RUHR-UNIVERSITÄT BOCHUM
Training – Density Calculations of
Metrology for LNG | Aberdeen, Scotland | 26.10.2018
N. von Preetzmann, P. Eckmann, M. Richter
2von Preetzmann et al. | Training „Metrology for LNG“ – LNG Density | 26th October 2018
LNG Research at RUB
P. Eckmann R. Kleinrahm N. v. Preetzmann
R. Span R. Lentner M. Richter
3von Preetzmann et al. | Training „Metrology for LNG“ – LNG Density | 26th October 2018
Primary Densimeter for “Metrology for LNG”
Technical specifications
• T-range: (90 to 300) K• p-range: (0.05 to 12) MPa• Hom. Densities (liquid and gas)
& saturated liquid density• U(ρ(T,p,x)) = 0.02 % (k = 2)
4von Preetzmann et al. | Training „Metrology for LNG“ – LNG Density | 26th October 2018
LNG Custody Transfer
General Formula for Calculating the LNG Energy Transferred(According to GIIGNL - LNG Custody Transfer Handbook)
E : the total net energy transferred from the loading facilities to the LNG carrier, or from the LNG carrier to the unloading facilities.
VLNG : the volume of LNG loaded or unloaded in m³.
ρLNG : the density of LNG loaded or unloaded in kg/m³.
GCVS,LNG: the gross calorific value of the LNG loaded or unloadedin MMBTU/kg.
Eg,displaced : the net energy of the displaced gas in MMBTU
E = VLNG ∙ ρLNG(T, p, x) ∙ GCVS,LNG − Eg, displaced [MMBTU]
5von Preetzmann et al. | Training „Metrology for LNG“ – LNG Density | 26th October 2018
LNG Density Calculation Methods – cf. CTH by GIIGNL
Reference manual for custody transfer procedures and equipment
• Widely used in Europe and Asia
• Including recommended methods for LNG property determination
• No accurate in-situ densimeters at LNG operating conditions available(large uncertainties)
• Determination of density by means of calculation methods is recommended
• A variety of calculation methods exists {
In general:• Fundamental Equation of States• Cubic Equation of States• Simplified Engineering Models
International Group of Liquefied Natural Gas Importers (2017)
6von Preetzmann et al. | Training „Metrology for LNG“ – LNG Density | 26th October 2018
LNG Density Calculation Methods – cf. CTH by GIIGNL
Revised Klosek-McKinley method (RKM) of R. D. McCarty (1980)
• ISO Standard (ISO 6578)
• Well-established for LNG custody transfer
• Calculation of saturated liquid densities
• Range of validity: T < 115 K
• Uncertainty: Δρ/ρ = 0.10 %
• Results often deviate from true density atpressures above saturation pressure
• Not usable for processes at elevated pressures (e.g., small scale applications)
𝑀𝑚𝑖𝑥
𝜌𝑚𝑖𝑥= 𝑣𝑚𝑖𝑥(𝑇) =
𝑖
𝑥𝑖 ∙ 𝑣𝑖 − 𝑘1 + 𝑘2 − 𝑘1 ∙𝑥𝑁2
0.0425∙ 𝑥𝐶𝐻4
7von Preetzmann et al. | Training „Metrology for LNG“ – LNG Density | 26th October 2018
LNG Density Calculation Methods – cf. CTH by GIIGNL
Enhanced Revised Klosek-McKinley (ERKM) method for saturated and pressurized LNG
• Range of validity: 100 ≤ T / K ≤ 135 Kp ≤ 10 MPa
• Uncertainties: for 100 ≤ T / K ≤ 115, Δρ/ρ = 0.10 %
for 115 < T / K ≤ 135, Δρ/ρ = 0.15 %
𝜌𝐿𝑁𝐺 = 𝜌𝑅𝐾𝑀 ∙ 1 + 𝑘𝑝
𝑘𝑝 = (𝑝 − 𝑝𝑠,𝑚𝑖𝑥) ∙ 4.06 ∙𝑇𝑃𝐶
𝑇𝑃𝐶 − 𝑇
1.79
The original RKM Pressure-dependent term
Approximation for the mixture‘s vapor pressure
Pseudo-critical temperature to avoid deviations at higher temperatures
Tietz, Richter, Kleinrahm, Span, Fuel Proc. Technol. 165 (2017) 19-26