1、Designation: D7607 11Standard Test Method forAnalysis of Oxygen in Gaseous Fuels (ElectrochemicalSensor Method)1This standard is issued under the fixed designation D7607; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、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 the determination of oxygen (O2)in gaseous fuels and fuel type gases. It is applicable to them
3、easurement of oxygen in natural gas and other gaseous fuels.This method can be used to measure oxygen in helium,hydrogen, nitrogen, argon, carbon dioxide, mixed gases, pro-cess gases, and ambient air. The applicable range is 0.1 ppm(v)to 25% by volume.1.2 The values stated in either SI units or inch
4、-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.3 This standard does not purport
5、to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D4150 T
6、erminology Relating to Gaseous FuelsD5503 Practice for Natural Gas Sample-Handling and Con-ditioning Systems for Pipeline Instrumentation3. Terminology3.1 For general terminology see Terminology D41503.2 Definitions:3.2.1 electrochemical sensorAchemical sensor that quan-titatively measures an analyt
7、e by the electrical output producedby the sensor.3.2.2 span calibrationThe adjustment of the transmitterelectronics to the sensors signal output for a given oxygenstandard.3.2.3 zero calibrationThe adjustment of the transmitterelectronics to the sensors signal output for a sample gascontaining less
8、than 0.1ppm(v) oxygen.4. Summary of Test Method4.1 Measurement of oxygen is accomplished by comparingthe electrical signal produced by an unknown sample with thatof a known standard using an oxygen specific electrochemicalsensor. A gaseous sample at constant flow and temperature ispassed over the el
9、ectrochemical cell. Oxygen diffuses into thesensor and reacts chemically at the sensing electrode toproduce an electrical current output proportional to the oxygenconcentration in the gas phase. Experience has shown that thetypes of sensors supplied with equipment used in this standardtypically have
10、 a linear response over the ranges of applicationwhich remains stable during the sensors useful life. Theanalyzer consists of a sensor, a sample flow system, and theelectronics to accurately determine the sensor signal.5. Significance and Use5.1 This test method is primarily used to monitor theconce
11、ntration of oxygen in gases to verify gas quality foroperational needs and contractual obligations. Oxygen contentis a major factor influencing internal corrosion, fuel quality, gasquality, and user and operator safety.6. Interferences6.1 Interfering gases such as oxides of sulfur, oxides ofnitrogen
12、, and hydrogen sulfide can produce false readings andreduce the expected life of the sensor. Scrubbers are used toremove these compounds. Special sensors suitable for gascontaining high fractions of carbon dioxide are available frommanufacturers.7. Apparatus7.1 SensorThe sealed sensor is contained i
13、n a housingconstructed of stainless steel or other non-permeable material.The sensor contains a cathode and an anode in an electrolytesolution.Afluorocarbon membrane allows the oxygen from thesample to diffuse into the sensor. Oxygen in the sample isreduced at the cathode and is simultaneously oxidi
14、zed at theanode. The electrons released at the surface of the anode flowto the cathode surface when an external electrical path is1This test method is under the jurisdiction ofASTM Committee D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.12 on On-Line/At-LineAnalysis of Gas
15、eous Fuels.Current edition approved June 1, 2011. Published July 2011. DOI: 10.1520/D7607-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document
16、Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.provided. The current is proportional to the amount of oxygenreaching the cathode and is used to measure the oxygenconcentration in the gas phase. The el
17、ectrochemical reactionsfor a lead anode cell are as follows:O21 2H2O 1 4e24OH(cathode half reaction)2Pb 1 4OH22PbO 1 2H2O 1 4e2(anode half reaction)2Pb 1 O22PbO (overall cell reaction)Any electrochemical cell with different materials can be employed if the cell cangive the same performance for selec
18、tive oxygen detection with similar sensitiv-ity.7.2 ElectronicsVarious electronic circuits are used toamplify and filter the sensor signal. The signal output may becorrected for the gas sample temperature.7.3 OutputAutomatic digital or range selectable analogdisplay of parts per million or percent o
19、xygen reading byvolume.7.4 Sampling SystemSample gas must be introduced tothe sensor of the analyzer. A flow control metering valve ispositioned upstream of the analyzer to provide a gas sampleflow rate of 0.5 to 2 L/min 1 to 5 SCFM. If necessary, apressure regulator with a metallic diaphragm can be
20、 usedupstream of the flow control valve to provide 35 to 200 kPa 5to 30 psig inlet pressure. A leak-free sample pump may beused for low pressure sampling. Stainless steel tubing andconnections should be used to minimize any air intrusion intothe sampling system. Gas scrubbers may be necessary toremo
21、ve interfering gases such as oxides of sulfur, oxides ofnitrogen, and hydrogen sulfide. A suitable coalescing or par-ticulate filter can be used to remove condensation, moisture,and/or particulates to prevent erroneous analysis readings anddamage to the sensor. A meter, such as a rotameter, is used
22、tomonitor the sample gas flow through the analyzer.8. Hazards8.1 Use safe and proper venting if using this method for theanalysis of hazardous or flammable gases. Failure to followmanufacturers instructions for the instrumentation used in thistest method may result in a hazardous condition.8.2 Do no
23、t open the sensor. The sensor contains a corrosiveliquid electrolyte that could be harmful if touched or ingested.Refer to the Material Safety Data Sheet provided by the sensormanufacturer.9. Preparation of Apparatus and Calibration9.1 Zero alibrationIn theory the oxygen sensor producesno signal whe
24、n exposed to oxygen free sample gas. In reality,expect the sensor to generate an oxygen reading when sam-pling oxygen-free sample gas due to minor leakage in thesample line connections, residual oxygen in the sensorselectrolyte, and tolerances of the electronic components of theanalyzer. Zero calibr
25、ation is required after a new sensor isinstalled.9.1.1 The sensor is exposed to the sample gas with less than0.1 ppm oxygen. Follow the instrument manufacturers recom-mended inlet sample flow rate and pressure, usually a flow rateof 1 liter per min or 2 SCFH is recommended for optimumperformance.9.1
26、.2 Allow the analyzer output to stabilize. This may takeup several hours if a new sensor has been installed.9.1.3 Follow the instrument manufacturers instructions forzero calibration of the instrument.9.2 Span Calibration of InstrumentCertified gas standardscan be obtained from a gas standard vendor
27、. Span calibration isrequired after a new sensor is installed.9.2.1 Flow the gas standard through the analyzer. Thestandard should approximate the sample gas to be tested andcontain oxygen levels in the range of interest of the user.9.2.2 Allow the analyzer output to stabilize. This may takeseveral
28、min.9.2.3 Follow the instrument manufacturers instructions forspan calibration of the instrument.10. Conditioning10.1 Purge oxygen free or low ppm oxygen gas through theapparatus if it is not to be used immediately after calibration.Allow the display reading to stabilize before disconnecting.This is
29、 to minimize the oxygen exposure (reaction) to thesensor during storage or stand-by.11. Procedure11.1 SamplingDue to the large volume of sample thatmay be required for this analysis it is advisable to analyze foroxygen at the sample source such as directly from a gaspipeline or storage vessel.11.2 B
30、lank AnalysisSensor performance and sample sys-tem integrity may be verified by passing low oxygen contentgas across the sensor. Higher than expected readings may beindicative of sensor failure or sample system leaks.11.3 Sample AnalysisPrior to flowing sample gas to thesensor, establish the flow ra
31、te in the sample line, allow sampleto vent to atmosphere long enough to purge the line free of air,then connect the sample gas to the sensor. Avoid any leaks inthe tubing that transports the sample to the analyzer and makesure there are no restrictions in the analyzer outlet vent.Permanent sensor da
32、mage can occur from backpressure on thesensor. The sample conditions should closely approximate thecalibration conditions for maximum accuracy.11.4 The analyzer displays a direct readout of oxygen in thesample. Do not attempt to take a reading until the readoutstabilizes. Standard connections are av
33、ailable for the signaloutput to a data logger or computer data system. Measurementsbelow 10 ppm usually require 20 min if the sensor has been inservice at ppm levels for at least two weeks, and 60 min if thesensor is new assuming the zero/purge/sample gas has anoxygen concentration below 1 ppm. Meas
34、urements above 100ppm require less than 10 min.11.5 Quality AssuranceThe following quality assuranceprocedures are suggested.11.5.1 Calibration Checkthe primary calibration standardis reanalyzed daily. Results that vary by more than 5% of theaccepted value indicate an analyzer or sampling problem an
35、dmay warrant investigation.11.5.2 Secondary Calibration Checksecondary standardsmay be analyzed as a crosscheck to assure primary standardvalidity. Results that vary by more than 10% of the acceptedvalue may indicate a problem with the standard in use.11.5.3 Linearity ChecksKnown concentrations of o
36、xygenat differing levels may be introduced to the sensor for analysis.D7607 112Deviation from linearity may indicate sampling system leaks orsensor problems and should be investigated. Acceptable linear-ity limits are determined by the users application.12. Calculation or Interpretation of Results12
37、.1 If a sample scrubber is used for sensor protection frominterfering gases the oxygen concentration should be correctedas follows:X 5 A / 1 2 B ! (1)Where:X = corrected oxygen in sampleA = oxygen readingB = Mol Fraction of interfering gases removed by scrubber12.2 Conversion from volume to mass con
38、centration (W) ofoxygen in milligrams per cubic meter at 25 degrees C and 760mm Hg 101.3 kPa is obtained by multiplying ppm bymolecular weight and dividing by 24.45 (Molar Volume):W 5 X 32 / 24.45! (2)Where:W = mass concentration, mg/m3, andX = Oxygen concentration in sample, ppmv13. Precision and B
39、ias13.1 PrecisionThe precision of this test method as deter-mined by the statistical examination of the inter-laboratory testresults is as follows.13.1.1 RepeatabilityThe difference between successivetest results obtained by the same operator with the sameapparatus under constant operating condition
40、s on identical testmaterial would, in the long run, in the normal and correctoperation of the test method, exceed the following values byonly one case in twenty. See Table 1.13.1.2 ReproducibilityThe difference between two singleand independent results obtained by different operators work-ing in dif
41、ferent laboratories on identical test material would, inthe long run, exceed the following values only one case intwenty. (Experimental results to be determined.)13.2 BiasSince there is no accepted reference materialfor determining the bias, no statement on bias can be made.14. Keywords14.1 oxygen;
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43、rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additio
44、nal standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the A
45、STM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the ab
46、oveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).TABLE 1 Repeatability of Oxygen Measurement at VariousLevelsConcentration Standard Deviation Repeatability1.34 ppm 0.02 ppm 0.05 ppm10.24 ppm 0.05 ppm 0.15 ppm103.3 ppm 0.11 ppm 0.31 ppm0.20 % 0.01 % 0.02 %20.0 % 0.04% 0.11 %D7607 113
