Why does fresh coal make popping sounds?

Y'all who burn nut or larger prolly know what I'm talking about. I dunno if rice in a stoker also does the snap, crackle, & pop that I'm referring to.

Anyways......My twice a day routine is to shake my hand-fired inert really well, scoop out the ash & such, sit in front of her with the ash door open to get the coal bed really cookin', and then throw a bucket of fresh coal on top.
When I do that.....I'm rewarded with pretty blue licks of flame wandering around the black mound of coal and a frenzy of snaps, crackles, and pops from the new coal.

My guess is that it's not moisture in the coal expanding as we usually see (hear) when burning wood, but rather it's the extremely fast expansion of the outer area of the coal nugget versus the stodgy "unwilling to expand" cooler center of the nugget. That creates tension within the nugget which causes the hot expanding shell to shear from the stubborn cooler center.
I dunno how much coal/carbon actually expands with heat, but even just a little oughtta cause shear & thus popping.

Believe it or not....I'm not even drinking when I come up with these thoughts while sitting in front of the fire!

Chime in and tell me if I'm on track or in outer space!
:toothy7:

Gary in Pennsylvania wrote:My guess is that it's not moisture in the coal expanding as we usually see (hear) when burning wood, but rather it's the extremely fast expansion of the outer area of the coal nugget versus the stodgy "unwilling to expand" cooler center of the nugget. That creates tension within the nugget which causes the hot expanding shell to shear from the stubborn cooler center.

Sounds plausible, my only guess is you have a chemical reaction going on and something is expanding. The heat maybe creating gases which don't have anywhere to go, hence the reson it begins so quickly. Same principal if it was water. May even be water especially if you have coal with porous seams.

Before I add fresh coal to my top-loading hopper, I usually stick a gloved hand into the hooper and push the coal to the sides so that I have a nice large hollow into which to dump the new coal. When I do the pushing around, tiny flakes and chips of coal fall through the hopper and onto the firebed. When the flakes and chips hit the intense heat in the firebox, there is rapid oxidation, an they dance around like fireflies. I also hear the popping sounds, resulting from the very rapid burn of the coal dust/chips. That may explain what you are hearing.

One word of caution - be careful as I had a small piece of coal come flying out of the stove when I had the door open after it popped like that. The little sucker hit me about a half-inch below my eye and left a nice burn. Good thing it wasn't just a smidge higher...

I'm familiar with your ritiual Gary. The blue flame is quite rewarding.

My grandfather (84) calls the popping and crackling you are talking about "the sulphur breaking". That’s an old timer term, but I think this sums it up. This saying goes along with what our friendly admin said, about the gases escaping. If you open your stove, or you’re outside and downwind of your chimney, you know you’ll get a whiff of the coal gas / sulphur smell. Once the popping stops, the blue flame dies down after a little while and there is no smell. The "sulpher broke".

Is this term just from Archbald Pa, or did anyone else ever hear it?

I notice that the new coal is actually breaking apart, sometimes I get hit with coal shrapnel while I'm loading my Mark 3. Sometimes I'm glad I have glasses on. On occasion I really get some good cracks that I can hear upstairs and I go down to make sure nothing is blown up.
Chad

Coal does have some moisture content, it may just be turning to steam and popping like a kernal of dried corn. Carbon I would think, will transfer heat quick like ceramics but being so hard would just crack. It can't give at all, even steel will flex somewhat.