Should a tuyere be designed to be angled vertically?

Hi all. I'm in the process of designing a propane furnace out of a keg. My design is currently based around some previous constructions posted here: essentially 2 inches of Superwool around the inner diameter of the keg, with 1 inch of Kast-O-Lite 30 LI surrounding the Superwool for the hot face. I'm now at the step of designing the tuyere as an integral part of the Kast-O-Lite hot face.

I know the tuyere should be tangential to the inner diameter of the hotface, but I am uncertain if it should be angled (e.g. 5° relative to the ground) or parallel to the ground. I suspect it should be angled so as to facilitate a rising vortex within the furnace (the burner will be positioned at the bottom of the furnace pointing slightly upward), but wanted to verify or refute this with those having more experience than me.

 

Super wool? I don't think it matters if you try to point that thing upwards or downwards really. The big thing is keep the metal part of the tuyere OUT of the inside of the furnace. I angle cut a piece of exhaust pipe and welded it to the outside of my furnace. I stuck a cardboard tube in that pipe and extended it inside the furnace a few inches. This way, when the refractory cured, I still retained that funky angled shape. Kinda hard to explain. Wrap cardboard you use in saran wrap so it doesn't "go limp" from the moisture of your kast o lite. The last thing you EVER want to do is to reshape refractory cement after it cures. It's some of the hardest stuff to cut/drill.

Welcome btw... It appears you have been doing your homework. Good on you!

 

Parallel to the ground is the norm. You're already going to have a cold spot in the bore below the tuyere. No need to make it higher.

 

Thanks for the welcomes! Seems like the consensus is to have it either parallel to the ground, or slightly pointing downward to bring the furnace floor to temperature. Thanks for the guidance!

Hi Jason, to my understanding, Superwool 607 HT Blanket is the safer alternative to Kaowool with regard to the respiratory system. Both are manufactured by Morgan Thermal Ceramics, with Superwool HT being able to handle up to 1300°C / 2372°F. Here's an excerpt from a brochure on the product (from here: http://www.morganthermalceramics.com/media/1141/english-superwool_brochure_single_pages.pdf).

I still intend on sealing it behind rigidizer / Kast-O-Lite, but I'll breath a little easier knowing it won't pose as bad of a health risk as Kaowool should something go wrong.

 

I dont believe any of this stuff is "safe".
We are all big boys, know the risks, do what you can to mitigate them and still end up with cancer. I think they call this life.

 

Supposedly, the fibers are "bio-soluble" so I guess that means, in the short term, the airborne fibers are just as unpleasant to inhale but they're not permanently stuck in you're lungs so they're less likely to do long term damage. That said however, I think prudence dictates you should take all necessary precautions to avoid inhaling them either way.

 

Welcome to the forum. If I had a crystal ball I would probably see waste oil or diesel in your future and your furnace will definitely be up to the task. Kastolite 30 li is an insulating refractory rated at 3000f and will protect your lower rated wool so you can melt iron in it. The reason I bring that up is because propane and oil behave a little differently and I think gas would be less affected by a downward tilt than oil would. I can't dispute others' observations about performance with a downward angle using oil, but I know from my own experience that any obstruction to my oil mist will cause pooling and subsequent fire where I don't want fire, like underneath the furnace. Tangential is a must, and I might try a bit of a downward angle if I ever build a new furnace or smaller burner, but I wouldn't cast a tight fitting tuyere that way. As Jason and Kelly both touched on casting the tuyere a little oversized would allow for experimentation and would be much easier to adjust than modifying your refractory would be.
When I made my last oil burner I just cut the end of the pipe off square and the extra steel sticking inside the furnace "self adjusted" pretty rapidly. There are some good template calculators online to help with the tangent angles and there are some pretty savvy guys here too that could help if needed. If not, just ask and I'll dig up the calculator I used when I built my last furnace. I'm looking forward to watching your progress.

Pete

 

Welcome

When I put my Tuyere I pointed it down on a 5° angle. Knowing I was going to be burning vegetable oil, I wanted to use some of the floor as more space for ignition and for extra radiant heat. I’m running to torches with just under 100 mL per minute (1.5 g/h) each torch, that’s why you see two little swirls. If you look closely at the floor, where it is really white that’s where it glows. My torch is put off a heavy mist. My air speed is a little faster than the norm. But still the same CFM as all the other guys here. My idea with this is, the air/fuel droplets would make more rotations making more hot side wall. I went with two torches to have a more uniform helical screw and reduce the fuel one torch had to handle.

Edit; I made my tuyere through the brick about 1/8 of an inch bigger then my torch. I wish I made it about 3/16 bigger.

 

Hi Jeff, thanks for the welcome! I'm starting out primarily with aluminum, brass, and copper. If I learn enough about fuel combustion and burner designs, I can see myself incorporating steel and iron into my endeavors. It's mainly why I'm designing the furnace with 2" of insulation with a 1" hotface shell within: future proofing!

I'll still be as cautious with the Superwool that I was with refractory cement and Kaowool: wearing a respirator while working with it, sealing away the insulation, etc. I enjoy this hobby, and don't want the hobby to shorten the time I can enjoy it.

Thanks for the welcome, Pete! I have been interested in waste oil / diesel as fuel, but haven't done my homework on those yet. Just been tackling one thing at a time and working in milestones. I'm still in the drafting phase of the furnace and burner design, with both being incomplete at the moment, but once I have something ready to start constructing, I'll be sure to post it. I'm doing all of my drafting in Onshape, a cloud-based 3D modeling software, mainly to force myself to learn CAD modeling.