Handbook for Methane Control in Mining - AMMSA

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exhaust gas volume to yield the available inert gas volume. 5 Hot gas velocities can be measuredwith a pitot tube installed in the gas delivery pipe. The readings must be corrected for air densityusing a value of 0.0415 lb/ft 3 to reflect the elevated temperature of about 500 °F.For the system tested, the minimum cooled gas volume found during testing with the combinedengine exhaust was 50 ft 3 /min. The maximum rate of coal removal was 42 ft 3 /min. This calculatesto a 16% excess volume of inert gas for the worst-case conditions—minimum gas volumeand maximum coal removal.Oxygen concentration. If the oxygen concentration can be maintained at 12% or less, measurementof the oxygen concentration alone is sufficient to indicate the inert condition of the gas.These measurements could be made with a handheld oxygen detector or an in-line continuousoxygen detector.During testing [Volkwein and Ulery 1993], a level of 12% oxygen was maintained along with6% carbon dioxide. Since combustion engines always produce carbon dioxide in addition tolowering the oxygen level, the presence of carbon dioxide will provide a safety factor if theoxygen is 12% or less.Placement of the stub pipe and purging the starter hole. For inert gas to be continuouslymaintained at the front of the auger hole, the region just inside the collar of the hole must becontinuously provided with inert gas. However, when the head and lead guide augers are startingthe drilling, there is no room to insert the stub pipe. The ideal time to extend the stub pipeinto the collar of the hole is after a smaller-diameter auger is attached and the hole is just deepenough to make room for the stub pipe (see Figure 10–2). Then the auger is stopped and the stubpipe is installed. After the stub pipe is installed, the auger is not rotated until the starter hole ispurged with inert gas.139When placing a stub pipe, be certain that it extends at least5 ft into the hole. The jet from a shorter stub pipe mightentrain outside air.Purging of the starter hole is necessary because of the air drawn in by the head and lead guideaugers. The time required to purge the starter hole depends on the volume of the hole and thegas flow rate. During testing in the Volkwein and Ulery study, the empty hole volume was216 ft 3 (3.25 ft diameter by 26 ft deep) with about one-half of this volume occupied by the augersteel and cut coal, leaving 108 ft 3 . At an inert gas flow rate of 56 ft 3 /min, one complete airchange occurred in less than 2 min. During testing, engines were run for about 4 min to fill thestarter hole with inert gas before augering proceeded.When insertion of the inert gas stub pipe is delayed, deeper starter holes require much longertimes to become inert. For example, during testing when the hole was augered 44 ft beforeinserting the stub pipe, it took about 12 min to reach inert conditions. By contrast, a 26-ft hole5 This seems like a surprisingly large reduction in volume, but much of it is due to water vapor condensation.
140required only 4 min. As a result, timely placement of the stub pipe is important so that the starterhole does not become too deep before inert gas is added.PRECAUTIONS TO TAKE DURING MININGAn inert gas system will not prevent explosions if it is not operating properly. During mining,the operator of the system must ensure that the concentration of engine exhaust gases stays at orbelow 12% oxygen, that the workplace is free of carbon monoxide, and that there is a steadymovement of gas from the hole.The oxygen level in the engine exhaust gases is easily measuredwith a real-time oxygen indicator that has a readout and providesa warning if the level rises above 12%.Because the exhaust gas from engines contains carbon monoxide, personal exposure to carbonmonoxide should be monitored. During the testing by Volkwein and Ulery [1993], the highestpersonal exposure to carbon monoxide measured with the passive dosimeters was less than20 ppm. This occurred near the auger pin puller. The conveyor side helper had only a trace ofexposure, and the machine operator had no detectable exposure. The combination of dilutionand distance from the collar of the hole accounted for the observed low personal exposure tocarbon monoxide.A steady movement of inert gas from the hole will keep out the surrounding air. This requiresthe operator to observe the direction of movement of dust or smoke during periods of maximumauger penetration. This direction of movement should always be out of the hole.Auger removal. The inert gas system should be left on during auger removal so that the dilutionof gas in the hole takes place with inert gas rather than with air. However, auger removal isusually rapid––about 25 sec per cycle, with 15 sec of that cycle required for pin pulling andstacking of the auger. During the testing by Volkwein and Ulery [1993], rapid removal of theauger steel volume slightly exceeded the inert gas volume, but this excess was not consideredto be significant.REFERENCESFWQA [1970]. Feasibility study on mining coal in an oxygen-free atmosphere. Washington,DC: U.S. Department of the Interior, Federal Water Quality Administration. NTIS No.PB197446.Volkwein JC, Ulery JP [1993]. A method to eliminate explosion hazards in auger highwallmining. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 9462.Zabetakis MG, Stahl RW, Watson HA [1959]. Determining the explosibility of mine atmospheres.Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, IC 7901.
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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
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
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: 138exhaust. The remaining diesel ex
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 and 154: 148air in a 6-ft by 9-ft by 6.5-ft
Page 155 and 156: 150represents flammable mixtures. F
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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