Thermodynamic Properties of Liquefied Natural Gases

Thermodynamic Properties of
Liquefied Natural Gases
M. Thol, R. Lentner, C. Tietz, R. Kleinrahm, R. Span, M. Richter
Research on LNG Properties at RUB
 Measurements on Liquefied Natural Gases (LNG)
 Multicomponent mixtures
 Binary mixtures
 Equations of State
 Enhanced revised Klosek-McKinley equation (eRKM)
 Binary mixtures
Fundamental equation of state in
terms of the Helmholtz energy
 Multicomponent mixtures
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Thol et al. | LNG Metrology Workshop 2017, Noordwijk
Accurate Density Measurements on LNG
Multicomponent mixtures
 3 mixtures including
 3 mixtures including
methane, ethane, propane, butane, nitrogen
(Set I)
methane, ethane, propane, butane, isobutane,
pentane, isopentane, nitrogen
(Set II)
Binary mixtures (Set III)
 Methane + propane
 Methane + isobutane
 Methane + pentane
 Methane + nitrogen
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(xC1 = 0.88)
(xC1 = 0.97)
Identify binary mixtures,
which have to be measured
to improve a fundamental
equation of state
(xC1 = 0.99)
(xC1 = 0.70, xC1 = 0.97, xC1 = 0.99)
Thol et al. | LNG Metrology Workshop 2017, Noordwijk
Binary systems with
high methane content
Equations of State
Revised Klosek-McKinley EOS1
Enhanced Revised Klosek-McKinley EOS2


Range of validity






Saturated liquid density ρ‘(T)
100 K ≤ T ≤ 115 K at ps
Uncertainty
Range of validity

Δρ/ρ = 0.1%
Saturated liquid density ρ‘(T)
Homogeneous liquid density ρ(T,p)
100 K ≤ T ≤ 135 K for ps ≤ p ≤ 10 MPa
Uncertainty
Δρ/ρ = 0.1%, for 100 K ≤ T ≤ 115 K
Δρ/ρ = 0.15%, for 115 K < T ≤ 135 K

International standard, GIIGNL handbook
1R.D.
2C.

International standard, GIIGNL handbook
McCarty, Mathematical Models for the Prediction of Liquefied-Natural-Gas Densities, J. Chem. Thermodyn. 14: 837-854 (1982)
Tietz, M. Richter, R. Kleinrahm, R. Span, Enhancement of the Revised Klosek and McKinley Method for Density Calculations of
Liquefied Natural Gas (LNG) over the Temperature Range from (100 to 135) K at Pressures up to 10 MPa, Fuel Process. Technol. (2016)
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Thol et al. | LNG Metrology Workshop 2017, Noordwijk
Fundamental Equation of State (EOS-LNG)
Helmholtz energy for mixtures
Ideal gas contribution
Reducing parameters
correspond to critical
parameters of pure fluids
Residual fluid contribution
Reducing parameters as
functions of composition
Pure fluid contribution at Departure term
corresponding states
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Thol et al. | LNG Metrology Workshop 2017, Noordwijk
Fundamental Equation of State (EOS-LNG)
Reducing parameters
Departure term
Combination of polynomial,
exponential and special
exponential terms
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Thol et al. | LNG Metrology Workshop 2017, Noordwijk
Adjustable parameters:
coefficients, temperature and
density exponents, exponential
parameters, number of terms
Fundamental Equation of State (EOS-LNG)
C1C3
No adjustment needed
C1C4i
New binary specific functions required
Deviations
calculated with:
C1N2
C1C5
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Thol et al. | LNG Metrology Workshop 2017, Noordwijk
 GERG-2008
Fundamental Equation of State (EOS-LNG)
C1C4i
C1C4i
C1C5
C1C5
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Thol et al. | LNG Metrology Workshop 2017, Noordwijk
Deviations
calculated with:
 GERG-2008
 EOS-LNG
Fundamental Equation of State (EOS-LNG)
Adjustment of binary specific function for C1C4
Libya
Methane
Ethane
Propane
n-Butane
Nitrogen
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81.56 mol-%
13.37 mol-%
3.68 mol-%
0.69 mol-%
0.70 mol-%
Oman
Methane
Ethane
Propane
n-Butane
Nitrogen
Thol et al. | LNG Metrology Workshop 2017, Noordwijk
87.89 mol-%
7.27 mol-%
2.93 mol-%
1.56 mol-%
0.35 mol-%
Norway
Methane
Ethane
Propane
n-Butane
Nitrogen
91.80 mol-%
5.70 mol-%
1.30 mol-%
0.40 mol-%
0.81 mol-%
Fundamental Equation of State (EOS-LNG)
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LNG2
LNG5
LNG7
Methane 84.64 mol-%
Ethane
12.80 mol-%
Propane
1.50 mol-%
n-Butane
0.21 mol-%
i-Butane
0.22 mol-%
Pentane
0.03 mol-%
i-Pentane 0.02 mol-%
Nitrogen
0.59 mol-%
Methane 87.97 mol-%
Ethane
7.24 mol-%
Propane
2.90 mol-%
n-Butane
0.69 mol-%
i-Butane
0.64 mol-%
Pentane
0.10 mol-%
i-Pentane 0.11 mol-%
Nitrogen
0.34 mol-%
Methane 97.89 mol-%
Ethane
1.00 mol-%
Propane
0.50 mol-%
n-Butane
0.21 mol-%
i-Butane
0.18 mol-%
Pentane
0.02 mol-%
i-Pentane 0.02 mol-%
Nitrogen
0.19 mol-%
Thol et al. | LNG Metrology Workshop 2017, Noordwijk
Adjustment of binary
specific functions for:
 C1C4
 C1C4i
 C1C5
 C1C5i
Methane + Nitrogen
Libya
LNG2
Norway
Deviations calculated with:
 GERG-2008
 Modified GERG-2008: C1N2 with Lorentz-Berthelot mixing rule
Possible reason maybe many-body interaction in multicomponent system???
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Thol et al. | LNG Metrology Workshop 2017, Noordwijk
xC1 / mol-% xN2 / mol-%
Libya
81.56
0.6953
LNG2
84.64
0.5854
Norway
91.80
0.8050
Liquid-Liquid Equilibria
 In the literature, only methane + hexane and
L
C1C5:
xC1 = 0.5
VLE
LLE
higher-order hydrocarbons are known to exhibit
liquid-liquid equilibria
 Liquid-liquid equilibria can be found even for
“simple” mixtures such as methane + pentanes
or butanes
V
 Liquid-liquid equilibria have to be considered
L
LLE
C1C5i:
xC1 = 0.5
VLE
V
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Thol et al. | LNG Metrology Workshop 2017, Noordwijk
not only for modeling but also during
measurements:
unreasonable movement of sinker was detected
when measuring methane + n-pentane
Summary
 Based on investigations of multicomponent LNG mixtures, binary systems
with high methane content were comprehensively studied:


New liquid density measurements of C1C3, C1C4i, C1C5 and C1N2
New binary specific functions for C1C4, C1C4i, C1C5 and C1C5i
 Representation of multicomponent systems was significantly improved:
 5 of 6 systems: Δρ/ρ < 0.05%
 Maximum deviation of LNG2: Δρ/ρ = 0.061%
 Liquid-liquid equilibria were found for C1C4, C1C4i, C1C5, C1C5i
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Thol et al. | LNG Metrology Workshop 2017, Noordwijk
Outlook

The current EOS-LNG has to be evaluated for the representation of other
thermodynamic data than density

Experimental investigation of additional binary mixtures, e.g. C1C4 or C1C5i
filling system of single-sinker densimeter needs to be modified

Additional thermodynamic properties have to be measured, in particular
speed of sound and vapor-liquid equilibrium

Liquid-liquid equilibria have to be considered, even for “simple” systems such as
C1C4, C1C4i, C1C5, or C1C5i

Fitting techniques have to be modified to allow for:


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the simultaneous optimization of binary specific functions
the application of measurements of multicomponent systems to the fit
Thol et al. | LNG Metrology Workshop 2017, Noordwijk
RESEARCH
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Thol et al. | LNG Metrology Workshop 2017, Noordwijk

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