Page 153 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

QC: IML/FFX
T1: IML
P1: IML/FFX
P2: IML/FFX
AT029-Manual-v7.cls
14:23
June 22, 2007
AT029-Manual
AT029-03
3. CHARACTERIZATION OF PETROLEUM FRACTIONS 133
Solution—API = 86 and M = 86. From Eq. (2.4), SG = 0.65
and from Eq. (2.56), T b = 338 K. Since only T b and SG are ifications require that its value be limited to 900 in summer,
1000 in fall/spring, and 1150 in the winter season. Automobile
known, Eq. (3.103) is used to calculate the RVP. From Eqs. manufacturers in France require their own specifications
(2.55) and (2.56) we get T c = 501.2 K and P c = 28.82 bar. From that the value of FVI not be exceeded by 850 in summer [24]. --`,```,`,``````,`,````,```,,-`-`,,`,,`,`,,`---
Eq. (3.103), T r = 0.6205, X = 1.3364, and Y =−3.7235. Thus
we calculate RVP = 0.696 bar or 10.1 psia. The experimental 3.6.1.3 Flash Point
value is 11.1 psia [63]. Flash point of petroleum fractions is the lowest temperature
at which vapors arising from the oil will ignite, i.e. flash,
3.6.1.2 V/L Ratio and Volatility Index when exposed to a flame under specified conditions. There-
fore, the flash point of a fuel indicates the maximum tem-
Once RVP is known it can be used to determine two other
volatility characteristics, namely vapor liquid ratio (V/L) and perature that it can be stored without serious fire hazard.
fuel volatility index (FVI), which are specific characteristics Flash point is related to volatility of a fuel and presence of
of spark-ignition engine fuels such as gasolines. V/L ratio is a light and volatile components, the higher vapor pressure cor-
volatility criterion that is mainly used in the United States and responds to lower flash points. Generally for crude oils with
◦
Japan, while FVI is used in France and Europe [24]. The V/L RVP greater than 0.2 bar the flash point is less than 20 C [24].
ratio at a given temperature represents the volume of vapor Flash point is an important characteristics of light petroleum
formed per unit volume of liquid initially at 0 C. The proce- fractions and products under high temperature environment
◦
dure of measuring V/L ratio is standardized as ASTM D 2533. and is directly related to the safe storage and handling of
The volatility of a fuel is expressed as the temperature levels at such petroleum products. There are several methods of de-
which V/L ratio is equal to certain values. Usually V/L values termining flash points of petroleum fractions. The Closed
of 12, 20, and 36 are of interest. The corresponding tempera- Tag method (ASTM D 56) is used for petroleum stocks with
◦
◦
tures may be calculated from the following relations [24]: flash points below 80 C (175 F). The Pensky–Martens method
(ASTM D 93) is used for all petroleum products except waxes,
T (V/L)12 = 88.5 − 0.19E70 − 42.5RVP solvents, and asphalts. Equipment to measure flash point ac-
(3.106) T (V/L)20 = 90.6 − 0.25E70 − 39.2RVP cording to ASTM D 93 test method is shown in Fig. 3.28.
The Cleveland Open Cup method (ASTM D 92) is used for
T (V/L)36 = 94.7 − 0.36E70 − 32.3RVP
petroleum fractions with flash points above 80 C (175 F) ex-
◦
◦
◦
where T (V/L)x is the temperature in C at which V/L = x. cluding fuel oil. This method usually gives flash points 3–6 C
◦
Parameter E70 is the percentage of volume distilled at 70 C. higher than the above two methods [61]. There are a number
◦
E70 and RVP are expressed in percent distilled and bar, of correlations to estimate flash point of hydrocarbons and
respectively. Through Lagrange interpolation formula it is petroleum fractions.
possible to derive a general relation to determine temper- Butler et al. [70] noticed that there is a linear relationship
ature for any V/L ratio. E70 can be calculated through a between flash point and normal boiling point of hydrocar-
distribution function for distillation curve such as Eq. (3.35) bons. They also found that at the flash point temperatures, the
in which by rearrangement of this equation we get product of molecular weight (M) and vapor pressure (P vap ) for
pure hydrocarbons is almost constant and equal to 1.096 bar
B
B 343.15 − T ◦ (15.19 psia).
(3.107) E70 = 100 − 100 exp −
A vap
(3.111) MP = 1.096
T ◦
where T ◦ is the initial boiling point in kelvin and together Another simple relation for estimation of flash point of hydro-
with parameters A and B can be determined from the carbon mixtures from vapor pressure was proposed by Walsh
method discussed in Section 3.2.3. Another simple relation and Mortimer [71].
to calculate T (V/L)20 is given in terms of RVP and distillation vap
temperatures at 10 and 50% [61]: (3.112) T F = 231.2 − 40 log P
◦
◦
(3.108) T (V/L)20 = 52.5 + 0.2T 10 + 0.17T 50 − 33 RVP where P vap is the vapor pressure at 37.8 C (100 F) in bar and
T F is the flash point in kelvin. For simplicity RVP may be used
where T 10 and T 50 are temperatures at 10 and 50 vol% distilled for P vap . Methods of calculation of vapor pressure are dis-
on the ASTM D 86 distillation curve. All temperatures are cussed in Chapter 7. Various oil companies have developed
in C and RVP is in bar. For cases that T 10 is not available it special relations for estimation of flash points of petroleum
◦
may be estimated through reversed form of Eq. (3.17) with T 50 fractions. Lenoir [72] extended Eq. (3.111) to defined mix-
and SG. Several petroleum refining companies in the United tures through use of equilibrium ratios.
States such as Exxon and Mobil use the critical vapor locking The most widely used relation for estimation of flash point
index (CVLI), which is also related to the volatility index [61]. is the API method [2], which was developed by Riazi and
(3.109) CVLI = 4.27 + 0.24E70 + 0.069 RVP Daubert [73]. They used vapor pressure relation from Clasius–
Clapeyron (Chapter 6) together with the molecular weight
The fuel volatility index is expressed by the following relation relation form Eq. (2.50) in Eq. (3.111) to develop the following
[24]: relation between flash point and boiling point:
(3.110) FVI = 1000 RVP + 7E70 (3.113) 1/T F = a + b/T b + c ln T b + d ln SG
where RVP is in bar. FVI is a characteristic of a fuel for its per- where T b is the normal boiling point of pure hydrocarbons.
formance during hot operation of the engine. In France, spec- It was observed that the coefficient d is very small and T F is

Copyright ASTM International
Provided by IHS Markit under license with ASTM Licensee=International Dealers Demo/2222333001, User=Anggiansah, Erick
No reproduction or networking permitted without license from IHS Not for Resale, 08/26/2021 21:56:35 MDT