Here is a photo of a clinker. It is as our forum leader [he prefers administrator] said, a bunch of ash fused together.
The clinker you see is one piece, the can in the background is a standard size spray can. This clinker is about 18" long and 8" wide. It was created by burning high-ash, low AFT bituminous coal. AFT is ash fusion temperature, or the temperature that the ash will become liquid and flow and stick together.
It doesn't show real well in the photo, but there are lots of areas that look like melted glass.
Anthracite usually won't make any clinker, or very little. The AFT of anthracite is about 2700*, but it is half that for Bituminous. The coal I was burning that made this clinker was very poor coal. That clinker was pulled off the grate of my firebox after three days of burning the lousy bitum. coal. I would notice after two days that the fire wouldn't burn as hot and by the third day, I couldn't keep the fire going. So I would shovel out the unburnt coal and ashes, and then with a hoe and a hook pull up and remove the sheet of fused ash.... the clinker.
It would completely cover the grate, blocking the air to the coal fire.
Anthracite might ocasionally have a few pieces of ash fuse together, but I've yet to see anything bigger that 1-2" around. I have several old coal burning brochures that say not to poke into the hot coal bed, that this causes clinkers. I guess you force the pieces of ash together when they are near molten, then they stick together.
Hope this answers your question. Greg L
I can take and post more photos of clinkers if you wish, I saved a few because of their appearance.
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Last edited by LsFarm
on Thu Dec 21, 2006 8:43 pm, edited 1 time in total.