煤粉尘爆炸风险.doc

COAL DUST EXPLOSION HAZARDS 煤粉尘爆炸风险9 g' e# Z, q/ l' Z( r0 U" A' q+ Z  Gby : B* V& I7 , |3 a+ J作者& k( ) f  d9 F! z% , g" o$ Y6 2 bCLETE R. STEPHAN, P.E. * V% s# _2 Q& W* y$ x- E/ ) W. 8 p/ g- b' t. I1 L- m( I6 I  t8 D- c  g* Q6 j4 fMINE SAFETY AND HEALTH ADMININSTRATION 1 h1 N8 D2 6 P+ PITTSBURGH, PENNSYLVANIA 1 L: o$ V# _& ! g0 p6 d矿业安全和健康管理协会* R3 |+ x' B- X4 g7 |1 q$ P匹斯堡 宾西法尼亚( X# D* i7 V% o4 c! TABSTRACT " U) F/ d2 ?! _' M8 |  w9 q摘要- o, d! T7 N- ) p" x) W/ s: z* z6 D- b! lThere are a large number of facilities throughout the world which handle coal, such as preparation plants. Many other facilities use coal as a fuel, such as cement and lime factories. Although coal can be handled safely and can be an efficient fuel, there are explosion hazards which are accentuated as the particle size is reduced. Particle sizes of coal which can fuel a propagating explosion occur within thermal dryers, cyclones, baghouses, pulverized-fuel systems, grinding mills, and other process or conveyance equipment. This paper discusses how explosions can occur within these facilities. ( n- b# / c2 ?- w7 L: B  l世界上有很多工厂需要处理煤炭，比如制剂厂。很多其它工厂以煤炭为生产原料，如水泥厂和石灰石厂。虽然煤炭能安全的处理并有效的燃烧，但随着煤炭颗粒尺寸的减小，存在爆炸的危险在增大。颗粒尺寸的原煤可以燃烧并导致连锁性爆炸，爆炸经常出现在热干燥系统，旋风除尘系统，库房和粉状燃料系统系统，磨机和其它工艺或输送设备中。本文主要讨论暴炸是如何在这些工厂中发生的。9 x+ ! ' o% m2 D& J( A! p  4 m2 P: F5 o  q8 s* 1 o) yFIRE TRIANGLE AND EXPLOSION PENTAGON / f) _1 Y8 , 燃烧三要素和爆炸五边形（要素）8 S; o0 Z4 v6 L1 P7 I& B) & q' l, G, S2 d5 5 a  V0 iThere are three necessary elements which must occur ! i; u6 n8 r; S9 l8 Psimultaneously to cause a fire: fuel, heat, and oxygen. These 8 x# I9 v7 b4 v. T0 d. * J% V* Lelements form the three legs of the fire triangle. By removing " 6 W( K* V8 ?6 R; U4 Y' b$ Eany one of these elements, a fire becomes impossible. For $ F8 P% P& S, Xexample, if there were very little or no oxygen present, a fire ) J8 e8 d" s: c, P, ?( _- ycould not occur regardless of the quantities of fuel and heat $ D& J) C# x( m0 Rthat were present. Likewise, if insufficient heat were 1 E& e7 8 e$ b3 ) r" R/ I3 w* v' A0 A* ?available, no concentrations of fuel and oxygen could result in a ' R! U/ u- U* ! x8 O' 9 bfire. " x5 s! j& J  u7 p! q% E需要以下三个要素同时存在才能导致燃烧：燃料，热和氧的存在，这些元素形成了燃烧三角型的三个边。如果去掉任何一个因素，燃烧是不可能发生的，举个例子，如果不存在氧气或者只有很少氧气存在，无论热量有多大，有多少燃料，都不会燃烧。同样的，如果没有充足的热量，没有一定浓度的燃料和氧气也无法燃烧。  X/ d5 Y4 E9 k. Y: d8 c' g, WOn the other hand, for an explosion to occur, there are five ; V' c; s' X9 T, W" _# Q0 anecessary elements which must occur simultaneously: fuel, heat, + ?$ z$ h/ |( ?  v1 qoxygen, suspension, and confinement. These form the five sides , u. q# y& B( J' * z0 y7 D, Aof the explosion pentagon. Like the fire triangle, removing any % b! N- Y5 C* one of these requirements would prevent an explosion from 9 q' 6 i9 Z2 K/ ?: gpropagating. For example, if fuel, heat, oxygen, and confinement 9 i5 Z/ ) j; # q" boccurred together in proper quantities, an explosion would still + f3 F) c2 t. y4 Pnot be possible without the suspension of the fuel. However, in " L. ?( I3 ?& 8 U, E1 d: mthis case, a fire could occur. If the burning fuel were then 5 D/ J5 a, N; L7 Q1 J& i, xplaced in suspension by a sudden blast of air, all five sides of / x1 S- f; K6 8 3 w, C# Xthe explosion pentagon would be satisfied and an explosion would 8 c6 _9 N9 0 |be imminent. 9 e9 C( D6 F9 l8 & p% S另一方面，对于爆炸现象的出现，需要以下5个因素同时存在：当燃料，热和氧气，悬浮，并且在密闭空间中，形成了爆炸五边型（要素）。就像三角型一样，取除任何一个所需要因素，都可以阻止爆炸的传播（发生）举个例子，如果燃料，热源和氧气在密闭空间中，处在一个合适的范围内，但并不是悬浮状态，则不会发生爆炸，但是在该情形下，会发生燃烧。如果燃烧的燃料被阵风吹起悬浮起来，则同时满足了爆炸五边型所需的所有条件，爆炸即将发生。1 c2 / R% Y5 C- H3 r  3 T- s# n8 Q# h+ L# D% d# R, l, " ' b" x2 R! t+ q0 v" j. L1 7 e2 l2   a5 s' H& KRemembering the three sides of the fire triangle (fuel, heat, 9 ! o$ O  W+ e, Boxygen) and the five sides of the explosion pentagon (fuel, heat, ' A7 Z( h+ M! T  h% Xoxygen, suspension, confinement) is important in preventing fires ! u2 P. U3 m5 and explosions at any facility. By eliminating the possibility 4 q2 u% c/ i) m; J4 Y* of either suspension or confinement, an explosion cannot occur, ( % b( 4 2 w& l& z: c$ dbut a fire may occur. By eliminating the fuel, the heat, or the . q# ) f$ w  f9 C6 h. |  Foxygen requirements, neither a fire nor an explosion can occur. 1 q# l! t  9 j2 S& L1 g在工厂阻止爆炸的发生，就需要牢记燃烧三要素（燃料，热，氧气）和爆炸五要素（燃料，热，氧气，悬浮，密闭空间）。8 i& n4 z. n# S/ m# : r/ Q: _; K+ 6 7 vFuel + q6 , a) X3 v) X: E! tCoal, as a primary fuel, must meet several requirements in order 2 D( |1 f  S6 1 Z  Uto be explosive. These requirements are volatile ratio, particle 4 y! v+ J7 S' G1 P3 i6 o& Tsize, and quantity. The volatile ratio is a value established $ P- k7 X' J! Y: O& Pby the former United States Bureau of Mines to evaluate the # v! D+ U! : n5 h9 : t5 Xexplosibility of coals based on large-scale tests in the ! , I7 Q+ I" B1 o4 ; . H2 W' Y: qExperimental Coal Mine. To calculate the volatile ratio, a proximate analysis must be performed in the laboratory on a / q0 L' u0 W2 g: g) Vsample of the coal. This analysis determines the volatile matter / y# d9 * 4 h  x- P9 b6 Rand fixed carbon quantities of the coal along with moisture and 9 f" w- M$ q5 T* n& K; Kash. The volatile ratio is defined as the volatile matter - I7 c: L% q6 k( n) # B! L2 divided by the summation of volatile matter and fixed carbon of 6 M1 Y4 m  H7 j  t+ p! gthe coal. 0 U3 m* Z: _+ ! _# O* 3 w) |' v( B燃料3 O8 u9 P% _0 y煤，作为一种主要燃料，需要满足几个条件才会发生爆炸。这些条件是挥发份，颗粒尺寸和数量，前美国矿业局在实验性煤矿为评估煤的爆炸性能进行了大规模的实验，证明了挥发份是很有价值的（参数）。为了计算挥发率，需要在实验室先对煤样做一个初步的分析。该分析确定了煤中挥发性物质和固定炭含量，包括水份和灰份，挥发份定义是由煤中挥发性物质除挥发性物质和固定炭之和。4 C+ o* q2 i1 E- ! 9 G, ?3 D, s2 a: 5 A% LThis method for calculating the volatile ratio produces a value - 0 B+ G. Q* X/ Z7 g9 independent of the natural or added incombustible in the coal. + K/ E5 _5 s( M8 J4 b2 S8 RIt has been determined that coals with a volatile ratio exceeding 8 Y) Q+ H% N+ D! B. v0 i0.12 present a dust explosion hazard./ g$ g2 / 7 5 Q. o- X/ All bituminous coals fall into this category. Since anthracite coals, by definition, have + D% l( t3 l2 a, R7 % va volatile ratio of 0.12 or less, they do not present an 6 V. : g8 P3 q0 V& 9 v" Fexplosion hazard. ' y/ n2 c% m9 . a: 0 WIt is important to note that both bituminous 6 # U1 O# p0 V+ ?and anthracite coals can be involved in fires, but only 7 P2 p6 X! X* u1 jbituminous coals can be involved in explosions. % ( X: q& O; J9 V  Z2 r- g* iAnother important requirement of the fuel is related to particle . H; ( I( L2 W$ # I3 M* L; Jsize. Experiments have shown that bituminous coal particles 6 . j. M" o$ g8 Y3 * # I9 Npassing through a U.S. standard 20-mesh sieve can participate in : 8 j" S# c% ka coal dust explosion. . 2 g3 g2 N# 0 T2 m' ?* NA 20-mesh sieve allows particles up to 841 microns or about 0.03 inch to pass and these are the largest particles that contribute to a coal dust explosion. ) T/ X( J* v# K9 m( N% M该计算模式提供了一个独立于煤炭自然特性或煤中附加不可燃成分的有价值数据，已经证明了，若煤粉中挥发份超过0.12，存在爆炸风险。所有的烟煤都属于此类，既然无烟煤通过确认，挥发份不大于0.12，它们不存在爆炸风险。非常值得注意的是，烟煤和无烟煤都会引起燃烧，但只有烟煤会导致爆炸。另一个重要的条件是粒度，实验已经证明了若烟煤的粒度小于美国标准20目筛则参与煤粉爆炸（则参与爆炸反应）20目筛子可以保证颗粒通过841微米，大约0.03英寸，这是能对爆炸产生左右的最大尺寸。（大于20目的颗粒，不会发生爆炸）8 A* L/ q: K5 D2 FAs the % l9 0 J- Q$ q  g- - n7 N6 k* _particle size is reduced even further, a more severe explosion 6 Q  |  q+ N& p/ F( w, H" ?hazard is realized. Typically, in pulverized-fuel systems, the , ?/ & L) z  7 Rcoal is reduced to a particle size where more than 85% will pass + / n* G! K$ fa U.S. standard 200-mesh sieve with openings of 74 microns or 6 j+ G% H  G7 b) q) S8 D6 aabout 0.003 inch. 9 w2 . a9 z3 * f4 F, K( VThese coal dust particles require less energy or temperature to ignite and, since heat transfers more quickly between smaller particles, the pressure and rate of pressure rise during an explosion are accentuated. & 8 X, y# r8 F* 3 U3 F( w4 d' & T2 f, 随着颗粒尺寸的缩小，爆炸危险会增加。通常在磨粉系统中，煤的颗粒尺寸通常有85%以上通过美标200目筛子，小于74微米，或0.003英寸。. O3 % U  Q' P6 C, Q! R. y  Y点燃这些煤尘的所需要的能量更少，温度更低；既然在小颗粒中，热传递速度更快，那么爆炸产生的压力和产生速度加快了。（爆炸速度和强度增加）4 z& j: s2 z; : Y- ?8 U4 8 l3 H5 a4 6 A4 c2 / z8 & I: I/ p- NThe third requirement for explosibility is related to the $ k# Z$ L( _9 quantity of coal dust available,1 P/ _0 M' g' |2 Sknown as the minimum explosive concentration (MEC). This is the minimum quantity of dust in suspension that will propagate a coal dust explosion and generate sufficient pressure to cause damage. ( B/ h0 x# k+ z! J2 T/ |The MEC for bituminous coal is approximately 0.10 ounce per cubic foot or 100 grams per cubic meter.7 o! # m' c+ d! R3 x3 ?第三个与爆炸有关的是煤粉能达到的浓度。以知最低爆炸浓度（MEC），在该最低悬浮浓度煤粉会传播爆炸（连锁燃烧，爆炸），且产生具有破坏性的压力。1 X5 E8 a' M1 |( c( Q烟煤的最低煤粉爆炸浓度大约是0.10盎司/立方英尺，或者100g/立方米。/ J# v" A  w; y2 Y9 ?$ 8 j. r+ O, Q5 Y: ?4 k- Y9 h" d When pulverized coal dust at the MEC was dispersed in an 3 S  F8 ?7 k: Z! i6 nentry, a cap lamp 10-feet within the cloud was not visible to 8 z9 |" 1 C8 a) observers standing in front of the dispersed dust. 8 u( M. x5 B& a0 v8 B2 M  h7 bAlso, a person cannot breathe in an atmosphere containing dust at the 0 ) p; J' r: G: F) MMEC. This amount of dust in the air is 25,000 times greater than ! S+ d* q8 a/ t4 c! A6 D4 mthe average concentration of respirable dust to which a coal 4 Y, e$ Q: u' 6 I6 ?- B8 b4 gminer may be exposed during an 8-hour shift. , T2 3 g! ( r- h. : k当煤粉浓度在入口处到达最低爆炸浓度时，在被驱散的煤尘之前无法看到在煤尘中10米远带灯罩的路灯。同样，人在MEC浓度的空气中无法呼吸。该数量相当与一个普通8小时轮班矿工可吸入粉尘浓度的25000倍。! b: G6 T3 S! # K# p2 y0 B8 - I6 ?& d; _, C) RA layer of ) p/ G;   D2 P# V8 B% Ypulverized coal dust at the MEC deposited on the floor of the 8 V1 d+ y7 u3 u, A# T8 DExperimental Coal Mine in Bruceton, Pennsylvania averaged 0.005inch / y/ u" ) |6 c8 Q0 |thick. . U- Z% K- n+ y. d  X  rThis thickness is almost unobservable. In other / X  P! A' e) K" _# 9 words, if footprints are visible in coal dust on the floor or the   d! f& T( k. Pcoal dust is seen on the walls of a plant, then there is enough   m" d/ W# m) h; 5 Z3 r- coal dust at that particular location to propagate an explosion. " Y+ t* V2 M& Y* k  _. n! l0 L4 Z9 z在宾西法尼亚布鲁斯顿的煤矿实验室中，MEC浓度的煤粉沉降到地板上厚度是0.005英寸厚。该厚度几乎无法观察到，换句话说，如果在工厂的地板上或墙上看到了脚印，那么现场的煤粉浓度足以引发爆炸。' z7 & I2 I9 r% Q( u6 C( c9 + d2 q1 l! T, g& GThe upper explosive limit is not well-defined and experiments + w" m0 D. D" v- I* have shown that a coal dust loading of 3.8 ounces per cubic foot 4 A. m3 q! M3 m' n) X- qwould propagate a low-velocity explosion and that a 5.0 ounces ) x1 A% N) f4 gper cubic foot loading would quench itself within 10 feet of 1 S! B5 o: P1 n! oignition. + s4 s9 p, / q- cThe presence of other flammable dusts or gases can lower the MEC of the coal, which increases the hazard. On the other hand, the hazard can be lessened with the addition of ash, rock dust, inert gas, and any other inert material. 4 8 e! ?% L8 U7 ; 8 F5 爆炸浓度的上限并没有完美的测定；实验表明，3.8盎司/立方英尺的煤尘浓度会引发低强度的爆炸，5.0盎司/立方英尺的浓度会将在点燃处10远的距离熄灭（距离燃火中心外10米处熄灭）。其它可燃性灰尘和气体可导致煤的MEC值降低，在另一方面，如果增加灰份的含量，岩石粉，惰性气体和其它惰性材料可降低爆炸风险。( w. , C" . e+ Y) T; 9 y( p9 D3 hHeat 1 m9 O$ P4 D6 D( |  wThe heat requirements to complete the fire triangle or the 1 X  T. R/ B" v: X" 5 I( b3 d3 cexplosion pentagon can be in the form of temperature or energy. + ; B4 P6 l: Z' w6 8 T2 T3 XThe ignition temperature of a coal dust cloud decreases as the 2 % e' U- n* Mvolatile content increases. At high volatile contents, the . V$ f& C. E3 Z+ l4 p) lignition temperature of a coal dust cloud approaches a limiting 5 d. D- B' j& s) G# w0 c% ntemperature as low as 440C (824F). The ignition temperature of + j/ o0 e! U  A. ka Pittsburgh Seam coal dust cloud is fairly constant as the 2 D7 a- _+ i% 8 2 X; O* oparticle size increases to about 180 microns. Further increases " * W) a; j' N6 p/ Qin size result in rapid rise in the ignition temperature , u5 ?& |- - S, & N! grequirements. As the particle size decreases, the coal dust 5 T" B& L; K% u" K$ Nbecomes easier to ignite. 2 H/ I( u5 , n: : X( m! v热2 o* C( J! ?. y" X满足燃烧三要素和爆炸五边型所需的热通常以温度和能量的形式表现出来。煤尘的点燃温度随着煤挥发性的升高而降低，在高挥发份时，煤粉的点燃温度接近极440度的限温度（华氏824），匹斯堡煤层煤粉的粒度在180微米以下时点燃温度几乎是个常数，随着颗粒尺寸的增加，需要更高的煤粉的点燃温度。随着颗粒尺寸的缩小，煤粉更加容易点燃。, O# F) 9 K% |% k1 x, R8 i$ R( H/ L9 B! P; n1 U+ c  oThe ignition temperature of a coal dust layer also decreases as ( K" H' 0 N! M3 K. c0 i) ethe volatile content increases. & P2 |! i! _- & e8 dAt high volatile contents, the 3 M2 i8 q. 6 " V/ Eignition temperature of a coal dust layer approaches a limiting + h) R& U( c! k; |$ ktemperature as low as 160C (320F). With dust layers on hot - B4 ?* w! * L0 J) o. % surfaces, the minimum ignition temperature decreases sharply as 9 q2 L  w8 5 & % N2 D" Lthe thickness of the deposit is increased. This is due to the 7 U- R3 $ X" Q+   gfact that thicker dust layers capture and hold heat more readily. + A% p! G% K& / F6 X& l煤粉层的点燃温度随着挥发份的升高而降低。，在高挥发份时，煤粉层的点燃温度接近与极限温度160C，当煤粉聚集在热表面上时，最低点燃温度随着煤粉沉集厚度的增加迅速降低。这实际上是由于较厚的粉尘可吸收和储存了热量更迅速。9 h% m5 + w4 V7 j% _7 I2 " O1   g3 _) v3 Y/ - |6 i0 Y1 To illustrate the variety of coals, the minimum ignition # l7 y: R7 % N0 n. Ntemperatures to ignite clouds of various ranks of coal are as 5 z7 k0 n$ / G' ; Y2 a* gfollows: ' i$ h9 ! i6 Z" Y- c4 k3 G/ Q举个例说明不同的煤种，煤粉雾的最低点燃温度归类如下 ! n$ ! i) v  u. p  E; S  b7 n% p+ 0 ?$ U! H/ M: V. I/ r煤等级或种类        最低点燃温度  1 P7 A, g& d( n3 d! u" 波卡洪塔思 煤层烟煤        610& e* r9 I. j8 k: 3 p% f匹斯堡  煤层烟煤        525-5607 o: D5 D! y! O7 ( V# U1 Y) U次烟煤 混合煤（收到基）        475+ u9 b1 , D- B3 I5 V6 R; j2 D" b: t8 N次烟煤 混合煤（干基）        4557 t& N: |: + D+ m7 u; O褐煤  （收到基）        450-6003 a6 r) x' S1 U褐煤   （干基）        425-5550 ?- K1 c' & B5 - m: A: u$ j6 S& a' H4 T0 b1 O: HVisually, a temperature of approximately 537EC (1000EF) is & K. d2 q% p9 " A5 m1 jobtained when an object is heated to a dull red in a darkened 5 o' m# n, s& j$ O% h  room. Resistors in controllers or other electrical components ( U6 L. e7 v% i+ R1 J) e7 m8 Cmay exceed this temperature. Also, temperatures at the top of a 5 Y1 v* O2 T1 S, R: g# K200-watt incandescent bulb approach 250EC and, at the top of a 0 q* W6 D  Q) Z5 u0 d5 q3 1500-watt incandescent bulb, can exceed 300EC. 9 7 n* p5 b- G, p4 从视觉上来说，温度大约537度时，（1000华氏度）当在黑暗的房间里可以看到暗红色。一些控制器里的电阻或者其它电器部件可能超过该温度。同样的，200瓦百炽灯可以达到250度，1500瓦白炽灯的最高温度可超过300度。/ ?7 7 p3 n2 d/ c- y/ P& Z. E3 c) T" k- ! P8 tThere is also a variation in the minimum ignition temperature of * ' g0 ?7 E) n0 v: Dcoal dust layers as follows: / h' k+ ; E; N0 D以下还有几个不同煤种的最低点燃温度8 R( s  j. K3 j: b9 R5 v0 u0 k& u* i煤等级或种类        最低点燃温度( T- $ V5 ' 0 M% q% K" K匹斯堡煤层        170& x0 f" k* s' t& A4 J罗得岛（克兰斯敦）无烟煤        5204 x7 X, |2 " + S伊利挪死 7号烟煤        160* Q2 I" ( t6 P% M5 S9 e6 s. % e波卡洪塔斯煤层烟煤        220( Z" _) 3 5 % z! x1 l0 W# e" k' % r" k0 sElectrical or frictional sparks can also provide the heat source 6 m+ O0 t7 H' T+ # V3 kfor initiating a fire or explosion. Ex