1、GPA Standard 2166435 Obtaining Natural Gas Samples for Analysis by Gas Chromatography Adopted as a Tentative Standard, 1966 Revised and Adopted as a Standard, 1968 Revised 1986. 2005 Gas Processors Association 6526 East 601h Street Tulsa, Oklahoma 74145 DISCLAIMER GPA publications necessarily addre
2、ss problems of a general nature and may be used by anyone desiring to do so. Every effort has been made by GPA to assure accuracy and reliability of the information contained in its publications. With respect to particular circumstances, local, state, and federal laws and regulations should be revie
3、wed. It is not the intent of GPA to assume the duties of employers, manufacturers, or suppliers to warn and properly train employees, or others exposed, concerning health and safety risks or precautions. GPA makes no representation, warranty, or guarantee in connection with this publication and here
4、by expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict, or for any infringement of letters of patent regarding apparatus, equipment, or method so cov
5、ered. “Copyright 2005 by Gas Processors Association. All rights reserved. No part of this Report may be reproduced without written consent of the Gas Processors Association.“ This 2005 revision of GPA (Gas Processors Association) Publication 2166 contains major changes from the 1986 version. The inc
6、orporated changes are the result of a cooperative sampling program carried out by the API (American Petroleum Institute) workgroup on Natural Gas Sampling. Data from the API project combined with data from a GPA project published in 1985 provide the impetus for this latest revision. A “definitions“
7、sedion has been added to help the reader understand the terms used throughout this dowment. Words in bold type are defined in the “definitions“ sedion. First uses of TIAS (Three Letter Acronyms) are followed by an explanation in parentheses. Subsequent use of the TU is not followed by a parenthetica
8、l explanation. This publication indudes detailed sampling procedures for each of 8 test methods: 1. Purging - Fill 8 Empty Method 2. Purging - Controlled Rate Method 3. Evacuated Container Method 4. Reduced Pressure Method 5. Helium “Pop“ Method 6. Glycol or Water Displacement Method 7. Floating Pis
9、ton Cylinder Method 8. Portable and On-Line Gas Chromatographs Not all methods are appropriate for all sampling conditions. Appropriate sampling conditions for each method are discussed in this standard. It is important to have a thorough knowledge of the phase behavior of the product to be sampled
10、and of the Jouie-Thomson Effect. Discussion of the Phase Diagram and the Joule-Thomson Effect can be found in API Chapter 14.1. The sampling methods listed in this dowment require that the sampling components are clean and free of contaminants. It may be necessary to clean sample cylinders and sampl
11、ing system components between uses. Appendix A of this doaiment discusses cleaning of sample system components. The data from the API 14.1 sampling project dearly demonstrated that misuse of the Gas Sampling Separator could distort the sample. The wmnt revision of this GPA publication includes langu
12、age to clany the proper use of the separator. It discusses when the Gas Sampling Separator would be appropriate and explores the potential pitfalls associated with its misuse. 3 Obtaining Natural Gas Samples for Analysis by Gas Chromatography 1.1. represent the composition of the vapor phase portion
13、 of the system being analyzed. These representative samples are subsequently transported to a laboratory and analyzed for cornposition and/or trace contaminants or analyzed onsite by portable or on-line chromatographs. The purpose of this publication is to recommend procedures for obtaining samples
14、from flowing natural gas streams that 1.2. Hydrocarbon Dew Point temperature. As the temperature of the flowing stream decreases or the pressure increases to impinge upon the Hydrocarbon Dew Point, it becomes increasingly difficult to obtain a representative sample of the flowing stream. This standa
15、rd does not address accounting for the liquid hydrocarbon portion of two-phase systems. The methods outlined in this publication are designed for sampling natural gas from systems that are at or above the 1.3. periods) systems. For information on composite sampling, the reader is referred to API 14.
16、1 and ASTM 05287. The scope of this standard does not indude composite gas sampling (samples taken in increments over relatively long time 1.4. Due to a la pp 579 and 580; “Process Analyzer Sample Conditioning System Technology“ by Robert E. Sherman; Wiley Interscience, and modified for Gas Compress
17、ibility by ABB Totaifiow Projed Engineering. 11 7.2.2.2. Diameter The diameter should be as small as possible while ensuring adequate flow through the system. For spot sampling, the transfer line should have a minimum diameter of li4 in (6 mm). To ensure that refrigeration associated with the Joule-
18、Thomson Effect occurs some distance down stream of the Sample Container, the smallest diameter component in the spot sample system should be the orifice in the drilled plug at the end of the Extension Tube (“Pigtail“) attached to the outlet of the sample cylinder. The drilled plug can be replaced wi
19、th a flow control valve provided that the intemal diameter of the flow control valve is smaller than any other component in the sampling system. For the portable and on-line gas chromatograph method, the sample transfer line would generally have a diameter of 1/16 in (1.5 mm) to % in (6mm). For the
20、portable or on-line gas chromatograph method, sample transport lag time calculations are helpful in determining appropriate sample line diameter. 7.2.3. Insulation and Heating Sample transfer lines must be maintained above the Hydrocarbon Dew Point (see Note 3, section 2.1.3). See section Section 8
21、for heating requirements. For very short connections between the sample point and the Sample Container, the sample transfer line can be insulated without supplemental heating. Care should be taken to ensure that this short transfer line is at the same temperature as the sample source prior to transf
22、emng sample to the Sample Container. 7.2.4. Cleaning Oil in the transfer line can selectively absorb and desorb hydrocarbon components, altering the sample composition. Since new stainless steel tubing may have machine oil from the manufaduring process, sample transfer lines should be steam cleaned
23、and dried prior to installation. Refer to Appendix A for deaning guidelines. Other deaning methods are acceptable if they can be demonstrated to leave no residue. 7.3. Sample Line Separators and Filters 7.3.1. Separators and Membrane Fitters. These devices are intended, and must be appropriately des
24、igned, to remove contaminants from natural gas sampling systems without altering the sample qualky. The objective is to remove contaminants without removing components that are part of the vapor-phase of the flowing gas stream. Contaminants indude, but are not limited to, oil, glycol, amines, water
25、and free-flowing condensed hydrocarbon liquids. Fitters should be frequently dwhd for contamination and deaned or replaced if necessary. Separators and filters must have a pressure rating equal to or higher than the pressure of the sample source. Research has shown that misuse of sample line separat
26、ors and filters can cause sample distortion. Refer to Appendix B. 7.3.1.1. It is imperative that the Gas Sampling Separator temperature and pressure match the flowing natural gas temperature and pressure throughout the sampling process. 7.3.1.2. It is imperative that the temperature and pressure of
27、filters that are used as a separator (installed upstream of any pressure-reducing regulator) match the flowing natural gas temperature and pressure throughout the sampling process. 7.3.1.3. Fitters that are installed in the sample system after a pressure-reduang regulator must be operated above the
28、Hydrocarbon Dew Point (see Note 3, sedion 2.1.3). The Joule-Thomson EM from the pressure drop across a filter must also be considered when determining the heating requirements. See Section 8, Heating Requirements. 7.3.2. Special care must be used when using the Gas Sampling Separator (See Figure 3).
29、 The separator must be insulated. A thermometer must be installed to ensure that the separator is operating at line temperature. If the temperature is Mow line temperature, twill tend to remove heavy (high temperature boiling point, high heating value) components from the sample stream. If it is abo
30、ve line temperature, it will tend to increase the concentration of heavy components in the sample. The outlet of the separator may require supplemental heat to ensure that the produd from this point to the sample cylinder is completety in the vapor phase. See section Section 8, Heating Requirements.
31、 The separator is only useful for sample streams containing unwanted condensed hydrocarbon droplets, oil, amine, glycol. water or other contaminants For clean, dry sample streams above the Hydrocarbon Dew Point (see Note 3, section 2.1.3), the separator serves no useful purpose and its misuse could
32、compt the sample. See sedion Appendii B on the use of the Gas Sampling Separator. 12 Figure 3 Gas Sampling Separator Insulation Pressure Ga Thermometer I Separator Drain Val Extension Tube Extension Tube O ut I et Va Ive LLU I 7.3.3. ne. This type of filter is, by virtue of its location in the pipe,
33、 at the same temperature and pressure as the sample source. This ?litninates condensation or vaporization of heavy components due to changes in temperature or pressure. See section Appendix B for discussion of the use of membrane filters. An acceptable method for removal of unwanted contaminants is
34、a membrane filter (See Figure 4) inserted directly in the 7.3.4. must be operated at line temperature. If it is above line temperature, it may vaporize liquid contaminants to artificially enrich the sample. If it is below line temperature. it may condense components to artificially reduce heavy comp
35、onents in the sample. External fitters may be used to eliminate contaminants from the sample stream. If the filter is operated at line pressure, it If external fitters are used after pressure reduction or after a separator or membrane filter, the fitters must be operated above the Hydrocarbon Dew Po
36、int (see Note 3, section 2.1.3). 7.3.5. Requirements. Separators and filters used for sampling natural gas must be dean and free of leaks. See section Appendix A on Cleaning 13 7.4. Figure 4 Membrane insertion probe with regulator Pressure Mjustnent SP-lng Outiei Body N PT Thermal Fins Seat and Popp
37、et 4sSenbiy H 7.5.2.1. Probe Length Calculation SI Units The maximum insertion probe length (from the end of the probe to the point of attachment) can be calculated (from EEMUA Publication No. 138:1988) using the following formula: Where: L= Fm = OD = ID = S= V= E= r= Permissible Probe Length (mm) V
38、irtual mass factor - a constant to take account of the extra mass of the cylinder due to the fluid surrounding it & vibrating with it. For a gas, Fm = 1 .O and for water & other liquids Fm = 0.9 Outside Diameter of the Probe (mm) Inside Diameter of the Probe (mm) Strouhal number - dependent on the R
39、eynolds number and the shape of the cylinder, but can be taken as 0.4 for worst case or 0.2 as suggested by API Chapter 8. Veioc-Q of fluid (misec) Modulus of Elasticity of probe material (kg/cm2) Density of probe material (kglm3) 7.5.2.2. Probe Length Calculation American Engineering System Units T
40、he maximum insertion probe length (from the end of the probe to the point of attachment) can be calculated (based on EEMUA Publication No. 138:1988) using the following formula: Where: L = Fm = with it. For a gas. Fm = 1 .O and for water 8 other liquids Fm = 0.9 OD = ID = S = V = E = r = Permissible
41、 Probe Length (inches) Virtual mass factor - a constant to take account of the extra mass of the cylinder due to the fluid surrounding it & vibrating Outside Diameter of the Probe (inches) Inside Diameter of the Probe (inches) Strouhal number - Use 0.4 for worst case Velocity of fluid (fsec) Modulus
42、 of Elasticity of probe material (psi) Density of probe material (g/cm3) 16 7.5.3. Under no circumstances should the Sample Probe be longer than IO. 7.5.3. flowing gas stream. Caution: Harmonics may cause embnttlement of the metal. Poorly designed Sample Probes may bend or break off in the 7.5.4. Th
43、is section (section 7.5) should be carefully considered when designing a Sample Probe. 7.6. Pressure Regulators Regulators may be used to reduce sample pressure from the source pressure to a useable pressure for the sampling equipment or analytical devices. They may also be used to reduce pressure t
44、o keep the stream below the Hydrocarbon Dew Point pressure. The regulator may need to be heated to prevent condensation from the Joule-Thomson Effect cooling or to prevent Retrograde Condensation. Pressure regulators can be pari of the insertion probe (Figure 4). This allows heat from the flowing pr
45、oduct stream to assist in heating the sample back up to sample point temperature. The flow rate through insertion probe regulator affects the recovery of product temperature. It is necessary to venfy that the sample is sufficiently heated. Supplemental heating may be necessary. See section 8, Heatin
46、g Requirements. 7.7. The smallest diameter portion of the sample system will be the point of maximum pressure drop. This pressure drop causes reduction in temperature due to the Joule-Thomson Effect. Extension Tubes (“Pigtails“) are used to thermally isolate the outlet valve of Sample Containers fro
47、m this cooling effect during the purging process. This piece of tubing is typically %, in diameter and at least 36 in length. If it is coiled, the user is cautioned to leave enough air gaps between coils to prevent thermal coupling of the coils. Extension Tube (“Pigtail“) (Figure 7) Figure 6 Extensi
48、on Tube (“Pigtail“) Sample Container O ut let Va Ive fi Sample Container I I II Sample Container Inlet Valve Purge Valve- Wn d Po Extension Tube or “Pigtail“ Extension Tube Outlet Valve and Drilled Flow Plug 17 7.7.1. To ensure that cooling from flow regulation occurs at the outlet end of the pigtai
49、l, a flow regulating valve or flow regulating plug must be installed at the end of the pigiail. The internal diameter of the flow regulating valve must be the smallest diameter of all the sampling system components. The hole in the plugs should be the smallest diameter part of the sample system. Details of the flow plug are shown in Figures 7 and 8. To achieve the optimum heat-of-compression results in the Purging-Fill and Empty Method, the optimum diameter for the hole in the flow control plug or the pori diameter of the flow control valve should be 111 6“ to 118“.
