Folks use lump coal around here pretty often. Use a grate and get a good wood fire going first then put the coal on it.
Burns hot so have a nice thick metal stove.
Maybe this is a stupid question. What the heck is “nut coal”.
I would be hesitant to use lump or briquettes in my tent stove because it’s fairly thin walled. Maybe an extra metal plate in the base. If I was desperate I would. But pretty much stick to wood.