Introduction to Wet Sulfuric Acid Plants Optimization - UPCommons

196 Pages·2009·10.6 MB·English

Introduction to Wet Sulfuric Acid
Plants Optimization Through
Exergoeconomics
Master’s thesis
Borja Xicoy Almirall
Professor:
Prof. Dr.-Ing. Günter Wozny
Tutor:
Dipl.-Ing. Jan Schöneberger
June 2009
Kurzfassung
Die Diplomarbeit ist eine Einleitung zur thermoökonomische Analyse in Schwe-
felsäure Anlagen. Eine Referenzanlage mit der folgenden charakteristiken wird
analysiert: eineSchwefelbrennkammerzurOxidationschwefelwasserstoffhaltigerGase,
eindurchLuftzufuhrabgekühlterNaß-KatalyseProzessundeineAbsorptionskolonne
zur Produzierung von Schwefelsäure mit 78 Massenprozent H SO . Außerdem wird
2 4
Wasserdampf von 40 bar und 5 bar erzeugt.
Die thermoökonomische Analyse besteht aus drei Schritten: Zuerst wird eine Ex-
ergieanalyseunterAnwendungderkommerziellenSoftwareCHEMCADunddesHil-
fsprogramms CHEMEX durchgeführt. CHEMEX wurde im Rahmen dieser Diplo-
marbeit entwickelt und dient zur Berechnung der chemischen Exergie von Elek-
trolytlösungen. Im nächsten Schritt wird eine Wirtschaftlichkeitsanalyse zur der
Berechnung der nivellierten Kosten der Anlage mittels PEC und weiteren Kosten-
schätzungsmethoden durchgeführt. Im dritten Schritt der Analyse werden Exergie-
und Wirtschaftlichkeitsanalyse durch die Aufteilung der nivellierten Kosten auf alle
Strömen der gesamten Anlage bezüglich ihrer Exergiewerte kombiniert. Dafür ist
ein lineares Gleichungssystem mit den Kostbilanzen jeweiliger Analgenkomponente
und komponentenspezifischen Hilfsgleichungen zu lösen. Schließlich werden drei
kosteneffektive Optimierungsschritte auf die Referenzanlage angewendet, wobei ex-
ergoökonomische Kennzahlen die jeweiligen Optimierungsschritte motivieren.
i
Abstract
This thesis pretends to be an introduction to the use of thermoeconomics in sulfuric
acid plants. A reference plant with the followings features is examined: a sulfur
burner which oxidizes hydrogen sulfide gases, a wet-catalysis process which is cooled
by means of air quenching, and an absorbtion column that produces sulfuric acid of
78 wt.%. Moreover, the plant has two heat-recovery boilers that produce steam at
40bar and 5bar.
The thermoeconomic evaluation consists of three steps: In the first step, an
exergy analysis is performed by using the commercial software CHEMCAD and
the tool CHEMEX, which was designed for this work and takes into account the
activity coefficients of water and sulfuric acid in liquid mixtures for the calculation
of the chemical exergies; In the second step, an economic evaluation is carried out in
order to calculate the plant levelized costs by means of the PEC and cost estimating
techniques; In the third step, both exergy and economic analyses are combined by
distributing the levelized costs among all plant streams, regarding to its exergy
value, in terms of a linear equation system composed of the cost equation of each
plant component and some auxiliary equations. Finally, three possible cost-effective
optimizations are studied regarding to the reference plant by applying the methods
of the thermoeconomic optimization based on thermoeconomic key indicators.
ii
Contents
Kurzfassung i
Abstract ii
Contents iii
List of Tables vi
List of Figures xi
List of Acronyms xiv
Nomenclature and Units xvi
1 Introduction 1
1.1 The Process and its Development . . . . . . . . . . . . . . . . . . . . 2
1.2 An Introduction to Contact Processes . . . . . . . . . . . . . . . . . . 4
1.2.1 Catalytic Oxidation of Sulfur Dioxide . . . . . . . . . . . . . . 4
1.2.2 Absorption of Sulfur Trioxide . . . . . . . . . . . . . . . . . . 6
1.2.3 Constructive Elements . . . . . . . . . . . . . . . . . . . . . . 7
2 Case Study Process 18
2.1 An Introduction to Wet-Catalysis Processes . . . . . . . . . . . . . . 18
2.2 Reference on Considered Process . . . . . . . . . . . . . . . . . . . . 20
3 Exergy Analysis 29
3.1 The Exergy Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.1.1 Environment and Dead States . . . . . . . . . . . . . . . . . . 32
3.2 The Exergy Components . . . . . . . . . . . . . . . . . . . . . . . . . 33
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CONTENTS Sulfuric acid plant optimization
3.2.1 Physical Exergy . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.2.2 Chemical Exergy . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.3 Exergy Rate Balance for Control Volumes at Steady State . . . . . . 39
3.4 Exergy Destruction and Loss . . . . . . . . . . . . . . . . . . . . . . . 40
3.5 Exergy ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.5.1 Exergetic efficiency . . . . . . . . . . . . . . . . . . . . . . . . 43
3.5.2 Exergy Destruction and Exergy Loss Ratios . . . . . . . . . . 45
4 Economic Analysis 51
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.2 Estimation of the Total Capital Investment . . . . . . . . . . . . . . . 52
4.2.1 Purchased-equipment costs . . . . . . . . . . . . . . . . . . . . 54
4.2.2 Direct Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
4.2.3 Indirect Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.2.4 Other Outlays . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.3 Calculation of the Total Revenue Requirement . . . . . . . . . . . . . 70
4.4 Levelized costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5 Thermoeconomic Analysis 82
5.1 Fundamentals of thermoeconomics . . . . . . . . . . . . . . . . . . . . 83
5.1.1 Costing of Exergy Loss Streams . . . . . . . . . . . . . . . . . 86
5.1.2 Exergy Costing for the Considered Process Components . . . 87
5.2 Thermoeconomic analysis of the Considered Process . . . . . . . . . . 92
5.3 Thermoeconomic Variables . . . . . . . . . . . . . . . . . . . . . . . . 103
5.3.1 Average Unit Cost of Fuel and Product . . . . . . . . . . . . . 103
5.3.2 Cost Rate of Exergy Destruction . . . . . . . . . . . . . . . . 103
5.3.3 Exergoeconomic Factor . . . . . . . . . . . . . . . . . . . . . . 108
5.4 Thermoeconomic Evaluation . . . . . . . . . . . . . . . . . . . . . . . 109
5.4.1 Reference Case Evaluation . . . . . . . . . . . . . . . . . . . . 110
6 Thermoeconomic Optimization 113
6.1 Decision Variables and System Constrains . . . . . . . . . . . . . . . 114
6.2 Possible Plant Optimizations . . . . . . . . . . . . . . . . . . . . . . . 118
6.2.1 Improvement I . . . . . . . . . . . . . . . . . . . . . . . . . . 118
iv
CONTENTS Sulfuric acid plant optimization
6.2.2 Improvement II . . . . . . . . . . . . . . . . . . . . . . . . . . 123
6.2.3 Improvement III . . . . . . . . . . . . . . . . . . . . . . . . . 125
6.3 Optimization Summary and Conclusions . . . . . . . . . . . . . . . . 127
7 Conclusions 132
Bibliography 140
Appendices 144
A 144
A.1 Interests During Plant Operation (ROI) . . . . . . . . . . . . . . . . 145
A.1.1 Favorable Case . . . . . . . . . . . . . . . . . . . . . . . . . . 145
A.1.2 Unfavorable Case . . . . . . . . . . . . . . . . . . . . . . . . . 146
A.2 Total Required Revenue (TCR) . . . . . . . . . . . . . . . . . . . . . 147
A.2.1 Favorable Case . . . . . . . . . . . . . . . . . . . . . . . . . . 147
A.2.2 Unfavorable Case . . . . . . . . . . . . . . . . . . . . . . . . . 148
B 149
C 164
C.1 AD_12_FOR.FOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
C.2 EXTERNALENTROPIE.FOR . . . . . . . . . . . . . . . . . . . . . . 168
C.3 EXTERNALCHEMEXERGIE.FOR . . . . . . . . . . . . . . . . . . . 168
C.4 ECH_TAB2FOR.FOR . . . . . . . . . . . . . . . . . . . . . . . . . . 170
C.5 COEF_ACTIV.FOR . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
C.6 COEF_ACTIV.FOR . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
v
List of Tables
2.1 Surrounding conditions . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.2 Parameter temperatures . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.3 Process table: main stream; 1Hydrogen cyanide molar composition =
0.21; 2see Eq. 2.5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.4 Process table: atmospheric air and water; 1see Eq. 2.2; 2see Eq. 2.3;
3see Eq. 2.4; 4see Eq. 2.6 . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.3 Activity coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.1 Exergy table: main stream . . . . . . . . . . . . . . . . . . . . . . . . 47
3.2 Exergy table: atmospheric air and water . . . . . . . . . . . . . . . . 48
3.4 Exergy destruction table for all acid plant components, calculated by
the entropy generation and by the exergy balance methods . . . . . . 49
3.5 Work rates of the compressor and the pumps . . . . . . . . . . . . . . 49
3.6 Exergy destruction rates for all acid plant components in order de-
creasingly, calculated by the entropy generation method. . . . . . . . 50
4.1 Contact group, size and mass specifications . . . . . . . . . . . . . . . 58
4.2 Purchase Equipment Costs (PEC) (rounded values) . . . . . . . . . . 60
4.3 Economic and plant parameters . . . . . . . . . . . . . . . . . . . . . 64
4.4 Annual operating and maintenance costs . . . . . . . . . . . . . . . . 65
4.5 Working capital and associated costs . . . . . . . . . . . . . . . . . . 66
4.6 Plan financing fractions and required returns on capital . . . . . . . . 67
4.7 Release dates for plant expenses [5] . . . . . . . . . . . . . . . . . . . 67
4.8 Calculation of AFUDC (end-2011 values) (all values are rounded and
given in thousands of euros) . . . . . . . . . . . . . . . . . . . . . . . 69
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LIST OF TABLES Sulfuric acid plant optimization
4.9 Total capital investment and related costs I (all costs are rounded
and expressed in thousands of escalated euros) . . . . . . . . . . . . . 71
4.10 Total capital investment and related costs II (all costs are rounded
and expressed in thousands of mid-2008 euros) . . . . . . . . . . . . . 72
4.11 Year-by-year distribution of capital recovery and interests generated
during plant operation (ROI) (all costs are rounded and expressed in
thousands of escalated euros) . . . . . . . . . . . . . . . . . . . . . . 75
4.12 Year-by-year revenue requirement analysis for the medium case (all
costs are rounded and expressed in thousands of mid-2008 euros).
The terms TRR and TRR correspond with the escalated values
cu ct
and the values brought to the middle of the year 2011 of the total
revenue requirement, respectively. . . . . . . . . . . . . . . . . . . . . 76
5.1 Z˙ −costs associated to the plant components; except to pumps, mix-
ers, and splitters, which its purchase costs are neglected. The pur-
chased costs are expressed in rounded mid-2008 euros. . . . . . . . . . 84
5.2 Thermoeconomic results for the reference plant: main stream (Inter-
mediate case) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
5.3 Thermoeconomic results for the reference plant: atmospheric air and
water (Intermediate case) . . . . . . . . . . . . . . . . . . . . . . . . 99
5.4 Costs associated with compressor and pumps power for the reference
plant (Intermediate case) . . . . . . . . . . . . . . . . . . . . . . . . . 100
5.5 Product prices in cents of euro per kilogram of both thermoeconomic
and economic analysis for the reference plant. The differences in
H SO prices are due to fact that the steam prices are different in
2 4
both analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
5.6 Rounded average costs per unit of exergy of the plant products cal-
culated through an economic and a thermoeconomic analysis for the
reference plant (Intermediate case). The terms c and c correspond
E m
to the specific costs per exergy and mass, respectively. . . . . . . . . . 104
5.7 Definition and average costs of the fuel and product from all system
components for the reference plant (Intermediate case) . . . . . . . . 105
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LIST OF TABLES Sulfuric acid plant optimization
5.8 Thermoeconomic variables from the reference plant in order decreas-
ingly, accordingly to the sum Z˙ +C˙ (Intermediate case) . . . . . . . 111
D
6.1 Decision variables of the sulfuric acid plant in the initial case with its
constrains and ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
6.2 Thermoeconomic variables decreasingly ordered according to the sum
Z˙ +C˙ for the Improvement I (Intermediate case) . . . . . . . . . . . 122
D
6.3 Product prices in cents of euro per kilogram of both thermoeconomic
and economic analysis for the Improvement I . . . . . . . . . . . . . . 123
6.4 Thermoeconomic variables from the reference case decreasingly or-
dered, accordingly to the sum Z˙ +C˙ for the Improvement II (Inter-
D
mediate case) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
6.5 Thermoeconomic variables from the reference plant decreasingly or-
dered, accordingly to the sum Z˙ +C˙ for the Improvement III (In-
D
termediate case) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
6.6 Decision variables and purchase costs of the first and second heat
exchanger for the reference plant and possible improvements (Inter-
mediate cases); 1In the Improvement II, T , T , and m correspond
9 15 13
with T , T , and m , respectively . . . . . . . . . . . . . . . . . . . 129
8 14 12
6.7 Results for the reference case and possible improvements: levelized
total required revenue, TRR ; reduction of the TRR regarding to
L L
the reference plant; plant exergetic efficiency; and annual exergy from
the total generated steam (Intermediate cases) . . . . . . . . . . . . . 129
6.8 Comparison between both thermoeconomic and economic analysis for
thereferencecaseandpossibleimprovementsthroughthepercentages
of the revenue obtained by the sale of sulfuric acid and steam regard-
ing to the total required revenue (TRR ), as well as the specific cost
L
of the sulfuric acid from both thermoeconomic and economic analysis
(Intermediate cases) . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
A.1 Year-by-year distribution of capital recovery and interests generated
during plant operation (ROI) for the favorable case (all costs are
rounded and expressed in thousands of escalated euros) . . . . . . . . 145
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LIST OF TABLES Sulfuric acid plant optimization
A.2 Year-by-year distribution of capital recovery and interests generated
during plant operation (ROI) for the unfavorable case (all costs are
rounded and expressed in thousands of escalated euros) . . . . . . . . 146
A.3 Year-by-year revenue requirement analyisis for the favorable case (all
costs are rounded and expressed in thousands of escalated euros) . . . 147
A.4 Year-by-year revenue requirement analyisis for the unfavorable case
(all costs are rounded and expressed in thousands of escalated euros) 148
B.1 Thermoeconomic results for the Improvement I: main stream (Inter-
mediate case) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
B.2 Thermoeconomic results for the Improvement I: atmospheric air and
water (Intermediate case) . . . . . . . . . . . . . . . . . . . . . . . . 154
B.3 Thermoeconomic results for the Improvement II: main stream (Inter-
mediate case) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
B.4 Thermoeconomic results for the Improvement II: atmospheric air and
water (Intermediate case) . . . . . . . . . . . . . . . . . . . . . . . . 156
B.5 Thermoeconomic results for the Improvement III: main stream (In-
termediate case) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
B.6 ThermoeconomicresultsfortheImprovementIII:atmosphericairand
water (Intermediate case) . . . . . . . . . . . . . . . . . . . . . . . . 158
B.7 Costs associated with compressor and pumps power for the Improve-
ment I (Intermediate case) . . . . . . . . . . . . . . . . . . . . . . . . 159
B.8 Costs associated with compressor and pumps power for the Improve-
ment II (Intermediate case) . . . . . . . . . . . . . . . . . . . . . . . 159
B.9 Costs associated with compressor and pumps power for the Improve-
ment III (Intermediate case) . . . . . . . . . . . . . . . . . . . . . . . 159
B.10 Rounded average costs per unit of exergy of the plant products cal-
culated through an economic and a thermoeconomic analysis for the
Improvement I (Intermediate case) . . . . . . . . . . . . . . . . . . . 160
B.11 Rounded average costs per unit of exergy of the plant products cal-
culated through an economic and a thermoeconomic analysis for the
Improvement II (Intermediate case) . . . . . . . . . . . . . . . . . . . 161
ix