Tgp chi khoa hgc Truing Bgi hgc Quy Nhdn • So 1, Tgp VII ndm 2013
METHOD OF PRACTICE FOR CALCULATION OF RELATIVE DENSITY, REID VAPOR PRESSURE, AVERAGE MOLECULAR WEIGHT AND PRO/BU FRACTION OF THE LIQUIFIED PETROLEUM
GASES SAMPLE FROM COMPOSITIONAL ANALYSIS RESULT
BUI HONG HANH', NGUYEN DINH KtEW 1. INTRODUCTION
L P G is a g e n e r a l a b b r e v i a t e d n a m e of a certain number of mixtures of hydrocarbons such as butane, propane, iso-propane, butane-propane mixture in the liquid state. In normal conditions and under certain pressure which is greater than atmospheric pressure, LPG isstorable, transportable as a liquid, but at atmospheric pressure it is vaporized and used as a gas. LPG is a sub-product of refinery and natural gas separation plant. It is a burning gas which is convenient for transportation due to hquefaction at not too high pressure and at normal temperature. LPG is used as fuel and widely used iji industry, commerce, tourism, power generation, transportation, civil using (heating, cooking, heating, lighting,...).
The composition of a sample of Liquefied Petroleum Gase (LPG) is obtaijied by using Test Method ASTM D 2163 or other acceptable method. From the analysis (expressed in hquid volume percent), the certain Physical Properties of LPG (vapor pressure, relative density, molecular weight and pro/bu fraction) may be determined.
2. EXPERIMENTAL METHOD 2.1. Definition, significance and use
2.1.1. Density
Density is mass per unit volume at a specified temperature. The mass of liquid p e r unit volume at I5°C and its saturation p r e s s u r e with the standard unit of measurement being kilograms per cubic metre.
Density is a fundamental physical property that can be used in conjunction with other properties to characterize both the light and heavy fractions of petroleum and petroleum products.
Relative density is the ratio of the density of a material at a stated temperature to the density of water at a stated temperature.
Relative density is a necessary specification for determination of filhng densities and custody transfer. It becomes of value only when related to vapor pressure and
BUI HONG HANH°.NGUYEN DINH KIEN^
volatility. Relative density is of importance in meeting transportation and storage requirements for all liquefied petroleum gas products.
The density or relative density of light hydrocarbons and liquefied petroleum gases is used in custody transfer quantity calculations or to satisfy transportation, storage, and regulatory requirements.
2.1.2. Reid vapor pressure
Reid vapor pressure is the pressure exerted by the vapor of a liquid when in equilibrium with the liquid. Vapor pressure becomes more significant when it is related to volatility.
Information on the reid vapor pressures of liquefied petroleum gas products under temperature conditions from 37.8 to 70"C (100 to 158"F) is pertinent to selection of properly designed storage vessels, shipping containers, and customer utilization equipment to ensure safe handling of these products.
Determination of the reid vapor pressure of Uquefied petroleum gas is important for safety reasons to ensure that the maximum operating design pressures of storage, handling, and fuel systems will not be exceeded under normal operating temperature conditions.
2.1.3. Average molecular weight
Molecular mass is the mass of a molecule is measured in units of carbon. Molecular weight of the total mass of the atom in the molecule. The molecular mass can be calculated as the sum of the individual isotopic masses of all the atoms in any molecule.
The concept of molecular mass is important for all molecules, especially for complex molecules like polymers and biopolymers such as proteins and carbohydrates.
The determination of their molecular mass is often difficult, and is usually inferred from gel permeation chromatography and mass spectrometry.
Molecular mass and density is used in custody transfer quantity calculations or to satisfy transportation and storage.
2.1.4. Commercial pro-bu mixtures
Mixtures of propane and butane for use where intermediate volatility is required.
Commercial butane: a hydrocarbon product for use where low volatility is required.
Commercial propane: a hydrocarbon product for use where high volatility is required.
Conversion of a compositional analysis from mole, gas-volume, or weight basis to liquid-volume is obtained by using ASTM D 2421 or other suitable method (see table 2).
2.2. Calculation m e t h o d
After taking LPG sample, components in a sample of LPG are physically separated by gas chromatography and c o m p a r e d to corresponding components
METHOD OF PRACTICE FOR CALCULATION OF RELATIVE DENSITY 45 separated under identical operating conditions from a reference standard mixture of
known composition or from use of pure hydrocarbons. The chromatogram of the sample is interpreted by comparing peak heights or areas with those obtained on the reference standard mixture of pure hydrocarbons.
The composition of a sample of LPG is obtained by using Test Method D 2163.
From the analysis (expressed in liquid volume percent), the vapor pressure, relative density, average molecular weight and pro/bu fraction of the sample may be determined.
3. RESULT AND DISCUSSION
3.1. Calculate the relative density of each component in the mixture as follows Relative weight of component = (rd x C)/100, where:
rd: relative density of the pure component at 15.6"C (60"F) (see Table 2) C: liquid volume percent of component in the mixture.
Add the relative mass of all components, rounding the total to three decimal places. The total is reported as the relative density of the mixture.
3.2. Calculate the reid vapor pressure due to each component in the mixture as foUovcs Partial reid vapor pressure = (vp x C)/IOO, where:
vp: vapor pressure factor of specific component at SV.S^C (100"F) (see Table 1) C: liquid volume percent of component in the mixture.
Add the partial gage vapor pressures due to all components, rounding to the nearest 7kPa (Ipsi). The total is reported as the reid vapor pressure of the sample, kPa gauge at37.8"*C(IOO"F).
Table 1. Factors for Determining the Physical Charateristics of LPG
Component
Methane Ethane Propane Propene n-Butane i-Butane
Vapor Pressure Blend Factor, kPa (psig) at37.8»C(100°F)
17547(2545) 4213(611)
1200(174) 1469(213) 255 (37) 400 (58)
Relative density at 15.6"C (60"F)
0.3 0.35639 0.50736 0.52264 0.58407 0.56293
BUIHONG HANH'.NGUYENDINH KIEN^
Table 2. Mass-Volume Data for Liquefied Petroleum Gases and low Boiling Hydrocarbons
Compound
Methane Ethane Acetylene Ethylene Propane Propylene Propadiene Methylacelylene n-Butane Isobutane l-Butene Trans-2-Butene Cis-2-Butane Isobutylene 1,2-Butadiene 1,3-Butadiene Elhylacetylene n-Pentane Isopentane Neopentane l-Pentene Trans-2-pentene Cis-2-pentene 2-methyl-l-bulene 3-methyl-l-butene 2-methyl-2-butene Cyclopentane Isoprene l-trans-3-Penladiene 1-cis-Pentadiene 1,2-Pentadiene
Column 1 Molecular weight 16.043 30.07 26.038 28.054 44.097 42.081 40.06 40.06 58.123 58.123 56.108 56.108 56.108 56.108 54.092 54.092 54.09 72.15 72.15 72.15 70.134 70.13 70.13 70.13 70.13 70.13 70.134 68.119 68.12 68.12 68.12
Column 2 Liquid Volume in mL of 1 mL of ideal gas at 15.6»C (60"F) and 101.3 kPa (760 mm Hg)
0.002261 0.003565 0.00263 0.005029 0.003672 0.003402 0.00282 0.00273 0.004205 0.004362 0.003949 0.003879 0.003772 0.003941 0.003474 0.003644 0.00328 0.00483 0.004881
0.00511 0.004591 0.004537 0.004482 0.004519 0.004684 0.00447 0.003947 0.004195 0.004224 0.004133 0.004125
Column 3 Relative Density
15.6/13.6''C (60/60°F) (Vacuum)
0.3 0.35639
0.418 0.23569 0.50736 0.52264 0.6 0.621 0.58407 0.56293 0.60035 0.61116 0.62858 0.60153 0.65798 0.62722 0.696 0.63111 0.62459 0.59665 0.64538 0.653 0.6611 0.6557 0.6325 0.663 0.75077 0.68614 0.6815 0.6964 0.6976
Source
GPA 2145-00 GPA 2145-00
Estimate GPA 2145-00 GPA 2145-00 GPA 2145-00
API-88 API-88 GPA 2145-00 GPA 2145-00
GPSA GPSA GPSA GPSA GPSA GPSA API-88 GPA 2145-00 GPA 2145-00
GPSA GPSA TRC TRG TRC TRC TRC GPSA GPSA API API API
METHOD OF PRACTICE FOR CALCULATION OF RELATIVE DENSITY
33. Calculate the average molecular weight of each component in the mixture as follows Partial molecular weight of component = (M x m)/100, where:
M: molecular weight of component (see Table 2) m: moi percent of component in mixture.
Add the partial molecular mass of all components and rounding the total to three decimal places. The total is reported as the calculated average molecular weight of the mixture.
3.4. Calculate the pro/bu fraction
Factor C3 = -xIOO
(Mc3 X m^j + Mc4 X mc4) Factor C4 = 100 - Factor C3
Result of the LPG sample analysis can be reported in table 2 such as:
Table 2. LPG composition analysis report
KJK
Peak 1 2 3 4 5 6 7 Total
Ret.Time 1.862 2.107 2.745 2.841 3.954 4.218 4.394
Area 5781411 270613262
85368920 132634087
611987 9191208 2526562 506727437
Height 4583688 09242113 30914076 36904850 331483 3697723 1254602 86928535
Cone.
2.259 62.182 14.529 19.606 0.068 1.113 0.244 100.000
Units
%mol
%mol
%mol
%mol
%moI
%mol
%moI
Compound Name Ethane Propane Iso-hutane
N-butane Neo-Pentane
Iso-pentane N-pentane
From the analysis resuh in table 2, we apphed above calculation formulas at excel program and got a calculation program of physical properties of LPG from composition (table 3) such as:
BUI HONG HANH'. NGUYEN DINH K E N '
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METHOD OF PRACTICE FOR CALCULATION OF RELATIVE DENSITY
From the calculation program of physical properties of LPG in table 3, we used calculation and got a result about density, average moleular weight, C3/C4 fraction and Ried vapour pressure (table 4) such as:
Table 4. Calculation result of Physical Properties of LPG from Composition Analysis
1
2 3 4 5 6 7 8 3 10 11 12 13 14 fc K 1/
IH IH
?n 21 22
n
24
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A I B I C I D I E I F I G I H I I I J I K
T a b l e 4 C a l c u l M i o n of P h j m c a l P r o p e n r e i of L P G h o m C o m p c i H i o n * ! A n a l ^ t l s ( A S T M 0 - 2 5 3 8 )
GOMPOSIIIOn
M e t h a n e eitiane piopane piocene tso-bulane n-biMane 1-2- bulene 1-butene
•EO-bUene ois-2-buiene npo-penlane n-oefMane l-Demen*
„.n,-2-o.™™
cis-2-f>entene Moi
0
£259 62,18 0 14 53 B 6 1
0 0 0 0 0 068
1113 0 244 0 0 0 lOOX
•BO Volume
0000 2069 58673 0.000 16 265 21185 0 000 0 000 0000 0 000 0 089 1336 0303 0.000 0 000 0 000 100.00 CALCULATED RESULTS Calciiat*dden£i)>
Measured densRv MolecUai
We«h<
FaotoiC3 Fac«oiC4 RiedVapou
kqfl kflrt
y.\i\
XWi kpa psi
05316 0 5332 48 368 58 013 41981 910.43 13202
Vapor Blend kPaal' 37BoC rioooF) 17547 4213 1200 1469 4 X 255
Blend pilgat 37 8oC (lOOoF) 2545
611 MA 213 58 37
Cohunnl Molecular M u t
16 043 30 070 44 097 42 0S1 58123 58123 56108 56108 56108 56138 72150 72150 72150 70134 70130 70130
Column 2 LlquKJ Volume in mL of ImLol ideal 15 60CI6O0F) and 1013l(Pa(760
mmHg) 0 00226- 0 003S65 0 003672 0 003402 0 004362 0 004205 0 003873 0 003343 0 003341 0 003772 0 00511 0 004881 000483 0 004591 0 004537 0 004482
Columns Relative
•entity 15 6115 60C
(60/eaoF]
(Vacuum]
03 0 35633 0 50736 0 5Z284 0 56233 058407 0 61116 0 60035 0 60153 0 62858 0 S9655 0 62459 0.63111 0 64538 0 653 0 6611
column 2
C 0 008053 0 228332 C 0 063375 0 062443 C C C C 0 000347 0 00543;
0 00117S C C C 0 38916;
256.3644 Moleoular
Matt
C 67 9281;
2742 0397 t 844 46907 T139 5595
C C C C 4 9062 80 30235 17 6048 C G C 48 968
>:Welght
0 1 3871314 55 936446
0 17 245289 23 271467 0 0 0 0 01001318 16339033 0 36 0 00 0 00 0 00 100
_
Two results of density in Table 4 are approximately equal, showmg high accuracy of two methods of measuring by hand (experimental measure) and the calculation method as in the paper. The results of the average molecular mass, reid vapor pressure and C3/C4 ratio is very accurate.
4. CONCLUSIONS
Through the compositional analysis figures of LPG in Table 2, we have applied algorithms, formulas in excel program to calculate as shown in Table 3 and obtained a good result about density, reid vapor pressure, average molecular weight and C3/C4 ratio as shown in table 4.
It is very important for calculating the quality specifications of LPG sample, if above calulation reaches a high accuracy, it will be of great advantage to analysts working in oil and gas field.
BUIHONG HANH'.NGUYENDINHK1E>P' REFERENCES
[1] Processing technology for oil chemistry and petroleum products. Vietnam petrolimex corporation. Hanoi 1997.
[21 ASTM Standards (For referenced ASTM standards, visit the ASTM website, www.astm.org. or contact ASTM Customer Service at [email protected]. For Armual Book of ASTM Standards volume information, refer to the standard's Document Summary page on the ASTM website):
D 1657 Test Method for Density or Relative Density of Liquid Hydrocarbons by Pressure Thermohydrometer
D 1835 Specification for Liquefied Petroleum (LP) Gases
D 2163 Test Method for Analysis of Liquefied Petroleum (LP) Gases and Propane Concentrates by Gas Chromatography
D 1267 Standard Test Method for Gage Vapor Pressure of Liquefied Petroleum (LP) Gases (LP-Gas Method)
T6M TAT
P H U G N G PHAP TfNH TOAN TY TRONG, AP SUAT H O I B A O H 6 A , KHOI L U O N G PHAN TLT TRUNG BINH VA TY LE C3/C4 CUA MAU KHf H 6 A LONG TlT K I T
QUA PHAN TfCH THANH PHAN
Bui Hdng Hanh, Nguyin Dinh Kiin Trong bai b^o nay, chiing toi trinh bay y nghla, u'ng dung va dinh nghla v l c5c chi tieu ky thuat quan trong cua san pham khi hda long (LPG), trinh b^y chi ti^t v^ tiTdng minh each tinh toin chi tieu ty trong, i p sua't hdi bao hda, khd'i li/0ng phSn tu" Uiing binh, ty le €3/0^ ciia LPG iH ket qua phan tich ih^nh phln mau sdn phim LPG dieo cac tidu chuan quoc te. Tif dd, i p dung cac cong thiJc tinh toan v i o chiTdng trinh excel.
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Ngay nh^n bai: 13/02/2012; Ngay nhSn dSng: 06/4/2012.