i a graphical method for simultaneous targeting and design...

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A Graphical Method for Simultaneous Targeting and Design of Multiple Utility Systems

MOHSEN CHEZGHANI

A thesis submitted in fulfilment of the

requirements for the award of the degree of

Master of Engineering (Chemical)

Faculty of Chemical Engineering

Universiti Teknologi Malaysia

September 2012

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I dedicated this entire work to my beloved mother and father and who always be my side

For all their selfless love, supprt, inspiration and encouragement…

Thanks…

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ABSTRACT

Multiple utility targeting has been one of the most important steps in process

integration and has direct effect on total cost. Indeed, the majority amount of

investments in any plant especially chemical plant is allocated for supplying hot and

cold utilities. Regarding to this fact having realistic design to show the exact amount of

the minimum hot and cold utility has been serious concerns among designers and plant

owners. Composite Curves (CCs), Grand Composite Curves (GCC), Balanced

Composite Curves (BCC) and Balanced Grand Composite Curves (BGCC) have been

the common graphical tools to achieve this aim. The current graphical methods may

have acceptable results in terms of energy targeting. However, these tools cannot offer

sufficient guidance for individual stream matching which is vital to have realistic

surface area targeting as well as multiple utility targeting. This research presents a new

graphical method for simultaneous targeting and design of multiple utility systems based

on stream temperature versus enthalpy plot (STEP) method. Systems including variable-

temperature utilities (Flow Gas, Cooling Water) are considered and some limitations of

current graphical method (CCs, GCC, BCC, BGCC) have been highlighted. In addition,

some examples are provided to demonstrate different limitations of mentioned graphical

tools in terms of utility targeting and minimum surface area targeting. The presented

method is more realistic as compared to the current graphical methods and can helps

designers to have better understanding of multiple utility systems including variable-

temperature utilities as well as constant-temperature utilities.

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ABSTRAK

Kaedah mensasarkan utiliti pelbagai kian menjadi salah satu langkah yang

penting dalam proses integrasi dan ia mempunyai kesan langsung ke atas jumlah kos.

Malah sebahagian besar peratus pelaburan dalam sebuah loji terutamanya loji kimia

adalah untuk membekalkan utiliti panas dan sejuk. Maka, berikutan fakta ini,

mempunyai reka bentuk yang realistik untuk menunjukkan jumlah sebenar utiliti

minimum yang panas dan sejuk telah menjadi kebimbangan serius di kalangan pereka

dan pemilik loji. Lengkung Komposit, Lengkung Komposit Besar and Keluk Komposit

Seimbang telah menjadi alat grafik yang lazim untuk mencapai matlamat ini. Kaedah

grafik semasa boleh memberi keputusan yang boleh diterima dari segi mensasarkan

tenaga tetapi ia tidak boleh memberikan panduan yang cukup bagi penyesuaian aliran

individu yang amat penting untuk memberi sasaran luas permukaan yang realistik serta

sasaran utiliti pelbagai. Untuk memperoleh sasaran luas permukaan dan untuk

mengetahui aliran proses padankan terhadap tahap dan jenis utiliti, suhu masuk dan suhu

alur untuk aliran setiap individu diperlukan yang tidak boleh diperolehi daripada keluk

komposit. Dalam kajian ini, beberapa batasan kaedah graf semasa telah diserlahkan.

Penyelidikan ini membentangkan kaedah grafik yang baru untuk penyasaran serentak

dan reka bentuk sistem pelbagai utiliti yang berdasarkan suhu arus melawanentalpi

plot(STEP). Di samping itu, beberapa contoh disediakan untuk menunjukkan pelbagai

batasan bagi Lengkung Komposit, Lengkung Komposit Besar serta Keluk Seimbang

Komposit dari segi mensasarkan utiliti dan luas permukaan minimum. Kaedah yang

dibentangkan adalah lebih realistik berbanding kepada kaedah grafik semasa dan boleh

membantu para pereka mendapat pemahaman yang lebih baik sistem terhadap utiliti

pelbagai termasuk suhu ubah utiliti serta suhu malar utiliti.

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TABLE OF CONTENTS

CHAPTER SUBJECT PAGE

DECLARATION ii

DEDICATION iii

ABSTRACT iv

ABSTRAK v

TABLE OF CONTENTS vi

LIST OF TABLES x

LIST OF FIGURES viii

NOMENCLATURES xiv

1 INTRODUCTION 1

1.1 Background 1

1.2 Outlook on energy 2

1.3 Problem Background 4

1.4 Problem Statement 4

1.5 Objective 5

1.6 Scope of the Study 6

1.7 Research Contribution 6

1.8 Summary of the Thesis 7

2 LITERATURE REVIEW

2.1 Introduction 8

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2.2 Reviews on Graphical Approach in Energy Targeting 9

2.2.1 Pinch Technology 10

2.2.2 Data Extraction 10

2.2.3 Energy Targeting 11

2.2.4 Multiple Utility Targeting 13

2.2.4.1 Balanced Composite Curves 15

2.2.4.2 Grand Composite Curves 16

2.3 Overview of Heat Exchanger Area Targeting 25

2.4 Review of Cost Targeting 26

2.5 Review of Heat Exchanger Network Design

Methodology 27

2.6 Stream Temperature vs Enthalpy Plot (STEP) 27

2.7 Limitation CCs and GCC, BCC and STEP 29

3 RESEARCH METHODOLOGY 31

3.1 Introduction 31

3.2 Different types of hot variable-temperature utilities 32

3.3 Methodology 32

3.3.1 Construct STEP 33

3.3.1.1 Data Extraction 33

3.3.1.2 Plot Continuous Hot and Cold STEPs 34

3.3.2 Determine QHmin and QCmin 34

3.3.3 Determine Temperature Limiting Point (TLP) 34

3.3.4 Draw the Utility Lines 34

3.3.5 The minimum Flow rate calculation 37

3.3.6 Divide utility lines 37

3.4 The minimum area targeting for

Variable-temperature utilities 40

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4 RESULTS AND DISCUSSION 51

4.1 Introduction 51

4.2 The negative effect of utility pinch on

Variable-temperature Utility targeting 52

4.3 Inappropriate variable-temperature utility targeting 64

4.4 Acid Dew Point (ADP) limitation 72

5 Conclusion and Recommendation 81

5.1 Conclusion 83

5.2 Recommendations 83

REFERENCES 84

APPENDIX A 88

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LIST OF TABLES

TABLE NO TITLE

3.1 Data Extraction to build STEP 33

3.2 Data Extracted from Fig 3.8 45

3.3 Data obtained from Fig 3.9 46



4.1 Stream data for Example 4.1 53




4.5 Data extracted from Fig 4.23 79

5.1 Comparison between CCs and STEP 82

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LIST OF FIGURES

FIGURE NO TITLE

1.1 World market energy consumption by region, 2007 – 2035 2

1.2 World industrial sector energy consumption (percent of total)

by major energy intensive industry shares in 2007 3

2.1 Plotting Composite Curves 11

2.2 Pinch point and energy targeting 12

2.3 Extensions of T-Q diagram 14

2.4 The Balanced Grid diagram 15

2.5 Balanced Composite Curves 17

2.6 Composite Curves and Grand Composite Curves 19

2.7 Construction of the utility grand composite curves 20

2.8 Balanced Grand Composite Curves 21

2.9 Composite curves with multiple pinch points and

the “inverse pinch” point. 23

2.10 Energy penalty caused by the too low value of outlet hot utility 24

3.1 ∆Qc, ∆QH and TLP determination by STEP 34

3.2 Drawing the Variable-temperature utility line 36

3.3 Variable-Temperature utility targeting using STEP 38

3.4 Heat Exchanger network design using HEAT 39

3.5 Heat Exchanger network design 40

3.6 Simple schematic of countercurrent shell-tube heat exchanger. 41

3.7 Hot streams in different temperature intervals before combine 42

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3.8 The first possibility for Process-Utility stream matching 44

3.9 The second possibility for Process-Utility stream matching 45

3.10 The third possibility for Process-Utility stream matching 46

3.11 Case 1, process-utility stream matching based on presented graphical

method in this work 47

3.12 Methodology process flow chart 49

4.1 Energy targeting by CCs for Example 4. 1 54

4.2 Utility targeting by the GCC for Example 4. 1 55

4.3 BCC for Example 4.1 55

4.4 The BCC and stream manipulating for Example 4. 1 56

4.5 BGCC for Example 4.1 based on the FCp calculated by the GCC 60

4.6 Energy utility and area targeting by STEP 66

4.7 Completed STEP including variable-temperature

Utility targeting and HEAT 62

4.8 The BGCC for Ex 4.1 based on the FCp targeted by the STEP 65

4.9 Energy targeting for Example 4.2 by CCs 66

4.10 Utility targeting for Example 4.2 by the GCC 67

4.11 BCC for Example 4. 2 68

4.12 Stream replacement for Example 4.2 68

4.13 The BGCC for Ex 4.2, baced on the FCp targeted by the GCC 68

4.14 Variable-temperature utility targeting by STEP for Example 4.2 69

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4.15 The BGCC for Example 4.2 based on FCp targeted by STEP 70

4.16 STEP including variable-temperature utility targeting and HEAT 71

4.17 The Energy targeting for Example 4.3 by the CCs 73

4.18 Utility targeting for Example 4.3 by the GCC 74

4.19 The BCC for Example 4.3 75

4.20 The BCC and stream replacement for Example 4.3 75

4.21 The BGCC for Example 4.3 with FCp targeted by the GCC 75

4.22 Energy, Area and utility targeting by STEP 77

4.23 The BGCC for Ex 4.3 based on the FCp targeted by the STEP 77

4.24 The STEP including variable-temperature utility targeting

and HEAT 78

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Nomenclature

Amin Minimum Network Area

ADP Acid Dew Point

BCC Balanced composite curves

BGCC Balanced grand composite curves

C Cold stream

CCs Composite Curves

CGCC Cumulative grand composite curves

CW Cooling Water

CHP Combine Heat and Power

FCp Heat capacity flowrate (kW/◦C)

FG Flue Gas

GCC Grand Composite Curve

H Hot stream

HE Heat exchanger

∆H Enthalpy change (kW)

HEAT HEat Allocation and Targeting

HPS High Pressure Steam

HEX Heat Exchanger

IEO International Energy Outlook

IPTA Improved Problem Table Algorithm

LPS Low Pressure Steam

MHA Maximum Heat Allocation

MPS Middle Pressure Steam

OECD Organization for Economic Cooperation and Development

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PTA Problem Table Algorithm

PDM Pinch Design Method

Q Heat duty (kW)

QC Cooler

QC,min Minimum cold utility (kW)

QH Heater

QH,min Minimum hot utility (kW)

STEP Stream Temperature vs Enthalpy Plot

Tpinch Pinch temperature (◦C)

′ Supply temperature (◦C)

′ Shifted supply temperature (◦C)

Tt Target temperature (◦C)

∆Tmin Minimum temperature difference (◦C)

TLP Temperature Limiting Point

ULP Utility Limitation Profile

USL Utility Stream Line

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CHAPTER 1

INTRODUCTION

1.1 Background

Energy is fundamental in industrial economies and yet is often overlooked in the

drive for profitability. Recent energy-market developments, increasing oil and gas

prices, as well as the effect of combustion gas on climate change (CO2 is a greenhouse

gas), have enhanced the emphasis on energy management. Plant owners are seeking

alternatives for fossil fuel or ways to reduce energy and consumption of other utilities in

order to minimize utility costs as well as maximizing profitability. In energy

management, process integration based on pinch technology is one of the ways to reduce

utility consumption in a systematic way based on thermodynamic rules.

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1.2 Outlook on energy

From international energy outlook 2010 (IEO, 2010), world market energy

consumption is projected to grow by 49 % from 2007 to 2030. The total energy required

in non-OECD (Organization for Economic Cooperation and Development) countries has

risen by 84 percent, whereas, the increase in OECD countries is just around 14 %. The

total world energy use is predicted to increase from 495 quadrillion (Btu) in 2007 to 590

quadrillion Btu in 2020 and 739 quadrillion Btu in 2035. (U.S. Energy Information,

2010) (see, Figure 1.1).

Figure1.1 World market energy consumption by region, 2007 – 2035

(U.S. Energy Information, 2010)

Based on data from the International Energy Outlook (2010), about one-half of

the world’s total delivered energy is consumed in industrial sector and close to two-

third of this amount of energy are used for heating and cooling as well as for powering

equipment in plants. Over the 28-year projection, worldwide industrial energy

consumption grows from 184 quadrillion Btu in 2007 to 262 quadrillion Btu in 2035.

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The notable point is that around 50% of all energy produced in the world is used in only

five industrial sectors (Figure 1.2). Chemical industries by 22% use maximum amount

of energy among surveyed sectors which is followed by iron and steel 15%, nonmetallic

minerals by 6%, pulp and paper 4% and the minimum percentage belongs to nonferrous

metals by just 3%. The quantity and fuel mix of future industrial energy consumption

will be determined largely by energy use in those five industries. In addition, the same

industries emit large quantities of carbon dioxide, related to both their energy use and

their production processes.

Figure 1.2 World industrial sector energy consumption (percent of total) by major

energy intensive industry shares in 2007. (U.S. Energy Information, 2010)

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1.3 Problem Background

For many years, plant designers have applied graphical tools to obtain the best

combination of available utilities. The Grand Composite Curve (GCC) has been one of

the most common graphical methods to achieve this aim. The GCC is a plot based on

problem table algorithm (PTA) or composite curves (CCs) information. Since CC and

GCC methods involve combining individual streams as composite streams, it is difficult

to graphically match and allocate the utilities with individual process streams. Hence, in

this research, it is proposed to use individual curve method to solve this and use it to

represent all multiple utilities and area targeting method that have been proposed based

on composite nature.

Some limitations of composite curves are listed below (Wan Alwi and Manan, 2010):

1. Heat exchange between individual cold and hot streams cannot be represented,

completely.

2. Insufficient guidance is offered in terms of individual stream matching.

3. Composite curves cannot be used for designing heat exchanger networks.

4. The minimum heat exchanger area and the optimum ∆Tmin cannot be obtained

correctly due to the use of composite streams instead of individual streams.

5. The integration between utilities and each process streams cannot be

conveniently demonstrated.

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1.4 Problem statement

Given a process that involves a set of hot and cold streams, it is required to

develop a graphical approach to simultaneously target and design a maximum heat

recovery network with the appropriate utility levels and type, stream matches and

possible process modifications that can yield the minimum cost in terms of utilities and

heat exchanger area costs. The graphical approach should be able to consider individual

stream matches between process to utility streams and in particular, taking into account

of utilities with variable supply and target temperatures.

1.5 Objective

The main objective of this research is to develop a new graphical approach for

simultaneous targeting and design of multiple utility systems. The key focus of the

work is the development of new techniques to interface individual process-utility

systems with variable supply and target temperatures.

1.6 Scope of the Study

1. Analysis on current graphical tools for multiple utilities targeting and highlighting

their advantages, disadvantages and limitations.

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2. Develop a graphical tool for simultaneous heat exchanger network targeting and

design with multiple utilities level.

3. Comparing the new developed graphical method with current graphical methods in

term of result reliability.

4. Assessing the new developed method and state the overall its advantages and

disadvantages.

5. Discussing about probable drawbacks of the new developed method and suggest

some solutions to improve and modify it in the future works.

1.7 Research Contributions

The research contribution in this study is to assess the current graphical methods

in terms of utility targeting as well as stream matching and to find out their limitations.

Moreover, the main contribution in this work is the development of a new graphical

approach and heuristics (guidelines) for simultaneous targeting and design of heat

exchanger network with multiple utility levels.

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1.8 Summary of the Thesis

This thesis consists of 5 chapters as follows:

1) Chapter 1 presents an outlook on the worldwide demand of energy, the research

background,the main reseach objective, research scope and the importance of the

research.

2) Chapter 2 reviews the previous research and approaches on graphical tools in

terms of multiple utility targeting and the minimum area targeting.

3) Chapter 3 illustrates the concepts and detailes of methodology based on the new

method.

4) Chapter 4 presents results of this study and some limitations of current graphical

methods has been considered through three diffenent case studies.

5) Chapter 5 presents conclusion on resuls of this research and offers some

recommendations to improve limitations of the proposed method.

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