Getting My Furnace(s) Up and Running

Discussion in 'Burners and their construction' started by HotRodTractor, Jan 14, 2021.

  1. HotRodTractor

    HotRodTractor Copper

    A couple of weeks ago I picked up a couple of commercial furnaces. Both of them Speedy Melts - one is a B16 unit and is entirely complete. The other I can best describe as an older version of a B-702. This larger furnace does not have a burner system with it - only the shell and refractory.

    In the long term, I think I want to run these two furnaces on oil - either waste oil, diesel, or a mixture of both. As of right now, I am sitting on over 300 gallons of waste oil generated from the equipment on the farm and various antique cars/tractors.... I usually have this collected by a local business that uses it for shop heat. I also usually have a couple of hundred gallons of bulk off-road diesel on hand. So in my knee jerk - this seems like a good way to go.

    For the moment I am going to concentrate on getting the B16 up and running. I have found and printed out the manual, and might very well start out on a couple of propane bottles in the short term. I do have a few propane bottles and some propane fitting, hosing, and other hardware from playing with antique LP powered tractors. Unfortunately, I am setting the furnace up in a storage building that is at my house and not my main shop - otherwise, I would just tie into the existing propane system there.

    It is my understanding from the reading on the forum that if going the route of an oil-fired furnace that two things need to be different: 1) there needs to be more clearance around the crucible than a gas-fired unit, 2) The burner inlet into the furnace needs to be larger to accommodate more air for a complete oil burn.

    Does this mean that I need to go with a smaller crucible than an A16 to increase my hot face to crucible distance? Just dropping to an A12 doesn't look like I gain anything of note.....

    The current inlet pipe has an ID of 2" - If I want to match the BTU output of the furnace as originally intended - can I do that with a burner that will fit in there? (475k BTUs)

    Am I better off getting a good consistent propane supply and just sticking with that?

    Thanks,

    Jason
     
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    What's the clearance between the B16 furnace wall and the A16 crucible? Was the previous 475kbtu through the 2" tube rating a natural gas burner?

    Best,
    Kelly
     
  3. HotRodTractor

    HotRodTractor Copper

    About an 1-3/8" clearance if my math is right - based on the top dimension. I don't have a crucible, don't these bow out a bit in the middle? That would shrink that some.

    Teh 475K BTU through the 2" ID tube is for natural gas/propane. They market these as "multifuel" in that they don't have an orifice and you can adjust it to work with either.
     
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Maybe slightly on the tight side but I would think workable for an oil burner. Bilge crucibles are slightly larger at mid-height than they are at the top but A-style crucibles are widest at the top.
    I think a 2" Tuyere tube can support an a very large energy level with an oil burner, supported by a decent blower. The other factor is related to furnace volume and is why I asked about the bore. There is a limit to how much fuel/air you can introduce and get it to burn completely and the latter is related to a number of things like flame propagation speed of the fuel you're burning, the degree of atomization of the fuel, and control and tune in general. What fuel you choose to use is mostly economics and practicality. If you are going to melt a lot, it's hard to beat burning free waste oil. If only occasional, diesel is very convenient. Waste oil can be a little more finicky with seasonal temperature changes but that can be overcome. Then there is style of burner and the pros/cons there which can become a little lengthier discussion, but plenty of experience here on the forum on that.

    Best,
    Kelly
     
  5. HotRodTractor

    HotRodTractor Copper

    At a high level, I was considering building something similar to the one that I see myfordboy run - or at least inspired by. An air siphon spray nozzle and a blower - both sized as appropriately as I can.

    I do plan to melt a lot. I have a lot of parts to produce once I get things up and running. I have big ambitions that include some cylinder heads and associated parts. Along the way some batches of some widgets will be made to sell to help support the larger project. Don't worry - I do have some much simpler stuff to start with than a cylinder head. Mostly I plan on casting aluminum - with some brass/bronze along the way. I wouldn't mind being able to do iron for some of the projects along the way, but that is a much longer-term goal that I'm not concerned with today.
     
  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    This becomes a horses for courses discussion. I'm sure others will chime in too but here's my take.

    Aluminum is not at all challenging to melt, but it benefits from a very lean furnace atmosphere. I think this is somewhat easier to control with propane or natural gas, not that you can't have a lean burn with other fuels, but propane is clean and fuel rich furnace atmospheres can produce hydrogen porosity in aluminum. I use a resistive electric furnace for aluminum because you just can't get much leaner than that. This is very important topic for aluminum castings that have more challenging mechanical property requirements like a cylinder head....not so much for ornaments.

    Copper alloys like rich (very low O2) environments because they react strongly with any available oxygen. They don't particularly care about unburnt hydrocarbons. Iron needs a lot of heat and usually a fine tune burner for fuel fired hobby furnaces and most use diesel/oils for that task.

    So, I'd say you either need to get very familiar with your oil burner or maybe think about a couple burners. Propane burners are so simple, you can build and get comfortable with one in a couple hours. Oil burners usually require a little more experimentation, but they both have their strong points.

    Best,
    Kelly
     
    Tobho Mott likes this.
  7. HotRodTractor

    HotRodTractor Copper

    Porosity sucks. I definitely need to do all I can to avoid that. I was already planning on building a degassing lance for the small furnace and probably a small rotary degasser for the larger furnace. But those are subjects for an entirely different thread.

    The atmosphere in the furnace is definitely something that I know I need to keep clean - I just assumed that I could make an efficient oil burner that could run lean enough to keep it clean. Even if that means it's straight diesel and not waste oil.
     
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    ....and I think that's doable........just will take a little extra effort and what I meant about getting to know your burner and refining/improving with every pour.

    Best,
    Kelly
     
    HotRodTractor likes this.
  9. HotRodTractor

    HotRodTractor Copper

    I took the time to hook electric up to my burner unit for the B16 to make sure everything works. The blower fired right up, automatic spark ignition was zapping hard. I'm ready to hook up some gas and see what it does. I have to scrounge up a high-pressure propane regulator and an odd fitting that I'll just order off of Amazon, and I will be ready to fire the B16 and make sure it works on a 20lb tank. I'll use that to help judge how soon I try out a fuel-fired burner.

    PXL_20210114_232520782.jpg

    I have started looking for parts for an oil burner. My big hang-up is that it looks like I need a 200cfm blower for the big furnace (if the online calculator I found is right - I haven't done the math myself to verify). Finding a 200ish plus cfm pressure blower is looking like it will cause me to spend some decent money. That might just have to wait until I get other things setup and castings start happening with the smaller unit.
     
    Billy Elmore likes this.
  10. master53yoda

    master53yoda Silver

    I think that you will find it somewhat difficult to get 475kbtu through a 2 " burner with propane or NG. a 2 inch burner normally limits at about 250K. To get beyond that you will need to use a high pressure fan like a Shop Vac or leaf blower. A backward inclined blade fan can get about 3 to 4" static pressure. A squirrel cage fan can only get about 1'' which isn't sufficient pressure for our furnaces. The waste oil nozzle also provides about 20 to 30% of the needed combustion air.

    I fire my tilting furnace with a combination waste oil and Propane . Each burner puts out about 375 to 400btuh. My furnace is capable of melting 250 lbs aluminum per hour. Our crucible furnaces for nonferrous melts will seldom need more them 250kbtuh, you would need the higher firing rate for Iron. The thing I like about air atomized "'siphon" nozzle burners is there ability to vary the firing rate by simply varying the oil feed pressure. I also have needle valve control on my burners as I vary from the 375k to 75K based on furnace temps and exhaust temps. My waste oil is also heated to 150F.

    You will need to go to a larger than 20lb propane tank because it will freeze to quickly. I use the 7 gallon tanks from an RV I think they are rated at 60lb. It will feed both my 80k propane stabilization burners at the same time for an hour with out freezing up even if I start with them half full.
     
    Last edited: Mar 22, 2021
    HotRodTractor likes this.
  11. HotRodTractor

    HotRodTractor Copper

    I'm only using the 20lb tank to test things out - its a short term solution while I work on the long term one. I've kept 20lb cylinders in a tank of hot water before to keep pressure up. (As well as used heated blankets and heat guns on nitrous tanks at the drag strip... lol )

    I scored a nice pressure blower used for conveying material - its probably a little big, but its where I am going to start on making the fuel oil burner. I picked up some fuel oil siphon nozzles with lots of different tips for tuning things in while I figure out what I really need. I'm just quoting the BTU requirements I found listed for the commercial units I have, or at least similar to.
     

Share This Page