1、Designation: D 7278 06An American National StandardStandard Guide forPrediction of Analyzer Sample System Lag Times1This standard is issued under the fixed designation D 7278; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the yea
2、r 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.INTRODUCTIONLag time, as used in this guide, is the time required to transport a representative sample from theprocess tap t
3、o the analyzer. Sample system designs have infinite configurations so this guide gives theuser guidance, based on basic design considerations, when calculating the lag time of on-line sampledelivery systems. Lag time of the analyzer sample system is a required system characteristic whenperforming sy
4、stem validation in Practice D 3764 or D 6122 and in general the proper operation of anyon-line analytical system. The guide lists the components of the system that need to be consideredwhen determining lag time plus a means to judge the type of flow and need for multiple flushes beforeanalysis on an
5、y sample.1. Scope1.1 This guide covers the application of routine calculationsto estimate sample system lag time, in seconds, for gas, liquid,and mixed phase systems.1.2 This guide considers the sources of lag time from theprocess sample tap, tap conditioning, sample transport, pre-analysis conditio
6、ning and analysis.1.3 Lag times are estimated based on a prediction of flowcharacteristics, turbulent, nonturbulent, or laminar, and thecorresponding purge requirements.1.4 Mixed phase systems prevent reliable representativesampling so system lag times should not be used to predictsample representat
7、ion of the stream.1.5 This standard does not purport 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 u
8、se.2. Referenced Documents2.1 ASTM Standards:2D 3764 Practice for Validation of Process Stream AnalyzerSystemsD 6122 Practice for Validation of Multivariate Process In-frared Spectrophotometers3. Terminology3.1 Definitions:3.1.1 continuous analyzer unit cycle timethe time intervalrequired to replace
9、 the volume of the analyzer measurementcell.3.1.2 intermittent analyzer unit cycle timethe time inter-val between successive updates of the analyzer output.3.1.3 purge volumethe combined volume of the fullanalyzer sampling and conditioning systems.3.1.4 sample system lag timethe time required to tra
10、nsporta representative sample from the process tap to the analyzer.3.1.5 system response timethe sum of the analyzer unitresponse time and the analyzer sample system lag time.3.2 Abbreviations:3.2.1 I.D.Internal Diameter3.2.2 ReReynolds Number4. Summary4.1 The lag time of an analyzer sample system i
11、s estimatedby first determining the flow characteristics. The flow isassigned as turbulent or non-turbulent to assign the number ofpurges required to change out the sample. Based on thehardware employed in the sample system an estimation of thelag time can be calculated.5. Significance and Use5.1 Th
12、e analyzer sample system lag time estimated by thisguide can be used in conjunction with the analyzer output toaid in optimizing control of blender facilities or process units.1This guide is under the jurisdiction of ASTM Committee D02 on PetroleumProducts and Lubricants and is the direct responsibi
13、lity of Subcommittee D02.25 onPerformance Assessment and Validation of Process Stream Analyzer Systems forPetroleum and Petroleum Products.Current edition approved July 1, 2006. Published August 2006.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Servic
14、e at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.2 The lag time can be used in the tuning of
15、controlprograms to set the proper optimization frequency.5.3 The application of this guide is not for the design of asample system but to estimate the performance of existingsample systems. The principles listed in this guide are there tohelp understand design concepts and allow the application ofth
16、is guide for its intended scope. Additional detailed informa-tion can be found in the references provided in the sectionentitled Additional Reading Material.6. Basic Design Considerations6.1 Acceptable Lag TimeAs a general rule, a one to twominute sample system lag time should be maintained wherepos
17、sible to give acceptable performance. Flow is a keycomponent in the determination of sample system lag time. Inmost systems the desired system lag time is impossible toachieve with maximum allowable sample flow rate to theanalyzer. To improve lag time a fast loop or bypass can be usedto increase sam
18、ple velocities through the system to a point justupstream of the analyzer.Aslipstream is taken from the bypassto feed the analyzer at its optimum flowrate. Excess sample inthe slipstream is vented to atmosphere, to flare or to the processstream dependant upon application and regulatory require-ments
19、.6.2 Physical State of Sample:6.2.1 Liquid SamplesPressure drop properties often gov-ern the design of a liquid system. This is due for the most parton the close relationship between pressure drop and systemflowrate and the fixed pressure differential available from theprocess for sample transport.
20、The sizing of the sample compo-nents is a tradeoff between pressure drop and sample flowrate.High sample flowrates in small sized component systems causehigh-pressure drops and low sample transport times. The sameflowrate in a larger tubing system will yield significant im-provements in pressure dro
21、p through the system, but will alsoincrease the time for sample transport significantly.6.2.2 Vapor SamplesVapor phase sampling is governedless by pressure drop and more by pressure compressionproperties of gases when compared to liquids. In compressiblegases the higher the pressure in a given volum
22、e, the moresample present in that volume. For this reason, and differentfrom liquids, the selection and location of pressure regulatingdevices in the vapor sample system has a great impact on theoverall system design. The optimal location for a high-pressureregulator in a vapor sample is immediately
23、 downstream of thesample tap or high-pressure location thereby limiting thevolume of the system under high pressure. Since the density ofa compressible fluid is a function of the pressure, compressiblefluid flow rate calculations are sometimes done over segmentallengths where average properties adeq
24、uately represent the fluidconditions of the line segment.6.2.3 Liquid to Vapor SamplesA change of phase due tosample vaporization can impact the sample lag time. Thevolume change from the liquid phase to the vapor phase issubstantial. Typical flow rates in gaseous sample lines down-stream of the vap
25、orizer can represent very small liquid feedrates to the vaporizer. Deadheaded sample line lengths up-stream of the vaporizer can, in turn, represent appreciable lagtimes.6.2.4 Phase SeparationThis guide is not intended to dealwith duel phase samples as the volume and flow characteristicsare outside
26、the scope.6.3 Sample TemperatureTemperature also impacts samplesystem lag time but to a lesser degree than pressure. Increasedtemperature of a sample lowers the sample density thuslowering the amount of sample flow needed to purge a givenvolume. Temperature impact is generally so minute that it isig
27、nored in rough estimations of sample system lag time.6.4 Typical Sources of Lag Time to Consider:6.4.1 Process Sample Tap:6.4.1.1 Sample taps can be a significant source of lag time ifa sampling probe is not used, need to know the design insidethe sample stream. See Fig. X1.1.6.4.1.2 Sample taps can
28、 present a problem for liquid vapor-izing systems with high volume and low flow on the liquidside. See Fig. X1.2.NOTE 1This refers to the case where the vaporizing regulator islocated at the sample tap and one then has a length of liquid filled linefrom the probe/process interface to the inlet of th
29、e vaporizing regulator.This situation can be mitigated by using a sample probe that takes thepressure drop, and subsequent vaporization, at the probe/process interfaceso that one extracts a gaseous sample only. The sensible heat of the bulkprocess stream flowing past the tip of the sample probe prov
30、ides theenergy necessary to vaporize the sample that is extracted.6.4.2 At-Tap Conditioning:6.4.2.1 Filters and Strainers at Sample StreamDependingon design and size these can add large volumes to the samplesystem that may not be turbulent flow.NOTE 2For filters with diameters greater than the sampl
31、e tubingdiameter calculate the internal volume and use the 3 times the volume ruleto account for the delay attributable to the filter.6.4.2.2 Flow or Pressure RegulatorsInternal volume ofthe regulator(s) needs to part of the system calculation.6.4.3 Vaporizing RegulatorsInternal volume of the regu-l
32、ator needs to part of the system calculation.6.4.3.1 The volume change from a liquid to a gas is on theorder of 300 to 600 volumes of gas per volume of liquid so thelag time of the liquid filled slipstream tubing length from a fastloop to a vaporizing regulator can represent very large lagtimes. See
33、 Fig. X1.3.6.4.3.2 A system designed on the basis of a good gasvolumetric flow rate can represent a very small liquid flow rate.6.5 Sample delivery tubing all needs to be taken intoaccount and this can sometimes be a significant run lengthdepending on the analyzer location to the process stream.6.5.
34、1 Sample Conditioning at Analyzer:6.5.1.1 FilteringDepending on design and size filters canadd large volumes to the sample system that may not beturbulent flow. See Note 2.7. Procedure7.1 Determination of Flow Characteristics:7.1.1 Calculate the Reynolds number, Re, of each section ofthe sample syst
35、em using the tubing / pipe internal diameter(I.D.), the flow velocity, density of the sample stream, andviscosity of the sample stream.Re 5 I.D.!3Velocity!3Density!# / Viscosity (1)D7278062NOTE 3Various forms of this equation exist for different units.7.1.2 Use Reynolds number, Re, to determine whet
36、her thesample flow is turbulent or non-turbulent in a particular sectionof the sample system.7.1.2.1 Assume turbulent flow for sections with aRe 4000.7.1.2.2 Assume non-turbulent flow for sections with aRe 2100 to Re 4000. See Figs. X1.4 andX1.5.7.2.2 Assume three purge volumes are required for adeq
37、uatesample exchange in systems with non-turbulent flow,Re 93%RID (inches) 2.0000 NA 0.1800 NA 269.12 3 Purge 97%RFlow (SLPM) 5.5000 5.5000 5.5000 0.5000 358.83 4 Purge 98%RVolume (litres) 0.6175 0.0100 0.7502 0.0200Pressure corrected purge volume 6.1620 0.0998 1.5157 0.0404Single Purge Time (seconds
38、) 67.2223 1.0887 16.5354 4.8490Average Velocity (FPS) 0.0149 NA 9.0714 NAFlow Type (w/o Transition) Non Turbulent Non Turbulent Non Turbulent Non TurbulentNon-Turb Components (Sec) 67.2223 1.1000 16.5354 4.8500 89.71Turbulent Components (Sec) 0.0000 0.0000 0.0000 0.0000 0.00FIG. X1.1 Gas Sample With
39、out Tap ProbeD7278064Lag Time CalcSS Component Seconds Flow Characteristic Seconds x PurgesLiq Process Tap 21.40 Non-Turbulent 64.20Vaporizing Reg 28.60 Non-Turbulent 85.80Vapor Transport 8.30 Turbulent 8.30Sample Cond 4.80 Non-Turbulent 14.40Total 172.7000Liquid Propane Process Tap Tap Sam Cond Vap
40、orized Propane Sample Transport Analyzer Sam SysApproximate liq density (lbs/cf) 31.6 31.600 Molecular weight of sample gas 44 44Viscosity of liquid (cP) 0.120 0.120 Temperature of sample gas, C 25 25Reynolds Number 822 1 Approximate gas density (lbs/cf) 0.227 0.227L (feet) 3.0 NA Viscosity of sampl
41、e gas (cP) 0.017 0.017ID (inches) 0.180 NA Reynolds Number 5365 1Flow (LPM) 0.042 0.042 Pressure (PSIG) 15.0 15.0Volume (litres) 0.015 0.020 L (feet) 150.0 NASingle Purge Time (seconds) 21.435 28.571 ID (inches) 0.180 NAAverage Velocity (FPS) 0.140 NA Flow (SLPM) 11.00 0.50Flow Type (w/o Transition)
42、 Non-Turbulent Non-Turbulent Volume (litres) 0.750 0.020Non-Turb Components (Sec) 21.435 28.571 Pressure corrected purge volume 1.516 0.040Turbulent Components (Sec) 0.000 0.000 Single Purge Time (seconds) 8.268 4.849Average Velocity (FPS) 18.143 NAFlow Type (w/o Transition) Turbulent Non TurbulentN
43、on-Turb Components (Sec) 0.000 4.849Turbulent Components (Sec) 8.268 0.000FIG. X1.2 Vaporizing Regulator Near TapD7278065Lag Time CalcSS Component Seconds Flow Characteristic Seconds x PurgesLiq Process Tap 0.90 Turbulent 0.90Liq Transport 45.00 Turbulent 45.00Vaporizing Reg 15.00 Non-Turbulent 45.0
44、0Sample Cond 0.10 Non-Turbulent 0.30Total 91.2000Liquid Propane Process Tap Sample Transport Analyzer Sam Sys Vaporized Propane Analyzer Sam SysApproximate liq density (lbs/cf) 31.600 31.600 31.600 Molecular weight of sample gas 44.000Viscosity of liquid (cP) 0.120 0.120 0.120 Temperature of sample
45、gas, C 25.000Reynolds Number 19570.474 19570.474 1.000 Approximate gas density (lbs/cf) 0.227L (feet) 3.000 150.000 NA Viscosity of sample gas (cP) 0.017ID (inches) 0.180 0.180 NA Reynolds Number 1.000Flow (LPM) 1.000 1.000 0.040 Pressure (PSIG) 15.000Volume (litres) 0.015 0.750 0.010 L (feet) NASin
46、gle Purge Time (seconds) 0.900 45.013 15.000 ID (inches) NAAverage Velocity (FPS) 3.332 3.332 NA Flow (SLPM) 10.500Flow Type (w/o Transition) Turbulent Turbulent Non-Turbulent Volume (litres) 0.010Non-Turb Components (Sec) 0.000 0.000 15.000 Pressure corrected purge volume 0.020Turbulent Components
47、(Sec) 0.900 45.013 0.000 Single Purge Time (seconds) 0.115Average Velocity (FPS) NAFlow Type (w/o Transition) Non TurbulentNon-Turb Components (Sec) 0.115Turbulent Components (Sec) 0.000FIG. X1.3 Vaporizing Regulator Near AnalyzerD7278066Process Tap Tap Sam Cond Sample Transport Analyzer Sam Sys Lag
48、timesMolecular weight of sample gas 30 30 30 30 secondsTemperature of sample gas, C 25 25 25 25Approximate gas density (lbs/cf) 0.7637 0.7637 0.1546 0.1546Viscosity of sample gas (cP) 0.0171 0.0171 0.0171 0.0171Reynolds Number 5155 NA 5155 NAPressure (PSIG) 132 132 15 15 11.68 1 Purge 75%RL (feet) 3
49、 NA 150 NA 16.92 2 Purge 93%RID (inches) 0.1800 NA 0.1800 NA 22.16 3 Purge 97%RFlow (SLPM) 15.5000 15.5000 15.5000 0.5000 27.39 4 Purge 98%RVolume (litres) 0.0150 0.0100 0.7502 0.0200Pressure corrected purge volume 0.1497 0.0998 1.5157 0.0404Single Purge Time (seconds) 0.5796 0.3863 5.8674 4.8490Average Velocity (FPS) 5.1757 NA 25.5649 NAFlow Type (w/o Transition) Turbulent Non Turbulent Turbulent Non TurbulentNon-Turb Components (Sec) 0.0000 0.3860 0.0000 4.8500 5.24Turbulent Components (Sec) 0.5796 0.0000 5.8674 0.0000 6.45FIG. X1.4 Gas SampleFast Respon
