Another keg furnace

A nub on the bottom of the plinth would probably work better than a pin just for the purposes of alignment. If a pin doesn't break right off it will probably wear down to a nub pretty quickly anyway especially if you're taking it out and in frequently. I doubt tungsten rebar will help. And if the initial fitment is close it will most likely bind up on you at some point. One of the things I've found about refractory is that although it's extremely hard, it's really quite weak like an eggshell. It took me awhile to finally get past the idea that it would perform anything like concrete, especially once it's exposed to heat.
I really like your idea for the burn chamber and I'm thinking that once you find the optimal shape for the plinth leave it in there as a permenant pedestal. Just my two cents.

Pete

 

Pete
The pin on the bottom came to be as an after thought. I incorporated a drain hole in the original furnace that just by luck happened to be in the right place. This pith or whatever shape pith eventually replaces it will be a semi permanent part of the furnace. It will only be removed occasionally for service. I am somewhat worried about the tungsten rod having vastly different expansion properties than the refractory. It might cause more problems than it solves. This is yet to be seen. I want to try this pith in several shapes. One thought will to make the platform part of the pith somewhat thinner to reduce thermal mas. I don’t know how thin will be practical. Another shape I am considering is to make the pith the same dimensions except make the thick platform part the crucible sets on into a bowl.
Kelly
I do remember this post and it has influenced my design somewhat. I just could not remember exactly who had posted it. Every since I herd about the Ursutz style burner. It has interested me greatly. I think with the separate burn chamber it should be easier to control the environment within the furnace more evenly. With my design I have left a 1+ inch wide gap completely around the pith where I hope the heat will be distributed evenly at a velocity that can easily be matched to the furnaces needs.
As with most on the form. I am not a spring chicken so progress is very slow. Translation “ I am old and lazy” but things are moving along and I do hope to be pouring metal soon!
I found my old molding bench the other day buried in the pile. I have not dug down to it yet but that might answer where my missing crucible are. I am also hoping there are a few flask in it along with? I will be digging it out in the next week or two.
Joe

 

I can't see tungsten changing dimension that much. When I change them like socks after dipping during tig welding they sure seem to come out of my torch super easy. I've even had them fall out of the torch while welding. I had a batch of weak collets. You picked the right material for that one, a novice would have selected steel or stainless rods. Expensive choice, but still the best in this application. What size are the rods and how many did you stuff in that plug?

 

I will be out to the shop in the morning and look at the diameter of the rods. There is a total of 6 rods 3" long each being ½ the length of a new tig rod.
The 3" tungsten rods were placed in a circle at iregular angels running near or around the center of the locator pin.
In my mind the tungsten was the obvious choice of material for this application. I have considered placing several tungsten rods in the flame path close to the nozzle to act like a glow plug to help in ignition. But that is an experiment for another day.

Joe

 

Ha! Hooked up to a harbor freight junk tig box and you're all set!

 

I made it out to the shop but my stay was cut short by the Honey-do list so minimal progress was made. To answer your question Jason. The TIG rods are 3/32 inch 7 inches long 2% Thorium. I used a small piece of exhaust pipe as a flange. When I modified it to fit I damaged the
end and somewhat egged the shape. It only took a couple of minutes to flood every thing with refractory but took hours of grinding to clean up my sloppy work
I had experimented with and intended to use a 2" water pipe but due to limited space in the base i went with a 2 inch O.D. thin walled piece of tubing. The next part of the project will be the burner and fuel system.
Joe

 

Nothing worse than hardened refractory. I bet a diamond wheel would make the job easier..

 

On grinding the refractory out after it has air set. I found that a 1/4" carbide ball end mill in a dye grinder cut it faster than grinding. It was still a pain but a magnitude faster.
I have redesign my burner. These pictures are from post 121 where I had used a piece of 2 inch water pipe.
When I relined the furnace and burn chamber I opted to go with a 2 inch “burn hole”. As most of you know I wont even try to spell the t word for “burn hole”.
Now I am somewhat concerned with air flow velocity. I plan on using a thin waled 2" O.D. exhaust pipe as the burner along with a siphon nozzle.
As of now the plan is to wrap a single piece of stainless steel around the nozzle and attaching it to the pipe at 1 point rather than the 3 bolt centering set up I previously had.
I ask the for the thoughts and collective wisdom of those on the form. How did you hang your siphon nozzle if you are using one? If you are using one or not how would you go about it. The I.D. would be around 1.85" minus the diameter of the nozzle, .75" and the bracket to hold it in place. After you do the math things are getting a bit tight.
With every thing I have read. High velocity air entering the burn chamber is not a good thing and should be avoided when possible. I know the diameter tube for the burner will work as others have used similar with good results but at the same time I can not stop thinking that. The burner tube is a carburetor and as such the only way to supply the right amount of fuel air. If this is a fixed fuel ratio without changing the air velocity is to increase decrease the intake size.
I know it is a very small furnace with having only a 10" bore but caution now is better than problems later. This furnace burn chamber shape is built more for experimentation at this point than any thing else. It will be interesting to see how it works out.

Joe

 

I just used a female section of exhaust pipe for my burn hole and its matching Male 2inch exhaust pipe for the burner section. Plugs in and fits like a champ. Males and females work like this contrary to what Netflix would have you believe.

 

The pipe fit is not a problem so much as keeping the air passage as open as possible. I think the new burner arrangement will be a much better fit for the furnace and as I had said. It will work. I am just trying to avoid any problems hat might arise.
Joe

 

It's not really a carburetor, the carburetor part is all in the siphon nozzle. I think high velocity in the burner tube is a good thing: it keeps the flame from coming back into the tuyere. You will reduce the velocity as soon as the mixture enters the furnace.

 

I'd run some experiments trying to get flames starting in the tuyere in the past. The only way I could get a propane flame inside the tuyere/burn hole was to have an area of still air for the flame front to start from. A small steel disc like a 1" panel beater's washer just behind the nozzle works for gas. I'd imagine a much faster burning fuel like hydrogen may not need it as it burns at 7 metres/second or 23 feet/second and may be faster than the airflow speed.

 

Just for the sake of discussion I’d like to gently consider that point without knowing for sure the “right” answer. I am going to make my best argument for slower injection is better. ( I have never seen the flame actually begin within the burn tube even at initial just-cracked-open combustion air flow, incidentally). I am perfectly willing and interested to learn why the following argument is faulty.

1) I think it is worth discussion since I am pretty sure it is important to provide enough time within the furnace for largely complete combustion to occur. And the earlier that combustion occurs within the swirl, the more time hot gases can bathe the crucible.

2) it is certainly true that as the air/fuel mix enters the furnace it will slow some.

3) The swirling flame within the furnace is swirling to a significant degree simply due the fact that the air fuel mix is injected under pressure at velocity. You can see that if you don’t even light the burner but just blow in air. For a given volume of gas, the smaller the entry tube the higher the velocity of the gas. Momentum is conserved, so the more rapid the gas movement, the more rapid the swirl and therefore the further from the tuyere opening the various layers of flame occur and the later heat is released.

4) I think it should be true that the velocity of the gas exiting the chimney should be the same whether a small or large tuyere is used if the same volume per minute of air/fuel is injected regardless of tuyere size.

5) How does the slowing occur from injection to exit? Turbulence—-eddy currents. Are they good or bad? Well, the best I can guess about that is related to common observations of oxy/ac and propane flames. Good clean tips with smoothly flowing gas produce more heat than partially plugged sputtering confused-flow tips.

So, high velocity small burn tubes are bad because they prevent low-in-the-furnace combustion and they increase flame confusion (eddy currents around and impinging the flame cone) of the flame cone. A slower, quieter, more orderly flame cone approximates a quietly burning candle, but a high-velocity flame cone approximates a sputtering candle seen in a drafty room.

Is all of the above true? Not sure, but it seems reasonable and the most likely ( to me) scenario.

Listening....

Denis

 

Hi Denis, all of your points seem logical to me, I'd like to add that propane gas as a fuel is easy to use, burns fast and doesn't seem to need earlier ignition in the tuyere to perform well. My limited reading and experimental observations with oil so far include:

1. Compared to gas, fuel oils have a much reduced flame propagation speed (speed that the flame will travel at) but this can be compensated by higher temperatures and higher compression as mentioned by others.
2. I believe that starting the fuel oil flame in the tuyere will allow the fuel to be preheated to high levels and increase the flame propagation speed and also making a vapour of the droplets ideally before entering the furnace (precombustion).
3. It's very difficult to have a suitable oil spray nozzle with a 15 degree cone and fine droplet size. Most fine spray nozzles have a 90 degree cone so it can only go a few inches back in a 4" tuyere before the spray hits the tuyere sides and dribbles into the furnace, a 15 degree cone spray would let you go back about 12"/30cm before that happens.
4. I have had a spray nozzle 12" back in the tuyere but again fuel spray hitting the wall was an issue and the furnace became loud with a deep rumble from an unstable flame. The large droplet size of the nozzle was causing problems too.
5. A 90 degree cone angle super fine mist nozzle right up at the entrance to the furnace performs much better than the coarse droplet 15 degree nozzle 12" back up the tuyere: fine droplets burn faster than tuyere preignited coarse droplets.
6. It's possible to burn fuel too fast to use the heat output in a furnace so slower combustion with time to transfer the heat is more efficient.
7. A mist nozzle with a narrow spray angle would be needed to burn fuel oil in the tuyere (to make it physically practical).

Again these are just my experimental observations and aren't yet a suitable way to build an oil fired furnace.

 

While at the foundry today I decided to see what the Hago siphon burner spray angle is.
I should have taken a picture but that was not very convenient at the time. But I can say that it seems to spray at 60 to 90 degrees for the first inch or so but then , similar to a contrail, the fog stream seemed to expand very slowly. So, I think one could locate a siphon nozzle 4 to 6 inches within the burner tube and expect minimal accumulation of fuel on the tube walls. I had no combustion air on at the time I looked and was running a fairly standard 4-5 PSI atomizing air. Running normal combustion air would contain the fog in a more confined stream. I may try moving the nozzle back a ways and certainly would not hesitate to try it if building a new tube. It would be trivial to trim off a few inches if you did not like it.

Denis

 

It might be worthwhile taking this topic over to the burner construction channel, I'm a past master at derailing/sidetracking other peoples forum posts onto other topics . An advantage of a fine mist spray nozzle is that the air soon slows the fine droplets and like you say, they can be moved with forced airflow in the right direction. I found some tiny cheap all-metal (without the O ring) nozzles that look promising if you use more than one at a time, they still have a 80-90 degree spray cone at 40+ PSI. I used 8 of them after mistakenly testing them at 3 litres per hour to arrive at that 60 litre per hour flow rate.

 

Are the Hagos outrageously expensive or not available down under?

 

This is for a compressor free furnace build, I have a 1HP motor driving a gearpump/oil filter and pressure regulator. I went through the exercise of looking for oil furnace hardware a while back, it's just nonexistent locally: nobody uses oil heating in my town, the few boilers in laundromats are all gas fired. Fuel oil can't be bought either, when it was last being sold in the 1980's it was actually diesel with some sort of carbon rich oil mixed in to prevent it's use in car engines for tax reasons. Don't Hagos and Delevans have rubber seals in them?, these small bore mist nozzles are all metal construction and cost US 50 cents if you buy 20 or so. They are also sold in large hardware store chains too.

 

Yes, they have a Viton o-ring. I haven’t needed to change my o-ring in 18 month or more. I won’t have to unless I forget to pull my burn tube out of the furnace after firing like I did one time the first or second firing of my first furnace. Should I forget I have a spare o-ring taped to the burn tube and it would require five minutes to change it out. I don’t see the o-ring as any major problem.

I just burn diesel (nearly identical to fuel oil) in mine and some sump jet fuel (free and nearly identical to diesel ). A simple 100 dollar pancake compressor supplies adequate compressed air on about a 50% duty cycle. Right now I have a 5 hp classic 2-stage compressor available and use it since it is all plumbed and is quieter. If I had to use the pancake regularly , I’d put it in a acoustic box.
.

I like the siphon as it has been refined over decades time and has all the bugs worked out so it is very efficient and reliable right out of the box. No need to figure out how to make it work.

Denis