LECTURE 10 THE CONTENTS OF THIS LECTURE ARE AS FOLLOWS: 1.0 TESTING PROCEDURE OF METHANE. 1.1 Accumulation Test. 1.

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1 LECTURE 10 THE CONTENTS OF THIS LECTURE ARE AS FOLLOWS: 1.0 TESTING PROCEDURE OF METHANE 1.1 Accumulatin Test 1.2 Percentage Test 2.0 WORKING OF FLAME SAFETY LAMP 2.1 Precautins t be taken if Firedamp (Methane) Starts Burning within the Gauze Wire 2.2 Limitatins f the Nrmal Flame Safety Lamp 3.0 METHANOMETERS 3.1 Test Prcedure REFERENCES Page 1 f 9

2 1.0 TESTING PROCEDURE OF METHANE Test fr methane is usually dne in tw stages. The tw stages are: Accumulatin test Percentage test 1.1 Accumulatin Test It is carried ut with a luminus flame f standard height. This test gives a better indicatin f methane. This is because luminus-flame test prduces mre heat inside the lamp which causes better lamp ventilatin resulting in a larger quantity f methane being drawn inside the lamp. Als fr carrying ut accumulatin test it is nt necessary t create a dark surrunding. The test carried ut indicates that the flame spires/jump, if the percentage f methane in the air is 3% r mre. It is because f this reasn that we have t raise the lamp t the rf very slwly/cautiusly s that we can see the behavir f flame as well. If the flame spires/jumps, it indicates that the methane cntent in the air is mre than 3% and percentage test is nt necessary in this case. 1.2 Percentage Test This test is als called cap test. The surrunding is made dark, befre carrying ut this test. This test is carried ut with a reduced flame. The flame can be reduced with the help f the regulating knb. The flame shuld be reduced t an extent such that there appears a cntinuus blue line just abve a speck (a very small mark r shape) f white/yellw light. The lamp is raised slwly t the rf and the percentage f methane is indicated by the height f the cap prduced. The height f the cap prduced is dependent n the fllwing factrs: Page 2 f 9 - Width f the wick: The wider the wick, the lnger is the cap.

3 - Nature f fuel: Lesser is the biling pint f the fuel used, the lnger is the cap prduced. - Shape f the wick: Flat wick gives mre accurate results cmpared t rund nes. 2.0 WORKING OF FLAME SAFETY LAMP In methane air mixture, the flame safety lamp burns with a flame having blue clred cap. The height f the cap is dependent n the methane cncentratin. At lwer cncentratin f methane, the heat prduced by flame is nt enugh t ignite the gas beynd a certain limit. As the cncentratin f methane increases, mre heat is prduced and it can make the temperature higher than the ignitin temperature f methane in slightly larger vicinity, causing the height f cap t increase (Fig. 1). It is interesting t knw what will happen when the cncentratin f methane is in the explsive range (5-15%). When the cncentratin is in the explsive range, explsin in the lamp takes place prducing carbn dixide and extinguishing the flame. 2.1 Precautins t be Taken if Firedamp (Methane) Starts Burning within the Gauze Wire: - The lamp shuld be lwered dwn t flr and shuld allw fresh-air t enter. This will cause the dilutin f methane as fresh air near flr has very lw methane cncentratin. - If the abve step fails, the flame shuld be smthered by cutting ff the xygen supply. It can be dne by cvering the gas inlet air hles using clth. Page 3 f 9

4 Page 4 f 9 Fig. 1 Gas caps in flame safety lamp with different cncentratins f methane (after Karmakar, 2001)

5 2.2 Limitatins f the Nrmal Flame Safety Lamp It is nt capable f measuring methane cncentratins belw 1.5%. Hence, it is f n use fr measuring methane cncentratins under statutry permissible limits as prescribed by DGMS. Trained persns are required fr perating it. It can be used nly in accessible places. It extinguishes when air is methane free and xygen cntent f air is less than 16%. Fr methane-air mixtures (regardless f methane cntent), it extinguishes nce xygen cncentratin is lwer than 13% (Hartman, et.al.,1982). 3.0 METHANOMETERS This is a hand held instrument. It weights arund 0.47 kg. This makes it suitable fr taking spt cncentratins f methane in the range f 0 5%. It wrks n the principle f wheatstne bridge (Fig. 2). This enables t have prvisins fr adjustment f resistances. It als has sensitive galvanmeter which is directly calibrated fr 0 5 % methane. A rechargeable battery is prvided fr peratin f the circuit. All the abve mentined cmpnents are enclsed in an anti-static plastic case with an pening at the tp fr sample inlet. Under nrmal cnditins, the inlet prt (sample inlet) is cvered with a plastic cap which is remved at the time f taking measurements. This is t see that the mine air can diffuse in the detectr/sensing chamber. There is als a prvisin fr attaching a telescpic prbe f 1.4 m length which cmes alng with the instrument (Fig. 3). This telescpic prbe can be screwed n t the inlet prt s that sample frm inaccessible pints (like rf level, inside wide cracks, brehle end etc) can be aspirated using an aspirated bulb s that air enters the instrument thrugh fur hles at the end f the prbe. The schematic diagram f MSA D6 methanmeter is shwn in Fig. 4. As stated earlier, this apparatus utilizes the principle f wheatstne bridge. It is well knwn that the resistance f a wire will increase n heating by cmbustin f methane. Thus a balanced wheat stne bridge circuit becmes unbalanced and Page 5 f 9

6 therefre it starts passing current thrugh the galvanmeter. The amunt f current flw is calibrated against percentage f methane present in air. Nw, let us have a lk at Fig. 4. Air sample is drawn in the detectr chamber (D) and cmpensatry chamber (C) using the aspiratr bulb. The detectr filament is made f activated platinum and hence methane burns by the heated filament. The cmpensatry filament n the ther hand is made f de-activated platinum. Due t this, even when current passes thrugh the circuit, the temperature f the filament is nt sufficient t burn methane. The ther tw filaments marked as A and B in Fig. 4 are in a sealed chamber cntaining pure air. When mine air cntaining methane is drawn using the aspiratr bulb, the resistance f the detectr filament changes (as methane present in the air drawn burns here) causing unbalance f the wheatstne bridge. The amunt f unbalance is indicated by the current flw in the galvanmeter which is directly calibrated against methane percentage. Fig. 2 MSA D6 methanmeter wheatstne bridge circuit (after Karmakar, 2001) Page 6 f 9

7 Fig. 3 MSA D6 methanmeter telescpic prbe (after, Karmakar, 2001) Page 7 f 9

8 Fig. 4 MSA D6 methanmeter schematic line diagram (after, Karmakar, 2001) 3.1 Test Prcedure The test prcedure fr determining methane cncentratin in mines is as fllws (after Karmakar, 2001): - Check the vltage f the battery by pressing the vltage check buttn. The pinter shuld lie in the red zne indicating a vltage f 2.2 t 2.8 Vlts. - Draw mine air sample by squeezing the aspiratr bulb. Arund 2 t 3 squeezes are enugh. - Press the methane check buttn fr secnds. The pinter swings with a jerk and cmes back t a steady psitin mmentarily indicating the methane percentage. Page 8 f 9

9 - Frm time t time, zer errr f the scale shuld be checked in pure air. If necessary, it can be adjusted by the zer-setting knb. REFERENCES Deshmukh, D. J. (2008); Elements f Mining Technlgy, Vl. II ; Denett & C., Nagpur, India. Hartman, H. L., Mutmansky, J. M. & Wang, Y. J. (1982); Mine Ventilatin and Air Cnditining ; Jhn Wiley & Sns, New Yrk. Karmakar, N. C. (2001); Handbk f gas testing ; Lvely Prakashan, Dhanbad, India. McPhersn, M. J. (1993); Subsurface Ventilatin and Envirnmental Engineering ; Chapman & Hall, Lndn. Vutukuri, V. S. & Lama, R. D. (1986); Envirnmental Engineering in Mines ; Cambridge University Press, Cambridge. Page 9 f 9