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Publication Citation: Comparison of Five Natural Gas Equations of State Used for Flow and Energy Measurement

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Author(s): Aaron N. Johnson; William Johansen;
Title: Comparison of Five Natural Gas Equations of State Used for Flow and Energy Measurement
Published: August 14, 2009
Abstract: Measurements of the flow and the energy content of natural gas rely on equations of state to compute four thermodynamic properties: 1) compressibility factor; 2) critical flow factor; 3) speed of sound; and 4)isentropic exponent. We compare these computed properties using five equations of state (REFPROP 8,GERG 2004, AGA 8, AGA 10, REFPROP 7) for eight natural gas compositions. The compositions vary from 97 % methane to 80 % methane; the latter has high levels of ethane, nitrogen, or carbon dioxide. These comparisons span the pressure and temperature ranges 0.1 MPa to 10 MPa and 270 K to 330 K. The five equations of state predict mutually consistent properties at low pressures. However, at 7 MPa, inconsistencies among the speeds of sound exceed 0.1 % and inconsistencies among critical flow factors exceed 0.3 % when the ethane concentrations exceed 8 % or the carbon dioxide concentration exceeds 7 %. We discovered discontinuities of 0.075 % in the critical flow factor computed by AGA 10.
Proceedings: Annual International Symposium on Fluid Flow Measurement | 7th | | CEESI
Location: Anchorage, AK
Dates: August 12-14, 2009
Keywords: AGA 8; AGA 10; critical flow factor; GERG 2004; natural gas; Refprop
Research Areas: Gas Metrology, Flow, U.S. Measurement System, Metrology