility of a tub e failure always exists . When it does happ en,
high pressure gas will flow into the r efrigerant stream. The refrigerant
system i s usually designed f or a much lower pressure than that of the gas.
 - 53-

Normally there are r elief valves on the chiller which will pop if gas
leaks into the vessel, so the r e i s no danger of bur sting the vessel from
excessive pr essure .

The problem from a leaking tube is not so much one of overpr essur ing
the refrigerant system , but of contaminating the re f rigerant so that it
has to be drained and a new charge of r ef rigera nt added .

Detection of a small leak in a tube i s often difficu lt. It shows

..up in two ways :

1. The pressure in the refrigerant side of the ch iller rises .

2. The pressure on the di scharge side of the compressor ris e s .

Any time you suspect a l eaking tube, you should immediately confirm
it , a nd block in the gas stream before the leaking gas contaminates the
ref rigerant.

As we said , a leaking tube will ca use the pressure to rise in the

re frige rant side of the chi ller, and on the discharge side of the refrig-
erant comp r esso r . If propane i s the r efriger ant , some of t he l e aking
gas will dissolve in the propane . When th i s happens, it r aises the pres-
sure req uired to keep the propane in a liquid form . During the summer -
time, the p r opane out of the conde nser is usually abou t 43°C [l10°F ) and
its pressure is around 16 bars [230 psi] . I f it get s cont aminat ed wit h
1% gas , the pressure required to keep it in a liquid form increases about
3 bars [50 psi]. The pressure in the propane surge tank will ris e from
16 to 19 bars [230 to 280 psi] .

If freon is the refrigerant, gas will not dissolve i n th e freon .

It will go through the compresso r and end up in the freon con denser. It
will probably overload the vent i ng faci l ities insta l led on the condenser.
Gas in the condenser will block off some of the cond ense r tubes and cause
t he discharge pressure on the compresso r to rise .

In order to plug a leaking tube, it wil l be necessary to shut down

the r efr i geration sys tem an d depr essure the chi l le r . The r efrigerant in
 -54-

the chiller will have to be drained. You should have a definite plan
for getting the refrigerant out of the chiller into a storage tank or
some other vessel as quickly as possible to prevent excessive loss of
refrigerant while you are draining the chiller. Remember, when you de-
pressure the gas side of the chiller, the refrigerant will flow through
the leaking tube into the gas lines .

The likelihood of a tube failure in a chiller is renote. However,

the possibility exists and can be troublesome. You should be alert to
the signs of a leaking tube, and have a definite plan for immediately
blocking in and depressur1ng the gas line, and getting refrigerant out
of the chiller into a storage tank as quickly as possible .

KETTLE-TYPE EXCHANGERS OFTEN USED FOR CHILLERS

 - 55-
Table I
TYPICAL EXCHANGER COEFFICIENTS
A. SHELL AND TUBE EXCHANGERS
Water Coolers Coefficient
Metric Units English Units
Gas at 7 bars [100 psi] 340 kea l 70 BTU
Gas at 35 bars [500 psi] 390 ked 80 BTU
Gas at 70 bars [1000 psi] 440 keal 90 BTU
C2. C3 . C4 440 keal 90 BTU
Natural Gasoline 390 keal 80 BTU
Naphtha 390 keel 80 BTU
Kerosene 365 keal 75 BTU
Amine 680 keal 140 BTU
Ai r 100 keal 20 BTU
Water 850 keal 175 BTU
Water Co nd e nse rs
C2 , e3. C4 610 keal 125 BTU
St ill Overhead 390 kea l 80 BTU
Naphtha 365 keal 75 BTU
Amine Regenerato r 540 keal 110 BTU
Rebo i lers - Steam or Hot Oil
De e3. De C4 . Still 630 keal 130 BTU
Glycol Reconcentra tor 65 kea l 13 BTU
Miscellaneous
Lean Oil/Gas 390 keal 80 BTU
Lean Oil/Rich Oil 440 keal 90 BTU
Gas/Gas at 7 bars [100 psi] 195 kee l 40 BTU
Cas/Gas at 35 bars [500 psi] 245 keal 50 BTU
Gas/Gas at 70 bars [1000 psi] 290 keal 60 BTU
Gas Chiller - Propane Refrigerant 440 ke el 90 BTU
Lean Oil Chill er - Prop ane Refrige rant 460 keal 95 BTU
B. AERIAL COOLERS

Coe fficients
Metric Units EnSl ish Units
Propane, Butane 440 keal 90 BTU
St111 Overhead 365 keal 75 BTU
Steam 0-3 bars [0-50 psi J 610 kenl 125 BTU
Naphtha 365 keal 75 BTU
Amine St rippe r Ove rhead 390 keal 80 BTU
Na tur al Gasol ine 390 keal 80 BTU
Greon 365 ke al 75 BTU
Coolers
C3 • C4 440 keal 90 BTU 17 30
Natural Gasolin e 390 keal 80 BTU 17 30
Naphtha 340 kcal 70 BTU 17 30
Gas at 7 bars (IOO psi1 290 keal 60 BTU 11 20
Gas at 35 bars [ 500 ps i] 340 kea l 70 BTU 11 30
Gas at 70 hars [1000 psi ) 390 keal 80 BTU 17 30
Lube Oil 73 kenl 15 BTU 6 10

Note : All coe ffici ents on this page a r e hea t transfer per hour per unit area
per unit ~T . When keal is shown the actual unit is kcal/hr 'm2 , oC '
when Btu are shown the actual unit is Btu!hr·ft 2 . oF .
 - 56-

Table II

EXTERNAL SURFACE AREA OF HEAT EXCHANGER TUBES

Metric Units English Units

Tube Size, Square meters Tube Size, Square feet
of external of external
outside outside area per
area per
diameter! mm mm of tube diameter I in . ft of tube

12 0.0377 1/2 in . 0. 1309

14 0 . 0440 5/8 in . 0. 1636
16 0.0503 3/4 in . 0.1963
18 0.0566 7/8 i n. 0. 2291
20 0. 0628 1 in. 0.2618
25 0. 0785 1 1/4 in . 0. 3272
30 0 . 0943 1 1/2 in . 0 . 3927
35 0.1100 2 in . 0 . 5236
40 0. 1257 2 1/2 in . 0. 6540
50 0. 1571
60 0. 1885

Example :

A piece of 20 mm tubing 1 m long has an external surface area of

0.0628 square meters .

A piece of 1 in . tubing 1 ft long has an external surface area of

0 . 2618 square fect .
 -59-

HEAT EXCHANGERS VALIDATION Trainee _ _____ _

METR I C UNITS

The natural gasoline cooler shown below has 250 tubes , 18 mm in dia-
meter and 12 m long.

a. What is the total surface area of the exchanger?

b. What is the temperature difference?
c. What is the coefficient?
d. What is the duty?
e. What is the temperature approach?

NATURAL GASOLINE
OUT
t 38'C

('
.1 /1 '
~I Id 12 m
"' I
il'1
.ell
t32'C t 115'C
• WATER NATURAL GASOLINE
'"" IN IN

"
 -60-

SOLU1IONS TO PROBLEMS - METR IC UNITS

l. a. 2
b. 1

2. h..--'O
~
3 b

3. Weight of water ~ 900 kg

Temperature rise : 52.6 - 32 = 20.6°e
Hea t req uired 900 x 20.6 s 18 540 kcal
i8 540 keal
Fue l required
89 00 kcal/m 3

4.

- 93°c
WATER
60 0 e
•
6t - 44°C

- 49°C
AIR
- 27°e
li t .. 33°C

'T _ 44 + 33
a. Av g . u 2

b. Approach = 33°C

5. Lineal meter s of tub es '" 100 x 6 '" 600 m

2
Area per m of tube = 0 . 0785 m
2
Total area'" 600 x 0.0785 - 47 m

6. Q '" UA 6.T

U - 680 (From Table I)

2
A- 25 m
6T - 33°C
Q - 680 x 25 x 33
- 561 000 kcal/hr
 -61-

HEAT EXCHANGERS VALIDATION Trainee ____ __ _

ENGLISH UNITS

The natural gasolin e cooler shown be low has 250 tu bes, 3/4 In. in
diameter and 40 ft long.

a. What is the total surface area of the exchanger?

b. What is the temperature difference?
c. What is the coefficient?
d. What is the duty ?
e. What is the temperature approach?

NATURAL GASOLINE WATER

OUT OUT

t 100°F
250 - 3/4 in. tubes
-, t 120°F
. -__~~ L.-____~--------~

.,....~
I• 40 ft

~'" I
t 90°F t 240°F

"I WATER NATURAL GASOLINE

'0: 1 IN IN
\'>'1 •
I
I
1
1
1
1
I
1
1
1
I
1
 -62-

SOLUTIONS TO PROBLEMS - ENGLISH UNITS

1. a. 2
h. 1

3. Weight of water E 2000 Ibs

Temperature ri se ~ 187 - 90 = 37°F
Heat required - 2000 x 37 - 74 000 BTU

Fuel required - 106~ ~~~/~~ft - 74 Cll ft

4. D
20Q F. 140 D F.
WATER
lit m 80 D F
. 120DF
AIR
• BODF
lit c 60 D F

a. Av g . 6T ' 80 +2 60 • 70"F

h. Approach - 60°F

5. Lineal feet of tubes - 100 x 20 - 2000 ft

Area per foot of tube = 0.2618 sq ft (Table II) •
Total area = 2000 x 0.2618 - 524 59 ft

6. Q • UA liT
U • 140 (From Table I)
A = 250 sq ft
6T • 60 D F
Q = 140 x 250 x 60
• 2 100 000 or 2.1 MMBTU/hr
HEAT EXCHANGERS
HEAT EXCHANGERS introduces the learner to the phenomenon of heat
transfer as it is applied in modern refi n ing techniques. In Section 1: Heat
Transfer. conduction and convection as methods of heat transfer are explained
before the more practical matter of heat transfer in tubes is discussed.

Section 2: Heat Ex change Equipment first details the various parts of heat
exchangers as well as thei r functions. It then describes the various types of
shell and tube heat exchangers.

Section 3: Exchanger Operation and Maintenance goes into start up and

shutdow n procedures and deals with vario us probl ems of exchanger main-
tenance . It then describes the flow and mechanisms of various heat exchange
systems.
INSTRUCTIONS

This is a programed learning course.

Programed learning gives information in a series of steps

called frames. Each frame gives some information and asks
you to make use of it.

Here is how it works. First, cover the response column at the

right with a mask.

Read this frame and use the information it gives to fill in the
blank.

A micrometer is an instrument designed to measure in

thousandths of an inch.

A micrometer is a good tool for measuring very _ __ _ small

differences in size.
Move the mask down to uncover the word at the right of the
frame. 1f you have filled the blank with that word or a word
that means the same, you are ready to go ahead to the next
frame.

The drawing of a micrometer provides information that will

help you fill in the next blanks.

OBJECT
TO BE

Seven major parts are shown in the drawing, but only

the and the contact the object anvil, spindle
to be measured.
The next frame calls for a choice. Circle or underline the ap·
propriate word.

Of the two parts that contact the object, only the (anvil!
spindle) moves. spindle

A program is a series of frames that work like the ones you

have just done.

Read the frame.

Use the information to fill in the blanks or make a

choice.

Move the mask down and check the response column.

Go on to the next frame.

Remember to cover the response column with a mask before

you begin each page.
HEAT EXCHANGERS

Section 1: Heat Transfer

HEAT TRANSFER BY CONDUCTION

Exhibits 1 through 10 are printed in a special pull-out section in

the center 01 this book. Please puff them out now so that you can
refer to them as they are mentioned in the text.

1. Heat is a form of energy.

Like other forms 01energy, heat ca n be _ __ moved, or transferred
from one place to another.

2. The process by which heat travels through a substance is

ca ll ed conduction.

Thus . the material through w hich heat passes is called the

conductor

3. Suppose a container of hot water is placed next to a con-

taine r ho lding an equal amount of co ld water.

If the containers are touching , eventually the temperature

of the cold water ( increases / dec reases). increases

4. And, the temperature of the hot water _ __ decreases

5. Heat has been conducted from the container of hot water

to the container of cold water.

When the water in the two conta in ers reaches the same
temperature, heat transfer ( stops / still cOJ1tinues ), stops

6. In other words, conduction of heat continues until the heat

is evenly distributed throughout the substance.

The final tem perature is ( greater than I less than I ~

average of ) the two beginning temperatures. an average of

7. One thing that the rate at which heat is conducted through

a conducting material depends on is the nature of the
material.
Some materials are better _~_____ than others . conductors
8. Copper, for example, is a better cond uctor of heat than
cast iron.

A stove made of solid copper conducts heat (more rapidly more rapidly
I more slowly) than one made of cast iron.

9. Suppose equal amounts of heat are applied to a one-inch

thick piece of steel and to a two-inch thick piece of steel.

1" 2"

i _-r------,\

A B

It takes longer for heat to pass through the metal in exam- B

ple (A I B ).

10. Suppose two steel rods are heated at one end.

It takes longer for heat to pass from one end to the other
ofrod (A I B). B

2
11 . Look at this drawing of two sets of containers.

A B A B

Fig. Fig.2
In Figure 1, the difference in temperature between con-
tainer A and container B is _~~__

12. In Figure 2, the difference in temperature is _ _ _

13. Conduction takes place at a faster rate in Figure 2.

Therefore, the rate of conduction varies with the size of
the temperature _ _ _ _ _ __ difference

14. A standard measure of the rate at which conduction takes

place is called thermal conductivity .
Thermal conductivity takes into account whether the mate-
rial is a conductor, the ___ good; thickness
and of the conductor, and the amount length
of the temperature _ _ _ __ difference

HEAT TRANSFER B Y CONVECTI ON

15. This drawing represents a room containing a heat source

in one corner.

-..,--
I
•

The air which tou ches the heat source is heated by

cond uction

3
16. As the air touch ing the heat source is heated, it expands
and becomes ( lighter I heavier) than the. air in the rest of lighter
the room .

17. Because it is lighter, the warm air ( rises I falls). rises

18. Cooler air from the floor level moves up and contacts the
_______ sou rce . heat

19. 11 too becomes lighter from expansion and ( ri§es I falls J. rises

20. This process is repeal ed again and again and produces a

circular flow pattern .
As the air flows around the room it carries _ _ _ __ _ heat
with it.

21 . As warm and cold ai r meet near the center of the room ,

the circu lar flow pattern is interrupted and turbulence
occurs.

Warm air and cold air are mixed together, and heat is
transferred from the to the _ _ _ __ warm; cold
air.

22. Convection is heat transfer from one point to another

within a liquid or gas by the mixing of one portion with
another.
Heat is transferred from the heat source to the air by
( conduction I convection ) and from the warm air to the conduction
cold air by ( conducti on I convection ). convection

4
HEAT TRANSFER THROUGH TUBES

23. If the temperature of a fluid flowing inside a tube is differ-

ent from the temperature of the atmosphere outside the
tube. flows through the tube wall. heat

24. The amount of heat that flows depends on the tempera-

ture between the fluid and the outside difference
atmosphere.

25. Typically, fluids flow in tubes in two distinct ways.

LAMINAR FLOW

TURBULENT FLOW

There is a great deal of mixing in ( turbulent I laminar) turbulent

flow.

26, The type of flow in which the fluid flows in smooth stream-
lines is flow. lami nar

27. As the fluid flows. the molecules of the fluid rub against
one another.
The friction of the molecules against each other causes
a resistance to flow. wh ich tends to ( speed up / slow
down ) flow. slowdown

5
28. This drawing shows flu id flowing near the wall of a tube .

STATIC FILM MAINSTREAM

The fluid that is flo wi ng closestto the tube wall (is / is not J is not
turbulent.

29. The friction of the fluid closest to the tube wa ll causes this
fluid to flow ( quickly / slowly J. slowly

30. This slow-flowi ng fluid acts as a stat ic film coveri ng the

tube wall.
Heat travels through the tube wall by conduction , and, in
order for the heat to reach the main stream, it must pass
through the static film by also. conduction

31. In a turbulent stream, the flu id mol ecules mix to a great

extent.
As the mixing process contin ues, (many / few J fluid mole- many
cules come in contact wi th the stat ic fi lm.

~hen th ese flui d mo lec ules come in contact with the

static film , they (abSJ b I give off ) heat. absorb

33. Th e molecules which have absorbed heat from the static

fil m some of the heat to other molecules transfer
in the ma instream.

34. Heat is transferred to the molecu les that come in contact

with the static film by ( conduction I con_yegtion J. conduction

35. These molec ules carry the heat to another part of the
mainstrea m and transfer some of the heat to oth er mole-
cules.
This is heat transfer by _ _ __ _ __ convection

36. In turbu lent flow , the transfer of heat from the stat ic fitm
to the mainstream is by and _ _ _ _ __ conduction; convection

37 . Fluid farther from the tu be wall flows ( faster I slowe r J. faster

38. The fluid that is flowing fastest is ( in the center / at the in the center
edges J of the mainstream.

6
·39. Fluid in laminar flow acts much as if it consisted of many,
thin-walled tubes of the fluid , one inside the other.

In order for the mainstream to absorb heat. the heat must

be from layer to layer. conducted, or transferred

40. A fluid ca n be expected to absorb heat at a faster rate in

( turbu lent / laminar) flow. turbulent

41. In comparison to metals, fluids are poor conductors .

In comparison to the tube wall , the time it takes for heat

to transfer through the stat ic film is (greater / Iess). less

)
42. The thicker the static film, the ( greater /Iess ) the heat less
transfer time.

43. Heat transfer time can be decreased by ( increasing /

decreasing ) the thickness of the static film. decreasing

44. The thickness of the static film depends on the amount of

turbulence. When turbulence is slight, the static film is
thick.

As turbulence becomes greater, the static film becomes

thinner, or less

45. Heat transfer time through the static film can be decreased
by increasing the of the fluid. turbulence

7
46. Different fluids are ftowing on both sides of a tube.

~~r7~~~:~~
~ FLUID
.STATIC FILM

WA LL

- - - - INSIDE FLUID

_STATIC FILM

! - -- · TUBE WA LL

~~~~~~~~~~~
~ - -
FILM
- - OUTSIDE FLUI D

)
The friction of the outside flu id on the tube wall causes the
fluid closest to the wall to ftow ( Quickly I slowly ). Slowly

47. The fluid closest tothe tube wall becomes a ______ static
film .

48. Assume that the fluid outside the tube is hotter than the
fluid inside the tube .

Heat flows from ( inside to outside I outside to inside) of outside to inside

the tube .

49. In order for the heat to reach the tube wall, it must pass
from the mainstream through the static _ _ _ _ __ _ film

50. The greater the turbulence outside the tube, the ( thicker I
thinner ) the static film . thinner

51 . The greater the turbulence outside the tube, the ( more / more
fewer ) molecules come in contact with the static film.

52 . The factors affecting heat flow inside and outside tubes

are ( simi lar I different ). similar
 53. This drawing illustrates flow inside and outside a tube.

Tt WARM
T6

T 8 COO L

T fhUBE WA LL
FLUIO INSIDE TUBE

INSIDE FLUID FILM

I INSID E FOULING MAT ERIAL

FLUID OUTSIDE TUBE OUTSIDE FOULING MATER IAL

OUTSIDE FLUID FILM

T j, the temperature inside the tube, is ( higher than / higher than

lower than) T8, the temperatu re outside the tube.

54. The line segment between T2 and T3 represents the temp~

erature drop across the inside fluid film

55. TJ to T4 is the temperature drop across the inside scale

or fouling material.
Compared to the drop from T2 to T 3, the drop from T 3 to T4
is (steeper / less steep ). steeper
/
56. T 4 to T ~ represents the temperature drop through the tube
wall and T 5 to T 6 represents the drop throug h the outside
fouling material.
The t~mperature drop through the tube wall is close to
zero

9
57. The temperature drop is greater (through the tube wall I
through the inside and outside static films ). th rough the inside
and static films

58. The shape of the outside temperature curve is ( similar to / simi lar to
different from) the shape of the inside temperature curve .

Parallel Flow-Counterflow

59. Heat flows from one fluid to another if there is a _ _ __ difference

in temperature between the two fluids.

60. Assume that fluid is flowing along both the inside and the
outside of a tube and that both streams of fluid are flowing
in the same direction and that the fluid inside is hotter
than the fluid outside.
Heat is transferred from the _ _ _ _ _ _ fluid to the inside
_ _ _ _ _ _ fluid . outside

61. The temperature of the hotter fluid (increases / decreases). decreases

62. As heat is transferred to the colder fluid , its tem perature

increases

63. All the fluid represented here is flowing in the same direc-
tion .
POINT
POINT C

The temperature of the inside (hotter) fluid is greatest at

pOint ( A I B Ie). A

64. The temperatu re of the inside fluid is lowest at point

( A I B Ie). C

65. The temperature of the outside (colder) fluid is lowest at

point ( A I B Ie). A

10
66. The temperature of the outside flu id is highest at point
(A I B I C I. C

67. This graph shows the temperature of the two fluids in

relation to the length of the tube.

PARA LLEL FLOW

INSIDE FLUID

OUTSIDE FLUID

POINT A POINT B POINT C

The d ifference in temperature is greatest at point ( A / A

B I C I.

68 . The heat transfer rate ( depends / does not depend) on depends

the temperature difference.

69. The heat transfer rate is greatest at point (A / B / C ). A

70. At point C, there ( is / is no ) temperature difference. is no

71. At point C, heat ( is I is not) transferred. is not

72 . In parallel flow , when both fluids flow in the same direc·

tion , the hot f luid ( can I cannot) be cooled below the ca nnot
highest temperature of the cooler fluid.

73 . The fluids are flowing countercurrently.

POINT
POINT C

In this kind of flow the fluids are flowing in ( the same

direction I opposite directions ). opposite di rections

11
74. Suppose that two fluids are in counterflow inside and out-
side a tube, and the hotter fluid is ins ide.

The temperature of the hotter inside flu id is greatest at

I A / B / C }. A

75. The temperature of the inside fluid decreases in th e direc-

tion ( A to C / C to A J. A to C

76. The outside colder flu id is coolest at ( A I B I C ). C

77 . Th e outside flu id is hottest at (A / B / C J. A

78. This graph shows the temperature in relation to the length

01 the lube.

D
INSIDE FLUID

'
TEMPERATURE F==:==~~--~~;:::::~~~bc-
I OUTSIDE FLUID I

U I
I
I
POINT A
I
I
I
POINT 8 POINTe

In counterflow, the temperature difference along the tube

is ( more constant / Iess constant J than the temperature more constant
difference in parallel flow .

79. The heat transfer ra te in counterflow varies ( consider-

ably I little ) over the length of the tube . little

60 . Not ice the area o n the graph that is represented with a

double arrow.

Counterflow ( permits / prevents) cooling a fluid to a permits

temperature lower than the highest tem perature o f the
cooling fluid .

12
Section 2: Heat Exchanger Equipment

Introduction

81 . A simple heat exchanger is a set of steel tubes enclosed

in a tank.

HOT Oil

WATER
OVERF LOW

OUTLET

The tank represents the shell of the exchanger and, in

this case, is fi ll ed with _ _ _ _ _ __ water

82 . Heat is transferred from the hot oil flowing through the

tubes to the cool water around the tubes.

The conductor of the heat is the _ _ _ _ _ _ _ wal l. tube

83. The shell·side of an exchanger IS the area inside the shell

and outside the tubes.

The tube-side of an exchanger is the area _ _ _ _ __ inside

the tubes.

64 . In the example shown , the shell-side fluid is _ _ _ __ water

and the tube-side fluid is _ _ __ _ __ oi l

13
85. This drawing shows the construction of a typical shell and
tube exchanger.

The tubes are anchored between two _______ tubesheets

86. The combination of lubes and tubesheets is called the

tube __ bundle

87. This drawmg shows the fluid flow path through a shell and
tube exchanger.

TUBEStOE INLET SHEL L SIDE INLET

HOT OI L COOL WATER

SHELL SIDE OUTLET

WARM WATER

Hot oil flows into the tube-side inlet. through the tubes,
and out throu gh the _ _ outlet. tube-side

88. Cool water flows into the shell-side inlet. around the
_______ , and out through the shell-side ouilet. tubes

89. In this example, heat is transferred from the ( tube-side I

she ll-side ) fluid to the fluid . tube-side ; shell-side
TUBE BU N DLE

90. The greater the surface area of a conductor. the ( more I

less ) Quickly heat is conducted. more

91. A bundle of small lubes has ( more / less ) surface area more
than a single large tube.

92. Shell and tube exc hangers use a bundle of small tubes,
rather than a single large tube.
This ( increases I decreases) the area for heat transfer. increases

93. Exchanger tubes can be either plain or finned.

As these drawings show, fins are either ___ _ _ __ ins ide

or the tubes. outside

94. Fins ( add to / subtract from) the tube surface area. add to

95. Thus, they _ _ _ _ _ _ _ the rate of heat transfer. increase

96. If acarrasive fluid passes through either side of an exchanger,

something usually must be done to prevent _ _ _ __ corrosion

97 . Sometimes the tubes can be made of a metal which is not

easily _ _ _ _ __ corroded

Refer to Exhibit 1 for frames 98-100.

98 . The outside diameter (0 . D.) ranges from 1 / 4-inch to _ _ 2-1/2

inc hes.

99. In practice, the most common tube O. D.'s are the 1/2-inch,
the 3/4-inch , and the one-inch.
As the chart shows, tubes with O. D.'s at the extremes of
the range, either high or low, are usually produced in
( greater I fewer ) varieties of gauges than the more com- fewer
mon sizes.
100. So, tubi ng with a 2*112 inch O. D. is usually produced in
only one _ _ _ __ _ gauge, or thickness

101. Exchangers are usually produced in standard lengths of

8, 10, 12", 16, and 20 feet. Sixteen and 20 feet are the most
common lengths.
The particular application usually determines the _ __ length
of an exchanger.

102 . That is, exchanger design is determined by cost and the

particular operating _ _ _ _ __ conditions, or applications

103. As the length of an exchanger increases, its cost gener-

ally ( increases / decreases J. increases

104. One of the basic considerations in exchanger design is to

meet operating requirements while minimizing _ _ __ cost

TUBESHEETS

105. The tube bundle is made by fastening the tube ends into
openings in the tube sheet.

SHEET

Because the tubes cannot move in the tubesheets, the

tubesheets and tubes form a (solid / flexible J unit. solid
106. In some exchangers. the tube and tubesheets are fixed
to the she ll.

Therefore, they ( are free to move I are prevented from are prevented
moving ). from moving

107. Heat causes metal to ( expand I contract ). expand

108. When the tubes expand because of heat, stress is placed

on the tubes and tubesheet.

A tube can come loose. allowing fluid to leak between the

tube wall and the opening in the ~~~~~~_ tubesheet

109. This results in the contamination of one fluid by another.

To guard against th is. a double tubesheet can be used in

cases where a absolutely cannot be leak
tolerated .
110. Here is a design which can help reduce the possibility of
leaks at the tubesheet.

Th is design provides for a ________ between the space

tubesheets.

111 . If a leak occurs, fluid passes into thi s space .

Since the space between the tubesheets is open , flu id is

allowed to ( drain from I collect in ) the exchanger. dra in from

TUBE JOINTS

112. The tube joint is the connection between the tube and the
tubesheet .

The better the fit at the tube joint. the _ _ _ _ _ __ less

the possibility that there is leakage.
11 3. Tube joints are usually either rolled press fit or welded.

WELDED ROLLED
PRESS FIT
(EXAGGERATED)

Some metals cannot be welded, so tubes of these metals

are _~ _ _ roll ed

114. Rolled joints usually make a very good seal. and they can
be used in reasonably high pressure service, up to about
2.000 psi.
However. in spec ial cases or severe service. _ __ __ welded
tube joints are usually used.

115. An exchanger is likely to be more expensive if the tube

joints are ( rolled / welded ). welded

TUBE SHEET LAYOUT

1 16. Exchanger tubes can be installed in a variety of patterns.

TRIANGULAR IN· lINE TRIANGU LAR

IN· lINE SQUARE DIAMOND SQUARE

When the tubes are arranged in parallel rows , ve rtically

and horizontally, the pitch is called _ _ -_ _ __ in-line
pitch.
1l7. In·line square pitch offers the ( most 1 least ) resistance to least
shell·side flow through an exchanger.

11 B. The greater the resistance to flow . the greater the result·

ing pressure drop.
For th is reason . in·line square pitch is part ic ularly efficient
when conditions require a ( high I low) pressure drop. low

119. Staggering the tubes, as in the th ree other main types of

pitch. allows (more 1 fewer) tubes in a given area than the more
even spac ing in square pitch does .

120. A disadvantage of square pitch is the relatively _ _ __ low, or small

number of tubes in a given area.

121 . Compare the number of tubes in a given area in square

pitch and triangular pitch.

SQUAR E PITCH TRIANGULAR PITCH

Shell Number of Passes Number of P ••ses

I. D.
(Inches) 1 2 4 1 2 4
20 241 236 224 269 260 250
22 300 280 280 337 330 314
24 360 350 336 421 404 380
26 424 412 402 499 476 460
28 402 488 480 579 562 542
30 580 566 566 668 648 636
32 665 648 644 766 744 732
34 756 758 730 870 850 834
36 853 848 832 986 978 942
38 973 950 938 1108 1100 1060
40 1085 1064 1052 1236 1228 1200
42 1201 1176 11 62 1367 1350 1322

In a 42· inch . double·pass exchanger, there are _ _ __ 1, 176

tubes in a square pitch arrangement and _ _ _ _ tubes 1.350
in a triangular pitch arrangement.

122. The more tubes there are in a given area, the _ _ _ __ higher. orgreater
the heat transfer rate .

123. Si nce the square pitch arrangement results in the lowest

number of tubes in a given area. it also results in the
_ _ _ _ _ __ heat transfer rate. lowest

124. When the pitch is triangular. the pressure drop is ( hig her I higher
lower ) than when the pitch is square.

125. But. the heat transfer rate is greater when pitch is _ _ _ . triangu lar

20
126. For a given set of operat ing co nditions the ch o ice of pitch
arra ngements depends upon what pressure drop is needed
in re lation to the __ transfer rate desired . heat

BAFFLE S AND TYPES O F BAFF LES

127. The longer the tubes in an exchang er are, the ( heavier /

li ghter) they are. heavie r

128. Th e heav ier they are , the ________ the c hance greater
th at th ey will sag .

129. Baffles support the weight of the tubes .

Si nce they support the weig ht. baffles help to _ ' -_ __ decrease. or relieve
the stress on the tubing and tubesheet .

130. In both lami nar and turbulent flow, a laye r of fl uid sur·
rounds eac h tube, acting as an insu lator.

Th is layer of fluid acts to ( increase I decrease) the rate decrease

of heat transfer.

21
131. The thicker the insulating layer, the _ _ _ _ _ _ it more
decreases heat transfer.

132. The insulating layer is likely to be thicker when flow is

( laminar I turbulent ). laminar

133. In addition to supporting the tubes, baffles break up

_ _ _ _ _ _ flow, decreasing the layer of insulating laminar
fluid.

Segmental Baffles

134. A segmental baffle is a circle from which either a vertical

or horizontal portion has been cut.

VAPOR INLET

CONDENSATE OUTLET

In this case, the baffles are ( vertically cut I horizontally vertically cut
cut) segmental baffles.

135. Segmental baffles are positioned so that the cut·out areas

( all face in the same direction I face in alternate directions ). face in alternate directions

136. Alternating the baffles causes flow to _ _ _ _ _ the cross, or pass

tubes a number of times.

137. It also provides better _ _ _ _ __ for the tubes. support

138. In addition to the portion cut from the side or top of a seg-
mental baffle , a portion is often removed from the bottom ,

HOR IZONTA L

VERTICAL

Removing this portion ( all ows / prevents ) some contin- allows

uous flu id flow along the bottom of the exchanger.

139. Whether the baffle is cut ve rt ically or horizontally depends

on the type of fluid and on the operation ,
HORIZONTA L

The baffl e most likely to catch sus pended materials is the

(vertical/horizontal) baffle. horizontal

23
140. But, suppose horizontal baffles we re used in a condenser .

GAS I NLET

CONDENSED FLUID OUTLET

Condensed fluid builds up behind baffles A and C, thu s

_ _ _ __ _ flow. restricti ng

141 . Dra inage from the conden ser is prevented and the effi-
ciency of the exchanger is _ _ _ _ __ _ decreased

Disc and Doughnut Baffles

142 . The pattern of flow through disc and doughnut baffles is

relatively uniform .

But. if the fl uids are not clean. sediment builds up behind

the ( disc I doughnut ). doughnut
143. Since the cutout area of the bailie is in the center, the
flow of condensed fl uids along the bottom of the exchanger
can also be _ _ _ _ _ _~ restricted

144. For these reasons , disc and doughnut baffles are used
( more / Iess ) often than segmental baffles. less

Impingement Baffl es

145. At high inlet-fl uid velocities, the fluid can seriously erode
the tubes as it strikes Ihem.
If the inlet fluid contains suspended solid particles, the
problem is ( more / Iess ) severe. more

146. Imp ingem ent baffl es are sometimes placed at inlet fl ow

areas to the shell-side.

NO PLATE BAFFLE

~~
II
PLATE BAFF LE
VERTICA L CUTS

PLATE BAFFLE
HORIZONTAL CUTS

As this comparative illustratIon shows, the imp ingement

baffle helps to ( spread out / contain) fluid flow. spread out

147. An impingement baffle directs the flow ( toward the sides

of the exchanger / toward the tubes ). toward the sides of the
exchanger

148. The baffle effectively reduces the ____ . . . - of the erosion

tubes.

25
149. Besides reduc ing erosion. spread ing the fluid insures that
the fluid contacts all the tubes.
And increasing fluid-tube contact _______ the increases
heat transfer rate.

Longitudinal Baffles

150. Longitudinal baffles are sometimes used to split shell-side

flow into two or more passes.

As the drawing shows , the longitudinal baffle ( is somewhat

shorter than / extends the full length of ) the exchanger. is somewhat shorte r than

151. This allows for the return, or double pass. through the
exchanger.

Th ree longitudinal baff les would provide for ____ __ four

passes through the exchanger.

26
 152. This drawing illustrates the baff le position for divided fl ow.

In this case . fluid flow on the two sides of the tubes is (con-
secutive / simultaneous ). sim ultaneous

EFFE CTIVE HEAT TRANSFER SURFACE

153. The heat transfer surface depends on the number of tubes .

on the length of the tubes. and on the outside diameter of the
lubes.
As any of these increase. the effective heat transfer su rface
also _ _ _ _ . increases

" 154. The enti re length of a tube is not the effective length of the
tube. as far as heat transfer goes.
Since the tube extends through the tubesheet at each end
of the exchanger. the effective length is _ _ _ _ _ __ shorter, or less
than the actual length .

155. For 15-.00t tubes extending three inches through a tube-

sheet at each end. the effective lengthlis about _ __ 14-1/2
feet. (15feetminussix inches)

156. The formula for calcula ting the effective tube surface in an
exchanger is:
Effective surface = (square foot external surface per foot
length) x (net effective tube length) x (nu mber of tubes)
If the square foot of external surface per length is .2618
and the net effective tube length is 15.5 feet and the num-
ber of tubes is 882. then the effective tube surface is .2618x 15.5x682
x_ _ _ _ x ___ ~_

27
SHEll AN D TUBE FLOW ARRAN G EMENTS

Refarto Exhibit 2forframes 157-164 .

Shel~ide Flow Arra ngements

157. Shell-side flow arrangements are generally one of the six

illu strated in Exhibit 2.
In a one-pass shell , the shelf-side fluid enters one end of
the exchanger, flows through the exchanger. and exits
through (the same I the oppos ite) end of the exchang er. the opposite

158. A double pass requires that fluid enters and exits through
( the same~nd / different ends) of the exchanger. the same end

159 As the exhibit shows. a split flow arrangement divides

incoming shell fluid into separate streams. two

160. A double split flow divides shell fluid into _ _ __ _ _ four

separate streams.

161. In the divided flow arrangement shown. shell flu id enters

at the " of the exchanger, rather than at center, or midd le
the end.

162 . The kettle-type reboiler has ( split / divided ) flow and a divided
dome outlet for vapors.

163. The choice of shell arrangement depends on the amount

of cooling or heating required. on the pressure drop that
is needed, and on the type of service .

For instance. the shell arrangement that provides space kettle-type

for vapors to accumulate is the _ _ _ _~ ___ _ __ reboi ler

, 64 . The effective "time " that the shell~ide fluid is in contact

with the tubes increases as the number of passes _ __ increases

28
Tube-Side Arrangements

165. The drawing illustrates a single-pass tube arrangement.

SHELL SIDE INLET

COOLED OIL

SHELL SIDE OUTLET

WARM WATER

Tube-side fluid enters one end of the exchanger, flows

through all the tubes in the same • and direction
leaves at the opposite end of the exchanger.

166. A tube-side baffle can be built into the head end of the
exchanger to direct flow through the tubes .

.CH.","EL HEAD

CHANNEL BAFFLE

In a two-pass arrangement. fluid flows through half the

tubes in one direction and through the ot her half of the
tubes in the direction. opposite

167. This requires _______ channe l head baffle and one

no head baffle .

168. The c hannel head baffle in a two-pass tube arrangement

is positioned ( vertically I horizontally). horizontally

29
169. Compare the two-pass arrangement with the four-pass
arrangement.

A four-pass arrangement requires _ __ _ _ _ _ chan- two

nel head baffle (s) and floating head baf- one
ffe! s).

170. Increasing the number of passes requires - - - - - - increasing

the number of baff les .
TYPES OF SHELL AND TUBE EXCHANGERS

Fixed Tubesheet Exchangers

171. In the fixed tubesheet type exchanger, the tubesheet is
welded to the shell.

TUBE SHEET

The tu be bundl e ( can be removed from the shell I is per-

manently install ed J. is permanently installed

Now turn th e page,

turn the book over,
and go on.
172. Expansion and contraction because of temperature
changes place stress on the tube bund le.

In this type of exchanger. the tube bundle ( can expand

to compensate for the stress I is prevented from expand- is prevented from
ing ). expanding

173. Fixed tubesheet exchangers are used when the tempera-

tu re range is ( limited I wide ). limited

174. The drawing shows an expansion joint built into the shell
of a fixed tubesheet exchange r.

As the tubes become hotter. they ( expand I contract ). expand

175. The bu ilt-in joint allows the shell to _ _ _ _ __ also. expand

176. As the tubes and shell cool. the expansion join t and tubes
contract

177. Stress on the welding and on the tubes and shell is

lessened, or decreased

178. Because of the difficulties of inspecting and cleaning fixed

tubesheet exchangers, they are generally used where
shell-side fouling is ( li mited I extensive ). limited

179. Because the tube bundle cannot be removed from the

she ll. the shell side of a fixed tubesheet exchange r must
be cleaned ( mechanically I chemica lly ). chemically

Refer to Exhibit 3 for frames 180-189.

U-Tube or U-Bend Exchangers

180. Exhibit 3 shows a U-tube type exchanger.

As the drawing shows, a U-tube exchanger has ( on ly
only one
one I two ) tubesheet(s).

181 . A baffled channel IS bolted between the tubesheet and the

channel _ __ __ _ cover

31
182. The tubesheet and tube bundle form a unit.
By unbolting the channel from the shell. the tubesheet
and tube bundle can be removed from the shell so the
( inside I outsi~ ) of the tubes can be cleaned. outside

183. However, the bend in the tubes inhibits cleaning and

inspecting the of the tubes. inside

184 . Si nce the tube bundle in a U-tube exchanger is fastened

to only one tubesheet. the tubes are ( free to expand I
free to expand
prevented from expanding ).

185. U-tube exchangers can be used whe re the temperature

difference between sheH-side and tube-side flu ids is Quite
great. high. or large

186. Exhibit 3 also shows the flow patterns in a U-tube exchanger.

The baffle dividing the channel directs incoming tube-side
flu id through (a ll I only the upper half ) of the tube open- only the upper half
ings.

187. Tube-side fluid flows through the tubes. around the bend,
and through the chamber. lower

188. Tube-side flow. in this case . is ( one-pass I two-pass ) flow. two-pass

189. Shell-side flow in this exchanger is ( one-pass I two-pass) one-pass

flow

Floating Head Exchangers

PUll-THROUGH TYPE

190. In this exchanger, the tubesheet on the right is bolted

between the channel and shell in a fi xed position .

I FLOATING HE AO

But. the tubesheet on the left, together with a cover. floats

inside the shell . ( free to move I unable to move) hori- free to move
zontally.

32
191. Because o f the weight of the tube bundle, there ( is I is no ) is no
vertical movement.

192. But. since the tube bundle and fl oating head ca n move
horizontally. the tubes are free to and expand
contract

193. After unbolting the channel flange and the stationary tube-
sheet. the tube bundle and the floating head can be with-
drawn as a unit.

FLOATING HEAD

Th is permits cleaning and inspecting the _ _ _ _ _ __ outside

of the tubes.

194. In this illustration . the channel cover. the she ll cover, and
the floating head cover have been removed .

FLOATING HEAD COVER

This provides access to both tubesheets and to the

_ __ ____ o f the tubes insides

33
195. By removing the floating head cover and the channel
cover , it is possible to inspect and clean the _ _ __ _ _ inside
of the tubes .

196. In a pull-through type floating-head exchanger ( all / all

some ) parts of the exchanger can be inspected and
cleaned .

197. This drawing illustrates a disadvantage of the pull -through

exchanger.

C L EARANC=E_-,,:;!::'l~C:..:'

The clearance between the shell and the _ _ _ _--'_ _ tubes

is large.

198. This clearance is provided to accommodate the outside

diameter of the 110ating tubesheet.

Since no tubes can occupy this space, the space is

wasted

199. In addition, fluid is likely to move through the space rather

than past the tube _ _ __ _ __ bund les

200. For these reasons . the clearance space between the shel l
and tube bundle the efficiency or effect- reduces
iveness 01 the pull-through exchanger.

34
SPLIT BACKING·RIN G TYPE

201. A second floating head exchanger IS the split backing-

ring type .

FLOATING TUB ES HEET

Notice that the diameter of the shell cover is _ _ _ __ greater

than th e diameter of the rest of the shell holding the tubes .

202. The tubes and tubesheet and floating head cover (can be
pulled I cannot be pulled 1through the channel as a unit. cannot be pulled

Refer to Exhibit 4 for frames 203-215.

203. Compare the split backing-ring exchanger and the pull-

through exchanger.
An advantage of the pull·through exchanger is that the
bundle and head can be pulled th rough the channel as
_ _ _ _ _ _ unit. one

204 . In order to pull the tube bundle of the split ring type , the
fl oating head cover, shell cover, and the split ring must be
_ _ _ _ _ _ first. removed

205. However, clea ran ce between the tube bundle and shell
is smaller in the (split backing-ring I pull-through) exchanger. split backing·ring

206. If the same amou nt of space is available, more tubes can

be used in the ( split backing-ring I pull-through 1exchanger. split backing-ring

207. Therefore, the split backing-ring exchanger is _ _ __ more

efficient than pull-through exchangers .

35
208. But, the ( split backing-ring 1 pu ll-through) exchanger has split backing-ring
more parts.

209. Thus, it is _ _ _ _ __ _ expensive to build. more

210. The split backing-ring exchanger is also ( easier / harder) harder

to disassemble.

211 . First. the shell cover is unbolted from the ___ __ _ shell

212. Then, the float ing head cover and split backing-ring are
unbolted from the floating _ _ __ __ _ tubesheet

213. Then , the channel is unbolted from the other end of the
shell

214. And finally, the tube bundle is pulled from the _____ channel
end.

215. Since disassembly is more time-consu ming , it is also more

cost ly, or expensive

SIZE NUMBERING AND TYPE DESIGNATION

216. Exchanger size, as spec ified by the Tu bu lar Exchanger

Manufacturer's Association (T. E. M.A.), depends on the
diameter of the shell and length of the tubes in inches.
Since shel l diameter is spec ified first. a size 23- 192
exchanger has a diameter of inches and tubes 23
_ _ _ _ inches long. 192

217. When the shell diameter is between two numbers, suc h as

331 / 4 inches, it is rounded off to the nearest whole num-
bers.
An exchanger with a 331/4 inch diameter and 188 inch
long tubes would be designated size _ _ _ _ __ __ 33-188

Refer to Exhibit 2 again for frames 218-228.

216. As the exhibit shows. type designation includes·three vari-

ables: the type of stationary , the _ _ _ _ head; shell
type, and the type of head. rear

219. Desig nations are specified by letters of the alphabet.

The four designations of stationary head types are indi-
cated by the letters _ _ , _ _ , _ _ . and _ _ , A; B; C; D

Special high pressure stationary head closu res are indi-

cated by the letter _ _ , D

36
22 1. Shell types are indicated by the letters _ _ . _ _ . E; F
__. __, . and _ _ . G; H; J; K

222 . Any exchanger including the leiter K in its designation is

a kettle· type _ _ _ _ __ reboil er

223. Rear head types are specified with the letters ....h...-. L
_ _ , _ _ , _ _ , _,__ . _ _ , and _ _ , M; N; P; S; T; U

224 . An example of a complete exchange r designation is size

17-1 92 type AES.
Th is exchanger has a _ _-inch diameter and _ _- 17; 192
inch long tubes.

225. Accordi ng to the exh ibit. this exchanger has a ( removable

channel and cover I integral cover ). removable
channe l and cove r

226. It has a ( one·pass I two-pass / split flow) shell. one-pass

227. And . it has a ( fixed tubesheet / U·tube bundle / floating

head with backing device ). floating
head with back in g device
228. Suppose an exc hange r were described as a fixed-tube·
sheet exc hanger havi ng stat ionary and rear heads integral
wit h tube sheets. sing le·pass shell , 17-inch inside dia-
meter and tubes 16 feet long.
Its designation wou ld b~ size _ _ _ '_ _ _ Type 17-1 92
CEN

37
Section 3: Exchanger Operation and Maintenance

STARTUP AND SHUTDOWN

229. A mixture of hydrocarbons and air is dangerous because

of the possibility of ___' explos ion. or ignition

230. Therefore. before adding a liquid or a gaseous hydrocar-

bon to an exchanger. inert gas or steam is used to purge
_____ from the exchanger. air, or liquids

231 . The shell and tube bundle of an exc hanger may be made
of di ffe rent metals which react differently to temperature
changes.
In such a case, the she ll and tube bundle expa nd at ( dif-
ferent rates / the same rate) when heated to a particular differen t rates
temperature.

232 . If the shell and tube bundle do expand at different rates,

the meta l and structure are subjected to ______ stress

233 . A sudden temperature chang e causes ( rapid / moderate) rapid

expansion o r contraction .

234. The tube bundle and shell experience more _ _ _ _ __ st ress

than usual.

235 . As a result, tubes can be loosened from the tubesheets.

or tubes can be _ _ _ _ _ __ broken. or ru ptured

236. For these reasons. cold fluid shou ld never be sudden ly

introduced into a hot exchanger.
Sim ilarly. a hot fluid shou ld never be introduced suddenly
into a exc hang er. cold

237. During startup and shutdown. any temperature changes

shou ld be made ( slowly I rap idly ). slowly

238. During startup. the cooli ng fluid is int roduced first.

Then. the hot fluid is gradua lly added . and the exchanger
is brought to temperature . o perating , or correct

239 . During shu tdown . the flow of hot fluid is stopped first .
With no input of hot fl uid, the exchanger gradually ___ . cools

240. Th en the fl ow of _ _ _ _ fluid is stopped. cold

241 . The exc hanger shou ld not be va lved c losed while it is full
of fluid. I
Just li ke a solid , a liquid _ _ __ _ _ when it is heated . expands

38
 242. Th is is ca lled thermal expansion.
Whe n a liquid expands. its volume _ _ _ _ _ __ increases

243. If the expanding liquid is enclosed, it exerts _ __ _ _ force , or pressure

on its container.

244. Th erefore, a filled exchanger which is valved c losed can

be damaged by fluid . expanding

245. For this reason. the exchanger must be _ _ _ _ _ __ drained, or em ptied

before being valved closed.

246. If the outside temperature is low. water left in the exchanger

tubes can _______ freeze

247. When water freezes, it expands.

Expansion puts excess _ _~_ on the inside of pressure
th e tubes .

248. Excess pressure can cause _ _ _ _ _ __ damage

249. For th is reason , the operator must consider the tempera-

ture surround ing the exchanger.
It is usually best to com pletely _ __ _ _ _ _ _ the drain
exchan ger.
250. Water in the tubes can also freeze as a result of the rapid
depressurizing of light hydrocarbons in the shell side of
the exchanger.
If a light hyd rocarbon is suddenly depressurized. it (evapo-
rates / condenses ). evaporates

25 1. As a liquid evaporates. it cools the surface from which it

evaporates.
Th erefore, the evaporating hydrocarbon cools the inside
walls of the shell and the of the tubes. outside

252 . Sudden cooling causes water in the tubes to _ _ _ __ freeze

253. Just as in startup operations. ca re must be taken during

shutdown to avoid potentially ex plosive mixtures of _ _ air
and hydrocarbons.

254. Therefore. it is necessary to some exchangers purge, or clear

of air with steam or inert gas after sh utdown.

OPERATING PRESSURE AND TEMPERATURE

255. Every exchanger is designed to ope rate at a pressure and

temperature listed on a plate attached to the exchanger.
When the exchanger is operated at a pressure higher than
the rated pressure, chances of tube or shell failure ( increase /

--
decrease ). increase

39
256. Su ppose a high operating pressure resulted in rupture of
a tube or in a tube being pull ed from the tubesheet.
Th is ( would I would not ) result in flu id conta min ation . wou ld

257. In a typical recirculating cooling water system , corrosion

inhibitors and acid are added to prevent scale from form ing.
The sca le is still (d issolved in the fluids / soli d ). dissolved in the fluids

258. High tem perature causes this scale to precipitate out as

_______ in the excha nger. solids

259. Such precipitates collect in the tubes and _ _ _ _ flaw. restrict

260. In some fluids . preci pitat ion occurs if the temperature is

too low.
Tem peratu re must be held within the selected _ _ _ __ range
so that fou ling is prevented .

261 . In water dropou t processes where heat is used to separate

water from hydrocarbons . too ( low / high) a temperature low
dec reases efficiency.

262. If the outlet te mperatu re is too low. decreasing the rate of

water flow would ( increase I decrease) the rate at w hich decrease
heat leaves the exchanger.

263. So. temperatu re in the exchanger wou ld _ _ __ _ _ inc rease

264. One way of controlling temperature within the exchanger,

then . is by controlling the of water flow. rate

265. The velocity must not be allowed to drop too low and the
cooli ng water temperature must not be allowed to go too
high.
Otherwise. so lids may precipitate and _ _ _ __ _ the foUl, or plu g
exc hanger.

266. In some cases, the outlet temperature can be raised by

bypassing some of the product stream around the exchanger
and joining it to the product flow which has passed through
the exchanger.
In this method, ( part of the product I all of the product) part of the product
is cooled .
267. The exchanger is part of a system which consi sts of other
pieces of equipment.
Since they are conn ected. whatever happens in the way
of ph ysical change in one piece o f equipment ( affects / affects
has no effect on) the operat ion of each piece of equipment
withi n the system .

268. The operator should consider what changes will occur in

other parts of the if a change is made in system
the operation of an individual exchanger.

40
269. It is a good idea to observe temperatures. pressures. and
flow before and after changes are made.
This wi ll give the operator an aq::urate idea of how condi-
tions have actually changed. and he will be able to pin-
point in operation. difficulties. or problems

270. For the same reason. a record should be kept of how and
where changes are made.
In the event that changes produce unsatisfactory results.
the can be returned to its original operat- system
ing condition.

EXCHANGER FOULING

271. Fouling is a general term which describes the buildup of

various kinds of deposits on the parts of an exchanger.
Since foulin g particles adhere to the tube wa ll. fouling
effective ly _ _ _ __ __ the thickness of the tube increases
wall.

272. When the tube wa ll is fouled . it takes heat _ _ _ _ __ longer

to pass through the wall.

273. In other words. the time of heat transfer ( increase s /

decreases ). Increases

274. In addition. the flow of fluids through the eXChanger'" is

restricted. or decreased

275. Fouling in an exchanger causes a general _ _ _ _ __ loss. or decrease

of efficiency.

276. Trou ble in an exchanger is almost always indicated by

changes in temperatures and pressures.
If fouling restricts the passage of flui d. the drop in pressu re
across the excha nger will (increase / decrease J. increase

277. In addition. the flow rate may (increase / decrease J. decrease

278. The temperature will indicate that heat is tra nsferred

_ ______ effectively. less

279. One type of fouling is sedimentation.

As the name indicates. sed imentation involves ( a chem-
ical reaction / deposits of dirt and clay and dust J. deposits of dirt and clay
and dust
280 Corrosion products are another source of fouling deposi ts.
Corrosion products are formed when ( excha nger mater-
ials interact with the fluids / two fluids come in contact ). exchanger mater ials
interact with the fluids

41
281. Organic material growth includes algae growing in coo ling
water.
A lgae on the inside of tubes forms { a conducting / an
insulating } layer. - an insulating

282. Other types of fouling include coking. salt deposits. and

chemica l react ion.
Regardless of the type of fouling, deposits reduce the
rate 01 _ _ _ _ _ _ __ _ _ __ heat transfer

283. The kind and degree o f fouling are influenced by the

materials used in an exchanger .
For instance, surface roughness ( Qrovides cavities for /
discourages ) the buildup of deposits. provides cavities for

284. Some materials co rrode faster than others, providing cor-

rosion products which decrease heat transfer .
The higher the corrosion rate, the sooner _ _ _ _ __ fou ling
occurs.

285. The velocity of flow affects fouling rates.

The lower the rate of flow. the the sedi- more
ment that is allowed to drop out of the stream .

286. Up to a point. increasing the velocity the decreases

fou ling rate.

287. Fouling in an exchanger can be handled in a number of

ways.

Antifoulants ( prevent the formation of / break-up) deposits. prevent the formation of

288. Inhibi tors prevent chem ical reactions which m ight cause
_______ to build up. deposits

MAINTENAN CE

289. Dispersants prevent the coagulation of insoluble materi-

als that are suspended in the fluids .
Th e method used for removing the deposits depends on
what they are. kind

290. The seve rity of the deposits also determines the method
01 _ _ _ _ __ cleaning, or re moval

291 . If a fouling problem has been neglected for some ti me,

mechanical cleaning . such as cutting or scraping , may be
necessa ry.
The exchanger must be disassembled to use _ _ _ __ mechan ical
cleaning techniques.

42
292. However, many deposits can be removed without shutting
down the exchanger.
Cleaning while the exchanger is operating is called ( on-
line I off-line) maintenance. on-line

293. In a typical method used for on-line maintenance, chem-

icals are added to the flowing throug h flu ids, or liquids
the she ll-side or tube-side.

294. The drawing shows how sodium c hlo ride (salt) deposits
can be washed from the outside of tubes, whi le the exchanger
is in use.

HYDROCARBON

r:~~~~==~~~--
r ~FROM TOWER
OVERHEAD

PRODUCT -'1.,"-, ACCUMULATOR

WATER AND SALT

Water is injected into the ( hydrocarbon I cooling water ) hydrocarbon

inlet.

295. As the mixture of water and hydrocarbon flows over the

tubes, the water ___ _ __ the salt. dissolves

296. In the accumulator , the product and the salt water solu-
tion are _ _ _ _ _ __ separated

297. In some cases, it is advantageous to shut-down the exchanger

for either chemical or cleaning. mec hanica l

298. It is not necessary to dismantle the exchanger for ( chem-

i.c91 I mechanical) cleaning . chemical

299. A cleaning solution is circulated through the tubes or the

~~_ _ _ -side . shell

43
300. For mechanical methods of cleani ng , the exchanger is
partially or ___ _ _ _ dismantled. fully, or completely

301. The drawing shows a water jet used for hydroblasting, a

commonly used cleaning method.

Water , under high _ _ _ _ _ __ is sprayed on the pressure

outside or inside of the lubes.

302. The force of the water loosens the _ _ _ ____ and deposits
washes them away.

303. Steam jets are also commonly used for heavy hydrocarbon·
deposits.
The heat generated by the steam softens the deposits and
the of the steam jet washes them away . force , or pressure

304. For any kind of hydroblastina. the exchanger must be <It

least partially dismantled.
The end plates , or bonnet covers, must be removed to
expose the tube _ _ _ _ _ __ sheets

305. For the most difficult deposits whic h resist chemicals or

hydroblasting, methods are used. mechanical

306. The exchanger is fully _ _ _ _ _ __ dismant led

307 . Drills and other devices are used to cut and scrape the
_ _ _ _ _ _ _ from the parts of the exchangers. deposits

44
Testing for L ea ks

308. In the event that the operator suspects leaks inside the
exchanger, preliminary tests can be made wi t hou t dis·
mantling .
Such tests can be run on either the tube-side or _ _ __ shell
side o f the exchanger.

309. If the two fluid s in t he exchange r have different physical

properties (like water and oil) it is usually ( easy / difficult ) easy
to te ll them apart .

310 . T he easiest way to test for leaks is to take a samp le from

the ( higher / lower) pressure fluid . lower

311 . If the fluids are water and oi l, for example, then it is easy
to see if there is a leak by just at t he sample . looki ng

312 . If the fluids are very simila r, a c hemical test ( mE."t / may may
not ) be necessary.

313 . If visual or chemical tests do not indicate a leak , further

testing may be necessary.
These furth er tests are called hydrostatic tests, because
they u sual ly involve using und er pressure . water

3 14 . In the case o f tube side test, the shel l-side flu id is drained ,
and a drain point. such as a disconnected lower nozzle or
b leeder valve, is left ( open I c losed ). o pen

315 . The tube side fl uid is replaced with water u nde r pressure
which fil ls the tube bundle .
If there are leaks in the tubes o r at t h e tube ends, the pres-
surized water in the tube bundle w ill be forced through the
leak points into t he _ _ _ _ __ _ shell

316. Such fluid will accumulate in the bottom of the shell and
eventually run out the _ _ __ __ _ points where it drain
can be observed by the ope rator.

317. Because the leak may be small and because fluid must
accumulate in the shell b e fore it will run from the drain
point. such a test usually takes ( some t ime / little time ). some time

318. The same kind o f test ca n be made on the shell· side o f

the exchanger.
In that case, the tube-side of the exchanger is drained of
fluid , and a tube·side is left open. drain point

45
319. The shell is filled with water under pressure . Fluid running
from the tube-side drain point will indicate a ______ leak
in the tube bundle.

320. If preliminary tests indicate a leak, the exchanger is par-

tially dismantled to determine the of the source, or cause
leak through further tests .

321 . In the case of a f ixed tubesheet exchanger, the end plates

or bonnet covers are removed.

It is then possible to directly observe the tube _ __ _ sheets

and tube _ _ _ __ ends

322 . The shell is filled with water under pressure.

The pressurized fluid enters any leaking tube at the point

where the tube _ _ _ _ _ __ leaks

323. This fluid accumulates in the tube and runs out of the
tube end.

WATER
PRESSURE

By observing the tubesheet, it is possible to tell which

_ _ _ _ _ _ _ is leakin9. tube

46
324 . A leaking tube can be plugged at both ends with a tapere d
plug

325. The drawing shows a tube wh ich has come loose in the
tubesheet .

iD)
~\~
j(}roo
) !) 0
LOOSE rUSE

Such a leak can be easi ly observed on the face of the

tube _ _ _ _ __ sheet

326. To correct this . the tube must be rerolled or welded

back into the tubesheet.

47
327 . The drawing shows one method of testi ng a partiall y dis-
mantled floating head exchanger.

WATER UNDER PRESSU R E

FLOATING HEAD

SHELL

OBSERVE LEAKS

The shell cover has been removed, and the tube bundle is
filled with under pressure . water

328 . It is now possib le to observe the leak if it is located in the

floating head gasket or in the tube ends at the floating head.
If the leak is located in the tube walls farther back in the
exchanger or at the tube ends in the stationary head , flu id
will be observed in the _ _ _ _ _ __ shel l

329. However, the operator will not be able to locate the source
of such leaks because the tube bund le and stationary head
are not _ _ _ _ _ __ visible

330 . If the leak is coming from one o f these areas. a different

D
test is necessary.

WATER UNDER PRESSURE

~~~~C:>
-1 CHANNEL COVER

T EST
FLOATING
HEAD END

The channel cover is removed and tube side fl uid is

h • ~. drained

48
331. The shel l is fill ed with water under pressure.

Fluid wi ll enter the tubes at the points where they ___ , leak
accumu late in the tubes. and run out the tube ends .

332. By observi ng the tubesheet. the operator can tell which

_______ is leaking. tube

333. Normal test pressure IS usually 1.5 times the designed

operatin g pressure .
Pressures during lesling should never exceed the rated
test _ _ _ _ __ pressu re

334 . The operator must also be aware of dange r from thermal

_______ of fluids in an exchanger which is under expa nsion
test pressure .

335. A fluid expanding in a confined space can _ _ _ _ __ damage. or rupture

the exchanger .

H EAT EXC HA NGE SYSTEMS

Reier to Exhibit S /cr Irames 336~3S8.

336 . The heat exchanger system shown in Exhibit 5 includes a

depropanizer. a furnace. and a · type kettle
reboi ler.

337 . The depropanizer supplies the shell·side fluid. which is

liquid _ _ _ _ __ isobutane

338. From the reboiler , isobutane flows back to the depropan·

ize r as a _ _ _ _ _ __ vapor

339. The tub e·side fluid is _ _ _ _ _ _ __ hot o il

340. Cooled oi l from the reboilerflows back to the _ _ _ __ furnace

for reheating .

341. Because it relates two independent parts of the system,

the central part of this system is the _ _ _ _ _ __ reboiler

342 . The pu rpose of the sys tem is to cause isobutane to

_______ using heat generated by the furnace. vaporize

343 . This cutaway of the kettle·type reboi ler permits an inside

view of she ll ~s ide and tube-side flow.
The tube-side fluid in this system is _ __ __ oit

344. Notice that the tube bundle is U~shaped.

Th is is ( single~pass I double· pass ) flow. do ubl e· pass

49
3 45. Shell -side fluid , in this case isobutane, enters at one en d
of the reboil er and exits in liquid form ( at the same en d /
at the opposite end J. al the opposite end

346. This is the typical shell-side ( single-pass / double-pass) single-pass

arrangement.

347. The wei r pic tured at the right end of the reboiler functions
as a sort of dam.
By assuring that the tubes are always fu lly submerged in
oil , the weir ( increases / decreases) the efficiency of the increases
reboiler .

348. The greater the contact. the greate r the rate of heat
transfer

3 49 . The tube-side flu id, oil , provides the heat requ ired to cause
the shell-side isobutant to ___ _ _ __ bOi l, or vapori ze

350. The domed area of the reboiler allows the isobutane vapor
and liquid to _ _ _ _ __ separate

351. In this particular system , vapors from the reboi ler are used
to heat liquid in trays in the depropanizer.

The amount of vapor produced in the reboiler depends on

how muc h is needed in the _ _ __ _ _ _ depropanize r

352 . Suppose that the amount of vapo r in the depropanizer

needed to be inc reased.

To do th is, you would need to ( increase / decrease) the in crease

input of heat to t he reboi ler.

353. One way to do this is to ( increase / decrease) the tempera- increase

ture of the tube side oil .

354. Since the tube side fluid is pumped throug h the tubes,
circu lation in the reboi ler system is ( natural / forced ). forced

355. Anotherwaytoadd heat to the boiling flu id is to ( increase /

decrease) the rate of flow of the oil through the exchanger. increase

356. Adding heat to a boili ng liquid makes it ( hotter / boil '

!!§ler J. boi l faster

50
357. The faster the fluid boils, the _ _ _ _ _ _ vapor it more
produces in a given time .

358. By chang ing the flow rate of oil through the reboiler, it is
poss ible to control ( the amount of isobutane vapor / the
tempe rature of the isobutane vapor) going back to the
tower . the amount of isobutane
vapor

Thermosyphon Reboilers

Refer to Exhibit 6 for frames 359-371.

359. The exhibit shows an exchanger used as a thermosyphon

reboiler.

A liquid (propane and propyle ne) from the bottom of the

fractionating tower is heated in the reboiler and goes back
into the tower as a combination of liquid and _ _ _ __ vapor

360 A thermosyphon reboiler functions like a kettle reboiler

in that both break down a liquid into vapor and liquid
components.

However, the liquid and vapor are removed in separate

streams on ly from the ( kettle-type reboiler / thermosy-
phon reboiler ). kettle-type reboiler

361. Exhibit 6 also represents flow through the the rm osyphon

reboiler .

As it shows, the propane and propylene are ( shell side /

tube-side ). tube-side

362. The shell-side inl et fluid is _ _ _ _ __ steam

363. In the process of giving up heat to vaporize the propane

and propyl ene, the steam _ _ _ _ __ condenses

364. When the shell-side fluid leaves the exchanger, it has con-
densed and is a _ _ _ _ __ liquid

51
365. This drawing represents flow on the outside of one tube
and on the inside of another.

I NSIDE
OF TUBE

As the steam loses heat. it condenses on the outside of

the tubes as _______ water

366. The water collects and runs out the _ _ _____ of bottom
the exchanger.

367. Inside th e tubes, the heat given up by the steam causes

some of the propane-propylene to boiL
The boiling begins closer to the ( top f bottom ) of the tube botto m
bundle.

368. A mixture of vapor and liquid is ( heavier f lighter ) than an lighte r

equal volume of just liquid.

52
369. Since the vapor- liquid mixture is lighter than the liquid
entering the in let. it moves ( upward / downward ) in the upward
tubes.

370. For this reason , moving products through a thermosyphon

reboiler does not require a pump.
A fl ow of liquid is produ ced by the format ion of ___ _ vapor

371. Vapor in the tubes flows rapidly . carrying with it entrained

droplets of liquid .
Since they leave the exchanger in one stream , a dome
space ( is I is not ) necessary. is not

Shell and Tube Water Coolers

Refer to Exhibit 7 lor Irames 372-388.

372 . Coolers are used to lower the temperature of a liquid or

vapor.
In th is example , th e product being cooled is ____ _ kerosene

373. Before the kerose ne reac hes the coo lers , it has bee n pre-
cooled in two crude ___-___ exchangers . pre-heat

374. The cooling liq uid in the coolers is _ _ _ _ _ , _ water

375. The tube-side fluid is water, in thi s case, and it passes

through the exchang er ( once / tw ice ). twice

376. Kerosene, the shell flu id, makes a ( single / double ) pass sing le
through the shell .

377. In the she tt-side of the exchanger, there is a se ries of

baffles

378. These baffles continually chan ge the of direction

the kerosene flo w.

379. This maxim izes the between the kero- contact

sene and the tubes.

380. The efficiency of this single-pass exchanger is ( increased I inc reased

decreased) by the baffles.

38 1. In many cases, more than one unit is required to do the

heat transfer job.
In Exhibit 7, two heat exchangers are used 10 _ _-_ __ pre-heat
crude oil.

53
382. Two more are used to ~~~~~~__ kerosene for cool
storage.

383. This drawing shows two ways to connect heat transfer

units into a stream.

SERIES CON NECTION

ON THE TUBESIDE

PARALLEL CO NNECTION
ON THE TUBES IDE

The incoming flow is split in ( parallel I series) connec- parallel

tion .

384. In a series connection, ( all I only a part) of the stream all

goes through each exchanger.

385. In Exhibit 7, the kerosene (flows first through one cooler,

then out and into the next I flow is split, some flowing into flows first through one
one cooler and some flowing into the others ). cooler, then out and into
the next

386. The shell-side kerosene flows in ( series I parallel) through series

the coolers .

387. The tube-side water flows in ( series I parallel) through parallel

the coolers.

388. Notice the connections on the crude pre heaters.

They are connected in on the tube side parallel
and in on the shell-side. parallel

54
Waste Heat Boilers

Refer to Exhibit B for frames 389-41 O.

389 . Th e system shown in the exh ibit inc ludes a fractionating

tower, a steam drum and a waste heat boiler,
Heavy oil, the she ll-side fluid, is drawn off the bottom of
the tower. fractionating

390. The tube-side fluid is water drawn from the _ _ _ __ steam

drum

391 . The boiler uses the waste heat from the hot oil, which must
be cooled before it is stored, to produce _ _ _ _ __ steam
for the plant steam system.

392 . The shell-side of the exchanger or boiler has baffles ever

six inches.
Oil entering the shell flows ( straight through and out /
back and forth across the outside of the tubes J. back and forth ac ross the
outside of the tubes

393 . As it absorbs heat from the oil, some of the water starts to
boil in the first half of the tubes .

STEAM WATER DROPLETS

.. VAPOR BUBBLES

By the time the water gets to the other end, most of the
,
space in the tubes is taken up by _ _ _ _ __ vapor

394. At the end of the tu be, the steam blows along unvapor-
ized water in the form of small _ _ _ _ __ drop lets

395. The water leaves the boiler as a _ _ _ _ _ _ of steam mixture

and droplets of water.

396 . When the vapor-liquid mixture of water enters the steam

drum, the droplets of water fall to the bottom .
The lighter steam remains in the ( top / bottom) half of top
the steam drum.

55
397. The steam drum performs a similar function to the dome
in a kettle-type reboiler.
It permits the steam to be _____ _ from the water. separated

398. In order to maintain a constant amount of water circulat-

ing in the system , treated water make-up
is added at the bottom of the steam drum.

399. In the steam drum, the new incoming water mixes with the
( hot I cool) water recirculated from the boiler. hot

400. The steam drum is usually positioned above the boiler.

When the steam drum is overhead, boiling induces a flow
( upward I downward ). upward

401 . The boiler with a steam drum above it creates a natural

circulation similar to a reboiler. thermosyphon

402 . Water absorbs heat better than steam does.

For maximum heat transfer in a boiler, it is better to have
( steam I water ) in contact with the tube walls. water

403. In the boiler in this example, the tubes are extremely hot.

If the water does not flow rapidly through the tubes, it is

vaporized near the (end I beginning ) of ;:he tube . beginning

404. The steam then passes through the remainder of the tube
and absorbs ( less I more ) heat than the water would. less

405. If the water boils too soon, much of the heating surface of
the tube is wasted .
The hot oi l simply retains more of its heat and leaves the
boiler at a ( higher / lower) temperature. higher

56
406. Natural circu lat ion by thermosyphon action usually can-
not push water through the tubes fast enough .
To increase the flow rate of the water, there is a _ _ __ pump
in the line between the steam driver and the boi ler intake.

407 . The pump helps increase the _ _ _ __ _ _ of this efficie ncy

exchanger system.

408. The new makeup water is treated at water treatment facili-

ties to remove minerals.
Some minerals remain in the water even after treatment.
As the water is partl y boiled and the steam drawn off, then
the mineral concentration in the water tends to ( increase / increase
decrease ).

409 . To prevent the mineral content of the water from increas-

ing, a continuous is provided. blowdown

41 0. The blowdown drains off some of the recycled water to

_ _ _ _ _ _ _ the mineral content. -control

Troubleshooti ng Exc hanger Systems

Refer to Exhibit 9 for frames 411-430.

411 . In a fractionati ng tower, crude oil is separated into frac-

tions, or parts.
Light fract ions, such as gasoline and naphtha, are taken
from the higher levels, and heavy fractions are taken from
the levels. lower

41 2. The overhead vapors from the fractionator are fed to a

condenser

413 . In the conden ser, heat is transferred from the vapor to

the cooling fluid , which in th is case is _ _ _ _ _ __ wate r

414. When vapor cools , it _ _ _ ____ , or liQuities. condenses

415. Some of the condensed vapor is drawn off through the

p roduct lin e, and some of it is returned to the top of the
fractionator as refl ux

416. Suppose that the pressure in the fractionator is too high.

The problem may be caused by too high a _ _ _ _ rate. reflux

4 17. If the reflux rate is too high, the conde nser becomes over-
loaded with vapor .
The conde nser is not able to _ _ _ _ _ _ _ the vapor condense
Quickly enough .

57
418. The excess of vapor causes a pressure buildup in the
fractionator. or tower
4 19. To correct this, the ref lux rate must be ( increased /
redu ced ). red uced
420. Too much _ _ _ _ _ _ can also be caused by a mal- pressure
function ing condenser.
421 . If the condenser is not transferring heat effectively from
the vapor to the cooling water, the vapor will not condense.
An overload of vapor will bu ild up pressure in the over-
head vapor line and in the itself. condenser

422. A fouled condenser is often indicated by a pressure increase

on the water side or a water outlet temperature that is too
( high / low). low

423. If the condenser is fou led by debris accumulating at the

tubesheet , the debris can be loosened by backflowing the
cooling _ _ _ _ __ water

424. It is possible thai other maintenance must be performed

depending on the nature of the _ _ _ _ __ fou ling

425. Changes in pressure and temperature on the water side

may also in dicate problems with the _ _ _ __ _ water
supply.

426. Condenser malfunction may also be caused by ai r in the

cooling water system.
Air causes vapor binding, which reduces the efficie ncy
with which heat is _ _ _ _ __ exchanged, or transferred

427. To help eliminate vapor binding , a _ _ _ _ _ _ is vent

provided in the water exit line.

428. Noncondensible vapors in the process side of the exchanger

can also cause a buildup in the fraction- pressure
ator.

429. Because the vapors do not condense, they take up su rface

area in the exchanger.
A loss in surface area causes a loss in the _ _ _ _ __ cooli ng
capacity of the exchanger.

430. This can be corrected by venting the process side of the

exchanger to release the noncondensible _ _ _ __ vapors

Refer to Exhibit 10 for frames 431-460.

431 . Exhibit 10 shows the layout of a system involving a furnace,

a reactor, two primary heat exchangers, one secondary
heat exchanger, two reboilers, and a _ _ _ _ _ __ conde nser

58
43 2. Th e feed to this system cons ists of hydrog en and low
octa ne gasoline.
High octane gasoline if the _ _ _ _ __ prod uct

433. The reaction which raises the octane rating of the gaso-
line takes place in the ______ _ reactor

434. A temperatu re of 1000o F. is necessary for this reaction.

The heat to mainta in this temperature is provided by the
furnace

435. The reaction is promoted by the use of a ______ catalyst

436. Trace the pat h of the product stream in Exhibit 10.

The product leaves the reactor, flows through the second-
ary exc hanger, through two reboil ers, through two pri mary
exc hang ers. and finally passes through the _ _ _ __ condenser

437. When the product. high octane gasoline, leaves the reactor.
its temperature is of . 950

438. But. when the product leaves the co nden ser. its tempera-
ture has dropped to of . 100

439. In ot her words . the system of exchan gers. rebollers, and

condenser is used to the product stream . cool

440. Now trace the path of the feed stream.

The feed leaves the pump and passes through the primar
exc hangers. the . and the reactor. furnace

441 . Dur ing th is process, the feed a large absorbs

part of the heat given up by the product stream .

442. The product coo lin g system is used to pre- the heat
feed.

443. So me of the heat is also transferred thro ugh the ____ rebo ilers
to other processes.

444. Because heat is recaptu red in the system. the furnace

uses less fuel

44 5. The cooling problem is also si mplified.

Altogether. the entire process is ( more I less) efficient more

and economical.

446. First. the operator shou ld check temperatures at various

points along the system.

If the furn ace inl et temperature is stable at 70QoF, but the

outlet temperature is below the 10QQoF co ntrol point, the
problem Is probably in the _ _ _ _ __ furnace

59
447 . The by·pass valve also controls the amoun t of heat avai l·
able to the reboilers.
When the by-pass is closed and a maximum amount of
heat is transferred to the feed stream through the second-
ary exchange r. the temperature of the product strea m
( decreases / increases ). decreases

448. Therefore. ( less / more) heat is available to the reboi lers. less

449. Th ere is also less heat available to the _ _ __ _ _ _ primary

exchangers

450. Because of this . when readjusting the by-pass to get maxi-

mum heat to the feed stream. the operator must take care
to ma intain the necessary heat input to the reboilers

451. Anoth er cause for di ffic ulty in mai ntaining the 1000 0 F
control point might be an ove rl oad on the reboi lers.
Too much heat is being transferred through the _ __ reboilers
to the stream that leads outside th e system.

452 . To correct this . the operator should ( reduce / increase) reduce

the load on the rebOllers .

453. If. however. the in let temperature has dropped below the
700° F level. the problem may lie in the by-pass valve or
the exchanger load
The valve controls the flow of the product stream through
the ___ __ exc hanger. secondary

454. If the by-pass valve is completely closed . ( all / some ) of all

the produ ct stream will pass through the exchanger.

455. In that case. a maximum amount of heat will be tran sferred

to the __ ___ stream. feed

456. If th e by-pass valve is co mpletely open. most of the prod-

uct stream will bypass the secondary exchange r.
Therefore . a ( minimum / maximum) amount of heat will mi nimum
be transferred to the incoming feed stream .

457. When less heat is being transferred to the feed st ream

through the secondary exchanger. the temperature of the
feed stream at the inlet drops. furnace

458. It becomes di fficult for th e to ra ise the furnace

feed stream temperature to the necessary 1000oF.

459. Therefore , a drop in feed tempera ture at the furnace inlet

might be caused by a by-pass valve that is too far ( open / open
closed ).

460. To correct th is, the operator should read just th e ____ . by-pass

60