API MPMS 14.5:2009 pdf download
API MPMS 14.5:2009 pdf download.Calculation of Gross Heating Value,Relative Density, Compressibility and Theoretical Hydrocarbon Liquid Content for Natural Gas Mixtures forCustody Transfer.
In the examples, the component heating values, relative densities and GPMs are corrected for compressibility. The summation of ideal component values, such as ideal heating value, relative density and GPM, are not reported in the examples because their application beyond the use as intermediate steps in the analysis calculation can lead to misapplication and subsequent errors.
The calculations in the following examples use the physical properties for the components from
GPA 2 145-09.
Application Notes and Cautions
All calculations shall use the physical properties from the latest version of GPA 2145. If a component in the calculation is not present in CPA 2145, refer to CPA TP-17 for its properties.
A typical natural gas analysis determines the individual quantity of components lighter than hexanes, and groups the hexanes and heavier components into a single quantity. Characterization of the physical constants for hexanes and heavier components, commonly referred to as C6+, should use the most representative data available for the sample. Similar methodology can be used to group on a different component such as heptanes and heavier (C7+). This characterization may be:
• based upon the composition of the C6+ fraction determined in an extended chromatographic analysis performed in accordance with CPA 2286 or other equivalent method; (preferred method);
• generalized through an engineering evaluation; and
• as agreed upon among parties involved.
Table B.10 in Annex B provides example calculations for two commonly used characterizations.
5.4 Theoretical Hydrocarbon Liquid Content
The theoretical hydrocarbon liquid content is the amount of liquid hydrocarbon by component that theoretically could be condensed from a gas. In the U.S., this is commonly termed gallons of a particular hydrocarbon liquid per thousand cubic feet of natural gas at the analysis conditions (abbreviated GPM).
The gas portion of the volume ratio of gas to liquid reported in GPA 2145 is on an ideal basis, so the calculated value has the same basis. The ideal theoretical hydrocarbon liquid content must be corrected for compressibility factor to be on a real volume basis. For example, in the U.S., dividing GPM by Z results in gallons of a component per thousand cubic feet of real gas, which can then be applied consistently to a real volume of natural gas.
6 Summary of Method
From the composition of a natural gas sample, it is possible to calculate the gross heating value, relative density, compressibility factor and theoretical hydrocarbon liquid content for the sample.
The gas sample should be collected according to the latest version of GPA 2166, API MPMS Ch. 14.1 or other acceptable methods. To ensure accuracy of this method, the gas sample must be representative of the gas under consideration.
The sample analysis for hydrocarbons and inerts including helium and oxygen should conform to the latest version of GPA 2261, or other technically acceptable methods that meet or exceed GPA standards for repeatability and reproducibility. Hydrogen sulfide concentration should be determined in accordance with GPA 2377 or other industry standard method. Water content should be determined by a physical test or calculated according to the assumptions in this Standard or by other means as agreed to by the parties involved.
Component properties used in the calculations for gross heating value, relative density, compressibility factor and theoretical hydrocarbon liquid content appear in the latest edition of GPA 2145 and similar industry publications.
When analyzing a sample for composition, it is essential to include all components with mole fractions greater than or equal to 0.0001 in the analysis or within the detectable limits of the analyzing equipment, such as is covered by GPA 2261 or GPA 2286. A threshold of 0.0000 1 mole fraction or less may be used to identify trace constituents. The results of the compositional analysis should be expressed to the same precision. Some routine analyses ignore constituents such as water, helium, hydrogen sulfide and oxygen. This practice reduces the accuracy of the calculated results if one or more of these constituents are present. Note that hydrogen sulfide, when present as a contaminant that must be removed from the natural gas stream before final use, usually is assigned no heating value. Water vapor is treated similarly.
7 Equations for Custody Transfer Calculations
Gross Heating Value (Volumetric Basis)
The gross heating value as a function of composition is.:
