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Use of Gas Mixing Use of Gas Mixing Equations and Equations and

Simulation Approaches Simulation Approaches in Design of Mine in Design of Mine

Inertisation SystemsInertisation SystemsHW Wu and ADS Gillies HW Wu and ADS Gillies

13th United States/North American Mine 13th United States/North American Mine Ventilation Symposium, 13-16 June 2010 Ventilation Symposium, 13-16 June 2010

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Objective of the studyObjective of the study

To examine gas mixing and dilution approaches To examine gas mixing and dilution approaches to give a better understanding of how to give a better understanding of how acceptable levels of mine atmosphere acceptable levels of mine atmosphere contaminants can be evaluated. contaminants can be evaluated.

As an example the interaction between gases As an example the interaction between gases from inertisation systems and the underground from inertisation systems and the underground mine atmosphere can be evaluated to assist in mine atmosphere can be evaluated to assist in design of the mine inertisation system. design of the mine inertisation system.

Inertisation approaches include use of engine Inertisation approaches include use of engine exhausts, nitrogen, carbon dioxide, and diesel exhausts, nitrogen, carbon dioxide, and diesel fired boiler units. fired boiler units.

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IntroductionIntroduction New approaches allowing improvement in New approaches allowing improvement in

understanding use of inertisation understanding use of inertisation techniques have been examined. techniques have been examined.

Case studies used to examine available Case studies used to examine available calculation or computer simulation calculation or computer simulation approaches for predicting induced approaches for predicting induced inertisation gas interaction with the mine inertisation gas interaction with the mine ventilation system. ventilation system.

Comparisons are made of the use of Comparisons are made of the use of different approaches to estimate the time different approaches to estimate the time required to inert a sealed underground required to inert a sealed underground atmosphere situation.atmosphere situation.

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Approaches Adopted Approaches Adopted

Two direct calculation approaches are Two direct calculation approaches are the application of “commonly accepted the application of “commonly accepted

rules of thumb” for fluid dilution or rules of thumb” for fluid dilution or flushing of a mined space with a minimum flushing of a mined space with a minimum diluting gas requirement of for instance of diluting gas requirement of for instance of three times the void volume, andthree times the void volume, and

the direct utilization of gas mixing and the direct utilization of gas mixing and dilution equations (Hartman, et al 1997).dilution equations (Hartman, et al 1997).

The use of advanced fire simulation The use of advanced fire simulation network software, Ventgraph.network software, Ventgraph.

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Inertisation System - GAG-3A jet Inertisation System - GAG-3A jet engine exhaust unit (Gorniczy engine exhaust unit (Gorniczy

Agregat Gasniczy)Agregat Gasniczy)

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Inertisation System - Liquefied Inertisation System - Liquefied nitrogennitrogen

Inertisation System - Liquefied Inertisation System - Liquefied nitrogennitrogen

Inertisation System - Inertisation System - Tomlinson Tomlinson BoilerBoiler

Inertisation System - Membrane Inertisation System - Membrane

Floxal unitsFloxal units

GAG Docking PointGAG Docking Point

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Case Study I: Nitrogen Case Study I: Nitrogen inertisationinertisation

To provide an estimation of the time required to To provide an estimation of the time required to inert a single entry development in an underground inert a single entry development in an underground coal mines using a membrane nitrogen gas unit. coal mines using a membrane nitrogen gas unit.

Parameters of the single entry roadway are:Parameters of the single entry roadway are: Total length of sealed zone 280m with brattice sail Total length of sealed zone 280m with brattice sail

partition,partition, Dimension of the single entry roadway 2.6m by 5.3m., andDimension of the single entry roadway 2.6m by 5.3m., and Gas make CHGas make CH44 is 14 m is 14 m33/hour; CO/hour; CO22 is 7.2 m is 7.2 m33/hour./hour.

Parameters of the inertisation system proposedParameters of the inertisation system proposed A nitrogen gas inert unit with inert line into the sealed A nitrogen gas inert unit with inert line into the sealed

zone and an inert capacity of 1,100 mzone and an inert capacity of 1,100 m33/hour or 0.316 m/hour or 0.316 m33/s. /s. Inert gas output oxygen level of 0.01 percent.Inert gas output oxygen level of 0.01 percent.

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Layout of the seal and Layout of the seal and

inertisation arrangementsinertisation arrangements

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Dilution or flushing rule Dilution or flushing rule of thumb of thumb

Time determined from inert gas flow Time determined from inert gas flow rate and mined void volumerate and mined void volume

WhereWhere Y is volume of working space in mY is volume of working space in m33, ,

is time in seconds, is time in seconds,

Q is inertisation unit output, mQ is inertisation unit output, m33/s/s

C is a constant set at for instance 3.C is a constant set at for instance 3.

Q

YC

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Gas mixing and dilution Gas mixing and dilution Equation Equation

xQQQBQ

xQQQBQ

Q

Y

gg

gg 0ln

WhereWhere Y, Q and Y, Q and are as defined are as defined previouslypreviously

QQgg is the gas inflow, m is the gas inflow, m33/s/s

x is conc. of contaminant in the x is conc. of contaminant in the mixture, mixture,

xx00 is conc. of contaminant in the is conc. of contaminant in the space initially, space initially, B is conc. of contaminant in B is conc. of contaminant in normal intake airnormal intake air

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Times required with various Times required with various constant values used – Rule constant values used – Rule

of Thumbof Thumb

Constant Values UsedTime Required for the Inert

system to achieve(hours)

1 3.5

2 7.0

3 10.5

4 14.0

5 17.5

6 21.0

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Times required to achieve Times required to achieve various oxygen levels - various oxygen levels - Gas Gas

Equation Equation Resulting oxygen Level in the

Sealed area (%)

Time Required for the Inert system to achieve

(hours)

8.0 3.3

6.0 4.4

4.0 5.8

2.0 8.2

1.0 10.7

0.5 13.2

0.1 19.1

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Correlation between constant Correlation between constant vales, C and the resulting vales, C and the resulting

oxygen levels for dilution or oxygen levels for dilution or flushing rule of thumbflushing rule of thumb

Resulting O2 level = 19.997e-0.9745C

R2 = 0.9999

0

1

2

3

4

5

6

7

8

9

0 1 2 3 4 5 6

Constant Value, C

Re

su

ltin

g O

xy

ge

n le

ve

ls (

%)

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Times required to achieve Times required to achieve various oxygen levels – Rule various oxygen levels – Rule

of Thumbof ThumbConstant Values

Used

Time Required for the Inert system to achieve

(hours)

Resulting oxygen Level

(%)

1 3.5 7.6

2 7.0 2.9

3 10.5 1.1

4 14.0 0.4

5 17.5 0.2

6 21.0 0.1

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Snapshot from Ventgraph Snapshot from Ventgraph simulation after 10.2 hours with simulation after 10.2 hours with

oxygen level at about 1.1% percentoxygen level at about 1.1% percent

Branch 6

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Predicted Gas Concentration in the Predicted Gas Concentration in the Purge Pipe over time from Purge Pipe over time from

Ventgraph simulation outputsVentgraph simulation outputs Purge Pipe Gas Concentration over Time

O2 level = -3.4192Ln(Time) + 25.953

R2 = 0.94

0

5

10

15

20

25

30

0 60 120 180 240 300 360 420 480 540 600 660 720

Time (minute)

O2

or

CH

4 C

on

ce

ntr

ati

on

(%

)

O2 (%) CH4 (%) Log. (O2 (%))

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Case Study I SummaryCase Study I Summary Based on the simple gas dilution or flushing rule Based on the simple gas dilution or flushing rule

of thumb with three times volume, it will take of thumb with three times volume, it will take the membrane nitrogen inerting system about the membrane nitrogen inerting system about 10.5 hours to inert (O10.5 hours to inert (O22 ~1.1%) the sealed area. ~1.1%) the sealed area.

When applying the gas mixing and dilution When applying the gas mixing and dilution equation, it would take the membrane nitrogen equation, it would take the membrane nitrogen inertisation system about 10.7 hours to achieve inertisation system about 10.7 hours to achieve an oxygen level of 1.0 percent.an oxygen level of 1.0 percent.

From Ventgraph simulation it will take 10.2 From Ventgraph simulation it will take 10.2 hours for the membrane nitrogen inerting hours for the membrane nitrogen inerting system to reduce the oxygen level in the sealed system to reduce the oxygen level in the sealed area down to 1.1 percent with the assumptions area down to 1.1 percent with the assumptions of leakages (every 50m) from the wide side of of leakages (every 50m) from the wide side of the heading to the narrow side behind the the heading to the narrow side behind the brattice.brattice.

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Case Study II: Diesel Case Study II: Diesel Fired BoilerFired Boiler

to provide an estimation of the time required to to provide an estimation of the time required to inert a sealed coal Mains development in case inert a sealed coal Mains development in case of emergency using a diesel fired boiler of emergency using a diesel fired boiler inertisation unit.inertisation unit.

Parameters of the sealed Mains roadways are:Parameters of the sealed Mains roadways are: 66 roadways with a total length of 2,273m.66 roadways with a total length of 2,273m. Dimension of the roadway 2.7m by 5.0m.Dimension of the roadway 2.7m by 5.0m.

Parameters of the inertisation system proposedParameters of the inertisation system proposed Three inertisation boreholes, one 0.76m and two Three inertisation boreholes, one 0.76m and two

0.56m in diameter are located at 4 ct between B and 0.56m in diameter are located at 4 ct between B and C Headings.C Headings.

The boreholes are 54 m in length with a surface The boreholes are 54 m in length with a surface steel manifold structure to connect the boreholes to steel manifold structure to connect the boreholes to the inertisation unit.the inertisation unit.

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Layout of the Mains Layout of the Mains development area and inert development area and inert

boreholes arrangementsboreholes arrangements

Inertisation boreholes (uncapped)

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Times required to achieve Times required to achieve various oxygen levels – Rule various oxygen levels – Rule

of Thumbof ThumbConstant Values Used

Time Required for the Inert system to achieve

(hours)

Resulting oxygen Level

(%)

1.0 16.7 7.8

1.5 25.1 6.1

2.0 33.4 4.8

2.5 41.8 3.7

3.0 50.1 2.9

3.5 58.5 2.3

4.0 66.9 1.8

4.5 75.2 1.4

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Times required to achieve Times required to achieve various oxygen levels - various oxygen levels - Gas Gas

Equation Equation Resulting oxygen Level in the Sealed

area (% )

Time Required for the Inert system to achieve

(hours)

8.0 19.0

7.0 22.1

6.0 25.8

5.0 30.6

4.0 37.4

3.5 42.2

3.0 49.0

2.5 60.5

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Snapshots from Ventgraph simulation Snapshots from Ventgraph simulation after 50.5 hours with oxygen level at about 3.0 after 50.5 hours with oxygen level at about 3.0

percent percent with Portal seals, R=1,000 Nswith Portal seals, R=1,000 Ns22/m/m88

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Predicted oxygen levels over time Predicted oxygen levels over time from Ventgraph outputs from Ventgraph outputs

(Portal seals, R=1,000 Ns(Portal seals, R=1,000 Ns22/m/m88))

Oxygen Deficiency Over Time Using Diesel Boiler to Inert Mains Development Workings

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

22.0

0 5 10 15 20 25 30 35 40 45 50 55 60 65

Time (Hours)

Oxy

ge

n P

erc

en

tag

e (

%)

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Times required to achieve Times required to achieve various oxygen levels – various oxygen levels –

VentgraphVentgraph

Resulting oxygen level

(%)

Time required to achieve inert level in hours for varying seal resistances

R=100Ns2/m8

R=1,000Ns2/m8

R=10,000Ns2/m8

8.0 24.9 22.0 18.1

7.0 27.9 24.9 20.5

6.0 31.5 28.4 23.7

5.0 36.1 33.0 27.3

4.0 42.3 39.2 32.6

3.5 46.5 43.7 36.9

3.0 53.5 50.5 42.6

2.5 66.0 62.3 53.6

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Case Study II SummaryCase Study II Summary Based on the simple gas dilution or flushing rule Based on the simple gas dilution or flushing rule

of thumb with three times volume, it will take of thumb with three times volume, it will take the diesel boiler inerting system about 50.1 the diesel boiler inerting system about 50.1 hours to fully inert the sealed Mains area.hours to fully inert the sealed Mains area.

When applying the gas mixing and dilution When applying the gas mixing and dilution equation, it would take the diesel boiler equation, it would take the diesel boiler inertisation system about 49.0 hours to achieve inertisation system about 49.0 hours to achieve an oxygen level of 3.0 percent.an oxygen level of 3.0 percent.

From Ventgraph simulation it will take between From Ventgraph simulation it will take between 42.6 to 53.5 hours for the diesel boiler inerting 42.6 to 53.5 hours for the diesel boiler inerting system to reduce the oxygen level in the sealed system to reduce the oxygen level in the sealed Mains area down to 3.0 percent with Mains area down to 3.0 percent with assumptions of resistance values for the portal assumptions of resistance values for the portal seals ranging from 100 to 10,000 Nsseals ranging from 100 to 10,000 Ns22/m/m88..

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ConclusionsConclusions Case studies have been developed to Case studies have been developed to

examine usage of induced inertisation tools examine usage of induced inertisation tools available to the Australian coal mining available to the Australian coal mining industry. industry.

Comparisons made of estimations of the time Comparisons made of estimations of the time required to inert includerequired to inert include the application of “commonly accepted rules of the application of “commonly accepted rules of

thumb” for fluid dilution or flushing with minimum thumb” for fluid dilution or flushing with minimum three times quantity of inert gas requirements, three times quantity of inert gas requirements,

the utilization of gas mixing and dilution equations, the utilization of gas mixing and dilution equations, and and

the use of advanced fire simulation network software the use of advanced fire simulation network software for and modelling of the mine ventilation system.for and modelling of the mine ventilation system.

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ConclusionsConclusions These approaches all give reasonable These approaches all give reasonable

estimation of the times required to inert a estimation of the times required to inert a sealed area. sealed area.

However use of rule of thumb or the gas However use of rule of thumb or the gas equation calculations does not taken into equation calculations does not taken into consideration leakages in mine ventilation consideration leakages in mine ventilation systems and assumes prefect gas mixing. systems and assumes prefect gas mixing.

Use of the Ventgraph fire simulation program Use of the Ventgraph fire simulation program is able to take these into account but needs is able to take these into account but needs careful modelling to reflect the behavior of the careful modelling to reflect the behavior of the mine ventilation network under consideration.mine ventilation network under consideration.

The direct calculations are simpler and more The direct calculations are simpler and more approximate but do not require the effort to approximate but do not require the effort to set up the more complicated fire simulation set up the more complicated fire simulation model. model.

Cont.