Larger Moya???

Discussion in 'Burners and their construction' started by HT1, Jun 14, 2019.

  1. HT1

    HT1 Silver

    well that is interesting, I could definitely drill out the Propane side, I'm using a 50 Psi reg, but 3/8 hose is limited to 100,000 BTU per hour... that cannot be correct , I'm currently moving better then 300,000 BTU's per hour

    . I have the Means to move that way up I occasionally Plumb Food trucks so I can get 1 inch flex and even quick disconnects at wholesale, but I would think the regulator would become a bottle neck, I know how we deal with that on a food truck, but lord I dont want to do that for a furnace... Complicated Manifold and Multiple tanks ( we feed a 1 inch pipe or hose from multiple tanks )

    I like the needle valve idea, I have just been using the regulator

    Lots to Ponder

    Thanks Andy

    V/r HT1
  2. oldironfarmer

    oldironfarmer Silver

    I imagine the 100,000 BTU rating for 3/8" hose is for gas coming from a low pressure 6 ounce regulator. If you think about the volume of gas you are putting through a 1/16" drilled hole you'll see you can put a lot more through a 3/8" hose. 3/8" (I don't know your hose I.D.) is 36 times as big as 1/16".

    Putting a needle valve at the burner gives you control there but also keeps the hose pressurized. You can move a lot more propane under higher pressure. Just make sure the hose is rated for your regulator output. (not for you, for occasional readers)

    You are doing 300,000 BTU per hour? that would be at 50 psi?
  3. HT1

    HT1 Silver

    I'm running a Propane 3/8 hose SOO Rated at 300PSI I normally Run my Burner at 21-25 PSI shooting gas through that 1/16 hole. I burn about 4 gallons of propane an hour so Ballpark best SWAG about 300,000 BTU's per hour.

    I have the Means to test at least one thing, I have all the Parts to Build another Moya, so I could build one and drill that orifice out to 1/8 all I suspect will happen is I will run it on a lower PSI with exactly the same results . I'm sure one of these Science Genius college educated folk around here can probably tell me exactly what my New PSI will be... so why should I ??

    V/r HT1
  4. HT1

    HT1 Silver

  5. DavidF

    DavidF Administrator Staff Member Banner Member

    Why not just run a second moya burner???
  6. oldironfarmer

    oldironfarmer Silver

    The spreadsheet I use (which I did not create but seems to give good results) indicates 4 gal/hr is about 360,000 BTU/hr. But to push that much fuel through a 1/16" hole should take almost 60 psi. Did you just recently test your use per hour? It might be worth it to do a fresh before and after weigh if you haven't. Are you certain you hole is 1/16" and not 5/64"? The spreadsheet does indicate 4 gal/hr at 25 psi through a 5/64" hole. If you have 5/64" and can run your pressure up to 40 psi you'll be burning 472,000 BTU/hr, like the MIDCO.

    Are you running a neutral flame, or close to it? A bigger nozzle does not help you unless you can add air for the additional gas.

    If you want to run the same gas through a larger nozzle that will take less pressure. So if you're running 25 psi through a 1/16" hole and you change to a 1/8" hole you'll need to drop the pressure to 1.5 psi to get about the same flow. If you want to double your flow rate by going to a 1/8" orifice you need to run the pressure at 6 psi. But of course you need twice the air to get the same combustion.

    An 1/8" hole and 6 psi will give you about 450,000 BTU/hr.

    I think it's all about the air, can you put enough air in to pull the flame back down to the top of the furnace?
  7. HT1

    HT1 Silver

    well that would lock me into testing a single Variable multiple burners, I would really like to do some serious experimentation to see Just how far Hobbiests can get .
    Oldiron farmer has talked me into a n IFB build, probably not the Way he wants me to do it, but still there should be some improvement over my Insulated Castable... I looked up the Numbers IFB is 4 times more insulating
    remember I ran a cast Missou Furnace... 2 Hours for Brass can IFB give me another big jump.

    I dont think I did a Build tutorial on my current furnace. meant to... but didn't. one of the things i did was it was built around a 1 inch Trex burner when I went through the furnace wall I used the interior of the T rex Flare to cast the tuyere, so i think my burner held the Flame closer to the furnace wall before I started to add air ... Improvement??? potentially

    I still would like to test a larger forced air propane Burner with slower air , but once I cast the Base of the Furnace making a larger tuyere will be pure hell, though filling one up to Make it smaller not so Much of a deal..

    ANYHOW perhaps I will see if My Moya will burn outside of the Furnace, perhaps with the T rex Flare if it does I can put together the Other one and experiment a little without a furnace, because there will be some Plumbing to do and I will have to have a bigger blower then the Bucket vacuum

    V/r HT1
  8. HT1

    HT1 Silver

    You act like I work at a Machine shop:-( (I Moonlight at a machine shop occasionally) but yes it is possible the hole is .015625 oversized I drilled it with a cordless drill in a vice not on a lathe

    I'm right near Neutral, But My blower A bucket Vac is Maxed out, I adjust everything from the propane Regulator

    I need a Bigger Blower, and this is in the works

    Here is what I'm thinking Just for experimentation, Maybe I put together My other Moya, exactly the same as My current one, Buy a Larger blower (we will do some details on that in a second ) we see if My second Moya performs the same so we have apples to Apples if it does we increment up the orifice size and see what we get


    V/r HT1
  9. DavidF

    DavidF Administrator Staff Member Banner Member

    I'm pretty sure we could melt a hole to China if we wanted too. But finding a refractory to stand up to the plutonium 231 is eluding me....
  10. HT1

    HT1 Silver

    I would like to keep some simplicity in the Mix . I mean right now I probably have the Simplest Furnace of any of the Veterans Here , It's an enlarged version of Lionels Hobbymelter ,My first furnace, made with Insulated Castable running a moya on Propane only with a Bucket Vacuum, I could put together two good build threads, and there is No excuse for any SERIOUS hobbiest not to be able to reproduce what I have done, and not be able to cast Brass well!!! I've been doing it for 8 years.
    Now I know a lot about sand casting, But I certainly did not have to Build my own furnace in the Navy.

    and Maybe some of you have noticed watching people flounder just PO's me. I dont mind sharing My knowledge, and if I get a large improvement in hobby Furnaces I will share like a madman, i'll get a sandwich board and a bell and stand beside the road handing out blueprints wearing a tin foil hat so everyone know I'm a Master Furnace Builder

    V/r HT1
    _Jason likes this.
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I think I posted something similar in the other burner thread but you can roughly estimate the power potential of a burner by the burner tube diameter and fuel. When installed in a furnace, the potential power increases with combustion external to the burner, but blowing more fuel into the furnace than can be combusted at the burner opening can initially cool the furnace areas of the furnace with uncombusted mixture.

    If you look up flame speed you get a whole bunch of BS about laminar flame speeds, but with turbulence the flame speed can increase dramatically. I was (still am) looking at building an NG burner. MasterYoda (aka Art) indicated the flame speed of NG in an ejector (turbulent mix) is about 75ft/sec. If you do the math (yah I'm one of those college educated a-holes) you are going to be in the vicinity of ~20scfm of air for 100kbtu/hr. I'm fond of these 3-stage vacuum motors (used for central residential vacuums) which are about 100cfm so potential for 500kbtu/hr burner. They can be had for $45-$75 on eBay, run on 120vac (15amps), and can be speed controlled electrically or by restricting the air inlet. Being 3-stage, compared to other blowers they can develop great pressure and vacuum making them pretty much insensitive flow-wise to downstream conditions and furnace back pressure for our use.

    If you do the math again, you'll find you need at least a 2" ID burner tube to keep the exit velocity in the range of 75ft/sec for that 500kbtu mixture. Above this power level the burner won't stay ignited outside the hot furnace and combustion will need to be completed in the furnace. Below this velocity and the flame will creep back up the burner tube. A baffle that reduces the exit area and increases velocity can get the flame back in the right location or simply backing off the fuel/air supply which is what we intuitively do but this is typically at the furnace vent not the burner exit. This is all relative NG.

    Now propane requires about half as much oxygen as NG to burn completely. It would produce more energy within the same 2" ID burner tube with less air and at a comparable or faster flame speed may need a baffle to get the flame back out of the 2" burner tube.

    If you take this back to the MIFCO furnace, being fed by two, 2" pipe burners get's you in the vicinity of a million btu/hr potential furnace on NG burning at the burner opening. A lot of blah-blah-blah but since you want optimum results, it helps to pick parts that place you in the ball park. Other than that it's just pissing gas and air down a tube and lighting it.

  12. oldironfarmer

    oldironfarmer Silver

    Kelly's points are very well put. Minimum air to burn propane is 16 cfm per 100,000 BTU's. You need more than minimum to get good combustion. You really want to have a lot more air than you need because it's cheap and it lets you match air to the fuel you want.

    You can use a slightly smaller tube with a flare on the end which will slow the flow down and keep the flame at the end. Or you can have a refractory flare in your tuyere. If I wanted 500,000 BTU/hr I'd build a 1-1/2" tube with a flare to 2". A 1-1/2" tube would have about 110 ft/sec which keeps the flame out (at full flow). Flare to 2" brings the velocity down to 60 ft/sec. Most propane burners do poorly outside the furnace without a flare, but it can be just a larger piece of pipe slipped over the end of the burner, to get the flow down. Inside the furnace there is usually enough step of size to establish the flame right at the burner so long as the flow in the tube stays over 75 ft/sec. Methane and propane flame speeds are similar, and turbulent flame speed is expressed as a multiple of laminar flame speed. Short story, determine the BTU release you want then size the tube to burn at the end of the tube. A drip burner is much simpler, just squirt oil in at the end of the tube.

    You have said you want a slower velocity burner to allow more time for heat transfer to take place in the furnace. I've had trouble rationalizing that. From my perspective, the burner velocity is insignificant, it's the velocity in the furnace space around the crucible. If you want to burn 500,000 BTU per hour then you need 100 scfm (blower suction cfm). Measure the open cubic feet inside the furnace and you can calculate the residence time of the gas in the furnace whether it's coming from a fast propane burner, a slow natural gas burner, or something in between. If you have a 2 cubic ft interior space (around the crucible) and 100 cfm then you'll have 2/100=0.02 minutes or 1.2 seconds for the gas to heat the crucible and walls before it exits.
  13. HT1

    HT1 Silver

    Kelly , Andy you guys are really Helping, thanks,
    and andy if you have a link for the 3-stage vacuum motor you admire, that would be incredible

    Here is a great Diagram of Mifco's sytem:
    1) Notice they both baffle the burner end , and flare the refractory wall of the furnace ... any comments?
    2) look at the gas air mixer, here is something I have not seem on any of the Hobbiest furnaces it seems they are blowing the air from a slightly smaller pipe into a bigger pipe which would create a venturi dragging the fuel with it this would definitely create a massive and complete air fuel mixture , though i'm not exactly sure how I could manufacture this


    link to image for full size upload_2019-6-18_14-23-51.png & C Manual-2014.pdf

    Thanks in advance

    V/r HT1
  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Try this. If it's not readable as an image see if you can save the picture and enlarge it. Or download pdf at bottom of this post. It shows flow versus orice size/vacuum so you'd know ball park flow. As previously mentioned, probably only good for ~500kbtu/hr but that's a pretty potent hobby furnace.

    Ametek Lamb Blower 2.jpg Ametek Lamb Blower.jpg s-l1600.jpg

    If you search eBay for Central Vacuum Motor 3 STAGE METAL HORN you'll get similar hits to the link below.

    This is the Ametek unit that the data sheets reference.

    This is an aftermarket knockoff of same.

    This is less expensive, slightly lower output, but has a plastic horn. I like the metal horn for durability.

    They both are universal brush motors so can be speed controlled with a Router speed control or the like. They are a bit noisy, like a shop vac. If you put a 2" tube on the outlet you'd be impressed with the exit velocity and output, especially for it's size.

    It could be to insure it's tunable for different fuels or just to insure the plumbing size is large enough to support the maximum energy input. Easy to change a baffle. Harder to change the plumbing. If you have high pressure propane, the pressure to deliver the air through the burner tube is a non-issue but if you only have a few inches of water column of natural gas, a few inches of H20 pressure drop to deliver the air can affect the flow rate of NG through the metering orifice.......again, as long as you stay above the flame speed.

    I use them for vacuum assisted lost foam casting too. One can easily pull 8"Hg and if you stage two in series, 14" Hg.

    Certainly to produce good mixing and maybe turbulence, though I think that is important to promote that at the burner exit too for highest flame speed. A sudden expansion like the flare will not only drop velocity but usually creates separation/turbulence as well. I think the MIFCO design is consistent with the related discussion in the recent posts to this thread.


    Attached Files:

  15. PatJ

    PatJ Silver Banner Member

    I have not used that arrangement, but have used various types of spin vanes.
    From a functional standpoint, I cannot tell any difference with or without a spin vane, and my burner performance is good without the taper into the furnace.

    My slant on the taper at the burner entry to the furnace and venturi in the mixing chamber is to prevent flame from traveling back into the gas pipe.
    I don't think flame will travel from a lower pressure area to a higher pressure area (check me on that).

    There is a similar air gap on my home furnace, where they inject natural gas through an orifice into a tube that is physically separated via an air gap.
    I think part of it is mixing, and part of it is preventing flame backflow.

  16. oldironfarmer

    oldironfarmer Silver

    Part of the MiFCO design is a requirement for safety controls for a commercially produced unit. Like Kelly said the reduction in area (I would call it a nozzle not a baffle, to me a baffle is across the opening to restrict flow or sound, like in some mufflers.) increases the velocity, the the flare reduces it. The high velocity is designed to prevent the flame from traveling up the burner. It's less important for you because if you hear the burner swallow the flame you'll shut if off and restart. The commercial unit needs to be fool proof.

    Most home furnaces and naturally aspirated home foundry burners use the fuel jet to induce air flow. The length of the tube is to give the air and fuel time to mix before burning. The longer the better on burner tube length. It gets your valves away from the heat and promotes more mixing if you don't have a good venturi design. That why just a MIG tip and long straight burner tube works well. In your home furnace you'll see a tapered tube, much shorter, well designed for mixing with single preset gas pressure for a very stable flame.

    When you have an air blower you don't need a fuel jet, you can replace it with a longer burner tube. I inject my propane in my drip burner from just a fitting on the side of the pipe but it's about 17 inches from the end of the tube so plenty of time for mixing.

    You could build an air mixer using straight cones and get more fuel on lower pressure if you are using natural gas. You just jet the blower air into a slightly larger opening in the small end of a cone, the air jet will be reduced in diameter due to the vena contracta (same reason flow area reduces coming out of a faucet or hose) and the exit cone should start about at the center of the vena contracta to induce the maximum gas into the exit cone. If you stay with propane there is no value be cause you have plenty of pressure and can get all the fuel you want into the burner tube.

    For your burner you will have plenty of air pressure so you can afford to use a smaller tube to keep the velocity up instead of using an end nozzle (baffle) for flame control. The step at the end of the burner tube in the tuyere also acts as a flare.

    I would encourage you to drill out your existing orifice really big, like 3/16" then add a needle valve upstream so you can add a lot of fuel (or reduce it). Then put a high pressure blower like a leaf blower or the three stage central vacuum blower and see how much reduction in time you can get out of your existing burner. I think it will surprise you, since you know you are air limited currently. Leave everything else the same. I only harp on leaf blowers because they put out a lot of high pressure air (large diameter impellers, and pressure comes from diameter in fans) and are cheap but the central vacuum blower looks like the cat's meow if you want to spend the money.
    Last edited: Jun 18, 2019
  17. oldironfarmer

    oldironfarmer Silver

    The spin vane is an effort to atomize fuel, I believe, and you are using an atomizing nozzle so it makes sense it would not make an improvement.
    A real safety issue here. Flame travels based on velocity, not pressure. Often the two are interrelated but with an area of high pressure drop and rapid flow it's the velocity that keeps the flame at bay. Neither natural gas nor propane will burn unless you have oxygen so there is no danger of the gas pipe burning inside. Only pipe with a mixture of gas and air. So long as there is no oxygen in the mixing chamber barrel (well after startup) the flame would have no incentive to even go there.
    That small air gap is an accurately designed air induction area. If you have adequate gas pressure the flame will stand off the end of the mixing nozzle. In the old days if you had a leak in a gas pipeline the first thing you want to do is light it, before it finds a source of ignition and lights on it's own. Then you put it out when you have everything in place to make a repair. A runaway gas well is a bit different because it is blowing straight up and mixing with air but the experts generally don't want to extinguish them until they have the personnel and equipment there to attempt to seal it off.
  18. PatJ

    PatJ Silver Banner Member

    I think the spin vane is more of a method to mix the atomized fuel with the combustion air, and it can be seen on all Beckett-style combo burners.
    The combo burners are designed to fire into an open combustion chamber though, not necessarily a confined furnace space.

    Myfordboy was flip-flopping on a spin vane, and I think it may be more important with a drip style burner (I forget which style burner Myford is using).
    I think he said he did not need it, and then said it worked better with it (check me on that).

    I use spin vanes cut into the end of the burner tube on my siphon nozzle burner.
    The end of my new pressure nozzle burner is smooth (no spin vanes).
    I will do identical iron pours with the siphon-nozzle with spin vane burner and with the pressure-nozzle no spin vane (when I get the pressure nozzle burner completed), and see if there is a difference.

    Since the fuel and combustion air go into an immediate tight bend inside the furnace, and then swirl around the crucible, I would guess that with a siphon nozzle burner, the spin vane has little effect.
    With a drip-style burner, all bets are off as far as how effective a spin vane would be.

    oldironfarmer likes this.
  19. HT1

    HT1 Silver

    OK Guys lets say I'm going to use the 3 stage blower recommended . but I want to do Duel tangent Burners Running Propane Just like the Mifco, where do you guys think My Burner Size should be .... I'll start some doodles then so everyone can laugh at my artistry

    13 inch Diameter furnace 15 inch high

    Thanks in advance

    V/r HT1
  20. oldironfarmer

    oldironfarmer Silver

    First you need to state how much fuel you want to burn.

    Do you want 500,000 BTU/hr? (250,000 per burner?

    Are you going to duct air from one fan to both burners?

    I started dreaming about using six naturally aspirated burners (100,000 BTU each)around 3/4 of the furnace circumference.

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