1、PUBLISHED DOCUMENT PD CEN/TR 15281:2006 Guidance on Inerting for the Prevention of Explosions ICS 13.230 PD CEN/TR 15281:2006 This Published Document was published under the authority of the Standards Policy and Strategy Committee on 30 June 2006 BSI 2006 ISBN 0 580 47233 7 National foreword This Pu
2、blished Document is the official English language version of CEN/TR 15281:2006. The UK participation in its preparation 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 subcomm
3、ittee can be obtained on request to its secretary. Cross-references The British Standards which implement international 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 “
4、Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport 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 le
5、gal obligations. aid enquirers to understand the text; present to the responsible international/European committee 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. Summ
6、ary of pages This document comprises a front cover, an inside front cover, the CEN/TR title page, pages 2 to 53 and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. Date CommentsTECHNICALREPORT
7、 RAPPORTTECHNIQUE TECHNISCHERBERICHT CEN/TR15281 May2006 ICS13.230 EnglishVersion GuidanceonInertingforthePreventionofExplosions AtmosphresexplosiblesGuidedelinertagepourla prventiondesexplosions ThisTechnicalReportwasapprovedbyCENon8November2005.IthasbeendrawnupbytheTechnicalCommitteeCEN/TC305. CEN
8、membersarethenationalstandardsbodiesofAustria,Belgium,Cyprus,CzechRepublic,Denmark,Estonia,Finland,France, Germany,Greece,Hungary,Iceland,Ireland,Italy,Latvia,Lithuania,Luxembourg,Malta,Netherlands,Norway,Poland,Portugal, Romania, Slovakia,Slovenia,Spain,Sweden,SwitzerlandandUnitedKingdom. EUROPEANC
9、OMMITTEEFORSTANDARDIZATION COMITEUROPENDENORMALISATION EUROPISCHESKOMITEEFRNORMUNG ManagementCentre:ruedeStassart,36B1050Brussels 2006CEN Allrightsofexploitationinanyformandbyanymeansreserved worldwideforCENnationalMembers. Ref.No.CEN/TR15281:2006:E2 Contents Page Foreword4 1 Scope 5 2 Normative ref
10、erences 5 3 Terminology 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
11、parameters 15 6 Methods 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 Monitor
12、ing and control system . 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 pre
13、ssure-swing inerting 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 o
14、n inerting specific 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-
15、propane-nitrogen (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 c
16、oal (according to 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
17、 Figure 9 Influence 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 inerte
18、d vessel using a double 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
19、 equation 18 for various pipe diameters .51 Tables Table B.1 Typical rates of pressure rise for vacuum systems35 Table B.2 Selected values of k = C p /C vfor various inert gases.35 CEN/TR 15281:20064 Foreword This Technical Report (CEN/TR 15281:2006) has been prepared by Technical Committee CEN/TC 3
20、05 “Potentially explosive 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
21、 below a certain concentration 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 influ
22、ence the ignition and 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 atmos
23、pheres by wire mesh flame 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, exot
24、hermic reactions or a 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 documen
25、t (including any amendments) 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.
26、 prEN 14756, Determination 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-re
27、lated systems Part 1: 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).
28、IEC 61508-3, Functional 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, syste
29、m, hardware and software 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
30、 for the process industry 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 t
31、he following apply. 3.1 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 atmosphe
32、re when mixed with air 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 fo
33、r a given fuel/inert gas 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 w
34、ith anticipated upsets 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
35、 increase in temperature, 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 wit
36、hin which an explosion 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 concentratio
37、n at which the oxygen 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
38、 oxygen level from rising 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
39、-swing inerting reduction 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 admis
40、sion of inert gas 3.1.15 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
41、place 3.2 Abbreviations B bulk density of powder C 0initial oxygen concentration (fractional) C boxygen concentration in air in powder (usually 0,21) (fractional) C foxygen concentration after flow purging (fractional) C iconcentration of oxygen in inert gas C mmaximum allowable oxygen concentration
42、 C noxygen concentration after n purges C pspecific heat of inert gas at constant pressure C ststoichometric composition of the fuel in air C rrequired maximum fractional oxygen concentration in vessel C vspecific heat of inert gas at constant volume D vent diameter, inches F safety factor for flow
43、purging f void fraction h distance 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, C p /C vLOC limiting oxygen concentration M mean partical size, m MAOC maximum allowable concentration MOC
44、 Cminimum oxygen for combustion with carbon dioxide as diluent MOC Nminimum 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 P 1lower purge pressure (absolute) P 2upper purge pr
45、essure (absolute) Q purge gas flow-rate R upper/lower purge pressure ratio (absolute), i.e. P 2 /P 1S 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 V 0volume of oxygen in vessel at s
46、tart V* volume of oxygen in each bag V nvolume of oxygen in vessel after n thbag charged V sbulk volume of solids being charged V vvolume 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
47、these should be used. Where no units are shown, 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 conside
48、red carefully. Some material may react with steam, 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 over 3 bar might be used as an inert
