Hi, I was testing fuel efficiency between black coal and charcoal in forges and the cementation furnace, and it seems like the game does not reflect the burning times from the description in those cases. Despite the much longer burn time, I don't see the difference in my tests.
Regardless of fuel, when I add one piece of it in the forge, it heats up the material to around 900°C before it runs out. I tested it with charcoal and black coal, and the temperature it reached was just about the same.
The same thing happened when testing the cementation furnace. When I used two full piles of charcoal (2×32 items) and let it burn out, the result was a 19% progress in the process. When I used two full piles of black coal (again, 2×32 items) it also got to 19% of the process.
Is that intended? It seems like looking for coal is not worth it at all in the current state.