This building requires an open fertile space with trees and produces coal. When the Noblemen level is reached, two Charcoal burner's huts can be replaced by one Coal mine.
The Charcoal burner's hut requires 120 trees to be 100% productive.
Maintenance of two huts is lower than the maintenance of one mine, but the mine doesn't require the large land usage.
If you place trees manually, you can use these and woodcutter's huts to use all the extra tiles near the rough edges of your island, as the one tile placement of each tree allows for the most flexibility of any farm.