Feasibility Study for a new Densimeter for the Accurate Measurement of the Densities of Liquefied Natural Gas

Transcription

1 Feasibility Study for a new Densimeter for the Accurate Measurement of the Densities of Liquefied Natural Gas M. Richter, R. Kleinrahm, R. Span GERG Academic Network Event Brussels, June 3 rd, 2010

2 Contents Necessity and benefit of new measurements Literature study - Density measurements on LNG Densimeters for LNG and their uncertainties Expertise in density measurement at RUB Concept for a new densimeter for the accurate measurement of the densities of liquified natural gas Conclusion 2

3 Necessity and benefit of new measurments 100 ( r - r EOS )/r EOS 100 ( r - r EOS )/r EOS Detailed studies at RUB have shown: Comparison of GERG-2004 EOS and Revised Klosek- McKinley Method with saturated-liquid density * According to GIIGNL - LNG Custody Transfer Handbookmeasurements of LNG 1. Billing of LNG* (only low pressures) Problem: Haynes (1982) No model Hiza can & Haynes be(1980) clearly recommended! Haynes (1982) Haynes (1982) Haynes (1982) Haynes (1982) Hiza & Haynes (1980) Temperature / K Revised Klosek-McKinley Method GERG-2004 EOS Uncertainty of the measurements: Dr /r = 0.1% (given by the authors + uncertainty of the composition = Total uncertainty: 0.3%) (estimated by RUB) Revised Klosek and McKinley EOS for determination of densities (only liquid region: T = 90K to 115K, p 1bar, Dr/r = 0.1%???) New Reference EOS: GERG-2004 (entire fluid region: T = 90K to 450K, p 700bar, Dr/r = 0.1% to 0.5% for LNG in the liquid region) Revised Klosek-McKinley method was fitted to some of these experimental data Deviation between Klosek McK. and GERG-2004 up to 0.2% GERG-2004 EOS describes these data within the uncertainty of the EOS of 0.1 to 0.5% in this region 3

4 Comparison: GERG-2004 EOS and Revised Klosek-McKinley Method with saturated-liquid density measurements of LNG 100 ( r - r EOS )/r EOS Revised Klosek-McKinley Method Uncertainty of the measurements: Dr /r = 0.1% (given by the authors + uncertainty of the composition = Total uncertainty 0.3%) (estimated by RUB) 100 ( r - r EOS )/r EOS GERG-2004 EOS Temperature / K Haynes (1982) Hiza & Haynes (1980) Haynes (1982) Haynes (1982) Haynes (1982) Haynes (1982) Hiza & Haynes (1980) Revised Klosek-McKinley method was fitted to some of these experimental data GERG-2004 EOS describes these data within the given uncertainty of 0.1 to 0.5% in this region 4

5 Comparison: GERG-2004 EOS and Revised Klosek-McKinley Method with saturated-liquid density measurements Uncertainty of the measurements: - Haynes and Hiza (1977): Dr /r = 0.1% - Kleinrahm and Wagner (1986): Dr /r = 0.015% The revised Klosek-McKinley method was fitted to the data of Haynes and Hiza The GERG-2004 EOS describes accurate data of Kleinrahm and Wagner within its small uncertainties 5

6 Necessity and benefit of new measurments 100 ( r - r EOS )/r EOS 100 ( r - r EOS )/r EOS Detailed studies at RUB have shown: Revised Klosek-McKinley Method GERG-2004 EOS Temperature / K Comparison of GERG-2004 EOS and Revised Klosek- McKinley Method with saturated-liquid density measurements of LNG 2. Simulation of LNG related processes (entire liquid region) Mostly cubic EOS are used (e.g. Peng-Robinson, Redlich-Kwong-Soawe) Liquid region: large deviations between calculations with cubic EOS and GERG-2004 Uncertainty of the measurements: Dr /r = 0.1% (given by the authors + uncertainty of the composition = Total uncertainty: 0.3%) (estimated by RUB) Revised Klosek-McKinley method was fitted to some of these experimental data New reference data is essential to verify thermophysical models! Haynes (1982) Hiza & Haynes (1980) Haynes (1982) Haynes (1982) Haynes (1982) Haynes (1982) Hiza & Haynes (1980) GERG-2004 EOS describes these data within the uncertainty of the EOS of 0.1 to 0.5% in this region 6

7 Literature study Density measurements on LNG Fluid Authors p,t-range LNG Hiza + Haynes (1980) T: K p: MPa LNG Haynes (1982) T: K p: MPa LNG Klosek + McKinley (1968) CH 4 + N 2 CH 4 + N 2 CH 4 + CO 2 CH 4 + C 2 H 6 CH 4 + C 2 H 6 Hiza et al. (1977) Straty + Diller (1980) Magee + Ely (1988) Hiza et al. (1977) Haynes et al. (1985) CH 4 + Rodosevich + C 2 H 6 Miller (1973) CH 4 + C 2 H 6 Literature Research Hiza + Haynes (1978) Number of points Total r g r l r p>pk r Dr/r [%] Method Magnetically susp. sinker Magnetically susp. sinker T: K Pycnometer p: p u T: K p: MPa T: K p: MPa T: K p: 2-35 MPa T: K p: MPa T: K p: MPa T: K p: MPa T: K p: MPa Result: Poor data situation for LNG Summary: Number of measurements Magnetically susp. sinker 478 x x1 x Pycnometer 91 x x1 x Pycnometer Magnetically susp. sinker 414 x x1 x Pycnometer Pycnometer GERG-2004 database Haynes et al. (NIST) + Klosek McK. (Industry): 171 (sat. LNG) NIST: ca (pure fluids + mixtures) RUB: ca (pure fluids) Other experimenters: ca. 400 (pure fluids + mixtures) Industry: ca. 350 (pure fluids + mixtures) Conclusion: Only a few groups work in this experimental field No data available for LNG in the homogeneous liquid region Highest measurement accuracy: Densimeters at RUB Magnetically susp. sinker 7

8 Densimeters for LNG and their uncertainties Authors Klosek and McKinley (1968) Haynes and Frederick (1983) Kleinrahm and Wagner (1984) Brachthäuser, Kleinrahm, Lösch and Wagner (1993) Air Products, USA NIST RUB RUB Technique Pycnometer Magnetically suspended sinker two sinker hydrostatic balance with MSC single sinker hydrostatic balance with MSC t - range -150 C to -180 C -200 C to 50 C -210 C to 70 C -40 C to 250 C p - range p = p a p 350 bar p 120 bar p 300 bar Dr/r [%] 0.5% 0.1% (plus unc. of composition) 0.02% to 0.01% 0.02% Total: ~ 0.3% Main Problems VLE-Measurement demixing of the liquid only saturated liquid densities VLE-Measurement demixing of the liquid only saturated liquid densities Until today: mixtures measured only in gas phase Until today: mixtures measured only in gas phase 8

9 Expetise in density measurement at RUB Measurement technique (Archimedes principle) Single-sinker densimeter Two-sinker densimeter 9

10 p rt Measurements on Nitrogen (N 2 ) Experiences from previous Projects Total uncertainty: Dr/r = 0.01 % to % (k = 2) (Measured in the same fluid regions: Methane, Ethane, Propane, Carbon dioxide, etc. Published in: J. Chem. Thermodynamics, 1986 ff) 10

11 High-Accuracy Two-Sinker Densimeter for Natural Gas (Developed for E.ON Ruhrgas, 1991) Two-sinker Reference Densimeter for Natural Gas at Standard Conditions (Developed for E.ON Ruhrgas, 2004) Portable Reference Densimeter for Checking the Density Determination in Natural gas Meter Runs (Developed for E.ON Ruhrgas, 2001) 11

12 Specifications for a new LNG-Densimeter Quantity to be measured: Density of LNG: in the homogeneous liquid region on the saturated-liquid line, including vapour pressure in the homogeneous gas region Temperature Range: 90 K to 293 K Pressure Range: 0.05 MPa to 12 MPa Density Range: 10 kg/m 3 to 1000 kg/m 3 Total uncertainty Dr/r: 0.02 % (plus uncertainty resulting from gas analysis) Measuring principle: Single-Sinker method (Silicon sinker: V = 25.7 cm 3, m = 60 g) Temp. measurement: Pressure measurement: Density measurement: Gas analysis: Thermostating: Insulation: Uncertainty approx K Uncertainty approx % Uncertainty approx % (for liquids) Only one analysis of the m 3 gas cylinder is required Liquid nitrogen (LN 2 ) Outer cylinder, filled with Argon at about 2 kpa as insulation gas 12

13 p,t diagram of a typical natural gas Illustration of the measurement points (Calculated with the GERG-2004 equation of state) 13

14 Difficulties regarding the density measurement of LNG [see e.g. Klosek and McKinley (1968) or Haynes and Frederick (1981)] The three main problems Decomposition of the fluid during the filling process Accurate pressure measurement (or differential pressure measurement) at low temperatures is not possible Decomposition of the fluid in the measuring cell resulting from the existing VLE state (A gas phase is not avoidable because the pressure sensor is located at ambient temperature) Solutions Filling of the densimeter at ambient temperature T a up to a pressure p > p CP and then isobaric cooling (e.g. at 12 MPa) Pressure measurement at T a and integration of a special reference cell Controlled phase transition liquid-gas (VLE) in the reference cell and specific adjustment of the fluid pressure Only homegenous liquid phase in the measusring cell (due to the integration of a refenrence cell) Max. 1% - 3% vapour volume in the measuring cell during the measurement of saturated-liquid densities 14

15 p,t diagram of a typical natural gas Illustration of the filling and measurement procedure 15

16 Basic Design of the new LNG-Densimeter 16

17 Setup of the new LNG-Densimeter 17

18 Conclusion Results: New reference data needed! Two- and Single- Sinker hydrostatic balance with magnetic suspension coupling are most accurate measuring principles Main problems with LNG density measurement identified and solved within the present project Conceptual design for a new LNG-densimeter is done Outlook: Detail Engineering for LNG-densimeter is in progress as part of the GERG Project 1-67: Denisty of LNG and the EMRP (European Metrology Research Programme) First new reference data available for LNG by end of

19 Thank you for your attention! 19