Sandro Hanaehan Sirait1, Nuhindro PriagungWidodo1, Mikha Simanjuntak2

1Mining Engineering Department, Institut Teknologi Bandung2PT Cibaliung Sumberdaya

INDONESIA

International Symposium on Earth Science and Technology (CINEST)

Kyushu University, Fukuoka, JAPAN 2013

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PREFACE3

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Preface

1. Blasting in underground mine produces gas that may harm worker’s health

2. Gas produced: CO, NOx, NO2, NH4

3. Time needed to dilute the gas until certain level safe for worker are calledre-entry time

4. Mine ventilation system have significant role in determining re-entry time

5. The issue: if the re-entry time is too short, worker’s health would be endangered. If the re-entry time is too long, it would reduce mine productivity

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Locations

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Field experiment –PT Cibaliung Sumberdaya (CSD)

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PT Cibaliung Sumberdaya

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BASIC THEORY8

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Basic theoryAir in underground mine is flowing correspond to advection-diffusion phenomena expressed in equation:

𝐶 𝑥, 𝑡 =𝑉

2𝐴 𝜋𝐸𝑡exp

−(𝑥 − 𝑢𝑡)2

4𝐸𝑡

• C (x,t) = concentration at position x and time t (cc)

• V = total substance in its original state (m3)

• A = cross-sectional area of the flow (m2)

• ū= average velocity (m/s)

• E = effective diffusion coefficient (m2/s)9

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Basic theory – advection diffusion concept

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FIELD EXPERIMENT

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Field Experiment - FlowchartRecord

CO gas

data from

blasting

CO gas

concentration

vs Time Curve

Matching Curve between

measurement data vs Advection

Diffusion Equation

Match

the

curve?

Yes

Estimate Re-

entry time using

E value

No

Change variable:

CO Volume, E,

and ū

START

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Field Experiment - Methodology• Gas detector turned on and placed before blasting takes place, ie

when marking, drilling, or charging activity.

• Then, author must wait smoke clearing process in Lunchroom for safety consideration

• After 30 minutes or the blasting smoke is cleared away, author retrieve the instrument

• Import the measurements data to Microsoft Excel

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Field Experiment - Instrument

Gas Detector

• Using Riken Keiki GX-2003

• Import the data withSoftware Data Logger

• Data Interval 10 seconds

• Data accuration 1ppm

• CO gas maximum value= 500ppm

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Field Experiment• Gas detector is placed in a safe location from flyrock

and also from water seeping the walls

• Gas detector is hung on wiremesh or longstrap so that it couldn’t easily fall

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PT CSD Ventilation Summary• Using exhaust ventilation system

• Intake through Cikoneng portal

• Exhaust through :

• Cikoneng Shaft (Main fan 132kW)

• Cibitung Shaft (Main fan 132kW)

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Portal CikonengCikoneng Shaft Cibitung Shaft

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PT CSD Underground Mine Map

Data are taken at PT CSD in June 2013

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RESULTS AND DISCUSSIONS

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PT CSD Simplified Mine Ventilation Scheme

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CO Gas Measurement Scheme

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CO gas results –matching curve

220

100

200

300

400

500

600

700

0 5 10 15 20

CO

(p

pm

)

Time (minute)

50 meter 115 meter 165 meter

[1101 CBT-1]

CO Volume= 1,300,000 cc

ū=0.37 m/s; L/d= 11.2

E=7 m2/s

[1101 CBT-2]

CO Volume= 180,000 cc

ū=0.39 m/s; L/d= 25.7

E=10 m2/s

[1101 CBT-3]

CO Volume= 764,000 cc

ū=0.55 m/s; L/d= 36.8

E=15 m2/s

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Number of explosives by the amount of CO gas graph

230

500

1000

1500

2000

2500

3000

3500

4000

4500

0 20 40 60 80 100

CO

(l)

Explosives (kg)

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Summary of effective diffusion coefficient

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NoCO

Measurement Station

ū (m/s)

E (m2/s)

Re L/d

1 1135 CKN-1 0.16 10.0 43983 11.2

2 1135 CKN-2 0.24 13.0 68954 22.3

3 1135 CKN-3 0.23 13.0 65265 73.7

4 1135 CKN-4 0.23 3.5 65265 90.4

5 1065 CKN-1 0.17 3.0 48239 6.7

6 1065 CKN-2 0.14 5.5 39726 12.3

7 1065 CKN-3 0.22 8.0 62427 22.3

8 1120 CKN-1 0.19 1.0 52496 4.5

9 1120 CKN-2 0.28 3.0 79453 63.6

10 1061 CBT-1 0.24 5.2 68102 13.4

11 1061 CBT-2 0.18 10.0 51077 39.1

12 1061 CBT-3 0.24 11.0 68102 49.1

13 1101 CBT-1 0.37 7.0 104991 11.2

14 1101 CBT-2 0.39 10.00 110666 25.7

15 1101 CBT-3 0.55 15.0 156068 36.8

16 DEC CBT-1 0.23 10.00 65265 8.9

17 DEC CBT-2 0.30 25.00 85128 17.9

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Graph E to L / d

L/d is length with hydraulic diameter ratio

L/d can be a parameter to estimate the E value

For health and safety considerations, the equation as referencebecome

E* = 0.1595 (L/d) + 5.

25

E = 0.1595 (L/d)

E* = 0.1595 (L/d) + 5

0

5

10

15

20

1 10 100

E (

m2

/s)

L/d

E vs L/d E E*

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Re-entry time estimation• Using E*, E values are obtained 22.09 at Cikoneng

and 23.16 at Cibitung,

• Value of Cikoneng average speed is 0.21 m/s and Cibitung 0.31 m/s

• Largest amount of CO gas 3,550,000 cc

• Using advection diffusion equations to estimate the re-entry time in each area to reach the safety limit (using 25 ppm to get Safety Factor=2) of CO gas.

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Re-entry time estimation• Cibitung needs 72 minutes and Cikoneng needs

118 minutes

270

50

100

150

200

250

300

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

CO

(p

pm

)

Time (Minute)Cikoneng Cibitung

Vol CO= 3.550.000 cc

L/d= 107.1; ū=0.21 m/s

E= 22.09;

Time= 118 minutes

Vol CO= 3.550.000 cc

L/d= 113.8; ū=0.31 m/s

E= 23.16;

Time= 72 minutes

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CONCLUSION REMARKS

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Conclusion Remarks

1. Measured CO gas curve is needed to evaluate gas transportation in underground mine

2. In this study authors only consider CO gas and ignore the presence of other gas that may be harmful to worker’s health

3. In this study authors evaluate E to estimate re-entry time, further research about this topic is still needed

4. Recommendation for advance study about this topic are to conduct further experiments with numerical method to take into account airways variation and consider several curves representing variation of effective coefficient diffusion in each lane.

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THANK YOU!

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ARIGATOU GOZAIMASU!

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