Transcript Slide 1

Composition
Change Model
for Sealed
Atmosphere in
Coal Mines
R. Karl Zipf, Jr., Ph.D., P.E.
Khaled Morsy Mohamed, Ph.D.
Motivation
• Composition changes
over time.
• Effect of barometric
pressure changes.
• Quantity of gas leakage
out.
• 2 simple examples
• 2 design examples
– Design SA to stay inert
– Design returns for
outgas flow
Gob Assistant Program
• 1988 Foster-Miller
• How much gas
flowed in or out of
sealed gob?
• How much gas into
return airways?
• Ventilation planning
tool is no longer
available
Composition
Change Model
Methane
inflow Qm
Sealed Volume V
M = total mass of gas
M = Mm + Mn + Mo + Mc
Pt = Pm + Pn + Po + Pc
Air
leakage in
or
gas
leakage
out
•
•
•
•
•
•
Large volume
4 gases
Partial pressures
Methane flowing in
Air leaking in
Gas leaking out
QL  Lc
Pt (t )  Pv (t )
Assumptions
• Homogeneous
• Instant mixing
• Pressure inside
varies
• Total leakage only
• Constant T
• Constant V
Equations
•
•
•
•
4 unknown partial pressures – Pm Po Pn Pc
4 equations for in-gassing when P < Pbaro
4 equations for out-gassing when P > Pbaro
Below is the out-gassing equation for methane
dPm (t )  m RmT
Lc

Qm  Pm (t )
dt
V
V
P(t )  Pv (t )
Volume % of Gases
100
90
Volume % Concentration
80
Sealed Volume (m3) =
1,000,000
Leakage Coef (m3/Pa) =
0.00625
Methane Inflow (m3/s) =
0.25
V%_Methane
V%_Nitrogen
V%_Oxygen
70
V%_Carbon Dioxide
60
50
40
30
20
10
0
0
240
Time - hours
480
Leakage and Barometric Pressure vs Time
Leakage (m3/s)
Barometric Pressure (Pa)
Sealed Volume Pressure (Pa)
0.4500
Leakage - m3/s (in - or out +)
110,000
0.4000
108,000
106,000
0.3500
104,000
0.3000
102,000
0.2500
100,000
0.2000
98,000
0.1500
96,000
0.1000
94,000
0.0500
92,000
0.0000
90,000
0
240
Time - hours
480
Pressure - Pa
0.5000
Leakage and Barometric Pressure vs Time
Leakage (m3/s)
Barometric Pressure (Pa)
Sealed Volume Pressure (Pa)
0.4500
Leakage - m3/s (in - or out +)
110,000
0.4000
108,000
106,000
0.3500
104,000
0.3000
102,000
0.2500
100,000
0.2000
98,000
0.1500
96,000
0.1000
94,000
0.0500
92,000
0.0000
90,000
0
240
Time - hours
480
Pressure - Pa
0.5000
Change the Focus on Sealing
• Present focus – Seals as structures
• Preferred focus – Seals for leakage control
Two Design Examples
1. Design of a sealed area to stay inert
2. Design of returns to accommodate
the out-gassing from sealed areas
Parameters needed for design
• Sealed volume
• Methane inflow
• Leakage coefficient
QL  Lc Pt (t )  Pv (t )
1. Design sealed area to stay inert
• Few seals for big
area
• No major flow
paths through
sealed area
• Good ground for
seal locations –
barrier pillar
• Seal, re-pressurize,
go inert, outgas
only
1. Design sealed area to stay inert
•
Leakage and Barometric Pressure vs Time
Leakage (m3/s)
Barometric Pressure (Pa)
Sealed Volume Pressure (Pa)
0.4500
Leakage - m3/s (in - or out +)
110,000
0.4000
106,000
0.3500
104,000
0.3000
102,000
0.2500
100,000
0.2000
98,000
0.1500
96,000
0.1000
94,000
0.0500
92,000
0.0000
90,000
0
240
Time - hours
•
108,000
480
Pressure - Pa
0.5000
•
•
•
Measure
CH4 inflow
Choose
design
barometric
pressure
LC low (high
resistance)
Out-gassing
only
Measure LC
so less than
design LC
2. Design of returns to accommodate
the out-gassing from sealed areas
• How much ventilation air
across face of seals?
• Short answer – CH4 inflow
rate
• Long answer
– CH4 inflow rate
– Sealed volume size
– Barometric pressure
change
– Leakage coefficient
(resistance)
2. Design of returns to accommodate
the out-gassing from sealed areas
Multiplier for Out-gassing Flow
Maximum Leakage Rate
over
Methane Inflow Rate
Leakage/Inflow at 2 In Hg
Leakage/Inflow at 1 In Hg
5
4
3
2
1
0
0.0000
0.0050
0.0100
0.0150
Leakage Coefficient (m3/s/Pa1/2)
0.0200
Necessary Data for
Designing Sealed Areas
• Methane inflow rates
• Pressure within sealed area and across
seals
• Flows into and out of sealed areas
(in-gassing or out-gassing rates)
• Leakage coefficient (resistance)
Conclusions
• Composition change model (CCM)
• Leakage lags barometric pressure
change
• Design seals to control leakage
• Design returns to handle outgas flow
• Lack of data about sealed area
behavior
Composition Change Model for
Sealed Atmosphere in Coal Mines
Presented by: R. Karl Zipf, Jr.
Contact info: 412-386-4097 [email protected]
The Office of Mine Safety and Health Research is a division
of the National Institute for Occupational Safety and Health
(NIOSH) www.cdc.gov/niosh/mining
NIOSH is a division of the Centers for Disease Control and
Prevention within the Department of Health and Human
Services www.hhs.gov
The findings and conclusions in this presentation are those of the
authors and do not necessarily represent the views of NIOSH.
Mention of company names or products does not constitute
endorsement by the Centers for Disease Control and Prevention