A STUDY ON CORRELATION OF SAFETY, HEALTH AND ENVIRONMENTAL PROPERTIES AT INHERENT LEVEL: BENZENE ...

7/29/2019 A STUDY ON CORRELATION OF SAFETY, HEALTH AND ENVIRONMENTAL PROPERTIES AT INHERENT LEVEL: BENZENE SYNTHESIS ROUTES

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A STUDY ON CORRELATION OF SAFETY, HEALTH AND

ENVIRONMENTAL PROPERTIES AT INHERENT LEVEL: BENZENE

SYNTHESIS ROUTES


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UNIVERSITI TEKNOLOGI MALAYSIA

DECLARATION OF THESIS / UNDERGRADUATE PROJECT PAPER AND COPYRIGHT

Authors full name : YOUSUF ABDULKAREM ALI AL-HAMDANI

Date of birth : 1st

January 1983

Title :

Academic Session :

I declare that this thesis is classified as :

CONFIDENTIAL (Contains confidential information under the Official

Secret Act 1972)*

RESTRICTED (C t i t i t d i f ti ifi d b th


ENVIRONMENTAL PROPERTIES AT INHERENT LEVEL

2011/2012


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SUPERVISORS DECLARATION

I hereby declare that I have read this thesis and in my opinion this thesis is

sufficient in terms of scope and quality for the award of the degree of Master of

Science (Safety, Health and Environment).


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ENVIRONMENTAL PROPERTIES AT INHERENT LEVEL: BENZENE

SYNTHESIS ROUTES

YOUSEF ABDULKAREM ALI ALHAMDANI


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DECLARATION

I declare that this thesis entitled (A Study on Correlation of Safety, Health and

Environmental Properties at Inherent Level) is the result of my own research work

apart from as cited in the references. The thesis has not been accepted for any degree

and is not concurrently submitted in Candidature of any other degree.


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ACKNOWLEDGEMENT

First and foremost I would like to thank my God ALLAH (SWT) for

keeping me in His absolute grace and mercy while obtaining this task. There were

times when I could not imagine ever reaching the completion of this dissertation, but

through His grace, mercy and guidance, I have been blessed and supported to

complete this task on time. Alhamdulillahi Rabbilalamien.

I am greatly thankful and grateful to my supervisor, Dr. MIMI HARYANI

HASSIM for her time, encouragement, motivation, guidance and support from the

initial to the final level enabling me to improve this research.


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ABSTRACT

Selection of chemical process route at early stage is one of the major tasks

during the R&D stage of process design. Various criteria need to be evaluated

including economy, safety, health and environmental (SHE) aspects. The assessment

is more challenging at the research and development (R&D) stage since the only data

available are chemical properties and process conditions. Various methods have

been developed for inherent SHE assessment, but the question is; do the SHE

properties correlate with each other at inherent level. In this paper, a study is

conducted to determine the correlation between inherent safety, health and

environmental properties by applying six index methods to three process routes for

benzene production - toluene hydrodealkylation (TDA), pyrolysis gasoline


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TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE PAGE i

STUDENT DECLARATION ii

ACKNOWLEDGEMENT iii

ABSTRACT iv

vTABLE OF CONTENTS vi

LIST OF TABLES x


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2.3 Implementation of inherent safety 11

2.4 Evaluation of inherent safety 13

2.5 Methodology for ISL evaluation 14

2.6 Extension of inherent safety to other criteria 21

2.7 Comparison of index methods 23

2.8 Index methods for the study 25

2.8.1 Inherent safety index (ISI) 26

2.8.1.1 Formation of Inherent safety index (ISI) 26

2.8.1.2 Calculation of Inherent safety index (ISI) 27

2.8.2 iSafe analysis method 31

2.8.2.1 Formation of iSafe index 31

2.8.3 Process Route Healthiness Index (PRHI) 33

2.8.3.1 Formation of PRHI 33


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3 METHODODLOGY 68

3.1 Introduction 68

3.2 Project conception 70

3.3 The case study 70

3.4 Data collection 71

3.5 Selection of index methods for the assessment 71

3.6 Understanding the principles of the methods 72

3.7 Correlation method 74

3.8 Simulation method 74

3.9 Report and documentation 74

4 RESULTS AND DISCUSSION 75

4.1 Benzene Synthesis Routes case study 75

4.1.1 Case study 1: TDA process route 76

4 1 2 C t d 1 P t 76


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4.2.6 Environmental hazard index (EHI) assessment 104

4.3 Discussion of the indexes values 111

4.4 Correlation of index methods 115

4.4.1 Correlation between safety and health index methods 116

4.4.2 Correlation between safety and environmental index methods 118

4.4.3 Correlation between health and environmental index methods 118

4.4.4 Average correlation between SHE criteria 118

5 CONCLUSIONS 120

5.1 Conclusions 120

5.2 Recommendation 122

REFERENCES 123

Appendices AF 127-219


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LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Parameters used in the two-index; PIIS vs ISI system 16

2.2 Supplementary indexes 17

2.3 Inherent safety index (ISI) formation 27

2.4 Sub-indexes of chemical inherent safety index ICI and the score

formation for each sub-index

29

2.5 Sub-indexes of process inherent safety index IPI and the score

formation for each sub-index30


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4.2 Calculation of the sub-indexes of process inherent safety index

IPI for the TDA, Pygas and naphtha reforming case studies

82

4.3 Calculation of the inventory in the TDA, Pygas and naphtha

reforming process routes

83

4.4 Calculation of the i-Safe sub-indexes for the TDA, Pygas and

naphtha reforming process routes85

4.5 Calculations of the IOHI index for the TDA, Pygas and naphtha

reforming process routes

88

4.6 Calculations of ICPHI - Penalties for Activities (PA) for TDA,

Pygas and naphtha reforming process routes

90

4.7 Calculations of ICPHI - Penalties for process conditions (PC) for

TDA, Pygas and naphtha reforming process routes

91

4.8 Calculation of the Health Hazard Index (HHI)TDA processroute

93

4.9 Calculation of the Health Hazard Index (HHI)Pygas processroute

94

4 10 C l l ti f th H lth H d I d (HHI) hth 95


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4.18 Calculation of the environmental hazard index (EHI) for M.

cyclohexanePygas and naphtha reforming process routes108

4.19 Calculation of the environmental hazard index (EHI) for

cyclohexenePygas process route109

4.20 Calculation of the environmental hazard index (EHI) for n-

Hexanecatalytic naphtha reforming process route110

4.21 Evaluation of benzene production process routes based on

inherent safety index (ISI)

111

4.22 Evaluation of benzene production process routes iSafe index

method112

4.23 Assessment of benzene production process routes based on

inherent occupational health index (IOHI)

113


process route healthiness index (PRHI)

113


inherent environmental toxicity hazard (IETH)114


i h i l i i h d (EHI)

115


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LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Criteria used in the Inherent Safety Index and theiravailability

in the early stages

13

2.2 Inherently safer features become harder to install as a project

progresses

14

2.3 Comparison of ISI parameters values for the six routes of MMAusing graphical method

18

2.4 Framework to determine ISL at preliminary design stage 20

2.5 Unit world showing compartment volumes 49


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LIST OF APPENDICES

APPENDIX TITLE PAGE

A Ranking matrix for occupational disease 127

B Ranking matrix for occupational disease 128

C Example Calculations: Calculation of Z values 129

D Indices calculation for toluene hydrodealkylation (TDA) case study 130

E Indices calculation for pyrolysis gasoline hydrogenation (Pygas)

case study

152

F Indices calculation for the catalytic naphtha reforming case study 183


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CHAPTER 1

INTRODUCTION

Chemical industry has been traditionally percept to contribute to the presence

of threats to lives. It serves as a source of menace to workers and public as well as to

the environment. Direct harm to human is caused by the industrial related accidents

and the exposure to the hazardous materials involved. On the other hand, chemical

industry may also cause environmental destruction by its large input of greenhouse

i i h h I l l i i i f h


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Among the three pillars of sustainability which are the economic,

environmental and social, the environmental sustainability has received far more

attention. Many programs have been launched to support environmental

sustainability. Many, short and long-term commitments have been made by many

governments around the world to support environmental protection related issues. On

the other hand, many chemical companies have joined programs such as Responsible

Care which has been launched since 1985 (Hook, 1996) (Hassim, 2010). The aim of

such programs is to make progress towards sustainability in order to achieve the

betterment of society, environment and economy. The continuous improvement of

environmental, health and safety performance is also an essential target for which

these programs have been launched.

Based on the above-mentioned definition of sustainable development, human

well-being is at the center of concerns in order to achieve sustainable development. It

is also considered as an essential indicator of progress towards development

sustainable (Moldan et al., 2012). Health and safety are top consideration when


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aspects have been given an increasing attention as essential criteria to be taken into

account in choosing the chemical process route (Hassim and Edwards, 2006).

Based on public image, chemical plants are known as an inherently hazardous

to both workers and community in surrounding area as well as to the environment.

Such an impression becomes worsen after a series of catastrophic events involving

chemical plants including explosions of Flixborough plant in 1974, fires in Piper

Alpha Oil Platform in 1976 and toxic releases in Bhopal in 1984. These accidents

caused an immediate fatalities, severe injuries and serious illnesses to the workers and

public community. As for the environment, the negative impacts on the ecosystem

may be resulted from releases during normal operation or loss of containment due to

catastrophic accidents e.g. the Deep Water Horizon Oil Spill in April 2010.

In an attempt to control the hazards in chemical plants, added-on protective

systems are installed as the most reliable defense system for the plant. However,


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Most of the attention has been directed to safety aspect. On the other hand,

occupational health has received limited concern. In integrated ISHE methods health

has always been discussed only as minor part of the other aspects. Among the studies

that focus exclusively on occupational health were conducted by Johnson (2001)

(Occupational Health Hazard Index), and Hassim & Edwards (2006) (Process Route

Healthiness Index) (Hassim and Edwards, 2006).

1.1 Background of study

Several comparison-related studies have been conducted aiming to find if it is

possible to estimate all the SHE properties at inherent level using one single method.

Examples of these studies includes; Rahman et al. (2005) compared ISI (by Edwards

and Lawrence, 1993), another ISI (Heikkila, 1999) and iSafe method (Palaniappan et


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correlation, whereas, health vs. environment was less correlated. The study also

found that IOHI or ISI method alone can be used as a single index method for

estimating all the EHS properties for route selection in this case study (Hassim et al.,

2008).

Carrying out further studies on correlation between EHS indices is the area of

interest of this research. However in order to totally focus on inherent properties,

only pure inherent based indexes will be considered. Out of the 12 methods, only 6

fall under this category, two for each criterion. Benzene production is the case study

selected for this work. The aim of this correlation is to determine how strong these

indices can be correlated and then to find one index that can be used alone to evaluate

all the EHS properties for route selection in this case study. In addition, the

correlation for MMA production case study was recalculated again, this time only for

those six indices. The results from the MMA case study will be compared to benzene

case study for averaging and validation purpose.


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1.3 Case study

Benzene is an important product, which is widely used in manufacturing many

products such as tires and rubber. Benzene also is an ingredient of a variety of

painting such as base and top coat paints, lacquers, spray paints, sealers and stains.

Petroleum and oil refineries produce products that contain benzene, such as gasoline,

fuel oils and kerosene. Benzene is used in manufacturing chemical and plastic

products. Examples include resins, adhesives and synthetic products such as nylon,

styrene and Styrofoam. Hence, three process routes for benzene production were

selected as a case study.

The correlation between the six EHS index methods was conducted on three

alternative process routes for manufacturing benzene as a case study. The three routes

are Toluene Hydrodealkylation process (HDA), pyrolysis hydrogenation process route

and catalytic naphtha reforming process route.


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1.5 Scope

This study will cover a correlation between EHS properties at inherent level.

This study is limited to use six index methods to be used in carrying out this

correlation. Two index methods for each aspect of the three main aspects

(Environment, Health and Safety) will be selected.

Benzene was selected as the case study of this project. Only two process

routes of manufacturing benzene are involved in this study. The two process routes

are; Toluene Hydrodealkylation process (HAD) and pyrolysis process.

The aim of this study is to determine if the EHS properties can be correlated at

the inherent level. Also this study aims to simplify index-based EHS evaluations by

using only one index for the whole EHS evaluation.


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CHAPTER 2

LITERATURE REVIEW

2.1 Sustainability


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safety, health, and environmental (SHE) performance (Hook, 1996). EU directives

have also affected process development and design so that SHE aspects have to be

taken into consideration in earlier phase. The European Agency for Safety and

Health at Work (EU-OSHA) was set up in 1996. The purpose is to make the

workplaces in European countries safer, healthier, and more productive. The

European Risk observatory was also set up in 2005 as an integral part of the EU-

OSHA. It describes factors and anticipates changes in the working environment and

their possible consequences to health and safety (EU-OSHA, 2010). Its aim is to

identify new and emerging risks and to promote early preventive action. Therefore

SHE considerations in process development and design have become important

because of legal requirements, company image, and economic reasons (Hassim,

2010).

2.2 Inherent safety


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To control the hazards in chemical plants, added-on protective systems are

installed as the most reliable defense system for the plant (Hassim, 2010). However,

the approach of add-on control system alone has shown to a large extent the

deficiency in protecting workers lives and controlling hazards in chemical plants.

This fact has been further approved by a series of catastrophic events involving

chemical plants including explosions of Flixborough plant in 1974, fires in Piper

Alpha Oil Platform in 1976, and the Texas BP Refinery Plant 2005 (Zwetsloot and

Askounes, 1999) (Shariffet al., 2012).

So the better, more innovative approach is by trying to reduce or even to

avoid the hazards fundamentally rather than controlling them by added-on systems.

The approach was introduced after the Flixborough explosion, which was later

formalized as inherently safer design (Hassim, 2010).

The concept of inherent safety was introduced by Trevor Kletz who is


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highlighted that inherently safer design concept is a cost-effective option when

taking into consideration the lifetime costs of a process and its operation (Shariffet

al., 2012).

2.3 Implementation of inherent safety

In order to achieve the best results towards inherently safer process design,

the approach of inherent safety must be implemented at the earliest phase of design

lifecycle. Lifecycle of design starts with Research and Development stage (R&D)

and goes through other phases which are design, design, construction, operation,

modification, and decommissioning. The most important decisions, when

constructing a new chemical plant, are made at the process development and

preliminary engineering (conceptual design) phase. It is believed that this phase is


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al. (2002), some commentators have admitted the slow progress towards the actual

application of inherent safety philosophy. Kletz (2004) stated that there is a real

progress in the concept itself as principles but it has not been adopted in actual

design unlike quantitative risk assessment which was brought up into chemical

industries just a few years earlier (Hansson, 2010).

Gupta and Edwards (2002) have conducted an extensive survey with a set of

questionnaire was distributed among safety professionals; industrialists, academics

and regulators from different places in the world. Unlike the result Kletz came up

with in 1991, the results of this survey demonstrate a general appreciation and

awareness of inherently safe design (Gupta and Edwards, 2002). This can be

considered as a real progress towards the concept.

However, respondents have cited many reasons for the slow progress towards

the implementation of this concept. Lack of clear vision of the economic benefits


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2.4 Evaluation of inherent safety

As earlier mentioned, several obstacles and barriers stand against the

adoption of the inherently safe design. Lack of information in the early stage of

process lifecycle is among these problems (Hurme and Rahman, 2005). Currently,

safety evaluation is carried out at advanced stages when the process has already

designed and the chance for conceptual changes is no longer available (Leong and

Shariff, 2008). This explains most of the existing methods are applicable to the later

phases of process design lifecycle where more details required for evaluation are

available (Heikkil, 1999). In order to evaluate the inherent safety level (ISL) at

early process design, the available information at this stage must be utilized.


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2.5 Methodology for ISL evaluation

In relation to the evaluation of inherent safety at early phase of process design

lifecycle, many efforts have been done. Most of them have been focusing on the

development of index methods for inherent SHE assessment in chemical process

development and design. The index methods were designed to enable the utilization

of the information which is available at early process design stages so that ISL

evaluation can be conducted at these stages (Leong and Shariff, 2008).

The main aim of conducting the early inherent safety evaluation is to find out

if the ISL is either acceptable or not. If the ISL can be evaluated at early stages, the

changes or modifications, if required for safety, will be much easier and

economically cost-effective. Fig. 2.2 below shows how it does become harder to

install inherent safer design as a project is in progress.


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Many index methods have been developed for safety analysis. These

methods are based on different information that available through different phases of

process design lifecycle so that different methods are applicable to different phases.

For example, some methods require more detailed information such as Dow Fire and

Explosion Hazard Index (DOW, 1987), the Mond Index (ICI, 1985) and Hazop

(Kletz, 1992) (Heikkil, 1999). These methods are used for safety evaluation at

advanced process design stages.

Prototype Index for Inherent Safety (PIIS) is the first index method

introduced to evaluate inherent safety at early process design stage. This method

was proposed by Edwards and Lawrence (1993) (Leong and Shariff, 2008). In the

method, two parts were included, which are chemical and process score. Chemical

score composes of inventory, flammability, explosiveness, and toxicity. Process

score consists of temperature, pressure, and yield. The sum of the two score is the

total value of PIIS (Heikkil, 1999). A high value of the index indicates low degree

of inherent safety.


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Table 2.1 Parameters used in the two-index; PIIS vs ISI (Leong and Shariff, 2008)

Parameters Edwards and

Lawrence

(1993)

Heikkila (1999)

Inventory X X

Temperature X X

Pressure X X

Heat of main reaction X X

Heat of side reaction XFlammability X X

Explosiveness X X

Corrosiveness X

Toxicity X X

Chemical interaction X

Type of equipment X

Safety of process structure X

Towards computerizing the inherent safety methods, Palaniappan et al.

(2002) have developed a support tool called iSafe. This method was developed to

overcome the barriers that slow down the adoption of inherently safer approaches


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Table 2.2: Supplementary indexes (Palaniappan et al., 2004)

Supplementary index Description

Worst Chemical Index

(WCI)

Summation of maximum values of the

flammability, toxicity, reactivity, and

explosiveness indices of all the materials

involved in a reaction step.

Worst Reaction Index(WRI)

Summation of the maximum of the individual

indices of temperature, pressure, yield, andheat of reaction of all the reactions involved

in the process.

Total Chemical Index

(TCI)

a measure of the number of hazardous

chemicals involved in the route

Gupta and Edwards (2003) proposed a graphical method to measure inherent

safety index using the six process routes of methyl methacrylate (MMA) as a case

study (Leong and Shariff, 2008). By plotting the values of temperature, pressure and

a combined value for flammability, explosiveness and toxicity (FET) for each step


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Figure 2.3 Comparison of ISI parameters values for the six routes of MMA using graphical

method (Gupta and Edwards, 2003).


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process design stages. By applying this method on case studies, they came up with

the results which demonstrated that the risk level due to an explosion can be assessed

during the early process design stage so that designers still have the freedom to make

changes or modifications and at lower cost (Shariffet al., 2006).

In relation to the above mentioned approach, Leong and Shariff (2008) have

pointed out that iRET do not include the probability estimation when estimating the

risk at early design stages. To overcome this shortcoming, they have proposed a new

method called Inherent Safety Index Module (ISIM). This method uses the same

software used by Shariff et al. (2006), process design simulator (HYSYS). Unlike

iRET, the new method enables the information from process design simulator to be

extracted and analysed not only for the determination of inherent safety level and

consequence, but also for estimating the probability of unwanted incidences (Leong

and Shariff, 2008).


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Figure 2.4 Framework to determine ISL at preliminary design stage (Leong and Shariff, 2008)

Risk calculationRisk = Consequences x Probability

Risk comparison

Acce tableProceed with design

Criteri

Inherent safety index module

This module evaluates the

safety level. Will prompt

the component of the

index that may be lowered

HYSYS Process Simulator

Integrated Consequence

Estimation Tool (ICET)

This module estimates the

consequences of an

undesired event. Can also

evaluate multiple designs

Integrated Probability

Estimation Module (IPEM)

This module calculate

the probability of the

event happening based

on established database

Further

improve

Modify

design


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2.6 Extension of inherent safety to other criteria

The concept of inherent safety was developed and extended to include health

and environment aspects. The concept then is called inherent safety, health and

environment (ISHE). Based on the above-mentioned methods and tools, it is

noticeable that most of the effort is directed to safety aspect. Many qualitative and

quantitative indexing methods were developed for inherent safety assessment. The

examples of these methods (in addition to what has been mentioned previously)

includes: by Khan and Abbasi (1998a) (RRABD), Khan et al. (2001) (SweHI),

Mansfield (1997) (INSET) (Hassim and Edwards, 2006).

On the other hand, occupational health has received limited concern in

comparison to the other two main concepts (safety and environment). In integrated

ISHE methods, health has always been discussed only as minor part of the other

aspects. E.g. the EHS by Koller et al. (1999, 2000) discussed health aspect beside


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both the hazard from the chemicals present and the potential for the exposure of

workers to the chemicals. It can be used to either evaluate the level of inherent

occupational health hazards or to compare alternative process routes for these risks

(Hassim and Hurme, 2010a). Both PRHI and IOHI are selected as health assessment

methods for this study. These two methods will be discussed in more details later in

this chapter.

Then, a method called the Health Quotient Index (HQI) (Hassim and Hurme,

2010b) has been developed to quantify workers health risk from exposure to fugitive

emissions. The HQI is designed for the preliminary process design. This method

can be used to evaluate alternative process concepts or to quantify the risk level of

processes (Hassim and Hurme, 2010b). Occupational Health Index (OHI) is also a

method developed by Hassim and Hurme (2010c) for the basic engineering stage.

The OHI utilizes the information available in piping and instrumentation diagrams

(PIDs) and the plot plan (Hassim and Hurme, 2010c).


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2.7 Comparison of index methods

Several comparison-related studies have been conducted to compare different

indices for inherent SHE methods. Rahman et al. (2005) compared inherent safety

based methods including the PIIS (Edwards and Lawrence, 1993), the ISI (Heikkila,

1999) and iSafe method (Palaniappan et al., 2004). Hassim and Edwards (2006)

compared the results obtained from an inherent health assessment of methyl

methacrylate case study to those obtained from the PIIS (safety) (Edwards and

Lawrence, 1993) and EHI (environmental) (Cave and Edwards, 1997) (Adu et al.,

2007).

Koller et al. (2001) have compared methods which are used to assess the

hazard potential of processes during the design stage. Index based methods such as

PIIS, ISI, and Dow Fire & Explosion Index were involved in this comparison. The

comparison was conducted based on two aspects: (1) fire, explosion, reaction and


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In their paper, Rahman et al. (2005) have compared three index based

inherent safety methods with each other and with expert evaluations and also

discussed their limitations. These three index based methods are; Prototype Index of

Inherent Safety (PIIS) developed by Edwards and Lawrence (1993), Inherent Safety

Index (ISI) (Heikkila, 1999; Heikkila, Hurme, & Jarvelainen, 1996), i-Safe index

(Palaniappan, 2002; Palaniappan, Srinivasan & Tan, 2004). Methyl methacrylate

(MMA) process routes were selected as a case study for this comparison. It is

concluded that the ISI method gave the smallest difference to expert values both in

sub-process and process route evaluations. The difference of ISI to expert values is

about 10%, and both PIIS and i-Safe 15% in the sub-process evaluations. In process

route evaluations the differences is only 3.5% for ISI and about 9% for PIIS and 10%

for i-Safe (Rahman et al., 2005).

Adu et al. (2007) have compared 21 SHE index methods (7 safety methods, 4

health, and 10 environmental). Methyl methacrylate (MMA) production was

selected as a case study. They concluded that based on their study; there is no unique


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Prof Jai P. Gupta, the world known inherent safety expert, gave a personal

comment to the authors that the study conducted by Hassim et al. (2008) is very

interesting, but it needs at least two case studies to improve the reliability of the

results. Therefore in this study similar work to work has been done by Hassim et al.

(2008) will be conducted but on benzene production case study. Also now it is

decided to consider only pure inherent based methods, with application at the R&D

stage. Therefore only 6 out of 12 methods will be considered. In relation to that, the

correlation between the methods in Hassim et al. (2008) work will also be calculated

using the 6 methods selected so that the results from both studies can be fairly

compared and further analysed.

2.8 Index methods for the study


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The aim of this correlation is to determine how strong these indices can be

correlated and then to find one index method that can be used alone to evaluate all

the EHS properties for route selection in this case study. In addition, the correlation

for MMA production case study was recalculated again, this time only for those six

indices. The results from the MMA case study were compared to benzene case study

for averaging and validation purpose.

2.8.1 Inherent safety index (ISI)

Edwards and Lawrence (1993) proposed an inherent safety index named by

(PIIS). The aim of this method is to select the inherent safest reaction pathway

(Rahman et al., 2005). Heikkila (1996) pointed out that (PIIS) is more focusing on

reaction properties and does not take into account other parts of the process


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(1996) also analysed which of these principles can be further represented as inherent

safety indices, which can be calculated utilizing the available information (Rahman

et al., 2005). The total inherent safety index (ISI) includes two main indexes which

are; chemical inherent safety index and process inherent safety index. Both chemical

and process indexes are divided into two sub-indexes. Each sub-index is described

by several parameters. Table 2.3 below describes inherent safety and its sub-indexes

(Rahman et al., 2005).

Table 2.3: Inherent safety index (ISI) formation (Rahman et al., 2005)

Inherent Safety Index (ISI)

Chemical Inherent Safety Index ICI Process Inherent Safety Index IPI

1. Sub-indices for reaction hazards- Heat of the main reaction IRM- Heat of side reactions IRS- Chemical interaction IINT

1. Sub-indices for process condition- Inventory II- Process temperature IT- Process pressure IP

2. Sub-indices for hazardous substances

- Flammability IFL- Explosiveness IE

2. Sub-indices for process system

- Equipment IEQ- Process structure IST


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flammability, explosiveness, toxicity and corrosiveness of chemical substances used

in the process. Flammability, explosiveness and toxicity are calculated separately for

each substance in the process. Chemical reactivity composes of both the maximum

values of indices for heats of main and side reaction and the maximum value of

chemical interaction which describes the unintended reactions between chemical

substances present in the process area studied. On the other hand, the Process

Inherent Safety Index IPI (Eq. 2.3) represents the inherent safety of the process itself.

It contains the sub-indices of inventory, process temperature and pressure, equipment

safety and process structure (Rahman et al., 2005).

max,max,max,max,max, )( CORFETINTRSRMCI IIIIII (2.2)

max,max,max,max, STEQPTIPI IIIIII (2.3)

The worst case scenario is adopted when calculating inherent safety index.

The worst case scenario describes the most hazardous situation that can have place in

any alternative process. The higher value of the index indicates an inherently unsafer


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Table 2.4: Sub-indexes of chemical inherent safety index ICI and the score

formation for each sub-index (Rahman et al., 2005)

Sub-index Symbol Score formation Score

Heat of main reaction IRM Thermally neutral 200 J/g 0

Mildly exothermic < 600 J/g 1

Moderately exothermic < 1200 J/g 2

Strongly exothermic < 3000 J/g 3

Extremely exothermic 3000 J/g 4

Heat of side reaction,

max

IRS Thermally neutral 200 J/g 0

Mildly exothermic < 600 J/g 1Moderately exothermic < 1200 J/g 2

Strongly exothermic < 3000 J/g 3

Extremely exothermic 3000 J/g 4

Chemical interaction IINT Heat formation 13

Fire 4

Formation of harmless, nonflammable gas 1

Formation of toxic gas 23

Formation of flammable gas 23

Explosion 4

Rapid polymerization 23

Soluble toxic chemicals 1

Flammability IFL Non-flammable 0

Combustible (flash point > 55C) 1

Flammable (flash point 55C) 2

Easily flammable (flash point < 21C) 3


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Table 2.5: Sub-indexes of process inherent safety index IPI and the score formation

for each sub-index (Rahman et al., 2005)

Sub-index Symbol Score formation Score

Inventory II, ISBL 01 t 0

110 t 1

1050 t 2

50200 t 3

200500 t 4

5001000 t 5

II, OSBL 010 t 0

10100 t 1

100500 t 2

5002000 t 3

20005000 t 4

500010000 t 5

Process

temperature

IT < 0 C 1

070 C 0

70150 C 1

150300 C 2

300600 C 3

>600 C 4

Process pressure IP 0.55 bar 0


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2.8.2 i-Safe analysis method

Palaniappan et al (2004) have developed a methodology named by iSafe. It is

a computer-added tool that can automate inherent safety analysis during the early

stages of design. It is developed as a support tool with an important advantage which

is substantially to reduce the time and effort. The i-Safe is an analysis methodology

which is based on the inherent safety index. Several indexes are used in iSafe

analysis method. The parameters considered in iSafe analysis method are taken from

ISI index excluding the process yield which is from PIIS index. Subsequently, the

scoring and ranking used in iSafe method are based on the scoring and ranking

pattern used in Inherent Safety Index (ISI) (Palaniappan et al., 2004).

2.8.2.1 Formation of iSafe index


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flammability, toxicity and explosiveness (Eq. 2.7). In the other hand, individual

reaction index represents the value of each reaction involved in the process route.

The parameters used for calculating IRI are; temperature, pressure, yield and the heat

of the reaction (Eq. 2.8) (Palaniappan et al., 2004).

NeNtNfNrICI (2.7)

Where; Nr = NFPA reactivity rating

Nf = flammability index

Nt = toxicity index

Ne = explosiveness index

RhRyRpRtIRI (2.8)

Where; Rt = temperature sub-index

Rp = pressure sub-indexRy = yield sub-index

Rh = heat of reaction sub-index


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process route. The Equations (2.9, 2.10 and 2.11) below are used for calculating

WCI, WRI and TCI respectively (Palaniappan et al., 2004).

)max()max()max()max( NeNtNfNrWCI (2.9)

)max()max()max()max( RhRyRpRtWRI (2.10)

ICITCI (2.11)

2.8.3 Process Route Healthiness Index (PRHI)

This index method is developed by Hassim and Edwards (2006). Process

route healthiness index (PRHI) assesses and quantifies the inherent occupational

health hazards of the chemical process. The severity of health hazards is dependent

on two basic factors which are; the chemical involved in the process and the amount


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avgOEL

WECHHIMHIICPHIPRHI (2.12)

2.8.3.2 Calculation of PRHI

To obtain PRHI value, all indexes involved in equation (12) should becalculated.

Inherent Chemical and Process Hazard Index (ICPHI)

This index assesses the activities and process conditions that are involved in a

chemical process route by assigning a penalty for each. A higher penalty indicates a

higher hazard posed by the activity or the process condition. The probability of the


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Table 2.6: penalties for activities or operations (Hassim and Edwards, 2006)

Activity Operation Penalty

Transport

Pipe 1

Bag 2

Drum 3

Vibration 4

Mode of process

Continuous 1

Semi-continuous/Semi-batch 2

Batch 3

Venting or flaring

Scrub vent effluent 1

Above occupiable platform

level2

Occupiable platform level 3

Maintenance works

No 0

Yes 1

Agitation 1

Others

Others (sieving, filtering, and

so on)1

Solid handling 2

Size reduction 2

Extrusion 3

Air open mixing 3


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Table 2.7: penalties for process conditions and material properties (Hassim and

Edwards, 2006)

Condition Range Penalty

Temperature ( C) Low 0

High (> 92 C) 1

Pressure (atm) Low 0

High (> 68 atm) 1

Viscosity (cp) Low (0.11 cp) 1

Medium (110 cp) 2

High (10100 cp) 3

Ability to precipitate No 0

Yes 1

Density difference (sg) Low (01 sg) 1

Medium (01.5 sg) 2

High (02.5 sg) 3

Ability to cause corrosion No 0

Yes 1

Volume changes (%) Low (> 25%) 1

Medium (2532%) 2

High (3350%) 3

Solubility No 0


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the equation (21- HE code) and then the value is averaged over the maximum

ranking value of 20 and finally multiplied with maximum scale of 5. This is shown

below in Equation (2.14) (Hassim and Edwards, 2006).

520

21

HEcodeHHI (2.14)

Material Harm Index (MHI)

The calculation of MHI index is based on the health ranking of National Fire

and Protection Agencies (NFPA) (see appendix B). Chemicals involved in process

route are ranked based on their reactivity, flammability and ability to cause health

hazard. The NFPA values range from 1 for the lowest hazardous condition to 4

indicating the highest hazardous condition. The value of NFPA is taken are summed

up (Hassim and Edwards, 2006).


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Estimating Workplace Concentration (WC)

Workplace concentration WC of released chemicals that might be inhaled by

employees at workplace is considered as a key value that must be estimated for PRHI

calculation. For the purpose of estimating WC, small leaks and fugitive emissions

are considered as two main sources of chemicals releases into workplace. Equation

(2.16 and 2.17) shows the calculation of the maximum and minimum workplace

concentration (WC) (Hassim and Edwards, 2006).

minmax

Q

FEMSWC

(2.16)

maxmin

QFEMSWC (2.17)

Where:

MS: is the quantity of airborne material produced from small leaks

FE: is the quantity of airborne material produced from fugitive emission


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Determining the Airborne Quantity produced from Small Leaks SM

Airborne material can be produced from either gaseous release, flashing liquid or

evaporating from the surface of a pool. Airborne material from gaseous release is

calculated by Equation (2.19) below (Dow Chemicals, 1998).

27310751.4

26

T

MWPaDAQ

avg

g (2.19)

Where:

AQg: is the mass rate of vapour due to gaseous release, kg s-1

D: is the diameter of the hole

Pa: is the absolute pressureMWavg: is the average molecular weight for materials in each process

route

T: is the operating temperature,0C


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vaporization process is adiabatic (Eq. 2.22) (Hassim and Edwards, 2006).

LTTHvCp

AQ bsf

(2.22)

Where:

AQf: is the mass rate of vapour due to flashing, kg s-1

CP: is the specific heat at constant pressure, kJ kg-1 0

C-1

HV: is the heat of vaporization of the liquid, kJ kg-1

TS: is the storage or operating liquid temperature, 0C

Tb: is the normal liquid boiling point,0C

For the airborne material evaporation from the surface of a pool, the first step

is to calculate the maximum surface area of the pool AP. the AP is calculated by

using a typical value of spill thickness which is 1 cm (Eq. 2.23) (Dow Chemicals,

1998). The airborne quantity evaporated from the pool surface, AQp is given by

Equation (2.24) below (Dow Chemicals, 1998).

100Wp

AP (2.23)


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Where:

FA: is the emission factor, kg h-1

source-1

N: is the number of pieces of equipment of applicable equipment type in

the stream.

After determining ventilation rate Q, Airborne Quantity produced from Small

Leaks SM, and Airborne Quantity produced from Fugitive Emissions FE, the

maximum and minimum workplace concentration WC can be calculated by applying

the Equations (2.16 and 2.17) respectively. Finally, the maximum worker exposure

concentration WECmax is calculated by applying the equation (2.15) (Hassim and

Edwards, 2006).

Estimating Occupational Exposure Limit (OEL)


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The OELavg is calculated by multiplying the OEL value of each chemical with

its mass fraction (MFi) and then summing up the products (Eq. 2.26). For the

purpose of calculating PRHI, the minimum OEL is used (Hassim and Edwards,

2006).

MFiOELiOELavg (2.26)

After calculating all values required, the PRHI is calculated by applying

equation (12) above. The value resulted of applying this equation will be large

number. In order to get a manageable number, the PRHI value is divided by 108.

Finally, each PRHI value for each process route is scaled to make it more presentable

and to facilitate comparison. This is done by dividing the PRHI value of a processroute by the highest PRHI value calculated Eq. (2.27) (Hassim and Edwards, 2006).

100)(

)(

)( higest

teprocessrou

scaledPRHI

PRHIPRHI (2.27)


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2.8.4.1 Formation of IOHI

The level of health hazard is determined by accounting for two main factors

which are; the potential for harm and the potential for exposure to chemical that

might have the potential to cause this harm. Based on that, inherent occupational

health index is formulated to include two indexes; Index for Physical and Process

Hazards (IPPH) and Index for Health Hazards (IHH) (Eq. 2.28). The Physical and

Process Hazards Index represents the potential for exposure to chemicals, whereas

the Health Hazards Index represents the harm or the health effects and resulted from

the exposure (Hassim and Hurme, 2010a).

HHPPHIOHI III (2.28)

Both IPPH and IHH contain various factors, each factor is considered as a sub-

index. For the IPPH, all the factors with the ability to either directly or indirectly

increase risks of injuries or health effects are identified These factors include; Mode


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Determining of IPPH

For the purpose of quantifying the IPPH, each sub-index is assigned with a

number representing a penalty Table 2.8. The value of each penalty is based on the

degree of the probability of exposure; the higher the probability, the higher the

penalty. Each sub-index penalty evaluates the inherent occupational health hazard

level of each chemical involved in a process route. For the operating pressure sub-

index (IP), the penalty range follows the pressure scale used by Heikkila (1999) in the

Inherent Safety Index. For the temperature sub-index (IT), the score is formed based

on steam exposure event (Lawton & Laird, 2003; Ng & Chua, 2002; Encyclopaedia

of Human Biology, 1997). After determining the penalties of the sub-indexes, the

Physical and Process Hazards Index (IPPH) is calculated by summing up the penalty

for all sub-indexes, as shown in Eq. (2.29).

)max(I+)(Imax+I+I+I=I CVTPPMPPH (2.29)


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since it describes a chronic type of toxicity and demonstrates the actual working

situation. Occupational Exposure Limit (OEL) set by the UK Health and Safety

Commission. This data is readily available for most chemicals in process industry

and it is easily attainable. For solid, the exposure limits classification is made based

on the COSHH Essentials (Maidment, 1998; Brooke, 1998; Russell et al., 1998).

Meanwhile, the score formation for vapor is based on the Mond Index (ICI, 1985).

In both solid and vapor, chemicals with lower OEL values are assigned higher

penalties since they are more harmful to humans health Table 2.9.

On the other hand, the IR calculation is based on the R-phrases that describe

the human health risk associated with the chemicals (the European Union Risk

Phrases, 2001). In the IOHI, R-phrases are divided into two groups of acute and

chronic toxicity. Both acute and chronic toxicity effect have different range of

penalty. The chemicals with chronic toxicity effect have a higher range of penalty

(maximum value of 5) whereas those with acute effect have (maximum value of 4) in

the R-phrase based sub-index (IR) (Table 2.8). The R-phrases are classified based on


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Table 2.8: Physical and process hazards (IPPH) sub-indexes (Hassim and Hurme,

2010a)

Factor Score formation Penalty

Mode of process, IPM

Continuous 1

Semi-continuous/semi-batch 2

Batch 3

Material phase, IMS

Gas 1

Liquid 2

Solid 3

Volatility,

IV

Liquid

and gas

Very low volatility (boiling point >

1500C)

0

Low (150 C boiling point > 50 C) 1

Medium (50 C > boiling point > 0 C) 2

High (boiling point 0 C)3

solid

Non-dusty solids 0

Pellet-like, non-friable solids 1Crystalline, granular solids 2

Fine, light, powder 3

Pressure, IP (bar)

0.55 0

550 1

50200 2

>200 3


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Table 2.9: Health hazards (IHH) sub-indexes (Hassim and Hurme, 2010a)

Factor Score formation Penalty

Exposure

limit, IEL

Solid

(mg/m3)

OEL> 10 0OEL 10 1

OEL1 2

OEL 0.1 3

OEL 0.01 4

Vapor(ppm)

OEL> 1000 0

OEL 1000 1OEL 100 2

OEL 10 3

OEL1 4

R-phrase, IR

Acute

No acute toxicity effect 0

R36, R37, R38, R67 1

R20, R21, R22, R65 2

R23, R24, R25, R29, R31, R41, R42,R43

3

R26, R27, R28, R32, R34, R35 4

Chronic

No chronic toxicity effect 0

R66 1

R33, R68/20/21/22 2

R62, R63, R39/23/24/25,

R48/20/21/223


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2.8.5.1 Basic Data for the calculation of IETH

In order to obtain IETH value, relevant data must be provided for the

calculation of IETH. Data required are as following:

- Predicted Environmental Concentration (PEC) (mol/m3),

- Atmospheric Toxicity Hazard (ATI),- Aquatic and Terrestrial Environmental Hazard (WHIi and THIi),

- Atmospheric, Aquatic and Terrestrial Impact Hazard (HAi, HWi and HTi)

- Toxicity impact severity scale values of chemical i in the atmospheric,

aquatic and terrestrial environment (YAi, YWi, YTi)

2.8.5.2 Calculation of IETH


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Figure 2.5 Unit world showing compartment volumes (Gunasekera and Edwards,

2006).

For the purpose of calculating PEC, Fugacity capacity constant, Zi, values

must be estimated for each compartment (example for Methyl methacrylate provided

in the Appendix C showing Z calculation in details). The Zi values are multiplied


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Where: qi is the inventory of the chemical present in the plant.

Atmospheric Toxicity Hazard (ATI), HAi, YAi

The percentage of an animal population that would be killed when exposed to a

released chemical in a local environment is used to estimate the atmospheric toxicity.

To estimate these percentage of animals killed, the probit Eq. (2-34) for the toxic

exposure (Crowl & Louvar, 2001) is used (Gunasekera and Edwards, 2006).

)(21 LCiiLnKiKXi (2-34)

To estimate the above two constants (K1 and K2), two acute inhalation LC

(Lethal Concentration) values of the chemical pollutant are used. When obtaining

the two constants values K1and K2, the Xi Value then is estimated but relating to the

PEC by using Eq. (2-35).


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Aquatic and Terrestrial Environmental Hazard (WHIiand THIi)

To obtain the two values WHIi and THIi, The specific water hazard index

(SWHIi) and specific terrestrial hazard index (STHIi) for a chemical i should be

estimated using Eqs. (2-37) and (2-38) as defined by Cave and Edwards (1997):

.6

50

i 10SWHI xLC

PSECWi

(2-37)

xxi

sifxwiwx

iWtLD

PECTDIPECTDIdSTHI

50

(2-38)

The aquatic and terrestrial environmental hazards, due to the total inventory

of chemical qi, are calculated using Eqs. (2-39) and (2-40):

iii SWHIqWHI (2-39)


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For the purpose of estimating HTi, the value THIi is used to obtain the value

of number of terrestrial Animals Killed AK which is termed as the terrestrial impact

hazard HTi, Eq. (2-43).

1266)(274 ii THILnAK (2-43)

Where, iTi AKH .

Toxicity impact severity scale values of chemical i in the aquatic and terrestrial

environment (YWi, YTi)

In same manner of obtaining YAi, both HWi and HTi values are applied on the impact

severity scale. Then by a linear relationship between the logarithmic environmental

hazard values and the impact severity scale, the intermediate values of YW i and YTi

are estimated. The environmental hazard value in this case is the number of dead

fish or dead terrestrial animals (Gunasekera and Edwards, 2006). The equations used


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Finally, the obtained CHTHi values for all chemicals involved in a particular

chemical process route are summed up to arrive at a total Inherent Environmental

Toxicity Hazard (IETH) Eq. (2-47)

m

iiCHTHIETH

1

(2-47)

2.8.6 Environmental Hazard Index (EHI)

The environmental hazard index (EHI) was developed by Cave and Edwards

(1997). It is used to rank process routes by estimating the environmental impact of a

total release of a chemical inventory. When evaluating the inherently

environmentally hazards of the chemicals involved in a process route, the

catastrophic failure scenario of the plant is assumed and the impacts on the


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2.8.6.1 Calculation of EHI

The calculation of EHI starts by estimating the predicted environmental

concentration (PEC) (mol/m3) for each chemical in the process. The values of PEC

are estimated by using a model called (unit world) proposed by Mackay and Paterson

(1990) and the fugacity level I model proposed by Mackay (2001). The unit world

model consists of six compartments which are; air, water, biota (aquatic life), soil,

sediment and suspended sediment (Figure 2-5). In this index method, the predicted

environment concentrations for the water (PECwi) and soil (PECsi) are calculated for

each chemical in the process (Gunasekera and Edwards, 2003). The calculation of

PEC is discussed previously in detail (see Section 2.8.5.2).

After calculating the PECwi and PECsi, the specific water hazard index

(SWHIi) and the specific terrestrial hazard index (STHIi) need to be calculated for

each chemical. The SWHIi and STHIi are calculated from the following equations:


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The calculation methods for SWHI and STHI are based on the CMU-ET

(Hovarth, 1995) and 11 (Vighi and Calamari, 1992) indices which were both

developed to assess the environmental hazard of a chemical. In both cases a score is

assigned which is proportional to the quantity of chemical and the potential

environmental damage of the chemical (Gunasekera and Edwards, 2003). The Data

required for the calculation is taken from (HSDB, Hazardous Substances Data Bank,

http://toxnet.nlm.nih.gov).

The values SWHI and STHI of a chemical are summed up to calculate the

specific environmental hazard index (SEHIi) of that chemical. The SEHI is

calculated using Equation 2-50.

iii STHISWHISEHI (2-50)

Then, the value of SEHIi for each chemical is multiplied with the total

inventory (Qi) of each chemical in the plant. Finally, the products of (Qi x SEHI i) are


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products. Examples include resins, adhesives and synthetic products such as nylon,

styrene and Styrofoam.

The purpose of this study is to correlate EHS indexes at inherent level in

order to make a selection of the best correlated method which can be used alone later

as a single method to evaluate all EHS properties at inherent level. In order to

achieve this, benzene production will be used as a case study. Two alternative

process routes for manufacturing benzene will be considered in this study. The two

routes are toluene hydrodealkylation process (HDA) based route and pyrolysis based

route.

2.9.1 Toluene Hydrodealkylation process (TDA)


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C7H8 + H2 = C6H6 + CH4 (2-52)

Toluene + Hydrogen Benzene + Methane

The main reaction is accompanied by the side reaction:

2 Benzene Diphenyl + H2 (2-54)

A mixture of methane, benzene, toluene, and hydrogen stream (outlet of R-

101) then leaves the reactor at 24.81bar and 671oC. The stream then goes through a

cooling process in E-102. In this heat exchanger the produced mixture (methane,

benzene, toluene, and hydrogen) is cooled down to 380C. At this point, most of

toluene and benzene in the stream is condensed. The outlet of E-102 containing two-

phase mixture of benzene, methane, hydrogen and toluene is then introduced into a

high-pressure phase separator V-102. In this flash drum the vapor and liquid are

separated. The separation takes place in a splitter at a temperature of 380C and 23.9

bar. The overhead is mainly hydrogen and methane, and the bottom is some of


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from V-104 as a top outlet stream. The top outlet contains hydrogen and methane

then combined with the other gases streams: the overhead of the first separator V-

102, and the overhead of the second separator V-103, which are combined to be

discharged as fuel gas. The bottom of V-104 contains benzene which is then pumped

by P-102A/B (4.4 bar) into E-105 for cooling and then transported into storage. Part

of benzene is also pumped back to the T-101 for further purification (reflux) (see Fig.

2.15) (Turton et al., 1998).

59


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Figure 2.6: Skeleton Process Flow Diagram (PFD) for the Production of Benzene via the Hydrodealkylation of Toluene ( Turton et al., 1998)

60


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Table 2.10 Summary of the material balance in the hydrodealkylation of toluene process route (TDA) (Turton et al., 1998)

Streamnumber

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Component Mole Flow (kmol/h)

Toluene 108.7 143.2 0.0 144 0.7 144.0 0.04 1.05 36.0 35.0 34.6 0.88 1.22 1.22

Hydrogen 0.0 0.0 286 735.4 449.4 735.4 25.2 651.9 652.6 0.02 0.0 0.0 0.02 0.0

Benzene 0.0 1.0 0.0 7.6 6.6 7.6 0.37 9.55 116.0 106.3 1.1 184.3 289.46 289.46

Methane 0.0 0.0 15 317.3 302.2 317.3 16.95 438.3 442.3 0.88 0.0 0.0 0.88 0.0

Mole Flow

(kmol/h)108.7 144.2 301.0 1204.4 758.8 1204.4 42.6 1100.8 1247.0 142.2 35.7 185.2 290.7 290.7

Mass Flow

(tonne/h)10.0 13.3 0.82 20.5 6.41 20.5 0.36 9.2 20.9 11.6 3.27 14.0 22.7 22.7

Stream

number15 16 17 18 19

Component Mole Flow (kmol/h)

Toluene 0.4 0.31 0.03 35.0 0.0

Hydrogen 0.0 178.0 0.67 0.02 0.02

Benzene 105.2 2.85 0.26 106.3 0.0

Methane 0.0 123.05 3.10 0.88 0.88

Mole Flow

(kmol/h)105.6 304.2 4.06 142.2 0.90

Mass Flow

(tonne/h) 8.21 2.61 0.07 11.5 0.01

61


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2.9.2 Pyrolysis gasoline-based route

The cracked naphtha product which is also commonly known as pyrolysis

gasoline, contributes to the manufacture of aromatics by 26% taking second place

after catalytic reforming which produces 68% of aromatics [30]. Pyrolysis gasoline

typically consists of C6-C8 fraction aromatics, heavier aromatics with C9-C12 fraction,

and non-aromatic cyclic hydrocarbons (naphthenes) containing 6 or more carbon

atoms. Pyrolysis gasoline contains 60% aromatics, of which, 50% is benzene but it

also contains up to 5% diolefins [31]. This makes the compound unstable. However,

pyrolysis gasoline contributes to 48% of the world benzene production [30].

The pyrolysis gasoline has a high content of unsaturated components such as

olefins and di-olefins. Containing such unstable components makes it difficult to

desulfurize pyrolysis gasoline. Therefore, pyrolysis gasoline should go through

hydrogenation process to be free of sulphur compounds (Mostoufi et al., 2005). The

62


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hydrogenated liquid containing BTX components. Unreacted hydrogen and other

light components leave via the overhead of the separator whereas the hydrogenated

liquid leaves via the bottom to the stabilizer. Since the overhead contains mainly

unreacted hydrogen, some of the top stream is collected as fuel gas and some is

recycled back to the furnace. In the stabilizer, traces of unreacted hydrogen and

other light hydrocarbon are drawn from the overhead as fuel gas. The bottom

product from the stabilizer which is the hydrogenated BTX (C6-C8) is then sent into

splitter. In the splitter, benzene is separated from C7-C8 fraction (toluene and xylene)

and transported into a feed tank for further processing. The C7-C8 fraction (toluene

and xylene) leaves the bottom of the splitter and combined with the C 5 fraction

coming from the depentanizer column and sent to refinery.

Benzene is then introduced to further process which starts with feeding

benzene into the extractive distillation column. In this column, an extraction solvent,

such as N-formyl morpholine (NFM), is used. Benzene is dissolved in the extraction

solvent and separated from non-aromatics components which are called raffinate.

63


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Figure 2.7: Borealis polymer oy benzene plant at Provoo (Hassim et al., 2010)

64


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Table 2.11 Summary of the material balance in the pyrolysis gasoline hydrogenation process route (Pygas)

Unit in flowsheet DepentanizerBTX-Tower

DPG-2reactor

Flashdrum

Stabilizer Splitter ED-columnStripperColumn

DistillationColumn

Clay-tower CT

Standard process

moduleDistillation

Vacuum

DistillationPFR Flash Distillation Distillation Distillation

Vacuum

StripperDistillation

Ion

exchanger

Ion

exchanger

Module stream Feed (kg/h) Feed (kg/h)Feed

(kg/h)

Feed

(kg/h)Feed (kg/h) Feed (kg/h) Feed (kg/h) Feed (kg/h) Feed (kg/h) Feed (kg/h) Feed (kg/h)

Hydrogen 0 0 1713 1679 2 0 0 0 0 0 0

C6 4862 3974 4305 4411 4045 4040 12797 - - - -

C7 569 571 506 510 497 497 0.053 0 0 0 0

Benzene 7339 7305 7613 7537 7189 7186 18213 18854 18023 18023 18023

Mole Flow (kg/h) 24000 11850 14137 14137 11733 11723 31010 18854 18023 18023 18023

Mass Flow

(kmol/h) 284.6 206.9 1099.4 1082.5 147.6 145.6 388.94 241.377 230.73 230.73 230.73

Phase L L V V & L V(trace) & L L L L L L L

Temperature (c) 80 107 230 27 97 163 19.4 178.4 47.7 47.7 47.7

Pressure (Kpa) 600 194 2600 2400 890 854 500 257 33 33 33

65


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2.9.3 Catalytic reforming of naphtha

Naphtha feed normally contains about 300 chemical compounds. However,

Components like n-heptane, n-octane, methylcyclohexane, toluene, ethylbenzene,

and xylenes are usually present in significant concentrations. These components

represent more than 63% of naphtha cut (Yang et al., 2008).The other components

are present in much smaller amounts. All the compounds are present in the naphtha

feed as paraffins (4070 wt. %), naphthenes (2050 wt. %), aromatics (220 wt.

%) and olefins only (0 2 wt. %). This is the composition of typical straight-run

medium naphtha (Yang et al., 2008).

As shown in Figure 3 for the reforming process, naphtha feed is heated up to

400 540 C and then fed under pressure of 10 20 (bar). Naphtha feed passes

through series of catalyst-equipped reactors and furnaces between the reactors to

keep the reactions temperature at desired level (Hassim et al., 2010). The reactions

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Figure 2.8: Skeleton Process Flow Diagram (PFD) for the Production of Benzene via the catalytic reforming of naphtha

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Table 2.12 Summary of the material balance in catalytic naphtha reforming process route

Unit in flowsheet Reactor 1 Reactor 2 Reactor 3 Flash drum Stabil izer Spli tter ED-column Benzene Column

Module stream Feed (kg/h) Feed (kg/h) Feed (kg/h) Feed (kg/h) Feed (kg/h) Feed (kg/h) Feed (kg/h) Feed (kg/h)

Hydrogen 763.838 763.838 805.03 805.03 0 0 0 0

C1C2 613.797 613.797 613.797 613.797 0 0 0 0

C3 818.398 818.398 818.398 818.398 818.398 818.398 818.398 0

C4 285.589 285.589 285.589 285.589 285.589 285.589 285.589 0

n-Hexane 14878.99 13391.093 7191.513 7191.513 7191.513 7191.513 7191.513 0

Methyl cyclohexane 4463.697 1487.899 247.983 247.983 247.983 247.983 247.983 0

Benzene 1870.402 3400.732 5951 5951 5951 5951 5951 5951

Toluene 3585.228 6518.595 11407 11407 11407 11407 11407 11407


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CHAPTER 3

METHODOLOGY

3.1 Introduction

The research methodology introduced in this section serves as a method used

for achieving the purpose of this study. The purpose of this study is to correlate EHS

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69

START

Project conception

Literature review ThesesArticles

Specifying the methods

Methods for evaluationMethods for correlation

Linear regression 6 index-based methods

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70

3.2 Research conception

The conception of the research project was generated based on the study

conducted by Hassim et al. (2008). However instead of 12 based index methods

used in their work, only six were considered in this study. These six index methods

are pure inherent based indexes which are selected to totally focus on inherentproperties. Moreover, the six indexes consider the parameters which are based on

the information available in the early design stage which makes these indexes

applicable to early design stages. Besides the main goal of this study, the correlation

between the methods in Hassim et al. (2008) work was also recalculated using the six

methods selected and then the results from both studies were fairly compared and

further analysed.

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71

3.4 Data collection

Articles and theses of the studies that have been conducted on the same area

of this studys interest were collected to gather information required for the relevant

literature. The literature review was constructed to encompass all important and

relevant elements such as the concept of inherent safety (IS) and the development

and extension of this concept, the index methods developed for the evaluation of

IEHS properties, the six index based methods used in this study, the selected case

study and the previous comparison-based studies. All these elements are considered

to be necessary for understanding the area of this study.

3.5 Selection of index methods for the assessment

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(Hassim et al., 2006) were selected. These methods assess the inherent occupational

healthiness of a process. The assessment is based on the activity involved in the

operation also properties of the chemicals involved in the process and operating

conditions. The PRHI considers the fugitive emissions and the occupational

exposure limit as important variables to conduct the evaluation.

The inherent environmental evaluation methods are; The environmental

hazard index (EHI) (Cave and Edwards, 1997), and Inherent Environmental Toxicity

Hazard; IETH (Gunasekera and Edwards, 2006). These index methods consider the

catastrophic incident scenario and evaluate its short-term impacts on the

environment.

3.6 Understanding the principles of the methods

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Time scale of the impacts can be either short-term or long-term impacts.

Safety methods consider the short-term effects. On the other hand, occupational

health methods used in this study consider both short and long-term impacts. For the

environmental methods used in this study, the atmospheric hazard index (AHI)

considers both short and long-term impacts whereas inherent environmental toxicity

hazard (IETH) considers only the short-term impacts.

Table 3.1: Parameter types used in the index methods (Hassim et al., 2008)

Parameter ISI iSafe PRHI IOHI AHI IETH

Reaction chemistry X X

Inventory X X X X

Material state X X X X

Material toxicity X X X X X X

Process temp. & pres. X X X X

Proc. equipment X X X

Fugitive emissions X

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3.7 Correlation method

Pair-wise linear regression was used in this study as a correlation technique to

correlate between indexes values that were obtained for benzene process routes. The

coefficient (R2) is used as an indicator of the correlation between the methods

compared. The higher the value of R2, the stronger the correlation between the

correlated methods will be (Hassim et al., 2008). The method that has high

correlation, represented as R2, with other methods from all EHS aspects can be

selected as the best correlated method that can represent the three EHS aspects.

3.8 Simulation method


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CHAPTER 4

RESULTS AND DISCUSSION

This section discusses all the results of the study, which were obtained by

applying the six selected index methods on the three process routes of benzene

synthesis case study. After understanding the criteria and requirement of all the

index methods in detail, the first step was to collect or estimate the data needed for

the index calculation. The data for all the parameters is provided in Appendices D

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4.1.1 Case study 1: Toluene hydrodealkylation process route (TDA)

In the TDA process, toluene reacts with hydrogen to produce benzene and methane.

The reaction takes place at 630 C and 23 bar (Turton et. al. 1998). The TDA

process route comprises of two non-catalytic vapor-phase reactions. The first

reaction is the only main reaction which is accompanied by the side reaction as

shown below. The TDA process route is described in more details in Section 2.9.

Main reaction: Toluene + Hydrogen Benzene + Methane (4.1)

Side reaction: Benzene Diphenyl + Hydrogen (4.2)

4.1.2 Case study 2: Pyrolysis gasoline hydrogenation process route (Pygas)

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transported as a top outlet from BTX distillation column to the reactor for

hydrogenation. The hydrogenation in the reactor is done in vapor phase at

temperature of 230 C and pressure of 26 bar. However, the bottom outlet is then

transported through different distillation columns for more purification and then to

produce benzene (the PFD and detailed description of the process is provided in

Chapter 2). The formula below shows the hydrogenation of cyclohexene.

C6H10 + H2 C6H12 (4.3)

4.1.3 Catalytic reforming of naphtha process route

Naphtha feed normally contains about 300 chemical compounds.

Components like n-heptane, n-octane, methylcyclohexane, toluene, ethylbenzene,

and xylenes are usually present in significant concentrations These components

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final reactor. The formulas below show some of the reactions that take place in the

reactors.

266146 4)( HHCHCHexanenlizationDehydrocyc (4.4)

267147 3)( HHCHCohexaneMethylcyclationDehydrogen

(4.5)

The product from the last reactor is called reformate which is transported into

a high-pressure separator to remove the light cut C1-C2 (Antos and Aitani, 1997).

Reformate is then sent via the bottom outlet into a stabilizer for more purification by

separating the C3-C4 cuts from reformate cut (C5-C8+) (Yang et al., 2008).

Reformate is then transported into a reformate process unit for further processing to

produce benzene as the desired product. More details on catalytic naphtha reforming

process route are provided in Chapter 2.

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4.2.1 Inherent safety index (ISI) calculation

As mentioned earlier in Chapter 2, the inherent safety index (ISI) consists of

two main indexes. The chemical inherent safety index (ICI) and process inherent

safety index (IPI). For this case study, the calculation of the ICI index is summarized

in Table 4.1.

Table 4.1: Calculation of the sub-indexes of chemical inherent safety index ICI for

the TDA, Pygas and naphtha reforming case studies

TDA process routesCalculations of the ISI

Sub-indexes of the ICI

Chemicals IINT ICOR IRM IRS IF IE IT IFET

Main

reaction Toluene 3 0

4 0

3 1 2 5

Hydrogen 4 0 NA 4 0 4

Benzene 3 0 4 1 4 9

Methane 4 0 4 1 0 4

Penalty of worst chemical 4 0 4 0 4 1 4 9

Total ICI for the step; ICI = 4 + 0 + 4 + 0 + 9 = 17

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corrosiveness property on metals; therefore the ICOR is assigned a penalty of (0).

This value is determined based on the penalty system of the ICOR which is provided

in Chapter 2 (see Table 2.4). In the TDA case study, the two heat reaction sub-

indexes for main IRM and side reactions IRS were calculated to be (- 4134.65 j/g) and

(0 j/g) and hence are given penalties of 4 and 0, respectively. In Pygas and naphtha

reforming case studies no side reactions take place so that only the heat reaction for

the main reaction were calculated to be - 1405 j/g for Pygas and 3005.8 j/g for

naphtha reforming. Hence, the IRM was given a penalty of 3 for each. The heat

reaction for the main and side reactions was calculated using Equation (4.3). The

calculation in more details is provided in Appendix D1.

tsreactsreac

f

productdproducts

f HHHtantan

(4.3)

Where;

H, is the heat of a reaction

Hf, is the heat formation of a chemical

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9414 benzeneTEF

III (4.4)

After determining the penalties for all chemical sub-indexes, the ICI value was

obtained for each process route by applying Equation (2.2) as shown in Table 4.1. In

the TDA and naphtha reforming case studies the ICI was given a value of 17 for each.

On the other hand, ICI was given a value of 16 in the Pygas case study. This can be

i

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