ASTM E2019-2003(2007) Standard Test Method for Minimum Ignition Energy of a Dust Cloud in Air《空气中粉尘最小点火能的标准试验方法》.pdf

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1、Designation: E 2019 03 (Reapproved 2007)Standard Test Method forMinimum Ignition Energy of a Dust Cloud in Air1This standard is issued under the fixed designation E 2019; 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method determines the minimum ignitionenergy of a dust cloud in air by a high voltage spark.1.2 The Minimum

3、 Ignition Energy (MIE) of a dust-cloud isprimarily used to assess the likelihood of ignition duringprocessing and handling. The likelihood of ignition is used toevaluate the need for precautions such as explosion preventionsystems. The MIE is determined as the electrical energy storedin a capacitor

4、which, when released as a high voltage spark, isjust sufficient to ignite the dust cloud at its most easily ignitableconcentration in air. The laboratory test method described inthis standard does not optimize all test variables that affectMIE. Smaller MIE values might be determined by increasingthe

5、 number of repetitions or optimizing the spark dischargecircuit for each dust tested.1.3 In this test method, the test equipment is calibrated usinga series of reference dusts whose MIE values lie withinestablished limits. Once the test equipment is calibrated, therelative ignition sensitivity of ot

6、her dusts can be found bycomparing their MIE values with those of the reference dustsor with dusts whose ignition sensitivities are known fromexperience. X1.1 of this test method includes guidance on thesignificance of minimum ignition energy with respect toelectrostatic discharges.1.4 This standard

7、 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 use. Specific precau-tionary stateme

8、nts are given in 82. Referenced Documents2.1 ASTM Standards:2D 3173 Test Method for Moisture in theAnalysis Sample ofCoal and CokeD 3175 Test Method for Volatile Matter in the AnalysisSample of Coal and CokeE 582 Test Method for Minimum Ignition Energy andQuenching Distance in Gaseous MixturesE 789

9、Test Method for Dust Explosions in a 1.2-LitreClosed Cylindrical Vessel3E 1226 Test Method for Pressure and Rate of Pressure Risefor Combustible DustsE 1445 Terminology Relating to Hazard Potential ofChemicals2.2 IEC Standards:41241-2-3, 1994 ElectricalApparatus for Use in the Presenceof Combustible

10、 Dusts, Part 2: Test Method, Section 3:Method for Determining Minimum Ignition Energy ofDust-Air Mixtures3. Terminology3.1 Definitions of Terms Specific to This Standard: (See alsoTerminology E 1445):3.1.1 spark discharge, ntransient discrete electric dis-charge, which takes place between two conduc

11、tors, which areat different potentials. The discharge bridges the gap betweenthe conductors in the form of a single ionization channel.3.1.2 minimum ignition energy (MIE), nelectrical energydischarged from a capacitor, which is just sufficient to effectignition of the most easily ignitable concentra

12、tion of fuel in airunder the specific test conditions.3.1.3 ignition delay time, nthe time between the onset ofdispersion of the dust sample into a cloud and the activation ofthe ignition source.4. Summary of Test Method4.1 A dust cloud is formed in a laboratory chamber by anintroduction of the mate

13、rial with air.4.2 Ignition trials of this dust-air mixture are then at-tempted, after a specific ignition delay time, by a sparkdischarge from a charged capacitor.1This test method is under the jurisdiction of ASTM Committee E27 on HazardPotential of Chemicals and is the direct responsibility of Sub

14、committee E27.05 onExplosibility and Ignitability of Dust Clouds.Current edition approved Oct. 1, 2007. Published January 2008. Originallyapproved in 1999. Last previous edition approved in 2003 as E 201903.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer

15、 Service at serviceastm.org. For Annual Book of ASTMStandardsvolume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.4Available from IEC Case Postale 56, CH-1211 Geneva, 20, Switzerland.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Con

16、shohocken, PA 19428-2959, United States.4.3 The stored energy discharged into the spark and theoccurrence or nonoccurrence of flame are recorded.4.4 The minimum ignition energy is sought by varying thedust concentration, the spark discharge energy and optionallythe ignition delay time.4.5 Ignition i

17、s determined by visual observation of a flamepropagation away from the spark gap.5. Significance and Use5.1 This test method provides a procedure for performinglaboratory tests to determine the minimum ignition energy of adust cloud.NOTE 1For gases and vapors, see Test Method E 582.5.2 The data deve

18、loped by this test method may be used toassess the spark ignitibility of a dust cloud. Additional guid-ance on the significance of minimum ignition energy is inX1.1.5.3 The values obtained are specific to the sample tested, themethod used and the test equipment used. The values are not tobe consider

19、ed intrinsic material constants.5.4 The MIE of a dust as determined using this procedurecan be compared with the MIEs of reference dusts (using thesame procedure) to obtain the relative sensitivity of the dust tospark ignition. An understanding of the relative sensitivity tospark ignition can be use

20、d to minimize the probability ofexplosions due to spark ignition.6. Interferences6.1 Dust residue from previous tests may affect results. Thechamber must be cleaned before a new product is tested.6.2 Problems may arise due to electrical shortcircuits whenusing conductive materials.7. Apparatus7.1 Te

21、st ApparatusAlthough a number of different testapparatuses are used in practice, they all have the followingcomponents in common: A test chamber, spark electrodes, anda spark generation circuit. Various configurations of the sparkgeneration circuits are provided in the Appendix X1. Thepurpose of the

22、 test chamber is to produce a uniform, nontur-bulent and known density dust cloud in air at the time ofignition. The clear plastic or glass Hartmann tube, typically 0.5or 1.2 L and the 20-L sphere apparatus have been foundsuitable for this test method. These vessels are described inRefs (1-3, 10)5an

23、d Test Methods E 789 and E 1226. These andother suitable chambers can be used provided that the calibra-tion requirements in 10.1 are met.7.2 Spark Generation CircuitThe Appendix describessome suitable forms of circuits, all of which shall have thefollowing characteristics:7.2.1 Electrode Material,

24、such as tungsten, stainless steel,brass, or graphite.7.2.2 Electrode Diameter and Shape,26 1 mm. Forcircuits in which high voltage is maintained across the sparkgap prior to spark breakdown, a significant fraction of theenergy stored in the capacitor may drain away as coronadischarges from sharp ele

25、ctrode tips prior to the spark dis-charge. This is increasingly important at low stored energies.Electrodes with rounded tips can be used to reduce coronaeffects that can occur with pointed electrodes, which may giveincorrect values of spark energy. If pointed electrodes are used,corona effects shou

26、ld be considered carefully.7.2.3 Electrode Gapthe optimum spacing is typically ofthe order of 6 mm. For certain materials at low ignition energyvalues, however, the gap spacing may need to be reduced inorder to initiate the spark. Under these circumstances, the sparkgap can be reduced and the tests

27、carried out with the largest gappossible, but the gap should not be less than 2 mm.NOTE 2The capacitance of the electrodes and associated high voltagecables between the storage capacitor and the electrodes should be as lowas possible. It should be noted that cable capacitance may be of the order40pF

28、/m depending on its construction, which represents significantadditional stored energy at low storage capacitance and high voltage. Thestray capacitance of these components must be measured to determine ifit needs to be taken into account when calculating the stored circuitenergy.NOTE 3Insulation re

29、sistance between electrodes should be suffi-ciently high to prevent leakage currents prior to discharge. Typically, aminimum resistance between the electrodes of 1012V is required for aminimum ignition energy of 1 mJ, and 1010V for a minimum ignitionenergy of 100 mJ. Insulation resistance may decrea

30、se over time due tocontamination of the surface with carbon and other materials. Theresistance may be directly measured across the electrodes.Alternatively, adecrease may be inferred by the inability to hold constant voltage on theisolated storage capacitor for the timescale of a test.NOTE 4Almost a

31、ll electrostatic discharges in plant installations arecapacitive with negligible inductance. It has been found that for equalstored energies many dusts can be ignited more easily when a resistor oran inductance is placed in the discharge circuit to create longer durationsparks. Ideally, the MIE shou

32、ld correspond to circuits whose dischargeduration has been optimized for the dust in question using, for example,an inductance.8. Safety Precautions8.1 Prior to handling a test material, the toxicity of thesample and its combustion products must be considered. Thisinformation is generally obtained f

33、rom the manufacturer orsupplier. Appropriate safety precautions must be taken if thematerial has toxic or irritating characteristics. MIE-tests shouldbe conducted in a ventilated hood or other area havingadequate ventilation.8.2 Before initiating a test, check and secure the apparatus,fittings and g

34、askets to prevent leakage.8.3 All enclosures containing electrical equipment must beconnected to a common ground.8.4 The test method should not be used with recognizedexplosives, such as gunpowder or dynamite; pyrophoric sub-stances; or, substances or mixtures of substances, which mayunder some circ

35、umstances behave in a similar manner withoutconsidering the special hazards. Where any doubt exists aboutthe existence of a hazard due to explosive properties, expertadvice should be sought.8.5 Because the apparatus consists of a circuit with highvoltage components, adequate safeguards must be emplo

36、yed toprevent electrical shock to personnel.5The boldface numbers in parentheses refer to the list of references at the end ofthis standard.E 2019 03 (2007)28.6 The operator should work from a protected location,such as from outside a closed fume hood, in case of vessel orelectrical failure.8.7 Care

37、 should be taken not to clean acrylic Hartmanntubes with incompatible solvents, which can lead to embrittle-ment and cracking.9. Sampling9.1 It is not practical to specify a single method of samplingdust for test purposes because the character of the material andits available form affect selection o

38、f the sampling procedure.9.2 Minimum ignition energy decreases with decreasingparticle size (see Fig. 1). Although tests may be run on an“as-received” sample, explosible dust clouds often consistlargely of sub-200 mesh dust, which accumulates in suspensionwhen coarser bulk powder is handled. Therefo

39、re, it is recom-mended that the test sample be at least 95 % minus 200 mesh(75 m). In general, the sample tested should be at least as fineas the dust at the location being considered, which, in somecases, may require testing of sub-325 mesh or even finer dust.9.3 To achieve this particle fineness (

40、$ 95 % minus 200mesh) the sample may be ground or pulverized, or it may besieved.NOTE 5The operator should consider the thermal stability of the dustduring grinding or pulverizing.NOTE 6In some cases, it may be desirable to conduct dust deflagra-tion tests on material as sampled from a process becau

41、se process duststreams may contain a wide range of particle sizes or have a well-definedspecific moisture content. When a material is tested in the as-receivedstate, it should be recognized that the test results may not represent themost severe ignition hazards possible. Any process change resulting

42、 in ahigher fraction of fines or drier product may result in a lower MIE for theproduct.NOTE 7The possible reduction of the particle size due to attrition bythe dust dispersion system of the test apparatus should be considered.NOTE 8In sieving the material, the operator must verify that there isno s

43、elective separation of components in a dust that is not a puresubstance. Materials consisting of a mixture of chemicals may beseparated selectively on sieves and certain fibrous materials, which maynot pass through a relatively coarse screen may produce dust deflagra-tions.9.4 Minimum ignition energ

44、y for some dusts increases withincreased moisture content (see Fig. 2). Dusts should be testedeither in the dry state or approximating the moisture contentunder the handling conditions of interest. “Dry” samplesshould be transported to the test laboratory in sealed containersunder dry air or nitroge

45、n, and then stored in a desiccator.Desiccants, such as phosphorus pentoxide, may be moreeffective than silica gel in removing residual moisture.NOTE 9There is no single method for determining the moisturecontent or for drying a sample. Sample drying equally is complex due tothe presence of volatiles

46、, lack of or varying porosity (see Test MethodsD 3173 and D 3175), and sensitivity of the sample to heat; therefore, eachmust be dried in a manner that will not modify or destroy the integrity ofthe sample. Hygroscopic materials must be desiccated.10. Calibration and Standardization10.1 Calibration

47、tests should be carried out on at least threedifferent reference dusts. The results shall be within thefollowing ranges (measured without inductance):Irganox 10105: MIE=1to6mJAnthraquinone: MIE=1to11mJLycopodium6: MIE=10to30mJPittsburgh coal7: MIE=30to140mJ10.2 In addition to the initial calibration

48、 and standardizationprocedure, at least one standard dust should be retestedperiodically to verify that the dispersion and turbulence char-acteristics of the chamber have not changed.11. Procedure11.1 Test Description:6Irganox 1010: Tetrakis-Methylene(3,5-di-(tert)-butyl-4-hydroxyhydrocinnamate)meth

49、ane, available source: Ciba Specialty Chemicals,7Lycopodium Clavatum: Lycopodium is a natural plant spore having a narrowsize distribution with 100 % minus 200 mesh and a mass median diameter of ;28m.8The Pittsburgh coal has ; 80 % minus 200 mesh, a mass median diameter of; 45 m, and 36 % volatility.FIG. 1 Correlation of Median Particle Size and MIE (5)FIG. 2 Influence of the Humidity (Water Content) of CombustibleDusts (5)E 2019 03 (2007)311.1.1 Inspect equipment to be sure it is cleaned thoroughlyand in good operational condition.11.1.2 The combustible dust to