Handbook for Methane Control in Mining - AMMSA

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dealing directly with the ignition source. When a continuous miner cutter bit strikes rock, abrasionfrom the rock grinds down the rubbing surface of the bit, producing a glowing hot metalstreak on the rock surface behind the bit. The metal streak is often hot enough to ignite methane,causing a so-called frictional ignition.At continuous miner faces, there are two approaches to lower the incidence of frictional ignitions.The first approach concerns the bit itself—providing a regular change-out schedule toreplace worn bits, providing bits with a larger carbide tip to reduce wear, and possibly changingthe bit attack angle or the type of bit.The second approach is to mount a water spray behind each bit, aiming the spray toward thelocation on the rock where the hot metal streak is expected. This anti-ignition back sprayquenches the hot streak, reducing its temperature and the chance of a frictional ignition.Bit changes to reduce frictional ignitions. The most important action one can take to reducefrictional ignitions is to replace bits regularly, thus avoiding the formation of wear flats on thebits. Frictional ignition with a mining bit always involves a worn bit having a wear flat on the tipof the bit [Courtney 1990]. A small wear flat forms a small hot spot, which does not lead to anignition, whereas a large wear flat forms a large hot spot that is more likely to cause an ignition.Also, mining bits consist of a steel shank with a tungsten carbide tip. The steel is more incendiarythan the tungsten carbide tip, so if the tip is worn off and the steel shank exposed, the chanceof an ignition is much greater. As an example, Figure 3–12 shows the results of a test in which acutter bit was used to cut a sandstone block in the presence of an ignitable methane concentration.With the tungsten carbidetip in place, no ignitions wereobtained even after 200 or morecuts. With the steel shankexposed, ignitions quicklybegan. With as little as 0.3-cmbit wear, fewer than 10 cutswere necessary to produce anignition.49Bits that wear more slowly canbe changed less frequently. Bitwear is reduced by using bitsthat have larger carbide tips orby using bits that have a highlyabrasion-resistant polycrystallinediamond layer on the rake faceof the tip.Figure 3–12.—Effect of bit wear on frictional ignition [Courtney1990].Other methods to reduce frictionalignitions are to change theattack angle and tip angle ofconical bits [Courtney 1990] and
50to use radial bits instead of conical bits [Phillips 1996]. McNider et al. [1987] reported adecrease in frictional ignitions by using bits with larger carbide tips and by changing the bitattack angle. 17Anti-ignition back sprays. Anti-ignition back sprays, an effective method to reduce frictionalignitions, are discussed in the longwall chapter (Chapter 4). Bringing water to the cutter headon continuous miners has been an engineering challenge. However, in recent years, practical(if expensive) water seals for continuous miner heads have been developed. As a result, a few“wet-head” continuous miners equipped with anti-ignition back sprays have been installed inU.S. coal mines with a history of frictional ignition problems. Phillips [1997] has provided astatus report on wet-head cutting drums.A thorough review of frictional ignitions in mines,including metal-to-metal ignitions and those fromroof falls, is provided by Phillips [1996].REFERENCES68 Fed. Reg. 40132 [2003]. Mine Safety and Health Administration, 30 CFR Part 75: improvingand eliminating regulations, phase 5, miscellaneous technology improvements (methane testing);final rule.Campbell CD, Dupree WA [1991]. Evaluation of methane dilution capacity of a blowing faceventilation system using a water spray fan and dust scrubber. In: Proceedings of the Fifth U.S.Mine Ventilation Symposium (Morgantown, WV, June 3–5, 1991).CFR. Code of federal regulations. Washington DC: U.S. Government Printing Office, Office ofthe Federal Register.Courtney WG [1990]. Frictional ignition with coal mining bits. Pittsburgh, PA: U.S. Departmentof the Interior, Bureau of Mines, IC 9251. NTIS No. PB91110072.Denk JM, Smith GE, Stoltz RT [1989]. Face ventilation investigation: Wabash mine, I.D. No.11–00877, AMAX Coal Company, Keensburg, Wabash County, Illinois, August 29, 1989-September 1, 1989. Pittsburgh, PA: U.S. Department of Labor, Mine Safety and Health Administration,Pittsburgh Health Technology Center, Ventilation Division, Investigative ReportNo. P313–V218.Denk JM, Younger RK, Mott ML, Chuhta EJ [1988]. Face ventilation investigations: Mary LeeNo. 1 mine, I.D. No. 01–00515–0, Drummond Company, Incorporated, Goodsprings, WalkerCounty, Alabama, October 28-November 4, 1987, and October 18–26, 1988. Pittsburgh, PA:17 Changing the bit attack angle can also raise the cutting force, requiring a change in drum design.
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TMIC 9486Information Circular/2006H
Page 3 and 4: ORDERING INFORMATIONCopies of Natio
Page 5 and 6: ILLUSTRATIONS—ContinuedPage4-6. U
Page 8: HANDBOOK FOR METHANE CONTROL IN MIN
Page 11 and 12: 4Below 5%, called the lower explosi
Page 13 and 14: 6reduced pressure, except at very l
Page 15 and 16: 8Static electricity. Protection aga
Page 17 and 18: 10Figure 1-4.—Estimated methane c
Page 19 and 20: 12LAYERING OF METHANE AT THE MINE R
Page 21 and 22: 14good eyesight. 24methane level.Ot
Page 23 and 24: 16a material balance indicated that
Page 25 and 26: 18As an example, assume that themet
Page 27 and 28: 20Figure 1-10.—Relative frequency
Page 29 and 30: 22Davies AW, Isaac AK, Cook PM [200
Page 31 and 32: 24Margerson SNA, Robinson H, Wilkin
Page 33 and 34: CHAPTER 2.—SAMPLING FOR METHANE I
Page 35 and 36: 29USING PORTABLE METHANE DETECTORST
Page 37 and 38: Out-of-range gas concentrations in
Page 39 and 40: Figure 2-3.—Recorder chart from a
Page 41 and 42: 35Industrial Scientific Corp. [2004
Page 43 and 44: 38peaks, not the overallmethane lev
Page 45 and 46: 40hung on J-hook assemblies, which
Page 47 and 48: 42Methane dilution effectiveness.Th
Page 49 and 50: 44found that effective scrubber ope
Page 51 and 52: 46When the scrubber exhaust is not
Page 53: 48Methane monitors are usually moun
Page 57 and 58: 52Mott ML, Chuhta EJ [1991]. Face v
Page 59 and 60: 54Service, Centers for Disease Cont
Page 61 and 62: 56Methane accumulationsaround thesh
Page 63 and 64: 58corner and by 43% at supportNo. 4
Page 65 and 66: 60When using water sprays to reduce
Page 67 and 68: 62Cecala AB, Zimmer JA, Thimons ED
Page 69 and 70: 64DESIGNING BLEEDER SYSTEMSAs part
Page 71 and 72: 66Caved area characteristics. The c
Page 73 and 74: 68then move this gas into the activ
Page 75 and 76: 70perform tests to determine whethe
Page 77 and 78: 72A major purpose of the bleeder sy
Page 79 and 80: 74• Inlets to the pillared area n
Page 81 and 82: 76REFERENCESCFR. Code of federal re
Page 83 and 84: 78Methane is released into each min
Page 85 and 86: 80Figure 6-1.—Gas content of coal
Page 87 and 88: 82Figure 6-3.—Simplified illustra
Page 89 and 90: 842. In-mine inclined or vertical b
Page 91 and 92: 861. Packed cavity method and its v
Page 93 and 94: 88Table 6-3.—Methane capture rati
Page 95 and 96: 90Early experiences with this metho
Page 97 and 98: 9211. At the surface installation (
Page 99 and 100: 94• Estimated cost for moderately
Page 101 and 102: 96Thakur PC [1981]. Methane control
Page 103 and 104: 98Anomalous, unanticipated methane
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100Vertical methane drainage boreho
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102Figure 7-2 shows a mine entry ap
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104obvious solution to this problem
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106Figure 7-8.—Hypothetical gas c
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108Lama and Bodziony [1998] compile
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110In-mine methane drainage systems
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112Iannacchione AT, Ulery JP, Hyman
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114More sophisticated reservoir eng
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116coal lithotype on gas content is
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118FORECASTING REMAINING GAS-IN-PLA
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120⎛ y⎞⎜⎛⎞ ⎛ ⎞= ⎜
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122emissions. The geometry and size
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124Reservoir models require a subst
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126King GR, Ertekin T [1989a]. A su
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128an area of 314 ft 2 would requir
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130In the case of the abovementione
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132FILLING SHAFTS AT CLOSED MINESFi
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134Hinderfeld G [1995]. Ventilation
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136To calculate the effectiveinert,
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138exhaust. The remaining diesel ex
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140required only 4 min. As a result
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142Figure 11-1.—Desorption test a
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144enclosed in a tunnel-like struct
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146Kolada RJ [1985]. Investigation
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148air in a 6-ft by 9-ft by 6.5-ft
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150represents flammable mixtures. F
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152• In Eastern Europe, petroleum
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154Category II applies to domal sal
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1562. Monitoring for gas and taking
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158These mines typically have large
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160Dave Graham is the safety and he
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162Figure 13-2.—Examples of metha
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164REFERENCESAndrews JN [1987]. Nob
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166APPENDIX A.—ONTARIO OCCUPATION
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169CHAPTER 14.—PREVENTING METHANE
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Ways to confirm the presence of gas
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173The tunnel face is usually venti
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175Figure 14-5.—TBM ventilation s
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face. While one of these elements a
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179ELIMINATING IGNITION SOURCESElec
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181INDEXAAbnormally gassy faces....
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183NNatural ventilation, coal silos
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Delivering on the Nation’s Promis
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