API MPMS 14.1:2006 pdf download
API MPMS 14.1:2006 pdf download.Manual of Petroleum Measurement Standards Chapter 14—Natural Gas Fluids Measurement Section 1-Collecting and Handling of Natural Gas Samples for Custody Transfer.
The hydrocarbon dew point for a particular gas changes with temperature and pressure. Because the hydrocarbon dew point is not constant for all pressures and temperatures, the proper application of the methods in this standard may require the use of a phase diagram. The phase diagram is particularly useful when the pressure or temperature of the gas changes during the sampling process. This tool is discussed in detail in Appendix A.
Various equation of state (EOS) computer programs are capable of calculating the hydrocarbon dew point temperature at various pressures (see References 9, 10 and 11). The accuracy of the calculated hydrocarbon dew point temperature depends on the calculation method used and on the accuracy of the gas composition that is entered into the computer program.
5.1 INITIAL SAMPLING OF A GAS STREAM OF UNKNOWN HYDROCARBON DEW POINT AND COMPOSITION
In order to properly apply the methods discussed in this standard, it is necessary to start with a reliable value for the hydrocarbon dew point of the stream to be sampled.
For initial sampling of a gas stream of unknown composition, the following techniques are recommended in order of preference:
Measure the hydrocarbon dew point temperature and maintain the sample gas temperature above the measured hydrocarbon dew point temperature. NOTE: ASTM D 1142, Standard Test Method fr Water ‘2ipor content 0/ Gaseous Fuels by Measurement of Dew-Potni Temperati.ire. recommends that the sample should he 3°F (1.7°C) above the dew point. For the purposes of this standard, the sample should be maintained according to the recommendations in 6.6, General Discussion of Hearing.
When the hydrocarbon dew point temperature is not measured,
use a constant pressure spot sampling method while maintaining the sample gas temperature at or above the flowing gas temperature, perform an extended analysis, and calculate the hydrocarbon dew point temperature, or
• use a pressure-reducing sampling method, perform an extended analysis, and calculate the hydrocarbon dew point temperature (when using a sampling method involving a pressure reduction, provide sufficient heat, at, or prior to, the point of pressure reduction, to offset the Joule-Thomson effect), or
• use historical information, such as analyses or dew point measurements from a similar gas source, or
• take a spot sample at line pressure, heat the sample gas to at least 30°F above the flowing temperature at the time the sample was obtained, perform an extended analysis, and calculate the hydrocarbon dew point temperature. (See 6.6, General Discussion of Heating, for cautions regarding equipment heating.)
Once the calculated hydrocarbon dew point temperature is known, maintain the sample gas tcmpcrature at least 30°F (17°C) above the hydrocarbon dew point temperature as discussed in 6.6, General Discussion of Heating.
If the stream changes composition, pressure, or temperature, or if there is an indication that the hydrocarbon dew point has changed, repeat this process to ensure that the hydrocarbon dew point is known and that the gas temperature is maintained in the sampling system according to 6.6, General Discussion of Heating.
6 General Considerations for the Design of a Natural Gas Sampling System
The main consideration in the design of a natural gas sampling system is to deliver a representative sample of the gas from the sample source to an analytical device.
Issues that should be addressed when designing a sampling system include: expected gas quality, phase-change characteristics, type of sample/analysis, material to be used for sample delivery, ambient condition extremes, cleanliness, availability of power, flow rate, and transport time.
Further consideration should be given to the presence of inert compounds such as carbon dioxide (CO2) or nitrogen (N2). These compounds will not only impact the heating value and density of the gas. they also may determine the gas chromatograph carrier gas needed and whether or not the stream meets contractual specifications.
6.1 THE COMPONENTS OF TYPICAL SAMPLING SYSTEMS
Spot and composite sampling methods require the use of a sample container to transport the sample from the field location to the laboratory. Examples are shown in Figures 1 a and lb. Figure 1 a is an example of a spot sampling apparatus employing the purging-fill and empty method. Figure lb is an example of an application using a composite sampler.
