ࡱ> WYV'` ?bjbj"9"9 .X@S@S06xDdddd<$ ,2-,/,/,/,/,/,/,$-h`0S,-""""""S,,%%%""-,%""-,%%!(m( @*vd $9(,,0,A(,0$0m(m(0I)d4%2$S,S,% ,""""""""  d4@t ON THE NATURE OF COAL COMBUSTION, INCLUDING PREVENTING MINE EXPLOSIONS AND THE BUILDUP OF CARBON MONOXIDE IN COAL MINES SUMMARY Adequate ventilation is all that is required to prevent all coal mine explosions and the buildup of carbon monoxide in coal mines. A natural gas explosion is needed to set off one of coal dust. With this, gassy mines are more susceptible to coal mine explosions than other ones, making ventilation even more important in these. Preventing ignition sources in the coal mines is also an excellent idea. Measuring absolute CO levels in coal mine entre ways is adequate to describe the breathing danger from this gas, as more complicated evaluations, such as the CO Index, have been suggested. While Rock Dust has almost no effect on coal dust flame propagation in the laboratory over the entire range of flammable coal concentrations, it might have a worthwhile function in suppressing the aeration of coal dust in an actual coal mine. Purple K has been shown to be a chemical inhibitor of coal dust flames in the laboratory. However, it is a sticky solid that could cause other problems in a coal mine, such as with electrical connections on equipment there. The difference between coal and natural gas flames is that coal is propagated by radiation while natural gas is propagated mainly by convection. With this difference, a hefty spark cannot initiate a coal flame. Practically speaking, there is no upper flammability limit to a coal dust flame, even at 8 times the stoichiometric amount in the laboratory. It is expected that the measured coal dust burning velocity would vary with the particle size distribution and diameter of a laboratory burner, along with any external stabilization, until an emissivity of 1.0 is reached. Post-explosion devices, such as a passive water barrier or a carbon dioxide canister, are difficult to design and deploy strategically throughout an actual coal mine. Preventing the explosion in the first place through adequate ventilation throughout a mine is a much better idea. ON THE NATURE OF COAL COMBUSTION Coal dust explosions are always triggered by natural gas explosions. Natural gas (which is primarily composed of methane) is often found in pockets near coal seams. Flushing out the natural gas in concentrations below its flammability limit (around 4.5 to 5 percent, discussed in paper by Majid) is all that is needed to prevent coal dust explosions (purported in online article from the Coalition for Affordable and Reliable Energy). Coal flames and natural gas flames are very different from each other. A very miniscule spark is enough to ignite a natural gas flame, whereas even a huge spark is incapable of igniting a coal flame in the laboratory (see Fink, Dalverny, and Grumer paper). Therefore, something more energetic is needed for a coal flame to propagate in a mine. The only thing with this much energy present there is a natural gas explosion. Another difference is in their mechanism of flame propagation. Natural gas flames propagate mainly by convection, whereas coal flames propagate by radiation. With this, coal flames must reach a minimum size to be optically thick (estimated to be 30 to 38 centimeters to approach a total emissivity of 1.0). Coal flames smaller than this might well need some external stabilization, such as being surrounded by a hot gas. Consuming volatiles is a major part of this coal flame propagation (see Howard and Essenhigh paper). The natural gas explosion disperses the coal dust found in shaft floors, walls, and ceilings to reach flammable limits in the air (around 75 to 100 milligrams/liter). Thus, the coal flame can propagate with concentrations at this level or higher. Some coal dust on the floor can theoretically detonate too, adding to the fire and explosion impact. Natural gas and coal dust explosions in a coal mine set off pressure and velocity waves that can be lethal to coal miners. With these, the flames can actually propagate in both directions in a mine shaft, giving them a back-and-forth motion. The burning velocity is an experimentally determined quantity that is a measure of flame strength (see McGraw-Hill definition). Coal dust burning velocities for all concentrations are considerably less than those for stoichiometric methane, indicative of requiring a much larger ignition source and stabilization for propagation (discussed above). Perhaps the relative flame speeds in the work of Fink et al could be useful in estimating this experimental phenomena, as they remained constant in propagation for each coal or natural gas concentration all the way up the vertical duct. This was true both for flame propagations with the top open or closed prior to the onset of ignition at the bottom. Rock Dust has almost no effect on coal dust flame propagation in the laboratory over the entire range of flammable coal concentrations (see Grumer and Bruszak paper). However, it might have a worthwhile function in suppressing the aeration of coal dust in an actual coal mine. Purple K has been shown to be a chemical inhibitor of coal dust flames in the laboratory (see Grumer and Bruszak paper). However, it is a sticky solid that could cause other problems in a coal mine, For instance, Purple K can wreak havoc on electrical connections on equipment there. Small coal dust particles (such as with a fine dust mixture of <15 microns) are more explosive than larger ones (such as mine dust with some particles in excess of 100 microns). Highigh HH Coal Dust Concentrations (in excess of 1000 mg/l, which is around 8 times the stoichiometric amount, which is approximately 1000 mg/l) are still flammable. Therefore, we should assume no upper limit in practice for coal dust flames (with data presented in paper by Fink, Dalverny, and Grumer). Natural gas and coal dust mixtures can be very explosive, even more-so with fine coal dust particles (see papers by Fink, Dalverny, and Grumer and Shou-Xiang, Li Zhang, and Zi-Ru Guo). This might be of some advantage in natural gas furnaces, adding a small quantity of coal dust to a lean natural gas mixture to increase the flame intensity and to enhance greatly the radiation transfer to the furnace walls. However, ash building up on the furnace walls would decrease this transfer. Another type of solid or liquid droplet might be more advantageous for this (see Mechanical Engineering Department at the University of Leeds paper). Dispersing coal dust in the laboratory evenly has been a problem. This was handled at the Bureau of Mines with a disperser developed by Bruszak (pointed out in Agglomeration reference by Fink). This disperser could be used for generating exact coal concentrations from near-zero to over 1000 mg/l in both a vertical 15 cm round (in the work of Grumer and Bruszak) and a vertical 20 cm square (in the work of Fink, Dalverny, and Grumer) duct. Multiple dispersers of this type would probably work well with larger dust clouds. Carbon monoxide (CO) can find its way into a coal mine in two different ways: first, through spontaneous combustion of coal either in the seam or in piles along the floor, and second, as a product of incomplete combustion in a natural gas/coal dust explosion. For this latter case, miners can die of CO toxicity even if they survive the actual explosion. Carbon monoxide is a highly toxic gas, being lethal to humans in concentrations of parts per million in just a few minutes. Therefore, flushing out the air down to non-toxic levels with fresh ventilation is a good idea if CO is suspected in a coal mine. Some coal types are more prone to undergo spontaneous combustion than others (see paper by Nugroho, McIntosh, and Gibbs). Water is not particularly effective in stopping spontaneous combustion. If a mine is sealed off after an explosion, it can fill up with natural gas. Carbon monoxide at toxic levels can also accumulate under this condition. Heated air in the mine might also be a problem that fresh air ventilation would solve. Recovery of a sealed coal mine is a dangerous undertaking, going from a fuel-rich to a fuel-lean condition with natural gas (see paper by Fink, Dalverny, and Weinheimer). It is dangerous because only a very tiny spark is required to set of the natural gas (discussed above) when it is mixed with fresh air during the recovery. If a gassy mine is closed, it could possibly be used as a source of natural gas if this is economical. However, care would have to be taken to avoid air mixing with the natural gas in flammable (explosive) proportions. If a coal mine shaft is sealed up for any reason and this coal undergoes spontaneous combustion, it should be well ventilated before allowing people into it. Carbon monoxide is a colorless and odorless gas, and is lethal in concentration of parts per million for a period of only seconds. Suggestions for monitoring this danger in coal mine entree ways (both open and sealed) include the so-called CO Index (CO/O2), CO, and absolute CO values. The absolute values are adequate for this breathing dangerous evaluation. This was demonstrated in the U.S. Steel Paonia, Colorado coal mine in around 1973-4 and possibly longer. The mine was  wired up with plastic tubing and copper fittings to as many as 36 different points at the entre ways. Units from MSA were used to vacuum pump the gas samples into a separate room underground. Gases sampled included oxygen and CO. Methane and CO detectors are useful in trying to prevent a dangerous situation from occurring and in recovering a mine following an explosion. Oxygen tanks could help trapped miners breathe without inhaling CO until they are reached by a rescue team. Post-explosion safety ideas have been bandied around for decades. However, the actual design to suppress an ongoing explosion completely and strategic deployment throughout an actual coal mine is difficult. The former involves sizing these devices for a wide variety of conditions, such as explosion and flame strength, which depends, among other things, on the location and strength of the initial natural gas explosion and the shape of the mine itself; the latter is problematical because it forces the mines management to estimate where a possible coal explosion could occur. The simplest post-explosion device is a passive water barrier attached to shaft ceilings and triggered by the velocity/pressure of the explosion itself. If the timing is right, the water would put out the propagating coal flame completely. A carbon dioxide canister that would be blown open when triggered by an optical flame detector is another post-explosion possibility (see Health and Safety Executive article). One additional problem with this is that there would be insufficient air left to breathe in the vicinity of this canister. With difficulties like these with post-explosion techniques, it makes more sense to prevent the coal dust explosion from taking place at all rather than trying to put it out after the coal flame begins to propagate. As the old saying goes, An ounce of prevention is worth a pound of cure. Therefore, with something as simple as employing adequate ventilation, especially in gassy mines, we have no reason to tolerate coal mine explosions anywhere in the world. Despite of this, we have had them recently in China, South Africa, and the United States (in West Virginia). On the positive side, coal mine explosions are less common in the U.S. than what they used to be (see online explosion data by the United States Mine Rescue Association). It is a very good idea to prevent ignition sources in coal mines, since only a tiny spark is needed to set off a natural gas explosion. These would include cigarettes, cigars, lighters, and matches. Spark-proof electrical devices would also be highly recommended throughout the mines. Fresh ventilation is also an excellent idea for mines other than coal, such as gold or silver. This keeps the underground mine shafts more comfortable for the miners, helping to combat the naturally occurring heat that becomes increasingly worse the deeper underground you go. REFERENCES Coalition for Affordable and Reliable Energy - Online, Advanced Technology, Coal Mine Health & Safety (2005). Fink, Z., Agglomeration of Particles Flowing Down a Vertical Duct, Powder Technology, 12 (1975), 287-89. Fink, Z.F., Dalverny, L.E., and Grumer, J., Ultraviolet-Visible and Infrared Emission Spectra of Propagating Methane Coal-Dust Inhibitor Flames, U.S. Bureau of Mines, RI 7956 (1974). Fink, Z.F., Dalverny, L.E., and Weinheimer, J., Continuous Gas Monitoring Using Tube Bundles at the Joanne Mine Fire, U.S. Bureau of Mines, TPR 92 (1975). Grumer, J. and Bruszak, A.E., Inhibition of Coal Dust-Air Flames, U.S. Bureau of Mines, RI 7552 (1971) Health and Safety Executive Web Site, Inerting. Howard, J.B. and Essenhigh, R.H., Mechanism of Solid-Particle Combustion with Simultaneous Gas Phase Volatile Combustion, 11th International Symposium on Combustion, Pittsburgh, Pa., 1967, Pages 399-408. Majid, M. Basic Concepts in Hazardous Chemicals: Flammability, PRN Bulletins and Articles - Online. McGraw-Hill Encyclopedia of Science & Technology Online, Burning Velocity Measurement. Nugroho, Y.S., McIntosh, A.C., and Gibbs, B.M., Assessing the Risk of Spontaneous Ignition of Coal and Biomass, 18th ICDERS, 2001. School of Mechanical Engineering, University of Leeds, Combustion Research Group, Burning Velocity Enhancement Due to the Presence of Droplets. Shou-Xiang, Lu, Li Zhang, and Zi-Ru Guo, Interesting Flame Propagation Pattern of Gas Flame Interacting With Dust Deposit, 18th ICDERS, 2001. United States Mine Rescue Association - Online, Historical Data on Mine Disasters in the United States. 7Fwxz  >    5678C`ÿû˿ρ}y}uquh@{nh.h7hEhh6_h~Bh~BCJaJh~Bh~B5CJaJhF5CJaJh5CJaJhjPhshn;ch hh\lhFJ~hUgh-h~B5CJ\h\l5CJ\hFJ~5CJ\ hLZCJ hUgCJ hFtCJ *xyz{|  678$a$gd~BgdjPgd$a$gdFJ~?Y!Z!j#k#$$&&''(( <Fn|7ei?@BH[anrxy*LY\y#5WE ļĴhUgh2EhayhOvhPhtih%Ahm~\hh'(h h.Nh[h-hKmh6_h*hbKhwIG  /4CO[a,9EK)1@D8m?JKi  t !!Q!V!W!X!Z!!ÿhEh4hdhgdhJ:h`hhNFh2Eh8o hUg<h 6h.NhUghidhKmhz=hbKH!!"""""""##*#7#L#Q#V#]#h#i#k###$$%&K&N&U&&&&&?''(1(((()**M* ,,,, ..s.z....//040`0d0ļԠhRhDh 6h h_E|h_E|h36hn;c h_E|H*h_E|hhvhr vhGh,"hhhbKh."h h8h5]RhQ:AhhEhKm<(L*M*R,T,..//2233=4>4b5c5)7*7I8J8`9l9m9n999J:gdE$a$gd~Bgdd0n0y000001%1:1B1O11111122*2?2u22 33a3f33333=4>4|444444444444455a5c5n555555|666'7(7)7I8ؼhvh h%h4Nh&|1hch`hksh-hghIh[hhG+xh 6h/@hgahNKh hI888`9a9k9l9m9n999999999$:5:J:K:x:::;;;;<<A<B<C<<<<Ǽ|xtmeahRhEhid>* hEh?l h?l hid hEhidhEhG>* hEhGhEhH>>* hEhH> hEh'(hEhE>* hEhE hH>>* hw(hw(hw(h.hX] hw(>*h~Bh~B5>*CJaJhv5CJaJh~B5CJaJh~Bh$h\d#J:K:;;;;<<B<C<==z={===Z>[>>}???gdBMgdGgdH><<===a=b=o=x={=====>>>I>K>Z>[>>l?n?}???миhCghCg5h4NhBMhBMH*h4h,"h,"H*hBMh*)hrth7h($hCgh,"hnL hEh'(hEh'(H*,1h/ =!"#$% @@@ NormalCJ_HaJmH sH tH N@"N ," Heading 2dd@&[$\$5CJ$\aJ$J@J 4N Heading 4$<@&5CJ\aJDA@D Default Paragraph FontViV  Table Normal :V 44 la (k(No List 6>@6 Title$a$ 5CJ\B^@B ," Normal (Web)dd[$\$06X z z z z z z4+/06! Hv xyz{|678 YZjk L"M"q#r# %!%&&d(e(X)Y)**++q-r-..///&0'000O1P111W2X222Z3[3334444555/626!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!xyz{|678 YZjk L"M"q#r# %!%&&d(e(X)Y)**++q-r-..////&0'000O1P111W2X222Z3[3334444555/626000000000000000000000@00000000000000000000000000000000000000000@00000000000000000000000000000000000000000YZjk&&q-r-../0O11122Z34445526K00K00إK00K00K00 K00K00K00\RK00 K00 K00K00K00K0 0ԡI0 0I0 0I0 0 K00I00K00K00K00PsK00K00 K00K00K00K00 $I00K00 !d0I8<? $%&()+(J:?!#'*?"X04Y04TcZ04Կ22ԏ[04l+3\04#]04LS^04 #_04#`04 #a04#b04#ߌ2#d04#e04ęf042h04l/#i04G2,+3k04l04D~m04dn04#==K##,,,,,--)1)122224343@344456626     GPP##,,,,, - --1-16262>3C3C34445,6,626     B*urn:schemas-microsoft-com:office:smarttagscountry-region=*urn:schemas-microsoft-com:office:smarttags PlaceType=*urn:schemas-microsoft-com:office:smarttags PlaceName9*urn:schemas-microsoft-com:office:smarttagsState9*urn:schemas-microsoft-com:office:smarttagsplace8 *urn:schemas-microsoft-com:office:smarttagsCity |h [ ` HNSZ28=DU]cinr.5 & 0 ##0000\1d1p1z111122222[3`34$45595S5X5Y5\526^$j$'0000X223 34444555526::::::::::>>GGE8L"## %a&e(r((((D)D)U)Y)))**]++o-/2626r.@xh ^`OJQJo(8 ^`OJQJo(o8 pp^p`OJQJo(8 @ @ ^@ `OJQJo(8 ^`OJQJo(o8 ^`OJQJo(8 ^`OJQJo(8 ^`OJQJo(o8 PP^P`OJQJo(r.ȣ         HX J, ZͨE}R,I{%sW%{%Z?ͨ.%,IJ,,IZ?E}Ro >FmSXQa6cSJ,{c Ehz! e*bKR 7!`N-ZI3 ?l eU!,"."@$%QG'J'{O*-&|1 636w67O7"886 9J:e;z=H>/@}2@Q:A2E2EREGVMGHEHIIwI~IMBM.N4NE;NDO5P5]R?.SSTLZm~\X]d_*`_<`gaJYbn;cgdid"eUgn@{n8oqHEsrttFtr vG+xay_E|FJ~ &dv`Js@fOv3'( -6rgNFnP+1)b4q[[vRF h}R.Z>ksNK$*)sE _1=~B7nLw(kt+h6_\d"*/, "tiZ0CgF-H/D($Qj%A sjP\lEO1126@%%<;UU%%(H#H$06P@P,P\@UnknownGz Times New Roman5Symbol3& z Arial?5 z Courier New;Wingdings"qhߣ.b.b\24d663QHP(?2%ON THE NATURE OF COAL MINE EXPLOSIONS Zachary Fink Oh+'0 , L X dpx(ON THE NATURE OF COAL MINE EXPLOSIONS NormalZachary Fink3Microsoft Office Word@G@[z@2.՜.+,0  hp|   b6' &ON THE NATURE OF COAL MINE EXPLOSIONS Title  !"#$%&'()*+,./0123456789:;<=>?@ABCDEGHIJKLMOPQRSTUXRoot Entry FpZ1Table-0WordDocument.XSummaryInformation(FDocumentSummaryInformation8NCompObjq  FMicrosoft Office Word Document MSWordDocWord.Document.89q