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Mixture equations of state. SGERG-88, AGA8-DC92 (volumetric properties): compression factor, density (ISO 12213, GERG TM5, AGA report No.8) AGA8-DC92 (caloric properties): speed of sound, enthalpy (ISO 20765-1, AGA report No.10)GERG-2004: (ISO WD 20765-2, GERG TM15) compression factor
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1. Comparison of AGA ReportNo. 8 and GERG 2004Equations for Gas PropertyCalculations Eric W. Lemmon
Thermophysical Properties Division
National Institute of Standards and Technology
Boulder, Colorado
2. Mixture equations of state SGERG-88, AGA8-DC92 (volumetric properties):compression factor, density (ISO 12213, GERG TM5, AGA report No.8)
AGA8-DC92 (caloric properties): speed of sound, enthalpy (ISO 20765-1, AGA report No.10)
GERG-2004: (ISO WD 20765-2, GERG TM15)compression factor, caloric propertiesfundamental equation of state, vapor-liquid equilibrium, valid over the entire fluid region (single and 2-phase)
3. AGA-8 mixture model AGA Report No. 8, K.E. Starling and J.L. Savidge, Compressibility Factors of Natural Gas and Other Related Hydrocarbon Gases
Current industry standard
Valid for gas phase only, cannot calculate phase equilibrium
Temperature range: -130 şC to 400 şC (-200 şF to 760 şF)
Pressures up to 280 MPa (40,000 psia)
Detail characterization method for compressibility factor:“hybrid” type has features of virial EOS (power series in density) for low density calculations and exponential functions for high density calculations (similar to mBWR EOS)
5. Why not just use pressure for the independent variable in our equation of state?
7. Given density and temperature, all other properties can be calculated
Iterative solutions required given input conditions of pressure and temperature; pressure and enthalpy; pressure and entropy; saturation temperature; vapor pressure; etc.
8. Excess Helmholtz Energy Mixture Model Excess property model explicit in Helmholtz energy
Independent parameters are density and temperature
Generalized/Predictive
High accuracy
Requires accurate pure fluid equations of state
Calculates all thermodynamic properties, including heat capacities, speed of sound, vapor-liquid equilibria, liquid-liquid equilibria, and critical lines
11. Ranges of application for GERG-2004
12. Overview of components
13. Experimental data 21 components
70,000 experimental binary mixture data for correlation work (153) binary mixtures
22,000 experimental natural gas data and natural gas like multicomponent data for testing the new equation
More than 95% of all experimental natural gas and natural gas like multicomponent mixture data listed in the “GERG Databank of High-Accuracy Compression Factor Measurements” (GERG TM4 and TM7) are described with deviations of less than ± 0.1% .
14. Methane/Ethane VLE data
15. When to use AGA-8 vs. GERG-2004 ISO 20765 has two parts
Part 1 – AGA-8 in its Helmholtz form
Part 2 – GERG-2004
The ISO document currently allows AGA-8 (part 1) or GERG-2004 (part 2) to be used. The GERG equation should be used when the uncertainties in AGA-8 increase, but the ISO document does not specify where this occurs.
The uncertainties in AGA-8 increase at lower temperatures or lower methane concentrations (<80%).
A new AGA-8 taskgroup has been formed to investigate the differences between the two models and document the region where differences are within 0.05 %, 0.1 %, and 0.2% in density.
16. REFPROP - www.nist.gov/srd/nist23.htm
90 pure fluids
Mixtures with up to 20 components
All thermodynamic and transport properties, including heating value
GERG-2004 is main mixture model, but can use AGA-8 or cubics as well
Table and plot generation
Version 8.0 only allows mixtures up to octane, version 8.1 will allow mixtures with nonane, decane, and hydrogen sulfide
18. Methane
19. Methane/Ethane: 99/1
20. Methane/Ethane: 95/5
21. Methane/Ethane/Propane: 92/6/2
22. Methane/Ethane/Propane/Butane: 90/5/3/2
23. C1/C2/C3/C4/C5: 85/8/4/2/1
24. C1/C2/C3/C4/C5: 75/12/8/3/2
25. C1/C2/C3/C4/C5/N2/CO2: 75/8/4/2/1/2/8
26. C1/C2/C3/C4/C5/N2/CO2: 75/8/4/2/1/8/2
27. C1-8/N2/CO2: 80/6/3/1/.6/.2/.1/.1/2/7
28. C1/C2/C3/C4/C5/C6/C7/C8: 75/12/8/2/1/.8/.7/.5
29. A mini version of REFPROP is freely available for calculating the differences in density, speed of sound, or isobaric heat capacities between AGA-8 and GERG-2004 (but other properties are not calculated in this free version). The program is available at:
http://www.boulder.nist.gov/div838/theory/refprop/REF-DEVS/REF-DEVS.HTM
(upper/lower case is required in address)
(current program is very slow, an update will be available soon…)
30. Ken Hall’s Sample Compositions