Handbook for Methane Control in Mining - AMMSA

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The above paragraph means that the incombustible content of the dust in intakes must beincreased from 65% to 75% if the ventilating air contains 1% methane. Similarly, the incombustiblecontent of the dust in returns must be increased from 80% to 84% if the ventilating aircontains 1% methane. The incombustible content of the dust mixture includes the rock dust,the ash content of the coal dust, and the moisture content. These regulations are based onresearch conducted at the BEM [Rice and Greenwald 1929; Rice et al. 1933; Nagy 1981].There is an additional hazard when the rock dust is not well mixed with the coal dust. If there isa thin layer of float coal dust (dust that has been carried and deposited by the ventilation air) ontop of a thick layer of properly rock-dusted floor dust, a weak methane explosion may preferentiallylift the top layer of coal dust. The explosion can then continue to propagate through andbeyond the length of the float coal dust deposit. This has been demonstrated in full-scale experimentalmine tests [Nagy et al. 1965; Sapko et al. 1987b].149DANGERS OF HYBRID MIXTURES OF METHANE AND COAL DUSTChapter 1 discusses the lower flammable limit (LFL) 4 for methane and some of the ways thatmethane can be ignited. With only methane present, the LFL is 5% methane in air. However,when coal dust is added to the methane-air mixture, the LFL of the mixture is reduced. This canoccur at the mining face, where methane is being liberated and coal dust is being generated.The Le Chatelier linear mixing law 5 for the LFL of gases is also roughly applicable to a hybridmixture of methane gas and coal dust. Figure 12–1 shows flammable limit data from BEM tests[Cashdollar et al. 1987] for coaldust dispersed with methane.Additional laboratory data [Cashdollar1996; Cashdollar et al.1987] confirm the roughly linearrelationship for various coal dustsmixed with methane. In theexample in Figure 12–1, the LFLof methane alone is 5% and theLFL of the coal dust by itself is0.10 oz/ft 3 . It should be noted thatthis is only an example and thatthe LFL of various coal dusts willvary with the particle size andvolatility. The area below and tothe left of the dashed line in thefigure represents nonflammableFigure 12–1.—Flammable limits for mixtures of methane andcoal dust.mixtures. The area above andto the right of the dashed line4 Also called the lower explosive limit (LEL).5 See the section entitled “Addition of other flammable gases to air” in Chapter 1.
150represents flammable mixtures. For example, if 3.5% methane is present, then any coal dustconcentrations above 0.03 oz/ft 3 are flammable when mixed with the methane. If 2% methane ispresent, then any coal dust concentrations above 0.06 oz/ft 3 are flammable. This means that,if sufficient coal dust is present, an ignition can still occur at the mine face even if the methaneconcentration is below the 5% LFL.REFERENCESCashdollar KL [1996]. Coal dust explosibility. J Loss Prev Process Ind 9(1):65–76.Cashdollar KL, Sapko MJ, Weiss ES, Hertzberg M [1987]. Laboratory and mine dust explosionresearch at the Bureau of Mines. In: Industrial dust explosions. ASTM Special TechnicalPublication (STP) 958. West Conshohocken, PA: American Society for Testing and Materials,pp. 107–123.CFR. Code of federal regulations. Washington DC: U.S. Government Printing Office, Office ofthe Federal Register.Nagy J [1981]. The explosion hazard in mining. Arlington, VA: U.S. Department of Labor,Mine Safety and Health Administration, Informational Report (IR) 1119.Nagy J, Mitchell DW, Kawenski EM [1965]. Float coal hazard in mines: a progress report.Washington, DC: U.S. Department of the Interior, Bureau of Mines, RI 6581.Rice GS, Greenwald HP [1929]. Coal dust explosibility factors indicated by experimental mineinvestigations, 1911 to 1929. Washington, DC: U.S. Department of the Interior, Bureau ofMines, Technical Paper (TP) 464.Rice GS, Greenwald HP, Howarth HC [1933]. Explosion tests of Pittsburgh coal dust in theexperimental mine, 1925 to 1932 inclusive. Washington, DC: U.S. Department of the Interior,Bureau of Mines, Bulletin 369.Sapko MJ, Hertzberg M, Watson RW, Cashdollar KL [1987a]. Dust explosion size scaling. In:Proceedings of the Shenyang International Symposium on Dust Explosions (Shenyang, China,September 14–16, 1987).Sapko MJ, Weiss ES, Watson RW [1987b]. Explosibility of float coal dust distributed over acoal-rock dust substratum. In: Proceedings of the 22nd International Conference of Safety inMines Research Institutes (Beijing, China, November 2–6, 1987).
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TMIC 9486Information Circular/2006H
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ORDERING INFORMATIONCopies of Natio
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ILLUSTRATIONS—ContinuedPage4-6. U
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HANDBOOK FOR METHANE CONTROL IN MIN
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4Below 5%, called the lower explosi
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6reduced pressure, except at very l
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8Static electricity. Protection aga
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10Figure 1-4.—Estimated methane c
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12LAYERING OF METHANE AT THE MINE R
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14good eyesight. 24methane level.Ot
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16a material balance indicated that
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18As an example, assume that themet
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20Figure 1-10.—Relative frequency
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22Davies AW, Isaac AK, Cook PM [200
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24Margerson SNA, Robinson H, Wilkin
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CHAPTER 2.—SAMPLING FOR METHANE I
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29USING PORTABLE METHANE DETECTORST
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Out-of-range gas concentrations in
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Figure 2-3.—Recorder chart from a
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35Industrial Scientific Corp. [2004
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38peaks, not the overallmethane lev
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40hung on J-hook assemblies, which
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42Methane dilution effectiveness.Th
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44found that effective scrubber ope
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46When the scrubber exhaust is not
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48Methane monitors are usually moun
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50to use radial bits instead of con
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52Mott ML, Chuhta EJ [1991]. Face v
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54Service, Centers for Disease Cont
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56Methane accumulationsaround thesh
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58corner and by 43% at supportNo. 4
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60When using water sprays to reduce
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62Cecala AB, Zimmer JA, Thimons ED
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64DESIGNING BLEEDER SYSTEMSAs part
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66Caved area characteristics. The c
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68then move this gas into the activ
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70perform tests to determine whethe
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72A major purpose of the bleeder sy
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74• Inlets to the pillared area n
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76REFERENCESCFR. Code of federal re
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78Methane is released into each min
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80Figure 6-1.—Gas content of coal
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82Figure 6-3.—Simplified illustra
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842. In-mine inclined or vertical b
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861. Packed cavity method and its v
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88Table 6-3.—Methane capture rati
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90Early experiences with this metho
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9211. At the surface installation (
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94• Estimated cost for moderately
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96Thakur PC [1981]. Methane control
Page 103 and 104: 98Anomalous, unanticipated methane
Page 105 and 106: 100Vertical methane drainage boreho
Page 107 and 108: 102Figure 7-2 shows a mine entry ap
Page 109 and 110: 104obvious solution to this problem
Page 111 and 112: 106Figure 7-8.—Hypothetical gas c
Page 113 and 114: 108Lama and Bodziony [1998] compile
Page 115 and 116: 110In-mine methane drainage systems
Page 117 and 118: 112Iannacchione AT, Ulery JP, Hyman
Page 119 and 120: 114More sophisticated reservoir eng
Page 121 and 122: 116coal lithotype on gas content is
Page 123 and 124: 118FORECASTING REMAINING GAS-IN-PLA
Page 125 and 126: 120⎛ y⎞⎜⎛⎞ ⎛ ⎞= ⎜
Page 127 and 128: 122emissions. The geometry and size
Page 129 and 130: 124Reservoir models require a subst
Page 131 and 132: 126King GR, Ertekin T [1989a]. A su
Page 133 and 134: 128an area of 314 ft 2 would requir
Page 135 and 136: 130In the case of the abovementione
Page 137 and 138: 132FILLING SHAFTS AT CLOSED MINESFi
Page 139 and 140: 134Hinderfeld G [1995]. Ventilation
Page 141 and 142: 136To calculate the effectiveinert,
Page 143 and 144: 138exhaust. The remaining diesel ex
Page 145 and 146: 140required only 4 min. As a result
Page 147 and 148: 142Figure 11-1.—Desorption test a
Page 149 and 150: 144enclosed in a tunnel-like struct
Page 151 and 152: 146Kolada RJ [1985]. Investigation
Page 153: 148air in a 6-ft by 9-ft by 6.5-ft
Page 157 and 158: 152• In Eastern Europe, petroleum
Page 159 and 160: 154Category II applies to domal sal
Page 161 and 162: 1562. Monitoring for gas and taking
Page 163 and 164: 158These mines typically have large
Page 165 and 166: 160Dave Graham is the safety and he
Page 167 and 168: 162Figure 13-2.—Examples of metha
Page 169 and 170: 164REFERENCESAndrews JN [1987]. Nob
Page 171 and 172: 166APPENDIX A.—ONTARIO OCCUPATION
Page 174 and 175: 169CHAPTER 14.—PREVENTING METHANE
Page 176 and 177: Ways to confirm the presence of gas
Page 178 and 179: 173The tunnel face is usually venti
Page 180 and 181: 175Figure 14-5.—TBM ventilation s
Page 182 and 183: face. While one of these elements a
Page 184 and 185: 179ELIMINATING IGNITION SOURCESElec
Page 186 and 187: 181INDEXAAbnormally gassy faces....
Page 188 and 189: 183NNatural ventilation, coal silos
Page 190 and 191: Delivering on the Nation’s Promis
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