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I (thermo) how to calculate the temperature of a coal furnace (applied)

  1. Jun 18, 2017 #1
    I am an new EE with my FE, but my thermo knowledge is lacking in many areas. Its one area where i would like to become an expert. So i try to find ways of applying thermo analysis on my free time to imprve my skills. where here is one and I have no idea where to even start.

    a youtuber with a large following goes into the woods on his spare time and trys to make things from scratch building off previous things made in previous weeks. he is trying to smelt iron using his own designed forge

    here is the youtiube video of him collecting the material and adding flux to attempt to reduce the melting point.

    turn on Closed captions in the bottom right of the screen, he doesnt talk but adds subtitles for simple explaination (and maybe even inaccurate information). The charcoal he uses was made by him in a previous video. So whatever the natural specific heat of charcoal (carbon graphite) is 0.71 (kJ/(kg K))

    it seems like the slag left over at the end didnt get anywhere near hot enough to be extract most of the iron. how do i approach attempting to calculate the temperature of the furnace? i would assume just looking at this from the most basic PV=nRT he should cover the top to increase the pressure, but would that be enough to reach the ~1500*C needed to melt it? mathematically how does the temperature correlate with the air flow?
    i know measurements of everything isn't given in the video but if some scratch paper calculations were to be done how would I start? if the design cant reach 1500*C any general design that would be better?

  2. jcsd
  3. Jun 18, 2017 #2


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    Hi kyle,

    His furnace looks to be something a blacksmith from ye olden times would use to heat up an piece of iron to red yellow temperature or more to hammer into a shape. Think "horseshoes". 2000C temperature or more can be attained from a crafted design of furnace.

    The flux, calcium carbonate, limestone, would be used to pull impurities from the iron ore.
    The carbon, charcoal, is what reduces the oxidized iron ore to a metallic iron called pig iron, with a melting temperature of around 1200C, due to the high carbon content in the iron. Further processing is needed to pull the carbon out to then make steel with added ingredients.
    At least that is how it works for an industrial blast furnace and steel making.

    Having said that, the earliest method used to produce iron was with a bloomery.
    Here again the temperature of the furnace can be lower than the melting temperature of the pure iron as the reduction is through diffusion.
    I suppose that is what he is attempting to do with his furnace and mold of "iron bacteria". ie get wrought iron as his final product.

    As for the actual working temperature of the furnace - hmm.
    You can investigate the adiabatic flame temperature - constant pressure process since the burning is done in open air.
    I imagine several assumptions, ( mainly guesses as to the operating state of the furnace in the video ) can give a not too satisfactory answer.
    Some more reading and investigation on the bloomery to give the guesses more validity. After all, the experience of centuries is behind that type of furnace
  4. Jun 18, 2017 #3


    Thank you very much. i will review your material with the book i used to learn thermo "intro to thermodynamicas and statisical mechanics 2nd ed. - keith stowe" yes because its so old, in general we understand completely how this primitve furnace works which is why i thought it would be a cool side project to analyze and learn from. if you have any other recommendations on resources that may be helpful to analyzing crude thermo systems outside of a controlled enviorment where every little thing can be measured down to the purity of the gases and instead for a more crude approach that would be great. thanks again.
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