Natural Gas Properties

Transcription

1 TPG 4140 NTNU Natural Gas Proerties Professor Jon Steinar Gudmundsson Deartment of Petroleum Engineering and Alied Geohysics Norwegian University of Science and Technology Trondheim Setember 18, 2013

2 Outline Proerties used in natural gas calculations Phase diagrams and terminology (CCP & CCT) Real gas law, z-factor, density and FVF Corresonding states Comressibility factor (z-factor) Examle calculation (GPA gas comosition) Heat caacity and heat caacity ratio Viscosity of natural gas Calorific values (GCV & NCV) Summary

3 Proerties Used Density, need z-factor and molecular weight Flow in wells, need z-factor and viscosity Pressure dro in ielines, need density and viscosity Temerature 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 gross calorific value and relative density

4 Calculations and Data on Home Page

5 PHASE DIAGRAM Pedersen et al. (1989) Proerties of Oils and Natural Gases, Gulf Publishing Comany

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7 Rojey & Jaffret (1997)

8 Rojey & Jaffret (1997)

9 TERMINOLOGY Natural gas, C1-C5+, water, inert gases NGL (Natural Gas Liquids), under ressure LPG (Liquefied Petroleum Gas), roan+butan, -42 C LNG (Liquefied Natural Gas), -162 C, 1 atm CNG (Comressed Natural Gas), bar Condensate (liquid), C4-C7, transition gas-to-oil Oil, C6 and heavier fractions

10 TYPICAL SPECIFICATIONS Transort Secification Hydrocarbon dew oint, 5-10 C below ambient Water dew oint, about 5 C below HC dew oint Temerature, C Pressure, deends on receiving terminal Sales Secification (in addition to above) Heating value (GHV = Gross Heating Value), MJ/Sm 3 Wobbe Index (WI = GHV/(secific density) 0,5 Removal of non-hc gasser (inert gases) htt://

11 TYPICAL SPECIFICATIONS

12 COMPOSITION Generalization Non-Associated (dry gas) methane > 90 volume % Associated gas (wet gas) methane < 90 volume % Søtt gass (sweet gas) CO2 < 2 volume % Surt gass (sour gas) CO2 > 2 volume % Søtt gass (sweet gas) H2S < 1 volume % Surt gass (sour gas) H2S > 1 volume % Rojey & Jaffret (1997) fra Valais (1983)

13 Volume Rate at s.c. to Mass Rate Comress 7 MSm 3 /d from 80 to 160 bara Inlet temerature 30 C Molecular weight M = kg/kmol Atm. Pressure bara At s.c., ρ = kg/sm 3 (T = 15 C) Mass flow rate = kg/d Per second m = 70 kg/s M and ρ from Excel sheets

14 Real Gas Law z T T q q z T T V V z zrt v znrt V sc sc sc sc sc sc sc 1 1 1

15 Density and FVF B q q z T T B Sm m V V FVF B zrt M n V M znrt V sc sc sc sc 3 3

16 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 PVTsim.

17 Fletcher (1993) Real Gas Factor vs. Pressure at 25 C

18 Fletcher (1993) Real gas factor with reduced & T

19 Reduced & T T r T c r c T i r i r T ci ci y T T y i c i c Kay s Rule

20 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 seudo-reduced ressure or temerature in multicomonent systems. Commonly used when gas roerties (natural gas and other gases) are to be correlated and/or resented.

21 GPA (1998)

22 Rojey o.a. (1997)

23 Equations and Gravity c 4,892 0,405 ( MPa) T c 94,72 170,75 ( K ) M M gas air M gas Thomas o.a. (1970), fra Rojey o.a. (1997) 28,964 ( at s. c.)

24 Cambell (1984) Physical Constants of Natural Gas

25 GPA (1998) Examle Calculation for Natural Gas

26 GPA (1998) Gas Comosition (Excel sheet) Comonents Molecular weight Mole fraction Tci Tci Pci Pci g/mole yi or K sia Ma Methan, CH4 16,042 0, ,8 4,61 Ethan, C2H6 30,07 0, , ,88 Proan, C3H8 44,10 0, , ,25 i-butane, C4H10 58,12 0, , ,65 n-butane, C4H10 58,12 0, ,80 i-pentane C5H12 72,15 0, ,39 n-pentane C5H12 72,15 0, ,37 Hexane C6H14 86,18 0, ,01 Hetane C7H16 100, ,74 Hydogen, H2 2, ,29 Nitrogen, N2 28, , ,39 Oxygen, O2 32, , ,04 Carbon dioxid, CO2 44, , ,38 Hydrogensulfid, H2S 34, , ,01 Dihydrogenoksid, H2O 18, ,06 Σ Mole fraction 1,0000 Total molecular weight gas 20,43 g/mole

27 Phase Enveloe for GPA (1998) Gas

28 Beggs (1984)

29 Cambell (1984)

30 Heat Caacity blanding for massefraksjon masse bruk er Når blanding for molfraksjon bruk mol er Når K kmol kj C K kmol kj R T T R C CT BT A R C T T C CH CH ). / ( 10 0, ,092 0,2047 ). / 8,314 ( 10 2, ,081 1,

31 Smith o.a. (1996)

32 Heat Caacity Natural Gas Temerature, Pressure, Relative Density a = 0.90 b = c = C a b T T c d e f d = e = f = Moshfeghian, M. (2013)

33 Heat Caacity Ratio M = kg/kmol T = 30 C = 86 F = 80 bara k = 1.26 (from diagram) R = kj/kmol.k z = k = 1.26 (from old equation = ideal gas) k = 1.19 (from new equation = real gas)

34 Ratio of Secific Heat Caacity k C C v k C C R k C C zr k H U

35 Heat Caacity Ratio Hysys Estimation GPA (1998) Associated Gas

36 Comarison of Heat Caacity Ratio GPA (1998) Gas at 80 bara & 30 C k Diagram 1,26 Ideal gas 1,26 Ideal gas with z-correction 1,19 Hysys ideal gas 1,158 Hysys 1,714

37 Ideal Gas Comression m (kg/s) 70 M (kg/kmol) 20,43 R (J/kmolK) 8314,34 T innlø C 30 P ideal m M RT 1 k k1 2 1 k1 k 1 k (C/Cv) 1,26 innlø bara 80 utlø bara 160 P (MW) 6,44 T utlø C 77

38 Real k Gas Comression m (kg/s) 7 M (kg/kmol) 20,43 R (J/kmolK) 8314,34 T innlø C 30 P ideal m M RT 1 k k1 2 1 k1 k 1 k (C/Cv) 1,19 innlø bara 80 utlø bara 160 P (MW) 6,33 T utlø C 65

39 Viscosity from Diagram Diagram shows viscosity against temerature for gas comonents (methane, ethane, roane etc.) at atmosheric ressure. Emirical equation (shown under, based on kinetic theory of gases) 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 y M 1/ 2 i i i 1/ 2 yim i

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

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

42 Viscosity 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. The correlation is available as sreadsheet. K ex X y

43 Combined Cycle Power Plant

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45 Combustion and Calorific Value

46 Summary Several hysical and thermodynamic roerties of natural gas are used in natural gas calculations. Real gas law and reduced ressure and temerature used in diagrams to obtain z-factor. Emirical correlations used for transort roerties, for examle for viscosity. Heat caacity at constant ressure can be obtained from figures and equations. Also as function of ressure, temerature and relative density. Heat caacity ratio values uncertain. Equation Of State (EOS) used in comuter rograms for VT roerties (also thermodynamic roerties).

47 References Beggs, H.D. (1984): Gas Production Oerations, OGCI Publications, Tulsa, Oklahoma Cambell, J.M. (1994): Gas Conditioning and Processing, Cambell Petroleum Series, Norman, Oklahoma. Fletcher, P. (1993): Chemical Thermodynamics, Longman, Harlow, Essex. Gas Processors Association (1998): Engineering Data Book, Tulsa, Oklahoma. Guta, N. (2011): Overview of Ormen Lange Project, Guest Lecture, TPG 4140 Natural Gas, NTNU. 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 Moshfeghian, M. (2013): Variation of Natural Gas Heat Caacity with Temerature, Pressure and Relative Density, J.M. Cambell & Co., (Internett February 2013). Rojey, A. (1997): Natural Gas, Éditions Techni, Paris. Smith, J.M., Van Ness, H.C. & Abbott, M.M. (1996): Introduction to Chemical Engineeering Thermodynamics, McGraw-Hill, New York.

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