Practical diesel-fired furnace break-in

Discussion in 'Furnaces and their construction' started by Melterskelter, Jan 23, 2018.

  1. Melterskelter

    Melterskelter Gold Banner Member

    I am about to fire for the first time my Hago .75 gal/hr siphon burner furnace. It uses lightweight 1.25" thick refractory concrete as a hot face and will eventually be wrapped with 2" of ceramic blanket. It is large enough to accommodate an A20 crucible. I intend to fire the furnace empty initially.

    The cement manufacturer instruction literature recommends a very slow ramp to temperature over 12 or more hours. Obviously measuring and controlling firing temp to follow those instructions would be impractical.

    What procedure would folks follow? TIA.

    Denis
     
  2. PatJ

    PatJ Silver

    I used a propane burner on very low to start the drying process for my refractory shell, and increased the output slowly over about 3 hours. (I have never used a light bulb).
    I ran out of propane so I switched to an oil burner running on diesel with very low compressed air pressure (perhaps 5 psi) and very little fuel flow, and no combustion air blower, and ran that for another 3 hours, gradually increasing the oil flow over those three hours.

    Keep an eye on the steam coming out of the refractory (note that the term "concrete" generally refers to a different product than "refractory", and concrete generally will explode when heated; see videos on y-tube).
    There should be some steam coming out of the refractory during the drying process, but not very much.
    If a lot of steam begins to come out of the refractory, you should turn the burner down to avoid a steam explosion.

    Hope this helps.

    Edit:
    Here was my dryout, starting at post #55:
    http://forums.thehomefoundry.org/index.php?threads/a-thin-hotface-beer-keg-furnace.26/page-3

    Edit2:
    I suppose you could do the intire drying process with a diesel burner if you keep it turned down low enough.
     
    Last edited: Jan 23, 2018
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  3. J.Vibert

    J.Vibert Silver

    I did a preliminary dry out before a burner based "curing" by burning wood scraps in my furnace for a few hours. I'd be lying if I said that I kept tight tabs on the internal temp, but it doesn't take much thought to start with a little fire that's naturally aspirated, and then over time increase the fuel and introduce combustion air. Once the steam slowed down I increased the intensity. Once increasing the intensity revealed no further steam off, I stoked the wood based fire as hard as I could.

    Didn't do a burner (propane/oil) curing till a week or two later. That said, with the bulk of the moisture already driven out, I didn't waste too much time cranking the burner to it's max.

    The more experienced may argue this, but I find creating low heat with oil burners difficult. That may not go beyond me opting for a drip style rather than a nozzle.
     
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  4. master53yoda

    master53yoda Silver

    I would also do the initial firing with propane as the hago won't atomize the oil much below 1/2 gpm which is still 75kbtuh. that will take your furnace over 1000F in less then 10 minutes. I would suggest using the hago nozzle as a low pressure propane orifice without oil. by using a BBQ regulator and shut off valve, pipe the propane into the compressed air connection. The combustion air may need to be turned down a little as well but it will work at fairly low firing rates. if this doesn't make sense let me know and ill try to mark up a picture of my burner connected that way.

    Art B
     
  5. Petee716

    Petee716 Gold Banner Member

    I did the same as JVibert on all of my furnaces except once the bore was red hot with a stoked charcoal fire (after several hours of build-up from a slow steady wood fire), i inserted the oil burner and let'er have it and then held it for a couple hours. I had hung a lightbulb for about a week prior. The whole thing lasted 4 or 5 hours IIRC.
    I dont know the ceramic chemistry involved in curing but im convinced that most of our concern is removing the free water and liberating any combined water. Initially it has to be done slowly. I notice that some manufacturers refer to a "dry out schedule" as opposed to a "curing" schedule.

    Pete
     
  6. Jason

    Jason Gold

    What refractory did u use?
     
  7. Melterskelter

    Melterskelter Gold Banner Member

    Vesuvius low water castable Criterion 70

    CRITERION® 70 CASTABLE
    Product Information Sheet Monolithic Refractory
    CRITERION® 70 is a high alumina low cement vibration castable that requires only half the water needed for
    conventional castables, resulting in a product that has superior densities, lower porosities and higher
    strengths. It is designed for use in refractory consuming areas that require a castable with low iron content,
    high hot strengths, increased erosion resistance and reduced hot load deformation.
    Service Temperature: 1760 °C Material Required: 2627 kg/m3
    Typical Water Required: 5.0 - 6.0 % Maximum Grain Size: -
    Chemical Analysis
    SiO2 TiO2 Al2O3 Fe2O3 CaO Other
    22.9 2.3 71.4 1.0 1.8 0.6


    I went ahead and used my siphon nozzle without additional combustion air at its lowest stable settings to warm the hotface as slowly as possible. Considering the fact that Vesuvius recommends curing it over something like an 18 hour period, what I did was much too rapid. There is no practical way I could spend 18 hours ramping the temp in 50 degree increments even if I had a means of accurately measuring the temp internally.

    But, so far I see no ill effects. I ran the burner for 3 hours and did not get to an incandescent heat until I turned up the nozzle (but no additional combustion air) in the last 1/2 hour of the burn. After burning for 30 minutes, I just could detect a dull red glow of the lining. I was then out of time and had to shut down the burner, plug the hole in the lid with insulating blanket and call it a day. I just put the furnace away and can see no ill effects---no cracks, no spalling, bright and clean white lining.
    Hago burner (2).JPG Hago burner (1).JPG
    Tomorrow, I intend to hook up the blower to the burner and take it gradually up to full heat.

    Hopefully some pics of the furnace itself. Raining today and cold---not too conducive to pics or vids.
     
    Last edited: Jan 23, 2018
  8. Jason

    Jason Gold

    Vesuvius... Good name for a refractory cement. That burner looks fantastic. Low and slow and you'll be fine. I personally think 18hrs is BS.
     
  9. Melterskelter

    Melterskelter Gold Banner Member

    Here is a video of it being tested prior to installing in the furnace. I am impressed that the Hago does a superb job of atomizing the diesel.

     
  10. PatJ

    PatJ Silver

    Six hours total will do it if the shell is perhaps in the 1-2 inch thick range.
    Perhaps for a large commercial furnace with some thick refractory, the longer dry-out time may be needed.

    That is a pretty radical burner design.
    I guess you are aware that you will need to either pull the burner back from the furnace when you turn it off, or keep the combustion air going, else you may melt the o-ring in the nozzle.
     
  11. Melterskelter

    Melterskelter Gold Banner Member

    Surely cooked the o-ring today as I got a call and had to just shut down and leave. I better buy a few backup rings. The burner is pretty easy to remove as it is mounted to the furnace by the slotted fin with just two bolts. Impact driver or speed wrench makes quick work of them.
     
  12. PatJ

    PatJ Silver

    I have never melted an 0-ring, and have left the burner in the furnace for a few minutes after shutdown a couple of times, not intentionally.
    I think the o-ring can withstand some abuse.

    As a precaution I generally pull the burner tube back from the furnace after I turn it off.

    Maybe you could just use a pin instead of bolts to hold your burner tube in place, and you could pull the pin out, like the pin that hold the receiver to a trailer hitch.
    There is not much stress on the pin, so it would not take much to holds the burner tube in place.
    I usually support the outer end of the burner with a brick or a permanent adjustable stand, and generally don't attach it at the furnace, since the tuyere opening supports the end of the burner tube.
     
  13. Jason

    Jason Gold

    Never melted an O ring in my burner... Oh that's right! There isn't one in the Kwicky! :p
     
  14. PatJ

    PatJ Silver

    That sounds like a problem looking for a solution; you better add an o-ring to your burner. :cool:

    But seriously I have a design for a siphon nozzle that does not use an o-ring, but I just have not had any problems with o-rings, and there is no sense fixing something that is not broken.
    And I want to be able to swap out the nozzle tip should I ever need or want to.

    Here is one of my early burner designs.
    http://forums.thehomefoundry.org/in...ly-siphon-nozzle-burner-design.236/#post-3924
     
  15. Melterskelter

    Melterskelter Gold Banner Member


    Yes, the fin is coming off the tube this morning (cut-off blades for angle grinders might have been invented with me in mind :)). I think I will just cut the fin height down and weld it onto a piece of angle at the apex of the angle. The fin will attach to the furnace as before. Then the tube can just lay in “arms” of the angle and be secured with some simple retaining strap or even twisted baling wire. That way insertion and removal will be quick and easy and yet it will be fairly well supported.
     
  16. Melterskelter

    Melterskelter Gold Banner Member

    BTW, I was surprised that my o-ring survived. Maybe it didn't get cooked as I had only brought the furnace up to (guessing by color) 1100 or 1200 degrees F. Nevertheless, in the future, I will be sure to pull the burner tube out as I shut down. No sense tempting fate.
     
    Last edited: Jan 24, 2018
  17. PatJ

    PatJ Silver

    The o-rings will take some abuse.
    I have forgotten and left mine in the furnace a few times, and still did not have problems.

    For a very hot iron melt, the o-ring would probably not last as long if left in the furnace after a melt.
     
  18. Melterskelter

    Melterskelter Gold Banner Member

    Yesterday there was some discussion concerning protection of the siphon nozzle o-ring and removing the burner from the furnace at the end of a burn. My original setup consisted of a fin welded to the burner tube. The fin was attached to the base of the furnace with bolts. It seemed like this would be a cumbersome arrangement not well suited to frequent insertion and removal of the burner. So, the fin was cut off and a "tray" was made to hold the tube in position but still allow easy insertion and removal.

    I also added the blanket insulation to the hot face and secured the furnace shell with screws to the base. Hoping to fire it up again before dark. burner suport (3).JPG burner suport (4).JPG burner suport (1).JPG burner suport (2).JPG
     
  19. PatJ

    PatJ Silver

    I am stealing that idea if you don't mind.
     
  20. Melterskelter

    Melterskelter Gold Banner Member

    That's the idea of posting. I've stolen so many ideas.... Hate to try to invent it all from scratch.
     

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