CEN TR 15281-2006 Guidance on Inerting for the Prevention of Explosions《防爆用惰化指南》.pdf

1、PUBLISHED DOCUMENTPD CEN/TR 15281:2006Guidance on Inerting for the Prevention of ExplosionsICS 13.230g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g5

2、8PD CEN/TR 15281:2006This Published Document was published under the authority of the Standards Policy and Strategy Committee on 30 June 2006 BSI 2006ISBN 0 580 47233 7National forewordThis Published Document is the official English language version of CEN/TR 15281:2006.The UK participation in its p

3、reparation was entrusted to Technical Committee FSH/23, Fire precautions in industrial and chemical plant, which has the responsibility to: A list of organizations represented on this subcommittee can be obtained on request to its secretary.Cross-referencesThe British Standards which implement inter

4、national or European publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online.This publication does not purpo

5、rt to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a Published Document does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committ

6、ee any enquiries on the interpretation, or proposals for change, and keep UK interests informed; monitor related international and European developments and promulgate them in the UK.Summary of pagesThis document comprises a front cover, an inside front cover, the CEN/TR title page, pages 2 to 53 an

7、d a back cover.The BSI copyright notice displayed in this document indicates when the document was last issued.Amendments issued since publicationAmd. No. Date CommentsTECHNICAL REPORTRAPPORT TECHNIQUETECHNISCHER BERICHTCEN/TR 15281May 2006ICS 13.230English VersionGuidance on Inerting for the Preven

8、tion of ExplosionsAtmosphres explosibles - Guide de linertage pour laprvention des explosionsThis Technical Report was approved by CEN on 8 November 2005. It has been drawn up by the Technical Committee CEN/TC 305.CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Repub

9、lic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMIT EUROPEN DE NORM

10、ALISATIONEUROPISCHES KOMITEE FR NORMUNGManagement Centre: rue de Stassart, 36 B-1050 Brussels 2006 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. CEN/TR 15281:2006: E2 Contents Page Foreword4 1 Scope 5 2 Normative references 5 3 Termin

11、ology and abbreviations .6 3.1 Terminology .6 3.2 Abbreviations.7 4 Inert gases8 5 Influence of the oxygen concentration on explosive atmospheres .9 5.1 General9 5.2 Gas and vapour explosions. 10 5.3 Dust explosions 13 5.4 Hybrid mixtures. 15 5.5 Mists. 15 5.6 Influence of process parameters 15 6 Me

12、thods of Inerting. 18 6.1 General. 18 6.2 Pressure swing inerting . 19 6.3 Vacuum-swing inerting 19 6.4 Flow-through inerting. 20 6.5 Displacement inerting 21 6.6 Maintaining inert conditions 21 7 Inerting systems . 23 7.1 General introduction 23 7.2 Inert gas supply 23 7.3 Monitoring and control sy

13、stem . 24 7.4 Methods . 25 8 Reliability. 27 8.1 Demands for safety critical equipment 27 8.2 Inerting systems . 28 9 Personnel and environmental protection. 28 10 Information for use . 29 Annex A (informative) Oxygen monitoring technology 30 Annex B (informative) Equations for pressure-swing inerti

14、ng 33 Annex C (informative) Calculations for flow-through inerting.36 Annex D (informative) Addition of solids to an inerted vessel using a double valve arrangement 38 Annex E (informative) Addition of solids down a charge-chute to an open vessel 41 Annex F (informative) Examples on inerting specifi

15、c items of process equipment 45 Annex G (informative) Prevention of diffusion of air down vent pipes. 50 Bibliography. 52 CEN/TR 15281:20063 Figures Figure 1 Influence of inert gas on explosion limits of methane (according to 32, Figure 28).10 Figure 2 Flammability diagram for air-propane-nitrogen (

16、according to 8)11 Figure 3 Triangular flammability diagram for fuel-oxygen-nitrogen 12 Figure 4 Influence of oxygen concentration on the explosion pressure of brown coal (according to 7).13 Figure 5 Influence of oxygen concentration on the rate of explosion pressure rise of brown coal (according to

17、7).14 Figure 6 Influence of oxygen concentration on maximum explosion pressure for brown coal (according to 29).14 Figure 7 Effect of temperature on ignition sensitivity of dusts (according to 7)16 Figure 8 Temperature influence on limiting oxygen concentration (according to 29).17 Figure 9 Influenc

18、e of pressure on inerting brown coal (according to 29).17 Figure 10 Pressure influence on amount of inert gas required for inerting propane (according to 32, Figure 40) .18 Figure 11 Specification of safe limits for control .25 Figure D.1 Example of addition of solids for an inerted vessel using a d

19、ouble value arrangement 38 Figure F.1 Agitated pressure filter/dryer .45 Figure F.2 Top discharge centrifuge46 Figure F.3 Inverting filter horizontal basket centrifuge .47 Figure F.4 Pinned disc grinding mill48 Figure F.5 Horizontal paddle dryer 49 Figure G.1 Value of exponent N in equation 18 for v

20、arious pipe diameters .51 Tables Table B.1 Typical rates of pressure rise for vacuum systems35 Table B.2 Selected values of k = Cp/Cvfor various inert gases.35 CEN/TR 15281:20064 Foreword This Technical Report (CEN/TR 15281:2006) has been prepared by Technical Committee CEN/TC 305 “Potentially explo

21、sive atmospheres Explosion prevention and protection”, the secretariat of which is held by DIN. CEN/TR 15281:20065 1 Scope Inerting is a measure to prevent explosions. By feeding inert gas into a system which is to be protected against an explosion, the oxygen content is reduced below a certain conc

22、entration until no explosion can occur. The addition of sufficient inert gas to make any mixture non-flammable when mixed with air (absolute inerting) is only required in rare occasions. The requirements for absolute inerting will be discussed. Inerting may also be used to influence the ignition and

23、 explosion characteristics of an explosive atmosphere. The guidance given on inerting is also applicable to prevent an explosion in case of a fire. The following cases are not covered by the guideline: admixture of an inert dust to a combustible dust; inerting of flammable atmospheres by wire mesh f

24、lame traps in open spaces of vessels and tanks; fire fighting; avoiding an explosive atmosphere by exceeding the upper explosion limit of a flammable substance. Inerting which is sufficient to prevent an explosion is not a protective measure to prevent fires, self-ignition, exothermic reactions or a

25、 deflagration of dust layers and deposits. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amen

26、dments) applies. EN 1127-1:1997, Explosive atmospheres Explosion prevention and protection Part 1: Basic concepts and methodology. EN 14034-4, Determination of explosion characteristics of dust clouds Part 4: Determination of the limiting oxygen concentration LOC of dust clouds. prEN 14756, Determin

27、ation of the limiting oxygen concentration (LOC) for gases and vapours. EN 50104, Electrical apparatus for the detection and measurement of oxygen Performance requirements and test methods. IEC 61508-1, Functional safety of electrical/electronic/programmable electronic safety-related systems Part 1:

28、 General requirements (IEC 61508-1:1998 + Corrigendum 1999) IEC 61508-2, Functional safety of electrical/electronic/programmable electronic safety-related systems Part 2: Requirements for electrical/electronic/programmable electronic safety- related systems (IEC 61508-2:2000). IEC 61508-3, Functiona

29、l safety of electrical/electronic/programmable electronic safety-related systems Part 3: Software requirements (IEC 61508-3:1998 + Corrigendum 1999). IEC 61511-1, Functional safety Safety instrumented systems for the process industry sector Part 1: Framework, definitions, system, hardware and softwa

30、re requirements (IEC 61511-1:2003 + corrigendum 2004). IEC 61511-2, Functional safety Safety instrumented systems for the process industry sector Part 2: Guidelines for the application of IEC 61511-1 (IEC 61511-2:2003). IEC 61511-3, Functional safety Safety instrumented systems for the process indus

31、try sector Part 3: Guidance for the determination of the required safety integrity levels (IEC 61511-3:2003 + corrigendum 2004). CEN/TR 15281:20066 3 Terminology and abbreviations For the purposes of this Technical Report, the terms and definitions given in EN 1127-1:1997 and the following apply. 3.

32、1 Terminology 3.1.1 inerting replacement of atmospheric oxygen in a system by a non-reactive, non-flammable gas, to make the atmosphere within the system unable to propagate flame 3.1.2 absolute inerting absolutely inerted mixture is one which does not form a flammable atmosphere when mixed with air

33、 in any proportion because the ratio of inert to fuel is sufficiently high 3.1.3 Limiting Oxygen Concentration (LOC) experimentally determined oxygen concentration which will not allow an explosion in a fuel/air/inert gas mixture NOTE It is a characteristic which is specific for a given fuel/inert g

34、as combination. The determination should be in accordance with pr EN 14756 for gases and vapours and EN 14034-4 for dusts respectively. 3.1.4 Maximum Allowable Oxygen Concentration (MAOC) concentration which should not be exceeded in the system which has to be protected, even with anticipated upsets

35、 or operating errors NOTE It is set using a margin below the limiting oxygen concentration. This margin should consider variations in process conditions which might deviate from the experimental conditions. 3.1.5 explosion abrupt oxidation or decomposition reaction producing an increase in temperatu

36、re, pressure, or in both simultaneously EN 1127-1:1997, 3.6 3.1.6 Lower Explosion Limit (LEL) lower limit of the explosion range 3.1.7 Upper Explosion Limit (UEL) upper limit of the explosion range 3.1.8 explosion range range of concentration of a flammable substance in air within which an explosion

37、 can occur 3.1.9 Trip Point (TP) oxygen concentration at which the oxygen monitoring instrumentation initiates a shut down procedure to make the equipment safe and prevent the atmosphere inside from becoming flammable CEN/TR 15281:20067 3.1.10 Set Point (SP) oxygen concentration at which the oxygen

38、monitoring instrumentation controls the flow, pressure or quantity of inert gas NOTE A suitable allowance for variation of flows, temperatures and pressure fluctuations should be made to ensure that when the oxygen level reaches the set point, the control system can prevent the oxygen level from ris

39、ing to the trip point under normal operation and foreseeable disturbances. 3.1.11 safety margin difference between the trip point and the maximum allowable oxygen concentration 3.1.12 inert gas gas that neither reacts with oxygen nor with the gas, vapour or dust 3.1.13 pressure-swing inerting reduct

40、ion of oxidant concentration in a closed system by pressurising with inert gas and venting back to atmospheric pressure 3.1.14 vacuum-swing inerting reduction of oxidant concentration by the evacuation of a closed system, and the restoration to atmospheric pressure by the admission of inert gas 3.1.

41、15 flow-through inerting replacement of an oxidant by a continuous flow of inert gas into a system which is vented to atmosphere 3.1.16 displacement inerting displacement of an oxidant by an inert gas of a significantly different density, where significant mixing does not take place 3.2 Abbreviation

42、s B bulk density of powder C0initial oxygen concentration (fractional) Cboxygen concentration in air in powder (usually 0,21) (fractional) Cfoxygen concentration after flow purging (fractional) Ciconcentration of oxygen in inert gas Cmmaximum allowable oxygen concentration Cnoxygen concentration aft

43、er n purges Cpspecific heat of inert gas at constant pressure Cststoichometric composition of the fuel in air Crrequired maximum fractional oxygen concentration in vessel Cvspecific heat of inert gas at constant volume D vent diameter, inches F safety factor for flow purging f void fraction h distan

44、ce from end of vent, ft J rate of pressure rise in a vacuum system, mbar min-1CEN/TR 15281:20068 K weight of 1 bag of powder k ratio of specific heats of gases, Cp/CvLOC limiting oxygen concentration M mean partical size, m MAOC maximum allowable concentration MOCCminimum oxygen for combustion with

45、carbon dioxide as diluent MOCNminimum oxygen for combustion with nitrogen as diluent m molecular weight of purge gas N exponent in Husas 1964 equation dependent on vent diameter n number of cycles or additions P1lower purge pressure (absolute) P2upper purge pressure (absolute) Q purge gas flow-rate

46、R upper/lower purge pressure ratio (absolute), i.e. P2/P1S void fraction of bulk powder SP set point TP trip point t time t* time interval between start of charging of successive bags U vessel ullage volume V system volume V0volume of oxygen in vessel at start V* volume of oxygen in each bag Vnvolum

47、e of oxygen in vessel after nthbag charged Vsbulk volume of solids being charged Vvvolume of double valve arrangement v purge gas superficial velocity, ft/sec v/v volume/volume x required oxygen content % v/v NOTE Where units have specific units, then these should be used. Where no units are shown,

48、the variables are either dimensionless or any consistent set of units may be applied to the equation. 4 Inert gases Inerting may be achieved by using a non-flammable gas which will neither react with a given fuel nor with oxygen. This has to be considered carefully. Some material may react with stea

49、m, carbon dioxide or even nitrogen under some conditions. For example, molten lithium metal reacts with nitrogen. The most commonly used inert gases are: a) Nitrogen Nitrogen may either be received from a commercial supplier with an appropriate purity or may be generated from ambient air at technical quality by on-site facilities. b) Carbon dioxide Carbon dioxide may be received from a commercial supplier at an appropriate purity. CEN/TR 15281:20069 c) Steam Steam with pressures ove