Methane [like most other gases] has two explosion boundaries for its mixtures with air: it would not explode if the concentration is either too low or too high [either below 6 or above 14%]. The trouble is that even with the best ventilation there are gas pockets inside the coal seam with methane under some pressure, and when such a pocket is breached, the forceful gas stream will create locally high concentrations. The best way to concentrate the methane would be from dilute and safe [say, 3% methane] mixtures with air, outside the mineshaft, with the concentration occurring on/in some absorbent, and then releasing it from that absorbent in a separate circuit without much air in it.
This is certainly a safe method, the absorbers being out side of the mine.
It would most likely be expensive. Absorber beds would be large in volume and expensive to purchase. Rapid turnover of the air in a mine is the key in mine safety. So these absorber beds would have to be huge to handle the large volumes of air moving through the mine.
There would need to at least two banks of absorber beds because one would have to be in service while the other was being regenerated.
Regeneration of absorbers usually requires a great deal of energy because they typically are heated in order to get the absorber to release the captured gas.
Considering the cost of purchasing this technology and operating it, I don’t see this being a cost effective proposition.
But then the whole Green House Gas Global Warming thing doesn’t make any sense anyway.