Handbook for Methane Control in Mining - AMMSA

More documents

Recommendations

Info

87The angle of these boreholes withrespect to horizon varies from 20°to 50°, while the axis of the boreholeis inclined to the longwallaxis at 15° to 30°. At least onehole in the roof is drilled at eachsite, but several boreholes in theroof and floor can be drilled atvarying inclinations depending onthe degree of gassiness. Theseholes are then manifolded to alarger pipeline system, and gas iswithdrawn using a vacuum pump.Vacuum pressures vary from 4 to120 in w.g.Figure 6–8.—Partially filled longwall gob.The amount of methane capturedby the drainage system, expressedas a percentage of total methaneemission in the section, variesfrom 30% to 70%. Some typicaldata for U.K. and U.S. mines aregiven by Kimmins [1971] andThakur et al. [1983], respectively,and are shown in Table 6–3.The cross-measure boreholemethod is generally more successfulfor advancing longwallpanels than for retreat faces. Theflow from individual boreholes istypically 20 ft 3 /min, but can occasionallyreach 100 ft 3 /min fordeeper holes. Sealing of the casingat the collar of the borehole isvery important and is usuallydone with quick-setting cement.Sometimes a liner (a pipe ofsmaller diameter than the borehole)is inserted in the boreholeand sealed at the collar to preservethe production from theborehole even when it is shearedby rock movements.Figure 6–9.—Methane drainage with cross-measure boreholes.
88Table 6–3.—Methane capture ratios for postmining methane drainage techniquesMethane drainage technique andRemarksmethane capture ratiosPacked cavity method (after Lidin [1961]):20%–40% .............................................. Caving longwalls.30%–50% .............................................. Partially stowed longwalls.60%–80% .............................................. Fully stowed gobs.Cross-measure boreholes (afterKimmins [1971]):59%–70% .............................................. Highly gassy mines with specific emissions 3,000–6,000ft 3 per ton.Superjacent method:50% ....................................................... For multiple coal seams in the gas emission space.Vertical gob wells:30%–80% .............................................. The methane capture efficiency depends on the number ofgob wells per longwall panel and production techniques.3. Superjacent method: This method was used mainly for retreating longwall faces in highlygassy seams in French mines. Figure 6–10 shows a typical layout. A roadway is driven 70–120ft above the longwall face, preferably in an unworkable coal seam. The roadway is sealed, andvacuum pressures up to 120 in w.g. are applied. To improve the flow of gas, inclined boreholesin the roof and floor are drilled to intersect with other gassy coalbeds. If the mining scheme proceedsfrom the top to the bottom seams in a basin, the entries in a working mine can be used todrain coal seams at lower levels. Methane flow from these entries is high, averaging 700–1,000ft 3 /min for highly gassy seams. Nearly 50% of total emissions have been captured using thismethod.4. Vertical gob well method: This technique, most commonly used in longwall mining in theUnited States, is relatively new and differs from European systems in several ways. U.S. coalseams are generally thin, shallow, and relatively more permeable. Typically, only one seam ismined in a given area and retreat longwall mining is the only method being practiced at present.Methane emission rates from gobs in various coal basins vary depending on the geological conditions,but deep-seated longwall gobs (e.g., those in the Pocahontas No. 3 Seam in Virginia andthe Mary Lee Seam in Alabama) produce methane in the range of 1,800–18,000 ft 3 /min. Multipleentries (typically four) are driven to develop longwall panels so that necessary air quantitiescan be delivered to the longwall faces via the mine ventilation system. In many cases, however,some type of additional methane control becomes necessary.The most popular method of methane control is to drill vertical boreholes above the longwallprior to mining, as shown in Figure 6–11. Depending on the length of the longwall panel (typically10,000 ft) and the rate of mining, 3 to 30 vertical gob degas boreholes are needed. The firsthole is usually within 150–500 ft of the start line of the longwall face. The borehole is drilled towithin 30–90 ft from the top of the coal. The casing is cemented through the fresh water zonesnear the surface, and a slotted liner is provided over the lower open section to prevent closing ofthe hole by caving. These boreholes are completed prior to mining. Usually, no measurablemethane production is realized until the longwall face mines past the borehole.
Page 1 and 2:
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 and 54: 48Methane monitors are usually moun
Page 55 and 56: 50to use radial bits instead of con
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: 861. Packed cavity method and its v
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 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
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
show all

Handbook for Methane Control in Mining - AMMSA

Create successful ePaper yourself

Delete template?

Save as template?