Furnace
A furnace is a appliance that generates heat, usually from combustible material.
The controlled enviornment allows for greater efficiency and control over the reaction.
Uses
Depending on the design, furnaces serve a multitude of functions and form the basis of a wide variety processes.
The most common and important furnaces are used for food preparation and curing.
Food
By cooking food, it can be more digestible for humans.
The resulting smoke from the fire can be used to cure food more effectively for long term storage.
Boiling can sterilize water.
Materials
Curing
Firing clay allows the vessel to become permanently set.
This process applies to all pottery, roof shingles, bricks, and earthware.
Most drying processes can be accelerated with heat as the water evaporates faster[1].
Fuels
Great availabilty
Any dry plant matter will work to some degree.
Easily accesible sources of high yield fuels are wood and charcoal.
Both can be farmed on industrial scales or manufactured in small batches.
Good availabilty
Alcohol is a good source of liqid fuels that offer some advantes over solid fuels but also carries additonal risk.
Reliable combustion can be achieved with 50% to 60% alcohol content. To achieve this concentration, the alcohol needs to be distilled.
Situatoinal availabilty
Turf and dried lifestock dung can be burned. The smoke will be more irritating and harmful than other fuel soruces.
Nonetheless it serves as a vable alternative.
Natural Gas may be harvested in a bioreactor or sometimes found in nature.
Electricity
Heating elements made from resistive materials can be used to convert electricity into heat on demand in finely controlled quantities.
For steel production, plasma arcs are leveraged. Only the melting point of the electrodes limits the effective temperature of the furnace.
Alternatively, inductive heating can be used to effectively heat electrically condructive materials.
Construction
The basis of any common furnace type forms the chimney effect.
Heat rises out of the chimney, any vaguely tubular structure will do, and pulls in fresh air from the bottom inlet.
The fresh, cold air provides more oxygen and stokes the fire. This effect can be enhanced with forced convection to reach the necessary temperatures for smelting and forging metal.
By constriciting the air inlet, the rate of combustion can be adjusted.