I went out to turn some of my massive leaf compost pile today since it was pretty nice out, started digging through it and it’s like smoldering inside of there. So I guess it’s what they call a “hot” pile… I threw a few gallons of urine on it a couple months ago and put a tarp over it, first time I’ve turned it.
I think it’s extremely rare, but I have heard of compost piles combusting.
This is how mine was smoking today… it’s not as broken down as this stuff is though…
http://www.jpetersongardendesign.com/wp-content/uploads/2011/08/hot-compost-pile.jpg
Maybe you could tap it somehow and make a methane torch.