Page 162 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

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AT029-Manual
June 22, 2007
AT029-03
142 CHARACTERIZATION AND PROPERTIES OF PETROLEUM FRACTIONS
reported in wt% by Conradson method, which is designated
by %CCR. AT029-Manual-v7.cls T1: IML 14:23 lamp without smoking. It is expressed in millimeters and a
high smoke point indicates a fuel with low smoke-producing
Carbon residue can be correlated to a number of other prop- tendency [61]. Measurement of smoke point is described un-
erties. It increases with an increase in carbon-to-hydrogen der ASTM D 1322 (U.S.) or IP 57 (UK) and ISO 3014 test
ratio (CH), sulfur content, nitrogen content, asphaltenes con- methods. For a same fuel measured smoke point by IP test
tent, or viscosity of the oil. The most precise relation is method is higher than ASTM method by 0.5–1 mm for smoke
between CR and hydrogen content in which as hydrogen con- point values in the range of 20–30 mm [61].
tent increases the carbon residues decreases [7]. The hydro- Smoke point may be estimated from either the PNA com-
gen content is expressed in terms of H/C atomic ratio and position or from the aniline point. The SP of kerosenes from
the following relation may be used to estimate CCR from H/C IP test method may be estimated from the following relation
[81]. [90]:
(3.141) %CCR = 148.7 − 86.96 H/C SP = 1.65X − 0.0112X − 8.7
2
(3.144) 100
if H/C ≥ 1.71 (%CCR < 0), set %CCR = 0.0 and if H/C < 0.5
X =
(%CCR > 100), set %CCR = 100. H/C ratio can be estimated 0.61x P + 3.392x N + 13.518x A
from CH ratio methods given in Section 2.6.3. where SP is the smoke point by IP test method in mm and x P ,
The carbon residue is nearly a direct function of high boil- x N , and x A are the fraction of paraffin, naphthene, and aro-
ing asphaltic materials and Nelson has reported a linear re- matic content of kerosenes. The second method is proposed
lation between carbon residue and asphalt yield [82]. One by Jenkins and Walsh as follows [83]:
of the main characteristic of residuum is its asphaltene con-
tent. Asphaltenes are insoluble in low molecular weight n- SP =−255.26 + 2.04AP − 240.8 ln(SG) + 7727(SG/AP)
alkanes including n-pentane. Knowledge of n-pentane insol- (3.145)
ubles in residual oils is quite important in determining yields
◦
and products qualities for deasphalting, thermal visbreaking, where AP is the aniline point in C and SG is the specific grav-
◦
and hydrodesulfurization processing. The relation between ity at 15.5 C. Both Eqs. (3.144) and (3.145) estimate SP ac-
the normal pentane insolubles and carbon residue is as fol- cording to the IP test method. To estimate SP from the ASTM
lows [61]: D 1322 test method, 0.7 mm should be subtracted from the
calculated IP smoke point. Equations (3.144) and (3.145) are
(3.142) %NC 5 = 0.74195 (%CCR) + 0.01272 (%CCR) 2 based on data with specific gravity in the range of 0.76–0.82,
where %NC 5 is the wt% of n-pentane insolubles and %CCR is and smoke points in the range of 17–39 mm. Based on some
the wt% of Conradson carbon residue. Once %NC 5 is known, preliminary evaluations, Eq. (3.145) is expected to perform
the asphaltene content (asphaltene wt%) of a residue can be better than Eq. (3.144), because smoke point is very much re-
determined from the following empirical relation: lated to the aromatic content of the fuel which is expressed in
terms of aniline point in the Jenkins–Walsh method. In addi-
(3.143) %Asphaltene = a(%NC 5 ) tion the specific gravity, which is an indication of molecular
type, is also used in the equation. Equation (3.144) may be
where a is 0.385 for atmospheric residue and 0.455 for vac-
uum residues [61, 66]. These equations are approximate and used for cases that the aniline point is not available but ex-
do not provide accurate predictions. perimental PNA composition is available. Albahri et al [68]
also proposed the following relation for prediction of smoke
point using API gravity and boiling point:
Example 3.23—A vacuum residue of an Australian crude oil
has carbon-to-hydrogen weight ratio of 7.83. Estimate its car- (3.146) SP = 0.839(API) + 0.0182634(T b ) − 22.97
bon residue and asphaltene contents and compare the results
with the experimental values of 15.1 and 4.6%, respectively where SP is in mm (ASTM method) and T b is the average
[46]. boiling point in kelvin. This equation when tested for 136
petroleum fractions gave an average error of about 2 mm [68].
Solution—With CH=7.83, from Eq. (2.122), HC atomic ratio
is calculated as HC = 1.52. From Eq. (3.141), %CCR = 16.4% Example 3.24—A Nigerian kerosene has an API gravity of
and from Eq. (3.142), %NC 5 = 15.6%. From Eq. (3.143) with 41.2, aniline point of 55.6 C, and the PNA composition of
◦
36.4, 49.3, and 14.3%. Estimate the smoke point of this fuel
a = 0.455 (for vacuum residue) we calculate %Asphaltene =
7.1. The results show that while Eq. (3.141) provides a from. Equations (3.144)–(3.146) and compare with the exper-
good prediction for %CCR, prediction of %Asphaltene from imental value of 20 mm (Ref. [46], p. 342).
--`,```,`,``````,`,````,```,,-`-`,,`,,`,`,,`---
Eq. (3.143) is approximate.
Solution—To estimate SP from Eq. (3.144), we have x P =
3.6.9 Smoke Point 0.364, x N = 0.493, and x A = 0.143 which give X = 26.13. Cal-
culated SP is 26.8 mm according to the IP method or 26.1
Smoke point is a characteristic of aviation turbine fuels and mm according to the ASTM method. To use Eq. (3.145) we
kerosenes and indicates the tendency of a fuel to burn with have from API gravity, SG = 0.819, AP = 55.6 C, the calcu-
◦
a smoky flame. Higher amount of aromatics in a fuel causes lated SP is SP = 20 mm. The ASTM smoke point is then 19.3
a smoky characteristic for the flame and energy loss due to mm which is in very good agreement with the experimental
thermal radiation. The smoke point (SP) is a maximum flame value of 20 with deviation of −0.7 mm. Predicted value from
height at which a fuel can be burned in a standard wick-fed Eq. (3.146) is 17.6 mm.

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