Methane




  • GENERAL PROPERTIES:-
  1. Colorless, odorless and tasteless gas.
  2. 1kg of CH4 at NTP has a mass of 0.7168kg.
  3. Specific gravity = 0.559; which is lighter then that of air.
  4. CH becomes liquid below 112K and solidifies below 90.5K.
  5. Poorly soluble in water but is soluble in organic solvent(e.g., alcohol, ether, etc.)
  6. Burns with blue flame and produces CO2 & H2O as products.
  7. Its ignition temp. is nearly 650°C
  • EXPLOSIBILITY OF METHANE:-  The explosibility of  methane in air depends on the composition  of thee mixture.
  1. In normal air,methane concentrations upto 5% lead to no explosion,though theair can burn.
  2. Concentrations  higher then 14% do not form explosive mixtures as the excess methane absorbs a substantial amount of heat.
  3. Methane becomes explosive when the percentage of CH in the  mixture is between 5% to 14%. 
  • COWARD DIAGRAM:-  Coward diagram indicates the chances of fire damp explosion for different composition of methane air mixture.
The methane content of 9.5% in air forms the most explosive mixture.



  • Methane due to its low specific gravity,tends to rise to the roof of the mine workings.
  • Methane is inert as far as physiological action is concerned, but when present in large quantity in air, can cause serious oxygen depletion. 
 
  • METHANE DRAINAGE:-  Methane Drainage is practiced when methane emission in mine exceeds 20-25m3/tonne of coal produced.

                              There are various methods of methane drainage; Various parameters    that affect the choice of method to be used are:-

  1. Natural or induced permeability of the seam and associated strata.
  2. The method of mining.
  3. The reason for draining the gas.
Gas capture efficiency  of methane drainage system is defined as - 
  • METHODS OF METHANE DRAINAGE:-
  1. Cross-Measure Methane Drainage
  2. Hirschbach Method
  3. Pack Cavity Method
  • CROSS MEASURE METHANE DRAINAGE:- 
       This method is a very common method of methane extraction in the areas where the     of drilling of a borehole from the surface is difficult because of more depth . In this method ,cross measure borehole are drilled from roadways in working seams at some inclination . The hole may be drilled upward or downward. The upward drilled holes are preferred because methane usually accumulates in bed separation cavities and is driven out as the roof breaks or collapse . Capture efficiencies  for this method is usually in the range of 20% to 70%. Boreholes are drilled into the roof and if necessary drilled into the roof and if necessary also the floor strata . They are usually drilled in the return airway because the ventilating pressure drives the gas in the gob or goaf toward the return side . This is the dominant method of methane drainage and is particular applicable in advancing long wall panels .  

  • HIRSCHBACH METHOD :-
         The hirschbach technique of CH4 drainage is show in fig. salient feature of this technique are:-
  1.  Headings of cross-sectional area 5-6 m2 are driven at a height of about 25 to 30 on the top of the working seam.
  2. The positing of heading is done in such a way that their vertical projection line midway between the gate roads in the working seam.
  3. The drive is preferably location in a coal seam of thickness 0.3 m - 0.4 m, if possible otherwise they may be driven in stone.
  4. Because of economic reason an already existing drift or one driven for some other purpose may be used for methane drainage.
  5. Hole are drilled both along & across the seam.
  6. Heading are sealed at the outbye ends by dames through which pipes are left.
  7. Suctions pressure of 2-3kpa is applied through the pipes.

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