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Mining a coal seam below a heating goaf with a force auxiliary ventilation system at Longhua underground coal mine, China
International Journal of Mining Science and Technology 25 (2015) 67–72
Contents lists available at ScienceDirect
International Journal of Mining Science and Technology journal homepage: www.elsevier.com/locate/ijmst
Mining a coal seam below a heating goaf with a force auxiliary ventilation system at Longhua underground coal mine, China Wang Gang a, Xie Jun a,b,⇑, Xue Sheng b,c, Wang Haiyang a a
State Key Laboratory of Mining Disaster Prevention and Control, Shandong University of Science & Technology, Qingdao 266590, China CSIRO Earth Science and Resource Engineering, Kenmore 4069, Australia c School of Mining Engineering, Taiyuan University of Technology, Taiyuan 030024, China b
a r t i c l e
i n f o
Article history: Received 2 April 2014 Received in revised form 25 May 2014 Accepted 19 July 2014 Available online 7 February 2015 Keywords: Force auxiliary ventilation system Mining under a heating goaf Multiple seams of close spacing Pressure balance
a b s t r a c t Extraction of a coal seam which lies not far below a heating goaf can be a major safety challenge. A force auxiliary ventilation system was adopted as a control method in successful extraction and recovery of the panel 30110 of the #31 coal seam, which is about 30–40 m below the heating goaf of the #22 seam at Longhua underground coal mine, Shanxi Province, China. Booster fans and ventilation control devices such as doors and regulators were used in the system. The results show that, provided that a force auxiliary ventilation system is properly designed to achieve a pressure balance between a panel and its overlying goaf, the system can be used to extract a coal seam overlain by a heating goaf. This paper describes the design, installation and performance of the ventilation system during the extraction and recovery phases of the panel 30110. Ó 2015 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
1. Introduction When a coal seam lying not far below a heating goaf is extracted, the fractures both naturally occurred and mininginduced in the interburden between the seam and the goaf may provide migration passages for gases in goaf. And carbon monoxide (CO) and carbon dioxide (CO2) can flow into the working faces and threaten the safety production. Air in the working faces may also be leaked into the goaf through passages to intensify the goaf heating. Ideally, the goaf heating should be controlled or extinguished prior to the extraction of the coal seam below the goaf. However, sometimes the goaf heating can be quite extensive and difficult to be detected, located and controlled, and the cost of controlling the heating cannot be justified economically [1,2]. In these cases, one of practical alternatives is to consider the use of pressure balancing techniques to minimize pressure differential across the area affected [3]. Pressure balancing can be achieved by a number of methods such as reducing airflow and construction of balancing chambers, which depends on the range and nature of the pressure to get balance [4–7]. Some fundamental studies have been undertaken in the extraction of coal below a heating goaf. Numerical modelling and ⇑ Corresponding author. Tel.: +61 7 33274119. E-mail address: [email protected] (J. Xie).
statistical analyses were used to study fracture evolution in the floor strata of a heating goaf at Shigejie coal mine. It was concluded that heating had no significant effect on generation and propagation of fractures and the maximum height of the fractures formed in the floor strata was about 10 m [8,9]. A number of mathematical models have been developed to simulate the multi-component gases flow in the fractured interburden between a mining seam and its overlying heating goaf [10,11]. The use of a force auxiliary ventilation system in the seam extraction has been attempted as a control method in the prevention of air/gas flow between the mining seam and its overlying heating goaf with mixed results [12,13]. This paper describes a force auxiliary ventilation system, which is adopted in #30110 longwall panel at Longhua coal mine and its performance. The system aims to balance the pressure between the longwall face and its overlying heating goaf. The system consists of the booster fans, doors and regulators. A number of manometers and CO sensors were installed in and around the panel to monitor the system performance. The panel was successfully retreated and recovered with the system.
2. Site conditions 2.1. Longhua coal mine The Longhua coal mine is located in Yulin city, Shanxi province, China. The mine is a longwall operation which produces about
http://dx.doi.org/10.1016/j.ijmst.2014.11.009 2095-2686/Ó 2015 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
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G. Wang et al. / International Journal of Mining Science and Technology 25 (2015) 67–72 Table 1 Lithology of the interburden between the Nos. 31 and 22 seams.
Layer
Thickness (m)
Depth below surface (m)
Lithology
2.43-2.75
50-60
No. 2-2 seam
Mainly siltstone and finely grained sandstone, interbedded with two layers of medium grained sandstone (about 5 m thick).
30-40
2.79-3.10
4 Mt/a. The target seam of economic interest is the No. 31 seam. This seam is about 3 m thick and about 90–100 m below the ground surface. The seam lies about 30–40 m below the No. 22 seam which was mined with the border and pillar method. The goaf of the #22 seam undergoes self-heating. Both seams are near flat and free of major geological structures. The interburden between the seams is dominated by siltstone and finely grained sandstone. Table 1 shows the lithology of the interburden. 2.2. No. 30110 longwall panel The No. 30110 longwall panel of the #31 seam is 250 m wide, 1979 m long and 3.1 m high. The U-type exhausting ventilation system (Fig. 1) is used. Field investigations indicated that, close to the panel finish line, there was an extensive heating zone in the goaf of #22 seam directly above the panel 30110 and a large
30111 goaf
30110 panel
90-100
No. 3-1 seam
amount of hazardous gases were contained in the goaf. The CO concentration of the goaf was measured to be as high as 1.5%. As the panel started to retreat, the overburden roof units started to deform, fracture and cave. This resulted in the formation of three zones in the roof, i.e., caved zone, fractured zone and deformation zone. The combined height of the caved and fractured zones was estimated to be in the range of 41.1–58.9 m [14,15], which was larger than the thickness of the interburden between the panel and heating goaf, indicating that the extensive fractures existed in the interburden and the gases of the goaf such as CO could readily flow into the panel. It was proven to be the case that the CO concentration at the return corner of the face often was in the range of 2 105 to 5 105 at the initial stage of the panel retreat and CO was identified to be from the goaf of the 22 seam. Furthermore, the CO concentration at the return corner of the face showed a worrying increment trend as the panel retreat progressed.
30109 panel
Main recovery roadway Auxiliary recovery roadway
Secondary main gateroad
Main Return gateroad gateroad Main intake Main intake Main return
Heating zone boundary Fresh air Return air Seal
Fig. 1. Layout of the No. 30110 panel and heating zones in the goaf of the No. 22 seam.
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2.3. Heating in the goaf of the No. 22 seam Extensive heating zones in the goaf of the #22 seam develop due to two main factors. One factor is a large amount of coal left in the goaf because of a relatively low coal extraction rate with the border and pillar method used in the #22 seam extraction, and the other is the air leakage getting into the goaf from the ground surface because of its shallow buried depth (50–60 m below the ground surface). The Longhua coal mine had attempted to control the heating in the goaf with various techniques such as nitrogen inertisation, gel injection, and blockage of air leakage. However, these measures were proven to be ineffective and quite expensive. At the beginning of the panel 30110 retreat, there was still an extensive hot spot zone in the goaf of the 22 seam directly above the panel (Fig. 1). 3. A force auxiliary ventilation system A force auxiliary ventilation system was designed in the panel 30110 to stop the gas flow between the panel face and its overlying goaf of the 22 seam. On the one hand, the system could stop the goaf gases from flowing into the corner, meaning that they will not be able to flow into any points around the face, and on the other hand, it can prevent the fresh air of the face from leaking into the goaf. The best pressure balance point was designed to be at the middle position between the return corner of the face and the goaf of the 22 seam as the return corner was the lowest pressure point in the face in the U-type ventilation system. 3.1. System components The force auxiliary ventilation system includes booster fans, doors and regulators. Four booster fans were installed in the #1 cut-through of the panel, and two of them were connected in parallel and the other two were for backup. Each of the fans has a speed of 2960 r/min, a pressure range of 1100–6000 Pa and a flow rate between 730 and 400 m3/min. Two doors were installed in the panel intake gateroad and one regulator (mesh door in this case) was installed in the panel return gateroad. The exact location and layout of the system are shown in Fig. 2. 3.2. Estimate of gas pressure between the face return corner and the goaf A U-type water tube (manometer) was installed in the main panel recovery gateroad and was connected to the goaf of the
No. 22 seam. The gas pressure in the goaf was estimated by gas pressure at the recovery gateroad and the manometer, as shown in Fig. 3. Prior to the implementation of the force auxiliary ventilation system in the panel, gas pressure in the goaf of the #22 seam was higher than that in the panel face and can be calculated as:
Pgoaf ¼ p0 þ PU qgh
ð1Þ 2
where Pgoaf is the gas pressure in the goaf of the #2 seam, Pa; p0 the gas pressure in the main recovery gateroad, Pa; P U the reading of the manometer, Pa; q the density of air in the panel, 1.073 kg/ m3; g the gravitational acceleration, 9.8 N/kg; and h the thickness of the interburden between the Nos. 31 and 22 seams, 37.6 m. P U and p0 were measured to be 230 Pa and 87.98 kPa, respectively. Using Eq. (1), gas pressure in the goaf of the #22 seam is calculated to be 87.82 kPa. Let A, B, C, D denote four specific points around the panel, as shown in Fig. 2. Specifically, A represents the point next to the boost fans, B represents the face return corner, C represents the point just before the regulator, and D is the point just after the regulator. To make gas pressure balance point between the return corner and the goaf of the #22 seam at half way of the interburden (h/2), gas pressure at the return corner (PB) must satisfy Eq. (2) and was calculated to be 88.41 kPa.
3 PB ¼ P goaf þ qgh 2
ð2Þ
3.3. Estimate of gas pressure difference across the regulator With the force auxiliary ventilation system in the panel 30110, the pressure loss from points A to B (fAB) can be calculated as follows (ignoring the panel air leakage):
f AB ¼ ðP A PB Þ þ
q
A
2
m2A
qB 2 mB þ ðqA gzA qB gzB Þ ¼ RAB Q 2 2
ð3Þ
where PA is the gas pressure at point A, Pa; PB the gas pressure at point B, Pa; qA the air density at point A, kg/m3; qB the air density at point B, kg/m3; zA the elevation at point A above sea level, m; zB the elevation at point B above sea level, m; and RAB the frictional resistance between points A and B, kg/m7. mA is the velocity at point A, m/s; and mA ¼ Q =SA , where Q is the panel air flowrate, m3/s; and SA the cross sectional area at point A, m2. mB is the velocity at point B, m/s; and mB ¼ Q =SB , where SB is the cross sectional area at point B, m2. The pressure loss from points B to C (fBC) can be calculated as follows:
f BC ¼ ðP B PC Þ þ
q
B
2
m2B
qC 2 mC þ ðqB gzB qC gzC Þ ¼ RBC Q 2 2
ð4Þ
where PC is the gas pressure at point C, Pa; qC the air density at point C, kg/m3; zC the elevation at point C above sea level, m; and
B 30110 panel
Pgoaf
2-2goaf
Monitoring borehole
#1 Cut-through
h
C D Main intake Main intake Main return
Seal wall Air door Regulating air window Booster fan Fresh air Return air
Fig. 2. Force auxiliary ventilation system in the panel 30110.
PU P
30110 Main recovery roadway
U type water tube
Fig. 3. Layout of manometer at the main panel recovery gateroad.
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#E
#C
#D #90 support
#60 support
#B #30 support
#F
13
Main gateroad
12 11 10 9 8 7 6 #6
Main recovery roadway
5 4 3 21 #5 #4
Auxiliary recovery roadway
#7
DPCD ¼ PC PD
“U” type water tube CO sensor Boreholes connected to the 2-2 seam goaf Boreholes not connected to the 2-2 seam goaf
ð5Þ
Field measurements showed that: PA = 88,530 Pa, PB = 88,410 Pa, PD = 87,960 Pa, qA = 1.061 kg/m3, qB = 1.062 kg/m3, qC = 1.062 kg/m3, zA = 1094.4 m, zB = 1094.3 m, zC = 1094.0 m, SA = 12.8 m2, SB = 16.5 m2, SC = 14.9 m2, RAB = 0.234 kg/m7, and RBC = 0.086 kg/m7. Using Eqs. (3)–(5), gas pressure at point C was calculated to be 88,372 Pa and pressure difference from points C to D is 412 Pa. That means that in order to ensure the pressure balance point between the #30110 panel face and the goaf of the #22 seam is at half way of the interburden (h/2), pressure difference across the regulator should be around 412 Pa.
Secondary main gateroad
30110 panel Return gateroad
The pressure difference between points C and D (DPCD ) can be written as:
#A
A10 #1 A9 A8 #2 A7 A1 A6 #3 A2 A5 A4 A3
3.4. Adjustment to the system during its operation To account for actual mining and ventilation conditions in the panel 30110 and to allow for 10% shifting of the gas pressure balance position in the interburden, the pressure difference across the regulator was slightly adjusted during the operation of the force auxiliary ventilation system. With the force system in operation, gas pressure at the #30110 panel face was higher than that in the goaf of the #22 seam.
Fig. 4. Layout of manometers and CO sensors around the panel 30110.
RBC the frictional resistance between points B and C, kg/m7. mC is the velocity at point C, m/s; and mC ¼ Q =SC , where SC is the cross sectional area at point C, m2.
Pgoaf ¼ p0 PU q gh
ð6Þ
Table 2 Monitored results of CO and pressure difference in the panel 30110. Date
6.21 6.22 6.23 6.24 6.25 6.26 6.26 6.28 6.29 6.30 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 7.10 7.11 7.12 7.13 7.14 7.15 7.16 7.17 7.18 7.19 7.20 7.21 7.22 7.23 7.24 7.25 7.26 7.27 7.28 7.29
S1 (m)
S2 (m)
338 223 330 215 315 200 304 189 288 173 273 158 257.5 142.5 257.5 142.5 257.5 142.5 257.5 142.5 257.5 142.5 244.5 129.5 229.5 114.5 213.5 98.5 200 85 184 69 168 53 150 35 135 20 120 5 104.5 The face retreating directly under a heating zone 104.5 87.5 71.5 56.5 41 25 10 0 The panel recovery
CO (106)
Pressure difference (Pa) #1
#2
#3
#4
#5
110 110 110 100 110 120 110 110 100 100 110 90 110 120 110 110 100 120 120 80 80 80 100 90 100 110 120 120 100 120 130 110 120 120 120 120 120 100 110
120 130 120 120 110 120 100 120 130 120 120 110 110 100 110 120 120 100 100 80 80 80 100 100 100 100 120 120 100 120 120 110 120 120 140 130 130 120 130
110 120 100 100 110 110 110 120 110 120 130 110 120 120 100 110 100 110 120 100 100 100 120 120 110 120 150 120 120 130 120 130 130 130 130 130 120 140 130
130 150 150 140 130 150 120 150 120 130 130 130 120 150 120 150 140 150 140 150 130 150 130 150 130 160 130 140 110 150 130 140 130 160 120 150 120 160 100 180 120 180 120 180 130 170 120 130 150 130 140 120 180 150 120 150 140 150 150 150 130 150 140 130 The manometers dismantled face recovery
#6 180 170 180 170 190 190 190 180 180 190 200 200 200 180 180 200 200 190 190 210 220 220 210 160 170 180 120 180 150 100 160 130 due to the
#7
#A
#B
#C
#D
#E
350 360 360 360 350 360 360 360 360 360 360 350 350 360 360 360 350 360 340 340 350 360 350 360 330 340 350 340 340 340 340 340 330 340 340 330 320 320 350
0 1 2 0 0 0 1 0 3 1 1 2 2 0 0 0 3 0 2 2 2 1 0 0 0 1 1 2 4 1 0 3 1 1 2 3 0 0 0
1 2 1 2 4 1 0 3 1 0 3 0 0 2 1 3 2 0 0 2 2 4 4 3 2 0 0 0 6 5 4 3 3 1 1 0 0 5 2
2 2 0 5 3 3 0 4 0 5 5 5 3 6 3 3 2 0 4 4 2 3 1 2 2 3 0 2 1 2 1 2 3 4 4 0 5 3 3
2 4 4 3 5 4 5 5 3 3 1 0 0 3 6 3 5 4 6 4 3 3 3 5 2 0 4 3 3 2 0 2 2 4 2 4 3 3 1
5 3 6 4 4 4 5 6 5 5 3 4 6 6 6 5 4 4 3 5 5 7 6 3 3 4 6 5 5 8 2 0 4 4 6 5 7 6 6
Note: S1 is the distance from the panel face to the panel finish line; and S2 is the distance from the panel face to the boundary projected downward into the panel horizon from the overlying heating zone in the goaf.
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#6
ΔP (Pa)
100
7. 19
15 7.
7. 11
7. 07
03 7.
6. 29
6. 25
50 Date Fig. 6. Pressure difference monitored with manometers #4 to #6.
420 400
ð8Þ
“
” represents the range of (338 Pa, 417 Pa)
380 360 340 320 300
6. 21 6. 25 6. 29 7. 03 7. 07 7. 11 7. 15 7. 19 7. 23 7. 27
! DP > Pgoaf þ 75 qgh þ q2B m2B q2C m2C þ qB gzB qC gzC RB DP < Pgoaf þ 85 qgh þ q2B m2B q2C m2C þ qB gzB qC gzC RB
#5
150
ð7Þ
It was measured that, with the operation of the force ventilation system, the face flow rate (Q) was 13 m3/s, gas pressure (PC) before the regulator was 88370 Pa and PU was 380 Pa. Thus using Eq. (5), gas pressure after the regulator was calculated to be 87,990 Pa. Using Eqs. (4), (5) and (7), the range of pressure difference across the regulator (DPCD) can be calculated using Eq. (8) to be between 338 Pa and 417 Pa.
#4
200
ΔP (Pa)
Pgoaf
7 8 þ qgh < PB < Pgoaf þ qgh 5 5
250
6. 21
P U and p0 were measured to be 180 Pa and 88,360 Pa, respectively. Using Eq. (6), gas pressure in the goaf of the #22 seam was calculated to be 87,785 Pa. If the gas pressure balance position is allowed to shift by 10% in the interburden between the face return corner and the goaf of the #22 seam, then it should be kept within the zone of (2h/5, 3h/5) and gas pressure at the face return corner (PB) must satisfy Eq. (7).
Date
4. Performance of the force auxiliary ventilation system
160
#1
#2
#3
ΔP (Pa)
140 120 100 80
6.
21 6. 25 6. 29 7. 03 7. 07 7. 11 7. 15 7. 19 7. 23 7. 27
60 Date Fig. 5. Pressure difference monitored with manometers #1 to #3.
Fig. 7. Pressure difference monitored with manometer #7.
“ ” is the maximum allowable CO limit specified in “Coal Mine Safety Regulations”
#C
#D
#E
7. 11 7. 15 7. 19 7. 23 7. 27
7. 07
#B
7. 03
6. 29
#A
6. 25
28 24 20 16 12 8 4 0
6. 21
CO concentration (×10-6)
To study the performance of the force auxiliary ventilation system, three sets of key parameters are monitored. These were gas pressure difference between the #30110 panel and the goaf of the #22 seam, gas pressure difference across the regulator, and CO concentration in the panel 30110. Seven manometers (U-type tubes in this case) were installed in the panel. Six of them (#1 to #6) were used to monitor pressure difference between the panel and the goaf of the #22 seam and the other one (#7) was to monitor gas pressure difference across the regulator. Five CO sensors (#A, #B, #C, #D and #E) were used to monitor CO concentration at various positions in the panel face (from the intake corner to return corner). The exact location and layout of these manometers and CO sensors are shown in Fig. 4. The force auxiliary ventilation system became operational on the 21st of June, 2012 when the panel face was retreated 1346 m from its start-up line. The face was retreated directly under a heating zone of the goaf of the #22 seam on the 10th July. By the 19th of July, the face was retreated to its finish line and this was immediately followed by the face recovery phase. On the 29th of July the face was fully recovered. Monitored results for the period from June 21st to July 29th are shown in Table 2 and Figs. 5–8. The pressure difference between the panel face and the goaf of the #22 seam is an important indicator about the stability of the ventilation system, and a critical reference to decide if the ventilation system requires any adjustment. The results from Table 2 and Fig. 5 indicated that the pressure differences at manometers #1, #2 and #3 were kept around 100 Pa for most of the monitoring period except for about three days (from the 10th to 12th of July), and a
Date Fig. 8. CO concentrations in the #30110 panel face.
significant drop in the pressure difference (around 80 Pa) was observed. The pressure difference was back to around 100 Pa after the regulator was adjusted. The pressure differences at manometers #4 and #5 were kept around 140–150 Pa (Fig. 6). The results from Fig. 6 also indicated that the readings from monometer #6 were around 190 Pa, and a significant drop was observed after the 14th of July, however, it was again controlled to around 150 Pa after the regulator was adjusted. No. 7 manometer was used to monitor the pressure difference across the regulator. Fig. 7 indicated that the pressure difference was kept between 340 and 360 Pa for most of the operation period. This was within the range of 338–417 Pa, as recommended in Section 3 of this paper. Although the pressure difference across the regulator was dropped slightly below the lower limit of the recommended range during the longwall recovery phase (on the 23rd, 26th to 28th of July), it was brought into the safe range through prompt adjustments of the regulator and no adverse effect on the panel operation was resulted, indicating stable running of the force auxiliary ventilation system. CO concentration was monitored along the panel face with the force auxiliary ventilation system, and the monitored results are shown in Fig. 8. The results from Fig. 8 clearly showed that CO concentration in the face was below 8 106, well below the maximum allowable limit of 24 106 specified in ‘‘Coal Mine Safety Regulations’’ in China. No incidence of sudden CO rush from the goaf of the #22 seam into the #30110 panel face occurred with
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the force ventilation system in operation, and the panel was successfully retreated and recovered. 5. Conclusions Based on the studies in Longhua coal mine, the following conclusions can be drawn: (1) A force auxiliary ventilation system was used as an alternative and effective method to control gas flow between the panel 30110 and its overlying heating goaf lying about 30– 40 m above the panel. The system consists of four booster fans, two doors and one regulator. The system hazardous gases in the goaf were stopped from entering into the panel face and the air in the panel face was prevented from leaking into the goaf during the panel extraction. (2) The success in using a force auxiliary ventilation system depends on selection of the best gas pressure balance position between a panel face and its overlying heating goaf and pressure control at key points of the ventilation system. In the case of the panel 30110, pressure difference across the regulator should be controlled around 412 Pa and the pressure balance position between the face return corner and the goaf should be half way through their interburden. (3) Seven manometers and five CO sensors were installed to monitor gas pressure difference and CO concentration in the panel 30110. Gas pressure and CO monitoring at some key locations in the ventilation system and prompt adjustments of pressure distribution in the system (if required) were an integrated parts of the system design, its implementation to ensure safe and effective operation of the system.
Acknowledgments The work was supported by the Scientific Research Foundation of Shandong University of Science and Technology for Recruited
Talents and Science Research Innovative Group of Resources and Environment Engineering College of Shandong University of Science and Technology (No. 2012ZHTD06), the Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents (No. 2013RCJJ049), the China Postdoctoral Science Foundation (No. 2013M541942), and the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20133718120013). References [1] Colaizzi GJ. Prevention, control and/or extinguishment of coal seam fires using cellular grout. Int J Coal Geol 2004;59:75–81. [2] Cao K, Zhong X, Wang D, Shi G, Wang Y, Shao Z. Prevention and control of coalfield fire technology: a case study in the Antaibao open pit mine goaf burning area, China. Int J Min Sci Technol 2012;22:657–63. [3] Poborowski B, Chen A. Spontaneous combustion management comparison between Australia and China. In: Proceedings of Australian mine ventilation conference, Sydney; 2011. p. 79–83. [4] Ray S, Singh R. Recent developments and practices to control fire in underground coal mines. Fire Technol 2007;43(4):285–300. [5] Wang DM. Mine fires. Xuzhou: China University of Mining and Technology Press; 2009. [6] Cliff D, Rowlands D, Sleeman J. Spontaneous combustion in Australian underground coal mines. Queensland: SIMTARS; 1996. [7] Walker S. Uncontrolled fires in coal and coal wastes. London: IEA Coal Research-The Clean Coal Centre; 1999. [8] Wu Q, Tu S, Dou F, Wang F. Study on law of fracture development in multiseam mining below fire area. Coal Mine Saf 2010;3:13–5. [9] Pan RK, Cheng YP, Yu MG, Lu C, Yang K. New technological partition for ‘‘three zones’’ spontaneous coal combustion in goaf. Int J Min Sci Technol 2013;23:489–93. [10] Li Z, Lu Z, Wu Q, Zhang A. Numerical simulation study of goaf methane drainage and spontaneous combustion coupling. J China Univ Min Technol 2007;17(4):503–7. [11] Wolf KH, Bruining H. Modelling the interaction between underground coal fires and their roof rocks. Fuel 2007;86(17–18):2761–77. [12] Zhang Q, Wang S, Li S. Practical application of pressure regulating technique in burning section of Meiyukou coal mine. China Saf Sci J 2001;11(2):52–6. [13] Guo H, Wu B, Wang L, Zhao C. Treatment technology of multi-seam fire area in positive pressure ventilation. Coal Mine Saf 2012;5:33–5. [14] Xu X, Zhang N, Tian S. Mining-induced movement properties and fissure timespace evolution law in overlying strata. Int J Min Sci Technol 2012;22:817–20. [15] Zhang D, Qi X, Yin G, Zheng B. Coal and rock fissure evolution and distribution characteristics of multi-seam mining. Int J Min Sci Technol 2013;23:835–40.
Contents lists available at ScienceDirect
International Journal of Mining Science and Technology journal homepage: www.elsevier.com/locate/ijmst
Mining a coal seam below a heating goaf with a force auxiliary ventilation system at Longhua underground coal mine, China Wang Gang a, Xie Jun a,b,⇑, Xue Sheng b,c, Wang Haiyang a a
State Key Laboratory of Mining Disaster Prevention and Control, Shandong University of Science & Technology, Qingdao 266590, China CSIRO Earth Science and Resource Engineering, Kenmore 4069, Australia c School of Mining Engineering, Taiyuan University of Technology, Taiyuan 030024, China b
a r t i c l e
i n f o
Article history: Received 2 April 2014 Received in revised form 25 May 2014 Accepted 19 July 2014 Available online 7 February 2015 Keywords: Force auxiliary ventilation system Mining under a heating goaf Multiple seams of close spacing Pressure balance
a b s t r a c t Extraction of a coal seam which lies not far below a heating goaf can be a major safety challenge. A force auxiliary ventilation system was adopted as a control method in successful extraction and recovery of the panel 30110 of the #31 coal seam, which is about 30–40 m below the heating goaf of the #22 seam at Longhua underground coal mine, Shanxi Province, China. Booster fans and ventilation control devices such as doors and regulators were used in the system. The results show that, provided that a force auxiliary ventilation system is properly designed to achieve a pressure balance between a panel and its overlying goaf, the system can be used to extract a coal seam overlain by a heating goaf. This paper describes the design, installation and performance of the ventilation system during the extraction and recovery phases of the panel 30110. Ó 2015 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
1. Introduction When a coal seam lying not far below a heating goaf is extracted, the fractures both naturally occurred and mininginduced in the interburden between the seam and the goaf may provide migration passages for gases in goaf. And carbon monoxide (CO) and carbon dioxide (CO2) can flow into the working faces and threaten the safety production. Air in the working faces may also be leaked into the goaf through passages to intensify the goaf heating. Ideally, the goaf heating should be controlled or extinguished prior to the extraction of the coal seam below the goaf. However, sometimes the goaf heating can be quite extensive and difficult to be detected, located and controlled, and the cost of controlling the heating cannot be justified economically [1,2]. In these cases, one of practical alternatives is to consider the use of pressure balancing techniques to minimize pressure differential across the area affected [3]. Pressure balancing can be achieved by a number of methods such as reducing airflow and construction of balancing chambers, which depends on the range and nature of the pressure to get balance [4–7]. Some fundamental studies have been undertaken in the extraction of coal below a heating goaf. Numerical modelling and ⇑ Corresponding author. Tel.: +61 7 33274119. E-mail address: [email protected] (J. Xie).
statistical analyses were used to study fracture evolution in the floor strata of a heating goaf at Shigejie coal mine. It was concluded that heating had no significant effect on generation and propagation of fractures and the maximum height of the fractures formed in the floor strata was about 10 m [8,9]. A number of mathematical models have been developed to simulate the multi-component gases flow in the fractured interburden between a mining seam and its overlying heating goaf [10,11]. The use of a force auxiliary ventilation system in the seam extraction has been attempted as a control method in the prevention of air/gas flow between the mining seam and its overlying heating goaf with mixed results [12,13]. This paper describes a force auxiliary ventilation system, which is adopted in #30110 longwall panel at Longhua coal mine and its performance. The system aims to balance the pressure between the longwall face and its overlying heating goaf. The system consists of the booster fans, doors and regulators. A number of manometers and CO sensors were installed in and around the panel to monitor the system performance. The panel was successfully retreated and recovered with the system.
2. Site conditions 2.1. Longhua coal mine The Longhua coal mine is located in Yulin city, Shanxi province, China. The mine is a longwall operation which produces about
http://dx.doi.org/10.1016/j.ijmst.2014.11.009 2095-2686/Ó 2015 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
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G. Wang et al. / International Journal of Mining Science and Technology 25 (2015) 67–72 Table 1 Lithology of the interburden between the Nos. 31 and 22 seams.
Layer
Thickness (m)
Depth below surface (m)
Lithology
2.43-2.75
50-60
No. 2-2 seam
Mainly siltstone and finely grained sandstone, interbedded with two layers of medium grained sandstone (about 5 m thick).
30-40
2.79-3.10
4 Mt/a. The target seam of economic interest is the No. 31 seam. This seam is about 3 m thick and about 90–100 m below the ground surface. The seam lies about 30–40 m below the No. 22 seam which was mined with the border and pillar method. The goaf of the #22 seam undergoes self-heating. Both seams are near flat and free of major geological structures. The interburden between the seams is dominated by siltstone and finely grained sandstone. Table 1 shows the lithology of the interburden. 2.2. No. 30110 longwall panel The No. 30110 longwall panel of the #31 seam is 250 m wide, 1979 m long and 3.1 m high. The U-type exhausting ventilation system (Fig. 1) is used. Field investigations indicated that, close to the panel finish line, there was an extensive heating zone in the goaf of #22 seam directly above the panel 30110 and a large
30111 goaf
30110 panel
90-100
No. 3-1 seam
amount of hazardous gases were contained in the goaf. The CO concentration of the goaf was measured to be as high as 1.5%. As the panel started to retreat, the overburden roof units started to deform, fracture and cave. This resulted in the formation of three zones in the roof, i.e., caved zone, fractured zone and deformation zone. The combined height of the caved and fractured zones was estimated to be in the range of 41.1–58.9 m [14,15], which was larger than the thickness of the interburden between the panel and heating goaf, indicating that the extensive fractures existed in the interburden and the gases of the goaf such as CO could readily flow into the panel. It was proven to be the case that the CO concentration at the return corner of the face often was in the range of 2 105 to 5 105 at the initial stage of the panel retreat and CO was identified to be from the goaf of the 22 seam. Furthermore, the CO concentration at the return corner of the face showed a worrying increment trend as the panel retreat progressed.
30109 panel
Main recovery roadway Auxiliary recovery roadway
Secondary main gateroad
Main Return gateroad gateroad Main intake Main intake Main return
Heating zone boundary Fresh air Return air Seal
Fig. 1. Layout of the No. 30110 panel and heating zones in the goaf of the No. 22 seam.
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2.3. Heating in the goaf of the No. 22 seam Extensive heating zones in the goaf of the #22 seam develop due to two main factors. One factor is a large amount of coal left in the goaf because of a relatively low coal extraction rate with the border and pillar method used in the #22 seam extraction, and the other is the air leakage getting into the goaf from the ground surface because of its shallow buried depth (50–60 m below the ground surface). The Longhua coal mine had attempted to control the heating in the goaf with various techniques such as nitrogen inertisation, gel injection, and blockage of air leakage. However, these measures were proven to be ineffective and quite expensive. At the beginning of the panel 30110 retreat, there was still an extensive hot spot zone in the goaf of the 22 seam directly above the panel (Fig. 1). 3. A force auxiliary ventilation system A force auxiliary ventilation system was designed in the panel 30110 to stop the gas flow between the panel face and its overlying goaf of the 22 seam. On the one hand, the system could stop the goaf gases from flowing into the corner, meaning that they will not be able to flow into any points around the face, and on the other hand, it can prevent the fresh air of the face from leaking into the goaf. The best pressure balance point was designed to be at the middle position between the return corner of the face and the goaf of the 22 seam as the return corner was the lowest pressure point in the face in the U-type ventilation system. 3.1. System components The force auxiliary ventilation system includes booster fans, doors and regulators. Four booster fans were installed in the #1 cut-through of the panel, and two of them were connected in parallel and the other two were for backup. Each of the fans has a speed of 2960 r/min, a pressure range of 1100–6000 Pa and a flow rate between 730 and 400 m3/min. Two doors were installed in the panel intake gateroad and one regulator (mesh door in this case) was installed in the panel return gateroad. The exact location and layout of the system are shown in Fig. 2. 3.2. Estimate of gas pressure between the face return corner and the goaf A U-type water tube (manometer) was installed in the main panel recovery gateroad and was connected to the goaf of the
No. 22 seam. The gas pressure in the goaf was estimated by gas pressure at the recovery gateroad and the manometer, as shown in Fig. 3. Prior to the implementation of the force auxiliary ventilation system in the panel, gas pressure in the goaf of the #22 seam was higher than that in the panel face and can be calculated as:
Pgoaf ¼ p0 þ PU qgh
ð1Þ 2
where Pgoaf is the gas pressure in the goaf of the #2 seam, Pa; p0 the gas pressure in the main recovery gateroad, Pa; P U the reading of the manometer, Pa; q the density of air in the panel, 1.073 kg/ m3; g the gravitational acceleration, 9.8 N/kg; and h the thickness of the interburden between the Nos. 31 and 22 seams, 37.6 m. P U and p0 were measured to be 230 Pa and 87.98 kPa, respectively. Using Eq. (1), gas pressure in the goaf of the #22 seam is calculated to be 87.82 kPa. Let A, B, C, D denote four specific points around the panel, as shown in Fig. 2. Specifically, A represents the point next to the boost fans, B represents the face return corner, C represents the point just before the regulator, and D is the point just after the regulator. To make gas pressure balance point between the return corner and the goaf of the #22 seam at half way of the interburden (h/2), gas pressure at the return corner (PB) must satisfy Eq. (2) and was calculated to be 88.41 kPa.
3 PB ¼ P goaf þ qgh 2
ð2Þ
3.3. Estimate of gas pressure difference across the regulator With the force auxiliary ventilation system in the panel 30110, the pressure loss from points A to B (fAB) can be calculated as follows (ignoring the panel air leakage):
f AB ¼ ðP A PB Þ þ
q
A
2
m2A
qB 2 mB þ ðqA gzA qB gzB Þ ¼ RAB Q 2 2
ð3Þ
where PA is the gas pressure at point A, Pa; PB the gas pressure at point B, Pa; qA the air density at point A, kg/m3; qB the air density at point B, kg/m3; zA the elevation at point A above sea level, m; zB the elevation at point B above sea level, m; and RAB the frictional resistance between points A and B, kg/m7. mA is the velocity at point A, m/s; and mA ¼ Q =SA , where Q is the panel air flowrate, m3/s; and SA the cross sectional area at point A, m2. mB is the velocity at point B, m/s; and mB ¼ Q =SB , where SB is the cross sectional area at point B, m2. The pressure loss from points B to C (fBC) can be calculated as follows:
f BC ¼ ðP B PC Þ þ
q
B
2
m2B
qC 2 mC þ ðqB gzB qC gzC Þ ¼ RBC Q 2 2
ð4Þ
where PC is the gas pressure at point C, Pa; qC the air density at point C, kg/m3; zC the elevation at point C above sea level, m; and
B 30110 panel
Pgoaf
2-2goaf
Monitoring borehole
#1 Cut-through
h
C D Main intake Main intake Main return
Seal wall Air door Regulating air window Booster fan Fresh air Return air
Fig. 2. Force auxiliary ventilation system in the panel 30110.
PU P
30110 Main recovery roadway
U type water tube
Fig. 3. Layout of manometer at the main panel recovery gateroad.
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#E
#C
#D #90 support
#60 support
#B #30 support
#F
13
Main gateroad
12 11 10 9 8 7 6 #6
Main recovery roadway
5 4 3 21 #5 #4
Auxiliary recovery roadway
#7
DPCD ¼ PC PD
“U” type water tube CO sensor Boreholes connected to the 2-2 seam goaf Boreholes not connected to the 2-2 seam goaf
ð5Þ
Field measurements showed that: PA = 88,530 Pa, PB = 88,410 Pa, PD = 87,960 Pa, qA = 1.061 kg/m3, qB = 1.062 kg/m3, qC = 1.062 kg/m3, zA = 1094.4 m, zB = 1094.3 m, zC = 1094.0 m, SA = 12.8 m2, SB = 16.5 m2, SC = 14.9 m2, RAB = 0.234 kg/m7, and RBC = 0.086 kg/m7. Using Eqs. (3)–(5), gas pressure at point C was calculated to be 88,372 Pa and pressure difference from points C to D is 412 Pa. That means that in order to ensure the pressure balance point between the #30110 panel face and the goaf of the #22 seam is at half way of the interburden (h/2), pressure difference across the regulator should be around 412 Pa.
Secondary main gateroad
30110 panel Return gateroad
The pressure difference between points C and D (DPCD ) can be written as:
#A
A10 #1 A9 A8 #2 A7 A1 A6 #3 A2 A5 A4 A3
3.4. Adjustment to the system during its operation To account for actual mining and ventilation conditions in the panel 30110 and to allow for 10% shifting of the gas pressure balance position in the interburden, the pressure difference across the regulator was slightly adjusted during the operation of the force auxiliary ventilation system. With the force system in operation, gas pressure at the #30110 panel face was higher than that in the goaf of the #22 seam.
Fig. 4. Layout of manometers and CO sensors around the panel 30110.
RBC the frictional resistance between points B and C, kg/m7. mC is the velocity at point C, m/s; and mC ¼ Q =SC , where SC is the cross sectional area at point C, m2.
Pgoaf ¼ p0 PU q gh
ð6Þ
Table 2 Monitored results of CO and pressure difference in the panel 30110. Date
6.21 6.22 6.23 6.24 6.25 6.26 6.26 6.28 6.29 6.30 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 7.10 7.11 7.12 7.13 7.14 7.15 7.16 7.17 7.18 7.19 7.20 7.21 7.22 7.23 7.24 7.25 7.26 7.27 7.28 7.29
S1 (m)
S2 (m)
338 223 330 215 315 200 304 189 288 173 273 158 257.5 142.5 257.5 142.5 257.5 142.5 257.5 142.5 257.5 142.5 244.5 129.5 229.5 114.5 213.5 98.5 200 85 184 69 168 53 150 35 135 20 120 5 104.5 The face retreating directly under a heating zone 104.5 87.5 71.5 56.5 41 25 10 0 The panel recovery
CO (106)
Pressure difference (Pa) #1
#2
#3
#4
#5
110 110 110 100 110 120 110 110 100 100 110 90 110 120 110 110 100 120 120 80 80 80 100 90 100 110 120 120 100 120 130 110 120 120 120 120 120 100 110
120 130 120 120 110 120 100 120 130 120 120 110 110 100 110 120 120 100 100 80 80 80 100 100 100 100 120 120 100 120 120 110 120 120 140 130 130 120 130
110 120 100 100 110 110 110 120 110 120 130 110 120 120 100 110 100 110 120 100 100 100 120 120 110 120 150 120 120 130 120 130 130 130 130 130 120 140 130
130 150 150 140 130 150 120 150 120 130 130 130 120 150 120 150 140 150 140 150 130 150 130 150 130 160 130 140 110 150 130 140 130 160 120 150 120 160 100 180 120 180 120 180 130 170 120 130 150 130 140 120 180 150 120 150 140 150 150 150 130 150 140 130 The manometers dismantled face recovery
#6 180 170 180 170 190 190 190 180 180 190 200 200 200 180 180 200 200 190 190 210 220 220 210 160 170 180 120 180 150 100 160 130 due to the
#7
#A
#B
#C
#D
#E
350 360 360 360 350 360 360 360 360 360 360 350 350 360 360 360 350 360 340 340 350 360 350 360 330 340 350 340 340 340 340 340 330 340 340 330 320 320 350
0 1 2 0 0 0 1 0 3 1 1 2 2 0 0 0 3 0 2 2 2 1 0 0 0 1 1 2 4 1 0 3 1 1 2 3 0 0 0
1 2 1 2 4 1 0 3 1 0 3 0 0 2 1 3 2 0 0 2 2 4 4 3 2 0 0 0 6 5 4 3 3 1 1 0 0 5 2
2 2 0 5 3 3 0 4 0 5 5 5 3 6 3 3 2 0 4 4 2 3 1 2 2 3 0 2 1 2 1 2 3 4 4 0 5 3 3
2 4 4 3 5 4 5 5 3 3 1 0 0 3 6 3 5 4 6 4 3 3 3 5 2 0 4 3 3 2 0 2 2 4 2 4 3 3 1
5 3 6 4 4 4 5 6 5 5 3 4 6 6 6 5 4 4 3 5 5 7 6 3 3 4 6 5 5 8 2 0 4 4 6 5 7 6 6
Note: S1 is the distance from the panel face to the panel finish line; and S2 is the distance from the panel face to the boundary projected downward into the panel horizon from the overlying heating zone in the goaf.
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#6
ΔP (Pa)
100
7. 19
15 7.
7. 11
7. 07
03 7.
6. 29
6. 25
50 Date Fig. 6. Pressure difference monitored with manometers #4 to #6.
420 400
ð8Þ
“
” represents the range of (338 Pa, 417 Pa)
380 360 340 320 300
6. 21 6. 25 6. 29 7. 03 7. 07 7. 11 7. 15 7. 19 7. 23 7. 27
! DP > Pgoaf þ 75 qgh þ q2B m2B q2C m2C þ qB gzB qC gzC RB DP < Pgoaf þ 85 qgh þ q2B m2B q2C m2C þ qB gzB qC gzC RB
#5
150
ð7Þ
It was measured that, with the operation of the force ventilation system, the face flow rate (Q) was 13 m3/s, gas pressure (PC) before the regulator was 88370 Pa and PU was 380 Pa. Thus using Eq. (5), gas pressure after the regulator was calculated to be 87,990 Pa. Using Eqs. (4), (5) and (7), the range of pressure difference across the regulator (DPCD) can be calculated using Eq. (8) to be between 338 Pa and 417 Pa.
#4
200
ΔP (Pa)
Pgoaf
7 8 þ qgh < PB < Pgoaf þ qgh 5 5
250
6. 21
P U and p0 were measured to be 180 Pa and 88,360 Pa, respectively. Using Eq. (6), gas pressure in the goaf of the #22 seam was calculated to be 87,785 Pa. If the gas pressure balance position is allowed to shift by 10% in the interburden between the face return corner and the goaf of the #22 seam, then it should be kept within the zone of (2h/5, 3h/5) and gas pressure at the face return corner (PB) must satisfy Eq. (7).
Date
4. Performance of the force auxiliary ventilation system
160
#1
#2
#3
ΔP (Pa)
140 120 100 80
6.
21 6. 25 6. 29 7. 03 7. 07 7. 11 7. 15 7. 19 7. 23 7. 27
60 Date Fig. 5. Pressure difference monitored with manometers #1 to #3.
Fig. 7. Pressure difference monitored with manometer #7.
“ ” is the maximum allowable CO limit specified in “Coal Mine Safety Regulations”
#C
#D
#E
7. 11 7. 15 7. 19 7. 23 7. 27
7. 07
#B
7. 03
6. 29
#A
6. 25
28 24 20 16 12 8 4 0
6. 21
CO concentration (×10-6)
To study the performance of the force auxiliary ventilation system, three sets of key parameters are monitored. These were gas pressure difference between the #30110 panel and the goaf of the #22 seam, gas pressure difference across the regulator, and CO concentration in the panel 30110. Seven manometers (U-type tubes in this case) were installed in the panel. Six of them (#1 to #6) were used to monitor pressure difference between the panel and the goaf of the #22 seam and the other one (#7) was to monitor gas pressure difference across the regulator. Five CO sensors (#A, #B, #C, #D and #E) were used to monitor CO concentration at various positions in the panel face (from the intake corner to return corner). The exact location and layout of these manometers and CO sensors are shown in Fig. 4. The force auxiliary ventilation system became operational on the 21st of June, 2012 when the panel face was retreated 1346 m from its start-up line. The face was retreated directly under a heating zone of the goaf of the #22 seam on the 10th July. By the 19th of July, the face was retreated to its finish line and this was immediately followed by the face recovery phase. On the 29th of July the face was fully recovered. Monitored results for the period from June 21st to July 29th are shown in Table 2 and Figs. 5–8. The pressure difference between the panel face and the goaf of the #22 seam is an important indicator about the stability of the ventilation system, and a critical reference to decide if the ventilation system requires any adjustment. The results from Table 2 and Fig. 5 indicated that the pressure differences at manometers #1, #2 and #3 were kept around 100 Pa for most of the monitoring period except for about three days (from the 10th to 12th of July), and a
Date Fig. 8. CO concentrations in the #30110 panel face.
significant drop in the pressure difference (around 80 Pa) was observed. The pressure difference was back to around 100 Pa after the regulator was adjusted. The pressure differences at manometers #4 and #5 were kept around 140–150 Pa (Fig. 6). The results from Fig. 6 also indicated that the readings from monometer #6 were around 190 Pa, and a significant drop was observed after the 14th of July, however, it was again controlled to around 150 Pa after the regulator was adjusted. No. 7 manometer was used to monitor the pressure difference across the regulator. Fig. 7 indicated that the pressure difference was kept between 340 and 360 Pa for most of the operation period. This was within the range of 338–417 Pa, as recommended in Section 3 of this paper. Although the pressure difference across the regulator was dropped slightly below the lower limit of the recommended range during the longwall recovery phase (on the 23rd, 26th to 28th of July), it was brought into the safe range through prompt adjustments of the regulator and no adverse effect on the panel operation was resulted, indicating stable running of the force auxiliary ventilation system. CO concentration was monitored along the panel face with the force auxiliary ventilation system, and the monitored results are shown in Fig. 8. The results from Fig. 8 clearly showed that CO concentration in the face was below 8 106, well below the maximum allowable limit of 24 106 specified in ‘‘Coal Mine Safety Regulations’’ in China. No incidence of sudden CO rush from the goaf of the #22 seam into the #30110 panel face occurred with
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the force ventilation system in operation, and the panel was successfully retreated and recovered. 5. Conclusions Based on the studies in Longhua coal mine, the following conclusions can be drawn: (1) A force auxiliary ventilation system was used as an alternative and effective method to control gas flow between the panel 30110 and its overlying heating goaf lying about 30– 40 m above the panel. The system consists of four booster fans, two doors and one regulator. The system hazardous gases in the goaf were stopped from entering into the panel face and the air in the panel face was prevented from leaking into the goaf during the panel extraction. (2) The success in using a force auxiliary ventilation system depends on selection of the best gas pressure balance position between a panel face and its overlying heating goaf and pressure control at key points of the ventilation system. In the case of the panel 30110, pressure difference across the regulator should be controlled around 412 Pa and the pressure balance position between the face return corner and the goaf should be half way through their interburden. (3) Seven manometers and five CO sensors were installed to monitor gas pressure difference and CO concentration in the panel 30110. Gas pressure and CO monitoring at some key locations in the ventilation system and prompt adjustments of pressure distribution in the system (if required) were an integrated parts of the system design, its implementation to ensure safe and effective operation of the system.
Acknowledgments The work was supported by the Scientific Research Foundation of Shandong University of Science and Technology for Recruited
Talents and Science Research Innovative Group of Resources and Environment Engineering College of Shandong University of Science and Technology (No. 2012ZHTD06), the Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents (No. 2013RCJJ049), the China Postdoctoral Science Foundation (No. 2013M541942), and the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20133718120013). References [1] Colaizzi GJ. Prevention, control and/or extinguishment of coal seam fires using cellular grout. Int J Coal Geol 2004;59:75–81. [2] Cao K, Zhong X, Wang D, Shi G, Wang Y, Shao Z. Prevention and control of coalfield fire technology: a case study in the Antaibao open pit mine goaf burning area, China. Int J Min Sci Technol 2012;22:657–63. [3] Poborowski B, Chen A. Spontaneous combustion management comparison between Australia and China. In: Proceedings of Australian mine ventilation conference, Sydney; 2011. p. 79–83. [4] Ray S, Singh R. Recent developments and practices to control fire in underground coal mines. Fire Technol 2007;43(4):285–300. [5] Wang DM. Mine fires. Xuzhou: China University of Mining and Technology Press; 2009. [6] Cliff D, Rowlands D, Sleeman J. Spontaneous combustion in Australian underground coal mines. Queensland: SIMTARS; 1996. [7] Walker S. Uncontrolled fires in coal and coal wastes. London: IEA Coal Research-The Clean Coal Centre; 1999. [8] Wu Q, Tu S, Dou F, Wang F. Study on law of fracture development in multiseam mining below fire area. Coal Mine Saf 2010;3:13–5. [9] Pan RK, Cheng YP, Yu MG, Lu C, Yang K. New technological partition for ‘‘three zones’’ spontaneous coal combustion in goaf. Int J Min Sci Technol 2013;23:489–93. [10] Li Z, Lu Z, Wu Q, Zhang A. Numerical simulation study of goaf methane drainage and spontaneous combustion coupling. J China Univ Min Technol 2007;17(4):503–7. [11] Wolf KH, Bruining H. Modelling the interaction between underground coal fires and their roof rocks. Fuel 2007;86(17–18):2761–77. [12] Zhang Q, Wang S, Li S. Practical application of pressure regulating technique in burning section of Meiyukou coal mine. China Saf Sci J 2001;11(2):52–6. [13] Guo H, Wu B, Wang L, Zhao C. Treatment technology of multi-seam fire area in positive pressure ventilation. Coal Mine Saf 2012;5:33–5. [14] Xu X, Zhang N, Tian S. Mining-induced movement properties and fissure timespace evolution law in overlying strata. Int J Min Sci Technol 2012;22:817–20. [15] Zhang D, Qi X, Yin G, Zheng B. Coal and rock fissure evolution and distribution characteristics of multi-seam mining. Int J Min Sci Technol 2013;23:835–40.