PROPERTIES OF NATURAL GAS

Transcription

1 1 PROPERIES OF NAURAL GAS Jón Steinar Guðmundsson PG4140 Naturgass Setember 16, 2008 Introduction Equations and roerties used in course Real gas law, z-factor, density and FVF Corresonding states Viscosity of natural gas Heat caacity and heat caacity ratio Water vaour in natural gas Summary

2 2 Proerties Used in Equations Density, need z-factor and molecular weight Flow in wells, need z-factor and viscosity Pressure dro in ielines, need density and viscosity emerature in ielines, need heat caacity Comressor ower and exhaust temerature, need molecular weight and heat caacity ratio Molecular weight, need relative density (gravity) Reynolds number, need density and viscosity Wobbe index, need calorific value and relative density Hydrates and water, need water vaour in natural gas (diagram or PV ackage)

3 3 Real Gas Law z q q z V V z zr v znr V sc sc sc sc sc sc sc 1 1 1

4 4 Density and FVF ( ) B q q z B Sm m V V FVF B zr M n V M znr V sc sc sc sc 3 3 ρ ρ

5 5 Finding real gas factor (z-factor) Diagram based on corresonding states, reduced ressure and temerature for single comonents and seudo-reduced ressure and temerature for natural gas. Emirical equations matched to z-factor diagram for natural gas. Uses many constants and coefficients and in some cases iteration. Equation Of State (EOS) such as Peng-Robinson, Redlich-Kwong and Benedict-Webb-Rubin. Imlemented in many different comuter rograms. EOS imlemented in many commercial comuter ackages such as Hysys, Proser and PVsim.

6 6 Real gas factor with ressure at 25 C Fletcher (1993)

7 7 Real gas factor with reduced & Fletcher (1993)

8 8 Reduced & r c r c ( ) ( ) i r i r ci ci y y i c i c Kay s Rule

9 9 Corresonding States When ressure and temerature are normalized using critical ressure and temerature, then all roerties become the same/similar, irresective of comosition. Normalized ressure or temerature are called reduced ressure or temerature in one comonent systems. Normalized ressure or temerature are called seudoreduced ressure or temerature in multi-comonent systems. Commonly used when gas roerties (natural gas and other gases) are to be correlated and/or resented.

10 10 GPA (1998)

11 11 Rojey o.a. (1997)

12 12 Equations and Gravity c 4,892 0,405 γ ( MPa) c 94,72 170,75 γ ( o K ) γ M gass M M gass luft γ 28,964 ( ved s. c.) homas o.a. (1970), fra Rojey o.a. (1997)

13 13 Physical Constants of Natural Gas Cambell (1984)

14 14 Examle Calculation for Natural Gas GPA (1998)

15 15 Viscosity from Diagram Diagram shows viscosity against temerature for gas comonents (methane, ethane, roane etc.) at atmosheric ressure. Emirical equation (shown under) gives estimate of viscosity to natural gas (mixture of methane, ethane, roane etc.) at atmosheric ressure. Diagram gives viscosity ratio to viscosity at atmosheric ressure against reduced ressure and temerature μ μ y M 1/ 2 i i i 1/ 2 yim i

16 16 Katz o.a. (1959), fra Rojey o.a. (1997)

17 17 Katz o.a. (1959), fra Rojey o.a. (1997)

18 18 Viscosity from correlation Several correlations in literature, for examle Carr et al. (1954), Lee et al. (1966) and Pedersen et al. (1987). Lee et al. (1966) correlation has recently been evaluated by Jeje and Mattar (2004) and has the form shown below. K, X and y are given by emirical equations. he correlation is available as sreadsheet on home age to course, link shown below. μ K ex ( y Xρ )

19 19 Cambell (1984)

20 20 Beggs (1984)

21 21 Heat Caacity ( ) blanding for massefraksjon masse bruk er Når blanding for molfraksjon bruk mol er Når K kmol kj C K kmol kj R R C C B A R C C CH CH ). / ( 10 0, ,092 0,2047 ). / 8,314 ( 10 2, ,081 1, γ β α

22 22 Smith o.a. (1996)

23 23 GPA (1998)

24 24 ools, Data & Hysys BEREGNINGER DIVERSE (EXCEL) - Calculations Miscellaneous (Excel) GASS-SAMMENSENING EKSEMPLER - Gas Comosition Examles GASS-SAMMENSENING I EKSPORRØRLEDNINGER - Gas Comosition in Exort Pielines FLUIDEGENSKAPER - Fluid Proerties OM Å KOMME I GANG MED HYSYS (fra N. Nesse) LÆREPROGRAM - utorial INSALLASJON AV PROGRAMPAKKE - Installation of Program Package

25 25 Summary Several hysical and thermodynamic roerties of natural gas are used in course. Real gas law and reduced ressure and temerature used in diagrams. Emirical correlations used for transort roerties, for examle for viscosity. Heat caacity can be obtained from figures. Equation Of State (EOS) used in comuter rograms for V roerties (also thermodynamic roerties). Hysys available at NNU (see info. on home age).

26 26 References Beggs, H.D. (1984): Gas Production Oerations, OGCI Publications, ulsa, Oklahoma Cambell, J.S. (1994): Gas Conditioning and Processing, Cambell Petroleum Series, Norman, Oklahoma. Fletcher, P. (1993): Chemical hermodynamics, Longman, Harlow, Essex. Gas Processors Association (1998): Engineering Data Book, ulsa, Oklahoma. Jeje. O. & Mattar, L. (2004): Comarison of Correlations for Viscosity of Sour Natural Gas, 5th Canadian International Petroleum Conference, Calgary, Alberta, June 8-10, Paer Rojey, A. (1997): Natural Gas, Éditions echni, Paris. Smith, J.M., Van Ness, H.C. & Abbott, M.M. (1996): Introduction to Chemical Engineeering hermodynamics, McGraw-Hill, New York.