1、GPA Standard 21 03-03 Tentative Method for the Analysis of Natural Gas Condensate Mixtures Containing Nitrogen and Carbon Dioxide by Gas Chromatography Adopted as Tentative Standard, 2003 Gas Processors Association 6526 East 60th Street Tulsa, ktahorna 74145 DISCLAIMER GPA publications necessarily a
2、ddress 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 r
3、eviewed. 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
4、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, equipment, or method so
5、 covered. “Copyrignt 2003 by Gas Processors Association. All rights reserved. No part of this Report may be reproduced without written consent of the Gas Processors Association.” Tentative Method for the Analysis of Natural Gas Condensate Mixtures Containing Nitrogen and Carbon Dioxide by Gas Chroma
6、tography 1. SCQPE 1.1 This method is intended for the analysis of separator condensates containing nitrogenhir and carbon dioxide, that fall wiihin the compositional ranges listed in Table I. This method is intended for mixtures containing greater than 5 mole percent of heptanes and heavier fraction
7、s. Tabte I Components and Compositional Ranges Allowed 1 Components Conc. Range (moi %) Nitrogen 0.01 -50 Carbon Dioxide O O1 - 5.0 Methane 0.01 - 40 o Ethane 0.01 - 15.0 Propane 0.01 - 15.0 Iso-Butane 0.01 - 15.0 N-Butane and 2,2-Dimethylpropane 0.01 - 75.0 Iso-Pentane 0.01 - 15.0 N-Pentane 0.01 -
8、15.0 I 2,2-Dimethylbutane, 2,3-Dimethylbutane and 0.01 - 50.0 I 2-Methylpentane, 3-Methylpentane, Cyclopentane, N-Hexane Heptanes & Heavier 50-800 _I - 1.2 The heptanes and heavier fraction is ignored in the chromatographic analysis, or precut to vent and determined volumetrically with the physical
9、properties determined by direct measurement andlor calculation. 1.3 Reference documents are ASTM 0-2001 (modified for co n dens aie) “D epe n tan iza f ion of Gasoline and Naph th a s “ (a I tern at el y AST M D -86 “Stan da rd Test Method for Distillation of Petroleum Products at Atmospheric Pressu
10、re“, or equivalent, ASTM D-4052 “Standard Test Methad for Density and Relative Density of Liquids by Digital Density Meter“ (alternately ASTM D- 287 “Standard Test Method far API Gravity of Crude Petroleum and Petroleum Producfs (Hydrometer Method)“), UOP-I 58 “Molecular Weight Determination Using F
11、reezing Point Osmometer“ (alternately ASTM D- 66 or GPSA Engineering Data Book, Kragcoe correlation), API MPMS Chapter 20. I “Allocation Measurement“, API MPMS Chapter 12.2 Part 3 “Calculation of Net Standard Volumes and GPA 2177 Nnalysis of Natural Gas Liquid Mixtures Containing Nitrogen and Carbon
12、 Dioxide by Gas Chromatography : Note 1-Thrs method can be used for a hexanes-plus analysis by adjusting the timing of the precut event to occur following he elution of n-pentane from the precut column 1 2. SUMMARY OF METHOD 2.1 Components to be determined in a natural gas condensate mixture are phy
13、sically separated by gas chromatography and compared to calibration data obtained under identical operating conditions. A fixed volume of sample in the liquid phase is isolated in a suitable sample inlet system and flashed onto the chromatographic column. 2.1 .I Components nitrogdair through n-hexan
14、e are individually separated with the carrier flow in the forward direction. The numerous heavy end components are precut via a switching valve immediately following the elution of normal hexane. The heptanes-plus fraction may be ignored or precut to vent. (See Fig. I.) I- _- - Figure 1 - Chromatogr
15、am of Demethanized Hydrocarbon Liquid Mixture. (Frontal Carrier Gas Flow through N-Hexane. Precut Heptanes Plus). 2 I .2 The Heptanes-Plus fraction is determined separately by physically measuring its volume The physical properties, such as Molecular Weight, Density and Heating Value, of the Heptane
16、s-Plus are measured by other methods 2.2 The chromatogram is interpreted by comparing the areas of component peaks obtained from the unknown sample with corresponding areas obtained from a run of a selected reference standard. Any component in the unknown suspected to be outside the linearity range
17、of the detector, with reference to the known amount of that component in the reference standard, must be determhed by a response curve. (See Section 5.1 & 5.1.1 for further explanation of instrument linearity check procedures.) 3. APPARATUS 3.1.4 Chromatographic Columns 3.1.4, i Column No, 1(Analyti
18、cal Column) - A partition column must be provided capable of separating nitrogenlair, carbon dioxide and the hydrocarbons methane through normal hexane. (See Fig. 1) Separation of carbon dioxide must be sufficient so that a sample containing 0.01 mole percent carbon dioxide will produce a detectable
19、 peak on the chromatogram. (The Silicone 200/500 column. containing a 27-30 weight percent liquid phase load, has proven satisfactory for this type of analysis.) (See Paragraph 3-2. Appendix B, GPA Publication 2261 for further explanation and construction of column.) 3.1.4.2 Column No. 2 (Precut Col
20、umn) - A partition column similar to column No. 1, it must be of the same diameter as column No. 1. The column must be of an appropriate length to clearly separate the heptanes-plus fraction from the hexanes and lighter components. 3.1.5 Temperature Control - The chromatographic coiumn(s) and the de
21、tector shall be maintained at temperatures stable enough to achieve the precision requirements in Section 8. 3.15 Carrier Gas System - Components of the carrier gas system must provide the ability to control the pressure and/or flow stable enough to achieve the precision requirements in Section 8. I
22、t is desirable to use a carrier gas which contains minimal quantities of critical impurities (ie, oxygen, water and total hydrocarbons). 3.2 Integration Systems 3.2.1 Computerized Integration System - This is the preferred and recommended integration system. This type of system provides the highest
23、degree of precision, flexibility of data handling, and operator convenience. 3.2.2 Electronic Digital Integrator - Electronic digital integrators are able to integrate peak areas accurately via several different methods employing various correction adjustments. Note 3-CAUTION- The operator must ther
24、efore be well versed in integrator operation, preventing improper handling of data - ultimately resulting in false information. 3.3 Sample Containers 3.3.1 Floating Piston Cylinder - A strongly preferred and recommended device suitable for securing, containing and transferring samples into a liquid
25、sample valve and which preserves the integrity of the sample. (See Fig. 3.) (For proper operation refer to GPA 2174.) These cylinders must have an acceptable mixing device. 3.1 Any gas chromatograph may be used which meets the following specifications. 3.1.1 Detector - The detector shall be a therma
26、l conductivity type. It must be sufficiently sensitive to produce a detectable peak for each component of interest at 1 O0 ppm molar volume. 3.1.2 Sample Inlet System. Liquid - A liquid sampling valve must be provided, capable of entrapping a fixed volume of sample at a pressure at least 200 psi (i3
27、79 kPa) above the vapor pressure of the sample at valve temperature, and flashing this fixed volume into the carrier gas stream ahead of the analyzing column. A metering valve downstream of the liquid sampling valve is required to maintain the sample as a single-phase liquid through the entire sampl
28、e inlet system. (See Valve C in Figure 2)The fixed sample volume should not be of such volume as to impact instrument linearity and should be reproducible so thaf successive runs agree within f 1% on each component peak area. The liquid sampling valve should be mounted exterior of any type heated co
29、mparfmenf and thus be operated at laborafoty ambient conditions. A sample filter is an optional device to protect the liquid sampling valve from scoring due to the presence of foreign contaminants such as metal shavings, dit? etc., in the separator condensate sample. The filter should be of a small
30、total volume, of an inline type design and confain a replaceabie/disposable element. Note 2 - CAUTION: A filter may introduce error if not handled properly. The fitter should be clean and free of any residual product from previous samples so that a build up of heavy end hydrocarbon components does n
31、ot result. (May be accomplished by a heating / cooling process or inert gas purge, etc.) The filter element should be 15 micron size or larger so that during the purging process the sample is not flashed, preventing fractionation and bubble formation. 3.1.3 Sample inlet System. Gas (Optional for det
32、ermination of instrument linearity) - Provision may be made to introduce a gas phase sample into the carrier gas stream ahead of the chromatographic column so that linearity of the instrument can be estimated from response curves. The fixed volume loop in the gas sample valve shall be sized to deliv
33、er a total molar volume approximately equal to that delivered by the liquid sample valve described in 3.1.2. A 0.25 cc gas sample loop is approximately equal to a liquid sample sire of 1 t. (See Section 5.1 and 5.1 .I for further explanation of instrument linearity check procedures.) 2 3.3.2 Double
34、Valve Displacement Cylinder - An alternate device, used in the absence of a Floating Piston Cylinder, suitanle for securing, containing and transferring samples into a liquid sample valve. (See Figs. 4 & 5.) (For proper operation refer to GPA 2177.) Note 4 - CAUTION: This container is ONLY acceptabl
35、e when the displacement liquid does not appreciably affect the composition of the sample of interest. Specifically, components such as CO2 or aromatic hydrocarbons are partially soluble in many displacement liquids and thus use of those liquids may compromise the final analysis. This caution is of t
36、he ufmost importance and should be investigated prior to utilizing this technique. 3.4 Additional Equipment 3.4.1 ASTM D-2001 (alternately D-86, or equivalent) Distillation apparatus is required for the Heptanes-Plus fraction physical liquid volume measurement. The sampte residue is cut between n-He
37、xane and Heptanes-Plus compounds so that the physical properties can be measured Using a Hexanes-Plus cut point at 130 Deg. F and a Heptanes-Plus cut point at 185 Deg. F has been shown to be effective in most caces. If required, ,a more accurate cut point temperature can be determined by chromatogra
38、phic analysis of the residue and recovery from the distillations. 3.4.2 Heptanes-Plus Density may be measured by ASTM D-4052 (alternately ASTM D-287). See the selected method for equipment requirements. 3.4.3 Heptanes Plus Molecular Weight may be measured by UOP-158 (alternately, calculated from AST
39、M D-86 Mean Average Boiling Point and Specific Gravity, or calculated from Kragcoes correlation). Note 5 - The preferred method is listed first for each of the physical tests, followed by alternates in parentheses, in order of preference. See the referenced method for stated precision of each test.
40、I _ I 4. GC ANALYSIS PROCEDURE 4.1 The analytical procedures listed in GPA 2177, Section 4, should be followed for the chromatographic portions of this method. The only exception is that the Heptanes-Plus are independently measured in this method. Refer to GPA 2177. 5. GC CALIBRATION RUN 5.1 The cal
41、ibration procedure fisted in GPA 2177 should be used for this method. Since the Heptanes-Plus fraction is measured independently in this method, it is not necessary to calibrate the chromatograph for that component. Refer to GPA 2177. 6. UNKNOWN SAMPLE ANALYSIS 6.1 Obtain a chromatogram of the unkno
42、wn sample according to instructions outlined in Section 4. 6.1.1 Determine the peak areas from the chromatogram for all components, except Heptanes-Plus. These data shall be used to calculate the composition of all components in the unknown, except for HeptanesPlus, in accordance with instructions o
43、utlined in Section 7.2 under CALCULATIONS. 6.2 The Liquid volume fraction and physical properties of the Heptanes-plus are determined in accordance with the previously referenced methods. See Section 1.3. 7. GC CALCULATIONS 7.1 Calculation of response factors using a known reference standard. 7.1.1
44、Determine the peak area of each component nitrogen/air through hexanes (if applicable) from the chromatogram of the known reference standard. CRRILR GAS 1 *:AER 1 i TO COUJWN PRESSURE REGULATOR P INERT GAS FLOATING PISTON -3 I- - - Figure 2 - Repressuring System and Chromatographic Valving with Floa
45、ting Piston Cylinder. 3 PREISURE REGULATOR VENT VENT NEECLE VLVE b: CARRIEK BiS. CYLIWER CARRIER GAS OUTPUT VALVE TO COLUMY CHROMATOGRAPH LIOUH) SAMPLING VALVE NEEDLE VALVE i CYLINDER NEEDLE VALVE ._ _ - Figure 3 - Repressurrng System and Chromatographic Valving with Double Valve Displacement Cylind
46、er. I .- - Figure 4 - Pre-Cut Vaive Configuration 7.1.2 Calculate a response factor for each of the above components in accordance with the following relationship. (See Table il): where K = response factor M = volume percent of component in reference P = peak area in arbitrary units K= M/P standard
47、7.2 Catculation of volume percent of components in unknown sample. 7.2 1 Determine the peak area of each component nitrogen/air through hexanes from the chromatogram of the unknown sample using the same arbitrary units as in Section 7.1. 7.2.2 Calculate the concentration in volume percent of each of
48、 these components is performed in accordance with the following relationship (See Table 111): M=Px K where M = volume percent of component in unknown P = peak area of each component in unknown sampte. K = response factor as determined in Section 7. I Totalize volume percent values. 7.3 For the calcu
49、lation of the concentration of heptanec- plus and total sample analysis, refer to Appendix A. 8. PRECISION Repeatabttity is the expected precision within a laboratory using the same equipment and same analyst. Reproducibility is the expected precision when the same method is used by different laborafories using different equipment and different analysis. This condensate analysis method combines a number of different analytical methods with varying degrees of repeatability and reproducibility. Precision values for this method will be determined when a round robi
