1、 GPA RR-139 95 3824b99 0017bb3 247 = Research Report RR-139 Thermodynamic Properties of CO2 + C2H6 Mixtures A Joint Research Report by the Gas Processors Association and the Gas Research Institute Project 842 GRI Contract No. 5087-260-1449 H. Duarte-Garza C-A. Hwang M. W. Kidd W. W. R. Lau D. Mller
2、P. T. Eubank J. C. Holcte K. R. Hall Texas A and for the infringement of any patent or the violation of any federal, state or municipal law or regulation arising from the use of any information, apparatus, method or process disclosed in this report. GRI DISCLAIMER LEGAL NOTICE: This report was prepa
3、red by the Texas A or 2. Assumes any liability with respect to the use of, or for damages resulting from the use of, any information, apparatus, method or process disclosed in this report. . 111 Copyright Gas Processors Association Provided by IHS under license with GPANot for ResaleNo reproduction
4、or networking permitted without license from IHS-,- - GPA RR-LIY 95 R 3824699 0037667 992 R RESEARCH SUMMARY Title Contractor Texas A the pycnometer density measurements range from 240 to 350 K at pressures to 35 MPa. The isochoric densities and phase boundary conditions range from 235 to 400 K at p
5、ressures to 12 MPa. The calorimetric measurements are at 15 and 18 MPa at temperatures from 230 to 350 K. The accuracies of the densities are better than O. 1 % and are discussed in detail in the report. Energies and entropies derived from P-V-T measurements are about the same order of accuracy as t
6、he calorimetric measurements (estimated uncertainties about 2x experimental). The properties reported here are: densities, phase boundary conditions, virial coefficients (second, third and cross), energies, enthalpies and entropies. Because the number of laboratories capable of measuring fluid prope
7、rties accurately over extended ranges of temperature and pressure has diminished dramatically over the past two decades, we have adopted the approach of constructing several apparatus capable of rapid, automated measurements. The ranges of the various apparatus overlap to assure internal consistency
8、. Primary measurements agree within O. 1% for these apparatus. We use a Burnett apparatus, a Burnett-isochoric apparatus, a continuously weighed pycnometer, two isochoric apparatus and a flow calorimeter to measure fluid densities, energies, enthalpies, entropies and phase equilibria. The results fr
9、om these apparatus are sufticiently accurate and precise to permit stringent testing and development of equations of state and predictive correlations. Tech IZ ical Approach iv Copyright Gas Processors Association Provided by IHS under license with GPANot for ResaleNo reproduction or networking perm
10、itted without license from IHS-,- GPA RR-139 %5 3824699 0017668 829 D FOREWORD (GPA) Production, processing, and transmission of carbon dioxide-rich streams for use in enhanced oil recovery require detailed knowledge of high pressure thermal properties. Enthalpies are needed for compressor design, e
11、xchanger and cooler design, and for simulation of high temperature and pressure profiles in carbon dioxide wells. Near-critical fluids show large changes in thermodynamic properties in response to small variations in temperature, pressure and trace impurities. In many of the proposed applications of
12、 carbon dioxide, the fluid will be at near-critical or super-critical conditions. Project 842 has been designed to develop a reliable thermal properties data bank. High accuracy experimental thermal properties have been collected for carbon dioxide-rich mixtures containing small quantities of nitrog
13、en, hydrogen sulfide, and light hydrocarb0ns;e.g. , methane and ethane. This particular report presents the results for mixtures of carbon dioxide and ethane. Experimental measurements of densities for mixtures of carbon dioxide and ethane over a wide range of temperature and pressures are collected
14、 using four different experimental techniques. Other properties are evaluated using standard thermodynamic procedures. This report presents data for viiial coefficients, energies, enthalpies and entropies. This project has been funded as a joint venture between GFU and GPA. Arild Wilson Chairman GPA
15、 Enthalpy Steering Committee Lyman Yarborough Chairman Technical Section F Technical Data Development Jeff Savidge Project Manager Gas Research Institute V Copyright Gas Processors Association Provided by IHS under license with GPANot for ResaleNo reproduction or networking permitted without license
16、 from IHS-,- - GPA RR-137 75 E 3829699 O037669 765 TABLE OF CONTENTS REPORT DOCUMENTATION PAGE i1 GPA DISCLAIMER 111 GRI DISCLAIMER . ni RESEARCH SUMMARY . iv FOREWORD (GPA) . v LIST OF TABLES vi1 LIST OF FIGURES . vi11 INTRODUCTION 1 . . . RESULTS AND CONCLUSIONS . 1 DISCUSSION OF RESULTS . 2 EXPER
17、IMENTAL DETAILS . .5 EXPERIMENTAL UNCERTAINTY .6 REFERENCES 8 APPENDIX - Nomenclature . 9 vi Copyright Gas Processors Association Provided by IHS under license with GPANot for ResaleNo reproduction or networking permitted without license from IHS-,-Table LIST OF TABLES Page 1 . Experimental P-V-T va
18、lues for CO2 + C2H6 mixtures (Burnett apparatus) 10 11.1 . Derived second and third virial coefficients for CO2 + C2H6 mixtures . 11 11.2 . Derived cross virial coefficients for CO2 + C2H6 . 11 III . Experimental P-V-Tvalues for CO2 + C2H6 mixtures (pycnometer) . 12 IV. . Pressure residual propertie
19、s and correction terms for CO2 14 IV.2 . Pressure residual properties and correction terms for C2H6 16 IV.3 . Pressure residual properties and correction terms for 25.17 mol % CO2 + 74.83 mol % C2H6 . 18 IV.4 . Pressure residual properties and correction terms for 49.25 mol % CO2 + 50.75 mol % C2H6
20、20 IV.5 . Pressure residual properties and correction terms for 50.04 mol % CO2 + 49.96 mol % C2H6 . 22 IV.6 . Pressure residual properties and correction terms for 73.98 mol % CO2 + 26.02 mol % C2H6 . 23 IV.7 . Pressure residual properties and correction terms for 90.37 mol % CO2 + 9.63 mol % C2H6
21、25 V- 1 . Total properties for CO2 27 V.2 . V.3 . Total properties for C2H6 . 29 Total properties for 25.17 mol % CO2 + 74.83 mol % C2H6 31 V.4 . Totul properties for 49.25 mol % CO2 + 50.75 mol % C2H6 33 V.5 . Total properties for 50.04 mol % CO2 + 49.96 mol % C2H6 35 V.6 . Total properties for 73.
22、98 mol % CO2 + 26.02 mol % C2H6 36 V.7 . Total properties for 90.37 mol % CO2 + 9.63 mol % C2H6 38 VI . Physical constants. conversion factors. and molecular weights . 40 VTI.l . Experimental P-V-T values for 50.042 mol% CO2 + 49.958 mol% C2H6 (isochoric apparatus) 41 VIT.2 . Phase boundary conditio
23、ns for 50.042 mol% CO2 + 49.958 mol% CzH6 42 VITI . Experiineiital enthalpy increments for CO2 + C2H6 mixtures (flow calori- meter) . 42 IX . Eiitfialpies and entropies for CO2 and c2H6 in the ideal gas state 43 X . Parameters for 6Z vs p fitting equation for CO:! + C2H4 . 43 vii Copyright Gas Proce
24、ssors Association Provided by IHS under license with GPANot for ResaleNo reproduction or networking permitted without license from IHS-,-GPA RR-139 9.5 3824b94 OOL767L 313 LIST OF FIGURES Figure 1 . Schematic diagram of Burnett apparatus . 44 Figure 2 . Schematic cross section of pycnometer . 45 Fig
25、ure 3 . Schematic cross section of low pressure isochoric apparatus 46 Figure 4 . Schematic cross section of flow calorimeter 47 . Vlll Copyright Gas Processors Association Provided by IHS under license with GPANot for ResaleNo reproduction or networking permitted without license from IHS-,-INTRODUC
26、TION This report documents experimental measurements of densities, enthalpy differences, and phase boundaries for carbon dioxide + ethane mixtures covering a wide temperature and pressure range and using four different experimental techniques. A Burnett apparatus, which is a gas expansion technique,
27、 provides the densities at 300 and 320 K at pressures up to 7 MPa. Although this apparatus is capable of operating over wider conditions of temperature and pressure, it is slow to change temperature and at high pressures its accuracy deteriorates. A continuously weighed pycnometer supplies the densi
28、ties from 240 to 350 K up to 35 MPa. This apparatus is much faster for temperature changes and maintains accuracy at high pressures, but becomes less accurate at low pressures. An isochoric apparatus provides densities and phase boundaries from 230 to 400 K up to 12 MPa. The isochoric measurement is
29、 faster than the Burnett and more accurate than the pycnometer. Finally, a flow calorimeter produces enthalpy differences from 230 to 350 K at 15 and 18 MPa. Standard thermodynamic procedures permit evaluation of other properties given the densities. Those which concern this report are virial coeffi
30、cients, energies (internal, Helmholz, Gibbs), enthalpies and entropies. A new technique is presented in which the data provide correction terms for an equation of state model to calculate the derived thermal properties. This is a powerful model improvement technique which applies whenever data are a
31、vailable. RESULTS AND CONCLUSIONS Table 1 contains the experimental temperatures and pressures from the Burnett apparatus for five carbon dioxide + ethane mixtures. The temperatures are 300 and 320 K and the pressures range up to 10 MPa. Analysis of each isotherm using a maximum likelihood technique
32、 dcveloped by Embry (1980) yields the densities and compressibility factors, which also appear in Table I. Derived second and third virial coefficients (pure and cross) comprise Table II. Table III contains densities measured with the pycnometer and derived compressibility factors for the pures and
33、the five mixtures of carbon dioxide + ethane. These data cover temperatures from 225 to 350 K at pressures to 35 MPa. The pressure residual functions (Hi, Si) calculated from the model, in this case DDMIX, together with the correction terms (SZ, SEP, SSR) for the pures and mixtures appear in Tables
34、IV-1 to IV-7. Tables V-1 through V-7 contain the total U, H, A, G, S values along with densities and Compressibility factors for the pures and mixtures at even values of temperature and pressure. Molar masses (molecular weights) for these mixtures and factors for conversion of property values in SI
35、units into American engineering units are available in Table VI. Table VII-1 contains experimental P-V-T values collected on the isochoric apparatus for the 50 mol% CO;? mixture while Table VII-2 presents phase boundary points for the same mixture. Specific enthalpy increments measured using the flo
36、w calorimeter appear in Table VIII for pure CO;? and ten mixtures with ethane. Enthalpies and entropies from the TRC Thermodynamics Tables for CO;? (1984) and C2H6 (198 1) in the ideal gas state comprise Table IX. Table X contains the parameter values for the model correction term, 62. The experimen
37、tal data in this project are state of the art measurements and generally accurate within O. 1%. This information is suitable for both stringent testing and development of models and coil-elations. In fact, these data formed a significant contribution to the development 1 Copyright Gas Processors Ass
38、ociation Provided by IHS under license with GPANot for ResaleNo reproduction or networking permitted without license from IHS-,- GPA RR-139 95 3824699 O037673 L9b m of AGA-8. The data extension technique developed in this project can be extended to other models and form a general correction term for
39、 any equation of state. With this correction, the equations can be nearly as accurate in the near critical regions as they are in any other region. DISCUSSION OF RESULTS The data require no special discussion, being self-explanatory. However, the data extension technique does need some explanation.
40、Energies, enthalpies and entropies can be calculated from P-V-T data using the concept of residual functions. The density residual function is: and the pressure residual is: aR(T,P) = Q,(T,P)-Q,IG(T,P) Here denotes a property of a real fluid and QjIG denotes the property of an ideal gas at the same
41、conditions. All the residual functions are related to two dimensionless integrals involving P- V-T properties of the real fluids: RT O Isochoric measurements provide a direct determination of the derivative required to compute the integral I,. Because most of our data are isothermal P-V-T measuremen
42、ts, we have developed a modified approach to obtain accurate energy, enthalpy and entropy values. We utilize an accurate mathematical model (DDMIX) for mixtures containing carbon dioxide developed by Ely (1989). We use this mathematical model to calculate the fluid properties and then correct these
43、values using our P-V-T experimental values. The procedure is to define: 6z = zexp - z, = 6ZR = ar where 2 is the compressibility factor and Q, represents a thermodynamic property. The subscript exp denotes an experimental value while the subscript M denotes a value calculated with a mathematical mod
44、el, in this case DDMIX. The residual internal energy is: RT RT RT 2 Copyright Gas Processors Association Provided by IHS under license with GPANot for ResaleNo reproduction or networking permitted without license from IHS-,- GPA RR-337 75 3824677 0037674 O22 where O The residual enthalpy then become
45、s: HI - U su H(T,P,) = O SG(T,P,) = O We have used the ideal gas enthalpy and entropy values from the Thermodynamic Research Center (TRC) Tables. Total enthalpy values are calculated from: H(T,P)= HM +HG(T,P)+6HR where HM = H,(T,P) - HM(T, 1 mbar) The pure fluid enthalpies HlzG(T,P) are obtained fro
46、m the TRC Tables, and 6HR is the correction for inadequacies of the model. Total entropy values are calculated as follows: S(T,P)= S; +SG(T,P)+6SR where Si =S,(T,P)- S,(T,lmbar)-Rln SZG(T,P) = zxiS;“(T,P,) - Rxxi lnx, - Rln i i The pure fluid entropies SrfG(T,P) are obtained from the TRC Tables, and
47、 for inadequacies of the model. We use 1 mbar in the above equations to value from the model. The other energy functions are calculated from: U(T,P) = H(T,P) - ZRT G( T, P) = H( T, P) - TS( T, P) A( T, P) = U( T, P) - TS( T, P) SR is the correction provide an ideal gas 4 Copyright Gas Processors Ass
48、ociation Provided by IHS under license with GPANot for ResaleNo reproduction or networking permitted without license from IHS-,-EXPERIMENTAL DETAILS Burnett Apparatus The Burnett method is an experimental technique capable of producing accurate P-V-T data. No measurements of mass or volume are requi
49、red; only pressure and temperature of the sample fluid are measured. Figure 1 is the schematic of the Burnett apparatus, which is discussed in detail elsewhere (Hwang, 1988). The temperature is measured with a MINCO (model S 1059-2) platinum resistance thermometer (PRT) which is inside the Burnett cell between the primary volume VA and the secondary volume VB. The
