1、Designation: E1248 90 (Reapproved 2017)Standard Practice forShredder Explosion Protection1This standard is issued under the fixed designation E1248; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A numbe
2、r in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers general recommended design fea-tures and operating practices for shredder explosion protectionin resource recovery plan
3、ts and other refuse processing facili-ties.1.2 Hammermills and other types of size reduction equip-ment (collectively termed shredders) are employed at manyfacilities that mechanically process solid wastes for resourcerecovery. Flammable or explosive materials (for example,gases, vapors, powders, an
4、d commercial and military explo-sives) may be present in the as-received waste stream. There ispotential for these materials to be released, dispersed, andignited within or near a shredder. Therefore, explosion preven-tion and damage amelioration provisions are required.1.3 This standard does not pu
5、rport 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, health and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standa
6、rd was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Ref
7、erenced Documents2.1 National Fire Protection Association Standards:National Electrical CodeNFPA 13 Sprinkler SystemsNFPA 68 Guide for Explosion VentingNFPA 69 Explosion Prevention SystemsNFPA 497A Classification of Class I Hazardous (Classified)Locations for Electrical Installations in Chemical Pro
8、cessAreas3. Terminology3.1 Definitions:3.1.1 deflagrationan explosion in which the flame orreaction front propagates at a speed well below the speed ofsound in the unburned medium, such that the pressure isvirtually uniform throughout the enclosure (shredder) at anytime during the explosion.3.1.2 de
9、tonationan explosion in which the flame or reac-tion front propagates at a supersonic speed into the unburnedmedium, such that pressure increases occur in the form ofshock waves.3.1.3 explosiona rapid release of energy (usually bymeans of combustion) with a corresponding pressure buildupcapable of d
10、amaging equipment and building structures.3.1.4 explosion ventingthe provision of an opening(s) inthe shredder enclosure and contiguous enclosed areas to allowgases to escape during a deflagration and thus prevent pres-sures from reaching the damage threshold.3.1.5 explosion suppressionthe technique
11、 of detecting andextinguishing incipient explosions in the shredder enclosureand contiguous enclosed areas before pressures exceed thedamage threshold.3.1.6 inertingthe technique by which a combustible mix-ture is rendered nonflammable by addition of a gas incapable ofsupporting combustion.3.1.7 shr
12、eddera size-reduction machine that tears orgrinds materials to a smaller and more uniform particle size.4. Significance and Use4.1 Shredder explosions have occurred in most refuse pro-cessing plants with shredding facilities. Lessons learned inthese incidents have been incorporated into this practic
13、e alongwith results of relevant test programs and general industrialexplosion protection recommended practices. Recommenda-tions in this practice cover explosion protection aspects of thedesign and operation of shredding facilities and equipmentused therein.4.2 This practice is not intended to be a
14、substitute for anoperating manual or a detailed set of design specifications.Rather, it represents general principles and guidelines to beaddressed in detail in generating the operating manual anddesign specifications.1This practice is under the jurisdiction of ASTM Committee D34 on WasteManagement
15、and is the direct responsibility of Subcommittee D34.03 on Treatment,Recovery and Reuse.Current edition approved Sept. 1, 2017. Published September 2017. Originallyapproved in 1990. Last previous edition approved in 2009 as E1248 90 (2009).DOI: 10.1520/E1248-90R17.Copyright ASTM International, 100 B
16、arr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Reco
17、mmendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.15. Design Practices5.1 Design Rationale:5.1.1 Each of the following design features is better suitedfor some types of combustible/explosive materials and shred-ders than for others. The selection of a par
18、ticular combinationof explosion prevention features or damage control features, orboth, should be made with an understanding of the types ofrefuse entering the shredder, shredder operating conditions, theinherent strength of the shredder and surrounding structures,and the operating controls for scre
19、ening input materials andrestricting personnel access during shredding operations.5.1.2 Several of the following explosion protection designpractices are effective for deflagrations but not for detonations.Deflagrations usually result from accumulations of flammablegas-air, vapor-air, or powder (dus
20、t) air mixtures in or aroundthe shredder. However, commercial explosives and militaryordnance usually generate detonations. A few flammable gases(for example, acetylene and hydrogen) are also prone todetonate when dispersed in highly turbulent, strong ignitionsource environments such as exist inside
21、 a shredder. Becausemany explosion protection design practices are not applicableto detonations, rigorous visual detection and removal ofdetonable material before it enters the shredder is particularlyimportant (6.1).5.1.3 In view of the difficulties in preventing and controllingall types of shredde
22、r explosions, it is important to isolate theshredder and surrounding enclosure from vulnerable equip-ment and occupied areas in the plant. This is best achieved bylocating the shredder outdoors or, if indoors, in a locationsuitable for explosion venting directly outside. Locations in ornear the cent
23、er of a processing building are not desirable. If theshredder is situated in an isolated, explosion-resistant structure,the structure should be designed to withstand the explosionpressures specified in NFPA 68.5.1.4 The shredder and all contiguous enclosures should beequipped with an explosion prote
24、ction system consisting of oneor more of the following: inerting system (5.2); explosion vents(5.3); explosion suppression system (5.4). Water spray systems(5.5), combustible gas detectors (5.6), and industrial fireprotection systems (5.7) should also be installed for additionalprotection. Adjacent
25、structures and personnel should be pro-tected (5.8).5.2 Inerting Systems:5.2.1 An inerting system is intended to prevent combustionexplosions within a shredder (and contiguous enclosures) bymaintaining oxygen concentrations below the level required tosupport combustion.5.2.2 The following factors mu
26、st be accounted for in de-signing a shredder inerting system: inert gas source anddistribution; operating controls and associated instrumentation;leakage of inert gas from and entry of air into enclosures;maintenance and inspection constraints in an oxygen deficientatmosphere during normal operation
27、s; effect of inert gas onshredder materials and waste throughput; and contingencyplans for inert gas source supply interruption.5.2.3 Flue gas from an on-site furnace or boiler can be asuitable inert gas, providing there is a reliable means to preventflame propagation into the shredding system and p
28、roviding fluegas conditioning is installed to maintain suitable temperature(to prevent steam condensation or spontaneous ignition) andflue gas composition (including dew point, oxygen, carbonmonoxide, soot, and contaminant concentrations).5.2.4 Steam from an on-site boiler can be a suitable inert ga
29、sproviding the temperatures of the shredder and contiguousenclosures are sufficiently high (at least 180 F (82 C) toprevent steam condensation and the associated increase inoxygen and flammable gas concentrations.5.2.5 Oxygen concentrations in the shredder and all con-tiguous enclosures should be no
30、 higher than 10 % by volume,unless test data for the particular inert gas employed and thevariety of combustibles expected in the shredder demonstratethat a higher oxygen concentration can be tolerated withoutgenerating a flammable mixture. Test data for maximumoxygen concentrations for nitrogen and
31、 carbon dioxide inertingare as listed in Appendix C of NFPA 69.5.2.6 Reliable oxygen concentration monitors should beinstalled, calibrated, and maintained to verify that the maxi-mum oxygen concentration is not being exceeded in theshredder and contiguous enclosures. This will require multiplemonito
32、rs and sampling points, depending on the extent anduniformity of flow in the enclosed volume. Provision forcleaning and clearing sample lines, as recommended in 5.4.5,are needed.5.2.7 The inert gas distribution system should be designedin accordance with the provisions of Chapter 2 of NFPA 69.5.3 Ex
33、plosion Venting:5.3.1 Explosion venting is intended to limit structural dam-age incurred during deflagrations by allowing unburned gasand combustion products to be discharged from the shredder orcontiguous enclosures, or both, before combustion and theassociated potentially destructive pressure rise
34、 is completed.The effectiveness of explosion venting for a particular explo-sion depends on the rate of combustion versus the rate ofdischarge of gases through the explosion vents. The rate ofcombustion in the shredder or adjacent enclosure depends uponthe composition of the combustible gas-air, vap
35、or-air, ordust-air mixture, the size of the shredder/enclosure, and theturbulence level as determined by air flow rates and hammer tipspeed.5.3.2 In general, explosion venting is most effective withlarge vent areas, low vent deployment pressures, low ventpanel weight, and vent locations near the exp
36、ected ignitionsource (which is often hammer impact sparks within theshredder). The following quantitative guidelines for thesefactors are intended to protect against near worst-case flam-mable gas-air mixtures occupying the entire shredder internalvolume.5.3.3 Explosion vent areas should be sufficie
37、ntly large tomaintain explosion pressures under the damage threshold valuefor the particular shredder installation. Previously publishedguidelines relating peak pressure to vent area are not directlyapplicable to municipal solid waste (MSW) shredders becauseshredder hammer velocities can increase th
38、e combustion ratewell above that considered in establishing previous guidelines.E1248 90 (2017)2The following recommended relationship is based on propane-air explosion tests conducted in a full-scale large shreddermock-up, including rotating hammers (1).25.3.3.1 The vent area, Av, required to maint
39、ain explosionpressures under the shredder damage threshold (in units ofpsig), PM, is given by the equation:Av5 0.13V2/3PM20.435510.034vH! (1)where:V = shredder internal volume, andvH= hammer tip velocity, ft/s.The calculated vent area will be in the same units as V2/3.The metric equivalent, if PMis
40、in bar, and vHis in m/s, isAv5 0.041V2/3PM20.435510.112vH!(2)5.3.3.2 If the shredder discharge is at least 3 ft (0.91 m)above an unenclosed discharge conveyor, half the dischargearea can be credited toward attaining the required vent area, Av.The difference should be made up with unobstructed explos
41、ionvents. No credit should be taken for the inlet area which isusually too obstructed to be an effective vent.5.3.3.3 To illustrate the use of Eq 1 and 2, consider ahypothetical shredder with an internal volume of 1000 ft3(28.3 m3), including the portion of the inlet hood directlyabove the hammermil
42、l. Let us suppose that structural calcula-tions indicate that the weakest structural member can withstandan applied load equivalent to a hydrostatic pressure of 10 psig(0.70 bar). At the design shaft speed in this shredder, thehammer tip speed is 250 ft/s (76.2 m/s). Substitution of thesevalues into
43、 Eq 1 and 2 results in a calculated required vent areaof 64 ft2(5.95 m2). If the shredder discharge area is 20 ft2(1.9 m2), an explosion vent of at least 54 ft2(5.0 m2) areashould be installed on the shredder.5.3.4 The explosion vent opening should discharge combus-tion gases and flame into an unocc
44、upied outdoor area. If theshredder is situated inside a building, vent ducting will beneeded to channel gases and flame out of the building. Thisducting, which should have a strength at least equal to theshredder itself, should be kept as short as possible in order toavoid further burning and gas co
45、mpression during venting.5.3.4.1 Vent ducting of any length will cause the pressure toincrease significantly above the value expected for unrestrictedventing. The increased pressure can be related to the unre-stricted (no duct) vented explosion pressure through Fig. 1. Theparameter in Fig. 1 that de
46、termines this relationship is the ratioof vent duct volume to shredder volume. In the example in5.3.3.3, the use of only a 5.5-ft (1.7-m) long duct attached tothe 54-ft2(5.0-m2) vent area would represent a duct volume of300 ft3(8.5 m3), corresponding to a duct/shredder volume ratioof 0 to 3. Accordi
47、ng to Fig. 1, an explosion pressure of 10 psig(0.7 bar) without the duct would be increased to about 21 psig(1.5 bar) with a duct/shredder volume ratio of 0 to 3.5.3.4.2 If the pressure increases shown in Fig. 1 areintolerable, a duct with a diverging cross-section area shouldbe used. Apparently, th
48、ere have not been any published testdata on how much divergence is required to prevent significantpressure increases above the unrestricted vent values given byEq 1 and 2. Even with large divergence angles, the vent ductshould be designed to withstand a pressure equal to theshredder damage threshold
49、 pressure.5.3.4.3 It is desirable to prevent flammable gas from enter-ing and accumulating in a vent duct during normal shredderoperation. Although this is difficult to achieve, two possibleapproaches are use of a sturdy vent cover (5.3.5), or vent coverand projectile deflector to separate the shredder from the ventduct; or, as a less desirable alternative, use of air sweeping ofthe vent duct by the induced draft of the shredder or by ahigh-capacity dust collection or pneumatic transport system, orboth. These systems should be equipped with their ownexplosion protection sy
