1、Designation: D 5503 94 (Reapproved 2003)Standard Practice forNatural Gas Sample-Handling and Conditioning Systems forPipeline Instrumentation1This standard is issued under the fixed designation D 5503; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、 case 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 practice covers sample-handling and conditioningsystems for typical pipeline moni
3、toring instrumentation (gaschromatographs, moisture analyzers, and so forth). The selec-tion of the sample-handling and conditioning system dependsupon the operating conditions and stream composition.1.2 This practice is intended for single-phase mixtures thatvary in composition. A representative sa
4、mple cannot be ob-tained from a two-phase stream.1.3 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 re
5、gulatory limitations prior to use.1.4 The values stated in SI units are to be regarded asstandard. The values stated in English units are for informationonly.2. Referenced Documents2.1 ASTM Standards:D 1142 Test Method for Water Vapor Content of GaseousFuels by Measurement of Dew-Point Temperature2D
6、 3764 Practice for Validation of Process Stream Analyz-ers32.2 Other Documents:ANSI/API 2530 (AGA Report Number 3)4AGA Report Number 85NACE Standard MR-01-7563. Terminology3.1 Definitions:3.1.1 compressed natural gasnatural gas compressed toapproximately 3600 psi.3.1.2 densitymass per unit volume of
7、 the substance beingconsidered.3.1.3 dew pointthe temperature and pressure at which thefirst droplet of liquid forms from a vapor.3.1.4 lag timetime required to transport the sample to theanalyzer.3.1.5 natural gasmixture of low molecular weight hydro-carbons obtained from petroleum-bearing regions.
8、3.1.6 sample probedevice to extract a representativesample from the pipeline.3.1.7 system turnaround timethe time required to trans-port the sample to the analyzer and to measure the desiredcomponents.4. Significance and Use4.1 A well-designed sample-handling and conditioning sys-tem is essential to
9、 the accuracy and reliability of pipelineinstruments. Approximately 70 % of the problems encounteredare associated with the sampling system.5. Selection of Sample-Handling and ConditioningSystem5.1 The sample-handling and conditioning system mustextract a representative sample from a flowing pipelin
10、e, trans-port the sample to the analyzer, condition the sample to becompatible with the analyzer, switch sample streams andcalibration gases, transport excess sample to recovery (ordisposal), and resist corrosion by the sample.5.2 The sample probe should be located in a flowingpipeline where the flo
11、w is fully developed (little turbulence)and where the composition is representative. In areas of highturbulence, the contaminates that normally flow along thebottom or the wall of the pipeline will form aerosols.5.3 The purpose of the sample probe is to extract a repre-sentative sample by obtaining
12、it near the center of the pipelinewhere changes in stream composition can be quickly detected.1This practice is under the jurisdiction of ASTM Committee D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.01 on Collection andMeasurement of Gaseous Samples.Current edition approve
13、d May 10, 2003. Published August 2003. Originallyapproved in 1994. Last previous edition approved in 1994 as D 5503 94.2Annual Book of ASTM Standards, Vol 05.06.3Annual Book of ASTM Standards, Vol 05.02.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York,
14、 NY 10036.5Available from American Gas Association, 1515 Wilson Blvd., Arlington, VA22209.6Available from National Association of Corrosion Engineers, 1440-T S. CreekDr., Houston, TX 77084.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United Sta
15、tes.5.3.1 The tip in the sample probe should be positioned in thecenter one third of the pipeline, away from the pipeline wallwhere large particles accumulate.5.3.2 The probe should be a minimum of five pipe diametersfrom any device that could produce aerosols or significantpressure drop.5.3.3 The s
16、ample probe should not be located within adefined meter tube region (see ANSI/API 2530 AGA ReportNumber 3 and AGA Report Number 8 for more information).5.3.4 The sample probe should be mounted vertically fromthe top on horizontal pipelines. The sample probe should not belocated on vertical pipelines
17、.5.4 The sampling-handling system must transport thesample to the analyzer and dispose of excess sample. Since thesampling point and the analyzer may be separated by somedistance, the time required to transport the sample to theanalyzer can contribute significantly to the system turnaroundtime.5.4.1
18、 The analyzer should be located as close to the sam-pling point as is practical to minimize the sample lag time.5.4.2 The sample-handling system should be equipped witha full open ball valve and a particular filter.5.5 The sizing of the sample transport line will be influ-enced by a number of factor
19、s:5.5.1 The sample point pressure and the location of thepressure reduction regulator.5.5.2 The acceptable lag time between the sample point andthe analyzer.5.5.3 The requirements of the analyzer, such as flow rate,pressure, and temperature for the analysis. For multistreamsystems, the sample line a
20、nd associated manifold tubing shouldbe flushed with sufficient sample to assure a representativesample of the selected stream.5.5.4 The presence of sample-conditioning elements willcontribute to the lag time and must be considered in thecalculation of the minimum sample flow rate.5.5.4.1 Each elemen
21、t could be considered as an equivalentlength of sample line and added to the length of line from thesample point to the analyzer.5.5.4.2 The purge time of each element is calculated as thetime necessary for five volumes of sample to flow through theelement.5.5.5 A vapor sample must be kept at least
22、10C above thehydrocarbon dew point temperature to prevent condensation ofthe sample. The sample line should be heat traced and insulatedwhen appropriate.5.5.5.1 For compressed natural gas (CNG), the pressuremust be reduced in two stages to avoid condensation of liquidscaused by the Joule-Thompson ef
23、fect. In a heated zone atapproximately 50C, the pressure should be dropped to ap-proximately 10 MPa (1500 psig) and then to a suitable pressurefor the analyzer. Any conditioning of the sample must becompleted in the heated zone.5.5.5.2 The sample line from the heated zone to the analyzermust be heat
24、 traced to avoid partial condensation of the sample.6. Apparatus6.1 The following are common components of a sample-handling and conditioning system (see Refs (1) and (2)7formore information).6.1.1 Ball valves, needle valves, and solenoid valves aretypically used for stream switching, sample shutoff
25、, calibrationgas introduction, or sample vent and bypass systems.6.1.2 Most pipeline samples require some filtering. Since allfilter elements eventually plug, they should be replaced on aregular maintenance schedule. There are several types of filterdesigns.6.1.2.1 In-Line FilterAll of the sample pa
26、sses through anin-line filter. The active filter elements are available in Teflonpolypropylene, copolymer, or stainless steel. (See Fig. 1.)6.1.2.2 Bypass FilterOnly a small portion of the samplepasses through a bypass filter, while a majority of the samplepasses across its surface keeping it clean.
27、 The active filterelement is either a disposable cartridge or a reusable sinteredmetal element. (See Fig. 2.)6.1.2.3 Cyclone FilterThe cyclone filter is a centrifugalcleanup device. The sample enters at high velocity tangentiallyto the wall of a cylindrical-shaped vessel with a conical-shapedbottom.
28、 The centrifugal force developed by the spinning actionof the gas as it follows the shape of the vessel forces particlesand droplets to the wall where they are removed through thevent flow. (See Fig. 3.)6.1.2.4 Coalescing FilterCoalescers, also known as mem-brane separators, are used to force finely
29、 divided liquiddroplets to combine into larger droplets so they can beseparated by gravity. The design of the coalescer body forcesthe heavier phase out the bottom and the lighter phase out thetop. The flow rates out the top and the bottom are critical forproper operation. (See Fig. 4.)(1) Since thi
30、s process removes part of the sample, theimpact on sample composition must be considered.7The boldface numbers in parentheses refer to the list of references at the end ofthis practice.FIG. 1 Cross Section of Common In-Line FiltersD 5503 94 (2003)2(2) The coalescer should be located immediately upst
31、reamfrom the analyzer.6.1.3 The combination condenser/separator is used to re-move condensable liquids from a vapor sample. The sampleenters the separator and cools as it passes through the device.The condensed liquid phase is separated by gravity andremoved from the bottom of the separator. (See Fi
32、g. 5.)6.1.3.1 Since this process removes part of the sample, theimpact on sample composition must be considered.6.1.3.2 The condenser/separator should be located immedi-ately upstream from the analyzer.6.1.4 Pressure regulators are required to reduce and regulatepressure between the sampling point a
33、nd the analyzer. Theregulator must be constructed of the proper materials to allowfor the corrosive nature of the sample.6.1.4.1 A combination sample probe and regulator withthermal fins around the probe could be used to minimize theJoule-Thompson effect.6.1.5 Pressure gages should be installed down
34、stream of thepressure regulator. Since the sensing element of these devices(Bourdon tube) consists of unswept volume, the pressure gageshould be installed either in a bypass line or after the analyzer.6.1.6 Rotameters are used to indicate the flow rate of thesample. A typical rotameter consists of a
35、 ball or float mountedin a tapered tube. The reading is proportional to fluid densityand viscosity which may vary with the composition of thefluid.6.1.6.1 The rotameter should be located downstream of theanalyzer and used as an indicator of flow and system cleanli-ness. A clean tube and a freely mov
36、ing ball is an indicator of aclean system.6.1.7 Typical natural gas sample system. (See Fig. 6.)6.1.8 Compressed natural gas sample system. (See Fig. 7.)7. Materials7.1 Many of the common sample system components areconstructed of trademarked metals such as 316 stainless steel,Hastelloy, and Monel a
37、nd compatible trademarked plasticssuch as Kel-F, Teflon, and Kynar.FIG. 2 Cross Section of Common Bypass FiltersFIG. 3 Cyclone Filter/Centrifugal FilterFIG. 4 Coalescing FilterFIG. 5 Combination Condensor/SeparatorD 5503 94 (2003)37.1.1 The sample-handling and conditioning system shouldbe constructe
38、d of material capable of resisting corrosion fromthe sample and the environment.7.1.1.1 Sample system components should be chosen care-fully to avoid corrosion or adsorption by the sample.7.1.1.2 If sour gas (gas that contains hydrogen sulfide orcarbon dioxide, or both) is suspected, NACE Standard M
39、R-01-75 should be followed.7.2 The sample-handling and conditioning system shouldcontain the sample under the most severe conditions ofpressure, temperature, and vibration that the pipeline willexperience during normal and upset conditions.8. Calculation8.1 Sample transport time, or lag time, tlag,
40、is a function ofthe sample line length and diameter, the absolute pressure inthe line, and the sample flow rate. Lag time is calculated asfollows:tlag5VLP 1 Patm!FaPatm(1)where:tlag= sample transport time, min;V = volume of sample per unit length, cm3/m;L = equivalent length of sample length, m;P =
41、sample pressure, N/m2;Patm= atmospheric pressure, N/m2; andFa= actual average flow rate of the sample, cm3/min.8.1.1 ExampleConsider a sample point located 100 ftaway from an analyzer requiring 200 cm3/min of sample.Using standard conditions and 0.19-in. inside diameter tubing,a lag time of 75 min c
42、an be calculated. By increasing thesample flow to 2200 cm3/min and splitting the excess sampleto a high-speed loop, the lag time decreases to 7.5 min. Thesample pressure should be reduced at the analyzer.8.1.2 Reducing the pressure at the sample point rather thanthe analyzer can also decrease the la
43、g time. For a pressurereduction from 400 to 40 psig, the sample flow should be 2000cm3/min to compensate for the increase in sample volume.(See Fig. 8.)8.2 The equivalent length of sample line is calculated by thefollowing expression (see Ref (3) for more information):L 5 Ld1 Leq(2)where:L = equival
44、ent length of sample line, m;Ld= length of sample line, m; andLeq= equivalent length of valves and fittings, m.8.3 Calculation of sample line size is a trial and errorprocess:8.3.1 Select a sample line size that meets the flow rate needsof the analyzer.8.3.2 Calculate the Reynolds number, the ratio
45、of inertial-to-viscous forces by:Re5rdh(3)where:Re= Reynolds number;r = fluid density, Kg/m3; = fluid velocity, m/s;d = diameter of the pipe, m; andh = viscosity of the fluid, Ns/m2.8.3.3 Calculate the pressure drop using Darcys equation(see (3) for more information):dp 5frLu22 dg(4)where:dp = press
46、ure drop in the line, N/m2;f = frictional factor from Moodys tables;r = fluid density, Kg/m3;L = equivalent length of sample line, m;u = velocity of the fluid, m/s;d = diameter of the line, m; andg = acceleration of gravity, 9.81 m/s2.8.3.4 The available pressure drop should be compared withthe calc
47、ulated pressure drop. If the calculated pressure drop istoo great, then select a larger sample line and repeat lag time,equivalent length, and pressure drop calculations.8.3.5 The majority of sample transport problems are solvedby application of prior experience and by use of tables relatingFIG. 6 T
48、ypical Natural Gas Sampling SystemFIG. 7 Pressure Reduction System for Compressed Natural Gas(CNG)D 5503 94 (2003)4velocity to pressure drop for different sample line diameters(see Refs (4) and (5) for more information).8.4 The dew point calculation relies on the use of distribu-tion coefficients, K
49、i, which are defined as the ratio of the molefraction of the component in the vapor phase, Yi, to the molefraction in the liquid phase, xi.Ki5Yixi(5)8.4.1 Whenever possible, dew point should be calculatedusing a physical properties software package. Dew point can becalculated without the aid of a computer by the followingprocedure:8.4.1.1 Assume a dew point temperature. Using a De-Priester chart, determine the K at the highest pressure presentin the sample line and the assumed dew point for eachcomponent in the sample (see Ref (6) for more information).8.4.1.2
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