Oxygen concentrator for hotter burner ?

Discussion in 'Burners and their construction' started by metallab, Nov 11, 2023.

  1. metallab

    metallab Silver

    On some Youtube videos and in real life (glass blower) I saw medical oxygen concentrators which deliver highly O2 concentrated air up till 90% O2.
    I can buy one for about $300-$400 and want to feed the O2 hose into the input of the air blower of the burner of my furnace. The output is only 2 liters per minute, so it might increase the O2 in the air fed to the burner only with a few percent.
    Does that really increase the flame / furnace temperature ?
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I spent many years developing oxygen concentrators for commercial and military applications. It definitelywill increase flame temp but you will likely need more than 2 lpm of flow. As I recall, you have a very small furnace so it will be a matter of how much enrichment of the combustion air you can achieve. You will need to estimate your combustion air flow rate and calculate the level enrichment. You can probably make a rough estimate if you know your fuel consumption rate and then assume stoichiometric burn to derive amount of O2 and resulting air flow.

    I'd suggest you just buy or borrow a bottle of compressed O2 and experiment first to see what flow is need for a given increase in temperature.

  3. You could also burn a fuel that contains it's own oxygen like nitromethane at a considerably higher cost.
  4. metallab

    metallab Silver

    Indeed, CH3NO2 is considerably more expensive and it is a liquid, so harder to setup.
    I calculated whether it is effective.
    When melting on household natural gas, the gas meter counts 9 seconds per liter which means about 7 liters per minute. That requires twice the volume of oxygen according to :
    CH4 + 2O2 => CO2 + 2 H2O.
    That means 14 l O2 per minute, so adding 2 l extra (some sources say it delivers 5 l / min) might enrich the O2 content of air increase to about 30%.
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Most of the home health care O2 concentrators here in the US are either 3 or 5 lpm capacity at >90%. They utilize molecular sieves and pressure swing adsorption process. They can flow more gas at lower oxygen concentrations. The product gas will have very low pressure dew points because the molecular sieves and PSA process are a strong desicator.

    You'll find you need high concentrations of O2 to make it worth the effort and that will require multiple or a much larger oxygen concentrator. The primary benefit is not having to raise the temperature of the N2 in the air. Here in the US in the 1980s, many larger systems were sold into muffler shops for cutting steel with acetylene. 90% O2 limits the depth of cut and can increase fuel consumption but the economics were still favorable for cutting thin steel muffler tube versus buying/having commercial oxygen delievered.....at least back then.

  6. Ironsides

    Ironsides Silver

    Years ago I used bottled oxygen to enrich the blast on my cupola and used 4% . I was amazed on how well it worked the tap temperature was 120C above normal. That experiment was done twice to see if it was a fluke the first time around and was not. I'm sure a lower percentage could be used and still work. The downside is it is too expensive to use bottled oxygen because it is so expensive in Australia.

    I did find a oxygen concentrater in hard rubbish and have used it a lot with propane to do small jobs like silver soldering and bending small pieces of steel. There is one thing you have to watch when using one, if you use too much oxygen the oxygen level decreases so it will shut down. There is a waiting period before you can use it again and resets.
  7. Robert

    Robert Silver

    I have a medical O2 concentrator. It puts out about 4-5l/min. I use it to supply a small oxy-propane setup which is fine for brazing small parts. I can tell you that at max output it can barely make a small torch flame. It would not be inadequate for a typical furnace burner and I doubt it would get you to much higher temp. Maybe a slight improvement. Go with a blower.
    The camera makes the flame more impressive that it really is. The central blue cone is not visible and it about 3/4" long.
  8. mytwhyt

    mytwhyt Silver

    I've used that torch for years. Pretty much wore out the line covers. Found a new one online, with 5 tips under 30$. It does a great job for sizing rings and any other small soldering jobs. The tips it comes with are not large enough to melt a couple ounces of silver in the crucible of my Kerr casting machine.. I drilled my old largest tip until it did the job.. I do use regulators and large bottles so I don't know if small bottles and no regulators would do the job..
    Those used small Kerr machines can be found online for around 200$. I've used one for 50+ years [the same one] and have cast 1000s of pieces in gold and silver.
    It's interesting to see that the tiny torch can be run off those small bottles without the need for regulators. Especially for people with a small wallet only looking to try lost wax for jewelry. Would like to know how it works with small bottles and the tips the Tiny Torch comes with.
  9. Robert

    Robert Silver

    That is a home made tip in the pic but similar performance with the standard tips.
  10. So how about filling an 80 gallon air tank with O2 enriched air? I don't know how much pressure the enrichers put out but you don't need pressure much to store 45 minutes of flow to your burner.
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Without modifications the home helath care concentrators can only deliver to a couple psig. With mods, 15-30 psig depending.

    Just a caution, O2 is very reactive and when compressed can be a real fire hazard when stored in contact with incompatible materials and the list of compatible materials is small. At these pressures not so much but at high pressures, fires can easily occur through kindling chains. It starts with ignition of oily or dirty surface, which ignites a polymer, which then ignites a metal like aluminum which becomes high energy fuel in the presence of high pressure O2, then all holy hell breaks loose.

    Robert likes this.
  12. Ironsides

    Ironsides Silver

    So true.
  13. Really good points. I may have made the erroneous assumption that users here were familiar with the hazards of pure oxygen. Even so, it bears repeating.

    My thought was to run a vessel up to essentially the minimum pressure to operate the furnace for the expected run time. If you need 10 lpm, that's about 2.6 gallons per minute. For one hour that's about 150 cubic feet. For an 80 gallon tank that would be about 30 psi to start. That's probably too high.
  14. Robert

    Robert Silver

    There are videos on YT of guys using an O2 concentrator and pumping it into an empty propane tank under pressure. I would be VERY concerned about getting any oil in there from the pump or residue in the tank. That could create a bomb! I would not mess with it.
  15. nobodyspecial

    nobodyspecial Copper

    Please forgive my ignorance, I'm new here and come from a mostly forging background, but wouldn't a reducing, i.e. low oxygen atmosphere in the furnace be preferable to lessen oxidation in the metal? Perhaps not if it were being burned up, but it's often a serious issue in forge welding with novices that simply turn up the air blast to get the heat up fast. I've also noticed that I get more oxides in aluminum if air is swirling more directly over the crucible.
  16. Tobho Mott

    Tobho Mott Administrator Staff Member Banner Member

    Some do use a slightly reducing furnace for copper alloys, which can otherwise oxidize badly during a melt. For aluminum casting, a reducing furnace can lead to an excess of dissolved hydrogen in the metal, leading to porosity beneath the surface of castings. Some extra dross floating on the surface isn't a huge deal, you just skim it off and pour. Just try not to let it get stirred into the clean metal, that's when it can become a problem. I'm pretty sure most here generally aim for a very near neutral mixture, not more than slightly rich or lean.


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