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Flammability Limits StudyofVapour Mixtures
above Crude Oil at Low Temperatures
by
DebbieAloysius Sitiol
Dissertation submittedin partial fulfilmentof
the requirements for the
Bachelorof Engineering (Hons)
(Chemical Engineering)
MAY 2012
Universiti Teknologi PETRONAS
Bandar Sen Iskandar
31750 Tronoh
Perak Darul Ridzuan
CERTIFICATION OF APPROVAL
Flammability Limits Study ofVapour Mixtures
above Crude Oil at Low Temperatures
by
Debbie Aloysius Sitiol
A project dissertation submitted to the
Chemical Engineering Programme
Universiti Teknologi PETRONAS
In partial fulfilment of the requirements for the
BACHELOR OF ENGINEERING (Hons)
(CHEMICAL ENGINEERING)
(Dr. Mohanad EI-Harbawi)
W.W0H^ADEL-«ARB*1
Unbend
UNIVERSITI TEKNOLOGI PETRONAS
TRONOH, PERAK
MAY 2012
CERTIFICATION OF ORIGINALITY
This is to certify that I am responsible for the work submitted in this project, that the
original work is my own except as specified in the references and
acknowledgements, and that the original work contained herein have not been
undertaken or done by unspecified sources or person.
!&>
DEBBIE ALOYSIUS SITIOL
Abstract
Study of fire and explosion is very important mainly in oil and gas industries due to
the severity of fire and explosion incidents. Fire and explosion could cause property
damage and loss of lives. In this work, investigation had been carried out on the
flammability of crude oil at low temperatures 35°C, 40°C and 50°C. Hydrocarbon
components derived from refinery storage was assessed. The oil-liquid phase was
analyzed using Headspace-Gas Chromatography (HS-GC) and Gas Chromatography
Mass Spectrometry (GC-MS) to examine the composition of the sample.
Hydrocarbon compounds ranging from C6 to C9 were detected. Lower Flammability
Limits (LFLs) and Upper Flammability Limits (UFLs) for individual components
were calculated at each temperature using stoichiometric concentration method
proposed by Zabetakis et. al. Flammability limits of themixture, LFLmiX and UFLn^
were calculated using the Le Chatelier equation. Limiting Oxygen Concentration
(LOCs) for each temperature are calculated using Hansen and Crowl method, while
the estimation ofLOC for the mixtures (LOC„ux) is calculated using Zlowchower and
Green method. Flammability diagramwas constructed which is used to determinethe
flammability of the mixture at respective temperature. It is found that as the
temperature increases, the flammability range of vapours above crude oil increases
too. The findings of this studymay assist in minimizing fire hazards associated with
presence ofhydrocarbon vapours.
Acknowledgements
This dissertation for "Flammability limits Study of Vapour Mixtures above Crude
Oil at Low Temperatures" would not have been possible without the support,
guidance andmotivation from various individuals.
My utmost gratitude to my project supervisor, Dr. Mohanad El-Harbawi for his
continuous support and guidance throughout the project duration. He has beenvery
patient and committed in helping me to complete this project. His immeasurable
guidance has provided me a good opportunity to contribute to the success of this
research.
I would like to thank the Final Year Project Coordinators, Dr. Norhayati Bt. Mellon
and Puan Asna Bt. M Zain for disseminating required information effectively and
also for giving moral support to the students. Same goes to all lecturers and staffs of
Chemical Engineering Department, Universiti Teknologi PETRONAS.
Deepest thanks to Dr. IvyChai Ching Hsia and herteam from PETRONAS Research
Sdn. Bhd. for their support and cooperation in conducting some of the experimental
work needed in this research project.
Not forgetting, my family members and friends who have continuously given moral
support and encouragement to me to complete this project. Thank you for walking
beside me through the joy and rough patches of my life.
Thank You all.
u
TABLE OF CONTENTS
LIST OF FIGURES iv
LIST OF TABLES iv
ABBREVIATIONS AND NOMENCLATURES v
CHAPTER 1: INTRODUCTION 1
1.1. Background 1
1.2. Problem Statement 2
1.3. Objective 3
1.4. Scope of Study 3
CHAPTER 2: LITERATURE REVIEW 4
2.1. Introduction 4
2.3. Flammable Materials 7
2.4. Flammability Limits 8
2.5. Limiting Oxygen Concentrations 10
2.6. Flammability Diagram 10
2.7. Inherent Safety 12
CHAPTER 3: METHODOLOGY 13
3.1. Material and Method 13
3.2. Experimental and Theoretical Methods 13
3.2.1. Mole Fraction 15
3.2.2. Flammability Limits 15
3.2.3. Limiting Oxygen Concentration 18
3.2.4. Flammability Diagram 19
3.3. Gantt Chart 20
CHAPTER 4: RESULTS AND DISCUSSION 21
4.1. Components Identification 21
4.2. Mole Fraction in Vapour Phase 29
4.3. LFL5UFLandLOC 30
4.4. Flammability Diagram 33
4.5. Inherent Safety 35
CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS 37
5.1. Recommendations 37
References 38
Appendices 42
m
LIST OF FIGURES
Figure 1: Fire Triangle 7
Figure 2: Flammability Diagram of Methane at 25°C and 1 atm (Brooks & Crowl,
2007) 11
Figure 3: Methodology flowchart 14
Figure 4: Chromatogram at 35°C 23
Figure 5: Chromatogram at 40°C 24
Figure 6: Chromatogram at 50°C 25
Figure7: Mole fraction in vapourphase at (a) 35°C (b) 40°C and (c) 50°C 30
Figure 8: LFLmix vs. Temperature 32
Figure 9: UFLmjX vs. Temperature 32
Figure 10: LOCmix vs. Temperature 32
Figure 11:Flammability Diagramat 35CC 33
Figure 12: Flammability Diagram at40°C 34
Figure 13: Flammability Diagram at 50°C 34
LIST OF TABLES
Table 1: Type oftank contents (J. I. Chang & Lin, 2006) 5
Table 2: Type ofaccidents (J. I. Chang & Lin, 2006) 5
Table 3: Major Tank Incidents between 1963 and 2002 (J. I. Chang & Lin, 2006) 6
Table 4: Components at 35°C 26
Table 5: Components at 40°C 27
Table 6: Components at 50°C 28
Table 7: Flammability Limits and LOC at 35°C 31
Table 8: Flammability Limits and LOC at 40°C 31
Table 9: Flammability Limits and LOC at 50°C 31
Table 10: LFL, UFL and LOC at each temperature 32
iv
ABBREVIATIONS AND NOMENCLATURES
AIChE The American Institute ofChemical Engineers
AIT Autoignition Temperature
BTX Benzene, Toluene, Xylene
FP Flash Point
GC-MS Gas Chromatography-Mass Spectroscopy
HS-GC Headspace-Gas Chromatography
LFL Lower Flammability Limit
LFLmix Lower Flammability Limit ofmixture
LOC Limiting Oxygen Concentration
LOCmix LimitingOxygenConcentration ofmixture
LNG Liquefied Natural Gas
MIE Minimum Ignition Energy
UFL Upper Flammability Limit
UFLaux Upper Flammability Limit ofmixture
FP Flash Point
LPG Liquefied Petroleum Gas
CHAPTER 1
INTRODUCTION
1.1. Background
Crude oil is a mixture of hydrocarbons in different lengths and structure. It ranges
from the lightest compound to complex paraffin and aromatic molecules. Complex
molecules play major role in defining the properties and processing method of
different types ofcrude oil (Speight & Ebrary, 1999). Oil refining converts crude oil
into various products depending on its composition. Most common end-product of
refinery are petroleum gas, gasoline, naphtha, kerosene, gas oil and lubricating oils.
In the industries, incidents that can cause toxic effects, fire or explosion couldresults
in property damage, lost of production, environmental impact and serious injuries
(AIChE, 2010b). With respect to hydrocarbon components, highly flammable
compounds such as benzene, toluene, ethylbenzene and xylenes may be present and
they pose significant threat of fire hazard. Light ends components until medium
naphtha fractions are most flammable components. Some of these compounds can
evaporate and turn into vapour form at ambient temperature and atmospheric
pressure, thus formingflammable mixtureswith air.
In the presence of sufficient amount of fuel, oxidizer and ignition source, vapour
mixture will burn if its concentration is in between Lower Flammable Limit (LFL)
and Upper Flammable Limit (UFL). The presence of flammable mixtures exposes
storage system to the possibility of fire and explosion events.
1.2. Problem Statement
Crude oil in refineries contains hundreds of substances namely hydrocarbon. At
ambient temperature and atmospheric pressure, some of these components could
vaporize to the atmosphere forming vapour mixtures. Different components in crude
oil vaporize at different temperature and pressure. Vapour mixture might be
flammable depending on the composition of the vapourmixture.
Industries especially the ones thatare involved in theoil andgas operation havebeen
operating at a risk by maintaining operations of flammable vapour mixtures within
flammability ranges especially in storage areas. This has beena threat to the industry
where many fires and explosion incidents have occurred in the past 50 years
involving such flammable vapour mixtures.
Common practice in determining flammability of dustandvapour is by using closed
explosion chamber with various volumes. 20-L sphere explosion chamber is known
internationally as laboratory test apparatus in determining the combustion
characteristicsofcombustible dusts and gases (Wang et al, 2010).
Although sphere explosion chamber are internationally recognized, it is highly costly
to purchase the apparatus. Experts are needed to operate the apparatus as well.
Besides that, it is also expensive to run the sphere explosion chamber to determine
the flammability ofvapour mixture.
This work is aimed on the study of the effect of temperature on the flammability of
hydrocarbon mixtureby incorporating fundamentals of thermodynamics with process
safety concept.
1.3. Objective
The objectives of this project are:
1. To estimate the UFLn^, LFLmix and LOCmn of hydrocarbon vapour mixtures
above refinery crude oil by using fundamental of thermodynamics and
process safety concept
2. To determine the flammability range of vapour mixture above crude oil at
differentlow temperatures based on flammability diagrammethod
3. To investigate the possible presence of flammable mixture in oil refinery
storage spaces and recommend safetymethods to prevent fire and explosion
incidents
1.4. Scope of Study
Crude oil in refineries could volatize and form flammable vapour mixture. When
flammable vapour mixture is exposed to ignition source and oxidizer, fire or
explosion will occur. Experimental work will be conducted to determine the
components of crude oil by using Headspace-Gas Chromatography (HS-GC) and
Gas Chromatography - Mass Spectrometry (GC-MS). Components of the crude oil
in vapourphase will be determined by applyingfundamental ofthermodynamics.
LFLmix and WL^ at low temperatures (35°C, 40°C and 50°C) will be calculated
using Le Chatelier equation (Le Chatelier, 1891) to predict the range of flammability
of the vapour mixture. LOCn«x is estimated using Zlochower & Green (2009)
method. Lastly, flammability diagram will be constructed to determine the
flammability of the sample.
The results from this work will be used to recommend safety methods to prevent the
flammable mixture from occurring in storage system. This work can contribute to
minimizing the loss of production, property damage and ensuring safety of
personnel.
2.1. Introduction
CHAPTER 2
LITERATURE REVIEW
Fires, explosions and toxic releases are common accidents in chemical plant.
Accident resulting from fires andexplosions canbe prevented if engineers know well
about the fire and explosion properties of materials (Crowl & Louvar, 2011).
Zabetakis (1965), also mentioned that knowledge on flammability characteristics
could prevent unwanted fires and gas explosion.
Fire and explosion incidents in oil refineries are not uncommon. Study shows that
74% of accidents occurred in petroleum refineries, oil terminals or storage and 85%
of the accidents are fire and explosion (J. I. Chang & Lin, 2006).
Refineries are classified as majorhazard installation as it possess a largeinventory of
hazardous material which exceed the threshold quantities (Shalufet al, 2003). There
are various complex processes and hazardous components' storage in a refinery. As
mentioned by Chang and Lin (2006), storage tanks in refineries and chemical plants
contain flammable and hazardous chemicals which are stored in large volume. At
any event where there is leakage or release ofthese hazardous materials, there will be
potential risk of fire and explosion.
Understanding the properties of flammable and hazardous material is critical.
Unwanted fire and explosion incident canbe prevented by knowing the flammability
limits ofthe hazardous material.
2.2. Previous Accidents
Chang and Lin (2006) had reviewed 242 accidents that occurred in industrial
facilities over the last 40 years. Based on their findings, storage tanks accidents
occurrence is more frequent in petroleum refineries with weightage of 47.9%
followed by terminal and storage area (26.4%).
Types of tank contents are provided in Table 1 where crude oil and oil products
storage tank is themajor contributor to storage tank accidents.
Tabic 1: Type of tank contents (J. I. Chang & L n,2006)
Year1960-
1969
1970-
1979
1980-
1989
1990-
1999
2000-
2003Total
Crude Oil 6 8 17 23 12 66
Oil Products (Fuel oil,diesel, kerosene, lubricants)
3 7 14 19 16 59
Gasoline/Naptha 0 13 17 21 6 55
Petro-Chemicals 3 3 4 11 6 27
LPG 3 3 1 5 1 15
Waste oil water 2 2 0 4 1 9
Ammonia 0 0 0 0 3 3
Hydrochloric Acid 1 2 3
Caustic Soda 3 3
Molten Sulfur 1 1 2
Total 17 36 53 85 51 242
Also in Chang and Yin (2006) study, fire and explosion together carried 85% of the
totalcases. Statistics on types of accidents is illustrated in Table2.
Table:.: Tvpco1'accidcn(s(J. . Chun"& .in, 2006)
Year1960-
1969
1970-
1979
1980-
1989
1990-
1999
2000-
2003Total
Fire 8 26 31 59 21 145
Explosion 8 5 16 22 10 61
Spill 0 5 3 2 8 18
Toxic Gas Release 0 0 2 1 10 13
Misc. 1 1 1 2 5
Total 17 36 53 85 51 242
Meanwhile Table 3 is an extractionfrom Ching and Yin (2006)study. Therewere 10
major storage tanks incidents that were recorded from 1963 to2002.
Tab c 3: Major Tank incidents between l%3 and 2002 (J. I. Chang & Lin, 2006)
No. Date Location Loss Description
1 2/24/86Thessaloniki,Greece
330
Sparks from a flame cutting torch ignitedfuel from a tank spill in a dike of a fuel tank.The fire spread to other areas resulting indestruction of 10 out of 12 crude oil tanks.
2 4/3/77 UMM said Qatar 179
A 260 000-barrel tank containing 236 000barrels of refrigerated propane at -45°Ffailure massively. An adjoining refrigeratedbutane tank and most of the process areawere also destroyed by fire.
3 1/20/68Pernis
Netherlands141
Frothing occurred when hot oil and wateremulsion in a slop tank reacted with volatileslop, causing a violent vapour release andboil-over. The fire destroyed 3 hydrocarbon,a sulphur plant and 80 storage tanks
4 9/1/79Deer Park,Texas, USA
138
Nearly simultaneous explosion abroad a 70000 DWT tanker off-loading and in an 80000 barrel ethanol at a refinery occurredduring an electric storm.
5 5/30/78Texas City,Texas, USA
120
An unidentified failure led to the release of
light hydrocarbons which spread to anignition source. 11 tanks in this alkylationunit were destroyed
6 8/20/81 Kuwait 73
Fire destroyed 8 tanks and damaged severalothers. The cause of the fire has not beendisclosed
7 9/14/97Vishakhapatnam,India
64
LPG ignited during tank loading from a ship.A thick blanket of smoke spreading panicamong the residents. 15 storage tanks burnedfor two days
8 12/21/85 Naples, Italy 60
24 out of 32 tanks at a marine petroleumproducts terminal destroyed by fire thatbegan with a tank overfill. Explosion causedcomplete destruction of the terminalbuildings and nearby industrial andresidential structures.
9 1/7/83Newark, NewJersey, USA
52
An overfilling of a floating roof tank spilled1300 barrels of gasoline into the tank dike.The vapour cloud carried by wind to anearby incinerator and was ignited. 2adjacent tanks and terminal was destroyed.
10 5/26/83Prodhoe Bay,Alaska, USA
47
A low-pressure NGL feed drumruptured in acrude oil station, resulting in fire damage toone third of the module and exterior of
surrounding structure within 100 ft.
2.3. Flammable Materials
Flammable gases and liquids can be characterized based on its properties such as
Lower flammability limit (LFL), upper flammability limit (UFL), limiting oxygen
concentration (LOC), flashpoint (FP), minimum ignition energy (MIE) and
autoignition temperature (AIT) (Crowl, 2012). Fuel combustion always occurs in
vapour phase. Flammable liquids will be volatilized to vapour phase andflammable
solids are decomposed to vapour and then onlythe vapourphasewill be ignited.
The essential element for fire to occur is fuel, oxidant (which is mostly oxygen) and
also an ignition source/heat. In theevent whereby one oftheelements is missing, fire
will not occur. Fire triangle (Figure 1) is a graphical representation of the three
elements that need to present for a fire to start.
Figure I: Fire Triangle
Although all three elements are present, there are certain concentration limits for a
fire to be ignited. Fuel and oxidant needs to be available in certain concentration
while ignition source must be strong enough to start the fire. The most common
oxidant in fire occurrence is oxygen.
Crude oil is made of mostly of carbon (80-87%) and hydrogen (10-15%). These
compounds are called as hydrocarbons. In crude oil, hydrocarbon exists in various
length and structures. Carbon atoms serve as the backbone with hydrogen atoms
surrounding it. Hydrocarbon chains can be broken and linked in various ways by
different processes. Longhydrocarbon chains can be restructured into shorter chains
and vice versa. Besides hydrocarbons, small amount of other elements in crude oil
are sulphur (0-10%), nitrogen (0-1%) andoxygen (0-5%).
Crude oils characteristics and types are depending on its geographical location.
Crude oils from the South America are thick and tarry while crude from North Africa
are lighter with lower density (BP Educational Service, 2006).
In general, crude oil is highly flammable. It can be ignited easily by heat, sparks or
flames. In vapour form, it may form combustible mixtures with contact of air. Crude
at temperature lower than its boiling point will give up vapour to the surface until the
vapour is in equilibrium with the crude oil. Highly flammable components in crude
oil are BTX (Benzene, Toluene and Xylene), ethylbenzene, cyclohexane etc
(CountryMark, 2009).
2.4. Flammability Limits
Flammable vapour mixture mixed with air in the range of flammable concentration is
likely to be caught on fire with the presence of ignition source (Carson & Mumford,
2002). Knowledge on the flammability limit of vapour mixture could prevent the
formation of vapour mixture in the flammable range. Characterisation of chemical
substances are important to determine its flammability to prevent unwanted fire and
explosion accident due to poor handling ofthe chemicals.
Flammable vapour and volatile liquids are highly hazardous when in contact with air
within the flammable range. Each component in the mixture has its own flammability
limits. Flammability limits measure the ability of a flame to propagate away from the
ignition source.
Lower Flammable Limits (LFL,-) and Upper Flammable Limits (UFL,) are the lower
and upper flammability limit respectively for component i in fuel and air. Below the
LFL, there is not enough fuel to cause ignition (too lean) while above the UFL, there
is not sufficient oxygen to promote ignition (too rich). Vapour mixture will be
categorized as flammable if its concentration is in the flammable range which is in
between LFL and UFL.
Several experimental works have been conducted to predict the flammability limits.One well known apparatus to obtain flammability data is a 20-litres spherecombustion apparatus; Brooks and Crowl (2007) studied experimentally on vapourflammability above aqueous solutions of ethanol and acetonitrile. Liekhus et al.(2000), conducted experiments to predict the flammability ofgas mixtures containinghydrogen and flammable or non-flammable volatile organic compounds (VOCs) inair. Cashdollar et al. (1992), performed experiment using 120-L chamber under
quiescent and turbulent conditions to study on the flammable gas generation fromnuclear waste tanks. Petersen et al estimated LFL ofcrude oilvapour from relieftank
vents by constructing 1:50 scaled models ofrelief tanks (Petersen et al, 1997).
Mixture concentration outside the range of the flammable limits will not ignite.
Basically, wider flammable range poses higher risk of fire. Flammable range isclosely related to temperature. According to (Zabetakis et al, 1958), flammable
ranges increaseswith temperature.
Estimation of flammability limits is required for some situation where experimental
data is not available. LFL/ and UFL, of many hydrocarbon vapours are found to be a
function of stoichiometric concentration (Jones, 1938). Flammability characteristics
of about 500 different substances of pure hydrocarbon fluids were predicted using
structural group contribution method (Albahri, 2003). Meanwhile, Crowl &
Mashuga, (1999) predicted flammability zone using calculated adiabatic flame
temperatures (CAFT).
Empirically derived equations are used to estimate LFL,- and UFL, at different
temperatures. Various components in mixtures' flammability limits (LFLm/* and
UFLmfc) are computed using Le Chatelier equation (Le Chatelier, 1891) which are
still widely used today. Hanley (1998) correlated LFIw with a quantity
representative of the heatevolved during combustion (Vidal et al., 2004).
In recent studies, El-Harbawi et al. (2012) predicted the flammability of vapours
above refinery wastewater laden with hydrocarbon mixtures. The flammability
estimation was conducted by correlating thermodynamics with process safety
concepts (El-Harbawi et al, 2012).
2.5. Limiting Oxygen Concentrations
Limiting oxygen concentration (LOC) is the minimum oxygen concentration
required to propagate flame. Below LOC, reaction will not be able to generate
sufficient energy to heat the mixture. Thus, mixture could not self-propagate.
Reducing the concentration of oxygen could prevent fire and explosion from
occurring. Razus et al, (2004) estimated LOC using values of lower explosion limit
of fuel-air mixture and also calculated adiabatic flame temperature (CAFT).
Correlation was establishedbetween computed CAFT for fuel-air-nitrogen mixtures
at LOC and CAFT at LEL, for a large numberof flammable gases and vapors.
In the absence of literature data, LOC can be estimated using the stoichiomety from
the combustion reaction and LFL. Besides that, LOC can be estimated using method
proposedby Hansen& Crowl (2010);
LOC^.(LFLi-C^UFL)& (2-1)1_(-loc VbL
Meanwhile, LOCmix is estimated using Zlochower & Green (2009) method. This
method was from the studyon spark ignited explosions in large, spherical laboratory
vessels using 7% pressure-rise criterion for explosion propagation. The calculated
results using this method predicts theexperimental values accurately for hydrocarbon
mixtures (Zlochower & Green, 2009).
2.6. Flammability Diagram
Flammability diagram is representing the flammability of vapour. It is the best tool to
determine the flammability region and also to determine if a flammable mixture is
present as it has axes for fuel, oxygen and nitrogen (Mashuga & Crowl, 1999). An
example of flammability diagram can be seen in Figure 2. Concentration of fuel,
oxygen and inert material are plotted on each axes of the triangle. Referring to the
flammability diagram, air line represents all the possible concentrations of fuel and
air. Stoichiometric line signifies the combinations of fuel and oxygen. If
10
stoichiomeric line intersects the flammability zone bounded by LFL and UFL line,
vapour mixture is flammable and can cause fire.
Various individuals have used flammability diagram to represent the flammability of
components and mixtures. Flammability characteristics of 3-picoline/water mixtures
were studied using a 20-L vessel. Findings from the study was represented in
flammability diagram to show the possible flammable mixture ratio (Y. M. Chang et
al, 2006). Mao et al. (2011) also illustrated possible mixture composition using
standard flammability diagram in their study on backdraught in tunnel fires. The
flammability envelope plotted for mass fraction of n-heptane (fuel), oxygen and
nitrogen (Mao et al, 2011).
Flammability diagramis not only used to determine the flammability range of single
component fuel. Chang et al. (2006) studies the flammability on benzene and
methanol with different vapour mixing ratios under different initial conditions. The
flammability of benzene, methanol and their mixture was investigated in a 20-L
spherical explosion vessel (Y. M. Chang et al, 2006). A triangular diagram was
plotted with different ratios ofbenzene and methanol.
Figure 2: Ffctiimiability Diagram of Methane at 25°C arid 1 aim (Brooks & Crow!, 2007)
11
2.7. Inherent Safety
"What you don't have, can't leak" (T. A. Kletz, 1978) is a catchy line by Kletz
(1978) whom started the concept of reducing rather than controlling hazards.
Inherent Safety is defined as a condition in which the hazards associated with the
materials and operations used in the process have been reduced or eliminated
permanently (Bollinger & Crowl, 1997). There is no single index or numerical
values that could define Inherently Safer (Dowell Iii, 2006). Dowell Iii (2006), also
mentioned that there is always a trade-off between different types of hazards.
Eliminating onehazard might bring another newhazard to the situation.
Applying Inherent Safer design concepts can reduce the number of accidents in
industry. Applying this concept at the designing phase could benefit in having low
cleaning up cost in the future. Inherent safer design will enhance overall risk
management by reducing the frequency of potential accident such as fire and
explosion.
There are 11 approaches to inherent safer design: Substitution,
mmimization/intensification, moderation/attenuation, simplification, limitation of
hazardous effects, avoiding knock-on effect, making incorrect assembly impossible,
make status clear, tolerance, ease of control and administrative controls/procedures
(T. Kletz & Kletz, 1998).
AIChE Center for Chemical Process Safety (CCPS, 2009) reduced the 11 concepts of
inherently safer processes to four principles:
• Minimize the amount ofhazardous material present at any given time.
• Substitute hazardous materials by least hazardous materials.
• Moderate the operating conditions of pressure, temperature and
concentrations.
• Simplify the plant since simple process plants are easier to operate and
maintained with fewer chances of things going wrong.
12
CHAPTER 3
METHODOLOGY
3.1. Tools and Materials
1. Sample from one of the refinery in Malaysia
2. Gas Chromatography - Mass Spectrometer (GC-MS)
3. Gas Chromatography- Headspace (GC-HS)
3.2. Experimental and Theoretical Methods
Sample of crude oil is obtained from a refinery and was brought back to Universiti
Teknologi PETRONAS fully insulated in an air tight bottle. Simple distillation was
conducted to remove the water content in the sample. A portion of the sample was
analysed using HS-GC at 35°C, 40°C and 50°C. The crude sample analysis was
performed by PerkinElmer Clarus 500 Mass Spectrometer. MS spectra was
compared using Turbomass Gold Software. For all temperatures, samples were
injected into Perkin Elmer Elite 5MS N9316282 capillary column with 30m length,
0.22 mm i.d and 0.25 um film thickness. Inlet pressure of column is 15psi. Volume
of injected sample is 1.0 uL with electron energy 70 eV. Split vent is set to 20
ml/min with ratio of 19:1.
GC identifies various compounds at different retention times. From GC-MS, peak
areais proportional to the amount of compound presence in thesample.
Resulting data from the GC-MS will be screened and analysed. Compound with
>95% similarities with the library will be taken into consideration. Besides the
percentage of similarity, boiling points of each component selected will be studied.
Components with lower boiling points should be eluted and get detected earlier
compared to higher boiling points components. Thus, boiling points of each
13
component selected should be increasing together with the retention time. Boiling
points data are extracted from Yaws' Thermophysical Properties of Chemicals and
Hydrocarbons (Carl L; Yaws et al, 2009).
Sample collection
Identify the sample contents using HS-GC & GC-MS
Is the mixture flammable?
Estimate y;
Estimate LFLU UFLU andLOQat 30,40 & 50°C
Estimate LFLmix, UFLmi}L, and LOCmix at
30,40 & 50°C
J.Draw the flammability diagram
?igure3: Methodology flowchai
14
Yes
3.2.1. Mole Fraction
Mole fraction in vapour phase can be obtained from each compound's mass fraction.
Massfraction of eachcomponent in the vapour phaseof crudeoil is determined from
peak area data and will be calculatedusing Eq. (3-1):
Jxrr (3-1)
where xt - Massfraction of component/
A{ = Peak area of component i
AT = Peak area of all components
Depending on the temperature, some components in the liquidphasewill vaporise to
the vapour phase. Since fire and explosion occurs in the vapours phase, it is required
to know the concentration of hydrocarbon components in the vapourphase. The mass
fraction of each component in vapour phase can be converted to mole fraction in
vapour phase, yt using Eq. (3-2):
ytx; IMt
Hxi/M* (3-2)
Where Mt= the molecular weight of component i.
3.2.2.Flammability Limits
LFL, and UFL, ofeach component i in vapour mixture was calculated using equation
proposed by Jones (1938) in Eq. (3-3) and Eq. (3-4). Jones (1938) found that for
many hydrocarbon vapours, LFL and UFL both are functions of stoichiometric
concentration of fuel (Cst);
LFL =0.55C„ (3_3)
UFL =3.5C„ (3^}
15
The stoichiometric concentration for most organic compounds was determined using
the generalcombustionreaction(Eq. 3-5)
CmHxOy +z02 -> mC02 +\~\H20(3-5)
Where z is equivalent moles of (Vmoles fuel and can be found from Eq. (3-6);
jc yz~m + —
4 2
(3-6)The stoichiometric concentration (Cst)can befound asa function ofz (Eq. (3-7))
r r moles fuelCs( = [ ] x 100
moles fuel + moles air
100 (3-7)z
1 +0.21
LFL; and UFL, at 25°C are calculated by substituting Eq. (3-6) into Eq. (3-7) and
applying it into Eq. (3-3) and Eq. (3-4). The resulting equations are Eq. (3-8) and Eq.
(3-9) for LFL* and UFL,- respectively.
0.55(100)LFL25 4.76m +JJ9x-2.38y +l (3_8)
UFL„ =25 4.76m +1.19x-2.38y +l « «
3.50(100)
Calculation of LFL, and UFL, at 35, 40 and 50°C were calculated using empirically
derived equations (Zabetakis etal, 1958) (Eq. (3-10) andEq. (3-11)).
0 75LFLr =LFL«-—(r-25)
^ (3-10)
UFLr=UFL25 +̂ (T-25)^ (3-11)
16
Where AHC is the net heat of combustion in kcal/mole and T is the temperature in °C.
AHC for each components are obtained from Yaws' Handbook of Thermodynamic
and Physical Properties ofChemical Compounds (Yaws, 2003).
Le Chatelier (1891) proposed empirical models to calculate the LFL and UFL of
multiple fuel mixtures. The modelswere givenby;
LFL . (vol%)= ;mix n ,
I bAFLT)i = l (3-12)
UFLmix(vol%) = *1 btMLr)
i = l (3-13)
where, LFLT- the lower flammable limit for component i (in volume %) of
component i in fuel and air at T,
UFLT= the upper flammable limit for component i (involume %) of
component / in fuel and air at T
yt = the mole fraction ofcomponent i on a combustible basis and
n = the number of combustible species.
Saturated vapour pressure, P"at of each component was calculated using Antoine
equations (Eq. (3-14)). Antoine Coefficient were extracted from Yaws' Handbook of
Antoine Coefficients for Vapor Pressure (Carl L. Yaws et al, 2009).
logl0Psat=A BC+ T (3-14)
Where A, B and C are Antoine Coefficients. They are specific and vary for each
component. T is temperature in °C.
17
3.2.3.Limiting Oxygen Concentration
Limiting Oxygen Concentration of each component, LOC, is estimated using the
method proposed by Hansen & Crowl (2010) in Eq. (3-15):
L0Ci=(LFLi-CUK;UFLi)(UFI,)1-C^ "UFL
(3-15)
Where LOC,- = Limitingoxygenconcentration for component i
LFL* = Lower flammable limit for component i
UFL, = Upper flammable limit for component i UFL
UFL0 = Oxygen concentration at the upper flammable limit (vol% oxygen
in air)
Cloc = fitting constant
UFL0is calculated using Eq. (3-16)
UFL0=0.21(100-LFL,) (3-16)
Cloc is a fitting constant whereby according to Crowl, Cloc = -1.11 is valid for most
hydrocarbons (Hansen & Crowl, 2010).
According to Crowl (2011), Cloc = -1.11 is valid for most hydrocarbons. This value
was obtained from data analysis ofvarious experimental values.
Limiting oxygen concentration for the mixture, LOCmix is estimated usingZlochower
and Green (2009) method (Eq. (3-17));
LOC .= ^2"V'
L0C< (3-17)
18
3.2.4. Flammability Diagram
Flammability diagram at each temperature (35, 40 and 50°C) will be constructed to
study effect of flammability range with respect with temperature. Flammability
diagram consists of three axes namely fuel, oxygen and nitrogen/inert material. It is
diagram which could represent the flammability ofgaseous mixture.
There are a few methods to construct the flammability diagram. Crowl & Louvar,
(2001) describe in detail on the construction of flammability diagram. In this work,
flammability limits and limiting oxygen concentration will be used mainly in the
construction ofthe flammability diagram.
19
3.3
.G
an
ttC
hart
FY
Pl
FY
P2
#A
cti
on
item
s1
23
45
67
89
10
11
12
13
14
12
34
56
7
a
89
10
11
12
13
14
1S
elec
tion
ofP
roje
ctT
itle
2P
reli
min
ary
Res
earc
hW
ork
3S
ub
mis
sio
no
fE
xte
nd
ed
Pro
posa
l
4P
ropo
salD
efen
ce
5P
roje
ctW
ork
•at
a £ CO u a
6S
ub
mis
sio
no
fIn
teri
mD
raft
1
7S
ubm
issi
ono
fIn
teri
mR
epor
t1M at
Mi
9S
ubm
issi
ono
fPro
gres
sR
epor
tI
10
Pre
-ED
X|i
11
Su
bm
issi
on
of
Dra
ftR
epor
t11
12
Su
bm
issi
on
of
Dis
sert
ati
on
13
Sub
mis
sion
of
Tec
hnic
alP
aper
14
Ora
lP
rese
nta
tio
n
15
Su
bm
issi
on
of
Hard
Bo
un
d
Dis
sert
ati
on
20
CHAPTER 4
RESULTS AND DISCUSSION
4.1. Components Identification
Chromatogram at eachtemperature; 35°C, 40°C and 50°C were studied. Components
with matchingof more than 95% with the Mass-Spectroscopy library were taken into
considerations. Figure 4, Figure 5 and Figure 6 shows the chromatogram at each
temperature that shows the retention time and peak abundance.
From the first analysis, the components' boiling points were gathered. Boilingpoints
must be increasing together with the retention time. Components with lowerboiling
point will be eluted first thus should be detected at an earlier retention time.
There are 11, 9 and 16 components identified respectively for 35°C, 40°C and 50°C.
Components for each temperature are listed in Table 4,
21
Table 5 and Table 6 below; Components presence in the vapour mixture ranging
from Ce to C9 at lower temperatures. Most components are from the family of
Alkanes and Alkenes.
The mass fraction of each component was calculated by dividing the respective peak
area with the total peak areas of all components. (Eq.(3-1))
22
cru
de
oii
72
_3
5c
100-
,19
81
.84
1.8
0
2.0
7
1.7
8
%-
2.6
0 2.9
1
4.7
0
3.5
74
.06
6.1
1
J[A
VA
AA
;I""
II'
•••
0.9
81
.98
2.9
83
.98
4.9
8
}3
5C
,0
.5m
lsa
mp
lecru
de,
29
-May
-20
12
+1
2:2
9:1
5S
can
EI+
TIC
9.8
2e9
11
.30
"I1
''•'P
'''I"
"I1
"'I•'•'TT'1"1I'
fFT'Tl'll
II|IIII
|III
I|II
IIITl
II|T111)ll'ITI-PIII|IIII|IIIl|
I
5.9
86
.98
7.9
88
.98
9.9
81
0.9
81
1.9
81
2.9
81
3.9
81
4.9
8
^A
/VT
ime
Fig
ure
4:C
hru
mat
og
ny
siat
35
°C
23
Cru
de
Oil
_7
2_
40
C
100-
,2-
11
%-
1.9
6
T-l-
T
2.1
9
2.5
2/ 2
.77
5.0
63
.11
6.5
6
•!••••!
3.7
5-8
.12
12
.02
8.7
5T
""
-^
13
.75
ii
l.i
ii
iI
ii
ii
Ii
i1
8.7
52
3.7
5
I40
C,
0.5
ml
sam
ple
cru
de,
28
-May
-20
12
+1
2:3
9:4
0S
can
EI+
TIC
7.8
6e9
28
.75
Ii
''
'I
''
33
.75
••!•'•
38
.75
''
i'
'i
ii
ii
Tim
e4
3.7
5
Fig
ure
?:
Ch
rom
ato
Km
raat
40
°C
24
tn
LU 1- oc Tas coo
CO
+
©
I
©
0)
Ias
If)
©
id
o
n
O
in
O
te
Tab
le4
:C
om
po
nen
tsat
35
°C
No
.
Peak
Nu
mb
er
inG
C-
HS
Rete
nti
on
Tim
e(m
in)
Co
mp
ou
nd
Data
base
mat
ch(%
)F
orm
ula
CA
S
Boi
ling
Po
int
(°C
)
Are
a
(Ab
un
dan
ce)
Mass
Fra
ctio
n,
x;
14
2.2
1B
UT
AN
E,2
,2-D
IME
TH
YL
-9
8.8
CfiH
147
5-8
3-2
49
.73
82
54
72
72
0.1
04
29
2.9
1C
YC
LO
PE
NT
AN
E,
ME
TH
YL
-9
8.4
C«H
«9
6-3
7-7
71
.81
17
78
02
14
40
.22
4
31
23
.75
CY
CL
OP
EN
TA
NE
,1
,3-D
IME
TH
YL
-,C
IS-
95
.4C7
H14
25
32
-58
-39
0.7
73
58
70
79
20
.04
5
41
33
.86
CY
CL
OP
EN
TA
NE
,1
,3-D
IME
TH
YL
-,T
RA
NS
-9
8.1
C7H
U1
75
9-5
8-6
91
.73
55
28
78
80
0.0
70
51
44
.05
6H
EP
TA
NE
97
.6C7
Hlfi
14
2-8
2-5
98
.43
95
42
70
48
0.1
20
61
54
.7C
YC
LO
HE
XA
NE
,M
ET
HY
L-
98
.4C7
HU
10
8-8
7-2
10
0.9
32
17
11
05
44
0.2
74
71
76
.37
3H
EP
TA
NE
,3
-ME
TH
YL
-9
8.7
CRH1
R5
89
-81
-11
18
.93
28
26
66
14
0.0
36
81
86
.64
1,3
-DIM
ET
HY
LC
YC
LO
HE
XA
NE
,C
&T
98
CsH
lfi5
91
-21
-91
19
.95
25
15
87
40
0.0
32
91
96
.74
5C
YC
LO
HE
XA
NE
,1
,4-D
IME
TH
YL
-9
8.5
CsH
lfi5
89
-90
-21
22
.75
11
22
89
74
0.0
14
10
20
7.5
9O
CT
AN
E9
7.1
C*H
,*1
11
-65
-91
25
.68
26
20
59
90
0.0
33
11
29
11
.29
9P
-XY
LE
NE
99
.2C8
H10
10
6-4
2-3
13
8.3
63
77
00
49
60
.04
8
79
26
06
49
41
26
Tab
le5:
C01
11J.
oo
en
tsat
40
CC
No
.
Peak
Nu
mb
er
in
GC
-HS
Rete
nti
on
Tim
e(m
in)
Com
poun
dD
ata
base
mat
ch(%
)F
orm
ula
CA
S
Boi
ling
Po
int
CO
Are
a
(Abu
ndan
ce)
Mass
Fra
ctio
n,
x5
14
2.3
43
BU
TA
NE
,2,2
-DIM
ET
HY
L9
8.2
C6H
U7
5-8
3-2
49
.73
38
40
07
44
0.0
95
08
29
3.1
1C
YC
LO
PE
NT
AN
E,
ME
TH
YL
-9
7.7
CfiH
„9
6-3
7-7
71
.81
95
32
23
52
0.2
36
02
31
34
.13
7C
YC
LO
PE
NT
AN
E,
1,3
-DIM
ET
HY
L-,
TR
AN
S-
97
.5C7
H,4
17
59
-58
-69
1.7
32
76
61
58
20
.06
84
9
41
44
.34
8H
EP
TA
NE
96
.9C7
H16
14
2-8
2-5
98
.43
48
02
23
52
0.1
18
91
51
55
.05
2C
YC
LO
HE
XA
NE
,M
ET
HY
L-
98
C7H1
41
08
-87
-21
00
.93
12
51
48
19
20
.30
98
7
61
76
.83
6H
EP
TA
NE
,3
-ME
TH
YL
-9
8C8
H18
58
9-8
1-1
11
8.9
31
43
57
16
20
.03
55
5
71
87
.11
71,
3-D
IME
TH
YL
CY
CL
OH
EX
AN
E,
C&
T9
6.5
C8H1
fi5
91
-21
-91
19
.95
14
24
62
67
0.0
35
27
82
08
.11
8O
CT
AN
E9
5.9
CRH!
R1
11
-65
-91
25
.68
16
83
48
20
0.0
41
68
92
91
2.0
18
P-X
YL
EN
E9
9CR
H]n
10
6-4
2-3
13
8.3
62
38
74
62
40
.05
91
1
40
38
68
09
51
27
Tab
le6:
Co
mp
on
en
tsat
50
°C
No
.
Peak
Nu
mb
er
inG
C-
HS
Rete
nti
on
Tim
e
(min
)C
om
po
un
dD
ata
base
mat
ch(%
)F
orm
ula
CA
S
Boi
ling
Po
int
(°C
)
Are
a
(Abu
ndan
ce)
Mass
Fra
ctio
n,X
i
15
2.1
7B
UT
AN
E,
2,2
-DIM
ET
HY
L-
96
.80
CfiH
u7
5-8
3-2
49
.65
68
78
02
64
.00
0.0
60
0
29
2.8
8C
YC
LO
PE
NT
AN
E,
ME
TH
YL
-9
7.8
0Cf
iH1?
96
-37
-77
1.8
12
26
16
47
84
.00
0.1
97
4
31
33
.82
CY
CL
OP
EN
TA
NE
,1
,3-D
IME
TH
YL
L-,
CIS
-9
6.3
0C7
H14
25
32
-58
-39
0.7
77
53
89
54
4.0
00
.06
58
41
44
.01
HE
PT
AN
E9
6.4
0C7
H1fi
14
2-8
2-5
98
.43
14
04
24
57
6.0
00
.12
26
51
54
.66
CY
CL
OH
EX
AN
E,
ME
TH
YL
-9
8.4
0C7
H1d
10
8-8
7-2
10
0.9
33
54
46
32
32
.00
0.3
09
4
61
76
.35
HE
PT
AN
E,
3-M
ET
HY
L-
97
.20
C«H
,85
89
-81
-11
18
.93
48
88
26
04
.00
0.0
42
7
71
96
.72
CY
CL
OH
EX
AN
E,
1,4
-DIM
ET
HY
L-T
RA
NS
-9
6.8
0CS
H,6
22
07
-04
-71
19
.36
18
17
46
10
.00
0.0
15
9
82
06
.94
CY
CL
OH
EX
AN
E,
1,1
-DIM
ET
HY
L-
98
.10
C8H
lfi5
90
-66
-91
19
.55
99
49
91
6.0
00
.00
87
92
17
.48
CY
CL
OH
EX
AN
E,
1,2
-DIM
ET
HY
L-,
TR
AN
S-
96
.80
C*H
,fi6
87
6-2
3-9
12
3.4
31
65
54
43
9.0
00
.01
45
10
22
7.5
8O
CT
AN
E9
5.3
0CS
H,8
11
1-6
5-9
12
5.6
86
13
83
06
0.0
00
.05
36
11
23
7.8
0C
YC
LO
HE
XA
NE
,1
,4-D
IME
TH
YL
-9
7.8
0<
W*
58
9-9
0-2
12
5.8
91
08
55
64
3.0
00
.00
95
12
26
9.3
7H
EP
TA
NE
,2
,5-D
IME
TH
YL
-9
7.4
0<
W.
22
16
-30
-01
36
.01
99
30
82
3.0
00
.00
87
13
28
10
.77
ET
HY
LB
EN
ZE
NE
97
.90
CA
ft1
00
-41
-41
36
.20
95
62
89
9.0
00
.00
83
14
29
11
.36
P-X
YL
EN
E9
9.0
0C«
H1B
10
6-4
2-3
13
8.3
66
76
84
35
2.0
00
.05
91
15
30
11
.61
OC
TA
NE
,3
-ME
TH
YL
-9
7.7
0C
,H,»
22
16
-33
-31
44
.23
10
18
94
68
.00
0.0
08
9
16
31
12
.75
O-X
YL
EN
E9
7.1
0Cf
tHm
95
-47
-61
44
.43
17
17
68
46
.00
0.0
15
0
11
45
56
70
60
.00
1.0
0
28
4.2. Mole Fraction in Vapour Phase
Quantitative analysis of crude oil sample was conducted. Fat for each components
were calculated using Antoine Equation (Eq. (3-14). Antoine Coefficients for each
components are provided in Appendix A. In this work, Psat are generally ranging
from 15.25 mmHg to 766.7 mmHg. The large range of Fat gives wide variation in
the values of mole fraction in vapour phase, yh Heavier components with low
volatilityhave smallervalue oiyt.
Graphical representation of the mole fraction in vapour phase of each component at
35°C, 40°C and 50°Care illustrated in Figure 7.
(a)
co
tsmfa.
u.
V
o
S
* .O'S^,*F^<>^^^
^&
tf&
<?
V^-i^-t,^oP& &*
tv*
x^' c»o*&*cy»
Compounds
Compounds
29
#
<? xP* "V?
^ *f C^ $
/>v.J5N
4? <f <f «T <f ^ J* <f ^ <& ^ <f ^
y y <^to* ^
J" jf >£
<?
V £
</#
Compounds
^
#•y
Figure 7: Mole fraction iii vapour phase at (a) 35°C (b) 40°C and (c) 50°C
4.3. LFL, UFL and LOC
LFL, and UFL, of each component i in vapour phase at 25°C had been calculated as
given in Eq. (3-11) and Eq. (3-12). LFL,- and UFL/ ofeach component i are compared
with literature value obtained from DIPPR Project 801 (AIChE, 2010a). Graphical
comparison of literature values of LFL, and UFL, with calculated values is included
in Appendix B. Some literature value of LFL and UFL that could not be found in
other database or published literatures are not indicated in the appendix.
LFL,- and UFL, of each component i at 35, 40 and 50°C are calculated using Eq. (3-
13) and Eq. (3-14). Net heat of combustion, AHc for each component that was
obtained from Yaws* Handbook of Thermodynamic and Physical Properties of
Chemical Compounds are listed in Appendix C. Flammability limits of each
component are listed in Table 7, Table 8 and Table 9.
As mentioned earlier, Le Chatelier equation (Eq. (3-12) and Eq. (3-13)) is used to
obtain the LFLmix and UFLmix in the vapour mixture. Values obtained from the
calculation are summarised in Table 10.
LOC, of each component i is calculated using the method proposed by Hansen and
Crowl (2010) in Eq. (3-17). LOC values ofeach component are illustrated in Table 7,
30
Table 8 and Table 9. Meanwhile LOCmix is obtained by applying Zlochower andGreen (2009)methodin Eq. (3-18).
Table 7: Flammabilitv Limits andLOCat35DCNo. Components LF^ LFL35 UFL25 UFL35 LOC35
1 BUTANE,2,2-DIMETHYL- 1.19 1.18 7.57 7.58 11.6442 CYCLOPENTANE, METHYL- 125 1.25 7.98 7.99 11.5923 CYCLOPENTANE, 1,3-DIMETHYL-, CIS- 1.08 1.07 6.87 6.87 11.7334 CYCLOPENTANE, 1,3-DIMETHYL-, TRANS- 1.08 1.07 6.87 6.87 11.7335 HEPTANE 1.03 1.02 6.56 6.57 11.7726 CYCLOHEXANE, METHYL- 1.08 1.07 6.87 6.87 11.7337 HEPTANE, 3-METHYL- 0.91 0.90 5.79 5.79 11.8698 1,3-DIMETHYLCYCLOHEXANE,C&T 0.95 0.94 6.02 6.03 11.8409 CYCLOHEXANE, 1,4-DIMETHYL- 0.95 0.94 6.02 6.03 11.84010 OCTANE 0.91 0.90 5.79 5.79 11.86911 P-XYLENE 1.08 1.07 6.87 6.87 11.733
Tabic 8: Flammabilitv Limits and LOC at 40°C
No. Components LFL* LFL40 UFL?5 UFL40 LOC501 BUTANE,2,2-DIMETHYL 1.190 1.178 7.572 7.585 11.6382 CYCLOPENTANE, METHYL- 1.255 1.242 7.984 7.996 11.5863 CYCLOPENTANE, 1,3-DIMETHYL-, TRANS- 1.079 1.068 6.865 6.876 11.7274 HEPTANE 1.031 1.020 6.559 6.570 11.7665 CYCLOHEXANE, METHYL- 1.079 1.068 6.865 6.876 11.7276 HEPTANE, 3-METHYL- 0.909 0.900 5.785 5.794 11.8637 1,3-DIMETHYLCYCLOHEXANE. C&T 0.946 0.937 6.022 6.032 11.8338 OCTANE 0.909 0.900 5.785 5.794 11.8639 P-XYLENE 1.079 1.068 6.865 6.876 11.727
Table 9: Flammabilitv Limits and LOC at 50°C
No. Components LFL25 LFL50 UFL25 UFL50 LOC501 BUTANE, 2,2-DIMETHYL- 1.19 1.17 7.57 7.59 11.6252 CYCLOPENTANE, METHYL- 1.25 1.23 7.98 8.00 11.5743 CYCLOPENTANE, 1,3-DIMETHYLL-, CIS- 1.08 1.06 6.87 6.88 11.7154 HEPTANE 1.03 1.01 6.56 6.58 11.7535 CYCLOHEXANE, METHYL- 1.08 1.06 6.87 6.88 11.7156 HEPTANE, 3-METHYL- 0.91 0.89 5.79 5.80 11.8517 CYCLOHEXANE, 1,4-DIMETHYL- TRANS- 0.95 0.93 6.02 6.04 11.8218 CYCLOHEXANE, 1,1-DIMETHYL- 0.95 0.93 6.02 6.04 11.8219 CYCLOHEXANE, 1,2-DIMETHYL-, TRANS- 0.95 0.93 6.02 6.04 11.82110 OCTANE 0.91 0.89 5.79 5.80 11.85111 CYCLOHEXANE, 1,4-DIMETHYL- 0.95 0.93 6.02 6.04 11.82312 HEPTANE, 2,5-DIMETHYL- 0.81 0.80 5.17 5.19 11.92813 ETHYLBENZENE 1.08 1.06 6.87 6.88 11.71514 P-XYLENE 1.08 1.06 6.87 6.88 11.71515 OCTANE, 3-METHYL- 0.81 0.80 5.17 5.19 11.92816 O-XYLENE 1.08 1.06 6.87 6.88 11.715
31
Results from calculation are tabulated in Table 10 and represented graphically in
Figure 9, Figure 8 and Figure 10.
Table 10: lFL, UFL and LOC at each temi. erature
T 35°C 40°C 50°C
LFLmix 1.16058 1.15783 1.13466
UFUh 7.444245 7.456181 7.365457
LOCh 11.65627 11.65363 11.65360
1.11
1.10
1.09
1.08
1.07
1.06
1.099
LFLmix vs. Temperature
1.096
1.068
5035 40 ,„TemperaturefC)
Figure S: UFL„,ix vs. Temperature
UFLmix vs. Temperature
7.10 •)7.048 7"058
7.05 -i* i
9 7.00 -jX 6.95 1
J iLL.
36.90 -j6.85 A— —„_ —„ -,.„_„____—™__ _.
6.934
UQ
35 40Temperature(°C)
Figure 9: LFL,!lK vs. Temperature
LOCmix vs. Temperature
11.65627
35 40Temperature(°C)
iT vs. lemperanire
32
50
11.65360
50
4.4. Flammability Diagram
Flammability diagram is represented by three axes: Fuel (hydrocarbon vapour
mixture), inert material (nitrogen) and oxidizer (oxygen). Concentrations of fuel,
nitrogen and oxygen are required in order to plot the triangular flammability
diagram.
Air line in the flammability diagram is plotter by taking the composition of air
(assumed as 21% oxygen, 79% nitrogen). The intersection of the stoichiometric line
with oxygen axis is given by 100(z/l+z). LOC,^ is drawn by locating the \X)Cmix
value on the oxygen axis then drawing a parallel line until it intersects with the
stoichiometric line. Meanwhile \J¥\,mix and LFLm/x are located at the air line and
extended to show the flammability range.
Flammability diagram at 35°C, 40°C and 50°C were constructed to assess the
flammability region of vapour mixture above crude oil at those three various
temperatures. As can be seen in Figure 11, Figure 12 and Figure 13, at each
temperature, the stoichiometric line goes through the flammable zone. This shows
that crude oil could give off enoughvapour that could be ignited in the vapourphase.
Therefore, vapour released from the storage tank poses potential hazard and can be
ignited with the presence of ignition source.
•fliim-eoRW-^, -S^
?i«ure i 1: F! a mmability Diagram at 35°C
33
&n%
:LOC / V.•a
« \
\e\*
/ \ \ \\\ \* 1
\ v\* i Xc • *
.Sfeichi
/ A^Uy*L/ 7y HIFL \ \ \ -,
so- at JO. jy 50 60- id ^ as «ra.
WBrogen % LFL
I1-OS6voJ&)
riyure 52: Flammabiiity Diagram at 40°C
LOC
imjes4-jDi&r"\ s
Figure 33: Flammability Diagram a
34
5UUC
4.5. Inherent Safety
Flammable liquids are considered to be more hazardous when compared to
combustible liquids. Flammable liquids will ignite and burn easily atnormal working
temperature compared to combustible liquids. Most fire cases are contributed by the
presence of flammable liquids. Flammable liquids will not burnt by itself. As
mentioned earlier, flammable liquids will give off vapour which will burn with the
presence of ignition source.
The wanner the liquid's temperature, themore vapour components and concentration
will begiven off. Vaporization of flammable liquids depends onits temperature and
vapour pressure.
At studied temperatures (35°C, 40°C and 50°C) crude oil (flammable liquids) can
give off enough vapour to form flammable mixtures with air. Extra caution on each
components' LFL and UFL need tobetaken to minimize thepossibility of fire. Table
7, Table 8 and Table 9 illustrated the list of LFL and UFL of each component. It is
important to keep the concentration of these components outside of the flammable
range. Outside of theflammable range, thevapour could notbe ignited. Meanwhile,
combustible liquids at temperature above its flash point will release enough vapourwhich will be flammable too.
High concentration of flammable vapour mixture from storage tank is favourable to
beprevented from being released to the atmosphere. Flammable vapour mixture was
released from thestorage tankcantravel to an ignition source andcause fire. Firecan
be prevented by controlling and minimizing the ignition source such as hot works
(cutting and welding, electrical sparks, heating equipment etc), hot surfaces,
lightning, and open flames nearby the storage area. Besides that, hazardous
chemicals storage tanks should be designed in a way where there should not be a
domino effect in the eventof fireor explosion.
From theresults presented in this study, the following recommendations canbe made
to prevent fire from occurring by thepresence of flammable vapours:
35
1. Operation at less than LFL is often considered to be safer than operation at
above UFL.
2. Eliminate ignition sources from areas where flammable vapours may be
present or near enough for vapour to travel.
3. Storage tank vents should not be in a confined space where vapour mixture
can be accumulated and forming flammable mixture.
4. Storage tank must be placed some distances away from critical process area.
5. Samples should be taken frequently for analysis on its flammability limits.
36
CHAPTERS
CONCLUSIONS AND RECOMMENDATIONS
Crude oil mixture consists of various hydrocarbon chain; different structures and
length. At low temperatures, the liquid mixture could give off enough vapour that
could be ignited with the presence of oxygen and ignition source at the flammable
range.
Flammability of crude oil was analysed by correlating the principle of
thermodynamics and process safety. Identification of significant components was
conducted using gas chromatography and analysis of the flammability of each
component will be carried out at low temperature. Flammability range of the
components mixture was represented in flammability diagram whereby flammable
range were identified.
This study could be used to recommend safety methods that could prevent fire and
explosion due to the presence of flammable mixture. This work can contribute to
minimizing the loss of production, property damage andriskof personnel injury.
3.1.Recommendations
It should be noted that when all the necessary actions have been taken to evaluate the
root cause of fire and explosion incident, the hazards shall be controlled and
minimized accordingly as to avoid recurrence. Therefore, industries should adapt a
more preventive strategy such as prevention of ignition sources/hot works nearby
area with possible traces of hydrocarbons. Besides that, implementing good plant
layout design could avoid any domino effect in the event of fire.
For future works, experimental works can be conducted to study on flammability
limit of mixture using 20-L combustion chamber. Results obtained can be compared
with the theoretical values calculatedin this study.
37
Mashuga, C. V., & Crowl, D. A. (1999). Flammability zone prediction using
calculated adiabatic flame temperatures, Process Safety Progress, 18(3), 127-134,
Petersen, R. L., Watson, K. D., & Roehner, R. (1997). LFL estimates for crude oil
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40
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41
APPENDICES
42
APPENDIX A: Antoine Coefficients
No ComponentsCAS
RegistryA B C
1 2,2-dimethylbutane 75-83-2 6.93954 1169.51 238.418
2 1,1-dimethylcyclohexane 590-66-9 6.86464 1363.21 222.636
3 trans-l,2-dimethylcyclohexane 6876-23-9 6.92012 1420.58 228.259
4 1,3-dimethylcyclohexane, cis and trans 591-21-9 7.07327 1436.62 222.718
5 1,4-dimethylcyclohexane,(cis+trans) 589-90-2 7.07703 1446.39 221.94
6 cis-1,3-dimethylcyclopentane 2532-58-3 7.14306 1421.81 242.813
7 trans-1,3-dimethylcyclopentane 1759-58-6 7.07206 1369.35 234.986
8 ethylbenzene 100-41-4 7.1561 1559.55 228.582
9 heptane 142-82-5 7.04605 1341.89 223.733
10 methylcyclohexane 108-87-2 7.00107 1375.13 232.819
11 methylcyclopentane 96-37-7 7.06372 1304.45 240.043
12 3-methylheptane 589-81-1 7.12293 1477.48 229.359
13 3-methyloctane 2216-33-3 7.17567 1594.94 227.131
14 octane 111-65-9 7.14462 1498.96 225.874
15 o-xylene 95-47-6 7.14914 1566.59 222.596
16 p-xylene 106-42-3 7.15471 1553.95 225.23
17 trans-1,4-dimethylcyclohexane 2207-04-7 6.87792 1369.34 223.224
18 2,5-dimethylheptane 2216-30-0 7.03511 1458.75 215.134
43
APPENDIX B: Flammability Limits' Literature and Calculated values at25°C
No ComponentsCAS
RegistryLFL/,, LFL25>Cflfc UFLffi UFL25,cofc
1 2,2-dimethvlbutane 75-83-2 1.20 1.19 7.00 7.57
?, 1,1-dimethylcyclohexane 590-66-9 1.00 0.95 6.10 6.02
3
trans-1,2-dimethylcvclohexane
6876-23-9 1.00 0.95 6.50 6.02
4
1,3-dimethylcyclohexane,cis and trans
591-21-9 N/A 0.95 N/A 6.02
5
1,4-dimethylcyclohexane,(cis+trans)
589-90-2 N/A 0.95 N/A 6.02
6
cis-1,3-dimethvlcvclopentane
2532-58-3 1.10 1.08 7.30 6.87
7
trans-1,3-dimethvlcvclopentane
1759-58-6 1.10 1.08 7.30 6.87
8 ethvlbenzene 100-41-4 1.00 1.08 6.70 6.87
9 heptane 142-82-5 1.05 1.03 6.70 6.56
10 methvlcvclohexane 108-87-2 1.15 1.08 6.70 6.87
11 methvlcyclopentane 96-37-7 1.20 1.25 8.40 7.98
12 3-methylheptane 589-81-1 0.79 0.91 5.80 5.79
13 3-methvloctane 2216-33-3 0.76 0.81 5.40 5.17
14 octane 111-65-9 0.96 0.91 6.50 5.79
15 o-xylene 95-47-6 1.10 1.08 6.40 6.87
16 D-xvlene 106-42-3 1.10 1.08 6.60 6.87
17
trans-1,4-dimethylcyclohexane
2207-04-7 1.00 0.95 6.50 6.02
18 2,5-dimethylheptane 2216-30-0 N/A 0.81 N/A 5.17
44
APPENDIX C: Net Heat of Combustion (AHC)
No ComponentsCAS
RegistryAHC
(kCal/mol)1 2,2-dimethylbutane 75-83-2 918.52
2 1,1-dimethylcyclohexane 590-66-9 1163.74
3 trans-1,2-dimethylcyclohexane 6876-23-9 1163.83
4 1,3-dimethylcyclohexane, cis and trans 591-21-9 1162.76
5 1,4-dimethylcyclohexane, (cis+trans) 589-90-2 1238.76
6 cis-1,3-dimethylcyclopentane 2532-58-3 1023.04
7 trans-1,3-dimethylcyclopentane 1759-58-6 1039.
8 ethylbenzene 100-41-4 1039.89
9 heptane 142-82-5 1068.19
10 methylcyclohexane 108-87-2 1018.28
11 methylcyclopentane 96-37-7 878.68
12 3-methylheptane 589-81-1 1213.57
13 3-methyloctane 2216-33-3 1359.77
14 octane 111-65-9 1214.26
15 o-xylene 95-47-6 1037.04
16 p-xylene 106-42-3 1037.07
17 trans-1,4-dimethylcyclohexane 2207-04-7 1161.63
18 2,5-dimethylheptane 2216-30-0 1358.28
45