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Energy requirements inmulticomponent distillation
trains
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A Doctoral Thesis. Submitted in partial fullment of the requirements forthe award of Doctor of Philosophy of Loughborough University.
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Publisher: c Nada Bahjat Nakkash
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https://dspace.lboro.ac.uk/2134/14104This item was submitted to Loughborough University as a PhD thesis by the author and is made available in the Institutional Repository
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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
0113091 02 .
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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