1、 Method for the Extended Analysis of Natural Gas and Similar Gaseous Mixtures by Temperature Program Gas Chromatography Adopted as a Standard 1995 Revised 2014 Gas Processors Association 6526 East 60thStreet Tulsa, Oklahoma 74145GPA Standard 2286-14 DISCLAIMER GPA publications necessarily address pr
2、oblems 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 reviewed.
3、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 hereby ex
4、pressly 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 covered.
5、 “Copyright2014 by Gas Processors Association. All rights reserved. No part of this Report may be reproduced without the written consent of the Gas Processors Association.” Impact Statement Method of Extended Analysis of Natural Gas and Similar Gaseous Mixtures by Temperature Programmed Gas Chromato
6、graphy GPA 2286-14 Purpose This standard covers the determination of the chemical composition of natural gas streams where precise physical property data of the hexanes and heavier fraction is required. This procedure is applicable for gaseous hydrocarbon mixes which may contain nitrogen and carbon
7、dioxide and/or hydrocarbon complexes C1 through C14 that fall within the ranges listed in Table 1. This standard had previously seen only minor revisions since its adoption as a technical standard in 1986. In this revision, portions that had become obsolete and that did not reflect current industry
8、practices were revised. In addition, the example calculations that utilize GPA 2145 to reflect the 2009 revision of GPA 2145 and all calculations related to those presented in GPA 2172 were removed and referenced to GPA 2172. Also, the QA/QC related material previously included in this standard have
9、 been removed and referenced to GPA 2198. The most significant changes to the standard involve updates to the method to maintain consistency with current technologies. Contracts It is recognized that parties may enter into a contractual agreement different from this Standard. Economic / Commercial I
10、mpact GPA 2286 may currently be referenced in custody transfer contracts. There are no anticipated costs associated with the implementation of the revised method. However, companies should assess their own economic impact of implementing the method into their measurement, accounting and laboratory s
11、ystems. Environmental / Safety Impact GPA 2286-14 is expected to have no environmental or safety impact on the industry. Operations / Maintenance Impact GPA 2286-14 should result in no changes to programs, spreadsheets, and other software tools used to perform the analysis covered by this standard.
12、Facilities Design GPA 2286-14 is expected to have no impact on facilities design. Implementation It is proposed that this revised standard have an implementation date one year after publication. Method of Extended Analysis of Natural Gas and Similar Gaseous Mixtures by Temperature Programmed Gas Chr
13、omatography 1.0 Scope 1.1 This method is intended for the compositional analysis of natural gas and similar gaseous mixtures where precise physical property data of the hexanes and heavier fractions are required. The procedure is applicable for mixtures which may contain components of nitrogen, carb
14、on dioxide, and/or hydrocarbon compounds C1-C14. Table 1 Ranges of Natural Gas Components Covered Component Lower Region Round Robin Higher Region Nitrogen 0.01 - 0.1 0.1 - 30 30 Carbon Dioxide 0.01 - 0.1 0.1 - 30 30 Methane 0.01 - 40 40 - 100 N / A Ethane 0.01 - 0.1 0.1 - 10 10 Propane 0.01 - 0.1 0
15、.1 - 10 10 Isobutane 0.01 - 0.25 0.25 - 4 4 n-Butane 0.01 - 0.25 0.25 - 4 4 Isopentane 0.01 - 0.12 0.12 - 1.5 1.5 n-Pentane 0.01 - 0.12 0.12 - 1.5 1.5 * Hexanes Plus 0.01 - 0.1 0.1 - 1.5 1.5 * Heptanes Plus 0.01 - 0.1 0.1 - 1.5 1.5 *Data from round robin was only obtained for Hexanes Plus Table Note
16、: Uncertainty in the Lower region can easily be ten times greater and in the higher region two to three times greater than the center column. 2.0 Summary of Method 2.1 Components to be determined in a gaseous sample are physically separated by Gas Chromatography and compared to calibration data obta
17、ined under identical operating conditions on a mixture(s) of known composition. Fixed volumes of sample in the gaseous phases are isolated in suitable sample inlet valve. This may be accomplished using either a vacuum entry system method or purge method. Each volume is injected into a chromatographi
18、c system. The chromatographic system may be in the form of different instruments or combined into a single unit. 2.2 The chromatograms are interpreted by comparing the areas of the component peaks obtained from the unknown sample with corresponding areas obtained from an analysis of a selected refer
19、ence standard(s). 1 An electronic integrator/computer data station is utilized to provide area counts. Any component in the unknown, suspected to be outside the linear working range of the detector(s), with reference to the known amount of that component in the reference standard(s), must be determi
20、ned by a response curve or other method. 2.3 The analyses are then used to calculate the mole% of each component using the procedures of allocation and/or bridging. Details are shown in the calculations section of this method. 3.0 Apparatus 3.1 Any Gas Chromatograph may be used as long as the specif
21、ications for repeatability and reproducibility over the component ranges are met or exceeded. An acceptable configuration is as follows: 3.1.1 Detector(s). The instrument(s) shall be equipped with Thermal Conductivity (TCD) and/or Flame Ionization (FID) detection capability. 3.1.2 Sample inlet and v
22、alving systems. 3.1.2.1 TCD Section - Isothermal Packed Column/Capillary Column. A gas sampling valve capable of introducing sample volumes of up to 0.500 ml, must be provided to introduce a fixed volume into the carrier gas stream at the head of the analyzing column. The sample volume should be rep
23、roducible such that successive runs agree to 1.00% of the counts on each component peak. Refer to GPA Standard 2261. 3.1.2.2 FID Section - Temperature Programmed Packed Column/Capillary Column. A gas sampling valve as described in section 3.1.2.1 above must be used. The recommended sample volume sha
24、ll be sized based upon the type of column used, the column diameter and film thickness and may be achieved with or without the use of a sample splitter. The sample size should be optimized by balancing the need for detecting small peaks vs over loading the column. Refer to Table 1. CAUTION: Care sho
25、uld be taken to ensure that the sample splitter does not discriminate toward one end of the sample boiling range. To avoid this effect, it is recommended that the carrier gas stream be preheated,. The splitter temperature kept above the heavy components in the sample. Suspected splitter discriminati
26、on may be checked by analyzing a prepared gravimetric standard of approximately 96% n-Pentane (Hexanes Free) and 1% each n-Hexane, n-Octane, n-Decane and n-Dodecane. For the blend components used, the FID responds relative to mass (weight). Therefore, since the same mass of each of the four componen
27、ts was injected, the area under the individual peaks should be close to the same value. If not, adjust the inlet splitter temperature upward and repeat the test until the four peak areas agree to within +/- 1% relative. 2 In the case of a standard bore capillary column, a sample splitter is often ut
28、ilized to prevent column over load. When calculating the split ratio of the instrument, the following equations are used: Column ID Column Length Column Volume Methane Retention Time Column Flow Rate Vent Flow Rate Split Ratio 0.32 mm 60 M 4.825ml 284 sec 0.0169911ml/sec 3.398 ml/sec 200:1 Where: Co
29、lumn Volume = (Column ID / 20)2x PI x Column Length x 100 When Column ID is in mm and Column Length is in M. Column Flow Rate = Column Volume / Methane Retention Time When Column Volume is in ml and Methane Retention Time is in seconds. Split Ratio = Vent Flow Rate / Column Flow Rate These sample si
30、ze limitations are selected with the linearity of detector response and efficiency of column separation in mind. Column efficiency is also a function of column length, size and film thickness. 3.1.2.3 GPA Standard 2186, Appendix A describes another acceptable method using a packed column for the tem
31、perature programmed section of the analysis. 3.1.3 Chromatographic Columns. 3.1.3.1 Column #1 (TCD) - This column must separate oxygen, nitrogen and methane, by returning to the baseline after the elution of each peak. A Mole Sieve column has proven to be satisfactory for this purpose. (Please see A
32、ppendix B, GPA Standard 2261 for further information). 3.1.3.2 Column #2 (TCD) - This column must separate nitrogen (air), carbon dioxide, hydrogen sulfide and the hydrocarbons methane through n-Pentane. Silicone DC 200/500, 30% by weight on 80/100 mesh Chromasorb P, acid washed, packed into 30 x 1/
33、8” SS tubing has proven to be satisfactory for this purpose. 3.1.3.3 Column #3 (FID) - This column must separate higher boiling point components. The minimum acceptable column shall be capable of separating the 3 principal hydrocarbons i-C5 through n-C14. A 60 m X 0.25 mm I.D. fused silica column wi
34、th a 1.0 micron film thickness polydimethylsiloxane, bonded and cross linked. (i.e. DB-1 or equivalent), has proven to be satisfactory for this purpose. 3.1.4 Temperature Control. During the isothermal portion of this method, the chromatographic column temperature shall be maintained within +/- 0.20
35、 degrees C of the specified temperature. During the temperature programming portion of this method, the chromatographic column temperature shall be maintained and programmed as part of the analysis. The temperature rise versus time must be verified to determine that the temperature program is repeat
36、able. Note: The upper limit of the temperature program should never exceed the maximum recommended temperature limit of the materials used in the columns. Figure 1 A Simple Plumbing Diagram for a Capillary Column Splitter 3.2 Carrier Gas. Laboratory gases, with grade purity of 99.999% or better, sho
37、uld be used. Helium has proven to be effective for this purpose. 3.3 Pressure Reducing and flow Control Devices for Carrier Gas. Pressure reducing and flow control devices shall be used to provide a flow of Helium or other suitable carrier gas to pass through the chromatographic system. Two Stage re
38、gulators with stainless steel diaphragms have been shown to be satisfactory for this purpose. 3.4 Vacuum Systems. A vacuum system consists of; vacuum gauge/manometer, vacuum pump and vacuum relief. The selected vacuum gauge should be accurately graduated and easily readable with a scale covering the
39、 range of 0 to 900mm (36”) of mercury or larger. The vacuum pump must have the capability of producing a vacuum of 0.10 mm of mercury (absolute) or less. 4 3.5 Integration Systems. 3.5.1 Computerized Integration System. This is the preferred and recommended integration system. This type of system pr
40、ovides the highest degree of precision, flexibility of data handling, and operator convenience. Computerized Integration Systems have various integration event options to facilitate accurate peak interpretation. See Caution below. 3.5.2 Electronic Digital Integrator. Electronic digital integrators a
41、re able to integrate peak areas accurately via several different methods employing various correction adjustments. See Note 3. It is important to be able to produce a chromatogram, and the integrator should either be able to produce a printout, or provide a signal for a strip chart recorder. CAUTION
42、 - The operator must therefore be well versed in integrator operation, preventing improper handling of data, which could ultimately result in erroneous information. Integration parameters used during instrument calibration must be used for subsequent sample analyses. Figure 2 Possible Valve, Column
43、and Detector Configuration for a single instrument performing the GPA 2286 analysis 5 4.0 Calibration 4.1 The routine method of calibration is to use the response factor from a gas reference standard of known composition. This method may be used for those components in an unknown that lie within the
44、 proven linear range for a specific chromatographic instrument. 4.1.1 Connect the reference source to the inlet of the system. If using the vacuum system, then evacuate the system including the sample loop and check for leaks. 4.1.2 Open the valve to introduce the reference standard, up to pressure
45、decided for all injections. (Please see analytical procedure). 4.1.3 If using the purge system, then record the atmospheric pressure in the laboratory. 4.1.4 Determine the peak area counts from the TCD for all components of interest. This data should be used to calculate the response factors in acco
46、rdance with Section 7. Note: Reference GPA Method 2261, Section 6 “Calibration Procedure”. 5.0 Analytical Procedure 5.1 General. In the routine analysis of samples described in the scope of this method, it is possible to obtain all components of interest from a single analysis. Generally: TCD is use
47、d for low boiling point components and FID is used for high boiling point components. Each component detected by the TCD has an associated response factor determined from the respective reference standard. This data is then used to calculate the mole % for the components of interest, of the unknown.
48、 It has been determined that each component detected by the FID has a relative response factor close to 1.00, thus, making Peak Area %, essentially equal to Weight %. Note: Individual instruments, columns, and operating parameters will provide different separations and possibly some elution order di
49、fferences. The analyst should check particular identified components, pure components, and blends under normal operating conditions, in order to verify the exact retention times. Note: Flame ionization response factors are significant for benzene and toluene. These are also key components in natural gas streams. For this method the response factors (multiplying) is assumed to be 0.928 for benzene and 0.972 for toluene. All remaining components have assumed response factors relative to iso-pentane and normal pentane having relative response factors of 1.000 (Refer to Tables 2A and 2B
