Q. How to calculate the lower explosibility mixture (consists of methane and other hydrocarbons) ?
A. Let's put some facts here before solving main problem i.e explosibility mixture. Those are as follows:
(1) Presence of firedamp (mostly methane) in air between 5.4% and 14.8% forms an explosive mixture;
(2) The maximum explosive violence is produced when the explosive mixture contains 9% of firedamp;
(3) If temperature and pressure are increased substantially, a fire damp between 2% and 75% (including both the limit) might also form a explosive substance;
(4) If the percentage of black damp (CO2 and excess nitrogen) exceeds 35%, the atmosphere becomes non-explosive irrespective of any percentage of fire damp;
(5) Fine dry coal dust lowers the lower limit of explosibility of the methane-air mixture to well below the usual 5%.
Now, we have a tested formula for calculating the lower explosibility mixture(LEM) and that is :
LEM= 100/((G1/g1)+(G2/g2)+(G3/g3)+.....)
Where Gis (i=1,2,3....) are contents, in percent by volume , of each combustible component of the mixture
(That means sum total of Gis must be 100)
and gis (i=1,2,3.....) are lower explosion limit of each component
Let's take a example to apply the above stated formula. If we have a mine atmosphere data as follows:
CH4 (G1=70%,g1=5%), H2 (G2=15%, g2=4.1%), C2H6(G3=15% , g3=3.2%)
Then LEM = 7.5% approx
