Larger Moya???

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

  1. HT1

    HT1 Silver

    I apologize I was assuming I was being clear I wasn't
    Lets say I want to Reverse Engineer a Mifco B30 Now a B301 ONLY FOR PROPANE Mifco Rigs them for both

    Here is a pretty good picture of one
    but if I'm going to base it around a 100 CFM blower rather then Mifco's 150 CFM Blower SO limiting myself to 500KBTU ??? right ... (Just a quick note Kelly mixed in NG and LPG stuff, and I'm not 100% sure which goes where ) But he clearly stated NG requires about twice the air as LPG So is Mifcos' 150 CFM blower overkill to get 750K BTU's from NG ??? or does the furnace not get 750Kbtu's on Ng??? (my head hurts)
    1) only on propane what size burners do you all suggest,
    2) Pipe and regulator %
    3) anything I should avoid t
    4)to me the Plumbing on that furnace is all kinds of cerfuckered save it is doing Just what I wanted to do... when the Mixed air and fuel reach that Tee they will slow down and enter the Furnace at half speed , I know this has to be hard , because it is confusing me

    any help,

    V/r HT1

  2. oldironfarmer

    oldironfarmer Silver

    So based on 500,000 BTU/hr, that's 250,000 BTU/hr for each burner.

    500,000 BTU/hr will be burning 23#/hr of propane. That takes 80 CFM of air. The three stage 100 CFM blower probably has enough capability to put 80 CFM through the piping and burners. The data sheet Kelly provided looks like it will provide 80 CFM with some resistance.

    Parallel air flow is very sensitive to differences in resistance. That means each flow path needs to be identical, or have an orifice or other restriction to help even out the flow. In the picture the burner on the right has a lot more pipe so I assume they have a restriction in each pipe to make them flow the same. You don't want one burner getting 60% of the air but if you are mixing the fuel in before the tee it is still workable.

    Assuming you will limit the air flow to 80 CFM then if you want 75 ft/sec in each burner the burner tubes should be 1-1/4" or smaller to inhibit flame travel into the tube (for 40 CFM). You can still run more CFM but you want to keep the velocity above 75 ft/sec at your normal operating flow.

    If you are just going to inject propane at one location you can use a 3/32" orifice with about 25 psi. Or you could use a 5/64" orifice at each burner with 13 psi. Of course you'll have to be able to adjust above and below those pressures.
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I did say that but I went back and looked at my own post and I dorked it up. It's the other way around. It takes ~>twice as much air (actually about 2.4x) to burn a cubic foot of propane as it does natural gas. But you need to burn twice as much NG to get the same amount of heat/energy so your right back where you started with air consumption for either one at the same energy level.


  4. HT1

    HT1 Silver

    Thank you, I'm still bouncing this around in my noodle. Really think I want a bigger blower! and a couple of the design elements are evading me , especially getting the flow right out of both burners from one source of fuel and air . I would hope that mixing the two in advance would make balancing unnecessary. I've ran a Mifco many many years ago, and was astounded how fast it melted brass. I would love to replicate that without breaking the Bank

    V/r HT1
  5. HT1

    HT1 Silver

    No problem Brother lord Knows I make mistakes, trying not to here

    V/r HT1
  6. oldironfarmer

    oldironfarmer Silver

    Buy two leaf blowers. They are high head high production low cost and not much invested if you want to change. Could even sell them.

    You'll find just using brick goes a long way. I still think you should drill out your orifice and add a needle valve and leaf blower and see the difference. Low cost. If it doesn't work you pinch the needle valve and use your vacuum.
  7. ESC

    ESC Silver Banner Member

    Look on Craigslist for Bounce House Fans. When the castle gets a non repairable leak the fan goes for about $50 and puts out all the air you should need. I run at full speed, but over at AA I show making a damper for the inlet.
    I couldn't find any on my CL, but they are on Ebay.
    Last edited: Jun 20, 2019
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Here's how it shakes out. 100ft3/min of air is 6000 ft3/hr. Per the chart I posted above you could burn 6000/23.8 = 252 ft3 of propane in an hour and since propane is 2590 btu/hr, that would produce 653kbtu/hr. This would be stoichiometric (perfect) combustion.

    Using the same calcs, for natural gas 6000/11.0 x 1150, you could produce 627kbtu/hr.

    The total volumetric flow of fuel/air is about the same for each. So for a given size plumbing the exit velocity would be about the same. The relevance of the flame speed is to allow the burn to occur as completely as possible before it enters the furnace but without occurring in the tube. At higher velocities the cold fuel air mixture must enter the furnace before it can combust. Granted, a flare and the natural opening in the furnace can do this, but if calculate what size pipe would have a 75ft/sec exit velocity with 100scfm of flow you get 2" ID.

    So a single 2" burner tube could produce 653kbtu (probably about 90% of that with excess air and pressure drop) and a two, 2" Tuyere set up could produce twice that amount of heat with the burn occurring very near the exit, but you need twice the air and fuel to do so.

    So to answer your other question, the 150 scfm blower on the MIFCO is not gross over kill for 750kbtu/hr, but in theory could support about 980kbtu/hr at the 75ft/sec exit velocity. Since MIFCO are only running at 750kbtu/hr, the air flow and exit velocity will be lower in their 2" plumbing than the flame speed and that's why they have the exits at each of the 2" Tuyere necked down to get the exit velocity back up to the flame speed.

    So start with the maximum power you want to support, size the plumbing for that at flame speed, and if you want to run below that power, simply install a choke/baffle/reducer to tune the exit velocity to the flame speed.

    Like the MIFCO, I'd say have a single blower and fuel injection tube and symmetrically split/Y'd to the two will promote better mixing and balance.

    The other thing you may want to compare as already mentioned by Andy is the furnace volume and residence time of the combusted gas. My sense is, as long as the exit velocity is near the flame speed the furnace temperature will be good and may not affect melt times much, but you may burn more gas per melt and you'd see more flame above the furnace vent. Hard to say because you might also get better heat transfer to the crucible with higher internal gas velocity.

    Those bounce house fans are huge but they can of course be throttled. The 3-stage vacuum blowers are really designed to produce more head (actually vacuum or "air watts" as the vacuum nerds say) than sheer volume. But that does make their flow much less sensitive to pressure drop in plumbing and I would think with high pressure (above choked flow) propane, would produce a very stable tune once set. I don't recall how the size of your furnace compares to the MIFCO but if 90% of 653kbtu is realistic, then .9*653/750 = .78........then if your internal furnace volume (less crucible) is about 78% of the MIFCO, you'd be in the same ball park for residence time and internal furnace velocities.....

    Kelly out!
  9. HT1

    HT1 Silver

    Read that about 6 Times, think I mostly understand. and i'm in a little bit of a Pickle,
    I intend to build an entirely new furnace following the Mifco B301 Measurements, which is a 13 inch bore 15 inch high furnace chamber . My current furnace is 10 inch bore.

    I have promised Andy to use IFB , though I'm looking at using it differently then him, But will give us some nice data Points .

    Andy I dont like the two blower especially leaf blower idea, too many things to trip over, too loud, and two blowers is alot to coordinate , especially since I run by ear

    at this point it seems that the Blower Kelly recommended does not have enough ass for what I would like to try ... Seems the Sunlar
    is probably even a little underpowered at 125 cfm but better, seems like it of not I gotta step down somewhere

    Kinda head scratching at this point lets throw this Hypothetical out :

    if I put together another 1 inch Moya just like I'm running now with a bucket vac , and Plumb it like a Mifco and hook those up to Kelly's recommended 100cfm blower in an IFB furnace with 13 inch bore 15 inch tall chamber, thoretically I should be able to Double BTU's I'm currently running , and of course I know IFB is 4 times more insulative then the Insulated Castable of My current Furnace, it seems that would gie me a very significant improvement in melt times ????

    Quotas, comments, Suggestions

    Thanks in advance

    V/r HT1
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Funny, my small furnace is 10" bore but resistive electric. Being it's a lift off body, it can handle an A20. My larger furnace is 14" bore and 19" tall so a tad bigger than the MIFCO......and can accommodate my A60!

    That 3-stage unit wont get you to 750kbtu/hr but probably will get you very close to 2x your current set up, if that is indeed in the vicinity of 300kbtu/hr. Did you estimate that based upon fuel consumption?

    That looks like a nice unit to me and nice that it has a built in inlet air choke. If it really can support 125 cfm, compared to the theoretical calcs above, in a perfect world it could support 812kbtu/ maybe you could expect 80-90% if you had low pressure drop in your feed plumbing. It has a 2 1/2" discharge diameter so you could make the initial mixing tube that diameter and then Y into two, 2" tubes. If you didn't like the heavier pipe plumbing you could have a muffler shop bend the rest in 2" or just go to the local car parts joint and by some bends and straights and weld them to suit.

  11. HT1

    HT1 Silver

    I based 300K BTU on fuel consumption

    Actually I have access to a power pipe bender

    I'm leaning towards the sunlar . here is the smaller 2 inch 90 CFM I believe i posted a link earlier, notice he has the air choke closed ... I doubt that red hose is rated for fuel also.. but not my problem
  12. DavidF

    DavidF Administrator Staff Member Banner Member

    looks like there is a !" pipe inside the 2" pipe set screwed in place??
  13. oldironfarmer

    oldironfarmer Silver

    Sorry I think I misunderstood you. You said "if I'm going to base it around a 100 CFM".

    I'm with you now, and agree if you want 750,000 BTU/hr that is what you should build. It might be wise to look for a 150 CFM blower. The only thing about the Sunlar that concerns me are the "aluminum gears for durability". I say 150 CFM because you need to accept that the pressure drop in your system will likely reduce blower output. Looking at the Sunlar I almost pulled the trigger and I don't need one. I wonder how noisy they are.

    The blower Kelly recommended does come in larger sizes, a 6VMW4 is 166 CFM through a 2". But more money.
    Last edited: Jun 21, 2019
  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    It does? Are you talking about the 3-stage vacuum motor?

    Which one is that?

  15. oldironfarmer

    oldironfarmer Silver

  16. Al2O3

    Al2O3 Administrator Staff Member Banner Member


    Haven't used that particular one but that does illustrate the point I made about the 3-stage version being optimized for flow at pressure/vacuum versus free air flow. That unit you linked makes considerably more flow at the same current/power but being one stage certainly would suffer more reduction in flow if it encountered significant pressure drop, but in a 2" line and this type of duty you probably wouldn't see it.

    When I bought the 3-stage blowers it was originally intended for vacuum assist lost foam casting so I wanted the high vacuum potential. I made an offer to a seller and got a couple of the new metal horned ones for ~$50 each. They're pretty darn impressive for that. They do draw 15 amps though so if you were going to run multiples, you'd need separate household circuits of tap a leg of 220 to neutral. Problem with that is the neutral leg still must carry 30amps.

    A lot of development work has been put into vacuum motors and they are pretty high performance blowers. If you search "Vacuum Motor" on eBay you'll get a lot of hits. Many of the single stage units will be in the 150-160 cfm range for a 2" orifice. There were a few similar to the one you posted for <$100. I didn't look very hard. You just want a tangential exit so it's easy to plumb and convenient voltage.

  17. PatJ

    PatJ Silver Banner Member

    Did I mention my view right now?
    Sorry off topic.
  18. DavidF

    DavidF Administrator Staff Member Banner Member

    time for a new windshield....
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    To clean up my thread jacking of HT1s thread, I started a new thread on this bit, and moved the posts that were in this thread here. I dorked up the order of the and lost some/all of the related posts.

  20. Tobho Mott

    Tobho Mott Silver Banner Member

    Figured this was off topic for the over my head blower discussion this thread had turned into, but it turns out that stuff was what was straying out of its lane... Lol. I'm still not sure this'll be helpful to HT1, but hopefully it will. Here goes nothing:

    I started building an oversized Moya burner. Hoping it'll run on propane in my big furnace as well as my standard Moya does in the little one...


    Decided to lost foam cast the plug into the back end with the oil drip tube from the inside of a thrift store lamp held in place, running straight through the casting.


    Ugly welds have been ground down by now, slightly less hideous to look upon than here:


    Propane line dumps into the burner via a close 1/8" nipple I welded in place.

    Just gotta cut off the excess drip tube length and do a test run. Sadly, my leaf blower's tip fits the tee perfectly, but doesn't run off my dimmer switch as well as my shop vac does. At least in the mid ranges of the dimmer switch. Gets kinda jumpy I guess you'd say, so maybe I'll just keep using the shop vac. I have no way of checking cfm's etc., sorry about that. But at least I'll find out if the wider burner tube helps it run more stable on propane while preheating the bigger furnace, which will be helpful to know (at least for me).


Share This Page