1、Designation: D 4891 89 (Reapproved 2006)Standard Test Method forHeating Value of Gases in Natural Gas Range byStoichiometric Combustion1This standard is issued under the fixed designation D 4891; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the heatingvalue of natural gases and similar g
3、aseous mixtures within therange of composition shown in Table 1.1.2 This standard involves combustible gases. It is not thepurpose of this standard to address the safety concerns, if any,associated with their use. It is the responsibility of the user ofthis standard to establish appropriate safety a
4、nd health prac-tices and determine the applicability of regulatory limitationsprior to use.2. Referenced Documents2.1 ASTM Standards:2D 1826 Test Method for Calorific (Heating) Value of Gasesin Natural Gas Range by Continuous Recording Calorim-eterE 691 Practice for Conducting an Interlaboratory Stu
5、dy toDetermine the Precision of a Test Method3. Terminology3.1 All of the terms defined in Test Method D 1826 areincluded by reference.3.2 Descriptions of Terms:3.2.1 combustion ratiothe ratio of combustion air togaseous fuel.3.2.2 stoichiometric ratiothe combustion ratio when thequantity of combust
6、ion air is just sufficient to convert all of thecombustibles in the fuel to water and carbon dioxide.3.2.3 burned gas parametera property of the burned gasafter combustion which is a function of the combustion ratio.3.2.4 critical combustion ratiofor a specific burned gasparameter, the combustion ra
7、tio at which a plot of burned gasparameter versus combustion ratio has either maximum valueor maximum slope.4. Summary of Test Method4.1 Air is mixed with the gaseous fuel to be tested. Themixture is burned and the air-fuel ratio is adjusted so thatessentially a stoichiometric proportion of air is p
8、resent. Moreexactly, the adjustment is made so that the air-fuel ratio is in aconstant proportion to the stoichiometric ratio which is arelative measure of the heating value. To set this ratio, acharacteristic property of the burned gas is measured, such astemperature or oxygen concentration.5. Sign
9、ificance and Use5.1 This test method provides an accurate and reliableprocedure to measure the total heating value of a fuel gas, ona continuous basis, which is used for regulatory compliance,custody transfer, and process control.5.2 Some instruments which conform to the requirementsset forth in thi
10、s test method can have response times on theorder of 1 min or less and can be used for on-line measurementand control.5.3 The method is sensitive to the presence of oxygen andnonparaffin fuels. For components not listed and compositionranges that fall outside those in Table 1, modifications in theme
11、thod may be required to obtain correct results.6. Apparatus6.1 A suitable apparatus for carrying out the stoichiometriccombustion method will have at least the following fourcomponents: flow meter or regulator, or both; combustionchamber; burned gas sensor; and electronics. The requirementfor each o
12、f these components is discussed below. The detailed1This test method is under the jurisdiction ofASTM Committee D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.03 on Determination ofHeating Value and Relative Density of Gaseous Fuels.Current edition approved June 1, 2006. Pu
13、blished June 2006. Originallyapproved in 1989. Last previous edition approved in 2001 as D489189 (2001).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 standard
14、s Document Summary page onthe ASTM website.TABLE 1 Natural Gas Components and Range of CompositionCoveredCompound Concentration Range, mole, %Helium 0.01 to 5Nitrogen 0.01 to 20Carbon dioxide 0.01 to 10Methane 50 to 100Ethane 0.01 to 20Propane 0.01 to 20n-butane 0.01 to 10isobutane 0.01 to 10n-penta
15、ne 0.01 to 2Isopentane 0.01 to 2Hexanes and heavier 0.01 to 21Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.design of each of these components can vary. Two differentapparatus are shown in Fig. 1 and Fig. 2. In each figure theequiva
16、lent of the four necessary components are enclosed indashed lines.6.2 OverviewAir and fuel enter the apparatus and the flowof each is measured. Alternatively, only one gas flow need bemeasured if the flow of the other is kept the same duringmeasurement and calibration. This is illustrated in Fig. 2.
17、 Nextthere is a combustion chamber in which the air and fuel aremixed and burned. This can be as simple as a bunsen or meekerburner, but precautions should be taken that subsequent mea-surements of burned gas characteristics are not influenced byambient conditions. Finally, there is a sensor in the
18、burned gaswhich measures a property of this gas that is sensitive to thecombustion ratio and has a unique feature at the stoichiometricratio. Two such properties are temperature and oxygen concen-trations, and either can be measured.6.3 Flow Meter and/or RegulatorThe flow measurementpart of the appa
19、ratus should have an accuracy and precision ofthe order of 0.1 %. Likewise, if the flow is to be kept constant,the flow regulator should maintain this constant value within0.1 %.The meter or regulator for natural gas must maintain thisprecision and accuracy over the density and viscosity rangesconsi
20、stent with the composition range in Table 1.6.4 Combustion Chamber:6.4.1 There are two different types of combustion chambersthat may be used. In the first type the air and fuel are mixed andburned in a single burner. The apparatus shown in Fig. 1 hasthis type of combustion chamber.6.4.2 In the seco
21、nd type of combustion chamber, the air andfuel are each divided into two streams, and combustion takesplace simultaneously in two burners. The division of air flowmust be such that the proportion of air going to each burneralways remains the same. Likewise the division of fuel flowmust always remain
22、 the same even through fuel compositionchanges.Another requirement is that the flow divisions be suchthat one burner has a mixture with a slightly higher combustionratio than the other. The apparatus shown in Fig. 2 has this typeof combustion chamber.6.5 Burned Gas Sensor:6.5.1 The burned gas sensor
23、 must measure a characteristicof the burned gas which is a function of the combustion ratioand for which there is a critical combustion ratio related to thestoichiometric ratio. A combustion chamber of the first type(Fig. 1) would have one sensor in the burned gas and its outputsignal would constitu
24、te the desired measurement. In a combus-tion chamber of the second type (Fig. 2) there would be asensor in the burned gas from each burner. The differencebetween the two output signals would constitute the desiredmeasurement.6.5.2 There are several properties of the burned gas whichare related uniqu
25、ely to the combustion ratio. A burned gassensor may be selected which provides a measure of any one ofthese, for example, either temperature or oxygen partial pres-sure.6.6 ElectronicsElectronics are used to receive the signalsfrom the components described above to control the flow ofgases into the
26、combustion chamber in response to the signalfrom the burned gas sensor and to provide a digital or analogoutput signal, or both, which is proportional to the heatingvalue of the gaseous fuel.6.7 Temperature Stability and Operating EnvironmentThe method is capable of operating over a range of tempera
27、-tures limited only by the specific apparatus used to realize themethod. It is desirable to equilibrate the air and fuel tempera-tures before the gases are measured. The electronics shouldalso be stabilized against temperature changes and the burnedgas sensor should be insensitive to changes in the
28、ambientconditions.7. Reagents and Materials7.1 Physical ContaminationThe air and gas must be freeof dust, liquid, water, liquid hydrocarbons, and other entrainedsolids. Foreign materials should be removed by a sample linefilter. To avoid any problems in the line from any liquidaccumulation, pitch th
29、e line to a low point and provide a dripleg.7.2 Chemical ContaminationThe air must be free ofcombustible compounds. The oxygen content and the absolutehumidity of the air should be the same during measurement asduring calibration.FIG. 1 Gas Btu Transmitter (Functional Overview)FIG. 2 Stoichiometric
30、Combustion ApparatusD 4891 89 (2006)28. Calibration and Standardization8.1 The calibration factor, F, and the constant, B,intheequation, C=FR+B, are determined through an initial cali-bration, in which the critical combustion ratios of at least twostandard gases of known but different heating values
31、 aremeasured using the procedure described in 9.1.8.2 The calibration factor, F, is routinely redetermined atregular intervals under field conditions using a calibration gasof known heating value. The constant, B, is not adjusted in theroutine calibrations. The interval between routine calibrationsm
32、ust be determined under the specific operating conditions,and is usually of the order of 24 h. Determination of Festablishes the amount of net oxygen per standard volume ofcombustion air. Variations in net oxygen constant can becaused by several factors, such as changes in absolute humidityor the pr
33、esence of contaminants in the air supply.9. Procedure9.1 Measure the burned gas parameter at different combus-tion ratios and determine that combustion ratio for which theparameter has a specified characteristic such as a maximum,minimum, or maximum rate of change.9.1.1 Use an apparatus such as in F
34、ig. 1 or Fig. 2 where thecomponents of the apparatus meet the requirements of Section6. If the apparatus has two flow meters, the combustion ratio isthe ratio of the output of the air flow meter divided by theoutput of the fuel flow meter. If the apparatus has only one flowmeter, then the combustion
35、 ratio is set numerically equal toeither the output of the air flow meter or the reciprocal of theoutput of the fuel flow meter. The burned gas parameter is afunction of the combustion ratio and is measured at differentcombustion ratios. The critical combustion ratio, R, is taken asthat point where
36、this function has a maximum value, minimumvalue, or maximum rate of change. The heating value, C,iscalculated from the equationC 5 FR 1 B, (1)where the constants B and F are determined as described in8.1 and 8.2.9.1.2 This procedure may be automated, for example, byusing a microprocessor in the elec
37、tronics.9.2 For making laboratory measurements of highest preci-sion, use the following procedure:9.2.1 First calibrate the instrument as described in 8.2.Then, before measuring the test gases, measure two otherstandard gases of known heating value. After the test gasmeasurements, measure the two st
38、andard gases again. Theknown heating values of these standard gases, CAL.VAL.LOW and CAL.VAL.HIGH, should bracket that of the un-known gas. Combine the measured values of the standard gasesand the test gases to obtain a best estimate of the heating valueof the test gas. Do this using the following c
39、alculationprocedure.9.2.1.1 Step 1There are four measured values for thecalibration gases, two for the high calorific gas and two for thelow calorific gas. Average these four measurements together.The result is represented by the symbol, AV.STD.GASES.9.2.1.2 Step 2Average the two known heating value
40、s ofthe standard gases together. The result is represented by thesymbol, AV.CAL.VAL. Thus, AV.CAL.VAL = (CAL.VAL.HIGH) + (CAL.VAL.LOW)/2.9.2.1.3 Step 3Calculate a correction to the test gas mea-surements. This correction is represented by the symbol,CORR. The calculation is as follows:CORR = (AV.STD
41、.GASES) (AV.CAL.VAL).9.2.1.4 Step 4Subtract the quantity, CORR, that is calcu-lated in Step 3 from each of the test gas measurements to givethe corrected value.9.2.2 Example 1Standard gas low has CAL.VAL-.LOW = 1000 Btu/standard cubic foot and measured valuesafter calibration are 1002.0 and 1002.8.
42、(All heating values inExample 1 and Example 2 have units of Btu per standard cubicfoot.) Standard gas high has CAL.VAL.HIGH = 1200 andmeasured values of 1202.0 and 1203.2.AV.STD.GASES = (1002.0 + 1002.8 + 1202.0 + 1203.2)/4= 1102.5.AV.CAL.VAL = (1000.0 + 1200.0)/2 = 1100.0CORR = 1102.5 1100 = 2.5TES
43、T GAS MEASUREMENT = 1080.6CORRECTED VALUE = (1080.6 2.5) = 1078.19.2.3 Example 2:CAL.VAL.LOW = 1000 Btu/standard cubic foot.Measured values are 998.0 and 998.2.CAL.VAL.HIGH = 1200Measured values are 1199.0 and 1199.2AV.STD.VAL = (998.0 + 998.2 + 1199.0 + 1199.2)/4 =1098.6AV.CAL.VAL = 1100CORR = (109
44、8.6 1100) = 1.4TEST GAS MEASUREMENT = 1076.7CORRECTED VALUE = 1076.7 (1.4) = 1078.110. Precision and Bias10.1 To determine precision and bias, an interlaboratorystudy was carried out using two types of commercial instru-ments that implement the stoichiometric method. For each typeof instrument six d
45、ifferent laboratories each measured fivedifferent reference gases. Cylinders containing these referencegases were transported from laboratory to laboratory. Eachlaboratory used its own instrument and personnel to measurethe heating values of the gases in these cylinders. The samecalibration gas was
46、used to calibrate each instrument.10.2 The heating values of the reference gases were deter-mined prior to the study by the Institute of Gas Technology.These values were established by averaging three recordingcalorimeter measurements. The values were unknown to theparticipants in the interlaborator
47、y test program. At the end ofthe study, the heating values were remeasured at the Institute ofGas Technology to establish that the gas compositions did notchange. The statistical analysis of the results was in accordancewith the procedures in Practice E 691.10.2.1 RepeatabilityThe root mean square e
48、stimate of thewithin laboratory component of standard deviation was 0.76Btu/standard cubic foot. The corresponding 95 % confidencerepeatability interval was 2.1 Btu/standard cubic foot.D 4891 89 (2006)310.2.2 ReproducibilityThe root mean square estimate ofthe between laboratory component of standard
49、 deviation was1.67 Btu/standard cubic foot. The corresponding 95 % confi-dence reproducibility interval was 5.1 Btu/standard cubic foot.10.2.3 BiasThe average of all measurements agreed withthe average reference value within 0.1 %.11. Keywords11.1 natural gas range by stoichiometric conversionASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the
