It is a fantasy given that dwarves are miners and blacksmiths. This actually comes from Norse mythology. They were believed to create incredibly beautiful items from precious stones and metals for the gods and goddesses of Asgard.
When I think of dwarves, my first thoughts always go to the characters in The Lord of the Rings and The Hobbit. I read the books many times as a child, and the visual aesthetic that Peter Jackson and his team created in The Desolation of Smaug is similar to what I had in mind for the furnaces in my created world.
image from scifimoviezone.com
The problem is that I actually have no idea how furnaces work and while I really like the look of these furnaces in Erebor (the Lonely Mountain) I have it on good authority that they are far from practical or realistic. My long suffering husband works for a re-smelting company and deals with industrial grade furnaces to manufacture Aluminium so I quizzed him on the furnaces he uses with the hope of retro-fitting it to work in my world.
simple furnace diagram courtesy of my husband
Modern industrial furnace
The smelting process courtesy of my husband
my designs for a dwarven furnace
I had to simplify some of the mechanical elements from the diagrams my husband drew to make them believable in a world that does not possess electricity or technology. The aluminium plant has a very complex metal casting system that uses water and oil and a casting pit that is over 7m deep to create 7m logs of aluminium. That in itself is far to modern for my world, so instead I looked to the industrial revolution for inspiration. I decided that the casting method my dwarves will use will be the same that was used to make cast iron in foundries like the one in Bersham that belonged to Wilkinson. The method makes metal called pig iron. In this method they cast the molten metal into shallow troughs in a sand pit that look similar in shape to a sow feeding piglets, hence the name.
Pig iron casting in the industrial revolution (image of Blaenavon Iron Works from we-are-bright.com)