Dry Gas Properties
1
Dry Gas Properties
Instructional Objectives:

Reproduce the ideal gas equation of state in volume, molar volume, specific volume, or
density.

Define gas compressibility factor (zfactor) and show the shape of a zfactorpressure
isotherm.

Reproduce the compressibility equation of state in volume, molar volume, specific
volume, or density.

Estimate a value of zfactor from composition at a given temperature and pressure using
Kay’s method.

Estimate a value of zfactor from composition at a given temperature and pressure using
the more accurate PiperMcCainCorredor method.

Define gas specific gravity.

Calculate the apparent molecular weight of a gas from its composition.

Calculate the specific gravity of a gas from its apparent molecular weight.

Define standard conditions, define standard cubic feet, and show the relationship
between standard cubic feet and mass in pound moles.

Define gas formation volume factor,
B
g
, show the typical shape of a
B
g
versus pressure
isotherm, and write the equation for calculating
B
g
.

Define the coefficient of isothermal compressibility of a gas,
c
g
, and show the typical
shape of a
c
g
versus pressure isotherm.

Show the typical shape of a gas viscosity versus pressure isotherm.

Discuss the relationship between viscosity units of centipoise and centistoke.

Show the typical shape of a gas density versus pressure isotherm.

List the variables required to estimate values of gas formation volume factor, gas density,
gas viscosity, and the coefficient of isothermal compressibility of a gas.

Define gasheating value and explain the meanings of gross, net, wet, and dry as used in
determining values of heating value.
Ideal Gases:
Ideal Gas Equation of State:
nRT
pV
=
Where,
n
=
number of moles
p
= pressure
R
=
universal gas constant
T
= temperature
V
= volume
The ideal gas equation of state can be written in different forms.
Assumptions of Ideal Gas law:

Volume occupied by molecules is insignificant compared to volume of gas.

There are no attractive or repulsive forces between molecules.

All collisions are perfectly elastic.
Mixtures of Ideal Gases:
Apparent molecular weight
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View Full DocumentDry Gas Properties
2
j
i
a
M
y
M
∑
=
Where,
M
a
=
Apparent molecular weight of mixture
y
j
=
Mole fraction of component j
M
j
=
Molecular weight of component j
Physical Constants:
Critical Constants
Compound
Formula
Molar Mass,
molecular weight
Pressure,
psia
Temperature,
°
F
Methane
CH
4
16.043
666.4
116.67
Ethane
C
2
H
6
30.070
706.5
89.92
Propane
C
3
H
8
44.097
616.0
206.06
Isobutane
C
4
H
10
58.123
527.9
274.46
nButane
C
4
H
10
58.123
500.6
305.62
Isopentane
C
5
H
12
72.150
490.4
369.10
nPentane
C
5
H
12
72.150
488.6
385.8
Neopentane
C
5
H
12
72.150
464.0
321.13
nHexane
C
6
H
14
86.177
436.9
453.6
2Methylpentane
C
6
H
14
86.177
436.6
435.83
3Methylepntane
C
6
H
14
86.177
453.1
448.4
Neophexane
C
6
H
14
86.177
446.8
420.13
2,3Dimethylbutane
C
6
H
14
86.177
453.5
440.29
Hydrogen sulfide
H
2
S
34.08
1300.
212.45
Carbon Dioxide
CO
2
44.010
1071.
87.91
Nitrogen
N
2
28.0134
493.1
232.51
Argon
A
39.944
704.2
188.53
Oxygen
O
2
31.999
731.4
181.43
Example1
: Calculate Apparent Molecular Weight of Gas Mixture.
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 Spring '10
 ahmedalbamby
 Pseudocritical Properties, Dry Gas Properties

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