Well I was thinking that if coal is a fuel why can't you put a bit of coal dust into a furnace and use it as a fuel.
Now I'm rubbish at balancing but I think that the coal bust would burn for about 75 seconds (about 7.5 smelts) since a bit of the coal was lost in the process of macerating.
If you have any feedback please post!!
[Edit] I forgot that you don't get 2 coal dust ( it was actually one )in macerating coal in the process so it will be 7.5 smelts! Sorry!!