f open gob collapses suddenly, a windblast is produced that can cause
considerable damage throughout the infrastructure of a mine. In a few cases, the windblast has
been accompanied by ignitions of methane and/or coal dust. Analytical and numerical analyses
investigated the transient behavior of the air through the small time period during which the roof
is falling. This is sufficiently short to allow adiabatic compression of the air, i.e. negligible heat
transfer to rock surfaces. Controlled escape of the air via interconnecting entries limits the build-
up of air pressure. However, this same phenomenum causes the potential energy of the falling
strata to be concentrated into a diminishing mass of air. Computer simulations predicted that the
temperature of the air would increase rapidly as the roof descends, reaching values that are
capable of igniting either methane or coal dust.
This thesis concentrates on a series of laboratory tests involving the compression of mixtures of
air, methane and coal dust under a falling weight and while allowing controlled escape of the
mixture. The transient responses on pressure and temperature sensors were recorded. In addition
to an analysis of those records, the thesis highlights those conditions in which ignitions occurred. iii
Acknowledgments
I wish to express my sincere appreciation to Dr. McPherson, my academic advisor and committee
chairman, for his guidance and help throughout this study.
I wish to thank, also, the members of my committee, Dr. Karfakis and Dr. Karmis.
I would like to recognize the effort of Mr. Wayne of the Department of Mining and Minerals
Engineering, who assisted with the construction of the test rig and with the set-up and conduct of
the tests. I also thank Dr. Loomis, a former Ph.D student of this department, who helped me to
complete the laboratory tests.
More than two years in the Department of Mining and Minerals Engineering at Virginia Tech
have been a wonderful and unforgettable experience. I wish to thank all the people in the
department who helped me with my study and life. iv
Table of Contents
Section
Description
Page
Cover
Abstract
Acknowledgments
iii
Table of Contents
iv
List of Figures
v
List of Tables
ix
List of Plates
x
1
Introduction
1
1.1
The Problem Statement
1
1.2
Case Study
1
1.2.1
Coalbrook Colliery, South Africa
2
1.2.2
Wa Jing Wan Colliery, China
2
1.2.3
Moura No. 4 Coal Mine, Australia
2
2
Background Theory
3
2.1
The Bounded System (No Leakage)
3
2.2
The Leakage System
7
3
The Setup of Laboratory Tests
14
3.1
The Purpose
14
3.2
Test Parameters
14
3.2.1
Test Loads
14
3.2.2
Cylinder
16
3.2.3
Chamber
19
3.2.4
Methane
19
3.2.4.1
The Nature of Methane
19
3.2.4.2
The Explosible Limits of Methane
21
3.2.4.3
The Methane Concentrations for the Laboratory Tests
22
3.2.5
Coal Dust
22
3.2.5.1
The Definition of Coal Dust
22
3.2.5.2
The Formation of Coal Dust in Mines
23
3.2.5.3
Mechanism of Coal Dust Explosion
24
3.2.5.4
Ignition Sensitivity of Coal Dust
25
3.2.5.5
Coal Dust Concentrations of Laboratory Tests
26
3.3
The Monitor System
27
3.3.1
Pressure Transducer
27
3.3.2
Temperature Sensor
27
3.3.3
The DATA 6000 Logger
29 v
Section
Description
Page
3.3.3.1
The General Description of DATA 6000
29
3.3.3.2
The Setup of DATA 6000
29
3.3.3.3
The Calibration of the Pressure Signals
30
3.3.3.4
The Calibration of the Temperature Signals
30
3.3.3.5
The Combination of the Monitor System
30
3.4
The Final Model of Laboratory Tests
31
4
Results
37
4.1
The Start-up Testing
37
4.2
Test Procedures
37
4.3
The Transformation of Test Data
42
4.4
Test 1 Group
48
4.4.1
Pressure Profile
48
4.4.2
Temperature Profile
48
4.5
Test 2 Group
52
4.5.1
Pressure Profile
52
4.5.2
Temperature Profile
52
4.6
Test 3 Group
57
4.6.1
Pressure Profile
57
4.6.2
Temperature Profile
57
4.7
Test 4 Group
62
4.7.1
Pressure Profile
62
4.7.2
Temperature Profile
62
5
Discussion, Conclusions and Recommendations
67
5.1
Primary Observations
67
5.2
Computer Simulation Results
68
5.3
Conclusion
69
5.4
Recommendations
69
Appendix
73
Reference
75
Vita
78 vi
List of Figures
Figure
Description
Page
2.1
Air is Compressed beneath a Falling Mass in a Bounded
4
System (No Leakage)
2.2
Example of the Variation in Roof Height (a), Air Pressure (b)
9
and Temperature (c) under a 4m Thick Falling Slab with a
Damping Factor 3 and No Leakage
2.3
Flowpaths of Air Escaping from Collapsing Gob
10
2.4
Example of Transient Variations in Height (a), Air Pressure
13
in Gob (b), Air Temperature in Gob (c) and Air Pressure
in Adjoining Entries (d)
3.1
A Schematic Diagram of the Combined Test Loads
15
Simulating the Falling Roof
3.2
A Schematic Diagram of the Cylinder Simulating the
17
Compressed Zone
3.3
A Schematic Diagram of Chamber Simulated the Entries
20
Immediately Adjacent to Gob Area and Remained
Mine Infrastructure
3.4
The Coward Diagram for Methane in Air
22
3.5
A Schematic Diagram of Self - Made Methane Injector
23
3.6
A Schematic Diagram of Self - Made Coal Dust Injector
26
3.7
PCB Piezotronics Calibration Curve
31
3.8
The Typical Calibration Chart for the Temperature Sensor
32
3.9
A Schematic Connection Diagram of the Monitor System
33
3.10
A Schematic Diagram of Laboratory Tests Assembly
35
4.1
Variation of Air Pressure during a Laboratory Test
39
4.2
Variation of Air Temperature during a Laboratory Test
40
4.3
Variation in Air Pressure under Coal Dust 0 g/m
3
,
49
Methane Concentration 0%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.4
Variation in Air Pressure under Coal Dust 0 g/m
3
,
49
Methane Concentration 2.5%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.5
Variation in Air Pressure under Coal Dust 0 g/m
3
,
50
Methane Concentration 5%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.6
Variation in Air Pressure under Coal Dust 0 g/m
3
,
50
Methane Concentration 10%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.7
Variation in Air Pressure under Coal Dust 0 g/m
3
,
51
Methane Concentration 15%, Loads 600 kg, Drop Height vii
Figure
Description
Page
0.91 m and Orifice Diameter 1.6 mm
4.8
Variation in Air Pressure under Coal Dust 0 g/m
3
,
51
Methane Concentration 20%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.9
Variation in Air Pressure under Coal Dust 1316 g/m
3
,
53
Methane Concentration 0%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.10
Variation in Air Pressure under Coal Dust 1316 g/m
3
,
53
Methane Concentration 2.5%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.11
Variation in Air Pressure under Coal Dust 1316 g/m
3
,
54
Methane Concentration 5%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.12
Variation in Air Pressure under Coal Dust 1316 g/m
3
,
54
Methane Concentration 10%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.13
Variation in Air Pressure under Coal Dust 1316 g/m
3
,
55
Methane Concentration 15%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.14
Variation in Air Pressure under Coal Dust 1316 g/m
3
,
55
Methane Concentration 20%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.15
Variation in Air Pressure under Coal Dust 2632 g/m
3
,
58
Methane Concentration 0%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.16
Variation in Air Pressure under Coal Dust 2632 g/m
3
,
58
Methane Concentration 2.5%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.17
Variation in Air Pressure under Coal Dust 2632 g/m
3
,
59
Methane Concentration 5%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.18
Variation in Air Pressure under Coal Dust 2632 g/m
3
,
59
Methane Concentration 10%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.19
Variation in Air Pressure under Coal Dust 2632 g/m
3
,
60
Methane Concentration 15%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.20
Variation in Air Pressure under Coal Dust 2632 g/m
3
,
60
Methane Concentration 20%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.21
Variation in Air Pressure under Coal Dust 3948 g/m
3
,
63 viii
Figure
Description
Page
Methane Concentration 0%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.22
Variation in Air Pressure under Coal Dust 3948 g/m
3
,
63
Methane Concentration 2.5%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.23
Variation in Air Pressure under Coal Dust 3948 g/m
3
,
64
Methane Concentration 5%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.24
Variation in Air Pressure under Coal Dust 3948 g/m
3
,
64
Methane Concentration 10%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.25
Variation in Air Pressure under Coal Dust 3948 g/m
3
,
65
Methane Concentration 15%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
4.26
Variation in Air Pressure under Coal Dust 3948 g/m
3
,
65
Methane Concentration 20%, Loads 600 kg, Drop Height
0.91 m and Orifice Diameter 1.6 mm
5.1
The Simulation Results of Height(a), Air Pressure(b) and
71
Temperature(c) for a Laboratory Test
5.2
Comparison between the Actual Pressure Trace(a) and the
72
Simulated Pressure Curve(b) during a Laboratory Test
without Methane and Coal Dust ix
List of Tables
Table
Description
Page
3.1
Variation of Coal Dust Explosibility with Respect to
26
Volatile Content
3.2
Specification of Model 118A
28
3.3
The Main Technical Data of the Resistance Temperature
29
Detector
4.1
The Tests Parameters Data Collection Sheet
41
4.2
The Test Schedule Matrix
42
4.3
A Typical Data Transformation from DAT