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Advice on a recent ribbon burner build


hotplot

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I've just finished the initial prototype of a ribbon burner that I intend to use for general forging in a brick pile forge, and would like some advice before I continue casting the refractory block.

The design is inspired by Frosty's T-burner instructions and the various ribbon burners shown in these forums. I say "inspired" because NZ is currently under quarantine and I do not have access to any hardware or tools that aren't already in my garage. I had to improvise the connection between the LPG hose and the MIG tip.

First some pictures:

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For the hose connection, I brazed a M12 nut onto the T joint and then drilled and tapped some threaded rod to accept the MIG tip in one end and some M6 threaded rod with hole drilled through it in the other end. Once the quarantine is over I may try to find a better way to do this, but it seems to be functional.

Here is a video of a test firing, with 13 x 8.0 mm nozzles and pressure at about 30 kPa (~4.5 PSI):

Now, the questions I have:

  1. Firstly, safety: is there anything that might pose an unexpected risk with ribbon burners, or LPG burners in general? I have plenty of general experience working in hot and dangerous environments (as an industrial electrician who does bronze casting as a hobby), but I don't have any specific knowledge about gas burners beyond what I've found on this forum. The idea of lighting a home-made bomb disguised as a gas burner terrifies me! The LPG hose is connected to an adjustable regulator with pressure gauge, but I don't have a flashback arrestor installed since **in theory** the LPG is not in a combustible mixture until it exits the MIG tip. Of course if there's a hole upstream of the MIG tip then all bets are off...
  2. In Frosty's NARB thread he seems to be using 19 crayon-sized holes, which he says are slightly under 3/8" (9.5 mm) dia. In my test block I only have 17 holes at 8.0 mm each, and still had to block up four of them to prevent the burner from immediately backfiring. Is this likely because I have my burner in open air and will need the extra holes once it's inside a forge? Or is the circular vs. linear layout of the holes or some other design difference to blame? It occurs to me now that the nozzles will have higher resistance once they're cast in the deeper refractory block too.
  3. It's a bit hard to see what distance from the block the flames are igniting, but does the burner appear to be behaving roughly as expected tuning wise etc?
  4. Is the loud pop as the gas ignites inside the plenum normal when shutting off a burner? It seems like having the flame travel back into the plenum is unavoidable once the cylinder valve is closed and the gas velocity starts to taper off, but if there's a way to avoid it I would love to know!

Thanks for any help you can give :)

Sam

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I can't help with the ribbon burner, but I hope the hose is rated for propane (LPG). It looks like air hose in the picture. I would recommend taking the galvanizing off the tube & tee with a vinagar soak, although it shouldn't get hot enough to present a hazard but better to be safe than sorry.

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Multiport burners have characteristic flow ranges that give a stable flame.  Different configurations, burner types, diffusion plates, hole sizes... have better turn down properties than others.  Pine Ridge, a manufacturer of such burners, recommends that you run them full out and don't turn them down at all.  I've run Joppa Glassworks multiport burners which have circular pattern holes for many years, and they have a pretty good turn down range (also most of the time I used a forced air burner, which is easier to tune).  Still those burner heads have more, smaller holes than you are using.  By going your own way with a design you will need to experiment more than if you directly follow an accepted design, and it is even more difficult with a NA burner than a blown (or gun) style burner.

In my experience the burners should be designed for stable operation at the lower end of their firing rate if you plan on using them inside a forge.  Firing inside a chamber you start at the low rate, then gradually increase that rate as the chamber heats up.  With a heated chamber the flame burns back faster towards the burner and consequently it can push more air/fuel mixture to the outlets without lifting too far off the face of the burner block and blowing out.  This works until you hit the practical limit for the number and size of outlets, and the interior temperature the forge can achieve (one way of addressing this is the method the old Johnson gas forges used with metal slide gates that opened and closed numbers of burner outlet ports - or at least that is how I remember them from the 70's when I last used one).  However, as you have noticed, burn back is a definite problem when turning down the burner (even more so in a heated forge).  You need to install a 1/4 turn shut off gas rated ball valve to quickly shut off the gas flow.

You may also need to tune your burner.  Very hard to tell in your video with all that ambient light and a wooden burner block, but you may not be inducing enough air at lower gas flowrates (pressure).  You may need to reduce the size of your MIG tip, or change it's position relative to the mixing tube.  I'll let Frosty advise you on that as he has a lot more experience with that type of burner.  It also appears that you are not directly following the T-burner instructions and are not using a reducing T.  That will also have a great effect on how much air you can induce.

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With the wood on the burner block I can't evaluate how well it's burning. The wood would make any flame very rich long and fluttery. It could be perfect or lean and it'd still look rich. 

If you'll pull the wood and take pics in dim light or against a dark background so we can see the flame I'll tell you what I see happening.

Frosty The Lucky. 

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Thanks Frosty and Latticino.

Here's a better video of the flame using a new test block. This one has 24 x 6.0 mm nozzles, and is similar to some of the Joppa Glassworks burners Latticino mentioned. The block is burnt from previous use, but is wet and not burning in this video.

It looks to me like it's running quite rich, and the way the outer flames start much further from the nozzles suggests it could benefit from a diffuser (no idea whether that's actually correct, just guessing here). I already have the MIG tip adjusted as far back as it can reasonably go, so I'll cut it shorter tomorrow and put a diffuser in the plenum before trying again.

Latticino, you are correct that I used the wrong T... Unfortunately at this point I cannot go buy a reducing one so this will have to do for the time being.

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It's still rich. but better Turn it down things will even out.

The reason the flames on the outside have more fuel air mix available is because of the open space between the outlets and the plenum wall. They aren't competing as much with the other outlets for fuel air. Forget the diffusers.  

Drill a couple more holes around the outside and see how that works. Before you do though, light it and start turning the psi down gradually until it burns back into the plenum and note the pressure. Do NOT turn it back up once it starts burning back, just close the valve.

Frosty The Lucky.

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Hi Frosty

The flames start to move back toward the plenum between 20-30 kPa (3-4.3 PSI) and touch it somewhere around 10 kPa. Hard to tell as the gauge doesn't read below 20 kPa. The flames didn't burn back into the plenum at any pressure using this block. I assume the smaller holes (6.0 mm vs. 8.0 mm) and rich mixture are responsible for that. It is nice being able to extinguish the burner without any loud pops :)

I tried a block with 25 x 6.0 mm holes in a rectangular grid today and it seems to burn well too.

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These are wood burner blocks right? I'd keep increasing the number of outlets till it starts burning back. The above pic looks to me like it needs more outlets, I'd be looking for the upper limit and ease back. Ah, the pops aren't a thing, they only startle you the first time or two. It's kind of fun not to let guests know when they're visiting. The NARBS only pop, it's not loud or particularly frightening if folk are expecting it, not even an annoyance really.

Frosty The Lucky.

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  • 3 weeks later...

Thanks Frosty. You're right, the pops did quickly stop being a shock. I quite enjoy turning the burner off now.

Once I added an additional 4 holes it started burning back at very low pressure. I ended up casting a block with 29 x 6.25 mm holes and it worked well in the brick pile forge, despite the fact that the uneven bricks meant the forge was almost more gap than brick.

I ended up making another small forge out of some scrap stainless and kaowool. The burner certainly gets it hot but it runs very rich. Adjusting the position of the MIG tip doesn't help much, and I assume the inlets on the 3/4" T are too small to let sufficient air in regardless of MIG tip position.

Do you think it would help to trim the shoulders off the T so that the inlet area is increased? Or is that likely to cause other problems?

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