煤粉塵爆炸風(fēng)險(xiǎn)

1、coal dust explosion hazards % m$ z7 j. |. ; a煤粉塵爆炸風(fēng)險(xiǎn)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

2、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礦業(yè)安全和健康管理協(xié)會(huì)* r3 |+ x' b- x4 g7 |1 q$ p匹斯堡 賓西法尼亞( 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

3、 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 acce

4、ntuated 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 faci

5、lities. ( n- b# / c2 ?- w7 l: b  l世界上有很多工廠需要處理煤炭，比如制劑廠。很多其它工廠以煤炭為生產(chǎn)原料，如水泥廠和石灰石廠。雖然煤炭能安全的處理并有效的燃燒，但隨著煤炭顆粒尺寸的減小，存在爆炸的危險(xiǎn)在增大。顆粒尺寸的原煤可以燃燒并導(dǎo)致連鎖性爆炸，爆炸經(jīng)常出現(xiàn)在熱干燥系統(tǒng)，旋風(fēng)除塵系統(tǒng)，庫房和粉狀燃料系統(tǒng)系統(tǒng)，磨機(jī)和其它工藝或輸送設(shè)備中。本文主要討論暴炸是如何在這些工廠中發(fā)生的。9 x+ ! ' o% m2 d& j( a! p  4 m2 p: f5 o  q8 s* 1 o) yf

6、ire triangle and explosion pentagon / f) _1 y8 , 燃燒三要素和爆炸五邊形（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%

7、 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 regar

8、dless 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

9、60; u7 p! q% e需要以下三個(gè)要素同時(shí)存在才能導(dǎo)致燃燒：燃料，熱和氧的存在，這些元素形成了燃燒三角型的三個(gè)邊。如果去掉任何一個(gè)因素，燃燒是不可能發(fā)生的，舉個(gè)例子，如果不存在氧氣或者只有很少氧氣存在，無論熱量有多大，有多少燃料，都不會(huì)燃燒。同樣的，如果沒有充足的熱量，沒有一定濃度的燃料和氧氣也無法燃燒。  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" _

10、# 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 requirem

11、ents 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 &qu

12、ot; 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 immi

13、nent. 9 e9 c( d6 f9 l8 & p% s另一方面，對(duì)于爆炸現(xiàn)象的出現(xiàn)，需要以下5個(gè)因素同時(shí)存在：當(dāng)燃料，熱和氧氣，懸浮，并且在密閉空間中，形成了爆炸五邊型（要素）。就像三角型一樣，取除任何一個(gè)所需要因素，都可以阻止爆炸的傳播（發(fā)生）舉個(gè)例子，如果燃料，熱源和氧氣在密閉空間中，處在一個(gè)合適的范圍內(nèi)，但并不是懸浮狀態(tài)，則不會(huì)發(fā)生爆炸，但是在該情形下，會(huì)發(fā)生燃燒。如果燃燒的燃料被陣風(fēng)吹起懸浮起來，則同時(shí)滿足了爆炸五邊型所需的所有條件，爆炸即將發(fā)生。1 c2 / r% y5 c- h3 r  3 t- s# n8 q# h+ l# d% d# r, l,

14、" ' 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, confi

15、nement) 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

16、 . 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在工廠阻止爆炸的發(fā)生，就需要牢記燃燒三要素（燃料，熱，氧氣）和爆炸五要素（燃料，熱，氧氣，懸浮，密閉空間）。8 i& n4 z. n# s/ m# : r/ q: _; k+ 6 7 vfuel + q6 , a) x3 v) x: e! tcoal, as a primary fuel, mu

17、st 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 bur

18、eau 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) vsam

19、ple 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 summa

20、tion 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，作為一種主要燃料，需要滿足幾個(gè)條件才會(huì)發(fā)生爆炸。這些條件是揮發(fā)份，顆粒尺寸和數(shù)量，前美國礦業(yè)局在實(shí)驗(yàn)性煤礦為評(píng)估煤的爆炸性能進(jìn)行了大規(guī)模的實(shí)驗(yàn)，證明了揮發(fā)份是很有價(jià)值的（參數(shù)）。為了計(jì)算揮發(fā)率，需要在實(shí)驗(yàn)室先對(duì)煤樣做一個(gè)初步的分析。該分析確定了煤中揮發(fā)性物質(zhì)和固定炭含量，包括水份和灰份，揮

21、發(fā)份定義是由煤中揮發(fā)性物質(zhì)除揮發(fā)性物質(zhì)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

22、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" fex

23、plosion 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 o

24、f 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

25、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該計(jì)算模式提供了一個(gè)獨(dú)立于煤炭自然特性或煤中附加不可燃成分的有價(jià)值數(shù)據(jù)，已經(jīng)證明了，若煤粉中揮發(fā)份超過0.12，存在爆炸風(fēng)險(xiǎn)。所有的煙煤都屬于此類，既然無煙煤通過確認(rèn)，揮發(fā)份不大于0.12，它們不存在爆炸風(fēng)險(xiǎn)。非常值得注意的是，煙煤和無煙煤都會(huì)引起燃燒，但只有

26、煙煤會(huì)導(dǎo)致爆炸。另一個(gè)重要的條件是粒度，實(shí)驗(yàn)已經(jīng)證明了若煙煤的粒度小于美國標(biāo)準(zhǔn)20目篩則參與煤粉爆炸（則參與爆炸反應(yīng)）20目篩子可以保證顆粒通過841微米，大約0.03英寸，這是能對(duì)爆炸產(chǎn)生左右的最大尺寸。（大于20目的顆粒，不會(huì)發(fā)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&qu

27、ot; ?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 .

28、 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, 隨著顆粒尺寸的縮小，爆炸危險(xiǎn)會(huì)增加。

29、通常在磨粉系統(tǒng)中，煤的顆粒尺寸通常有85%以上通過美標(biāo)200目篩子，小于74微米，或0.003英寸。. o3 % u  q' p6 c, q! r. y  y點(diǎn)燃這些煤塵的所需要的能量更少，溫度更低；既然在小顆粒中，熱傳遞速度更快，那么爆炸產(chǎn)生的壓力和產(chǎn)生速度加快了。（爆炸速度和強(qiáng)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#

30、 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 b

31、ituminous coal is approximately 0.10 ounce per cubic foot or 100 grams per cubic meter.7 o! # m' c+ d! r3 x3 ?第三個(gè)與爆炸有關(guān)的是煤粉能達(dá)到的濃度。以知最低爆炸濃度（mec），在該最低懸浮濃度煤粉會(huì)傳播爆炸（連鎖燃燒，爆炸），且產(chǎn)生具有破壞性的壓力。1 x5 e8 a' m1 |( c( q煙煤的最低煤粉爆炸濃度大約是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:

32、 ?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

33、 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-h

34、our shift. , t2 3 g! ( r- h. : k當(dāng)煤粉濃度在入口處到達(dá)最低爆炸濃度時(shí)，在被驅(qū)散的煤塵之前無法看到在煤塵中10米遠(yuǎn)帶燈罩的路燈。同樣，人在mec濃度的空氣中無法呼吸。該數(shù)量相當(dāng)與一個(gè)普通8小時(shí)輪班礦工可吸入粉塵濃度的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

35、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 floo

36、r 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在賓西法尼亞布魯斯頓的煤礦實(shí)驗(yàn)室中，mec濃度的煤粉沉降到地板上厚度是0.0

37、05英寸厚。該厚度幾乎無法觀察到，換句話說，如果在工廠的地板上或墻上看到了腳印，那么現(xiàn)場的煤粉濃度足以引發(fā)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- qw

38、ould 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 othe

39、r 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 爆炸濃度的上限并沒有完美的測定；實(shí)驗(yàn)表明，3.8盎司/立方英尺的煤塵濃度會(huì)引發(fā)低強(qiáng)度的爆炸，5.0盎司/立方英尺的濃度會(huì)將在點(diǎn)燃處10遠(yuǎn)的距離熄滅（距離燃火中心外10米處熄滅）。其它可燃性灰塵和氣體可導(dǎo)致煤的mec值降低，在另一方面，如果增加灰份的含量，巖石粉，惰性氣體和其它惰性材料可降低爆炸風(fēng)險(xiǎn)。( w. , c"

40、 . 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 coa

41、l 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

42、/ 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! grequiremen

43、ts. 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熱2 o* c( j! ?. y" x滿足燃燒三要素和爆炸五邊型所需的熱通常以溫度和能量的形式表現(xiàn)出來。煤塵的點(diǎn)燃溫度隨著煤揮發(fā)性的升高而降低，在高揮發(fā)份時(shí)，煤粉的點(diǎn)燃溫度接近極440度的限溫度（華氏824），匹斯堡煤層煤粉的粒度在180微米以下時(shí)點(diǎn)燃溫度幾乎是個(gè)常數(shù)，隨著顆粒尺寸的增加，需要更高的煤粉的點(diǎn)燃溫度。隨

44、著顆粒尺寸的縮小，煤粉更加容易點(diǎn)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/ eignit

45、ion 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 depos

46、it 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煤粉層的點(diǎn)燃溫度隨著揮發(fā)份的升高而降低。，在高揮發(fā)份時(shí)，煤粉層的點(diǎn)燃溫度接近與極限溫度160c，當(dāng)煤粉聚集在熱表面上時(shí)，最低點(diǎn)燃溫度隨著煤粉沉集厚度的增加迅速降低。這實(shí)際上是由于較厚的粉塵可吸收和儲(chǔ)存了熱量更迅速。9 h% m5 + w4 v7 j% _7 i2 &

47、quot; 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舉個(gè)例說明不同的煤種，煤粉霧的最低點(diǎn)燃溫度歸類如下 ! n$ ! i) v

48、0; u. p  e; s  b7 n% p+ 0 ?$ u! h/ m: v. i/ r煤等級(jí)或種類        最低點(diǎn)燃溫度  1 p7 a, g& d( n3 d! u" 波卡洪塔思 煤層煙煤        610& e* r9 i. j8 k: 3 p% f匹斯堡  煤層煙煤        525-5607 o: d5 d! y! o7 ( v# u1

49、 y) u次煙煤 混合煤（收到基）        475+ u9 b1 , d- b3 i5 v6 r; j2 d" b: t8 n次煙煤 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'

50、; & 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 com

51、ponents ( 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 從視覺上來說，溫度

52、大約537度時(shí)，（1000華氏度）當(dāng)在黑暗的房間里可以看到暗紅色。一些控制器里的電阻或者其它電器部件可能超過該溫度。同樣的，200瓦百熾燈可以達(dá)到250度，1500瓦白熾燈的最高溫度可超過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以下還有幾個(gè)不

53、同煤種的最低點(diǎn)燃溫度8 r( s  j. k3 j: b9 r5 v0 u0 k& u* i煤等級(jí)或種類        最低點(diǎn)燃溫度( t- $ v5 ' 0 m% q% k" k匹斯堡煤層        170& x0 f" k* s' t& a4 j羅得島（克蘭斯敦）無煙煤        5204 x7 x, |2 " + s伊利挪死 7號(hào)煙煤     

54、   160* q2 i" ( t6 p% m5 s9 e6 s. % e波卡洪塔斯煤層煙煤        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. experiments have shown th

55、at / q$ o7 d) ?/ q& t# wa coal dust cloud can be ignited directly by frictional sparks in 1 i2 ?) i% e+ o  g$ lthe absence of methane. dust clouds of lignite and subbituminous - g( 6 ) ; n/ p3 wcoals can ignite with as little as 30 millijoules of , & j8 c( z3 energy. bituminous coa

56、l from kentucky and from the experimental - d  b8 w# v& jcoal mine (pittsburgh seam) in bruceton, pennsylvania required 30 : a" a7 k- x- and 60 millijoules, respectively, as the minimum ignition energy   q$ p7 a* u) k9 l# xof a cloud. below a moisture content of between

57、5%-8%, there is 0 ) g5 i7 o% |8 j- rno effect on the explosibility parameters for minus 200-mesh 1 v5 z5 l, s7 h% i! a2 d6 i7 jpittsburgh seam coal dust. beyond 8% moisture, the minimum 8 |4 g1 + k; : p0 camount of energy required for an explosion increases dramatically - s$ t# k% q% p! g6 c- pand,

58、at 15% moisture, about ten times more energy is required. 9 w" c1 _' _5 g9 g/ r& u電和摩擦火花同樣能提供點(diǎn)燃火焰和爆炸所需的熱源，實(shí)驗(yàn)已經(jīng)證明了煤粉可以在沒有甲烷的環(huán)境里直接被磨擦火花點(diǎn)燃，無煙煤和次煙煤的粉塵霧可以被0.03焦能量點(diǎn)燃。從肯塔基和實(shí)驗(yàn)煤礦（匹斯堡）布魯斯通賓西法尼亞來的煤粉“霧”最少分別需要0.030和0.060焦能量。當(dāng)水分含量在5%8%之下，并沒有有效的匹斯堡煤粉爆炸參數(shù)，當(dāng)水分含量超過8%時(shí)，爆炸所需的最小能量急劇增加，當(dāng)水分含量超過15%的時(shí)候，（爆炸）需要超過

59、10倍以上的能量。( x2 o5 v6   / y: g5 o- c( j2 m0 m8 x$ also, the minimum ignition energy of coal dust varies with oxygen 3 p; h3 g1 ?/ i3 |9 b5 d' gcontent of the atmosphere, volatile content, and the amount of + % x0 t/ u, # n+ fine dust that will pass a u.s. standard no. 200-mesh sieve (74

60、* l# z5 d1 ; b# dmicrons). * o! f0 l% l- t+ _0 y4 i+ acoals are easier to ignite with increases in the 2 i- j5 p* + f* t4 v! u2 moxygen content, or the volatile content, or in the amount of fine . g8 p8 b# c: l3 ?2 v4 v5 coal. however, there is a limiting value of minimum ignition 3 j# t' : i: h

61、energy which varies for each coal. ! y8 n# v9 f) z+ x+ p- l" u5 * l$ j" a9 e( a; u) s. d, s. z7 j# k( _2 fall coal dusts should be regarded as prone to ignition when * v( y" p2 5 k- l0 bexposed to the frictional sparks of badly maintained machinery or - w8 r1 m1 v3 when they become co

62、ntaminated with tramp metal. for mixtures of coal dust and flammable gas, the critical minimum ignition energy is that which affects the gas. when ignited, the gas releases sufficient energy to suspend and ignite a coal dust cloud. 0 p$ s" h/ s2 k3 u! a同樣的，在含氧的空氣中，煤粉爆炸的最低能量，揮發(fā)份含量和通過美標(biāo)200目的篩的細(xì)煤粉

63、（74微米）含量，隨著氧含量，揮發(fā)份含量，洗煤含量的增加爆炸危險(xiǎn)性增大。然而，無論如何不同煤種仍然存在最低爆炸能量。所有被暴露在維護(hù)不好的機(jī)器產(chǎn)生的火花下，或者密閉在堅(jiān)實(shí)機(jī)器中的煤粉都應(yīng)當(dāng)被認(rèn)為是具有爆炸性的。對(duì)煤粉和易燃?xì)怏w混合物來說，關(guān)鍵的最低爆炸能量主要受氣體確定，當(dāng)被點(diǎn)燃時(shí)，氣體釋放的能量足以使煤粉懸浮并點(diǎn)燃煤粉。, m$ 0 g: k- d  * n$ v: u* s+ h' 4 o, k% w/ z3 v, p* h7 m2 t3 b, s0 p* 3 o+ n1 c/ v6 p2 f4 w, ?# l, c- p$ moxygen 8 l5 q  x1 x  m% h氧氣0 s4 y# s& z! l& g5 / o" l; g1 p1 h% g