Handbook for Methane Control in Mining - AMMSA

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techniques rely on matching the actual gas production data plots (prepared with the same set ofunits and graphical form as in the type-curves) to the theoretical curves. These techniques canalso be used to analyze production decline curves to predict remaining gas-in-place and futureemissions for mine safety assessments [Chen and Teufel 2000]. In addition, if the gas productionis exclusively from the coalbed to be mined, type-curve analysis can provide other reservoirinformation that needs to be determined for emission forecasting studies (e.g., modeling).In summary, type-curves can contribute to:• Stimulation (fracturing) effectiveness diagnosis• Recovery efficiency (recovery factor based on initial gas-in-place)• Estimation of reservoir flow properties (permeability, flow capacity, etc.)• Reservoir storage properties• Future prediction of production119Both production decline analysis and type-curve matchingtechniques can be used to analyze methane drainageboreholes for future production rates and thus predict theremaining gas-in-place at the time of mining. However,gas emissions from different gas sources may becommingled, especially during longwall mining.Therefore, one can expect higher emission rates duringmining compared to what is predicted by the analysis.PREDICTING GAS EMISSIONS DURING MININGThe main sources for gas (generally predominantly methane) that can be released into the undergroundmine workings are the mined and adjacent coalbeds and other surrounding gas-bearingstrata [Mucho et al. 2000; Diamond et al. 1992]. Mining activities disturb the existing stressequilibrium in the rock mass and create changes to the structural integrity of the affected strata.The mining processes can thus create sudden and unstable gas problems, which may increase therisk of an explosion in the underground workplace. Gas flow from these sources is initiated andmaintained by differential pressures between the source (higher pressure) and the mine workings(lower pressure). The flow paths are both the naturally occurring rock joints, faults, and coalcleat, as well as mining-induced fractures in the surrounding strata.It is generally observed that the amount of gas released during the mining process is greater thanthat contained in the actual volume of coal mined at the face [Kissell et al. 1973]. This apparentdiscrepancy is due to the continual emission of gas from the coal that is left in place as ribs andpillars, as well as the migration of gas from the surrounding strata, including the longwall gob[Mucho et al. 2000]. Methane emission rates change over time in the life cycle of a minebecause of the interaction of variable geotechnical, mine design, and operational factors. Thefollowing mathematical formula by Lunarzewski [1998] addresses this phenomenon and calculatesthe quantity of gas released into a mine during various stages in the life of a mine:
120⎛ y⎞⎜⎛⎞ ⎛ ⎞= ⎜ ⎟ + − ⎜ ⎟ + ⎟⎜∑ + 1mymgQ ( y)C 1 ∑C1 ,CA⎟⎝⎝0 ⎠ ⎝ 0 ⎠ ⎠(4)where Q(y) is the average methane emission (cubic meters of methane) in a year “Y” of the mine’sexistence, CA is the coal output in 1 year only (tons), C is the total coal output for the life of themine up to year “Y”, and g and m are coefficients dependent upon geological and miningconditions.The highest gas emissions can be expected as the coal is extracted and the floor and roof strataare relaxed. The instantaneous volume of gas released from all potential sources when 1 ton of coalis extracted can be calculated, and practical experience has shown that gas emissions are related todaily and weekly coal production levels and to the time factor, as follows [Lunarzewski 1998]:Q = a CP + b ,(5)where Q is the total methane emission rate expressed in liters of methane per second, CP is thedaily coal production rate in tons, and a and b are empirical constants related to weekly coalproduction levels and number of working days per week [Lunarzewski 1998].Figure 8–3.—PFG/FGK method to predict gas emissions in apreviously disturbed zone [Noack 1998]. PFG = degree of gasemission curve for the roof; FGK = degree of gas emission curvefor the floor.Another empirical method to predictthe total gas emissions fromlongwall mining is the use ofdegree-of-gas emission curves.Figure 8–3 is an example of adegree-of-gas emission curve forpreviously disturbed roof andfloor strata in a slightly to moderatelydipping coalbed [Noack1998]. In such a condition, theprediction can be made assumingthat the emitted methane proportionis not a function of the initialgas content, but rather a functionof the geometric location withrespect to the longwall face[Noack 1998]. For practicalpurposes, the upper boundary ofthe zone from which gas can bereleased is assumed to be at+541 ft (+165 m), whereas thelower boundary is at -194 ft(-59 m). In the absence of gasemission measurements, a meandegree of gas emission of 75% ofthe gas content in the mined
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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
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
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: 118FORECASTING REMAINING GAS-IN-PLA
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 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
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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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