1、 Method for the Extended Analysis of Hydrocarbon Liquid Mixtures Containing Nitrogen and Carbon Dioxide by Temperature Programmed Gas Chromatography Adopted as a Standard 2002 Revised 2014 Gas Processors Association 6526 East 60th Street Tulsa, Oklahoma 74145 GPA Standard 2186-14 DISCLAIMER GPA publ
2、ications necessarily address 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 r
3、egulations should be reviewed. 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
4、 this publication and hereby 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, e
5、quipment, or method so covered. “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 for the Extended Analysis of Liquid Hydrocarbon Mixtures Containing Nitr
6、ogen and Carbon Dioxide by Temperature Programmed Gas Chromatography GPA 2186 Purpose This standard covers the determination of the chemical composition of natural gas liquid streams where precise physical property data of the hexanes and heavier fraction is required. This procedure is applicable fo
7、r liquid hydrocarbon mixes which may contain nitrogen and carbon dioxide and/or hydrocarbon complexes C1 through C10 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 th
8、at had become obsolete and that did not reflect current industry 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
9、 QA/QC related material previously included in this standard have 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 contractua
10、l agreement different from this Standard. Economic / Commercial Impact GPA 2186 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 implementi
11、ng the method into their measurement, accounting and laboratory systems. Environmental / Safety Impact GPA 2186-14 is expected to have no environmental or safety impact on the industry. Operations / Maintenance Impact GPA 2186-14 should result in no changes to programs, spreadsheets, and other softw
12、are tools used to perform the analysis that are covered by this standard. Facilities Design GPA 2186-14 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. 1 Method for the Extended Analy
13、sis of Hydrocarbon Liquid Mixtures Containing Nitrogen and Carbon Dioxide by Temperature Programmed Gas Chromatography 1.0 Scope 1.1 This method is intended for the compositional analysis of natural gas liquid mixtures where precise physical property data of the hexanes and heavier fraction are requ
14、ired. The procedure is applicable for mixtures which may contain components of nitrogen, carbon dioxide, and/or hydrocarbon compounds C1- C14. Table 1 - Components and Recommended Compositional Ranges Components Concentration Range (mole %) Nitrogen 0.01 5.0Carbon Dioxide 0.01 5.0Methane 0.01 5.0Eth
15、ane 0.01 95.0Propane 0.01 100.0Iso-Butane 0.01 100.0N-Butane and 2,2-Dimethylpropane 0.01 100.0Iso-Pentane 0.01 15.0N-Pentane 0.01 15.02,2-Dimethylbutane, 2,2-Dimethylbutane,and 2-Methylpentane, 3-Methylpentane, Cyclopentane, N-Hexane 0.01 15.0 Heptanes & Heavier 0.01 5.02.0 Summary of Method 2.1 Co
16、mponents to be determined in a natural gas liquid sample are physically separated by Gas Chromatography and compared to calibration data obtained under identical operating conditions on a mixture (or mixtures) of known composition. 2.2 A fixed volume of sample in the liquid phases is isolated in a s
17、uitable sample inlet valve. The fixed volume is injected into a chromatographic system. 2.2.1 The Hexanes Plus components are individually separated using a capillary column, temperature programming and a flame ionization detector (FID). (See Figure 2A and Figure 2B.) Appendix A contains a packed co
18、lumn alternative to the capillary column method. 2.2.2 Nitrogen/Air, Carbon Dioxide and C1 to C5 or Hexanes Plus hydrocarbons are analyzed using GPA Standard 2177 (Analysis of Natural Gas Liquid Mixtures Containing Nitrogen and Carbon Dioxide by Gas Chromatography), latest version. 2 2.2.2.1 If the
19、allocation calculation method is chosen, the C6 plus portion of the GPA 2177 analysis must be reported. 2.2.2.2 If the bridging calculation method is used, the C6 plus portion of the GPA 2177 analysis is not required. 2.2.2.3 Future reference to the nitrogen through pentanes or hexanes analysis will
20、 be called, “GPA 2177 analysis”. 2.2.2.4 Future references to the hexanes plus individual component separation will be called, “this standard”. 2.2.3 The combined GPA 2177 analysis and analysis from this standard may be performed using two different instruments or may be combined into a single chrom
21、atograph. (see Figure 1) Figure 1 Possible Valve, Column and Detector Configuration for a single instrument performing the GPA 2186 Analysis 2.3 An electronic integrator/computer data station is utilized to provide peak area information and to perform calculations. Individual component peak areas of
22、 the unknown sample are mathematically compared to peak areas of corresponding components in a known reference standard (or standards). 2.4 The GPA 2177 analysis and the GPA 2186 analysis are then used to calculate the weight, mole and liquid volume percent of each component using one of the calcula
23、tion procedures (allocation or bridging). 3 2.4.1 The allocation and bridging calculation procedures differ only in the way the weight percent of the hexanes plus components are calculated. GPA studies have shown that, when performed correctly, both procedures produce final results that are essentia
24、lly identical. Note 1: The term “Cn” is used in this document. The subscript “n” refers to the carbon number of the largest hydrocarbon molecule expected in the sample. For example, if dodecane (C12) is the largest hydrocarbon molecule, then “n” would be “12”. Figure 2A Chromatogram of Natural Gas L
25、iquid Blend Using a Capillary Column 4 Figure 2B Chromatogram of Natural Gas Liquid Blend Using a Capillary Column 2.5 The hexanes + analysis (2,2 dimethylbutane to Cn) result from the bridging or allocation calculation procedures is then used to calculate two physical constants for the hexanes + fr
26、action: 2.5.1 Average molecular weight. 2.5.2 Average density (usually expressed as #/ gal or #/Bbl). 2.5.3 These constants are incorporated in an analytical report as example calculation reports shown in Appendix A. 5 Table 2A List of Typical Components in a Natural Gas Liquid Sample6 Table 2B List
27、 of Typical Components in a Natural Gas Liquid Sample 2.6 Section 7 describes the procedures to be performed to produce a report that mathematically combines the two analyses into a nitrogen, carbon dioxide and methane to Cnformat. Section 7 also describes the procedures to calculate the average mol
28、ecular weight and average density of the hexanes plus portion of the sample. 7 3.0 Apparatus 3.1 Any Gas Chromatograph may be used as long as the specifications for repeatability and reproducibility over the component ranges are met or exceeded. An acceptable configuration is as follows: 3.2 Detecto
29、rs. The instrument shall be equipped with a detector at the chromatograph column effluent that has sufficient sensitivity and rapid response to be able to detect and represent the components that elute from the column end. A detector system that has been shown to perform satisfactorily is to use a F
30、lame Ionization Detector (FID) for the iso-pentane to Cncapillary column analysis. 3.3 Sample Inlet System. The sample inlet system for a capillary column system must present a representative sample at the inlet of the capillary column that is large enough to produce sufficient peak areas and that i
31、s small enough to ensure that the column can adequately separate the individual components. 3.3.1 Sample Inlet Sample Valve. 3.3.1.1 The liquid sample valve must be capable of entrapping a fixed volume of sample at a pressure at least 200 psi (1279 kPa) above the vapor pressure of the sample at valv
32、e temperature and must be able to introduce the trapped sample volume into the carrier gas stream to the column inlet. The liquid sample valve should be mounted exterior to any heated zone and operate at laboratory ambient conditions. 3.3.1.2 The volume of sample introduced on the capillary column m
33、ust be very small relative to the sample volume for packed columns. Small bore capillary columns (which provide better component separation than large bore capillary columns) require a smaller sample volume than wide bore capillary columns. 3.3.1.3 For wide bore capillary columns it may be possible
34、to achieve the required sample volume by use of a high-pressure liquid sample valve of very small sample inject volume and inject the entire sample directly on column. Typical high pressure liquid sample valve volumes for the capillary column are 0.06 microliters and 0.10 microliters. 3.3.2 Sample S
35、plitters. 3.3.2.1 For a small bore capillary column a sample splitter is often used to prevent column sample overload. The splitter is plumbed between the 8 sample valve outlet and the column inlet. The splitter is heated to ensure that the entire sample is vaporized and well mixed. A portion of thi
36、s vaporized sample is then vented to atmosphere and the remaining portion is introduced to the column inlet. (Refer to Figure 3) 3.3.2.2 Prior to the actual split process, the sample and carrier gas must be heated sufficiently to ensure that the sample is entirely vaporized. If a portion of the samp
37、le is in the vapor phase and a portion of the sample is in the liquid phase, the compositions of the two phases will differ from each other and from the composition of the sample. 3.3.2.3 To ensure that the sample is completely vaporized and mixed, a test for splitter discrimination must be performe
38、d. A liquid sample, in normal pentane, containing 1% by weight of several of the normal paraffins from normal hexane to NCnand including normal hexane and NCnshould be injected and analyzed. Since, for a FID detector, the peak area for normal paraffins is nearly proportional to the weight %, the pea
39、k areas for each of the normal paraffins should agree within 1% relative to each other. If not, increase the temperature of the splitter and retest. Figure 3 A Simple Plumbing Diagram for a Capillary Column Splitter 3.3.2.4 Preheating the carrier gas stream just prior to the splitter inlet facilitat
40、es the vaporization of the sample. 9 3.3.2.5 Typical split ratios range from 1:100 to 1:400. For example, a split ratio of 1:100 would mean that 1 cc would flow to the column inlet and 100 cc would flow to vent. Most modern chromatographs allow the user to set the split ratio through the GC controls
41、 or software. 3.3.2.6 The flow to vent can be measured with a flow meter. It is sometimes difficult to accurately measure the flow through the capillary column, so an alternate calculation can be performed by dividing the internal volume of the column by the retention time of the methane peak. Ensur
42、e that the units of volume and time match the units of volume and time from the flow meter measurement of the vent flow. Sample calculations are shown in the example below. Column ID Column Length Column Volume Methane Retention Time Column Flow Rate Vent Flow Rate Split Ratio 0.32 mm 60 M 4.825 ml
43、284 sec 0.0169911 ml/sec 3.398 ml/sec 200:1 Where: Column 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 Rati
44、o = Vent Flow Rate / Column Flow Rate NOTE 2: The sample size is limited by the detector linearity and column efficiency. The column efficiency is a function of column ID, length and film thickness. 3.3.3 Sample Filters. A sample filter is an optional device used to protect the liquid sampling valve
45、 from scoring due to the presence of foreign contaminants such as metal shavings or dirt in a natural gas liquid (NGL) sample. The filter should have a small internal volume, be non-absorbent of sample components, have an in-line design and contain a replaceable / disposable element. Caution: a filt
46、er may introduce error if not handled properly. The filter should be clean and free of any residual product from previous samples so that build up of heavy end hydrocarbon components does not result. (This may be prevented by a heating / cooling process or inert gas purge.) The filter element should
47、 be of sufficient size, usually 7 micron, to prevent fractionation or bubble formation during the purging process. 10 3.3.4 Capillary Column Back Flush Valve. Provision may be made for an optional back flush valve in the capillary system (refer to back flush valve configuration in GPA 2177). The val
48、ve and accompanying fittings must be of a suitable size and type compatible to capillary systems. A back flush valve allows grouping of negligible peak areas in the extended portion of the analysis and provides ease of operation when flushing columns or analyzing relatively light hydrocarbon mixes.
49、Back flushing can assure that all components have eluted from the column. During the elution of the back-flush peak, the column ovens temperature should be held equal to or higher than its temperature at the time of the back flush. The length of time that is required for the back flush is influenced by the sample components, column oven temperature and carrier gas flow rate. 3.4 Instrument Linearity is discussed at length in GPA 2177 (latest version). Linearity should be checked across the expected ranges of concentration for all components of interest in th
