GCPS 2011 __________________________________________________________________________
Mohanad El-Harbawi
Department of Chemical Engineering
Universiti Teknologi PETRONAS
31750, Tronoh, Perak, Malaysia
+605-3687581
mohanad_elharbawi@petronas.com.my
Siti Nurul Asikhin Bt. Shaaran
Reliability Integrity Engineering
Petronas Carigali Sdn Bhd, Petronas
Jln Belia, 88000 Kota Kinabalu, Sabah, Malaysia
Fatihah Ahmad and Muhammad Aizat Abd Wahi
Department of Chemical Engineering
Universiti Teknologi PETRONAS
31750, Tronoh, Perak, Malaysia
Prepared for Presentation at
American Institute of Chemical Engineers
2011 Spring Meeting
7th Global Congress on Process Safety
Chicago, Illinois
March 13-16, 2011
UNPUBLISHED
AIChE shall not be responsible for statements or opinions contained
in papers or printed in its publications
GCPS 2011 __________________________________________________________________________
An Investigation of Fire and Explosion Accident in the Drainage System
Related to Process Industries
Mohanad El-Harbawi1,*, Siti Nurul Asikhin Bt. Shaaran2, Fatihah Ahmad1 and Muhammad Aizat Abd Wahi1
1
2
Department of Chemical Engineering, Universiti Teknologi PETRONAS, 31750, Tronoh, Perak, Malaysia
Reliability Integrity Engineering, Petronas Carigali Sdn Bhd, Petronas, Jln Belia, 88000 Kota Kinabalu, Sabah, Malaysia
Corresponding author: Tel: +605-3687581, Email: mohanad_elharbawi@petronas.com.my
Abstract
The study of fire in process industries has displayed significant potential for further research in the oil and
gas business. The aim of the study is to investigate the possibility for the occurrence of fire incidents due to
the vaporization of hydrocarbon components above the wastewater flowing through a refinery’s drain. The
study covers both experimental and theoretical aspects. The experimental part is initiated by collecting the
liquid sample from one of the refinery’s drainage systems. The liquid sample contains mixture of
hydrocarbon products and water. The liquid sample in the initial stage was subjected to undergo the
distillation process to extract oil and remove water contents. Then, the oily liquid is analyzed using Gas
Chromatography Mass Spectrometry (GC-MS) to examine the compositions of the sample. The results
obtained indicated that there are 77 hydrocarbon components ranging from C9 to C22. The mole fractions of
the components in the liquid phase were obtained from the GC results. Whereas, the mole fractions of the
components in the gas phase were calculated according to Raoult’s law. The Lower Flammability Limits
(LFLs) and Upper Flammability Limits (UFLs) for each mixture component were calculated using
stoichiometric concentration method. The values were compared with others obtained from different
literatures and database. The LFL and UFL for the mixture were calculated with accordance to Le Chatelier
equations. LFLmix and UFLmix values were used to draw the flammability diagram and to examine if the
mixture is flammable or not. The results of this study may contribute to minimizing the loss of properties,
business and life due to fire accidents.
Keywords: Fire, Gas chromatography, Compositions, LFL, UFL, Flammability diagram.
1.0
Introduction
A refinery plant is a plant that produces various products such as Liquefied Petroleum Gas (LPG),
petrochemical naphtha, motor gasoline, kerosene, diesel and many other products. Drainage systems in
these plants contain various types of wastewater collected from all processes involved with different
chemicals and process conditions. Refineries can generate large volumes of polluted wastewaters that
contain various petroleum hydrocarbons, heavy metals, sulfur and ammonia [1]. Hydrocarbon containing
refinery wastewaters may be composed of flammable substances such as; benzene, toluene, ethylbenzene
and xylenes. Over the time, the mixture of water and hydrocarbon in the drainage system at certain
conditions will naturally separate and form distinct liquid phases based on density and polarity of the material
[2]. However, some compounds can vaporizes and turn into vapour form at the ambient temperature and
atmospheric pressure. The vapour can form flammable mixtures when mix with the air. The presence
flammable mixture exposes the drainage system to the possibility of fire and explosion events. Fire triangle
indicates that three elements necessary to ignite ordinary burning and fires are fuel, oxygen and heat.
Hydrocarbons fall in the fuel category. Fire might end up in explosion, provided that certain parameters, i.e.
the Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL) of the hydrocarbon are met.
GCPS 2011 __________________________________________________________________________
It is necessary to understand the flammable material properties, when we deal or handle dangerous
substances. Fires and explosions in industries can be prevented by understanding the flammable limits of
gases. Therefore, knowing flammability limits and related information are crucial in the process industries
where serious hazards may be encountered within the flammability limits. There are innumerable situations
where gases, liquids, and hazardous chemicals are produced, stored, or used in a process that, if released,
could potentially result in a hazardous fire and/or explosive incident. It is important to analyze all materials
and reactions associated with a particular process, including production, manufacturing, storage, or
treatment facilities in order to minimize the opportunity for a undesirable situation. Each process needs to
be analyzed with respect to the potential for the occurrence of fire and explosion in the work place.
There have been many tunnel and underground fire and explosion accidents in the past. Probably the most
serious tunnel explosion occurred in the United Kingdom (UK) in 1984, which killed 16 people, and has
been attributed to accumulated methane beneath a petrol station.
Prediction of explosion/flammability limits is of great practical significance to safety decision making. The
following analysis should be used to identify the ‘fire and explosion properties’ that affect a material's
flammability as defined above:
Composition
Refinery wastewater that flow through the drain contains various hydrocarbon components including
naphtha, gasoline, kerosene, diesel and heavier liquids. The composition of the waste can be identified by
gas chromatography (GC). Several techniques such as gas chromatography–isotope ratio mass
spectrometry (GC–IRMS) and Gas chromatography-mass spectrometry (GCMS) are currently utilized by
many researches in different fields such as fire and explosive investigations, environmental analysis and
environmental chemistry. However, their potential to be used in the instigation of ignitable liquids is clear
[3]. Therefore, the use of GCMS is to separate the mixtures of chemicals into its individual components.
Generally, the substances are identified (qualitatively) by the order in which they emerge (elute) from the
column and by the retention time in the column.
The analysis of the compositions of the sample is not enough to predict whether the mixture is considered
flammable. Therefore material's ignition resistance is a critical measure of flammability because if there is
no fire hazard, ignition does not occur [4].
Lewis and Von Elbe, [5], Mullins [6,7] have prepared excellent reviews of the process associated with
spark ignition and spontaneous ignition of a flammable mixture.
LFL and UFL
The lower flammability limits (LFL) and upper flammability limits (UFL) data for pure hydrocarbons are
available in different literatures. However, hydrocarbon mixtures with different components and different
mole fraction are often presented in the industry with significant contributions to fire and explosion
accidents. Vapour-air mixtures will ignite and burn only over a well-specified range of compositions. The
mixture will not burn when the composition is lower than the lower flammable limit (LFL); the mixture is
too lean for combustion. The mixture is also not combustible when the composition is too rich; that is,
when it is above the upper flammable limit (UFL). A mixture is flammable only when the composition is
between the LFL and the UFL [8].
The flammability limits can be measured using flammability apparatus. However the flammability limits
can be determined without experimental data [8]. There are several methods, database and software
recently available and provide sufficient information for various hydrocarbon substances. These can be
found in [9-11].
There are several documents that indicate to the hazards of flammability and explosibility of hydrocarbons
gas and mixtures. These include the work of Zabetakis [10], Sax [12], Kuchta [13], Lees [14], Ohtani et al.,
GCPS 2011 __________________________________________________________________________
[15], Brooks and Crowl, [16]. However, the study of the flammability of the equilibrium vapor above
aqueous solution is well discussed as for pure gases or mixtures. Brooks and Crowl [17] have
experimentally measured the LFL, Limiting Oxygen Concentration (LOC) and the maximum safe solvent
concentration (MSSC) for ethanol and acetonitrile above aqueous solutions.
Limiting Oxygen Concentration (LOC)
The limiting oxygen concentration (LOC) is the minimum oxygen concentration in a mixture of fuel, air,
and an inert gas that will propagate flame. Therefore, LOC is required to propagate a flame. The reaction
cannot generate enough energy to heat the entire gas mixtures and generate self-propagation if the oxygen
concentration is less than the LOC. LOC is a useful parameter, because explosions and fires can be
prevented by reducing the oxygen concentration regardless of the concentration of the fuel. This concept is
the basis for the common procedure called inerting [8,18].
The LOC can be measured experimentally using flammable apparatus. Furthermore, LOC can be found
from different resources [19,20]. If experimental and literature data are not available, the LOC is estimated
by using the stoichiometry from the combustion reaction and the LEL. This procedure works quite well for
many different hydrocarbons [8,21].
This paper will discuss how to estimate flammability limits of mixture of gasses in absence of using
traditional experimental apparatus. This is can be done by using a knowledge of thermodynamics. The
output of this work can be useful and helpful to investigate the root causes of fire incident in the drainage
systems due to the flammable mixtures.
2.0
Methodology
The methodology in this paper will discus how to examine the flammability of the vapour mixture above a
liquid hydrocarbon contaminated in the industrial drains. Experimental and theoretical methods were
applied in order to estimate the flammability of the vapour mixture. The below sections elaborated the
procedure of the methodology.
2.1
Experimental and Theoretical Methods
2.1.1 Liquid Phase
The liquid sample has been collected from one of the refinery drainage lines in Malaysia. The water content
was removed from the sample by using a sample distillation technique. The composition of the sample was
analyzed using the Gas Chromatography (GC), which is Shimadzu GCMS-QP5050 type. The GC settings
are as the follows: Electron impact ionization, electron energy 70 eV, scan range 40 to 500 amu at 1 scan/s.
Helium is at a flow rate of 1.5 cm3/min. Samples were injected on-column onto a 30 m HP5 fused silica
capillary column, 0.25 mm i.d, and the temperature held at 55◦C for 2 min, then increased from 55◦C to
300◦C at 5◦C/min, thereafter held at 300◦C for 40 minutes.
GC-MS is used to identify the compounds in the evaporated fraction of the liquid. GC will identify
different compounds at different times depending on their chemical structures. The times are known as
retention times and can be used to identify the various components of a mixture. The results from the GCMS show peak areas and retention times. The area of the peak is proportional to the amount of compound
contained in the injected sample. The more compound yields a larger peak area.
The mole fractions of each component contents in the sample can be calculated from GC data. The mole
fraction in the liquid phase can be found from the ratio of the area of a peak to the amount of compounds
(Eq. 1):
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xi =
Ai
AT
[1]
where
xi is the mole fraction of component i, (%),
Ai is the peak area of component i, and
AT is the peak area of all components.
2.1.2 Vapour Phase
The liquid hydrocarbon will vaporize some components at ambient temperature or if it is exposed to some
heat. Therefore it is necessary to measure the components in the vapour phase, which contribute to the
flammable mixture. Modified Raoult’s Law can be used to estimate the amount of liquid vaporized to the
atmosphere at ambient temperature. Eq. 2 is used to calculate the mole fraction in the vapour phase.
γ i xi Pi sat = ϕ i yi Pt
[2]
where,
γ i is the activity coefficient for component i,
ϕ i is the fugacity coefficient for component i,
y i is the mole fraction of component i in the vapour phase, (%),
Pt is the total pressure of the system, and
Pi sat is the vapour pressure of compound i as a pure component.
The activity coefficient, γ i for ideal solution is equal to 1. However, in this study, the mixture is non-ideal.
Therefore, the activity coefficient can be calculated using an established method. The UNIversal Functional
Activity Coefficient (UNIFAC) method was chosen to estimate the activity for non-ideal (real) mixture.
The UNIFAC method articulated the activity coefficient as the sum of a combinatorial part, ln γ iC and a
residual part, ln γ iR (Eq. 3) [22]:
[3]
lnγi = lnγiC + lnγiR
The configurational part, ln γ iC is given by Eq. (4):
ln γ iC = ln
Φi z
θ
Φ
+ qi . ln i + li + i
Φi
xi 2
xi
M
∑ x .l
j
j
[5]
j =1
z
(rj − q j ) − (rj − 1)
[6]
2
where, z is the average number of nearest neighbours around the group in solution (constant value is used
which is z=10).
lj ≡
The segment fraction, Φi and surface area fraction, θi are defined respectively by Eq. (7) and Eq. (8):
rx
Φi = M i i
∑ rj x j
j =1
[7]
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θi =
qi xi
[8]
M
∑q x
j
j
k =1
In Eq. (7), the molecular volume, rj is defined by the sum of its constituent group as given by Eq. (9):
N
rj = ∑ vkj . Rk
[9]
k =1
where,
ν kj is the number of k groups in molecule j
Rk is the volume of group k
The molecular surface area, qj is found by summing the individual group areas in the molecules as given by
Eq. (10):
N
q j = ∑ vkj . Qk
[10]
k =1
where, Qk is the group surface area.
The residual part, ln γ iR can be calculated from the group activity coefficient, Γk (Eq. 11):
[
N
ln y iR = ∑ v ki ln Γk − ln Γki
k =1
]
[11]
The concentration dependency of the group activity coefficients in the mixture Γk and in the pure
i
component ln Γk can be calculated using Eq. (12):
⎧
⎡
⎤⎫
⎪
N
N ⎢
⎥ ⎪⎪
Θ .ψ
⎛
⎞
⎪
ln Γk = Qk ⎨1 − ln⎜ ∑ Θ m .ψ mk ⎟ − ∑ ⎢ N m km ⎥ ⎬
⎝ m =1
⎠ m =1 ⎢ Θ .ψ ⎥ ⎪
⎪
n
nm ⎥
⎢⎣ ∑
⎪⎩
n =1
⎦ ⎪⎭
In Eq. (12), the group interaction parameters, ψ mk are defined by Eq. (13):
ψ mk = e
−
amk
T
, amk ≠ akm
[12]
[13]
where a mk is group interaction parameters between the groups n and m .
The surface contribution, Θ m and the mole fraction of the group, Xm is defined by Eq. (14) and Eq. (15)
respectively.
Q .X
Θm ≡ N m m
[14]
∑ Qn . X n
n =1
M
Xm ≡
∑v
j
m
j =1
M N
.xj
∑∑ v . x
j =1 n =1
j
n
[15]
j
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Fugacity coefficient, ϕ i for each component in the mixture can be found using Peng Robinson method. The
Peng–Robinson equation for pure fluids is given by Eq. (16) [23].
⎛ 2∑ i xi aik bk ⎞ ⎛ Z + 2.414 B ⎞
b
A
[16]
ln ϕ i = k (Z − 1) − ln (Z − B ) −
×⎜
− ⎟ ln⎜
⎟
b
a
b ⎟⎠ ⎝ Z − 2.414 B ⎠
2 2 B ⎜⎝
where,
ϕ i is the fugacity coefficient,
b is van der Waals covolume, defined by Eq. (17),
Z is the compressibility factor defined by Eq. (18),
B is constant defined by Eq. (19), and
A is constant defined by Eq. (20),
x is the mole fraction, and
a is the attraction parameter defined by Eq. (21).
b = ∑ xi bi
[17]
i
Pν
RT
bP
B=
RT
aP
A= 2 2
R T
a = ∑∑ xi x j aij
Z=
i
[18]
[19]
[20]
[21]
j
where,
P is the pressure, defined by Eq. (22),
T is the temperature,
v is the molar volume,
R is the universal gas constant,
aij is defined by Eq. (23), and
i, j , k are component identifications.
RT
a(T )
P=
− 2
ν − b ν + 2bν − b 2
aij = (1 − δ ij )a i1 2 a 1j 2
[22]
[23]
where, δ ij is the interaction coefficient.
Applying Eq. (22) at the critical point, we obtain:
(RTc )2
a(Tc ) = 0.45724
Pc
RT
b(Tc ) = 0.07780 c
Pc
Z c = 0.307
At temperature other than the critical:
a(T ) = a(Tc ). a(Tr , ω )
b(T ) = b(Tc )
[24]
[25]
[26]
[27]
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where,
a (Tr , ω ) is a dimensionless function of reduced temperature, and
ω is the acentric factor of the species.
Total pressure for the mixture can be calculated from Eq. (28):
Pt = ∑ γ i xi pisat
[28]
The vapour pressure of the components was calculated according to the Antoine equation (Eq. 29) and
extended Antoine equation (Eq. 30):
B
log10 P sat = A −
[30]
C +T
B
[31]
log 10 P sat = A − + C log 10 T + D T + E T 2
T
Where A, B, C, and D are the component-specific constants. These constants were collected from different
resources [24-25].
2.2.1 LFL and UFL
For some situations it may be necessary to estimate the flammability limits without experimental data.
Jones [26] found that for many hydrocarbon vapours the LFL and UFL are a function of the stoichiometric
concentration of fuel. Jones [26] found that for many hydrocarbon vapours the LFL and the UFL are a
function of the stoichiometric concentration (Cst) of fuel (Eq. 32 and Eq. 33):
LFL = 0.55Cst
[32]
LFL = 3.5Cst
[33]
where,
0.55 and 3.5 are constants, and
C st is the stoichiometric concentration which can be expressed as Eq. (36).
The stoichiometric concentration for most organic compounds is determined using the general combustion
reaction:
⎛x⎞
[34]
Cm H xOy + zO2 → mCO2 + ⎜ ⎟ H 2O
⎝2⎠
z is equivalent to moles O2/moles fuel and can be found from Eq. (35):
x y
[35]
z =m+ −
4 2
Stoichiometric concentration ( C st ) can be found as a function of z by Eq. (36):
C st = [moles fuel/ (moles fuel + moles air)]×100
100
[36]
=
[1 + (z 0.21)]
Substituting Eq. (35) into Eq. (36) and applying Eq. (32) and Eq. (33), then that will yield Eq. (37) and
Eq. (38):
0.55(100 )
LFL =
[37]
4.76m + 1.19x − 2.38y + 1
3.50(100 )
UFL =
[38]
4.76m + 1.19x − 2.38y + 1
GCPS 2011 __________________________________________________________________________
LFLmix and UFLmix for mixtures are computed using the Le Chatelier equation (Eq. 39 and Eq. 40) [27]:
1
LFL
=
[39]
mix
∑( y i /LFLi )
1
UFLmix =
[40]
∑( y i /UFLi )
where,
LFLi , is the lower flammable limit for component i (in volume %) of component i in fuel and air,
UFLi , is the upper flammable limit for component i (in volume %) of component i in fuel and air, and
n is the number of combustible species.
2.2.2
Limiting Oxygen Concentration (LOC)
LOC can be estimated using the stoichiometry of the combustion reaction and the LFL. Eq. (41) can be
used to estimate LOC [28]:
LOC mix = ∑ y i Ri / ∑ y i / L*i = ∑ y i Ri / ∑ y i Ri LOC i
[41]
L*i = LOC i Ri
[42]
where,
LOC mix is the limiting oxygen concentration for the vapour mixture,
Ri is the stoichiometric molar ratio of oxygen to compound i in the vapour phase, and
LOC i is the limiting oxygen concentration for individual compound.
Figure 1 show the steps of the methodology of this work.
2.0
Results and Discussion
Compositions
The compositions of the liquid sample were measured using GC-MS. The results of the GC show that there
are 77 components presented in the liquid phase. Figure 2 shows the retention time and peak abundance
data for the 77 components. Table 1 presented different components presents in the liquid phase with some
of their properties, which are useful for this study. GC results show that the liquid sample contains large
numbers of hydrocarbon components (CH-) varying from C9 to C22. From the analysis, the majority of the
components are Alkane and Alkene groups with some species from the Haloalkane and Arene. It can be
noted that peak numbers 21, 34, 47 and 59 made up more than 5 % from the sample. These peaks contain
species from Alkane group, which are: Undecane, 4-tert-butylstyrene, and N-tridecane.
Figure 3, shows the result distributions from the GC for the mole fraction in the liquid phase, xi (%) for
each component in the liquid phase. Mole fractions of the components were calculated using compositional
data determined by GC analysis. The mole fraction of each component is calculated by dividing the
individual peak area of each component with the total peak areas as described by Eq. (1).
Mole Fraction in Vapour Phase
To be able to estimate the mole fraction in the vapour phase using modified Raoult’s law (Eq. 2), we
require the vapour pressure, the activity and the fugacity coefficients of each component. The activity
coefficients were calculated using a UNIFAC method, which were described by Eq. (3) - Eq. (15). The
GCPS 2011 __________________________________________________________________________
activity coefficient for each component in the vapour mixture was calculated and the values are illustrated
in Table 1. The average activity coefficient for the vapour mixture was found equal to 1.17. Hence, the
fugacity coefficient for each component was calculated in accordance to Peng Robinson method, which
was described by Eq. (16) - Eq. (27). The detail of the fugacity coefficient results are presented in Table 1.
The average fugacity coefficient for the vapour mixture was estimated equal to 0.89.
The vapour pressure for each component was calculated using the Antoine equation (Eq. 30) and the
extended Antoine equation (Eq. 31). It should be noted that the vapour pressure for some components were
obtained from ChemSpider website [29].
Figure 4 displays is the mole fraction of each component in the vapour phase, yi (%). It should be noted
that the values of yi for each component are small. This is due to the mixture contains heavy hydrocarbon
components as illustrated by the GC data. The total mole fraction of the vapour mixture was obtained
0.0893 %. Its can be concluded that the air content in the mixture is equal to 99.9107. Therefore, the
percentage of N2 and O2 in the mixture will be 78.9295% % and 20.98% respectively.
Is the mixture
flammable?
Are LFL and UFL
experimental data
available?
Yes
No
Is the mixture
ideal?
No
Yes
Estimate the activity and fugacity
using UNIFAC method
Estimate xi and yi
Estimate xi and yi
Estimate LFLi, UFLi, and LOCi
Estimate LFLmix, UFLmix, and
LOCmix
Draw the flammability diagram
Stop
GCPS 2011 __________________________________________________________________________
Fig. 1: Flowchart describes the methodology steps.
5E+07
34
4E+07
47
21
59
Abundance
3E+07
7
2E+07
69
1E+07
1
77
0
10
15
20
25
30
35
Retention Time (min)
Fig. 2: GS analysis for the liquid sample. Key for peak identification is given in Table 1.
LFL and UFL
LFL and UFL for each mixture components have been calculated with accordance to stoichiometric
concentration method proposed by Jones [22] and given by Eq. (37) - Eq. (38). The results are illustrated in
Table 1. The values are compared with others obtained from database and different literatures. The results
of LFL show that the calculated values have good agreement with others obtained from literatures. Whereas
the UFL results show a fair agreement with the others obtained from literatures. It should be noted that LFL
and UFL values for some components are not available in the established database and published
literatures. Therefore, we were unable to obtain them and compare them with the calculated one. The LFL
and UFL values of these components were left blank in Table 1.
LFLmix and UFLmix for mixtures are calculated according to the Le Chatelier equations (Eq. 39 and Eq. 40).
The values were obtained are 8.288 and 52.727 respectively.
Limiting Oxygen Concentration (LOC)
GCPS 2011 __________________________________________________________________________
LOC for each mixture component is calculated and presented in Table 1. LOC for the mixture is calculated
using Eq. (41). The LOCmix value was found 11.425. LOC value is important in drawing the flammability
diagram.
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GCPS 2011 __________________________________________________________________________
12
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Compounds
Fig. 3: Percentage of mole fractions in the liquid phase.
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8.9E-05
1.2E-03
8.4E-07
1.1E-03
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2.4E-03
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6.9E-03
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3.1E-05
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2.8E-05
1.8E-04
4.4E-04
2.2E-03
4.6E-04
9.6E-04
9.7E-05
1.4E-04
3.6E-05
8.7E-03
2.2E-04
8.0E-04
1.2E-03
2.1E-04
5.2E-05
6.0E-09
1.1E-04
6.1E-04
7.3E-05
3.5E-06
3.4E-04
2.2E-05
5.8E-03
5.5E-04
2.1E-04
2.4E-06
1.3E-05
3.4E-05
3.7E-03
5.4E-05
9.3E-05
5.2E-05
1.2E-07
1.9E-04
7.7E-04
5.2E-04
1.5E-06
2.2E-05
1.4E-05
4.5E-05
2.1E-06
3.4E-06
1.5E-06
2.0E-05
3.3E-04
2.3E-05
9.0E-04
1.1E-04
2.8E-06
7.5E-07
1.1E-04
8.1E-06
5.8E-06
4.2E-03
1.2E-03
1.4E-03
8.1E-04
5.6E-04
9.3E-04
yi (%)
GCPS 2011 __________________________________________________________________________
3.0E-02
2.0E-02
1.5E-02
Compounds
Fig. 4: Percentage of mole fractions in the vapour phase.
GCPS 2011 __________________________________________________________________________
Table 1. Compound names and their relevant properties to estimate the flammability characteristics
GCPS 2011 __________________________________________________________________________
Results Summary
LFLmix(vol. %)
UFLmix(vol. %)
LOCmix
Stoichiometry
Air
N2 = (79%*99.9107)
O2 = (21%*99.9107)
8.288
52.727
11.425
94.815
99.9107
78.9295%
20.9800%
GCPS 2011
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1.2
1
L F L (% )
0.8
LFL (Cal.)
0.6
LFL (Lit.)
0.4
0.2
0
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
41
43
45
47
49
51
53
55
57
59
61
63
65
67
69
71
73
75
77
Compound Number
Fig. 5: Comparison between calculated and litterature values of LFL.
10
9
8
UFL (%)
7
6
UFL (Cal.)
5
UFL (Lit.)
4
3
2
1
0
1
3
5 7
9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77
Compound Number
`Fig. 6: Comparison between calculated and litterature values of UFL.
Flammability Diagram
Flammability diagram is a general way to represent the flammability of mixture of gases.
The flammability diagram represented by three axes, which are: fuel (hydrocarbon
vapour mixture in this study), inert material and oxygen. To plot the flammability
diagram, concentrations of fuel, oxygen, and inert material (in volume or mole %) are
required. Air line is plotted by taking the compositions of air from Table 1: 78.9295 %
nitrogen and 20.98 % oxygen. The intersection of the stoichiometric line with the oxygen
axis is given by 100 ( z 1 + z ) [8]. The LOCmix line can be drawn by locating LOCmix value
on the air axis. Then drawing a parallel line until intersects with the stoichiometric line.
The value of LOCmix is calculated equal to 11.425using Eq. 41.
To plot the flammability zone, the values of LFLmix and UFLmix are required. The LFLmix
and UFLmix values are located on the air line, and then the flammability zone is
GCPS 2011
__________________________________________________________________________
considered the only area to the right of the air line. Figure 6 represents the above
procedure using the results presented in Table 1 to generate the flammability diagram of
the hydrocarbon mixture. It can be clearly visible that the stoichiometric line does not
cross the flammable zone as shown in Fig. 6. Therefore, it can be concluded that the
flammable mixture does not exists.
Fig. 6: Tringular flammability diagram of the hydrocarbon mixture.
3.0
Conclusion
The results presented in this work show that some waste generated by the refineries can
be dangerous and generate flammable mixtures, which can cause fire. However, results
from the case study which presented in this paper show that the vapour mixture is not
flammable. The finding from this study indicated that several hydrocarbon compounds
were presented in a waste sample collected from a refinery’s drain. Experimental and
theoretical works were applied in order to estimate the LFL, UFL, and LOC. The
experimental work was conducted using GC to identify the compositions of the sample.
The theoretical works included thermodynamic fundamentals and flammability
calculations were applied in order to estimate the flammability limits and examine if the
GCPS 2011
__________________________________________________________________________
mixture is flammable or not. As a conclusion, the results from study can give some
method and guidelines to those who are involved in the relevant fields.
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www.chemspider.com