The modern method of iron refining still uses a blast furnace. That amounts to filling a tall, cylindrical structure with layers of coal and iron, lighting it, and then blowing air into the bottom until molten iron starts leaking out. Of course it's a bit more elegant than that, but I don't think there's any large-scale production of iron anywhere in the world that simply cooks the iron in a crucible.

Primitive Technology has a good example of how it would be done in earlier times.