Longwall goaf gas flow patterns
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Goaf gas drainage optimisation – surface goaf holes
Goaf inertisation
Panel seal-off / Open goaf – active longwalls

• Changing permeabilities • Multi-components gases i.e. O2, CH4, CO2 and N2. • Goaf holes and inertisation injection
Longwall Goaf Gas Flow Models
- Base Model Results
9 17 16

13
18
20
19
10
17
16

12 4 12 1 6
TERM INAL BOX
18
20
14
15
5
3
2
Longwall Goaf Gas Flow Models - Fundamentals
Longwall goaf treated as Porous Media, gas flow observes momentum equation as well as continuity equation:
Effect of seals
Longwall Goaf Gas Flow Models - Parametric studies – seam dips
Face start-off line
Face
Face
Goaf
Goaf
MG
MG
Level panel
TG at higher elevation
Longwall Goaf Gas Flow Models
- Model development
• 3D models with > 200,000 cells • Modelling both turbulent (face) and laminar (goaf) flow • UDF sub-routines developed to handle
Plan View (Top) Roof
Surface goaf drainage holes
Hole locations Spacing Suction pressure Hole-bottom elevations Number of holes operating Captured gas compositions
11

17 16
To provide fundamental and scientific understanding of goaf gas flow behaviour and the influence of various factors in complicated 3D longwall goafs To assist goaf gas drainage and management Prevention of heatings/explosions in goafs Optimisation of inertisation operations
Longwall dust controls
Headings Longwall faces
Longwall Goaf Gas Flow Models
- Objectives
TUBE 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Black Gre y W hite C le ar Dk Brown Lt Brown Dk Gre e n Lt Gre e n Dk Blue Lt Blue Re d Pink Purple Ye llow O range Mint Fluro Pink Gold Stone Apricot
NO TE Tube 10,16,17,18,19,20 + 9, 8, 5 to be use d for C SIRO goaf gas monitoring
18 8
20
19
10
Proposed new locations for tubes after longw all face retreat
CFD Modelling for Mine Gas and Heatings Control 采空区瓦斯运移规律的CFD模拟及其应用
Exploration and Mining CSIRO
CFD - What is it?
CFD stands for Computational Fluid Dynamics – it models the dynamics of objects that flow using computers;
- Fundamentals
Fac
eA
Face
B
M in
in g d
ir e c t
io n
Stress distribution
x’
Panel A x
Panel B
Floor level
25m above
40m above
Permeability
3D Stress and Permeability Distribution in longwall Goaf
77 min 3 ppb
180 min 16 ppb
91 min 1200 ppb 3 min 8000 ppb
Tracer gas release
point
24 100 20 16 12 8 4 0 0 200 400 600 800 40 20 0 1000 O2 % CH4 % CO2 % 80 60
假设长壁工作面采空区为多孔介质, 采空区气体运移规律符合质量和动量守恒方程,同时, 采空区气体运移符合质量守 恒定律,即连续性方程:
Momentum Equation
ui ui u j p ij gi Si t x j xi x j
Si 1
Momentum Source Equation

vi C2
vi2
2
Continuity equation:
( i ) Sm t xi
Sm- Source term 采空区瓦斯流入单相连续流体(continuous phase)的涌出量(mass)。
Longwall Goaf Gas Flow Models
Tr
po
CO2 & CH4 %
Oxygen (O2) %
Distance behind longwall face, m
CFD simulation of gas flow
Fully coupled gas-water-strata modelling - COSFLOW
Longwall Goaf Gas Flow Models
- Applications – goaf gas drainage
Longwall return gas concentration levels during field trials
LW return gas level, % 2.5
2.0
Gas flowrate, l/s
Field demonstration studies
TUBE LO C ATIO NS G100 B Se al W e ste rn Mains A hdg Hunte r Tunne l G101 Intake G102 Longwall Re turn Main Re turn At Shaft Surface Tube Bundle Room LW 2 Inbye se als LW 2 Tailgate Intake 101 A 13 ct - LW 2 goaf LW 2 Se als 23 c/t G100 B hdg se ale d goaf LW 1 Se als 12 c/t G104 Re turn G103 Re turn 101 102 102 102 101 A A A A A 17 ct - LW 2 goaf 22ct - LW 2 goaf 21 ct - LW 2 goaf 20 ct - LW 2 goaf 15 ct - LW 2 goaf
CH4 only
Side View Floor Roof
One cut -through open for back -return
Return Longwall face Secondary inle t Primary inlet
80% CO2
Side View Floor
Longwall Goaf Gas Flow Models
3D Modelling of Gas Gas Flow Patterns
O2
CH4
Longwall Goaf Gas Flow Models
- Base Results Validation
151 min 29 ppb

Tracer gas studies Goaf gas distribution – tube bundle data Ventilation pressures in goaf
U ventilation 1600-1800m3/min, goaf gas emission 30m3/min
Face start-off line
Face
Face start-off line