(MBS I A publi- Rer#ence MBSIR 82-240 Heatmg Values of Natural Gas and Its Components U.S. DEPARTMENT OF COMMERCE National Bureau of Standards Center for Chemical Physics Chemical Thermodynamics Division Washington, DC 20234 May 1982 Technical Report Issued August 1982 red by e International des Importateurs Gaz natural Liquifie (GIIGNAL) aXTIOBAlf BUHUAU O# enrAJta>AKva tlMBAMT NBSIR 82-2401 AUG 1 9 1982 HEATING VALUES OF NATURAL GAS I C>-_ AND ITS COMPONENTS . Slo e- George T. Armstrong Thomas L. Jobe, Jr. U.S. DEPARTMENT OF COMMERCE National Bureau of Standards Center for Chemical Physics Chemical Thermodynamics Division Washington, DC 20234 May 1982 Technical Report Issued August 1 982 Sponsored by Groupe International des Importateurs de Gaz Natural Liquifie (GlIGNAL) U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director ( f 'i I i ''i ji ‘ f Preface The Office of Standard Reference Data of the National Bureau of Standards is responsible for a broad-based program to provide reliable physical and chemical reference data to the U.S. technical community. Under this program a number of data evaluation centers both at N3S and at universities and other private institutions are supported and coordinated; these activities are collectively known as the National Standard Reference Data System (NSRDS). Important areas of the physical sciences are covered systematically by NSRDS data centers, and data bases with broad utility are prepared and disseminated. These centers can also take on special compila- tions of data addressing specific applications. The existence of an ongoing program permits the collection of data for these special compilations to be carried out in an efficient and timely manner. This Report on the Heating Values of Natural Gas and Its Components was prepared with the assistance of the Chemical Thermodynamics Data Canter of the National Bureau of Standards. We hope that it will provide a useful source of reference data and computational methods for all those concerned with the heating value of natural gas. David R. tide, Jr. Chief Office of Standard Reference Data Dr. George Thompson Armstrong, the senior author, died on March 9, 1982. At that time an almost complete, well written draft was at hand and had been reviewed by several of his colleagues, including myself. It has been my privilege to help prepare the final version. The original organi- zation and wording have been retained wherever possible. Several sections have been completed, based on indications in the text. New atomic masses and heat capacities have been selected and a discussion of the enthalpy of combustion of methane (in Appendix 7) has been written. All of these were influenced by notes and letters, but, at times, go beyond them. I hope that the spirit and quality of the original has been maintained. There is one section missing: acknowledgements. Neither Mr. Jobe nor I can reconstruct a record of the many persons who were consulted, who advised or who sent in material. We thank all who have helped and hope that this report will both be useful to them and meet with their approval. David Garvin Chemical Thermodynamics Data Center Abstract This document gives the basic data needed, recommended procedures and illustrative calculations for computing heating values of natural gas mixtures from the composition of the mixtures and the properties of the components at commonly used reference conditions for gas measurement. Much of the data is given in the form of tables, and sufficient informa- tion is given for calculating properties at conditions other than those for which tables are given. Symbols and terms used are defined, units of measurement are defined and conversion factors and physical constants are given. The standard enthalpies of combustion and heat capacities of the pure hydrocarbon gases to are selected from prior initial evaluations of experimental measurements. The enthalpies of combustion of the ideal gases at the reference temperatures 273.15 K (0 °C), 288.15 K (15 °C), 288.71 K (60 °F), and 298.15 K (25 °C) on a molar basis, and a volumetric basis are given. Tables are for the dry gases, and information is given to calculate the enthalpy of combustion of the ideal water-saturated gas on a volumetric basis. The calculation of enthalpies of combustion of ideal gas mixtures on a molar, mass, or volumetric basis is described. Second virial coefficients as functions of temperature for the pure substances and for binary interactions with methane as one component are presented as selected from recent compilations based on experimental measurements. Tables are given for molar volumes, ethalpic effects (H-H°), and the heating values of the dry real-gas hydrocarbons on a molar basis, a mass basis, and a volumetric basis at two reference conditions, 288.15 K (15 °C), 101 325 Pa; and 288.71 (60 °F), 101 560 Pa (14.73 psia). The procedure used in calculating these tables is described and information is provided for making similar calculations for other reference conditions. An analysis of the uncertainties of the data is presented, together with procedures for calculating the propagation of errors and the effects of these errors on calculated heating values. Supporting data, sources of the data, and discussions of the relationships involved are presented in a series of appendixes. KEYWORDS: Calorific value, enthalpy of combustion; fuel gas mixtures; heat capacities; heating value; hydrocarbons; liquefied natural gas; natural gas; propagation of errors; reference conditions. i V Table of Contents Page number Preface i Abstract i i i 1. Introduction 1 2. Symbols 4 3. Definitions of terms 5 4. Units of measurement 6 5. Physical constants 7 6. Reference conditions of measurement 10 7. Thermodynamic data for auxiliary substances 12 8. Thermodynamic quantities for hydrocarbons - ideal gas, molar basis 15 9. Standard- state volumetric properties of hydrocarbons 18 10. Properties of the real gases 24 11. Volumetric enthalpy of combustion of the real gas 32 12. Calculating the heating values of gas mixtures 37 13. Uncertainties 48 General list of references 55 Figures 1 and 2 58,59 Appendix 1. Proposed composition limits 60 Appendix 2. Symbols 61 Appendix 3. Definitions of terms used in this document 64 Appendix 4. Units of measurement and conversion factors 72 Appendix 5. Discussion of physical constants 74 Appendix 6. Discussion of reference conditions 92 Appendix 7. Thermodynamic data: their sources and uncertai nti es 96 \/ Appendix 8. Relationships between thermodynamic quantities in Tables 3 and 4 128 Appendix 9. Non- ideality effects and the virial equation of state 133 Appendix 10. Propagation of uncertainties 147 VI List of Tables : Page No. Table 1. Physical constants 8 a. Relative atomic and molecular masses used in this document 8 b. Other physical constants used in this document 9 Table 2. Reference conditions of measurement used in this document 11 Table 3. Thermodynamic data for selected (auxiliary) substances: 13 - a, Standard heat capacity at r = 298.15 K, [H°(298.15 K) for = 288.15 K, 288.71 K and 273.15 K 13 b. Standard enthalpy of formation at r = 298.15 K, 288.15 K, 288.71 K and 273.15 K 14 Table 4.. Thermodynamic data for gaseous hydrocarbons (ideal gas, molar basis) 16 a. Heat capacity and enthalpy difference between 298.15 K and 288.15 K, 288.71 K and 273.15 K 16 b. Enthalpy of combustion (in kJ mol ^) at 298.15 K, 288.15 K, 288.71 K and 273.15 K 17 Table 5. Molar volume and density at various reference conditions 21 Table 6. Combustion data for selected gaseous hydrocarbons (ideal gas, volumetric basis) in SI units at ISO/ANSI/ ASTM reference conditions of temperature and pressure, p = 101.325 kPa; T = 288.15 K 22 , Table 7. Combustion data for selected gaseous hydrocarbons (ideal gas, volumetric basis) in SI and U.S. Customary units at ANSI/ASTM/API reference conditions of temperature and pressure p = 101.560 kPa; T - 288.71 K 23 Table 8. Virial coefficients for pure substances and mixtures 26 a. Second virial coefficients, B{T) for pure substances 26 b. Second virial coefficients, , for binary mixtures 28 Table 8. Enthalpy of combustion of real-gas hydrocarbons on molar, mass and volume bases; in SI units and at ISO/ ANSI/ASTM metric reference conditions p = 101.325 kPa; T = 288.15 K 30 Table 10. Enthalpy of combustion of the real-gas hydrocarbons on molar, mass and volume bases; in U.S. Customary units and at ANSI/ASTM/API reference conditions p = 101.560 kPa (14.73 Psi); T = 288.71 K (60 °F) 31 Table 11. Enthalpy correction for the real-gas and molar volume, V at ISO/ANSI/ASTM metric reference conditions = m , p 101.325 kPa; T = 288.15 K 35 Table 12. Enthalpy correction for the real-gas and molar volume, V at ANSI/ASTM/API U.S. Customary reference conditions m , p = 101.560 kPa; T = 288.71 K 36 Table 13. Sample calculation of enthalpy of combustion of a gaseous mixture assuming ideal gas behavior 40 Table 14. Sample calculation of enthalpy of combustion of a real- gas mixture assuming no interactions between different substances 43 vi i i Table 15. Estimated uncertainties in thermodynamic properties 51 Table Al, Proposed composition limits for pipeline quality natural gas 60 Table A2. Thermodynamic symbols used in this document 61 Table A4. Measurement quantities defined exactly in terms of SI units 72 Table A5. Atomic masses 76 a. Recent sets of relative atomic masses of the chemical elements and their period of recommendation by the International Union of Pure and Applied Chemistry (lUPAC) 76 b.