f s r ^ T r i h A f t ' f v c f - T r v p r ^ w n t p ? v " " " T U i,-», w v l S i i - . r U v > v V . i • - • i.; i v U i W-iV*^

MPtM^n • i i L. i i i »»'.*•'

I t*. • : 'V ' ! ti: V V . . t i. ii i &

i l i U ) -n " v " Ji * f t •'/••ft: ¥ * r>,: h ^ i l ^ i ' n i m i i t l f c t t m - M ^ u h

11 f t t. i ; ! : ? ! ! ' ' - c r r t *-• v »• i A t r r «•« if* f i j « f i s j p S r - ' ; t r j u r ^ u w m i Q f M u i x j x p i l a g n u & s t o LMTO

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

PERPUSTAKAAN UTHM

SCANNED AVAILABLE o n l i n e

* 3 0 0 0 0 0 0 1 8 8 3 5 2 5 *

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

DESIGN OF HEAT EXCHANGER NETWORK

USING PINCH METHOD

WAN NURDIYANA BINTI WAN MANSOR

A dissertation submitted as partial fulfillment of the requirement for the award of

the Master's Degree in Mechanical Engineering

Department of Mechanical Engineering

Faculty of Mechanical and Manufacturing Engineering

Kolej Universiti Teknologi Tun Hussein Onn

NOVEMBER 2006

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

I l l

S'OA, rivy, jxurui/ij,,

^VQ. C^HAJQA tt\& lUlXXMl2ti£LQ4lCl£ f<)Ate, CMu) tfl/COi UjfKM it tftuA-

toAU^ ^QAwivcAj.. ^e^t/ca£e<l ta a£i -tfi-o&c llei/i/eA}& v»t

tuJIvnAl&A, Q^ tuQAAUAX^.

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

xiv

ACKNOWLEDGEMENT

W i t h a deep sense o f gratitude, I wish to express m y sincere thanks to m y

supervisor, Professor Dr . V i j a y R. Raghavan for his immense help in p lanning and

executing the works in t ime. H e is not only a great professor w i th deep vision but

also and most importantly a k ind person. H i s trust and determination inspired me in

the most important moments o f m a k i n g right decisions and I am glad to work w i th

him. T h e confidence and dynamism with which P r o f V i j a y guided the work requires

no elaboration.

I also want to thank m y parents, who taught m e the value o f hard work by

their o w n example. I wou ld l ike to share this moment o f happiness wi th m y parents,

brothers and sisters. T h e y rendered me enormous support during the whole tenure o f

my studies.

F ina l ly , I w o u l d l ike to thank all whose direct and indirect helped me

complet ing m y thesis in t ime. PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

xiv

ABSTRACT

Chemica l or o i l ref ineiy processes ut i l ize huge amounts o f energy in their routine

operations. There fore , it is v i ta l for such industries to find ways o f m a x i m i z i n g the use

o f energy and make the system more eff ic ient through reduction in energy, water and

raw mater ial consumption. W a s t e energy can be transferred to another process and that

w i l l increase the prof i tabi l i ty o f the industries. W h e n the use o f a heat exchanger

network (HEN) is considered for these tasks, the f r a m e w o r k developed in this study can

be implemented to m a k e a cost-benefit analysis.

Th is thesis represents a f r a m e w o r k for generat ing the H E N over a specif ied range

o f variat ions in the f l o w rates and temperature o f the streams. So that the heat exchanger

area, n u m b e r o f heat exchange units and load on the heat exchangers can be estimated.

T h e proposed method to analyze and design the H E N is cal led pinch method, wh ich is

one o f the most practical tools and used to improve the ef f ic iency o f energy usage, fuel

and water consumption in industrial processes. Th is method investigates the energy

f lows wi th in a process and identif ies the most economical ways o f m a x i m i z i n g heat

recovery. Th is method consists o f five major steps to f o l l o w , w h i c h w i l l finally lead to

H E N design. T h e steps are: ( 1 ) choose a m i n i m u m temperature approach temperature

( D T m i n ) , ( 2 ) construct a temperature interval d iagram, ( 3 ) construct a cascade d iagram

and determine the m i n i m u m ut i l i ty requirements and the p inch temperature, ( 4 ) calculate

the m i n i m u m number o f heat exchangers above and b e l o w the pinch and (5 ) construct

the heat exchanger network .

T h e emphasis o f this work has been on the designing o f the H E N . H o w e v e r , to

demonstrate the practical impl icat ions o f p inch analysis, D T m i n and the heat exchanger

costs, it is necessary to estimate the heat transfer area o f the H E N , wh ich w i l l help in

arr iv ing at the total cost inc luding capital and running costs o f the designed H E N . T h e

effect o f changing the D T m i n gave a good indicat ion on the overal l costs.

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

xiv

ABSTRAK

Industri pemprosesan k i m i a atau penapisan minyak banyak menggunakan tenaga

dalam rutin harian mereka. M a k a industri-industri sebegini perlu mencari a l temat i f

untuk memaks imumkan penggunaan tenaga dan memast ikan sistem yang digunakan

adalah efisyen melalui pengurangan da lam penggunaan tenaga, air dan juga bahan

mentah. H a b a buangan daripada proses yang di jalankan boleh dikitar dan diguna semula

untuk digunakan di da lam proses yang lain. Jadi, b i ia alat penukar haba digunakan di

dalam proses yang disebutkan di atas, m a k a ke i ja di da lam tesis ini boleh digunakan

untuk mengurangkan penggunaan kos untuk industri tersebut.

Tesis ini mempersembahkan ja lan ke i j a untuk merekabentuk 'Rangkaian

Penukar Haba ' . Hasi lnya , kawasan yang diperlukan untuk membina alat-alat penukar

haba ini boleh dikira, begitu j u g a bi langan unit yang diperlukan dan bebanan yang

dikenakan kepada alat penukar haba boleh dianggarkan. Rangkaian yang diusulkan ini

menggunakan kaedah yang dikenal i sebagai Kaedah Pinch. ICaedah ini merupakan

kaedah yang pa l ing praktikal dan digunakan untuk meningkatkan penggunaan tenaga, air

dan bahan mentah secara efisyen. Kaedah ini mengenalpasti tenaga yang boleh dial irkan

dari buangan kepada proses yang berguna dan seterusnya dapat memaks imumkan

penggunaan tenaga. Kaedah ini mengandungi l i m a langkah yang per lu di ikuti: (1 ) p i l ih

suhu rendah yang dibenarkan, ( 2 ) b ina diagram jarak-suhu, ( 3 ) b ina diagram Cascade

dan tentukan keperluan tenaga m i n i m u m , (4 ) k ira bi langan alat penukar haba yang

diperlukan dan (5 ) b ina rangkaian alat penukar haba.

O b j e k t i f u tama tesis ini adalah merekabentuk rangkaian alat penukar haba,

namun sebagai pelengkap kepada keperluan ekonomi , tesis ini turut mendemonstrasi

kesan daripada penggunaan kaedah pinch ini dengan suhu m i n i m u m yang dipi l ih dan

j u g a kos untuk membina rangkaian alat penukar haba. Kos-kos ini termasuk kos untuk

m e m b i n a kawasan, kos pembuatan alat penukar haba dan lain-lain. Kos ini disebut

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

Vlll

sebagai kos u t a m a y a n g mei ibatkan kos permulaan untuk memulakan operasi. M a n a k a l a

kos tahunan atau kos yang perlu ditanggung sepanjang industri ini menjalankan operasi

mereka termasuk kos untuk membel i tenaga, minyak , air dan lain-lain. Dengan menukar

ni la i suhu m i n i m u m yang dipi l ih di da lam langkah (1), kos-kos yang disebutkan akan

berubah dan di sini akan w u j u d t i t ik op t imum yang boleh diaplikasi oleh pihak industri.

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

V l l l

T A B L E O F C O N T E N T S

C H A P T E R C O N T E N T S P A G E

D E C L A R A T I O N i i

D E D I C A T I O N in

A C K N O W L E D G E M E N T iv

A B S T R A C T v

A B S T R A K vi

T A B L E O F C O N T E N T S v i i i

L I S T O F T A B L E S xi

L I S T O F F I G U R E S x i i

N O M E N C L A T U R E x i v

L I S T O F A P P E N D I X E S xv i i

1 I N T R O D U C T I O N

1.1 Background o f the Prob lem 3

1.2 Object ives 4

1.3 Scope o f W o r k 5

1.4 T h e Importance o f the Research 5

I I L I T E R A T U R E R E V I E W

2.1 Introduction to Hea t Exchanger N e t w o r k Analysis 8

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

2.2 Pinch Design M e t h o d 9

2 .21 Pinch Appl icat ion 15

2.3 Mathemat ica l Programming Approach 17

2 .3 .1 Sequential Approach 17

2 .3 .2 Simultaneous Approach 18

RESEARCH METHODLOGY

3.1 Introduction 22

3.1.1 O v e r v i e w o f Pinch Design M e t h o d 22

3 .1 .2 W h a t is Pinch Technology? 23

3.1.3 Object ives o f P inch Analysis 24

3 .2 Steps in Pinch Analysis 26

3 .2 .1 Thermal Da ta for Process and U t i l i t y Streams 26

3 .2 .2 Step 1: Choose a M i n i m u m Approach Temperature

( D T m i n ) 2 7

3.2.3 Step 2: Construct a Temperature Interval D i a g r a m 28

3.2.4. Step 3: Construct a Cascade D i a g r a m 29

3.2.5 Step 4: Calculate the M i n i m u m N u m b e r o f H e a t

Exchanger 30

3 .2 .6 Step 5: Design the Heat Exchanger N e t w o r k 30

3.2.6.1 Design above the Pinch 31

3 .2 .6 .2 Des ign b e l o w the Pinch 32

3.3 Composi te Temperature Enthalpy D i a g r a m 32

3.4 H e a t Transfer Area Calculat ion 33

3.5 Basic Design Procedure o f a H e a t Exchanger 34

3.6 T h e Design o f Shel l -and-Tube H e a t Exchangers 35

3.6.1 Hea t Transfer and Pressure Drop Calculations 36

3 .6 .1 .1 Shel l -Side H e a t Transfer Coef f ic ient 3 7

3 .6 .1 .2 Shel l -Side Pressure Drop 39

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

3.6 .2 Rat ing Procedure 41

3.6.3 Approx imate Design M e t h o d 43

3.6.3.1 Exchanger D imens ion 44

I V A N A L Y S I S A N D D I S C U S S I O N

4.1 Introduction and the D a t a Prob lem 46

4.2 M i n i m u m temperature approach o f 10°C 4 7

4.3 Des ign A b o v e the Pinch 50

4.4 Des ign B e l o w the Pinch 52

4.5 Analysis for the M i n i m u m Temperature

Approach o f 15°C 56

4.6 Analysis for the M i n i m u m Temperature

Approach o f 20 °C 60

4 .7 Shel l -and-Tube H e a t Exchanger 65

4.8 H e a t Exchanger Specif ication 68

4.9 Discussion 69

V C O N C L U S I O N A N D R E C O M M E N D A T I O N

5.1 Conclusion 71

5.2 Recommendat ion 72

R E F E R E N C E S 73

A P P E N D I X E S 79

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

xiv

LIST OF TABLES

TABLE NO. TITLE PAGE

1.1 PS Gantt Chart 6

3.1 Typica l Va lues o f D T m i n in Industrial Processes 28

4.1 Stream and T h e r m a l D a t a for Pinch Analysis 4 7

4 .2 Processes-to-Process Exchanger A r e a 55

4.3 H o t U t i l i t y Exchanger Area 55

4.4 C o l d Ut i l i t y Exchanger Area 55

4.5 Processes-to-Process Exchanger A r e a 58

4.6 H o t Ut i l i ty Exchanger A r e a 59

4 .7 Cold Ut i l i ty Exchanger A r e a 59

4.8 Processes-to-Process Exchanger A r e a 62

4 .9 H o t Ut i l i ty Exchanger Area 63

4 .10 Co ld Ut i l i ty Exchanger Area 63

4.11 S u m m a i y o f the Calculated Stream D a t a 63

4 .12 Hea t Exchanger Specif ication Used in the Design 69

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

xn

LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.1 On ion D i a g r a m o f H ierarchy in Process Design 2

2.1 Shel ls-and-Tube Hea t Exchanger 8

3.1 Strategy for the H E N synthesis using pinch approach 25

3.2 Basic Log ic Structure for Process Hea t Exchanger Des ign 34

4.1 Temperature Intervals D iagram wi th D T m i n 10°C 64

4.2 Cascade D i a g r a m w i t h D T m i n 10°C 49

4.3 H e a t L o a d A b o v e the Pinch Point 50

4.4 Hea t L o a d B e l o w the Pinch 51

4.5 Des ign o f H E N A b o v e the Pinch Point 52

4.6 Des ign o f H E N B e l o w the Pinch 53

4 .7 Temperature Enthalpy D i a g r a m

for the Case o f D T m i n is 10°C 54

4.8 Temperature Interval D i a g r a m

for the Case o f D T m i n = l 5°C 56

4.9 Cascade D i a g r a m for the Case o f D T m i n = 1 5 ° C 57

4 .10 Designs A b o v e the Pinch 5 7

4 .11 Designs B e l o w the Pinch 58

4 .12 Temperature Interval D i a g r a m

for the Case o f D T m i n = 2 0 ° C 60

4.13 Cascade D i a g r a m 61

4 .14 Designs A b o v e the Pinch 61

4.15 Designs B e l o w the Pinch 62

4 .16 T h e Ef fect o f U s i n g D i f fe rent D T m i n 64

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

4.17 Shel l -and-Tube Hea t Exchanger w i th

one-shell and two-passes 65

4 .18 T h e Types o f Front E n d Used in the Design 66

4 .19 T h e Types o f Shells Used in the Des ign 67

4 .20 T h e Types o f Rear E n d Used in the Design 68

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

xiv

NOMENCLATURE

A H e a t Exchangers A r e a

As Shel l -Side or T u b e Outside Surface A r e a

Cp Specific H e a t Capacity

d0 T u b e D iamete r

DP s-actual Actual Pressure D r o p in the Shel l -Side

DPs-id Ideal Pressure D r o p in the Shel l -Side

A Shell D i a m e t e r

DTin, Temperature D i f fe rence at Each Interval

D T m i n M i n i m u m A l l o w a b l e Temperature D i f fe rence

F L M T D Correct ion Factor

F, Correction Factor for the T u b e Outside D iamete r and T u b e L a y o u t

F2 Correct ion Factor for the N u m b e r o f T u b e Passes

F3 Correct ion Factor Var ious R e a r - E n d H e a d Designs

h Heat Transfer Coef f ic ient

H D D H u m i d i f i c a t i o n - D e h u m i d i f i c a t i o n Desal inat ion

H E N Hea t Exchanger N e t w o r k

Ihd Ideal H e a t Transfer Coef f ic ient

hs Shel l -Side H e a t Transfer Coef f ic ient

Jb Correct ion Factor for B u n d l e

Jo Correct ion Factor for B a f f l e Conf igurat ion

Ji Correct ion Factor for B a f f l e Leakage Effects

Jr Correct ion Factor for A n y Adverse Temperature Gradient

Js Correction Factor for L a r g e r B a f f l e Spacing

k Therma l Conduct iv i ty

L T u b e Length

Leff Effect ive T u b e Length

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

xiv

L M T D Logar i thmic M e a n Temperature Di f ference

L P L inear Programming

m F l o w Rate

m C p Hea t Capacity F l o w Rate

MTT.P M i x e d Integer L inear Programming

M 3 N L P M i x e d Integer Nonl inear Programming

M O - M I L P M u l t i - O b j e c t i v e M i x e d - I n t e g e r L inear Programming

NH N u m b e r o f Baf f les

N L P Nonl inear Programming

NK CC N u m b e r o f T u b e R o w s Crossed D u r i n g F l o w Through One Crossf low in

the Exchanger

TV,. CTl. N u m b e r o f T u b e R o w s Crossed in Each Baf f le W i n d o w

N , N u m b e r O f Tubes

N u Nusselts N o .

P D M Pinch Design M e t h o d

Ps Temperature Effectiveness

O Hea t Supp ly /Demand

Qmailable Heat Ava i lab le

Q C Co ld Enthalpy

Q H H o t Enthalpy

O m t Hea t for Each Interval

RS Heat Capacity Rat io

S T H X Shel l -and-Tube Hea t Exchanger

T E M A Tubular Exchanger Manufacturers ' Association

T - H Temperature-Enthalpy

T - I Temperature Interval

T i n Supply Temperature

Tout Target Temperature

U Overal l Hea t Transfer Coef f ic ient

US Overal l Shel l -Side Heat Transfer Coeff ic ient

W W o r k D o n e

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

x v i

AH Enthalpy Change

AP Pressure Drop

APb,id Ideal Pressure Drop in the Central Section

APcr Pressure D r o p in the Central (Crossf low) Section

AP,-0 Pressure Drop in the Shel l -Side Inlet A n d Outlet Sections

APW Pressure D r o p in the W i n d o w Area

Q) Correction Factor for Bypass F l o w

Q Correct ion Factor for Tube - to -Ba f f l e and Baf f le - to-Shel l Leakage

Streams

6 ' Correction Factor for In le t and Outlet Sections

t| Viscosi ty

p Densi ty

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

xvii

LIST OF APPENDIXES

APPENDIX TITLE PAGE

A Tube outside (shell side) surface area A s as a function o f

shell inside diameter and effect ive tube length 80

B Va lues o f F i for Var ious T u b e Diameters and Layouts 81

C Va lues o f F2 for Var ious N u m b e r s o f Tube-Passes 82

D Va lues o f F 3 for Var ious T u b e Bundle Constructions 83

E Typ ica l Ref inery Process 84

F Or ig ina l Paper o f Barbara et al. ( 2 0 0 4 ) 85

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

1

C H A P T E R I

I N T R O D U C T I O N

T h e transfer o f thermal energy is one o f the most important and frequently

used processes in engineer ing. T h e transfer o f heat is usual ly accompl ished b y a heat

exchanger. A s a heat transfer device, it is the funct ion o f a heat exchanger to transfer

heat as e f f ic ient ly as possible. T h i s makes it the u l t imate device o f choice, for

instance, w h e n it comes to saving energy b y recover ing wasted heat and m a k i n g it

useful again. W h e n there is a waste o f energy or a hot stream that is not recovered, a

pre-heater or recuperator can convert that hot stream into a useful source o f heat i n

other applications.

W h e n designing heat exchangers and other unit operations, l imits exist that

constrain the design. These l imi tat ions are imposed by the first and second laws o f

thermodynamics . I n heat exchangers, a close approach b e t w e e n hot and cold streams

requires a large heat transfer area. W h e n e v e r the dr iv ing force for heat exchange is

smal l , the equipment needed for transfer becomes large and it is said that the design

has a "p inch" . W h e n considering systems o f m a n y heat exchangers, it is ca l led a heat

exchanger n e t w o r k ( H E N ) . T h e r e w i l l exist somewhere in the system a po int where

the dr iv ing force for energy exchange is m i n i m u m . Th is represents a p inch o r p inch

point . T h e successful design o f these ne tworks involves discover ing w h e r e the p i n c h

exists and using this in fo rmat ion at the p inch point to design the w h o l e ne twork . Th is

design process is cal led p i n c h technology.

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

2

T h e H E N synthesis has been one o f the most w e l l studied in process synthesis

dur ing the last three decades and has been w i d e l y appl ied, especial ly in the

pet ro leum re f in ing and petrochemical industry. T o i l lustrate the role o f H E N in the

overal l process design, consider the "on ion d iagram" ( L i n h o f f et. al., 1982 ) as s h o w n

be low. T h e design o f a process starts w i t h the reactors in the "core" o f the onion.

O n c e feeds, products, recycle concentrations and f lowrates are k n o w n , the separators

( the second layer o f the onion) can be designed. T h e basic process heat and mater ia l

balance is n o w in place, and the H E N (the third layer) can be designed. T h e

remain ing heat ing and cool ing duties are handled by the ut i l i ty system ( the four th

layer) . T h e process ut i l i ty system m a y be a part o f a centralised si tewide u t i l i ty

system.

R < i r i t : l a 6 9 r i p

o 2 (5 Cl <D

k00

V B

The heat and material balance is at this bounda'y

/ S . X \ / / * \ / / /

i ( ' , \

" t

w ^ \ * ; .Reactor) ; , 4 \ / I I . if / I

\ / U/Ltios-""'''

Site-wide Utilities

F igure 1.1: O n i o n D i a g r a m o f H i e r a r c h y in Process D e s i g n

T h e p inch analysis starts w i t h heat and mater ia l balances for the process.

U s i n g p inch technology, it is possible to ident i fy appropriate changes in the core

process condit ions that can have an impact on energy savings (on ion layers one and

two) . A f t e r the heat and mater ial balance is established, targets for energy saving can

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

3

be set prior to the design of the heat exchanger network. The pinch design method

ensures that these targets are achieved during the network design.

Process integration using pinch technology offers a chronicle approach to

generate targets for minimum energy consumption before heat recovery network

design. Heat recovery and utility system constraints are then considered in the design

of the core process. Interactions between the heat recovery and utility system are also

considered. The pinch design can reveal opportunities to modify the core process to

improve heat integration. The pinch approach is unique because it treats all processes

with multiple streams as a single, integrated system. This method helps to optimize

the heat transfer equipment during the design of the equipment.

1.1 Background of the Problem

As the heat exchanger consumes energy vastly, it is vital to find a method to

improve the use of energy and reduce capital and utilities cost. Finding ways to

reduce and conserving energy are always a smart way to cut cost. Reduced energy

usage is a big selling point for end users. If the functionality of a product is similar to

the competition, benefits like energy usage win customers. The benefit of reduced

usage cost over time allows manufacturers to charge a higher premium while saving

the customer money in the long run.

Excessive energy consumption by using hot and cold utilities influences the

global cost of industrial processes. The supply and removal of heat in a modern oil

refinery process plant represents an important problem in the process design of the

plant. The cost of facilities to accomplish the desired heat exchange between the hot

and cold media may cost up to one third of the total cost of the plant. To meet the

goal of maximum energy recovery or minimum energy requirement (MER) an

appropriate HEN is required. The design of such a network is not an easy task

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

4

considering the fact that most processes involve a huge number of process and utility

streams.

For this reason, one of the major worries of the designer has been the

reduction of utilities consumption, as well as the reduction of fixed cost in the

equipment. Thus, a lot of research work has been carried out to find the optimum

configuration of a HEN both in terms of total cost and operability. The major

challenge within HEN synthesis problem is to identify the best pair of process

streams to be connected with the heat exchangers, so as to minimize the energy

utilization.

The designing of HEN to be addressed in this thesis can be stated as follows:

A set of hot streams to be cooled and cold streams to be heated are given which

include multiperiod stream data with inlet and outlet stream temperatures, heat

capacity flow rates and heat transfer coefficients. The objective then is, within the

range of the operating conditions, to determine the HEN for energy recovery between

the given set of hot and cold streams, so that the heat exchanger areas can be

estimated. Hence, the annualized cost of the equipment plus the annual cost of

utilities can be minimized. Lastly, a set of heat exchanger designs which may consist

of process-to-process heat exchanger and utilities heat exchanger will be proposed.

1.2 Objectives

1) To design the HEN using Pinch Method.

2) To examine the effect of using three different values of minimum

temperature approach (DTmin).

3) To demonstrate the practical implications of pinch analysis, DTmin

and heat exchanger cost.

4) To propose the heat exchanger type and design.

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

5

1.3 Scope of Work

This project will be limited to these areas;

1) The design will be based on previous published data extracted from

practical examples.

2) The data taken will be altered to make it more realistic and applicable

to Malaysia's environment.

3) The project will synthesize HEN based on the pinch method analysis.

4) The designed HEN is only one of the numerous examples of the

design which might be generated using the same method.

5) Many a priori assumptions have been made to accommodate the

process of designing.

1.4 The Importance of the Research

This work is about presenting the importance of application pinch analysis in

process industry. Pinch analysis has evolved and its technique has been perfected.

Significant examples of pinch analysis utilization is in designing HEN in process

industry are those which may lead to energy saving, debottlenecking of the critical

areas in a given process, minimization of raw material used, waste minimization,

minimizing operating cost, minimizing capital investment and minimizing

engineering cost and effort.

While pinch technology experience is important to the success of a project.

There are several other factors that make the difference between saving money and

having just another interesting study such as process understanding or knowledge of

process improvement and familiarity to the oil and gas environment. Furthermore,

this research has benefited the author in designing heat exchangers in the real process

industry.

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

« .s U c s « o cn Ph

Jj s « H

y y

(N

y y

O

y

0\

y 00

w w

\o

w

in

w w

m

w

(N

w

-

AC

TIV

ITIE

S

Bri

ef st

udy

on H

EN, P

inch

Tec

hnol

ogy,

rev

iew

pr

evio

us w

ork

Get

use

d w

ith m

etho

d id

entif

ied

to s

ynth

esiz

e H

EN

Gat

her

data

fro

m in

dust

ry/in

stitu

tion

atta

ched

Dat

a an

alys

is a

nd e

valu

atio

n

Impr

ovem

ent o

n re

sult

achi

eved

Thes

is f

inal

wor

k

No - <N m IT) VO

3 O "O <u cd o <D

O <C

• -o c <u 00 0) J

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

73

R E F E R E N C E S

Aaltola, J. ( 2 0 0 3 ) . "Simul taneous Synthesis o f F lexible Heat Exchanger Networks" .

He ls ink i Un ivers i ty o f Technology Department o f Mechanica l Engineering.

Doctora l Thesis.

Barbara, A . B a g a j e w i c z , M . , V ipanurat , N . and Siemanond, K . (2004) . " A N M I L P

M o d e l for H e a t Exchanger Ne tworks Retrofi t" . Comp. and Chem. Eng. Vol. 28.

5.

Bel l , K . J. ( 1 9 6 3 ) . "She l l - and-Tube H e a t Exchangers". Un iv . De l . Eng. F ina l Report No .

5.

Bel l , K . J. ( 1 9 8 8 b ) . " H e a t Transfer Equ ipment Design". Washington D . C: Hemisphere

Publ ishing. 1 4 5 - 1 6 6 .

Bel l , K . J. ( 1 9 9 8 ) . " H e a t Exchanger Design Handbook". N e w York : Begel l House. Sec.

3 .1 .4 .

Bengtsson, C . , Kar lsson, M . , Berntsson, T . and Soderstom, M . (2001) . "Co-Ord inat ion

o f P inch Techno logy and the M I N D M e t h o d - A p p l i e d to a Swedish Board M i l l " .

Applied Thermal Engineering. Vol. 22. 133-144 .

Bjork, K . M . and Wester lund, T . (2002) . "G loba l Opt imizat ion o f Hea t Exchanger

N e t w o r k Synthesis Problems W i t h and Wi thou t the Isothermal M i x i n g

Assumpt ion" . Comp. Chem. Eng. Vol. 26. 1581-1593.

PTTAPERPUSTAKAAN

TUNKU TUN AMINAH

74

Bjork, K . M . and N o r d m a n , R . ( 2004 ) . "So lv ing Large-Scale Retrof i t Heat Exchanger

Network Synthesis Problems with Mathematical Optimization Methods"

Chemical Engineering and Processing. Vol. 44. 869 -876 .

Brodowicz , K . and M a r k o w s k i , M . , (2003) . "Calculat ion o f Heat Exchanger Ne tworks

for L i m i t i n g F o u l i n g Effects in the Petrochemical Industry". Applied Thermal

Engineering. Vol. 23. 2 2 4 1 - 2 2 5 3 .

C A N M E T Energy Techno logy Centre-Varennes. (2003 ) . "Pinch Analysis: For the

E f f i c i en t U s e o f Energy , W a t e r and Hydrogen" . Natural Resources Canada.

Ret r ieved on 16 t h August 2 0 0 6 from http://cetc-varennes.nrcan.gc.ca

Chen, C . L . , W a n g , B . W . and L e e , W . C . (2003) . " M u l t i - O b j e c t i v e Opt imizat ion for

Mu l t i -En te rpr ise Supply Cha in Networks" . Ind. Eng. Chem. Res. Vol. 42. 1 8 7 9 -

1889.

Chen, C . H . and H u n g , P.S. ( 2004 ) . " M u l t i c n t e r i a Synthesis o f F lex ib le Heat -Exchanger

N e t w o r k s w i t h Uncer ta in Source-Stream Temperatures". Chemical Engineering

and Processing. Vol. 44. 89-100.

Duran, M . A . and Grossmann, I. E. (1986) . "Simultaneous Opt imizat ion and Heat

Integrat ion o f C h e m i c a l Processess". American Institute of Chemical

Engineering Journal. Vol. 32. 123.

Ebrahim, M . and A l - K a w a r i ( 2000 ) . "Pinch Technology: an Ef f ic ient T o o l for

Chemica l -P lant Energy and Capi ta l -Cost Saving". Applied Energy. Vol. 65 . 45 -

49 .

Floudas C. A . and Ci r ic , A . R . ( 1989 ) . "Strategies for Overcoming Uncertainties in Heat

Exchanger N e t w o r k Synthesis". Comp. and Chem. Eng. Vol. 13(10). 1 1 3 3 - 1 1 5 2 .

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

75

Floudas, C. A. (1995) . "Nonl inear and M i x e d Integer Optimization". N e w York: Oxford

Universi ty Press.

Furman K . C. and Sahinidis, N . V . ( 2002) . " A Critical Rev iew and Annotated

Bibl iography for Hea t Exchanger Network Synthesis in the 20th Century", hid.

and Eng. Chem. Res. V o l . 41(10). 2335-2370 .

Geldermann, J., Tre i tz , M . and Rentz, O. (2005) . "Integrated Technique Assessment

Based on the Pinch Analysis Approach for the Design of Production Networks ".

European Journal of Operational Research. V o l . 171. 1020-1032.

Herrera, A . , Islas, J. and Arr iola, A. (2002) . "Pinch Technology Application in a

Hospital". Applied Thermal Engineering. Vol. 23. 127-139.

Houa, S., Y e b , S. and Zhang, H . (2005) . "Performance Optimization o f Solar

Humid i f ica t ion -Dehumid i f ica t ion Desalination Process Using Pinch

Technology" . Desalination. Vol. 183. 143 -149 .

Konukman, A.E.S. , Camurdan, M . C . and Akman, U. (2002) . "Simultaneous Flexibil i ty

Target ing and Synthesis o f M i n i m u m - U t i l i t y Heat Exchanger Networks wi th

Superstructure-Based M I L P Formulation". Chem. Eng. Processing. Vo l . 41.

5 0 1 - 5 1 8 .

L innhoff B „ Townsend D . W . , Boland D „ Hewi t t G. F., Thomas B. E. A. , Guy A. R „

and Mars land R. H . (1982) . "User Guide on Process Integration for the Eff icient

Use o f Energy". T h e Institution o f Chemical Engineers. Technical Report.

Linhoff , B . and F lower , JR. (1978) . "Synthesis o f Heat Exchanger Networks". AICheE

Journal. Vol. 2 4 . 6 3 3 - 6 4 3 .

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

76

M a r k o w s k i , M . ( 1 9 9 5 ) . " A P inch Based M e t h o d to Design Heat Exchanger Ne tworks

U n d e r Industr ia l Constraints on the Example o f P E T R O C H E M I A Plock (in

Pol ish)" . W a r s a w Un ivers i ty o f Technology. Ph .D . Dissertation.

Matijasevise, L . and Otmaese, H . ( 2001 ) . "Energy Recove iy by Pinch Technology" .

Applied Thermal Engineering. Vol. 22. 4 7 7 - 4 8 4 .

Mehta , R . K . C . , D e v a l k a r , S. K . , and Narasimhan, S. (2001 ) . "Opt imiza t ion Approach

for Evo lu t ionary Synthesis o f H e a t Exchanger Networks" . Transactions of the

Institute of Chemical Engineers. V o l . 79 ( P a r t A ) . 143.

Ozkan, S. and Din?er , S. ( 2000 ) . "Appl ica t ion for Pinch Design o f Heat Exchanger

N e t w o r k s b y U s e o f a C o m p u t e r Code E m p l o y i n g an Improved Problem

A l g o r i t h m T a b l e ". Energy Conversion and Management. Vol. 42. 2 0 4 3 - 2 0 5 1 .

Papoulias S. A . and Grossmann, I . E . ( 1983 ) . " A Structural Opt imizat ion Approach in

Process Synthesis-EI. H e a t Recovery Networks" . Comp. and Chem. Eng. Vol.

7 ( 6 ) . 7 0 7 - 7 2 1 .

Pethe, S., Singh, R . , and K n o p f ; F .C . ( 1989 ) . " A Simple Technique for Locat ing Loops

in H e a t Exchanger Ne tworks" . Computers and Chemical Engineering. Vol. 13

( 7 ) . 8 5 9 - 8 6 0 .

Pettersson, F . ( 2 0 0 4 ) . "Synthesis o f Large-Scale H e a t Exchanger Ne tworks Us ing an

Sequential M a t c h Reduct ion Approach". Computers and Chemical Engineering.

V o l . 29 . 9 9 3 - 1 0 0 7 .

Perry, R . H a n d Green , D . ( 1 9 8 4 ) . " C h e m i c a l Engineer ing Handbook" . 5 th Edi t ion, U S A :

M c G r a w H i l l . 6 4 6 - 6 6 3 .

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

77

Ravagnani, M . A . S . S . ( 1 9 9 4 ) . "Projeto e Ot imizac_~ao de Redes de Trocadores de

Calor" . F E Q - U N I C A M P Campinas SP. Brazi l . Ph.D. Thesis.

Ravagnani, M . A. S. S., S i lva, A . P., Ar royo , P. A . and Constantino, A. A. (2004) . " H e a t

Exchanger N e t w o r k Synthesis and Opt imizat ion Us ing Genetic Algor i thm".

Applied Thermal Engineering. Vol. 25. 1003 -1017 .

Ruyck, J. D . , L a v r i c , V . , Baetens, D . and Plesuc, V . (2002) . "Broadening the

Capabil i t ies o f Pinch Analysis Through V i r tua l Heat Exchanger Networks" .

Energy Conversion and Management. V o l . 44. 2 3 2 1 - 2 3 2 9 .

Shivakumar, K . and Naras imhan, S. (2002) . " A Robust and Eff ic ient N L P Formulat ion

Us ing Graph Theoret ic Principles for Synthesis o f Hea t Exchanger Networks" .

Computers and Chemical Engineering. Vol. 26. 1517-1532 .

Taborek, J. ( 1 9 9 8 ) . " H a n d b o o k o f Heat Exchanger Design". N e w Y o r k : Begel l House.

3 .3 .3 -1 to 3 .3 .11 -5 .

T E M A (1988) . "Standards o f Tubular Exchangers Manufactures Association". 6th

Edit ion. N e w Y o r k .

Turton, R . , Ba i l ie , R . C. , W h i t i n g , W . B. and Shaeiwitz , J. A. (2003 ) . "Analysis,

Synthesis, and Des ign o f Chemica l Processes". 2n d Edi t ion, Un i ted States o f

Amer ica : Prent ice Ha l l . 4 5 9 - 4 7 6 .

Yee, T . F . and Grossmann, E. I . ( 1 9 9 0 ) "Simultaneous Opt imizat ion M o d e l s for Heat

Integrat ion-H. Hea t Exchanger N e t w o r k Synthesis". Comp. Chem. Eng. Vol. 1.

1165.

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

78

Zhu, X . X . , O ' N e i l l , B . K „ Roach , J. R . and W o o d , R. M . (1995) . "a N e w M e t h o d for

H e a t Exchanger N e t w o r k Synthesis Us ing Area Target ing Procedures".

Computers and Chemical Engineering. Vol. 19. 197-222.

Zhu, X . X . and N i e , X . R . (2002 ) . "Pressure D r o p Considerations for Hea t Exchanger

N e t w o r k Grassroots Design" . Computers and Chemical Engineering. Vol. 26.

1 6 6 1 - 1 6 7 6 .

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

79

APPENDIXES

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

80

APPENDIX A

6 8 10 12

Effective tube longlh (m)

T u b e outside (shel l s ide) surface area A s as a funct ion o f shell inside d iameter and

e f fec t ive tube length.

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

81

APPENDIX A

Tube Outside T u b e Pitch [in.

Diameter [in. ( m m ) ] ( m m ) ]

5 / 8 ( 1 5 . 8 8 ) 1 3 / 1 6 ( 2 0 . 6 )

5/8 ( 15 .88 ) 13 /16 ( 2 0 . 6 )

3/4 (19 .05 ) 15 /16 ( 2 3 . 8 )

% (19 .05 ) 15 /16 ( 2 3 . 8 )

3/4 (19 .05 ) 1 ( 2 5 . 4 )

3/4 ( 19 .05 ) 1 ( 2 5 . 4 )

1 (25 .4 ) 1 V* ( 3 1 . 8 )

1 (25 .4 ) 1 V 4 ( 3 1 . 8 )

Layout F j

> \ / 0.90

• o . D 1.04

• V 1.00

•<>•• 1.16

1.14

• o . n 1.31

1.34

O.D 1.54

V a l u e s o f F i for V a r i o u s T u b e Diameters and Layouts PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

82

APPENDIX A

Inside Shell D i a m e t e r F 2 for N u m b e r o f Tube-S ide passes

[in. ( m m ) ]

2 4 6 8

U p to 12 ( 3 0 5 ) 1.20 1.40 1.80 -

13 % to 17 % ( 3 3 7 to 1.06 1.18 1.25 1.50

438 )

19 to 23 % ( 4 8 9 to 1.04 1.14 1.19 1.35

591)

25 to 33 (635 to 8 3 8 ) 1.03 1.12 1.16 1.20

35 to 45 (889 to 1 1 4 3 ) 1.02 1.08 1.12 1.16

48 to 60 ( 1 2 1 9 to 1 5 2 4 ) 1.02 1.05 1.08 1.12

Above 60 (above 1524 ) 1.01 1.03 1.04 1.06

V a l u e s o f F2 for V a r i o u s Numbers o f Tube-Passes PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

83

APPENDIX A

Type o f T u b e F 3 for Inside Shell D iameter [in. ( m m ) ]

Bundle U p to 12 13 -22 2 3 - 3 6 3 7 - 4 8 Above 48

Construction ( 3 0 5 ) ( 3 3 0 - 5 5 9 ) ( 5 8 4 - 9 1 4 ) ( 9 4 0 - 1 2 1 9 ) (above

1219)

Fixed tubesheet 1 .00 1.00 1.00 1.00 1.00

( T E M A L , M or

N )

Split backing ring 1 .30 1.15 1.09 1.06 1.04

( T E M A S)

Outside packed 1 .30 1.15 1.09 1.06 1.04

floating head

( T E M A P)

U- tube a ( T E M A 1.12 1.08 1.03 1.01 1.01

U )

Pull-through - 1.40 1.25 1.18 1.15

floating head

( T E M A T )

V a l u e s o f F 3 for Var ious T u b e Bundle Constructions

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

84

APPENDIX A

Hot crude »

FRACTION b Pt °cNumber of carbons »Refinery gas

1-4 Bottled gas, fuels

Uses

»Kerosine

»Bitumen

40 ~8 Fuel far cars

110 ~10 Raw material for chemicals and plastics.

180 ~15 Fuel for Aeroplanes

250 ~20 Fuel for cars and lorries

340 ~35 Fuel far Power Stations, Lubricants and grease

400+ 40+ Road surfacing.

It is important to realise that the column is hot at the bottom and cool at the top. The crude oil separates into fractions according to weight and boiling point. The lightest fractions, including petrol and liquid petroleum gas (LP6), vapourise and rise to the top of the tower. Kerosire (aviation fuel) and diesel oC stay in the middle of the tower Heavier liquids separate lower down. The heaviest fractions with the highest boiling points settle at the very bottom.

T y p i c a l Re f ine ry Process PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

85

APPENDIX A

Orig ina l Paper o f Barbara et al. ( 2 0 0 4 )

AN MILP Model for Heat Exchanger Networks Retrofit Andres Barbaro.b, Miguel Bagajewicz.b, Narumon Vipanurat", Kitipat Siemanond'

a The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok 10330, Thailand. E-mail:kitipat.s@chula.ac.th

b University of Oklahoma, 100 E. Boyd St., T-335, Norman, OK 73019, USA. E-mail:bagajewicz@ou.edu

This paper addresses the problem of automatically determining the optimal economic retrofit of heat exchanger networks. It is a rigorous MILP (Mixed Integer Linear Programming ) approach that considers rearrangement of the existing heat exchanger units, heat transfer area addition and new exchanger installation. We illustrate the method using a crude fractionation unit and we also compare this technique to one existing retrofit approach.

KEYWORDS

Retrofit, Heat Exchanger Networks, Mixed Integer Linear Programming

1. INTRODUCTION This paper is based on a recently accepted paper for grassroots HEN design. The method consists of a rigorous MILP strategy that is based on a transportation/transshipment strategy. This strategy can handle stream splits and non-isothermal mixing rigorously, without any approximations.

For the case of retrofit, we have added constraints that are able to handle the fact that there is an existing network. The proposed retrofit method as well as the previous HENS design procedure is able to solve complex systems. This is illustrated through 2 application examples.

2. OUTLINE APPROACH FOR RETROFIT The MILP model is based on the transportation-transshipment paradigm which has the following features:

o Counts heat exchangers units and shells e Determines the area required for each exchanger unit or shell ° Controls the total number of units ® Determines the flow rates in splits ® Handles non-isothermal mixing • Identifies bypasses in split situations when convenient

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

86

o Controls the temperature approximation (ATmm) when desired <> Can address areas or temperature zones o Allows multiple matches between two streams

The model considers a consecutive scries of heat exchangers. Meat transfer is accounted using the cumulative heat transferred from intervals up to a specific interval to other counterpart intervals. The key of the model and what differentiates it from other transport/transshipment models is the flow rate consistency equations that allow (racking flows in splits. For retrofit situations, the MJLP model is extended bv adding constraints as follows:

A-J <A;° + A.4? +A-" (1)

£ MjLC p) UfjZU'9 ma, (3)

!1 N ( „o\ 4 ^ m c f i - f ; ) W)

-where Ay is the new area of an exchanger between streams i and j . A~ its orinignal

area. AA', the additional area to the existing shell, A A ' the new area in new shells. •j ° 'J and U~j and U y the new and original number of shells, respectively. Maximum

, 0

values (A4^m ; K and f /^ max ) are also used. When original values are zero, then a new

match is added.

The objective function for tiie retrofit heat exchanger network structure is the total annualized cost which consisted of utility cost, additional area cost and fixed cost for new exchanger installation. All terms of the hot and cold utility cost are the same as in the grassroots design model, but the retrofit programming model has complicated functions for the area cost. In the following, the objective function for the proposed retrofit approach is expressed.

Mm Cost=V Y + v V V c ' F ^ + v v I. c^U^-U;' ) Z itHU* J^c' z ;-CU' i^H' ' ' it//"'

U.lKP e./>-f (3)

+ S Z I l f f M ? + c f A f ) + Z Z X U.j)=P ('Jl-f U.J)1B [t.j)tD

Especial constraints are added when more than one exchanger between two streams is allowed. We omit these and concentrate more in showing results.

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

87

3. EXAMPLES

In this section, two examples are solved to illustrate the rigorous MELP method. The optimization model was constructed in GAMS and run in a PC with a 2.4 GHz processor and 1 Gb of ram memory.

Example 1

Example 1 is the retrofit problem of crude distillation unit that composed of 18 streams and 18 existing exchangers. Streams properties are shown in Table 1 and Table 2 while the results of retrofit network are given in Table 3 and 4. Cost comparisons are given in Table 5. The retrofit soiution achieves 24.06% annual cost savings with two new exchanger units and three shells addition. The original and retrofit networks are shown in Figure 1 and Figure 2.

We report a solution that consumes 9577.781 sec. to reach 0.00% Gap. The original and retrofit networks are shown in Figure 1 and Figure 2. If solution time is an issue one can use several other solutions with smaller gap. One in particular has 20.8% annual cost savings with also two new exchanger units and three new shells that is obtained in 1001.062 seconds.

Table 1 Stream properties for Examplel

Stream F Cp Tin Tout h Table 2 Cost data for Examplel Ton/hr KJ/kR-C C C MJ/h-m2-C

11 155 1 3 161 319 4 244 1 4 653 Utilities Cost $/(MJ/hr-yr)

12 5 695 4.325 73 24 30 18 211 Utilities Cost $/(MJ/hr-yr)

M 151 2 293 263 5 ISO 2 4 S94 111 19 75

17 91.81 2 262 73.24 40 4 605 112 37 222 13 251.2 3.111 347 3 202 7 3 21 J4 1 861

2.573 202.7 45 2 278 J5 -6.494 15 26.03 3 041 45 203 2 4 674 J5 -6.494

2 689 203 2 110 3 952 J6 -12 747 16 86.14 2.831 110 147.3 4 835 Heat Exchanger Cost 5291 SH-77 7S8A S/>T

2.442 147 3 50 3 8 Heat Exchanger Cost 5291 SH-77 7S8A S/>T

IS 63.99 2 854 50 176 5 023 2 606 176 120 .1 846

19 239 1 2 595 167 1 116 1 4 995 Table 3 Model statistics for Examplel 2.372 116 1 69 55 4 88

Table 3 Model statistics for Examplel

110 133.S 6.074 146.7 126.7 1 807 Model Statistics 4.745 126 7 99 94 3 373

Single Variables 3024 9 464 99 94 73 24 6.878 Single Variables 3024

JI 519 2 314 30 108.1 1 858 Discrete Variables 459 2.645 3.34

108.1 211.3

2 1 1 3 232.2

2 356 2 212

Single Equations 5930

J2 496.4 3 54 232.2 343.3 2.835 Nan Zero Elements 29046 J3 96.87 13 076 226.2 228.7 11.971 T i m ; to reach a feasible solution 9577.781 sec

15.SOS 228 7 231.8 11 075 Oplimality G i p 0.00% 111 250 249 21 6 Oplimality G i p 0.00%

112 1000 500 0 4 J4 20 25 13 5 J5 124 125 21.6 J6 174 175 2 1 6

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

88

Table 4 Resulting of retrofit heat exchanger for Example 1

HE Original Load Retrofit Load Original Area Retrofit Area Area Addition Shell Addition Cost

MJ/lir MJ/hr m2 m2 m2 $ 1 160,311 20 155,868 90 4,303 20 3,926 25

2 6,903.09 6,903 09 59 40 63 80 4 40 342 03

3 17,118.40 9,628 07 33 40 21.53

4 658 00 6,560 99 2 30 16 63 14 33 YES 6,406 84

5 2,554.70 0 02 26 30 28 93 2.63 204 58

6 2,410.70 9,902.58 24 60 39S 53 373 93 YES 34,379 01

7 1,065.04 1,065 04 5 50 5 87 0 37 28 70

S 45,024 40 6,042 97 145 00 41 66

9 100,642 70 63,561 25 1,212 70 962 01

10 4,473 60 4,045 64 93 70 93 70

11 54,618 70 59,060.59 685 70 1,239 90 554 20 YES 48,402 09

12 6,293 80 3,373 45 40 00 44 00 4 00 311 15

13 58,044.30 58,042 28 183 30 182 39

14 36,903.20 36,903.23 101 60 101 47

15 36,917 40 0 93 90 0

16 67,053 08 67,053 08 278 10 2S8 97 10 87 845.32

17 7,913 77 7,913 77 53 50 52 24

IS 136,138 80 95,207 49 976 40 709 00

19 36,917 41 727.96 61,918 53

20 38,981 58 651 93 56,004 54

8,318.60 9,556 76 14.88% 3 208,842.80

Table 5 Annual cost comparison between original and retrofit network

COS! Exist ing Retrofit

S ' j T

Total utility cost 6 , 8 6 5 , 6 1 6 . 5 1 5 , 0 0 4 . 8 0 0 . 2 3 0

Total fixed and area cost - 2 0 8 , 8 4 2 . 8 0

Totat cost 6 , 8 6 5 , 6 1 6 . 5 1 5 , 2 1 3 , 6 4 3 . 0 3 1

Cost saving 2 4 . 0 6 %

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

Example 2

We now compare our method with Hypertargets (Briones and Kokossis, 1999). Table 6 shows the stream and cost data for crude distillation unit which consisted of 12 streams and 11 existing units. Figure 3 shows the original network and Figure 4 shows the retrofit structure generated by our MILP strategy. Hypertargets established two retrofit designs (B1 and B2) with the same utility cost and one new unit in each case. They are shown in Figure 5 and 6. Our MILP approach suggests using two new smaller exchangers and more utility. The results are shown in Tables 7 and 8 and the total annual cost in Table 9. The retrofit has a 4.17% saving over the original structure.

Table 6 Stream and cost data for Example 2

Stream FCp

kW/C

Tin

C

Tout

C

h

I;\V/m2-C Table 7 Model statistics for Exampl II 470.00 140.00 40.00 OS

12 825.00 160.00 120 00 0 8 Model Statistics

13 42.42 210.00 45 00 0 8 Single Vanables 3120

14 100.00 260,00 60 00 0 8 Discrete Vanables 382

15 357.14 280 00 210 00 0 8 Single Equations 6347

16 50.00 350.00 170 00 0 8 Non Zero Elements 23949

17 13(5.3d 380.00 ISO 00 OS Time to reach a feasible solution 411 41 sec

J1 826.09 270 00 385 00 0 8 Optimality Gap 0 00%

J2 500.00 130.00 27000 0 8

J3 363.64 20 00 130 00 0 8

IS 500 00 •199 00 0 8

J.1 20 00 40.00 0 8

Note: Exclianger cost=300xArea, stream cost=60$/kW yr.

coding water cost=5S/l;W yr

Figure 3 Original HEN for Example 2 Figure 4 Retrofit HEN for Example 2

Figure 5 Hypertarget retrofit designs B1 Figure 6 Flypertarget retrofit designs B2

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH

90

Table 8 Resulting of retrofit heat exchanger network for Example2 HE Original Load Retrofit Load Original Area Retrofit Area Area addition Shell Addition Cost

MJ/hr MJ/hr m2 m2 m2 S 1 47,000.00 47,000.00 2,363.86 2,402 06 38 19S

2 33,000.00 33,000.00 1,609 62 1,613.93 4 310 YES 1.293 106 3 7,000.00 7,000.00 230.69 242.32 11 628 YES 3.48S J65 4 10,200.00 8,711.41 692 14 692 14

5 9,800.00 11,287.49 3 3 9 8 0 366.26 26457

6 25,000.00 25,000.00 1,226.76 1,286.34 59 581 YES 1 ~,S"4 203 7 9,000.00 9,000.00 224 92 396.58 171 669 YES 51,500 690 8 20,800.00 20,813.59 1,211.00 1,211 00

9 9,200.00 1,127,37 141.47 20 48

10 95,000.00 86,942.11 1,434.98 1,344.35

11 5,000.00 6,475.20 53.31 66.93 13 617

12 1.10 0 05 NEW 15 300 13 8,058.24 298.33 NEW 89,499 000

9,528.54 9,940 77 4 33% 4 163.670 "63

Table 9 Annual cost comparison between Hypertargets and MILP algorithm

Cost Existing II>pertaiget B1 Hypertaiget B2 MILP S'yr S/yr S'yr S'yr

Total utility cost 6,330,000 5,607,200 5,607,200 5,902,113 Total fixed and area cost 531,900 576,720 163,671

Tola! cos! 6,330,000 6,139,100 6,183,920 6,C65,7&) MILP mete saving (S'yr) 264,216 73,316 118,136

4.17% 1.19% 1.91%

4. CONCLUSION

A new MfLP formulation for the retrofit of heat exchanger networks, which takes into account the retrofit options involving modification of the existing structure and new exchanger placement, was presented. The model is very robust and capablc of handling rigorously large networks such as those of crude distillation units.

5. REFERENCES

Barbara A. and M. Bagajewicz, New Rigorous One-step MILP Formulation for Heat Exchanger Network Synthesis. Computers and Chemical Engineering. Submitted. (available at http://www.ou. edu'class/che-design'unpub-papers/HEN-MILP.pdf) Jan 2004

V. Briones and A.C. Kokossis, 1999, Hypertargets: a Conceptual Programming Approach for the Optimisation of Industrial Heat Exchanger Networks-IL Retrofit Design. Chem.Eng.Sci, 54, 541-561.

PTTAPERP

USTAKAAN TUNKU T

UN AMINAH