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Got them ole' crumbling refractory blues...

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Nofossil, Dec 3, 2007.

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  1. Nofossil

    Nofossil Moderator Emeritus

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    I had an earlier thread on my attempts at a different combustion labyrinth for my EKO 25. While the design met the goals of faster startup, better heat transfer, and easier ash cleanout, my troubles are not yet over. An earlier inspection showed that the high-alumina lightweight refractory bricks were becoming high-alumina gravel. Also, the ceramic wool board that I use for the horizontal separator had melted where the flame hits directly under the nozzle.

    I placed a thin sheet of titanium over the ceramic board to protect it, as earlier efforts with stainless steel and ceramic tile had been less than encouraging. Here's a photo of the titanium sheet after a few weeks:

    [​IMG]

    Below is a picture showing the remains of one of the two firebricks that form the side of the top section as well as a photo of the whole assembly when it was new. The combustion happens in the top section, and the combustion gases then flow down and out towards the ash removal door. There, they flow out either side of the labyrinth and back along the sides to the back of the boiler.

    Anyone out there with any refractory material suggestions?

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  2. Eric Johnson

    Eric Johnson Mod Emeritus

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    Too bad; it looked so cool.

    It's quite possible that I'm missing something, but why don't you just build some wooden forms and cast your pieces out of the refractory cement that is used to fill the doors and other parts of the gasification chamber? You might be able to weld up a steel framework and fill that, although I don't know if the steel would hold up.
  3. Nofossil

    Nofossil Moderator Emeritus

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    It's still working, so don't be too upset. It's just not the final solution yet.

    I would try that as a last resort, unless I can find a refractory expert who increases my comfort level. I anticipate three problems with such a solution:

    1) It would have more mass and therefore delay the transition to full gasification
    2) It would be heavy and hard to remove when I need to clean behind it
    3) A monolithic structure seems more likely to crack given the temperature extremes from top to bottom.

    I could possibly address concern #1 by facing the hot side with some of the lightweight alumina, and I could cast it in sections to reduce the concerns. I was hoping for a solution that was as simple as possible, and where any part could easily be replaced if needs be. I'm down but not defeated on this one.
  4. Eric Johnson

    Eric Johnson Mod Emeritus

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    See, I was missing something!

    I was thinking more along the lines of casting individual pieces and then putting them together into a final assembly, similar to what you did with the alumina.

    But I can't do anything about the weight or the mass.

    Is it possible to blow air bubbles into the refractory mix before it sets up?
  5. Nofossil

    Nofossil Moderator Emeritus

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    At the end of the day, I'd want to have some reason to expect that what I cast would fare better than the 2300 degree alumina bricks did, and I don't know enough yet to have that confidence.

    I'm hoping that someone comes along and says something like "Oh! You need to use xyz and cast it in this particular way" and I'll be off and running. Google has not been the resource I would hope for on this problem.
  6. Jags

    Jags Moderate Moderator Staff Member

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    If you were to make your own forms, couldn't you use the alumina boards and cast refractory cement around them, making an oreo cookie kind of thing. It would be lighter than solid refractory material, and the cement would somewhat protect the alumina? Just thinking out loud. I probably shouldn't do that, it gets me in trouble.
  7. Nofossil

    Nofossil Moderator Emeritus

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    Seems reasonable. Of course, the alumina bricks seemed reasonable too - they're rated for 2300 degrees. I though that the titanium sheet was a good idea, but that didn't work so well either. I'm going to keep collecting ideas and hope for an expert to appear.
  8. Jags

    Jags Moderate Moderator Staff Member

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    Old space shuttle tiles????? (told you I shouldn't think out loud)
  9. Nofossil

    Nofossil Moderator Emeritus

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    That's essentially what the bricks in the initial post are. Incredibly light - like foamed rock. They didn't melt, but they did crumble. Maybe NASA reinforces them with something - wonder if they sell the used ones on eBay?
  10. Eric Johnson

    Eric Johnson Mod Emeritus

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    I think you could be fairly confident that it would hold up, since other components made like that, such as the gasification door, regularly see direct exposure to the flames. Or use the same stuff they make the stock bricks out of.

    Again, that doesn't address the weight issue.
  11. Nofossil

    Nofossil Moderator Emeritus

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    So.... what do they make those parts out of? Calling the factory isn't so easy.
  12. antknee2

    antknee2 New Member

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    How about use the factory unit but set it on small solid round stainless steel rods so it's rolls out easy for cleaning ?
  13. Eric Johnson

    Eric Johnson Mod Emeritus

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    I'm sure Zenon can get it or knows where you can get it. I've seen big industrial boilers with similar construction. If you go to Seton's website and click on his DIY boiler project, he's got the bags of refractory cement for pouring the heat sink for sale. I bet it's the same stuff.
  14. mikeyny

    mikeyny Feeling the Heat

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    you might try adding some perlite to the refractory mix to take up space and make it a bit lighter. It is lite weight cheap and fire proof. I used a mixture of refractory cement and perlite to insulate the top of the heat exchanger on my old hs tarm. It is snot anywhere near the flame path but has held up well for 4 yrs now. Try google on perlite and see what come up.
  15. Eric Johnson

    Eric Johnson Mod Emeritus

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    Perlite is a good idea. Vermiculite is another. Perlite is used by gardeners to aerate homemade soil mixes. It costs about $20 a yard. You can get vermiculite any place that sells masonry supplies. It's about the same price as perlite.

    I've always been intrigued by your design, nofossil. Looking at most of the commercial units out there, all seem to favor a curved base arrangement, so there must be some advantage to deflecting the heat back up and out from its point of impact. Your design forces the gas through a somewhat more tortured path and then into the ash door before allowing it to travel back into the hx tubes. You think that might be too much exposure on the brick?
  16. Nofossil

    Nofossil Moderator Emeritus

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    Seems like perlite or vermiculite (or maybe the crumbled remains of my alumina bricks) might do it. I wonder what the cure time/process is for a cast refractory? I bet the manufacturer would have lots of info.

    As far as I can tell, lengthening the flame path and reflecting heat back into the incoming gas stream seem to be the key points. Curved might be easier to cast, while rectangular is easier to make with blocks. Some designs add turbulence, presumably to improve the mixing of the gases and the fresh air. Clearly my design asks a lot of the materials. Part of the problem is that there's not much room to work with. I'm happy with the performance and the self-cleaning aspects of my design. Most of the ashes end up along the sides near the ash door.

    If you look at mine in operation, the combustion zone includes the wrap-around from top to bottom. The materials there seem to be all right. It's the top chamber where the flame comes out of the nozzle that takes a beating.
  17. leaddog

    leaddog Minister of Fire

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    Nofossil, Here is a link to a seller on ebay here in michigan that sells refactory material. He also sells bio-bricks. I've thought about trying some to see how they burn in a eko.http://stores.ebay.com/FIRE-and-ICE-Supplies
    leaddog
  18. Nofossil

    Nofossil Moderator Emeritus

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    Thanks. More research is underway.
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