1、Designation: D7493 08D7493 14Standard Test Method forOnline Measurement of Sulfur Compounds in Natural Gasand Gaseous Fuels by Gas Chromatograph andElectrochemical Detection1This standard is issued under the fixed designation D7493; the number immediately following the designation indicates the year
2、 oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method is for on-line measurement of volatile
3、sulfur-containing compounds in gaseous fuels by gaschromatography (GC) and electrochemical (EC) detection. TheThis test method is applicable to hydrogen sulfide, C1-C4 C1 to C4mercaptans, sulfides and tetrahydrothiophene (THT).1.1.1 Carbonyl sulfide (COS) is not covered in this test method.1.1.2 The
4、 detection range for sulfur compounds is approximately from 0.1 to 100 PPMv ppmv (mL/m3) or 0.1 to 100 mg/m3.The detection range may vary depending on the sample injection volume, chromatographic peak separation and the sensitivity ofto the specific EC detector.1.2 This test method describes a GC-EC
5、 method employing packed GC columns and a specific detector as an illustration fornatural gas and other gaseous fuel containing composed of mainly light (C4 and smaller) hydrocarbons. Alternative GC columns,detector designs and instrument parameters may be used for the same analysis or for different
6、 types of gaseous fuel, provided thatappropriate chromatographic separation and optimal detection of these compounds can be used, provided that chromatographicseparation, quality control and measurement objectives needed to comply with user, or regulator needs or both, are achieved.1.3 This test met
7、hod does not intend to identify and measure all individual sulfur species, and is mainly employed formonitoring natural sulfur and sulfur odorant naturally occurring reduced sulfur compounds commonly found in natural gas and fuelgases or employed as an odorous warning agent in fuelodorant in these g
8、ases.1.4 The test method is normallytypically employed forin repetitive or continuous on-line monitoring of sulfur components innatural gas and fuel gases withusing a single sulfur standard. The test method may be employed for laboratory-qualitymeasurement with more extensive calibration. (See calib
9、ration standard. Need for a multipoint calibration curve or quality controlprocedures can be satisfied by making use of procedures delineated in Test Methods D5504, D5623, D6228, D6968, ISO 19739,ISO 6326-2, and or GPA 2199.1.5 The test method can be used for measurement of all listed sulfur compoun
10、ds listed in Table 1 in air or other gases, gaseousmatrices, provided that no compound, whichcompounds that can interfere with the GC separation and electrochemical detection,isdetection are present.1.6 This test method is written in conjunction with as a companion to Practices D5287, D7165 and D716
11、6.1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish
12、 appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D3609 Practice for Calibration Techniques Using Permeation Tubes1 This test method is under the jurisdiction of ASTM Committee D03 on Gaseous Fuel
13、s and is the direct responsibility of Subcommittee D03.12 on On-Line/At-LineAnalysis of Gaseous Fuels.Current edition approved Dec. 15, 2008June 1, 2014. Published January 2009July 2014. Originally approved in 2008. Last previous edition approved as D7493-08. DOI:10.1520/D7493-08.10.1520/D7493-14.2
14、For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to p
15、rovide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof t
16、he standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1D4150 Terminology Relating to Gaseous FuelsD4626 Practice for Calculation of Gas Chromatographic Response Facto
17、rsD5287 Practice for Automatic Sampling of Gaseous FuelsD5504 Test Method for Determination of Sulfur Compounds in Natural Gas and Gaseous Fuels by Gas Chromatography andChemiluminescenceD5623 Test Method for Sulfur Compounds in Light Petroleum Liquids by Gas Chromatography and Sulfur Selective Dete
18、ctionD6228 Test Method for Determination of Sulfur Compounds in Natural Gas and Gaseous Fuels by Gas Chromatography andFlame Photometric DetectionD6968 Test Method for Simultaneous Measurement of Sulfur Compounds and Minor Hydrocarbons in Natural Gas and GaseousFuels by Gas Chromatography and Atomic
19、 Emission DetectionD7165 Practice for Gas Chromatograph Based On-line/At-line Analysis for Sulfur Content of Gaseous FuelsD7166 Practice for Total Sulfur Analyzer Based On-line/At-line for Sulfur Content of Gaseous Fuels2.2 ISO Standards:3ISO 19739 Natural Gasgas Determination of Sulfur Compoundssul
20、fur compounds by Gasgas chromatographyISO 6326-2 GasAnalysis Determination of Sulphur Compounds in Natural gas Part 2: Gas Chromatographic Method Usingan Electrochemical Detector for The Determination of Odoriferous Sulphur Compounds2.3 GPA Standard4GPA 2199 Determination - Determination of Specific
21、 Sulfur Compounds by Capillary Gas Chromatography and SulfurChemiluminescence Detection3. Terminology3.1 Common terminology used in this method are cited in Terminology D4150 3.2 . Sulfur compounds are commonly referredby their initials (chemical or formula), for example,3.2 Abbriviations:Abbreviati
22、ons:hydrogen sulfide = H2Smethyl mercaptan = MeSH (MM)ethyl mercaptan = EtSH (EM)dimethyl sulfide = DMSi-Propyl mercaptan = IPMn-Propyl mercaptan = NPMt-Butyl mercaptan = TBMtetrahydrothiophene = THT or Thiophane3 Available from International Organization for Standardization (ISO), 1, ch. de la Voie
23、-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http:/www.iso.ch.4 Available from Gas Processors Association (GPA), 6526 E. 60th St., Tulsa, OK 74145, http:/.TABLE 21 Typical Retention Times of Sulfur Components of Different GC-ECD RunsGC-ED instrument GC-ED #1 GC-ED #2 GC-ED #3GC-EC inst
24、rument GC-EC #1 GC-EC #2 GC-EC #3GC-Column andparameters18 in. ID 70cm L,N2, 12ml/min, 65 C1.6 mm ID 1200 mm L,N2, 100 ml/min, 20 C4 mm ID 400 mm L,N2, 100 ml/min, 20 CGC-Column andparameters18 in. ID 70 cm L,N2, 12 mL/min, 65 C1.6 mm ID 1200 mm L,N2, 100 mL/min, 20 C4 mm ID 400 mm L,N2, 100 mL/min,
25、 20 CDetector Size 520 mm 520 mm 3025 mmSulfur Compound RT (sec.) RT (sec.) RT (sec.)Hydrogen Sulfide, H2S 30 30 30Hydrogen sulfide, H2S 30 30 30Methyl mercaptan (MM) 70 66 60Methyl mercaptan (MeSH) 70 66 60Ethyl mercaptan (EtSH) 105 150 80Dimethyl sulfide (DMS) 120 200 80i-Propyl mercaptan (IPM) 16
26、0 240 160t-Butyl mercaptan (TBM) 220 342 240n-Propyl mercaptan (NPM) 265 426 290i-Butyl mercaptan (IBM) 440 . 560n-Butyl mercaptan (NBM) 585 . .Thiophane (THT) 900A 720A 2100AThe shorter GC column is employed for simltaneoussimultaneous accelerated analysis of THT.D7493 1424. Summary of Test Method4
27、.1 Gaseous fuel is directly sampled on-line for analysis of specific and normally reactive sulfur compounds. Samples areintroduced to an inert the GC instrument through an inert a sampling system. Sulfur compounds are separated by a GC columnand measured by an EC detector. The method requires freque
28、ntperiodic calibration using stablecertified standards. The test methodconforms to the standard practice ofpractices stated in Practice D7165.4.2 A fixed volume of the fuel gas sample (normally 0.25 mL) is injected into an isothermal a gas chromatograph where it ispassed through a 1.2 meter, 1.6 mm
29、I.D., Chromosorb W column. A varying amount of sample and other GC columns with orwithout column back-flush technique can be used for sensitive detection of sulfur with optimal separation.operating isothermallywhere components are separated using two chromatographic columns.4.3 Specific GC-separated
30、 sulfur compounds are detected bydetermined using an electrochemical detector utilizing a chromicacid electrolyte. Detectors with different physical designs are commercially available and may be employed.5. Significance and Use5.1 Gaseous fuels, such as natural gas, petroleum gases and bio-gases, co
31、ntain varying amounts and types of sulfur compounds.sulfur compounds that are naturally occurring or that are added as odorants for safety purposes. These sulfur compounds aregenerally odorous, corrosive to equipment, and can inhibit or destroy catalysts employed in gas processing and end use, such
32、asthose used in fuel cell. Their accurate on-line measurement is essentialother end uses. Their accurate continuous measurement isimportant to gas processing, operation and utilization, and is frequently of regulatory interest.5.2 Small amounts (typically, total 4-6 PPMv) of of 4 to 6 ppmv) of sulfu
33、r odorants are added to natural gas and other fuel gasesfor safety purposes. Some sulfur odorants can be are reactive, and may be oxidized, forming oxidized to form more stable sulfurcompounds having lower odor thresholds. These gaseous thresholds which adversely impact the potential safety of the g
34、as deliverysystems and gas users. Gaseous fuels are analyzed for sulfur odorants to help in monitoring compounds and odorant levels to assistin pipeline integrity surveillance and to ensure appropriate odorant levels for public safety.5.3 This method offers an on-line technique to continuously ident
35、ify and quantify individual target sulfur species in gaseous fuelwith automatic calibration and validation.6. Apparatus6.1 ChromatographIndustrial gas chromatograph with an isothermal oven and oven, automatic injection valve, and softwarenecessary for interfacing to a chromic acid electrochemical de
36、tector and designed for the intended application and performance.application. The GC system must be inert, well conditioned well-conditioned and passivated with a gas containing the sulfurcompounds of interest to ensure reliable results.6.1.1 Sample Inlet SystemThe gas sample is introduced to the GC
37、 by sample loop injection. An automated non-reactive gassampling valve is employed for a fixed sample loop injection. The sample injection port must be heated continuously at atemperature significantly (10C)(10 C) above the temperature at which the gas was sampled to avoid sample condensation anddis
38、crimination. Inert tubing made of non-permeable, non-sorbing and non-reactive materials, as short as possible and heat tracedat the same temperature, should be employed for transferring the sample from a sample source to the gas sampling valve and tothe GC inlet system. Silica-coated 316 stainless s
39、teel (s.s.) and non-permeable Teflon polytetrafluoroethylene (PTFE) type tubingare often employed. Different size fixed-volume samplingsample loops (0.25 to 10.0 mL) may be used for target concentrationranges, provided with adequate chromatographic separation. to target multiple concentration ranges
40、 for components in a gas,provided chromatographic separation and quality control objectives are obtained. The same non-reactive materials are used for thesamplingsample loop to avoid possible decomposition or absorption of reactive species. When necessary, a precision glass syringewith a gas-tight T
41、eflon-seated plunger is used to manually introduce sample or calibration standards through a PTFE septum at thefront of GC columns. The sampling and GC inlet system must be well conditioned and evaluated frequently for compatibility withtrace quantities of reactive sulfur compounds, such as tert-but
42、yl mercaptan.Aprogrammable and computer-controlled multi-streamsample selector can be used to sample fuel gases and calibration gases.6.1.2 Column TemperatureThe gas chromatograph must be capable of maintaining an isothermal temperature, normally at65 C, with temperature variation not exceeding 0.5
43、C60.5 C.6.1.3 Carrier and Detector Gas ControlConstant flow control of carrier and detector gases is necessary for optimum andconsistent analytical performance. Control is best provided by the use of pressure regulators and fixed flow restrictors.The gas flowrate is measured by any appropriate means
44、 and the required gas flow indicated by the use of a pressure gauge. using a gas flowmeter either volumetrically or based upon mass flow rates. Mass flow controllers, capable of maintaining gas flow constant to 61 61 % at the required flow rates can also should be used. The supply pressure of the ga
45、s delivered to the gas chromatograph mustbe at least 69 kPa (10 psig)psi) greater than the regulated gas at the instrument to compensate for the system back pressure.6.1.4 DetectorAn EC detector using chromic acid chemistry detector, whose operation is based upon the reduction/oxidationreaction betw
46、een reduced sulfur compounds and a solution of chromic acid (Fig. 1), is used in this method. The detector is setaccording to the manufacturers specifications for the this particular application. One EC detector is normally employed forD7493 143measurement.Asecond EC detector may be column is employ
47、ed for simultaneous detection of late-eluting sulfur compound, suchas THT, using a shorter GC column and/or at different optimal separation pounds, such as THT.6.1.4.1 The detector consists of a glass or methyl polymethacrylate container. The electrodes, two pieces of platinum gauze asgridsgrids, ar
48、e arranged vertically in parallel, and are welded in a borosilicate glass tube and separately tube. These grids areisolated from each other and other conductive materials and connected to an amplifier for data acquisition.6.1.4.2 The electrolyte, a solution of chromium (VI) oxide in distilled or dei
49、onized water (100 g/Lor 0.66 mole/L), is containedin a an acid-resistant vessel. A tube fitted with the electrodes dips is dipped into the solution such that the liquid is retained bycapillary action within the tube at a level approximately at midway between two grids.6.1.4.3 The gas flow from the GC column is discharged through a narrow glass or TeflonPTFE tube (2 mm ID) immediatelyabove the upper grid centrecenter (normally 5 mm). Each sulfur compound sequentially elutes and reacts with chromic acid.Possib
