API MPMS 14.5 2009 pdf download.Calculation of Gross Heating Value, Relative Density, Compressibility and Theoretical Hydrocarbon Liquid Content for Natural Gas Mixtures for Custody Transfer.
1 Scope This standard presents procedures for calculating, at base conditions from composition, the following properties of natural gas mixtures: gross heating value, relative density (real and ideal), compressibility factor and theoretical hydrocarbon liquid content which in the U.S. is typically expressed as GPM, the abbreviation for gallons of liquid per thousand cubic feet of gas. Rigorous calculation of the effect of water upon these calculations is complicated. Because this document relates primarily to custody transfer, the water effect included is an acceptable contractual calculation. Annex A of this standard contains a detailed investigation of the effect of water and detailed derivations of the equations presented in the standard. 2 Normative References The following documents contain provisions, which through reference in this text constitute provisions of this standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. For undated references, the latest edition of the normative document referred to applies. API Manual of Petroleum Measurement Standards (MPMS) Chapter 14.1, Collecting and Handling of Natural Gas Samples for Custody Transfer AGA Report No. 5 1 , Fuel Gas Energy Metering AGA Report No. 8, Compressibility Factor of Natural Gas and Related Hydrocarbon Gases GPA Standard 2145 2 , Table of Physical Properties for Hydrocarbons and Other Compounds of Interest to the Natural Gas Industry GPA Standard 2166, Obtaining Natural Gas Samples for Analysis by Gas Chromatography GPA Standard 2261, Analysis for Natural Gas and Similar Gaseous Mixtures by Gas Chromatography GPA Standard 2286, Tentative Method of Extended Analysis for Natural Gas and Similar Gaseous Mixtures by Temperature Programmed Gas Chromatography GPA Standard 2377, Test for Hydrogen Sulfide and Carbon Dioxide in Natural Gas Using Length of Stain Tubes GPA Standard 8173, 3.3 base conditions Base conditions are certain pressure and temperature conditions selected for a specific purpose such as defined by state and federal laws and regulations or to meet the needs of contracting parties. Common base pressures in the U.S. include 14.65 psia, 14.73 psia, and 15.025 psia. The base temperature in the U.S. is usually 60 °F. 3.4 Btu The Btu (British thermal unit) is a measurement unit for a quantity of energy transferred as heat. 3.5 compressibility factor The compressibility factor is the ratio of the actual volume of a given mass of gas to its volume calculated from the ideal gas law using given conditions of temperature and pressure. 3.6 dry gas Dry gas contains no water, however, for practical purposes, contracting parties often define “dry” to include small quantities of water. In the U.S., dry gas is typically specified to not exceed 7 lb of water per million standard cubic feet (MMSCF) of gas. 3.7 gross heating value higher heating value HHV The gross heating value, Hv id , is the amount of energy transferred as heat per mole, unit mass or unit volume from the complete, ideal combustion of the gas with oxygen at a base temperature in which all water formed by the reaction condenses to liquid. As explained in Annex A, this is a hypothetical state, but it is acceptable for custody transfer. Reporting the gross heating value on a volumetric rather than a mass or molar basis requires a base pressure along with a base temperature. Spectator water does not contribute to the gross heating value. 3.8 ideal gas An ideal gas is a hypothetical gas which would follow the characteristic equation PV = nRT under all conditions. 3.9 partially saturated gas Partially saturated gas contains some quantity of water vapor less than that present under saturated conditions, but more than dry, normally expressed in mass of water per unit volume of delivered gas at defined conditions.