As stated above. Some metals and stuff are fine if you were to throw them into say, a camp fire, so to smelt them you need… hotter fire? How does one achieve that hotter fire and how/ why does it work?
In: Chemistry
What you need to remember about burning things is that they *begin* burning at a certain temperature. They can also burn at a higher temperature than that. When they do burn, they release energy which is partly expressed as heat, making the temperature hotter.
The trick at this point is to trap the heat produced by burning by surrounding the flame with an insulator, such as clay or stone, while keeping it fed with oxygen and combustible materials. If you trap enough heat, it will become hot enough to melt your desired material.
The heat of the fire is energy. That energy was in the past absorbed when a chemical bond was formed.
As chemical compounds desintegrate and recombine into something else, that energy is released. Some other chemical reactions do the opposite, and the material cools down as new chemical bonds are formed which consumes energy.
The amount of heat depends on quality and quantity of fuel.
Different fuels have different atoms in their molecules, different bonds, so amount of heat per gram if fuel is different.
The quantity can be adjusted by atomizing (spraying) liquid fuel, increasing the area of contact with the oxidizer (oxygen).
Another way to get more heat is to make sure the fire isn’t starving: if you light up a pile of firewood, it burns hot, but the rate if burning is linited by oxygen. If you blow air onto the pile, instead of relying on gases naturally flowing, the burning will be more intense, and oroduce more heat. That how they smelted metals back in the day.
When I say “more heat”, I mean more heat per second. Regardless of how you burn your fuel, the total amount of heat depends on composition and mass of fuel.
By mass, hydrogen got 3 times more energy than diesel fuel, and diesel fuel is at least twice as rich as firewood.
Fire is a chemical reaction that generates energy – the temperature reached depends on how much mass there is, how much is reacting (I.e. burning), and how much is accumulating vs being lost (such as to the wind in a camp fire) – so to get higher temperatures, insulation (like brick ovens) can get higher temperatures, more reaction (I.e. higher surface area of wood, using pure oxygen vs warming up non reacting chemicals like nitrogen or water trapped inside the wood, maybe even bellows if the air is the limiting factor)
There’s three ways how a fire can generate higher temperatures:
1. Have a more energetic chemical reaction. Not all combustion is equal, some reactions just produce more heat than others. Not every fire has to be carbon combustion. Magnesium fires and Thermite are crazy hot.
2. Purifying the fuel. Stuff like coal has A LOT of junk. Wood is more junk than fuel. That junk either wastes heat by using it up in unwanted side reactions, or literally just wastes it by being heated. An example of the latter is water. When you burn wood or coal, a lot of heat is wasted on evaporating water. That’s why coke/charcoal burns hotter, it was preprocessed to remove as much junk as possible. Natural gas and other carbohydrates are even purer and better.
3. Have a more energy dense fuel and add more oxygen/oxidiser. If the chemical reaction itself doesn’t generate more energy (converting carbon to carbon dioxide has an upper limit) and the fuel is already as pure as it can be, you can always just have more of the reaction going on at once.
A campfire only gets so hot for a few different reasons. One is that a lot of the heat dissipate into the air, and is kinda lost. Confining the heat in an insulated chambers is a good start toward building higher temperatures. Another reason contained fuel can generate higher temperatures is concentrated oxygen supply. In a woodstove for instance, the chimney creates a natural draft (air flow), pulling fresh air directly to the flames as the exhaust rises up the chimney because of the fact that heat rises. The higher the chimney, the more intense this effect can be. Then, there’s also the possibility of super-charging the air flow artificially with something like a bellows (a modern equivalent would likely use an electric fan instead) to increase the oxygen supply to the fuel. The fuel burns out more quickly, and releases its energy more quickly.
Fire is the reaction of three things: fuel, oxygen and heat. Once the fire is going it is going to generate its own heat. So you need to play with the fuel and oxygen.
the easiest way to get a fire to burn hotter is to force more oxygen into the center of the burning fuel. Many fires (solid fuel external combustion, we are not doing internal combustion here) are oxygen starved so forcing more oxygen into the fire will allow more fuel to burn. You can see this in forges where the open coals have bellows or fans to improve air flow.
Fire is a general thing, it is how 1 thing reacts when there is enough heat and and fuel, it just looks similar. Burning a candle makes fire, burning wood makes fire, they look the same more or less but they are burning different things so won’t be the exact same fire, one hotter one colder. Blow extra air into it and you can make the fire happen faster and therefore hotter.
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