Primitive Technology: Natural Draft Iron Smelt
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00:00 Building the furnace
7:15 Smelt 1 (fresh ore)
11:12 Result/processing product
13:57 Modifying furnace
16:33 Smelt 2 (recycled slag)
20:50 Result/processing product
About This Video:
I built a natural draft furnace and smelted iron ore in it, producing a small amount of iron. A natural draft furnace is one where the draft is supplied by convection alone. This is opposed to a forced draft where bellows or fan is used to supply air flow instead. Natural draft furnaces are typically taller than forced draft furnaces to make use of the stack effect. They also often have multiple large air entries or tuyeres to help reduce resistance to air flow. Natural draft furnaces where used to smelt iron in ancient times in Europe and up to more recently in Africa where some are still standing. The lack of the need for bellows reduces labor and complexity.
The furnace was 1.5 m tall and 25 cm internal diameter with 4 tuyeres 5 cm internal diameter. Charcoal was used as a fuel and iron bacteria was used as an ore. The smelt produced about 4 g of iron prills but could probably be improved with a longer preheat and a higher charcoal to or ratio. A second smelt was run with slag from previous smelts using 8 tuyeres this time to increase air flow. But it made only about a gram of iron, possibly due to the slag not having much iron left in it.
Natural draft furnaces do not rely on bellows or blowers and so labor is significantly decreased during a smelt. They are also simpler to operate with less components to break down or maintain. However, I’ve read that they use more charcoal per iron made, possibly because part of the energy from the fuel goes into supplying the air flow through the furnace. With further experimentation, I believe that my natural draft furnaces can make better yields of iron.
About Primitive Technology:
Primitive technology is a hobby where you build things in the wild completely from scratch using no modern tools or materials. These are the strict rules: If you want a fire, use a fire stick – An axe, pick up a stone and shape it – A hut, build one from trees, mud, rocks etc. The challenge is seeing how far you can go without utilizing modern technology. I do not live in the wild, but enjoy building shelter, tools, and more, only utilizing natural materials. To find specific videos, visit my playlist tab for building videos focused on pyrotechnology, shelter, weapons, food & agriculture, tools & machines, and weaving & fiber.
#PrimitiveTechnology #Iron Smelt #Draft Furnace