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Energy requirements inmulticomponent distillation

trains

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Additional Information:

A Doctoral Thesis. Submitted in partial fulfilment of the requirementsfor the award of Doctor of Philosophy of Loughborough University.

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Publisher: c Nada Bahjat Nakkash

Please cite the published version.

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/ LOUGHBOROUGH

UNIVERSITY OF TECHNOLOGY LIBRARY

AUTHOR/FILING TiTlE

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--- --- ------------------------ -- --- ----- - - -_._--- ........ ACCESSION/COPY NO.

__________ _______ 1!~_~ ~_~)o.. 3: _________ - ---- ---VOL. NO. CLASS MARK

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,

ENERGY REQUIREMENTS IN MULTI COMPONENT

DISTILLATION TRAINS

by

NADA BAHJAT NAKKASH

B. Sc. (Baghdad)

A Doctoral thesis submitted in

partial fulfilment of the requirements

for the award of

Doctory of Philosophy

of the Loughborough University of Technology

March 1980 ,.,.- '.'.

Supervisor: Professor D. C. Freshwater Ph.D.

Department of Chemical Engineering

I L .... ,~b"r"\l9n. Ur,h,.rslty of T "cl\nolGOlt libllfY i... er~~ I;~:.' 'I:H'\ '/02-1

This thesis is respectfully dedicated

TO MY PARENTS

.' .

Acknowledgements

I would like to express my sincere thanks to the

following people who have made it possible for me to complete

and present this thesis.

'Professor D. C. Freshwater,for his continued

encouragement, assistance and patience and for his useful

comments during the preparation of this t~esis.

I would like to express my deep gratitude and thanks ,

to my dear'parents for encouraging and supporting me and

providing me with the opportunity for attempting the degree.

My thanks to B.P. Chemicals and Conoco Limited for

providing me with the data, to examine my work on their

mixtures, and for training me.

My sincere thanks to the department of Computer Studies

at Loughborough for helping me to develop the programmesJUse'd

to provide my results.

My thanks to the Iraqi Government and to the University

of Technology in Baghdad for granting me a Scholarship to

continue my studies.

I take this opportunity to thank all my friends for a

very pleasant and unforgettable time that I have had with them

at Loughborough.

Finally, I would like to give my sincere thanks to Mrs.

C. Sharpe for typing my thesis.

T'

TABLE OF CONTENTS

Page No.

ACKNOWLEDGEMENTS

ABSTRACT

LIST OF TABLES

LIST OF FIGURES

NOMENCLATURE

INTRODUCTION ,

CHAPTER 1.

1.1

1.2

1.3

1. 3.1

1.3.2

1.3.3

1.4

1.5

1.5.1

1.5.l.a

Review of Previous Work

Definition of energy of separation

Ideal energy of separation

Definition of thermodynamic effic~ency

in terms of first law and second

law.

Efficiency in terms of first law of

thermodynamics

Efficiency in terms of second law of-

thermodynamics,

Examples of thermodynamic efficiency,

using both first and second law

expressions

Sunnnary

Energy conservation schemes for

distillation processes.

Operating strategy for existing column

Quality specifications overhead and

bottom purity specifications which

i

iii

viii

xiii

I

9

9

9

18

18

21

23

37

41

42

r- 43 i

1.6

1.7

1.8

1.9

I.S.la.

1.5. lb.

I.S.lc.

I.S.ld.

1.5.2

1.5.3

1.7.1

1.7.2

1.7.2a.

1.7.2b.

1.7.2c.

1.7.3

1.8.1

1. 8.la.l

1.8.la.2

should be challenged.

Rate versus efficiency

Incorrect feed plate location

Column auxiliaries

Extensive modification of existing

equipment.

Page No.

43

44

44

46

46

Design of a new \system

A different approach to improving

the energy efficiency of process

has been put forward by Fitt(1977)

Methods of reducing energy consumption

in distillation and improving thermal

efficiency.

Inter reboilers and condensers

Heat pump or vapour recompression

process.

Direct vapour recompression process

Indirect vapour recompression process

Examples of vapour recompression

Multieffect Method

47

50

52

54

57

58

60

61

66

Application to multi-component distillation 75

Determination of the optimal sequence of

distillation.

Design Methods

Analytical Methods

Determination of the heat exchanger

75

78

85

network for optimal energy recovery 93

1.10

OlAPTER 2:

2.1

2.2

2.3

2.4

2.5 ,

2.5.1

2.5.1.1

2.6

OlAPTER 3:

3.1

3.2

3.3

3.4

3.5

3.6

3.2.1

3.2.2

3.2.3

3.2.4

',;'

Process synthesis methods

Application of Synthesis Strategy

Introduction

Method of Analysis

Variable specification

Design of distillation columns

according to energy integration

The concept of e~ergy integration

in distillation process

Energy saving by SEM

Four component mixtures

Energy saving with CEM

Results of design analysis with

respect to energy integration

Introduction

Effect of parameters on the

investigation of the possibility of

energy recovery.

Effect in changes in the intermediate

load

Feed composition

Effect of changing the degree of

recovery of the components.

Effect of changing the feed volatilites

Saving in total reboiler load

Discussion of the results

Application of pseudo components

Derivation of the mathematical model

Page No.

98

109

109

120

122

125

134

136

136

145

155

155

156

157

162

170

172

178

186

190

193

3.7

3.8

3.9

Chapter 4:

4.1

4.2

4.3

Chapter 5:

5.1

5.2

5.3

5.3.1

5.3.2

5.4

5.4.1

5.5

5.6

5.7

5.7.1

5.7.2.

Calculation procedure

Page No.

197

Presentation of the results 199

Effect of changing the product purity 207

Effect of energy matching on costs 208

Introduction 208

Effect of energy matching on cost of steam 208

Effect of energy matching on the annual 210

operating cost.

Results and Design Analysis with 222

respect to Energy '.Integration for Non-

Ideal System

Introduction 222

General problem of the thermodynamic 223

calculations of non-ideal system

Energy requirements for non-ideal systems. 227

Potential for energy saving 227

Method of reducing the energy requirements 232

in non-ideal distillation

Prediction of optimal sequence for non- 232

ideal systems.

Example 1 233

Method of Analysis 237

Specification of variables 238

Design calculation 245

Design calculation of columns 1 and 2 246

Design calculation of column (2a) 248

5.7.2.1 Material balance 250

5.7.2.2 Calculation of the minimmn reflux ratio upper 252

operating line and the lower operating line

equations. 5. 7. 2.3 Heat balances 256

5.8

5.9

5.10

5.11

5.10.1

5.10.2 \

5.11.1

5.11.2

5.11.3

5.11.4

5.12

5.13

5.l3.l

5.13.2

5.13.3

5.14

CHAPTER 6

h.l

6.2

6.3

Energy matching without

intermediate heating

Energy matching with intermediate

heating

Example 2 - Ethanol/Benzene/and

water system.

Azeotropic mixtures

Process description

Design calculation

Design of dehydration column

(column (1

Material balance

Design of the water recovery column

Heat balances for the three columns

Application of energy matching on

ethanol/Benzene and water cystem

Vapour reuse methods

Material balance

Calculation of the minimum reflux

ratio column (2)

Calculations of the operating lines

Conclusions

Application of Energy Integration

on a Real Mixtur~

Introduction

Separation of the light hydrocarbons

by disti llation.

Process description

y

Page No.

258

258

262

262